Method for determining interfacial tension (Machine-translation by Google Translate, not legally bin

专利摘要:
Method to determine interfacial tension. The present invention relates generally to methods for the characterization of fluids and, particularly, to methods for determining an interfacial tension between a first liquid and a second fluid, the method comprising the steps of: (a) introducing the second fluid into the first liquid at a constant flow rate to cause the second fluid to periodically form successive drops or bubbles; (b) record a heat change of step (a) as a function of time, obtaining a periodic profile of heat versus time; (c) obtain the period of heat change recorded in step (b); (d) provide a calibrated interface tension ratio as a function of the period for said constant flow rate and said second fluid; and (e) correlate the period obtained in step (c) with the calibrated ratio, and determine the interfacial tension between the first liquid and the second fluid for said constant flow rate. (Machine-translation by Google Translate, not legally binding)
公开号:ES2745339A1
申请号:ES201830848
申请日:2018-08-28
公开日:2020-02-28
发明作者:Guillen Angel Pineiro；Garrido Pablo Fernandez；Mesquita Bastos Margarida Maria Henriques
申请人:Universidade de Santiago de Compostela；Universidade do Porto；
IPC主号:

专利说明:

[0001]
[0002]
[0003] TECHNICAL FIELD OF THE INVENTION
[0004]
[0005] The present invention relates, in general, to methods for the characterization of fluids and, more particularly, to methods for determining the interfacial tension of fluids.
[0006]
[0007] STATE OF THE TECHNIQUE
[0008]
[0009] Several techniques are available to evaluate the structural, kinetic and energetic properties of molecules at interfaces (for example, interfacial tension), such as ellipsometry and different types of microscopy and spectroscopy [Javadi, A. et al. "Characterization Methods for Liquid Interfacial Layers". Eur. Phys. J. Spec. Top. 2013, 222 (1), 7-29; Dukhin, S. S. et al. “Dynamics of Adsorption at Liquid Interfaces: Theory, Experiment, Application; Studies in Interface Science ”. Elsevier Science: Amsterdam, Netherlands, 1995; Vol. 1; and "Surface Science Techniques." Bracco, G .; Holst, B., Eds. Springer-Verlag: Berlin, 2013].].
[0010]
[0011] Interfacial tension is one of the most basic properties and there are different devices for determining its value for a given liquid sample in contact with another fluid, for example, drop drop tensiometers (which determine the interfacial tension from the shape of a drop ), maximum volume drop tensiometers (which use the force balance between gravity and surface tension to obtain the value of the latter), bubble pressure tensiometers (which use the maximum pressure of a bubble to obtain surface tension of a liquid), rotary drop tensiometers (which determine interfacial tension from the shape of a drop under an imposed force), and Wilhelmy plate tension meters (which determine the interfacial tension from a force exerted on a plate thin in contact with the liquid).
[0012]
[0013] These instruments are specifically designed to obtain the surface or interfacial tension of standard liquids in contact with different fluids and do not provide Additional Information. In addition, they consume a large amount of sample, since each solution must be prepared independently and, since the surface and interfacial tension is extremely sensitive to concentration, the instrument must be thoroughly cleaned between measurements. Given the importance of this fundamental property, new methods capable of providing additional information while measuring interfacial tension (with respect to liquid-fluid interaction, liquid or gas or liquid) or surface tension (with respect to liquid interaction- gas), with reduced sample consumption and reduced human effort in the preparation of solutions and cleaning, would clearly present advantages over current methods.
[0014]
[0015] DESCRIPTION OF THE INVENTION
[0016]
[0017] The inventors of the present invention have observed that the kinetic calorimetric profile of heat by formation of drops or bubbles in different liquids after the injection of a fluid at a constant flow rate and measured by the use of a standard calorimeter exhibits a periodic signal fully reproducible. This signal data in the form of a heat profile versus time allows the interfacial voltage value for a given liquid sample to be determined with high precision.
[0018]
[0019] Therefore, the present invention provides a solution for the aforementioned problems based on the use of a standard calorimeter (or any other device for measuring calorimetry) to determine the interfacial fluid tension. To this end, a method based on the measurement and recording of the heat change of the successive drops or bubbles as a function of time is provided. The method of the invention allows data to be obtained in shorter periods of time and to use fewer resources compared to the methods conventionally used to measure interfacial tension.
[0020]
[0021] In addition, standard calorimeters already have an injection system that can be used to automatically vary the concentration without having to clean the instrument or prepare solutions manually when performing a series of experiments of the same solvent with different concentrations of a solute. This, together with the small volume of the sample cell of modern calorimeters, helps to save a significant amount of sample. Finally, calorimeters can provide additional information other than voltage measurements interfacial, the kinetic heat signal can be connected to different processes, including condensation and / or evaporation, and / or diffusion between the fluids involved, compression or expansion of the injected fluid, as well as drop / bubble formation, growth and release of it.
[0022]
[0023] Therefore, in a first inventive aspect, the invention provides a method for determining the interfacial tension between a first liquid and a second fluid, the method comprising the steps of:
[0024]
[0025] to. introducing the second fluid into the first liquid at a constant flow rate to cause the second fluid to periodically form successive drops or bubbles;
[0026] b. record the heat change of step (a) as a function of time, obtaining a periodic profile of heat versus time;
[0027] c. obtain the heat change period recorded in step (b);
[0028] d. providing a calibrated interface tension ratio as a function of the period for said constant flow rate and said second fluid; Y
[0029] and. correlate the period obtained in step (c) with the calibrated ratio and determine the interfacial tension between the first liquid and the second fluid for said constant flow rate.
[0030]
[0031] Therefore, the method of the present invention allows a highly reproducible periodic heat change to be obtained as a function of time that can be easily used to determine the interfacial tension values of different fluids by appropriate calibration of the interfacial tension as a function of the period for the formation of bubbles or drops.
[0032]
[0033] In a second inventive aspect, the invention provides a method for establishing the calibrated ratio provided in step (d) of the method according to the first inventive aspect, wherein this method for establishing the calibrated ratio comprises the steps of:
[0034] i. apply steps (a) to (c) of the method according to any of the embodiments of the first inventive aspect to at least two first pure liquids different from which the respective interfacial tension with the second fluid is known to be introduced in the step (to);
[0035] ii. plot their respective interfacial tensions based on their respective periods obtained; Y
[0036] iii. adjust the data plotted to a function, thus providing a relationship between the interfacial tension to be determined and the period for said flow rate.
[0037]
[0038] The kinetic calorimetric profile obtained by the method according to the first inventive aspect of the present invention exhibits a periodic heat signal fully reproducible as a function of time. This signal data is processed to recover its period, which will then be correlated with the calibrated ratio to obtain the interfacial voltage value of this first liquid.
[0039]
[0040] Surprisingly, a direct proportional relationship has been found between the period and the interfacial tension and, therefore, a calibration is sufficient to perform the correlation between the two.
[0041]
[0042] In one embodiment, the calibrated ratio can be obtained from the method according to the second inventive aspect of the invention. Preferably, the relationship between the interfacial tension and the period is adjusted to a linear function.
[0043]
[0044] In a preferred embodiment, the calibrated ratio is established by taking two pure liquids of known interfacial tension, one of high interfacial tension (water, for example) and another of low interfacial tension (such as cyclohexane, ethanol or the lowest point to be measured with a calorimeter). The bubble formation period for each injection flow rate to be used is measured for each pure liquid according to the method of the first inventive aspect of the present invention. As a result, with these two points the calibrated relationship is established from which the value of the interfacial tension is determined.
[0045]
[0046] Furthermore, in a third inventive aspect, the invention provides a data processing apparatus comprising means for carrying out steps (c) to (e) of any of the embodiments of the method for determining an interfacial tension according to the first inventive aspect. .
[0047]
[0048] In a fourth inventive aspect, the invention provides a computer program comprising instructions that, when the program is executed by a computer, causes the computer to carry out steps (c) to (e) of any of the embodiments of the method of determining an interfacial tension according to the first inventive aspect.
[0049]
[0050] In a fifth inventive aspect, the invention provides a computer-readable medium comprising instructions stored therein which, when executed, causes the computer to carry out steps (c) to (e) of any of the embodiments of the method of determining an interfacial tension according to the first inventive aspect.
[0051]
[0052] In addition, any of the embodiments of the methods of the present invention can be performed using commercially available devices for calorimetry measurements without any modification at all. Therefore, standard calorimeters can be used to determine the interfacial tension of the first liquid samples and the second fluid with high precision.
[0053]
[0054] The heat change profile depending on the time recorded with commercially available calorimeters or any other device for measuring calorimetry can carry unwanted noise produced during capture, storage, transmission, processing or any conversion thereof. Said non-useful information or the noise of the heat change profile as a function of the recorded time is reduced or mitigated by particular embodiments of the first inventive aspect.
[0055]
[0056] In another inventive aspect, the invention relates to the use of a calorimeter for the determination of the interfacial tension between a first liquid with a second fluid.
[0057]
[0058] In a final inventive aspect, the invention relates to the use of a calorimeter to carry out steps (a) and (b) of any of the embodiments of the method for determining an interfacial tension according to the first inventive aspect, the calorimeter comprising:
[0059]
[0060] - a container cell configured to separately accommodate a first liquid of a second fluid;
[0061] - a first capillary configured to introduce the second fluid into the first liquid;
[0062] - first means of transport in fluid communication with the first capillary, first conveying means configured to transport the second fluid at a constant flow rate to the first liquid such that said second fluid is introduced into the first liquid as drops or bubbles;
