西班牙专利ES2603603A1 Interfacial shear rheometer by magnetic needle and system and method of actuation (Machine-translati

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专利摘要:
Interfacial shear rheometer by magnetic needle and system and method of actuation thereof. The needle drive system of an interfacial magnetic needle shear rheometer comprises two permanent magnets (13) with magnetic axes perpendicular to the plane of the interface in which the magnetic needle (3) of the rheometer (30) is located. The magnets (13) are located at the same distance (h) from said plane and with their polarities inverted one with respect to the other. The drive system also comprises drive means (15) for moving the magnets (13) oscillatory at a frequency ω in a longitudinal direction parallel to the plane of the interface, keeping the distance between the magnets (d) constant. Among other advantages, the present invention allows an initial positioning of the needle (3) very precise, as well as a perfect characterization of the rheological properties of thin films at low frequencies. (Machine-translation by Google Translate, not legally binding)
公开号:ES2603603A1
申请号:ES201531113
申请日:2015-07-28
公开日:2017-02-28
发明作者:Javier TAJUELO RODRÍGUEZ；Miguel Ángel RUBIO ÁLVAREZ；Juan Manuel PASTOR RUIZ
申请人:Universidad Nacional de Educacion a Distancia UNED；Universidad Politecnica de Madrid；
IPC主号:

专利说明:

Field of the invention 5
This invention falls within the area of interfacial rheometers of shears by magnetic needle (hereinafter RICAM). These rheometers allow to measure the viscoelastic properties of thin films of materials of technological interest located in a liquid-gas or liquid-liquid interface by means of magnetic needles moved by magnetic fields. 10

Fine films that separate fluid phases occur in all industrial processes involving colloids, micelles, foams and aerosols, so that knowledge of the mechanical properties of these films has practical implications of great relevance. fifteen

Background of the invention
Rheology is the branch of mechanics that studies the properties of materials subjected to stresses that produce deformations and / or flows in said materials. In rheology, the properties of the materials are characterized by the relationship between stresses and the displacements of the elements of the material.

When the materials studied are arranged in thin layers (less than 1 micron thick) at the interface between two fluids (liquid-liquid or liquid-gas), we talk about interfacial rheology. This branch of rheology is very useful for characterizing the mechanical properties of systems in which the phenomena that occur at the interface dominate their behavior (colloidal systems, microemulsions, foams, etc.)

In interfacial rheology, systems are considered representable in a two-dimensional space (for example, a horizontal plane) and only movements 30 at the shear and compression type interface are considered. Compression movements (dilatational rheology) produce movements equivalent to a longitudinal wave in one of the directions of the plane, so that some areas of the film are subjected to expansion efforts and others to compression stresses. On the other hand, the movements
Shear are equivalent to a transverse wave in one of the directions of the plane. This is the excitation mode in which RICAM systems work.

RICAM systems measure the viscosity and elasticity properties of a material located at an interface. In a material that is an ideal elastic solid, elasticity 5 relates the tension exerted on it with the deformation that is recovered when said tension is removed. In a material that is a linear viscous fluid, the viscosity relates the stress exerted with the flow of a liquid. However, most of the materials subjected to shear stresses have both elastic and viscous components in their response. In order to obtain the viscoelasticity properties of a material it is necessary to be able to experimentally separate the elastic and viscous contributions from the deformation of the material. In the interfacial rheology, the objective is to extract the values of the dynamic modules (storage –elasticity- and superficial losses –viscosity-) of the material in a wide range of excitation frequencies.

Currently, in needle interfacial rheometers, it is used to prepare the sample that you want to measure an extensive but shallow container that is filled with the fluid that forms the subphase (usually ultrapure water) and the film to be studied is formed on the air interface -Water. The magnetic needle is placed at the interface and through a magnetic field 20 a force, oscillating in time, is exerted on the needle that transmits an effort (force / length) to the interface and the subphase fluid that are in contact with the needle The subsequent movement of the needle is affected by the fluid and the interface and allows obtaining the rheological properties of the interface.
A geometric parameter of the needle that is of great importance is its diameter, since the smaller the smaller the contact area of the probe with the subphase and the more easily the friction generated by the contact line between the film and the probe generated by the contact between the subphase and the probe (Brooks et al., 1999). In addition, smaller diameter probes generally have the advantage of having less inertia but the disadvantage of needing higher intensity magnetic fields to induce movement.

There is a commercial RICAM system, manufactured by Biolin-KSV, which uses magnetic needles consisting of a glass capillary, sealed at both ends, inside which a wire of magnetic material has been introduced. These probes are offered in different versions with diameters not less than 400 microns. With these needles a maximum resolution of 10-6 Pa.m.s in interfacial viscosity and 10-6 N / m in dynamic module can be achieved. 5 This commercial device generates the necessary magnetic field through a pair of coils through which a certain electric current flows. The force generated on the needle will be proportional to the intensity that circulates through the coils and the magnetic dipole moment of the needle, so the maximum force will depend on the maximum current that the coils can withstand and the volume of the needle itself . 10

Recently (Tajuelo et al., 2015), the use of needles in RICAM devices consisting of magnetic micro-wires encapsulated in glass, with total diameters between 15 and 25 microns, has been described. With these needles, a maximum resolution better than 10-7 Pa.m.s in interfacial viscosity and 10-7 N / m in dynamic module has been achieved. The use of this new type of needles, which significantly improve the sensitivity of the technique, is partially limited in traditional RICAM systems, since its lower magnetic dipole moment makes large field gradients necessary, difficult to achieve with traditional systems. by coils
It is important to mention that the only reported calibration and data processing procedure that is valid for both types of needles (macro and micro-needles) has been described in Tajuelo et al., 2015. This procedure adequately takes into account the withdrawal inertia of the micro-needles and the spatial structure of the hydrodynamic velocity field at both the interface and the subphase. 25

Indeed, each probe necessarily requires a specific calibration prior to each measurement, since the response depends on the magnetic and geometric characteristics of the needle, as well as the configuration of the magnetic field of the system and the capillary properties (tension surface, contact angle) of the fluids that determine the interface where the needle is located.