[0063] - detection means in thermal contact with the first liquid, and configured to detect the heat change associated with the periodic formation of successive droplets or bubbles; Y
[0064] - a recording unit associated with the detection means and configured to record the heat change detected by the detection means as a function of time.
[0065]
[0066] DESCRIPTION OF THE FIGURES
[0067]
[0068] These and other features and advantages of the invention will be clearly understood in view of the detailed description of the invention that becomes apparent from a preferred embodiment of the invention, given only as an example and not being limited thereto, with Reference to the figures.
[0069]
[0070] Figure 1 Schematic representation of the formation of bubbles and the change of heat (power) as a function of the time recorded during the formation of bubbles when injecting air at a constant flow rate in a liquid to determine the interfacial tension of said liquid.
[0071]
[0072] Figure 2 Heat change profile (power) as a function of the time corresponding to an experiment of air injection in water at a flow rate of 0.022 jL / s.
[0073]
[0074] Figure 3 Signals corresponding to the injection of air into three liquids (water, surfactant solution and ethanol) at different flow rates (0.111, 0.055, 0.028 and 0.022 jL / s, as indicated to the right of each row).
[0075]
[0076] Figure 4 Power profiles versus time corresponding to five independent experiments of air injection in water at 0.022 jL / s.
[0077]
[0078] Figure 5 Power profile versus time corresponding to an almost complete air injection experiment in a 0.55 mM solution of C ¹² G ² in water at 0.022 | jL / s.
[0079]
[0080] Figure 6 Interfacial tension of three liquids (71 mN / m for water; 35 mN / m for the solution of C ¹² G ² and 22 mN / m for ethanol) versus the average period between the minimums obtained in the calorimetric signal of 20 different bubbles for each liquid at flow rates of 0.111 (•), 0.055 (▲), 0.028 (■) and 0.022 (♦) ML / s.
[0081]
[0082] Figure 7 Power profiles versus time corresponding to an almost complete experiment of air injection in ethanol at 0.022 s / ^ L.
[0083]
[0084] Figure 8 Integral of the negative and positive contributions to the signals corresponding to several bubbles injected in pure water at 0.022 ^ L / s.
[0085] Figure 9a, b Four continuous profiles of heat change (power) as a function of the time recorded when a second particular fluid is introduced into a first liquid at a constant flow rate. In particular, air has been injected at 0.037 ^ L / s in a 2.96, 0.7 and 0.0 mM solution of C ¹⁰ G ² in water, and 0.028 ^ L / s in a 2.41 mM solution of C ¹⁰ G ² in water.
[0086]
[0087] Figure 10a, b Discretization and correction of the profiles shown in Figure 9a, b based on the respective reference curves for each one, such that the corrected heat change profiles oscillate around a constant value.
[0088]
[0089] Figure 11a, b Corrected heat change profiles that oscillate around a constant value (that is, 0) are shortened on the time axis to a particular time window that has an acceptable variance.
[0090]
[0091] Figure 12 Different examples of the application of any of the Fourier transform type techniques to the heat profile registered or corrected against time.
[0092]
[0093] Figure 13 The result of applying the Fourier transform in the corrected and shortened heat change profiles of Figures 11a, b, where peaks of more than one period can be seen.
[0094]
[0095] Figure 14 Set of periods for a given combination of liquid and fluid that varies the concentration of solute in the first liquid adjusted to a mathematical function for different flow rates.
[0096]
[0097] Figure 15 The profile of the Fourier transform corresponding to the air injected at 0.037 ^ L / s in a solution of 0.7 mM of C ¹⁰ G ² in water shown in Figure 13, decomposes into a number N of Gaussian functions.
[0098] Figure 16 A comparison of the interfacial tension obtained by the method of the present invention and the data from the literature for other standard methods is shown.
[0099]
[0100] Figure 17a-c A record of a heat profile was sampled vs. time while air was introduced at a flow rate of 0.028 ^ L / s in a solution of C ¹⁰ G ² in water of 2.96 mM. The sampled profile of Figure 17a is oversampled in Figure 17b, and averaged based on a 2D histogram in Figure 17c.
[0101]
[0102] Figure 18a, b The profile of Figure 17c after applying a Savitzy-Golay filter (Figure 18a) and the profile of Figure 18a after applying a moving average.
[0103]
[0104] Figure 19 A corrected heat change as the difference between the registered heat change and the base curve obtained from Figure 18b.
[0105]
[0106] Figure 20a-c The fast mobile Fourier transform was applied to Figure 19, M-FFT normalized in the area and final FFT obtained from the average of the ‘M-FFT normalized in the area’ of Figure 20b.
[0107]
[0108] DETAILED DESCRIPTION OF THE INVENTION
[0109]
[0110] All features described in this specification (including claims, description and drawings) and / or all steps of the described methods may be combined in any combination, with the exception of combinations of said features and / or mutually exclusive steps.
[0111]
[0112] In the context of the present invention, the term "interfacial tension" or "IFT" refers to the cohesion forces at the interface between a liquid and a fluid (gas or liquid). The molecules in the interface do not have an isotropic distribution of neighboring atoms and, therefore, interact more strongly with those directly associated with them at the interface. This forms an interface "film" with specific structural, mechanical, kinetic and energetic properties. In the case of a liquid and a gas, the term "surface tension" (SFT) is also used. There are several different units for interfacial and surface tension; Normally mN / m is used (which is equivalent to dynes / cm). This property is of paramount importance for the characterization of molecules in a number of chemical industries such as cleaning products, the cosmetics, the pharmaceutical and food industry, as well as for fundamental research, since the interfacial properties are connected with the ability of the molecules to self-assemble in solution.
[0113]
[0114] The inventors of the present invention have observed that the heat released or absorbed in the creation of liquid droplets or gas bubbles when injecting a fluid into a liquid sample makes it possible to determine the interfacial tension of the liquid samples with high precision. Simultaneously, the heat change signal itself contains useful information for the characterization of the system at the molecular level.
[0115]
[0116] Therefore, in the first inventive aspect, the present invention is directed to a method for determining an interfacial tension between a first liquid and a second fluid, the method comprising the steps of:
[0117]
[0118] to. introducing the second fluid into the first liquid at a constant flow rate to cause the second fluid to periodically form successive drops or bubbles;
[0119]
[0120] b. record the heat change of step (a) as a function of time, obtaining a periodic profile of heat versus time;
[0121]
[0122] c. obtain the heat change period recorded in step (b);
[0123]
[0124] d. providing a calibrated interface tension ratio as a function of the period for said constant flow rate and said second fluid; Y
[0125]
[0126] and. correlate the period obtained in step (c) with the calibrated ratio and determine the interfacial tension between the first liquid and the second fluid for said constant flow rate.
[0127]
[0128] As defined above, the method of the present invention comprises a step (a) of introducing the second fluid into the first liquid at a constant flow rate to cause the second fluid to periodically form successive droplets or bubbles.
[0129]
[0130] The term "fluid" refers to a substance that continuously deforms (flows) under an applied shear stress. Fluids are a subset of the phases of matter and include liquids, gases, plasmas and, to some extent, plastic solids. Fluids are substances that have a zero shear modulus or, in simpler terms, a fluid is a substance that cannot withstand any shear force that is applied to it. In the context of the present invention, the term "fluids" includes simple liquids, mixtures of liquids, gases, mixtures of gases and mixtures of liquids and gases.
[0131]
[0132] The term "liquid" refers to a fluid that conforms to the shape of its container but that maintains a constant volume independent of pressure. As such, it is one of the four fundamental states of matter (the others are solid, gas and plasma), and it is the only state with a defined volume but no fixed form. In the context of the present invention, the term "liquid" includes pure liquids (for example, water and alcohols) but also miscible and immiscible mixtures of two or more liquids, for example, a mixture of water and different organic solutes (alcohols, etc.), water and biological molecules, including sugar, lipids or proteins, or mixtures of other solvents with different solutes.
[0133]
[0134] Non-limiting examples of first liquids suitable for the method of the present invention are water, alcohols, acid alkanes, etc., as well as mixtures thereof.
[0135]
[0136] In a preferred embodiment, the first liquid is water, ethanol or aqueous solutions of different solutes (generally surfactant molecules).
[0137] In the method of the present invention, the second fluid is introduced into the first liquid to cause the second fluid to periodically form successive drops, if the second fluid is liquid, or bubbles, if the second fluid is a gas.
[0138]
[0139] Non-limiting examples of second fluids suitable for the method of the present invention are liquids such as organic solvents insoluble in the first liquid (for example, oil, cyclohexane or alkane molecules if the first liquid is water) and gases such as air, nitrogen , oxygen, hydrogen, methane, etc.
[0140]
[0141] In a preferred embodiment, the second fluid is a gas, more preferably air.
[0142]
[0143] In the context of the present invention, the term "air" refers to a mixture of approximately 78% nitrogen, 21% oxygen, water vapor, argon, carbon dioxide and very small amounts of other gases.
[0144] In step (a) of the method of the present invention, the second fluid is introduced into the first liquid at a constant flow rate.
[0145]
[0146] The term "flow rate" (also known as volumetric flow rate, volume flow rate, fluid flow rate or volume velocity) is the volume of fluid that passes per unit of time, generally represented by the symbol Q (sometimes V), being represented here by the variable ra throughout the description. There are several different units for the flow rate; Normally ^ L / s, m3 / s or L / s are used. In the context of the present invention, the "flow rate" refers to the volume of the second fluid introduced into the first liquid per unit of time. In the method of the present invention, the flow rate of the second fluid is constant.
[0147]
[0148] In a preferred embodiment, the constant flow rate of the second fluid ranges from 200 microliters in 9000 seconds and 200 microliters in 900 seconds.
[0149]
[0150] After the injection of the second fluid at a constant flow rate in the first liquid, the second fluid periodically forms successive drops or bubbles. The formation of drops or bubbles inside the first liquid causes a change of heat in it.
[0151]
[0152] In the context of the present invention, the term "heat change" refers to the thermal disturbance caused within the first liquid by the creation of successive drops or bubbles. In particular, and not limited to any particular theory, the inventors of the present invention believe that the heat change corresponds to: (i) the sudden formation of the drop or bubble in the liquid sample once a critical pressure is reached in the second fluid; and (ii) the growth of the drop or bubble until it reaches a maximum volume and is released into the first liquid (see Figure 1).
[0153]
[0154] Assuming that a calorimeter or other device is used to measure calorimetry within the method of the present invention, the following applies.
[0155]
[0156] In summary, the conditions for obtaining a periodic kinetic heat signal after the injection of a fluid in a liquid are the following:
[0157] • The injection flow rate must be slow enough to allow the device to follow the heat signal (ie, heat change), considering the response time of that device. This means that the entire process must be significantly slower than the response time of the device.
[0158] • The injection flow rate must be fast enough to produce a significant heat signal in the device. If the flow rate is too slow, the power could be below the detection threshold of the device, even if the total process energy is large.
[0159] • The bubble / drop must be large enough to be detectable by the device. This means that the heat exchanged during the formation of bubbles / drops and the release process is large enough to be detected by the device.
[0160] • The bubble / drop must be small enough to avoid contact with the walls of the measuring cell during its formation and release.
[0161] • The pressure after the release of each bubble / drop must be the same to obtain a periodic signal. This means that closed cells do not produce a true periodic signal due to the increase in pressure in the cell after continuous injection of the second fluid. Small variations in pressure are observed during the formation of each bubble / drop, but must be recovered in the release.
[0162]
[0163] A heat sensor must be in close contact with the calorimetric cell. In one embodiment, the heat sensor is a Peltier device implemented in the device.
[0164]
[0165] Within a calorimeter or other device for measuring heat exchange, the heat exchange is recorded through the first liquid, preferably by using a Peltier device in close contact with the outer walls of the sample cell where it is contained the first liquid.
[0166]
[0167] With all that, and as can be derived from the figures, the period obtained depends on the following factors:
[0168]
[0169] • Capillary diameter from which the fluid is injected.
[0170] • The diameter of the capillaries used is usually less than 1 mm, but may be modified whenever it is smaller than the width of the sample cell.
[0171] • Hydrostatic pressure at the tip of the capillary. Preferably, slightly above atmospheric pressure, that is, ~ 5-10 mb at the tip of the capillary, where bubbles or drops are formed.
[0172] • Injection flow rate. The optimal value depends on the response time and the sensitivity of the calorimeter or device for measuring the calorimetry. In one embodiment, the flow rate is 0.022 to 0.22 ^ l / s.
[0173] • Temperature of the sample cell and the injected fluid. The experiments were performed with the sample cell temperature between 10 and 60 ° C, while the external temperature ranged between 20 and 25 ° C.
[0174] • Interfacial tension between the two fluids (composition or chemical characteristics of the two fluids). Values of 22 to 72 mN / m were tested.
[0175]
[0176] In a preferred embodiment, the temperature is kept constant throughout steps (a) and (b) of the method of the present invention. In that case, the heat change is measured as the power applied to maintain the constant temperature inside the sample cell where the first liquid is located. Normally, ^ .cal / s are used as units for heat exchange that is equivalent to the applied power.
[0177]
[0178] The inventors of the present invention have observed that the heat change profile as a function of the time obtained by the method of the present invention shows a fully reproducible periodic signal that depends on the molecular composition of the first liquid. Examples of these fully reproducible periodic signals can be seen in Figures 2 to 5, 7 and 9 (a and b).
[0179]
[0180] In figure 1, a schematic representation of the bubble formation and the associated heat change (i.e. the power consumed by the calorimetry device used in the measurement) is shown as a function of the time recorded during the bubble formation.
[0181]
[0182] In Figure 2, the change in heat (power) is shown as a function of the time profile corresponding to an air-in-water injection experiment at an injection rate of 0.022 ^ L / s. The signal corresponding to 16 bubbles is clearly visible. The part of the profile corresponding to each bubble formed is perfectly reproducible and the signals are equally separated, which implies that all the bubbles have the Same volume and heat involved is similar.
[0183]
[0184] Figure 3 shows the signals corresponding to the injection of air into three different liquids (water, surfactant solution and ethanol) and at different flow rates (0.111, 0.055, 0.028 and 0.022 jL / s, as indicated to the right of each row). The experiment corresponding to 0.111 | jL / s ethanol is not shown since the bubbles overlap, that is, the bubbles form so quickly that several can be present in the sample cell at the same time. The x-axis of all graphs is on the same scale to facilitate comparison between experiments.
[0185]
[0186] Figure 4 shows the power profiles as a function of time corresponding to five experiments of air injection into water at a flow rate of 0.022 jL / s. In Figure 4, the signals corresponding to the formation of 3 bubbles are clearly seen in each experiment. As shown in Figure 2, the heat change profile caused by each bubble formation in the air injection is perfectly reproducible and, therefore, the signals are equally separated. This implies that all bubbles have the same volume and that the heat involved in each one is equivalent.
[0187]
[0188] Figure 5 shows the power profile versus time corresponding to an almost complete experiment of air injection in a 0.55 mM solution of C ¹² G ² in water at a flow rate of 0.022 jL / s. In Figure 5 the signals corresponding to 29 bubbles are clearly visible. The heat change profile caused by each bubble formation after the air injection is perfectly reproducible and the signals are separated equally, so that all the bubbles have the same volume and that the heat involved is equivalent.
[0189]
[0190] Figure 6 shows the interfacial tension of three liquid samples, that is, 71 mN / m for water, 35 mN / m for a solution of C ¹² G ² and 22 mN / m for ethanol compared to the average period between the minimums obtained in the calorimetric signal of 20 different bubbles for each sample liquid at flow rates of 0.111 (•), 0.055 (▲), 0.028 (■) and 0.022 (♦) jL / s. The lines are the linear adjustment of the results in each flow. All data correspond to a temperature of 298 K.
[0191]
[0192] Figure 7 shows a profile of heat change (power) as a function of time corresponding to an almost complete experiment of air injection in ethanol at a flow rate of 0.022 ^ L / s. A clear evolution of the signal profile is observed. This is probably due to the superposition and coalescence of the bubbles that remain attached to the capillary used for air injection while more bubbles are formed. The processing steps of the recorded data, as well as the modifications in the design of the injection system as described below, are desirable to avoid or mitigate this effect.
[0193]
[0194] In Figure 8, the integral of the negative and positive contributions to the signals corresponding to several bubbles injected in pure water at a flow rate of 0.022 ^ L / s is shown.
[0195]
[0196] Thus, after the injection of the second fluid as defined above, the method of the present invention comprises a step (b) of recording a heat change of step (a) as a function of time, obtaining a periodic heat profile. function of time.
[0197]
[0198] The method of the present invention can be performed using commercially available calorimetry devices without any modification.
[0199]
[0200] In a preferred embodiment, steps (a) and (b) of the method of the present invention are performed by using a calorimeter, more preferably by using an isothermal titration calorimeter (ITC).
[0201]
[0202] Next, different techniques will be described with respect to step (c) of the method according to the present invention to obtain the period of the heat change profile recorded in step (b). All these techniques are aimed at accurately recovering the period of the periodic heat change profile.
[0203]
[0204] After obtaining the profile in step (b), the period between drops or bubbles is determined. In the context of the present invention, the term "period" refers to the time elapsed between two consecutive drops or bubbles.
[0205]
[0206] The inventors of the present invention have observed that the period, in terms of the periodic heat change as a function of the time represented by the subsequent fall or Bubble creation, also depends significantly on the molecular composition of the first liquid.
[0207]
[0208] Figures 9a, b show four recorded continuous profiles of heat change (power) as a function of time while a particular second fluid is introduced into a first liquid at a constant flow rate. In these experiments, air has been injected at a flow rate of 0.037 ^ L / s in a solution of 2.96, 0.7 and 0.0 mM of C ¹⁰ G ² in water, and at a flow rate of 0.028 ^ L / s in a 2.41 mM solution of C ¹⁰ G ² in water, respectively.
[0209]
[0210] It should be noted that these registered periodic profiles tilt or shift as time increases. The causes can vary: change of the heat capacity of the medium by altering its properties (incorporation of air into the cell of the calorimetry device), initial drift of the baseline, foam formation, appearance of microbubbles, etc.
[0211]
[0212] As defined above, the method of the present invention also comprises a step (c) to obtain the period of the heat change profile recorded in step (b). Registered periodic profiles may be stable, oscillating around a constant value, or they may be affected by disturbances such as those explained above. For those cases in which the registered periodic profile tilts, moves or is altered by an outstanding noise as time increases, the following techniques are of special application.
[0213]
[0214] With the most common techniques for obtaining the period of a periodic function, it is necessary to eliminate or mitigate the signal deviation and correct it so that it oscillates around a constant value. To this end, a general corrective algorithm has been designed which, regardless of the alterations suffered in the experiment, can find the deviation of the data due to noise or deviation from a constant value and correct them.
[0215]
[0216] The most widespread technique for recovering the period of a periodic function is any of the Fourier transform types. Any of these techniques makes it possible to convert a periodic signal in the time domain (evolution of a magnitude, for example, heat change, over time) into a spectrum of frequency, that is, in the frequency domain. In this spectrum, the characteristic frequency (the one of greater amplitude) can be identified, being the calculation of its immediate period by the associated equation (T = 1 / f, where "T" denotes period and "f" denotes frequency). However, to correctly perform a Fourier transform, the signal must be oscillatory with respect to a constant value, which is not always fulfilled, as can be seen in the inclination or displacement of the periodic profiles of Figure 9a, as measured Increase the time.
[0217]
[0218] Accordingly, in a particular embodiment of the method according to the present invention, step (c) further comprises correcting the heat change recorded as a function of time based on a reference curve of said heat change, such that The corrected heat change oscillates around a constant value.
[0219]
[0220] In a particular embodiment, the above-mentioned correction of heat change based on the baseline curve comprises the following steps:
[0221]
[0222] c1 ’. obtain the heat change as a data set such that if the heat change is recorded continuously, the heat change is discretized in a data set, or if the heat change is recorded by sampling, the step c2 ';