Therefore, RICAM systems work in two successive stages:
i) Calibration of the needle response at the “clean” interface (without film) between the two fluids.
ii) Carrying out the measurements with the film already formed at the interface and subsequent treatment of the data obtained, in which the values of the parameters obtained in the needle calibration stage are used. 5

More in detail, the calibration procedure for magnetic needles of RICAM systems comprises the following steps:
1. Measurement of the displacement of the magnetic probe in a water-air interface without film in a frequency range ω, preferably selected from 10 between 0.01 and 100 s-1.
2. Obtaining, from these measures, the ratio of amplitudes and the offset between the force applied on the needle and its displacement.
3. Adjustment of the data obtained to a convenient theoretical model. In the case of traditional RICAM systems, the model currently used (Tajuelo et al., 15 2015) is based on the application of Newton's second law to a system consisting of an external oscillatory forcing, a harmonic well positioning constant elastic kpos and friction due to the subphase, calculated by the gradient of the velocity in the fluid layer in contact with the needle.
As for the stage of taking measurements for the film to be characterized and the treatment of the data, the most current method is based on the numerical / analytical resolution of the fluid velocity field, in the case of water-air interfaces (Reynaert et al., Journal of Rheology, 2008), adapted for the calculation of the dynamic modules of the films (Verwijlen et al., 2011). This procedure allows to correctly obtain the number of Boussinesq, Bo, which is an important parameter in the measurements since it represents the relationship between the resistance to the movement of the needle exerted by the interfacial film and the subphase, respectively. Therefore, the higher the Bo value, the more accurate and reliable the measurement is.
The breakdown in stages of this method of data processing is as follows:
1. Performing measurements at a film interface over a wide frequency range, ω (typically between 0.01 and 100 s-1).
2. Selection of an initial value for the constant Bo.
3. Numerical resolution of the velocity equations in the subphase and the film in the formulation described in Verwijlen et al., 2011, (equations 21 to 24) for the configuration corresponding to the experiments of step 1.
4. Correction of the Bo value by means of the quotient between the experimental amplitude response and that obtained in stage 3 (Verwijlen et al., 2011, equations 25 to 27). 5
5. Iterative repetition of stages 3 and 4 until convergence in the value of Bo is obtained.
6. Use of the Bo value to obtain the dynamic modules according to the expressions given in Verwijlen et al. (2011).

At the current point of development of RICAM systems, it is interesting to find 10 improvements in an aspect related to the ease / convenience of use of RICAM systems as routine laboratory use systems (satisfaction of user experience) and in Two aspects related to the useful measuring range of these systems:
 Improved ease of use of RICAM systems. One of the major problems 15 presented by current RICAM systems, in terms of ease of use, is the placement of the needle in a well-defined initial position (both in terms of the center of mass position of the needle and in terms of to its initial orientation with respect to the axis of the coils that create the magnetic field gradient). This problem is combined with the need to prevent, during measurements, the needle 20 from escaping from the visibility zone of the camera that registers its movement.

In order for the oscillation of the needle to have a well-defined initial position, it is necessary to magnetically generate a small potential well, so that the point of lowest potential of the well (equilibrium point) is the initial position of the needle and that when suppressed the oscillating field gradient the needle returns to that point. In most RICAM systems this potential well is generated by means of a pair of coils in Helmholtz configuration (Brooks et al., Reynaert et al., Verwijlen et al.). This type of system creates, in general, a well of shallow potential in relation to its width, so that the initial position 30 of the needle is poorly defined and turns out to be very sensitive to external disturbances (air currents on the cuvette of experimentation, surface temperature gradients, convection in the subphase, etc.). It makes getting a good
Initial needle positioning is a rather painful routine and it is common for the needle to exit the well during measurements.

In the system described in Tajuelo et al., (2015), on the contrary, the equilibrium position is fixed by means of a permanent magnet placed on the upper cover 5 of the container containing the subphase and the interface and with its axis of magnetization perpendicular to the interface in which the needle is located. This system (Tajuelo et al.) Creates a well of deeper potential, preventing the escape of the needle during the measurements and slightly improving the ease of initial needle positioning, in terms of the position of the needle. Needle end closest to 10 permanent magnet, but control of the initial orientation of the needle remains complicated.

It is important to note that both the procedure for creating the potential well by means of Helmholtz coils and the permanent magnet have undesirable effects on the resolution of RICAM systems at low oscillation frequency (Tajuelo et al., 2015), as It will be explained below.

 Increased resolution in measurements for movies with low values of dynamic modules. The resolution of the low frequency RICAM devices is mainly limited by the potential well that allows the initial positioning of the needle and that confines the movement of the needle within the viewing area of the camera.