[0223] c2 ’. select a percentage of data, said data being randomly selected .;
[0224] c3 ’. adjust the data to a smooth curve, preferably using a cubic spline function;
[0225] c4 ’. repeat steps c2 ’to c3’ for a plurality of different data sets and adjust those data sets to the corresponding smooth curve; c5 ’. obtain the average value of these smooth curves corresponding to each data set, obtaining a reference curve;
[0226] c6 ’. generate a corrected heat change as the difference between the original heat change and the curve represented as a function of time such that the corrected heat change oscillates around the value 0 over time.
[0227]
[0228] In a preferred embodiment, the heat change discretization in step c1 'of the method as defined above is performed by the Monte Carlo method.
[0229] Figures 10a, b show an example of the discretization and correction of the profiles shown in Figure 9a, b based on the respective reference curves for each one, such that the corrected heat change profiles oscillate around a constant value
[0230]
[0231] As mentioned, the signals recorded and shown in Figure 9a, b can be considered analog signals, that is, continuous signals for which the time-varying characteristic is, in this particular case, the "heat change" produced by the creation of bubbles or droplets. .
[0232]
[0233] The graphs on the left side of figures 10a, b show the discretized heat change in a given set of data. 1% of these data are randomly selected by a Monte Carlo method, and interpolated by a smooth curve, which will preferably be a cubic spline function.
[0234]
[0235] The latter is repeated a large number of times (preferably 1000 times or more) for a plurality of different data sets (also chosen by the Monte Carlo method, 1% each), and the resulting data sets are subsequently adjusted by the same smooth curve (for example, cubic spline function). Once the smooth curves corresponding to each data set are obtained, the average value between all is calculated, and this average value corresponds to the continuous baseline curve that can be seen in Figures 10a, b (side graphs left).
[0236]
[0237] The graphs on the right side of Figures 10a, b show the corrected heat change, which has been generated as the difference between the original heat change (i.e., the profiles in Figure 9a, b) and the obtained reference curve . As can be seen, the corrected heat change profile oscillates around a constant value over time (0 in this case), so it is chosen to apply any of the Fourier transformation techniques to obtain the period.
[0238]
[0239] In a particular embodiment, step (c) of the method of the present invention further comprises determining a particular time window of heat change or corrected heat change that has an acceptable variation with respect to the entire time interval.
[0240] In a preferred embodiment, such as determining the particular time window of the registered or corrected heat change, comprises the following steps:
[0241] • select at least one provisional time window of the heat change registered or corrected with a predetermined size, preferably a quarter of the full time range;
[0242] • calculate the variance of each of the provisional time constant windows and identify the provisional time window that has the lowest variance;
[0243] • sequentially increase the size of the identified time window for a predefined time, and calculate for each iteration the associated variance within said increased time window;
[0244] • Continue to increase the size of the provisional time window by the same predefined time size until:
[0245] or the associated variance reaches an unacceptable value, preferably until the associated variance of the last iteration doubles the variance of the previous iteration, or until
[0246] or the associated variance in each iteration converges, this convergence is achieved when a truncation error is less than a predetermined value;
[0247] • designate the last incremental time interval with an acceptable variance as the particular time window of the corrected heat change that has an acceptable variance with respect to the full time range.
[0248]
[0249] Figures 11a, b show an example of a corrected heat change profile that oscillates around a constant value (ie, 0) that is shortened on the time axis to a particular time window that has an acceptable variation. The reduced size is represented from the beginning of the recording by the respective continuous line.
[0250]
[0251] By correcting the heat change based on the time profile to obtain an oscillating signal around a constant value, the inventors of the present invention have observed that, in some cases, it is not possible to analyze the entire signal through the transform of Fourier
[0252]
[0253] Normally, from the 2000s on the signal recording, the amplitude of the oscillations are increased, which may affect the baseline and the periodicity of the signal; that is, alter the result in a way that can be difficult to quantify.
[0254]
[0255] To avoid this type of problem, in this implementation, the corrected heat change based on the time profile is reduced to a selected time interval that suffers less signal disturbance. To measure this alteration, the variance of the signal is preferably used.
[0256]
[0257] The following protocol has been used to obtain the graphs of figures 11a, b. A provisional time window of% of the total corrected heat change signal was selected, and moved along the time axis while calculating the variance of each modified provisional time window. Therefore, the provisional time window with the lowest variance was identified, and this intermediate time window identified was sequentially increased in a time size of 100 s, calculating the associated variance at the same time.
[0258]
[0259] As a stop condition, the size of the provisional time window (later corresponding to the profile of the shortened heat change versus time) was further increased until the associated variance reached an unacceptable value, in this particular case until the variance associated with the last iteration doubles the variance of the previous iteration.
[0260]
[0261] With respect to obtaining the period of a periodic function that is affected by the disturbances, as mentioned above, Figure 12 shows different examples of the application of any of the Fourier transform type techniques to a heat profile vs . time recorded or corrected to emphasize the importance of correcting the signal to obtain an identifiable period. The three examples apply to a particular heat profile as a function of the time recorded while air is injected at a flow rate of 0.028 ^ L s in a 2.96 mM solution. of C ¹⁰ G ² in water.
[0262]
[0263] The Fourier transformed type techniques applied are, respectively:
[0264]
[0265] The fast Global Fourier transform (the so-called G-FFT) was applied to all the heat change recorded without subtracting the baseline (that is, it was not corrected); Fast mobile Fourier transform (the so-called M-FFT) applied to the registered heat change without subtraction of the baseline, using a 20% time window; Y
[0266] The G-FFT was applied to the heat change recorded by subtracting the baseline, that is, to the heat change corrected as a function of time.
[0267]
[0268] As can be seen from these three transformed graphs, only the last one (the one applied to the corrected profile) has an identifiable period among all the others, while the first and second do not allow a period to be correctly identified.
[0269]
[0270] In a preferred embodiment, the period of heat change recorded as a function of time in step (c) of the method, as defined above, is recovered by applying any of the following techniques to the corrected heat change:
[0271] - Global Fourier transform over all the registered heat change profile; or - with the fast mobile Fourier transform, preferably in a 20% time window.
[0272]
[0273] In this sense, Figure 13 shows the results of applying the global Fourier transform to the corrected and shortened heat change profiles of Figures 11a, b, where peaks of more than one period can be seen.
[0274]
[0275] For this type of profiles with different periodic components, the Fourier transform may not reveal a single peak and, in addition, its width may be variable. Then, a characteristic frequency is not obtained, but a frequency distribution. In these cases, it is important to be able to discern which is the period corresponding to the formation of bubbles or drops, and which corresponds to other unwanted components of the signal.
[0276]
[0277] A person skilled in the art would take the period corresponding to the main peak, since it is clearly differentiable among all others, thus discouraging the search for other periods. However, this is not always correct, and to solve this indeterminacy, two techniques are proposed here, depending on whether the experiment is being analyzed individually or within a set of measurements.
[0278]
[0279] In the first case, an autocorrelation of the data is applied before the Fourier transform and the Fourier transform is applied over the autocorrelated data.
[0280] Therefore, in a particular embodiment, step (c) of the method of the present invention further comprises before obtaining the registered heat change period, the application of autocorrelation to the heat change recorded or corrected in the time domain.
[0281]
[0282] In the second case, the experiment is being analyzed within a set of experiments. In a particular embodiment, the first liquid has a given concentration of a solute with surface activity, and steps (a) to (b) are repeated at least once changing said given solute concentration, and at least two different heat changes in the time domain they are recorded for different concentrations of solute. In this case, after obtaining the period according to the method as defined above for each of these registered heat changes, the method further comprises applying the following steps to each of the transformed heat changes in the domain of the frequency:
[0283]
[0284] • determine the period with the highest amplitude for each of the at least two transformations of heat changes and represent the periods against the concentration of solutes;
[0285] • adjust the set of periods to a mathematical function;
[0286] • identify outliers between these periods, and:
[0287] or discard at least one of them, and / or
[0288] or readjust the period for at least one of these outliers for another period that falls within the adjusted mathematical function.
[0289]
[0290] In a preferred embodiment, the mathematical function to which the set of periods fits is of the Langmuir isothermal type or logarithmic polynomial function.
[0291]
[0292] Figure 14 shows an example of a set of periods obtained for a set of experiments in which a given fluid was injected at various flow rates in a liquid (solution of C ¹⁰ G ² in water) having a solute concentration. In the figure, periods are plotted as a function of solute concentration and fit a mathematical function for each flow rate. In these experiments, the same solute, fluid and liquid have been used and the experiments have been performed at the same temperature, thus varying the concentration of solute and the injection flow rate.
[0293] The expected correlation between the data has been used to minimize the ambiguity due to the appearance of several peaks and, therefore, to optimize the identification of the correct period. Within the behavior of the curves represented (which is obtained by adjusting to a type of Langmuir isotherm or a logarithmic polynomial function), it can be seen if a point has been calculated correctly. In this figure, the points corresponding to outliers (that is, outliers) in the set of results have already been adjusted.
[0294]
[0295] In Figure 14, the Extended Langmuir Isotherm function has been used for this purpose. The steps taken to obtain figure 14 are as follows:
[0296]
[0297] i. all the data of the experiments fit this mathematical function using the peak with the greatest amplitude in the FFT;
[0298] ii. ii. outliers are identified; Y
[0299] iii. iii. Since the period corresponding to other peaks is also identified, the period that is closest to the period predicted by the Extended Langmuir Isotherm is taken as a reference, if it does not coincide with that of maximum amplitude.
[0300]
[0301] With the adjustment to the data represented, it can be established around what period one would expect to obtain a value according to the trend of the rest of the experiments. Therefore, a wide range is taken around that value and the largest peak resulting from the FTT is searched in it (not in the total range).
[0302]
[0303] Therefore, the characteristic period for each concentration and flow rate is determined, but not the final value, since others in the vicinity can affect it. Due to the presence of other peaks in the Fourier transform near the characteristic period, an additional treatment is preferably applied in each of them to determine and correct its uncertainty.
[0304]
[0305] In an embodiment in which the heat change transform in the frequency domain after applying any of the techniques defined above comprises more than one period, identified as a main period corresponding to the period with the greatest amplitude and at least one secondary period. corresponding to the periods with smaller amplitudes, the method comprises in step (c) the following steps applied to the amplitude function as a function of the period resulting from the application of any of the techniques defined above:
[0306]
[0307] • break down the function into a number N of Gaussian functions over the main period of the function;
[0308] • evaluate the amplitude-width ratio for each Gaussian function, the one with the highest ratio is identified as the main Gaussian function;
[0309] • calculate the area of intersection of each remaining Gaussian function with the main Gaussian function;
[0310] • establish a weighting value for each Gaussian function based on that area of intersection; Y
[0311] • obtain the value of the period taking into account the contribution of each Gaussian function with its weighting value.
[0312]
[0313] In a preferred embodiment, steps (a) to (b) are repeated at least once under the same conditions for a first liquid with different solute concentrations, at least two different heat changes being recorded in the time domain, one corresponding at each concentration of solute. In this embodiment, the main Gaussian function is identified with that which has the period closest to the expected mathematical function according to the method as defined above.
[0314]
[0315] Figure 15 shows a particular example of the Fourier transform of the profile shown in Figure 13, corresponding to the air injected at a flow rate of 0.037 ^ L / s in a solution of 0.7 mM of C ¹⁰ G ² in water shown in Figure 13 but decomposed into a number N of Gaussian functions in the main period of the function.
[0316]
[0317] The profile of Figure 15 comprises 4 Gaussian functions around the main period («64 sec.), Of which the main Gaussian function is identified as having the greatest amplitude-width ratio, and the other three secondary periods corresponding to the periods with smaller amplitudes In other words, during an interval around the main period, an adjustment is made to the number of Gaussian functions (four in this example) and the one with the largest amplitude-width ratio is selected as the main one.
[0318]
[0319] The main peak is identified with the main period and three other peaks can be seen, which add uncertainty to the determination of the defined period of the measure.
[0320]
[0321] The normalized area of intersection of the rest of Gaussian functions with the main one is determined and a weighted average is made with a statistical weight proportional to that area (maximizing for the main Gaussian since its intersection with itself is 100%). After this, the value of the period is obtained taking into account the contribution of each Gaussian function with its weighting value.
[0322]
[0323] In other words, the final period is determined as the average of all periods (those corresponding to the different Gaussian functions identified), weighted by the intersection of each Gaussian with that corresponding to the main period.
[0324]
[0325] It should be noted that, in the case of several experiments, the reference peak is preferably identified as the closest to the period predicted by the extended Langmuir isotherm adjustment, for example. On the contrary, for individual measurements, including calibration points, the reference period is the one that preferably corresponds to the Gaussian with the greatest amplitude.
[0326]
[0327] Figure 16 shows a comparison of the interfacial tension obtained by the method of the present invention and the data from the literature for other standard methods.
[0328]
[0329] The inventors of the present invention have found that uncertainties within the method have the following contributions:
[0330] • Standard error obtained from the covariance matrix of the sum of the Gaussian function; I
[0331] • uncertainty inherent in the FFT.
[0332]
[0333] In this figure, the interfacial tension was determined using the present method according to the invention for ethanol and decyl-maltósido (C ¹⁰ G ² ) in aqueous solution for different concentrations (■), and are represented together with data from the literature for other standard methods for measuring interfacial tension for the same systems (•). The shadow indicates the calculated uncertainty of the data. In conclusion, it can be clearly seen that the accuracy of the present invention with respect to known literature is high.
[0334] Next, other data processing processes that improve the correct determination of the period are explained.
[0335]
[0336] As already mentioned, in a particular embodiment, step (c) of the method as defined above further comprises the correction of the heat change recorded as a function of time based on a reference curve of said heat change, such that The corrected heat change oscillates around a constant value. This led to the condition that any of the Fourier Transform techniques can be applied with a good expectation to determine a differentiable period.
[0337]
[0338] Alternatively to the methods explained here above, in a particular embodiment, the above-mentioned correction of heat change based on the reference curve comprises the following steps:
[0339] c1. obtain the heat change as a set of data such that:
[0340] if the heat change is recorded continuously, the heat change is discretized in a data set; or
[0341] if the heat change is recorded by sampling, step c2 is performed;
[0342]
[0343] c2. oversample said data set with randomly chosen data, and distribute it over the recorded data set,
[0344]
[0345] c3. represent the data of step c2 in a 2-D histogram, preferably each class of the 2-D histogram having a width equal to the square root of the size (L) of the original data set;
[0346]
[0347] c4. calculate the average value of heat change for each class of the 2-D histogram, and represent said calculated average value as a function of time;
[0348]
[0349] c5. interpolate the data resulting from the previous steps in a smooth curve, preferably by means of a cubic spline function, obtaining a reference curve; Y
[0350]
[0351] c6. generate a corrected heat change as the difference between the registered heat change and the reference curve represented as a function of the time in such a way that the corrected heat change generated oscillates around 0 over time.
[0352]
[0353] In a preferred embodiment, the discretization of the heat change in step c1 of the method as defined above is performed by the Monte Carlo method.
[0354] Figure 17a shows a heat profile vs. Sampled time while air is introduced at a flow rate of 0.028 ^ L / s in a 2.96 mM solution of C ¹⁰ G ² in water. In this figure, a set of heat change data has been obtained by sampling the recorded heat change every second. Since the general recording lasted 1 hour, 3600 points form this set of data in the matrix.
[0355]
[0356] In Figure 17b, this sampled profile has been oversampled 10 times, that is, now the number of points that make up this oversampled data set consists of 36,000 points in the matrix. In particular, the data to produce the oversampling are randomly selected by a Monte-Carlo method. Due to oversampling, many of the original recorded data sets are repeated, thus creating a new Z axis to measure the repetition of data as can be seen in Figure 17b.
[0357]
[0358] This process reduces the resolution of the original set of recorded data, thus highlighting the most densely populated regions in the heat change graph over time, which corresponds to the most representative data for the subsequent calculation of the baseline. On the other hand, noisy regions are more diluted, since oversampled data is less likely to fall into those regions.
[0359]
[0360] The information after oversampling is represented in a 2-D histogram, where the intervals of the 2-D histogram will have a constant width. In one embodiment, each class of the 2-D histogram has a width equal to the square root of the size of the original data set. That is, for the example in Figure 17, the width of each class of the 2-D histogram would be 60 s or 1 min, thus gathering all the points (including oversampling points) that fall within that minute of recording. . The average heat change value for these classes is calculated, thus obtaining the average heat change for each minute of recording, and decreasing the number of data in the time domain to 60 (one per minute, during the original recording time general).
[0361] In Figure 17c, the average heat change based on the previous 2D histogram is represented on the time axis.
[0362]
[0363] In another particular embodiment, after step c4 and before step c5, the method of the present invention further comprises applying a finite response filter to the pulse of the moving average type, preferably using a time window having a size corresponding to 10 % of the size of the set of discretized data from the registered heat change.
[0364]
[0365] In a preferred embodiment, after step c4 and before step c5, the method according to the present invention further comprises the following steps:
[0366]
[0367] ■ provide at least one time window;
[0368] ■ apply a Savitzy-Golay filter to the representation resulting from step c3 using a mathematical function and the time window provided, resulting in a filtered representation; Y
[0369] ■ if more than one time window is provided, average the representations obtained in a single function.
[0370]
[0371] In a more preferred embodiment, the three time windows have sizes of 20%, 30% and 40% of the time scale.
[0372]
[0373] Figures 18 a and b show a particular example of the profile of Figure 17c after applying a Savitzy-Golay filter. In particular, the Savitzy-Golay filter is used with a parabolic adjustment in this example. In addition, the filter is applied independently using three different time windows of 20%, 30% and 40% of the total time scale of the experiment. These time windows are wide enough to ensure that all types of fluctuations that may arise in the registered profile are mitigated.
[0374]
[0375] Since the filter is applied independently three times, in this example, the final result is taken as the average of the three resulting functions. Then, an interpolation was applied using cubic splines to obtain a complete reference vector for all time values.
[0376] It should be noted that, for the first and last points of this vector, since they cannot be interpolated, the heat change points are taken over time from the original experimental ones.
[0377]
[0378] In Figure 18b, a moving average has been applied to the filtered profile of Figure 18a. In particular, a 10% time window has been used. Advantageously, this is to decrease unlikely sudden abrupt changes in the previous estimated baseline.
[0379]