In fact, the introduction of said well introduces a term equal to the recovery constant of the potential well kpos in the ratio of amplitudes 25 deformation / force AR (ω). Since the term due to the resistance of the film is proportional to the frequency of oscillation, at a low frequency a regime is always reached in which the term due to the resistance of the film becomes much smaller than kpos and, consequently, the measurements at lower frequencies are no longer significant. Therefore, a direct way to improve the resolution of RICAM devices is, ideally, to eliminate (or, at least, sharply decrease) the potential well contribution in the force balance equation on the needle; that is, decrease or cancel the value of kpos.

It is interesting to improve this measurement threshold because the lack of resolution in the measurement of the mechanical properties of interfacial low viscosity films prevents the study of diluted films (low number of molecules per surface unit), whose mechanical properties are of great interest . For example, in the cosmetics industry this limitation in resolution prevents studying how much the surface concentration in the film can be decreased (i.e., the amount of surfactant molecules) while maintaining the desired properties of the coating, which may have repercussions. evident in both economic and environmental aspects. 10

 Increased magnetic force on the needle. The force induced by means of the coils is limited due to the need to use large coils but without air gap, since the interior space to the coils is occupied by the cuvette in which the fluids and the interface are located. fifteen

It is interesting to increase the intensity of the forces that can be applied on the needle since this would allow measurements to be made in interfacial systems of greater viscosity and elasticity such as films of molecules of biomedical interest (proteins, etc.) or water systems. surfactant-oil, which both interest arouse both in the field of oil extraction (secondary and tertiary recoveries) or in relation to the control of oil leaks in marine or river environment.

Bibliographic references 25 BROOKS, CT et al. An Interfacial Stress Rheometer To Study Transitions in Monolayers at the Air − Water Interface, Langmuir, Vol. 15, No. 7, March 11, 1999, pages 2450–2459.
REYNAERT, S et al. Analysis of the Magnetic Rod Interface Stress Rheometer. Journal of Rheology, Vol. 52, No. 1, 2008, pages 261-285. 30

VERWIJLEN, T et al. Study of the Flow Field in the Magnetic Rod Interface Stress Rheometer. Langmuir, Vol. 27, No. 15, June 22, 2011, pages 9345-9358.

TAJUELO, J et al. Magnetic microwire probes for the magnetic rod interfacial stress rheometer. Langmuir, Vol. 31, No. 4, December 15, 2014, pages 1410-1420.

Description of the invention
The invention relates to a new RICAM system in which the magnetic force application mechanism on the needle is not based on magnetic coils but on the precise displacement of a system of two permanent magnets of reduced dimensions. The magnets are placed in a horizontal plane at a height, also well defined and controllable, on the interface where the film is located, its magnetization axes are perpendicular to the interface and the platform on which the magnets are attached. it oscillates in the direction parallel to the axis of the needle. The pair of magnets creates a well of harmonic potential that we can characterize by an elastic constant that we will call ki. The movement of the platform that holds the magnets causes said potential well to describe oscillations in the direction parallel to the axis of the needle, generating a sinusoidal force on it.

A first aspect of the present invention relates to a needle drive system of a magnetic needle shear interfacial rheometer. Said drive system comprises two permanent magnets with magnetization axes perpendicular to the plane of the interface in which the magnetic needle of the rheometer is located. The magnets are located at the same distance from said plane and with their polarities reversed with respect to each other. The drive system also comprises drive means configured to move the magnets in a longitudinal direction parallel to the plane of the interface, keeping the distance between the magnets constant. The displacement is preferably performed in an oscillatory manner, at a frequency ω.

The drive system preferably comprises means for supporting the magnets responsible for supporting the magnets at a distance from the plane of the interface and transmitting the longitudinal movement from the actuation means to the magnets. In a preferred embodiment the support means comprise a plate with an intermediate groove between both magnets to allow the capture of the movement of the magnetic needle by the rheometer chamber. In another possible embodiment the means of
Support comprise a plate of transparent material. The support means can also be implemented as a separate support for each magnet.

The drive means may comprise a motor with a linear encoder to determine at every moment the longitudinal position of movement of the magnets. The actuation means are preferably configured to move the magnets, or the magnet support assembly, in the longitudinal direction of the rheometer channel.

The drive system may comprise a positioning system of the magnets in the longitudinal direction parallel to the plane of the interface configured to modify the distance between the magnets. This positioning system is a horizontal displacement system capable of moving the magnets away or closer to each other, by their relative displacement in the longitudinal direction parallel to the plane of the interface. This horizontal positioning system can be implemented in different ways, for example by means of a motor and independent linear encoder for each magnet. In a preferred embodiment, the drive means themselves can also be used as a horizontal positioning system. That is, the drive means can initially be used to establish the distance between the magnets. Subsequently, the actuation means would be used to move both magnets oscillatingly at a frequency ω in the longitudinal direction parallel to the plane of the interface, keeping the distance between the magnets constant.

The drive system may also comprise a positioning system for the magnets in the direction perpendicular to the interface plane, configured to modify the distance of the magnets to said plane. This positioning system is a system of vertical displacement capable of moving the magnets away or closer, or to the support-magnet assembly or to the support-magnet assembly-horizontal positioning system, with respect to the interface plane. This vertical positioning system can be implemented in different ways, for example by a motor and linear encoder.
The drive system preferably comprises a control unit responsible for controlling the drive means.