[0380] Figure 19 shows a corrected heat change as the difference between the registered heat change and the reference curve obtained from Figure 18b.
[0381]
[0382] An additional method for recovering the period of heat change recorded as a function of time in step (c) of the method according to the present invention is shown in Figures 20a to c and explained below:
[0383]
[0384] Figure 20a shows Figure 19 after applying the Fast Fourier Mobile Transform when a 20% time window is used. As can be seen, the FFT that begins at each moment is represented on the axis and with a gradient for the amplitude of each peak.
[0385]
[0386] In Figure 20b, the FFT shown on the y axis of Figure 20a is normalized by area. Therefore, FFT with several periods, that is, with several peaks, will have lower amplitudes. Advantageously, this diffuses the regions of the signal with less periodicity (or, what is the same, more noise).
[0387]
[0388] As a result, Figure 20c shows a final FFT obtained from the average of the ‘M-FFT normalized in the area’ of Figure 20b. In particular, in most cases, it provides a single peak that corresponds to the main period without the need to improve the processing of the data to recover the period.
[0389] In a preferred embodiment, steps (a) to (e) of the method of the present invention are repeated for a set of different flow rates while maintaining the same second fluid.
[0390]
[0391] As defined above, the method of the present invention also comprises a step (d) of providing a calibrated ratio of the interfacial tension as a function of the period for said constant flow rate and said second fluid.
[0392]
[0393] In this regard, another aspect of the present invention relates to a method for establishing the calibrated ratio provided in step (d) of the method as defined above, in which this method comprises the steps of:
[0394]
[0395] i. applying steps (a) to (c) of the method according to any one of claims 1 to 21 to at least two first pure liquids different from which the respective interfacial tension with the second fluid introduced in step (a) is known at a certain flow rate;
[0396] ii. represent their respective interfacial tensions according to their respective periods obtained; Y
[0397] iii. adjust the data plotted to a function thus providing a relationship between the interfacial tension to be determined and the period for said given flow rate.
[0398]
[0399] As a result of this method, the calibrated ratio of Figure 6 will be obtained, for example.
[0400]
[0401] In a preferred embodiment, steps (i) to (iii) are repeated for the same first different pure liquids in a set of different flow rates, where for each of these flow rates a different function is obtained.
[0402]
[0403] Another aspect of the present invention relates to a data processing apparatus comprising means for carrying out steps (c) to (e) of the method of the present invention.
[0404]
[0405] The present invention also relates to a computer program comprising instructions that, when the program is executed by a computer, causes the computer to carry out steps (c) to (e) of the method as defined above.
[0406]
[0407] Another aspect of the present invention relates to a computer-readable medium comprising instructions stored therein which, when executed, causes the computer to carry out steps (c) to (e) of the method as defined. previously.
[0408]
[0409] As mentioned above, the method of the present invention can be performed using commercially available calorimetry devices without any modification.
[0410]
[0411] Therefore, another aspect of the present invention relates to the use of a calorimeter for the determination of the interfacial tension between a first liquid fluid with a second fluid.
[0412]
[0413] In a preferred embodiment, the calorimeter is an isothermal titration calorimeter (ITC).
[0414]
[0415] Minor modifications in the calorimetry or the device for measuring the calorimetry would allow to determine the bubble formation processes with more resolution. This would allow quantifying both the thermodynamics and the kinetics of the process. Therefore, the recorded signal has less noise and, consequently, needs less data processing.
[0416]
[0417] In a particular embodiment, the calorimeter used to carry out steps (a) and (b) of the method of the present invention comprises:
[0418]
[0419] - a container cell configured to separately accommodate a first liquid of a second fluid;
[0420] - a first capillary configured to introduce the second fluid into the first liquid;
[0421] - first means of transporting fluid communication with the first capillary, the first means of transport are configured to transport the second fluid at a constant flow rate to the first liquid such that said second fluid is introduced into the first liquid as drops or bubbles; - detection means in thermal contact with the first liquid, and configured to detect the heat change associated with the periodic formation of successive drops or bubbles; Y
[0422] - a recording unit associated with the detection means and configured to record the heat change detected by the detection means in function weather.
[0423]
[0424] Surprisingly, the inventors of the present invention have observed that the wider capillaries result in different recorded data and, therefore, a different accuracy obtained, since the wider the capillaries are, the greater the accuracy of the registered heat change .
[0425]
[0426] In a particular embodiment, the calorimeter used to carry out steps (a) and (b) of the method of the present invention further comprises a second capillary configured to introduce a second different fluid into the first liquid, and a second means of transport in fluid communication with said second capillary, in which the second transport means are configured to transport said second different fluid at a constant flow rate to the first liquid.
[0427]
[0428] Therefore, according to this embodiment, it is possible to modify the solute concentration or the solvent nature of the first liquid in a single experiment.
[0429]
[0430] Advantageously, with two independent injection systems (one intended to change the composition of the first liquid in the sample cell and the other to introduce the second fluid) avoids the need to open the system to change the composition. This allows the total time of the experiment to be accelerated, since the time required to cover a variety of solvent mixtures is significantly reduced. Therefore, measurements of the fluid / fluid interfacial properties are greatly facilitated. By using two independent injectors, the change in heat in the formation of bubbles for each solute concentration could be measured, as well as the heat involved in the change of concentration in the volume phase.
[0431]
[0432] Advantageously, an injection system with improved pressure control achieves a dual effect since, on the one hand, the pressure control allows better control over the measurement of heat change and, on the other hand, the pressure control comes with a Pressure indication so that not only the information on the frequency of bubble formation and the associated heat is obtained by measuring the heat change, but also by the variation in pressure that the capillary undergoes when the bubble is released.
[0433]
[0434] In a preferred embodiment, the calorimeter sensing means is a thermistor or a thermoelectric device, such as a peltier module.
[0435]
[0436] EXAMPLES
[0437]
[0438] Interfacial Tension Measures
[0439]
[0440] In Figure 3, the interfacial tension of the three samples was measured at 298 ± 0.1 K using a Lauda drop volume tensiometer (TVT model 2, Germany) with the measuring cell connected to an external temperature bath. In all cases a capillary with an inner radius of 1.70 mm and a 2.5 ml syringe were used.
[0441]
[0442] In all experiments, ultrapure water (Elix 3 purification system, Milipore Corp.), ethanol (99.8% minimum purity of Panreac) and an aqueous solution of dodecyl-pD-maltopyranoside (C ¹² G ² ) 0 were used. , 55 mM. The surfactant (from Anatrace) and ethanol were used as received.
[0443]
[0444] The measurements were made using the "standard mode" programmed in the LAUDA software, that is, the flow rate is reduced sequentially 4 times from 0.81 s-1 ^ L for the water and surfactant solution and from 0.40 s-1 ^ L for ethanol, the maximum volume of the drop is recorded when it is separated from the capillary. The interfacial tension values obtained were 70.95 ± 0.11 mN / m, 21.85 ± 0.10 mN / m and 34.81 ± 0.20 mN / m for water, ethanol and the surfactant solution, respectively.
[0445]
[0446] The calorimetric experiments were performed with an Isothermal Titration Calorimeter instrument (VP-ITC of MicroCal, Inc). The injection syringe was carefully cleaned and filled with normal air at room pressure. The syringe air was continuously injected into the sample cell containing one of the liquids at fixed constant flow rates of 0.111, 0.055, 0.028 and 0.022 ^ L / s, according to the experiment. Rates lower than 0.022 ^ L / s are not allowed in the injection system used. Thus, a series of bubbles formed and released at the tip of the capillary. The stirrer was turned off in all measures to avoid mechanical disturbance of the bubbles and, therefore, ensure that they are released spontaneously when they reach a critical volume. No system was introduced to eliminate the released bubbles, so they can travel to the top of the sample cell shaped like a coin or higher up through the connected outlet tube, finally reaching the air space at the top of the tube, staying there until the end of the experiment. Parallel air injection experiments were performed outside the calorimeter in a simple pyrex flask to observe bubble injection.
[0447]
[0448] Raw ITC data (power versus time graphs) showed a highly reproducible periodic profile for experiments conducted at moderate flows. The formation of each bubble was clearly identified by an acute negative peak (exothermic process) followed by a positive plateau, before the signal returns to the baseline. This behavior was clear for the experiments carried out with water and the surfactant solution (Figs. 2, 3, 4 and 5) and reveals the presence of at least two kinetic processes for each bubble. For ethanol, the signal seems to evolve over time within the same experiment, and the period between bubbles is significantly shorter than that of water and the solution of C ¹² G ² (see Figs. 6 and 7). In addition, the signal corresponding to different bubbles in ethanol seems to overlap at 18 and 36 s / pL and, to a lesser extent, also at 45 s / pL and, therefore, a baseline between the bubbles is not detected (Fig . 3). If the flow rate is too high, it may not be possible to distinguish the formation of bubbles and, therefore, it was not possible to obtain a clear signal at 9 s / pL for this solvent due to the extremely high superposition of the calorimetric signal between bubbles at that flow rate.
[0449]
[0450] As expected, the faster the injection, the shorter the bubble formation period will be. For each flow rate, the interfacial tension of the different samples proved to be perfectly proportional to this period (see Fig. 4). This allows interfacial tension measurements to be made using ITC without modifications to the instrument, by obtaining a calibration curve for a variety of samples / mixtures, as in other methods for determining interfacial tension (for example, the maximum volume method of fall). The area of the signal corresponding to each bubble was integrated, separating the positive and negative contributions. A polynomial baseline correction was applied to perform this integration. Both contributions were well reproducible for different injections within the same experiment and also for different independent experiments (see Fig. 8). As mentioned earlier, these signals must contain information on at least two coupled processes. Using the experimental configuration of the instrument without modifications, the volume of the bubbles is expected to be between 3 and 9 pL, Depending on the liquid used.
[0451] Ċ

权利要求:
Claims (32)
[1]
1. - A method for determining the interfacial tension between a first liquid and a second fluid, the method comprising the steps of:
to. introducing the second fluid into the first liquid at a constant flow rate to cause the second fluid to periodically form successive drops or bubbles;
b. record the heat change of step (a) as a function of time, obtaining a periodic profile of heat versus time;
c. obtain the heat change period recorded in step (b);
d. providing a calibrated interface tension ratio as a function of the period for said constant flow rate and said second fluid; and e. correlate the period obtained in step (c) with the calibrated ratio and determine the interfacial tension between the first liquid and the second fluid for said constant flow rate.
[2]
2. - The method according to claim 1, wherein step (c) further comprises correcting the heat recorded as a function of time based on a reference curve of said heat change, such that the heat change corrected It oscillates around a constant value.
[3]
3. - The method according to claim 2, wherein correcting the heat change based on the reference curve comprises the following steps:
c1. obtain the heat change as a set of data such that:
if the heat change is recorded continuously, the heat change is discretized in a data set; or
if the heat change is recorded by sampling, step c2 is performed;
c2. oversample said data set with randomly chosen data, and distribute it over the recorded data set,
c3. represent the data of step c2 in a 2-D histogram, preferably each class of the 2-D histogram having a width equal to the square root of the size (L) of the original data set;
c4. calculate the average value of heat change for each class of the 2-D histogram, and represent said calculated average value as a function of time;
c5. interpolate the data resulting from the previous steps in a smooth curve, preferably by means of a cubic spline function, obtaining a reference curve; Y
c6. generate a corrected heat change as the difference between the registered heat change and the reference curve represented as a function of time in such a way that the corrected heat change generated oscillates around 0 over time.
[4]
4. The method according to claim 3, wherein after step c4 and before step c5 the method further comprises applying a finite impulse response filter of the moving average type, preferably using a time window having a size corresponding to 10% of the size of the data set discretized from the registered heat change
[5]
5. - The method according to any of claims 3 or 4, wherein after step c4 and before step c5, the method further comprises the following steps:
• provide at least one time window;
• apply a Savitzy-Golay filter to the representation resulting from step c3 using a mathematical function and the time window provided, resulting in a filtered representation; Y
• if more than one time window is provided, average the representations obtained in a single function.
[6]
6. - The method according to claim 5, wherein three time windows with sizes of 20%, 30% and 40% of the time scale are provided.
[7]
7. - The method according to claim 2, wherein correcting the heat change based on a reference curve comprises the following steps:
c1 ’. obtain the heat change as a data set such that if the heat change is recorded continuously, the heat change is discretized in a data set, or
if the heat change is recorded by sampling, step c2 'is performed;
c2 ’. select a percentage of data, said data being randomly selected .;
c3 ’. adjust the data to a smooth curve, preferably using a cubic splines function;
c4 ’. repeat steps c2 ’to c3’ for a plurality of different data sets and adjust those data sets to the corresponding smooth curve;
c5 ’. obtain the average value of these smooth curves corresponding to each data set, obtaining a reference curve;
c6 ’. generate a corrected heat change as the difference between the original heat change and the curve represented as a function of time such that the corrected heat change oscillates around the value 0 over time.
[8]
8. - The method, according to any of claims 3 to 7, where the heat change discretization is performed using the Monte Carlo method.
[9]
9. - The method according to any of claims 1 to 9, wherein in step (c) the period of heat change recorded as a function of time is obtained by applying any of the following techniques to the corrected heat change:
Global Fourier transform over all registered heat change profile; or fast mobile Fourier transform, preferably in a 20% time window.
[10]
10. - The method according to claim 9, wherein the first liquid has a given concentration of a solute with surface activity, and steps (a) to (b) are repeated at least once changing said given concentration of solute, at less two different heat changes are recorded in time domain for different solute concentrations;
wherein after obtaining the period according to claim 8 for each of these recorded heat changes, the method further comprises applying the Next steps to each of the transformed heat changes in the frequency domain:
• determine the period with the highest amplitude for each of the at least two heat changes transformed and represent the periods against the concentration of solutes;
• adjust the set of periods to a mathematical function;
• identify outliers between these periods, and:
or discard at least one of them, and / or
or readjust the period for at least one of these outliers for another period that falls within the adjusted mathematical function.
[11]
11. - The method according to claim 10, wherein the mathematical function to which the set of periods is adjusted is of the Langmuir Isotherm type or a logarithmic-polynomial function.
[12]
12. - The method according to any of claims 10 or 11, wherein the transformation of heat change into frequency domain after applying any of the techniques defined in claim 8 comprises more than one period identified as the corresponding main period to the period with the highest amplitude, and at least one secondary period corresponding to periods with smaller amplitudes;
wherein the method comprises in step (c) the following steps applied to the amplitude function versus period resulting from the application of any of the techniques defined in claim 9:
• break down the function into a number N of Gaussian functions over the main period of the function;
• evaluate the amplitude-width ratio for each Gaussian function, the one with the highest ratio is identified as the main Gaussian function;
• calculate the area of intersection of each remaining Gaussian function with the main Gaussian function;
• establish a weighting value for each Gaussian function based on that area of intersection; Y
• obtain the value of the period taking into account the contribution of each Gaussian function with its weighting value.
[13]
13. - The method according to claim 12, wherein steps (a) to (b) are repeated at least once in the same conditions, at least two different heat changes being recorded in the time domain corresponding to different solute concentrations;
wherein the main Gaussian function is identified with that which has the period closest to the expected mathematical function according to any of claims 10 or 11.
[14]
14. - The method according to claim 2 and any of claims 1 to 13, wherein step (c) further comprises determining a particular time interval of heat change or corrected heat change having an acceptable variance with respect to the full time interval.
[15]
15. - The method according to claim 2 and any one of claims 1 to 14, wherein the determination of the particular time window of the registered or corrected heat change comprises the following steps:
• select at least one provisional time window of the heat change registered or corrected with a predetermined size, preferably a quarter of the full time range;
• calculate the variance of each of the constant provisional time windows and identify the provisional time window that has the lowest variance;
• sequentially increase the size of the identified time window for a predefined time, and calculate for each iteration the associated variance within said increased time window;
• Continue to increase the size of the provisional time window by the same predefined time size until:
or the associated variance reaches an unacceptable value, preferably until the associated variance of the last iteration doubles the variance of the previous iteration, or until
or the associated variance in each iteration converges, this convergence is achieved when a truncation error is less than a value predetermined;
• designate the last incremental time interval with an acceptable variance as the particular time window of the corrected heat change that has an acceptable variance with respect to the full time range.
[16]
16. - The method according to any of claims 1 to 15, wherein step (c) further comprises, before obtaining the period of the registered heat change, the application of the autocorrelation to the heat change registered in the domain weather.
[17]
17. - The method according to any one of claims 1 to 16, wherein steps (a) to (e) are repeated for a set of different flow rates while maintaining the same second fluid.
[18]
18. - The method according to any of claims 1 to 17, wherein the second fluid is a gas, and preferably air.
[19]
19. - The method according to any of claims 1 to 18, wherein the constant flow rate at which the second fluid is introduced into the first liquid ranges between 200 microliters in 9000 seconds and 200 microliters in 900 seconds.
[20]
20. - The method according to any of claims 1 to 19, wherein the temperature is kept constant during steps (a) and (b).
[21]
21. - The method according to any one of claims 1 to 20, wherein steps (a) and (b) are carried out by using a calorimeter.
[22]
22. - A method for establishing the calibrated ratio provided in step (d) of the method according to any of claims 1 to 21, wherein this method comprises the steps of:
i. applying steps (a) to (c) of the method according to any one of claims 1 to 21 to at least two first pure liquids different from which the respective interfacial tension with the second fluid introduced in step (a) is known at a certain flow rate;
ii. plot their respective interfacial tensions as a function of their respective periods obtained; Y
iii. adjust the data plotted to a function thus providing a relationship between the interfacial tension to be determined and the period for said given flow rate.
[23]
23. - The method for establishing the calibrated ratio according to claim 22, wherein the method comprises repeating steps (i) to (iii) for the same first different pure liquids in a set of different flow rates, wherein for each of these flow rates gets a different function
[24]
24. - A data processing apparatus comprising means for carrying out steps (c) to (e) of the method according to any one of claims 1 to 21.
[25]
25. - A computer program comprising instructions that, when the program is executed by a computer, causes the computer to carry out steps (c) to (e) of the method according to any of claims 1 to 21.
[26]
26. - A medium readable by a computer comprising stored instructions thereon which, when executed, causes the computer to carry out steps (c) to (e) of the method according to any one of claims 1 to 21 .
[27]
27. - Use of a calorimeter to determine the interfacial tension between a first liquid fluid with a second fluid.
[28]
28. - Use of a calorimeter in the method according to any of claims 1 to 21 to carry out steps (a) and (b), the calorimeter comprising:
a container cell configured to separately accommodate a first liquid of a second fluid;
a first capillary configured to introduce the second fluid into the first liquid;
first means of transport in fluid communication with the first capillary, the first means of transport configured to transport the second fluid at a constant flow rate in the first liquid such that said second fluid is introduced into the first liquid in the form of droplets or bubbles;
detection means in thermal contact with the first liquid, and configured to detect the heat change associated with the periodic formation of droplets or bubbles successive; Y
a recording unit associated with the detection means and configured to record the heat change detected by the detection means as a function of time.
[29]
29. - Use of a calorimeter according to claim 28, wherein the calorimeter further comprises a second capillary configured to introduce a second different fluid into the first liquid, and a second means of transport in fluid communication with said second capillary, in that the second transport means is configured to transport said second fluid different from said constant flow rate in the first liquid
[30]
30. - Use of a calorimeter according to any of claims 28 or 29, wherein the first means of transport of the calorimeter comprises a pressure control sensor.
[31]
31. The calorimeter according to any of claims 28 to 30, wherein the detection means is a thermistor or a thermoelectric device, such as a peltier module.
[32]
32. - The calorimeter according to any of claims 27 to 31, wherein the calorimeter is an isothermal titration calorimeter.