A second aspect of the present invention relates to an interfacial shear rheometer
by magnetic needle comprising a cuvette in which the subphase is deposited, a chamber for capturing the movement of the magnetic needle and a channel within which the movement of the magnetic needle occurs. Additionally, the rheometer comprises a needle drive system as described above.
The rheometer may comprise a control unit responsible for controlling the camera and the actuation means of the needle drive system. The control unit is preferably configured to:
- Activate the drive means to move the two magnets oscillatingly at a frequency ω in the longitudinal direction of the channel. 10
- Obtain the position of the magnets from the information of the drive means.
- Obtain the position of the magnetic needle from the images captured by the camera.
- Obtain the offset and the ratio of amplitudes between the position of the magnets and the position of the magnetic needle.
- Obtain, in a previous calibration procedure, the elastic constant of the potential well created by the magnets on the magnetic needle.
- Calculate, using the elastic constant and the offset and ratio of amplitudes, the dynamic modules and the complex interfacial viscosity of the film for the frequency ω. twenty

The control unit is preferably configured to perform frequency scans ω within a frequency range and to obtain the dynamic modules and the complex interfacial viscosity of the film for said frequency range.
The rheometer can additionally comprise a transparent lower window, practiced at the base of the cuvette, and a light source to illuminate the magnetic needle through the lower window. The rheometer can comprise mobile barriers to control the spatial extent of the film inside the cuvette.
A third aspect of the present invention relates to a method of actuating the needle of a magnetic shear interfacial rheometer. The actuation method comprises moving, in a longitudinal direction parallel to the plane of the interface in which the magnetic needle of the rheometer is located, two permanent magnets with axes of
magnetization perpendicular to said plane, the magnets being located at the same distance from said plane and with their polarities reversed with respect to each other. The displacement is preferably performed in an oscillatory manner, at a frequency ω.

A fourth aspect of the present invention relates to a method of measuring the viscosity of a film using an interfacial rheometer shear by magnetic needle. The viscosity measurement method comprises using the drive method described above.

The viscosity measurement method preferably comprises:
- move the two magnets oscillatingly at a frequency ω in the longitudinal direction of the channel;
- get the position of the magnets;
- obtain the position of the magnetic needle;
- obtain the offset and the ratio of amplitudes between the position of the magnets and the position of the magnetic needle;
- obtain, in a previous calibration procedure, the elastic constant ki of the potential well created by the magnets on the magnetic needle;
- calculate, using the elastic constant and the offset and ratio of amplitudes, the dynamic modules and the complex interfacial viscosity of the film for the frequency ω. twenty

The viscosity measurement method may comprise performing frequency scans ω within a frequency range and obtaining the dynamic modules and the complex interfacial viscosity of the film for said frequency range.
In this system, both the separation between the magnets and the height of the magnets on the interface can be adjusted so that the constant is at all times the most appropriate for the experiment to be performed. In addition, it allows precise initial positioning both positional (precise control of the center of the needle's position) and orientation (precise control of the needle orientation), since the pair of magnets 30 creates a torque that tends to maintain the magnetic needle in the direction parallel to the axis that joins the center of the magnets. Since the force generated by the oscillation of the needle is due to the movement of the potential well itself, there is no possibility of the needle escaping from the potential well by making large displacements that destroy the film.
that you want to measure. This feature also makes the needle always stay within the viewing range of the camera that records the movement of the needle. The system is useful both for the movement of commercial needles (type ISR42 of Biolin-KSV) and for micro-needles.
In this new system there is no potential well that remains static to fix the equilibrium position of the needle, that is, the equivalent theoretical value of kpos is null, so the low resolution limitations are eliminated directly frequency due to the finite value of kpos that were present in the coil systems. The only source of limitation of the resolution of the system is the Boussinesq number, that is, the relative importance between the resistance opposed by the film and the opposite by the subphase.

In addition, the intensity of the magnetic force applied by the magnets on the needle is much higher than that which can be generated in systems that operate based on the field created by coils. In the calculations made for a particular configuration (separation between 15 3cm magnets and 1cm interface-magnet height) and a commercial probe (ISR42, Biolin-KSV) forces of up to 500 µN are obtained, exceeding the 30 µN reported for the original design of the coil systems (Brooks et al, 1999).

Another typical drawback of traditional RICAM systems is that during formation 20 of the thin film to be measured, it can happen that a pronounced increase in surface pressure (decrease in surface tension) causes the needle to sink into the subphase. In the new RICAM system, in addition to the elastic force and the aforementioned torque, the pair of magnets generates a vertical force in the positive direction (upwards) on the needle. Consequently, the risk of the needle sinking into the subphase by reducing surface tension is minimized.

Brief description of the drawings
A series of drawings that help to better understand the invention and that expressly relate to an embodiment of said invention that is presented as a non-limiting example thereof is described very briefly below.

Figure 1A shows a film being deformed by a magnetic needle. Figure 1B represents a vertical section of Figure 1A.

Figure 2 represents a diagram of a traditional RICAM equipment, that is, of an interfacial rheometer of shear by magnetic needle in which the force on the needle is generated by means of a system of two coils, according to the state of the art.
Figure 3 represents a scheme of the new RICAM equipment in which the force on the needle is generated by means of a system of two permanent magnets of small size that oscillatingly move in the longitudinal direction of the needle.

Figure 4 shows the result of the numerical calculation of the magnetic field created by a cylindrical magnet and the reference system used.