类似技术:

---

公开号 | 公开日 | 专利标题

---

Zielenkiewicz et al.1999|The Vapour Pressure and the Enthalpy of Sublimation: Determination by inert gas flow method

---

Horita1988|Hydrogen isotope analysis of natural waters using an H2-water equilibration method: a special implication to brines

---

Li et al.2017|Studies in vacuum membrane distillation with flat membranes

---

BR112012005888B1|2019-10-22|graphene nanopore sensors and method for evaluating a polymer molecule

---

ES2207649T3|2004-06-01|ENVIRONMENTAL CHECKING OF ORGANIC COMPOUNDS.

---

ES2536783T3|2015-05-28|Device for detecting volatile substances, device using said device and relevant operating method

---

Petrov et al.2010|A joint use of melting and freezing data in NMR cryoporometry

---

ES2745339A1|2020-02-28|Method for determining interfacial tension |

---

BR112012006182B1|2019-10-22|cutting device having at least one unipolar cutting block comprising a contact bridge and circuit breaker;

---

Roy et al.2013|Probing molecular interactions of ionic liquid in industrially important solvents by means of conductometric and spectroscopic approach

---

Kostoglou et al.2011|A new device for assessing film stability in foams: Experiment and theory

---

Bartels-Rausch et al.2013|Diffusion of volatile organics through porous snow: impact of surface adsorption and grain boundaries

---

Morgan et al.1992|Kinetics of recovery of hexadecyltrimethylammonium bromide by flotation

---

Piccinini et al.2004|Use of an automated spring balance for the simultaneous measurement of sorption and swelling in polymeric films

---

WO2020043792A1|2020-03-05|Method for determining interfacial tension

---

ES2787004T3|2020-10-14|Method to measure carbonation levels in open container beverages

---

Żarska et al.2017|Surface tensions and densities of concentrated aqueous solutions of citric acid

---

Bourg et al.2001|Hydrogen and oxygen isotopic composition of aqueous salt solutions by gas–water equilibration method

---

Gómez-Álvarez et al.2013|Excess second-order thermodynamic derivatives of the {2-propanol+ water} system from 313.15 K to 403.15 K up to 140 MPa. Experimental and Monte Carlo simulation study

---

ES2655203T3|2018-02-19|Enhanced vapor phase spectroscopy

---

Kostoglou et al.2015|On the identification of liquid surface properties using liquid bridges

---

Rodríguez et al.2018|Volumetric and acoustic properties of some sodium sulfonamides in dilute aqueous solutions at several temperatures

---

Mazinani et al.2011|Experimental study on equilibrium solubility |, density, viscosity and corrosion rate of carbon dioxide in aqueous solutions of ascorbic acid

---

Jóźwiak et al.2017|The physicochemical properties and viscosity behavior of crown ether 18C6 in the mixture of water with N, N-dimethylformamide

---

Nakai et al.2005|High precision volumetric gas adsorption apparatus

同族专利:

---

公开号 | 公开日

---

ES2745339B2|2021-08-31|

引用文献:

---

公开号 | 申请日 | 公开日 | 申请人 | 专利标题

---

US20140238117A1|2011-09-23|2014-08-28|Centre National De La Recherche Scientifique|Determination of interfacial tensions in supercritical conditions|

---

KR20160128554A|2015-04-28|2016-11-08|세종대학교산학협력단|Apparatus and method for analysing interfacial properties of oil|

---

CN105043936A|2015-07-08|2015-11-11|中国石油天然气股份有限公司|Device and method for measurement of contact angle and interfacial tension under simulative oil reservoir conditions|

---

US20180156939A1|2016-12-02|2018-06-07|Schlumberger Technology Corporation|Method for prediction of live oil interfacial tension at reservoir conditions from dead oil measurements|

---

法律状态:
2020-02-28| BA2A| Patent application published|Ref document number: 2745339 Country of ref document: ES Kind code of ref document: A1 Effective date: 20200228 |

---

2021-08-31| FG2A| Definitive protection|Ref document number: 2745339 Country of ref document: ES Kind code of ref document: B2 Effective date: 20210831 |

优先权:

---

申请号 | 申请日 | 专利标题

---

ES201830848A|ES2745339B2|2018-08-28|2018-08-28|Method for determining interfacial tension|ES201830848A| ES2745339B2|2018-08-28|2018-08-28|Method for determining interfacial tension|

---

PCT/EP2019/073001| WO2020043792A1|2018-08-28|2019-08-28|Method for determining interfacial tension|