Figure 5A schematically shows the physical arrangement of the magnets 13 and the needle 3 when it is displaced with respect to the equilibrium point. Figure 5B shows the graph of the theoretical value of the force exerted by the magnets on an ISR-15 needle 42 as a function of the displacement of the needle with respect to the equilibrium point for different heights, h, of the magnets on the needle. The same graphs as in Figure 5B are shown in Figure 5C but restricted to a small interval centered on the equilibrium point, together with the linear adjustment for each of the heights h. Figure 5D shows the resulting potential well for each of the heights h. twenty

Figure 6 shows the channel model, the needle and the pair of magnets, together with the reference system used in the formulation of the Navier-Stokes equation and the theoretical expressions corresponding to the ratio of amplitudes and offset. .
Figure 7 shows the data related to the displacements of the magnets and an ISR42 needle collected as a function of time during a calibration procedure for ω = 6.28 s-1, h = 40 mm.

Figures 8A and 8B show, respectively, the experimental values (points) and the 30 calibration curves (continuous curves) corresponding to the ratio of amplitudes and the phase difference between the displacements of the magnets and the commercial needle ISR-42, for various values of the height of the magnets on the needle, h.

Figure 9 shows the values of ki calculated by the calibration procedure described for the new RICAM system, as well as the curve obtained by the numerical calculation of the magnetic field created by the pair of magnets.

Figures 10A and 10B show, respectively, the experimental values (points) and the theoretical curve for a null value of kpos. (continuous curve) corresponding to the ratio of amplitudes and the phase difference between the instantaneous force exerted by the magnets and the displacement of the commercial needle ISR-42, for various values of the height of the magnets on the needle, h.
Figure 11A represents the ratio of amplitudes in the force-position representation measured on a clean water-air interface with a traditional RICAM system and with the new RICAM system of the present invention (the continuous curves represent the best adjustments resulting from the respective calibrations ). Experimental data equivalent to those of Figure 11A have been represented in Figure 11B but this time measured in a thin film of silicone oil with the traditional RICAM system and with the new RICAM system.

Figure 12 shows the results for the loss module and the complex viscosity obtained on a thin film of silicone oil using the new RICAM system 20 and the data processing procedure described herein.

Detailed description of the invention
The interfacial rheometers of magnetic needle shears (RICAM) allow to measure the viscoelastic properties of very thin layers (with thicknesses between nanometers and microns) 25 of a material by means of a magnetic needle 3 moved by magnetic fields. A typical system is illustrated in Figure 1A, consisting of a film 1 formed at the interface between two fluids and confined in one of its lateral directions between two flat walls 2 that remain at rest and form a channel of width W. The axis of the channel is a magnetic needle 3 resting at the interface in which the film 1 is formed. If a force F is exerted on the magnetic needle 3 in the direction of the channel axis, the needle moves longitudinally. In its displacement, it transmits a mechanical tension to the region of the film that is in contact with it, causing its deformation. If the displacement of the needle is d, the mechanical deformation of the surface will then be:
.2 / Wd

If the tension σ exerted by the magnetic needle 3 on the film 1 is periodic in time, the γ deformation obtained by measuring the position of the needle as a function of time will also be periodic with a certain amplitude, the same frequency of swing and a certain offset,. The dynamic module G is defined as the relationship between voltage σ and strain γ and, in general, depends on the frequency at which the measurement is made, that is, G is a function of. Using the complex exponential form you can write the form:) cos (0t) cos (0t
) (00)) ((0000)) (cos () cos () (itjtieeettG

Since it is a complex number, it is also called a complex module G *. It is therefore possible to separate its real and imaginary part:
) ('') (') (* iGGG

If the film exhibits viscoelastic behavior, in the elastic contribution the tension and deformation are proportional, while in the viscous contribution the tension is proportional to the rate of deformation. Taking into account that in an oscillatory movement 20 position and speed are 90 ° out of phase, it is concluded that the real part of the complex module is due to the elasticity of the film, while the imaginary part is due to the viscous component, that is, that we can identify:
 G ': Elastic or storage module (in coherence with the idea of elasticity as energy storage). 25
 G '': Viscous or loss module (consistent with the idea of viscosity as energy dissipation).

It can be concluded that the relationship between the elastic module G ’and the viscous module G’ ’is determined by the offset angle δ between tension and deformation: 30

) (tan) (') (' 'GG

In this way, if:
Purely elastic film.0''0) (tanº0) (G
Purely viscous film. 50 ') (tanº90) (G

Measuring the relationship between stress and strain is determined, and measuring the gap δ between stress and strain determines the relationship between the elastic and viscous part of G *.* G
A vertical section of Figure 1A can be seen in Figure 1B. The geometric characteristics of the magnetic needle 3 critically influence its behavior, especially in relation to the relationship between the resistance to movement experienced by the needle due to the film 1 and that suffered due to subphase 1 '(typically water ). Indeed, it can be considered that said resistance suffered by the magnetic needle 3 is due to two terms:
 On the one hand, the one that causes the film 1, and that occurs along the perimeter Pc (waterline) of the magnetic needle 3.
 On the other hand, the drag due to subphase 1 'of water, and that occurs along the entire surface Ac of contact between subphase 1' and magnetic needle 3. 20

The most common way to induce a longitudinal longitudinal movement over time in the magnetic needle 3 is by means of a magnetic field, as is done in traditional RICAM systems driven by Helmholtz coils, as shown in Figure 2. The Main elements of a traditional magnetic needle needle interfacial rheometer 20, operated by means of coils, are the following:
 Tray or bucket of Langmuir 4, usually made of Teflon or Delrin, where the subphase 1 ’of water is deposited on which the films 1 to be studied are generated.
 Camera 5, preferably a CCD camera, for the video capture of the movement of the magnetic needle 3 (the needle is not shown in the figure). 30
 Coils 6 for the generation of the oscillating magnetic field gradient that governs the movement of the magnetic needle 3.
 Channel 7, formed by two sheets of glass, or other material (Teflon, delrin, etc.), within which the movement of the magnetic needle 3 occurs.
 Bottom window 8 of glass or quartz through which the magnetic needle 3 is illuminated.
 Mobile barriers 9, usually Teflon or delrin, to control the spatial extent 5 of the film 1 which, therefore, allow varying the surface concentration of the film 1.
 Light source 10 to illuminate the magnetic needle 3 through the lower window.

In the center of the cuvette 4, channel 7 (schematically described in Figures 10 1A and 1B) is provided, formed by two parallel glass plates, separated by a distance W typically of about 2 cm, and of length much greater than the length of the needle. The needle used is composed of a magnetic core inside a glass capillary; for example, the needle ISR 42 has a total length L = 4.2 cm and mass m = 17.4 mg. In the center of the channel 7 the base of the cuvette 4 has the circular window 8 made of glass, about 2 cm in diameter, on whose vertical axis the light source 10 and, in the lower part, are arranged top, camera 5 connected to a zoom lens. This allows the position of one of the ends of the magnetic needle 3 to be detected at each instant.

The thin films 1 that it is desired to investigate are created on fluid-fluid interfaces 20 (usually water-air) in the Langmuir cuvette 4. In a typical experiment with a film in a water-air interface, the cuvette 4 is filled with the fluid that makes up the subphase (typically water). Next, the magnetic needle 3 is placed in the water-air interface, which is kept afloat by capillary forces, and the measures required to calibrate the mechanical resistance exerted by subphase 1 'are performed. Next, the film 1 is generated by spreading a solution of the material that will form the monolayer in a highly volatile solvent. Upon evaporation of the solvent, the film of the material will be formed on the water-air interface.

The measurements are made from the oscillatory longitudinal movement of the needle which is controlled by means of the action of an external magnetic field. For this, the axis of the channel 7 is made to coincide with the axis of two coils 6 placed symmetrically with respect to the center of the cuvette 4. These two coils are arranged in an anti-Helmholtz configuration, that is, separated by a distance equal to their radius, and crossed by the same current in
reverse direction. The coils 6 are connected to the output of a current amplifier. The input that governs the amplifier is connected to a digital function generator. Finally, a control unit 11 (for example, a computer) processes the images taken by the camera 5 to obtain the position of the end of the magnetic needle 3 in each image. 5

In this way it is possible to have precise values at each moment of the oscillations of the position of the magnetic needle 3 and of the current applied to the coils 6, which is the factor that determines the force exerted on the needle and, therefore, the mechanical tension exerted on the film. 10

From the relative phase and the relationship between the amplitudes of the current produced by the magnetic field gradient and the position of the needle, the complex dynamic module G * can be precisely obtained, with its elastic components G 'and viscose G '' The complex viscosity of the films can be obtained from the dynamic module G *. fifteen

To minimize the sensitivity of the system to impurities that are deposited in the water-air interface, a box consisting of methacrylate plates that surrounds the cuvette 4 and insulates it from the outside is usually used. In addition, this protects the interface of air currents that could generate flows that distort the measurement. twenty

The present invention relates to a new interfacial rheometer for magnetic needle shears driven by magnets with a magnetization axis perpendicular to the plane in which the needle moves. Figure 3 shows a diagram of the new magnetic needle shear interfacial rheometer 30 of the present invention, in which the movement of the needle 25 is induced by the displacement of two small permanent magnets 13 positioned so as to keep the needle 3 magnetic at a stable equilibrium point between them and with a perfectly defined orientation. As can be seen in Figure 3, the scheme is very similar to that of Figure 2 by replacing the pair of coils 6 with a support 14, for example a plate, on which the two magnets 13 are fixed with their polarities 30 inverted One respect to the other. The platform or support 14 is connected to an electromechanical system, drive means 15, with motor and linear encoder that allows it to be moved in the longitudinal direction of the channel 16 and to know its position at every moment. Although not shown in Figure 3, rheometer 30 may also have another system
of positioning that moves the plate in the vertical direction and that allows to control the height h of the plate and the magnets on the interface, which is a very important parameter in the system. Said positioning system in the vertical direction can be implemented in different ways, similar to how the horizontal displacement of the support 14 is performed, preferably using an electromechanical system (for example by a motor with a linear encoder). Finally, the system is connected to a control unit 22, for example a computer, which controls the movement of the motor 15 and receives and processes the encoder signal of the platform 14 and the images taken by the camera 12. The main elements they are, then:
 Tray or bucket of Langmuir 23, made of Teflon or Delrin, where the subphase 1 ’of water is deposited on which the films 1 to be studied are generated.
 Camera 12, preferably of the CCD type, for the video capture of the movement of the magnetic needle 3.
 Support plate 14 with permanent magnets 13, for the generation of the magnetic force 15 that acts on the needle and causes an oscillatory longitudinal movement, with a horizontal distance d of separation between magnets and a vertical distance h between magnets 13 and needle 3 The support 14 must allow the camera 12 to capture images of the needle 3, for which it can have a way that does not obstruct the camera 12 with the vision of the needle 3 (for example, two support clips of the 20 magnets joined by a longitudinal arm external to the vision of the chamber 12), or it can have an opening 21 made in its central part between the two magnets 13 (as in the example shown in Figure 3), or it can be manufactured in some transparent rigid material (glass, PMMA, polycarbonate, etc.). Although in this embodiment a plate is proposed as a support, another 25 types and forms of support could be contemplated in other alternative embodiments. An independent support for each magnet could also be contemplated, each support actuated by means of independent actuation so that the distance d between the magnets 13 can be modified at will and subsequently perform a synchronous movement thereof, being maintained at all times , during the operation of the rheometer to obtain the viscosity, the constant distance d once it has been set.
 Electromechanical system 15, consisting of motor and linear encoder, connected to support 14 and which allows it to move in the direction of channel 16.
 Channel 16, formed by two sheets of glass, or other material (Teflon, delrin, etc.), within which the movement of the magnetic needle 3 occurs.
 Transparent bottom window 17 of glass or quartz through which the magnetic needle 3 is illuminated.
 Teflon or delrin mobile barriers 18 to control the spatial extent of the film, which therefore allow the surface concentration of the film 1 to vary.
 Light source 19 to illuminate the needle through the lower window.

In contrast to the operation of a traditional RICAM device, in the rheometer of the present invention there are not two external forces acting on the magnetic needle 10 (force exerted by the coils and static well), but only one (dynamic well). The force generated on the magnetic needle 3 and which makes it oscillate now comes from a potential well that oscillates in the longitudinal direction of the device.

The force exerted by the pair of magnets 13 on a magnetic needle can be calculated numerically using standard electromagnetism methods. To do this, the magnetic field generated by a permanent magnet of the appropriate dimensions and magnetization is calculated numerically first (see Figure 4). Subsequently, the force exerted by the combined field of the pair of magnets 13 on a needle whose magnetic core has the dimensions and magnetic moment per unit of length 20 corresponding to the probe used is calculated.

As an example, Figure 5B shows the longitudinal force F that creates a pair of magnets 13 on a magnetic needle 3 (of type ISR-42) as a function of the displacement x of the needle with respect to the point of equilibrium (x = 0, situation centered with respect to the 25 magnets) for different vertical distances magnets-needle h (20mm, 30mm and 40mm). The physical arrangement of the magnets 13 and the needle 3 is shown schematically in Figure 5A. In this case the characteristics of the magnets 13 are magnetization, radius, height and separation between magnets, while those of the magnetic core of the needle 3 are length and magnetic moment per 30 unit length. The distance between magnets d may be greater or less than the length of the needle Lm as appropriate, depending on the needle and the magnetization of the magnets (in the particular case of Figure 5A the length of the needle Lm is greater than the distance between magnets d). The elastic force F exerted by the magnets 13 on the needle 3
when the center of mass 31 of the needle travels longitudinally with respect to the point of equilibrium (x = 0) it is a recovering force, in the opposite direction to the displacement, as shown in Figure 5A, where the needle 3 displaced to the right of the equilibrium point (in x +) and the resulting recovery force F in the opposite direction, applied in the center of mass 31 of the needle, which tends to take the needle 3 to the left, towards its equilibrium point ( x = 0).

The same graphs as in Figure 4A are shown in Figure 5C but restricted to a small interval of 1mm centered at the point of equilibrium (x = 0), together with the linear adjustment for each of the heights h. As can be seen in said Figure 5C, in the vicinity 10 of the equilibrium point or midpoint between the magnets (x = 0), the total force is well represented by an elastic force, proportional to the distance. Given that the typical oscillation amplitudes are less than 500 microns, it is perfectly justified to represent the force exerted on the needle by an expression of the form:
where ki is the slope of the linear fit of Figure 5C. Figure 5D shows the potential of the well as a function of the minimum distance for the three configurations corresponding to Figure 5C.

The theoretical model of the new RICAM system proposed in the present invention is explained below. Taking into account the reference system indicated in Figure 6, the z coordinate of the midpoint between the pair of magnets 13 is considered at each instant of time, which we will call zi (t). When the motor 15 that displaces the magnets 13 (in particular, displaces the support 14 of the magnets, not shown in Figure 6) performs a frequency oscillation ω and amplitude Ai, the position of the midpoint between the magnets in the system of Laboratory reference will be, using the complex exponent: 25

The z-coordinate of the center of the magnetic needle 3 is now considered, which we will call za (t). When the potential well generated by the magnets begins to oscillate, the needle will describe an oscillatory movement of equal frequency, of amplitude Aa and generally 30 offset a certain angle δpp with respect to the oscillation of the magnets, where the subscript pp refers to which is the gap between two positions, that of the magnets and the
of the magnetic needle. Therefore, the equation describing the oscillation performed by the magnetic needle 3 is:

where we have defined the complex magnitude Aa * as the product Aae-iδpp. During the movement of the well and magnetic needle 3, the center of mass 31 of the magnetic core is always close to the minimum of the well, and near the minimum the potential of the well can always be represented as a parabola, as shown in the Figure 5 D. Therefore, at each instant of time, the well will exert on the needle 3 a magnetic force that will be proportional to the distance between the center of the potential well, which is precisely zi, and the position of the center of the needle za: 10

where ki is the elastic constant of the potential well created by the magnets 13 on the magnetic needle 3. Assuming that the subphase 1 'is formed by water, and that the water-air interface is clean (without any thin film 1) as is the case during the calibration of the apparatus, the needle will suffer a friction due to the viscosity of subphase 15 1 '. Following the procedure described by Verwijlen et al (2011), said friction can be calculated numerically assuming a contact angle of 90 ° and a flat interface. The procedure is based on the calculation of the velocity profile in channel 16 from the Navier-Stokes equation. Considering the reference system in Figure 6, the Navier-Stokes equation takes the form 20
where Re is the Reynolds number, at the radius of the needle, p = ln (r / a), and g is a complex function that relates the displacement of each fluid element with the displacement of the needle:

This equation can be solved numerically (for finite differences, for example) with the appropriate boundary conditions:
                                    ()

Once the velocity profile in channel 16 is known, friction is calculated from the velocity gradient in the fluid layer in contact with the needle, and integrating over the entire surface thereof:
5 ∫ ()
where µ is the viscosity of subphase 1 ’. Knowing the force exerted on the needle 3 by the pair of magnets 13, as well as the friction due to subphase 1 ’, Newton's second law can be considered:
    ()
Substituting each of the terms that have been previously defined, the force balance equation takes the form:
    () ∫ ()

By rearranging terms, the ratio between the amplitudes of both oscillatory movements can be cleared:
                           ∫ ()

Again, the subscript pp refers to the fact that it concerns the ratio of amplitudes between two positions, that of the needle 3 and that of the magnets 13. The module of the complex amplitude ratio 20 defined in the previous equation will be equal to quotient between the amplitudes of the
oscillatory needle and magnet displacements, while the argument will be equal to the lag between both movements:
| | √ (∫ ([])) (∫ ([]))
() (∫ ([]) ∫ ([]))
where the subscript teo indicates that it is the ratio values of amplitudes and offset predicted by the theoretical model exposed. In the equations that define the relationship of amplitudes and the offset between the displacements of the needle and the magnets there is only one unknown term, the elastic constant ki, which will depend on the needle used (geometric dimensions and magnetic moment per unit of length), the distance 10 magnets-interface and the distance between the magnets. The device calibration procedure consists in determining the value of the constant ki for the different configurations related to the aspects mentioned above that are to be used. Both the ratio of amplitudes and the offset can be measured directly with the RICAM device of the present invention: the platform 14 that holds the magnets 15 13 is provided with a linear encoder that allows to know its position at every moment with great precision and The optical inspection system detects the position of the needle at every moment. In this way, Figure 7 can be constructed, in which the two signals are appreciated, position of the magnets pi and position of the needle pa in the coordinate z as a function of time t, for a specific case. By adjusting each of them to a sine function, the software of the control unit that controls the RICAM system calculates the ratio between both amplitudes and the offset. That is, the rheometer provides two experimental data: | | ()
where the subscript index indicates that it is experimental data. Therefore, the calibration of the device consists in performing frequency sweeps for those configurations that are desired to be used in the experiments, so that for each one
From the configurations, a value of ki can be calculated that adjusts the experimentally collected data to the theoretical equation that defines the ratio of amplitudes. Subsequently, the quality of the calibration can be checked by comparing the experimentally measured offset adjustment with that resulting from entering the calculated value of ki in the equation that defines the offset. In Figures 8A and 8B you can see the result of the calibration for the KSV-Biolin ISR-42 needle, a distance between 2 cm magnets and several magnet-interface distances h.

Figure 9 shows the values of ki versus the distance magnets-interface h obtained experimentally through the calibration procedure, as well as the curve 10 corresponding to the calculation of ki by the numerical resolution of the magnetic field created by the magnets described with anteriority. The excellent fit between the experimental values and the numerically calculated curve is particularly useful, since it confirms that the calculation of the magnetic force by the electromagnetism techniques allows to predict with great precision the value of ki corresponding to any distance h magnets-interface .

Similarly, if the interface height is the same each time the rheometer is used (this can be achieved by precise control of the added volume of water or liquid that forms the subphase), the rheometer calibration is not always necessary that is used, and experiments on thin films or monolayers can be carried out directly. It is usual to perform a first experimental calibration for each needle, to obtain the magnetic moment per unit of needle length. From there, no more calibrations are necessary, it would be enough with the numerical calculation to obtain the parameter ki. 25

A comparison is then made of the operation of the new RICAM system proposed in the present invention (Figure 3) with the traditional RICAM systems (Figure 2). In traditional RICAM systems, another type of representation is common, which we will denote with subscript fp, which relates the force applied to the displacement of the probe (this is because these two magnitudes are those measured by traditional RICAM devices). As will be seen below, this representation is equivalent to the pp representation set forth above and serves to illustrate the advantage of the new low frequency RICAM device. The relationship of
amplitudes and the offset between force and displacement ARfp and δfp respectively, where the subscript fp indicates that applied force and needle position are being related. First, we show how to pass the experimental data from the pp representation to the traditional fp representation:

Operating the quotient obtained, we calculate the module and argument:
| | √ | | () | |
() (() | | ())
Using the force balance equation, the theoretical expressions for the relation of amplitudes and offset in the fp representation can be calculated analogously:
| | √ (∫ ([])) (∫ ([])) () (∫ ([]) ∫ ([]))

Figures 10A and 10B show, respectively, the comparison between the ratio of 15 experimental and theoretical amplitudes and phase shifts. As can be seen, contrary to what happens in the pp representation, all the experimental data converges to the same curve, regardless of the value of ki, that is, regardless of the distance between magnets or the interphase-magnet distance. This is consistent with the theoretical prediction,
since ki does not appear in the pair of equations that define the relation of amplitudes and the offset in the representation fp.

To illustrate the differences with traditional RICAM devices, it should be remembered that in these there is a situation similar to a damped forced oscillator, in which there is an external forcing thanks to the field created by a pair of coils, a damping due to friction with the subphase, and a force that keeps the balance position of the needle fixed; This force is due to a well of potential created, either by another pair of coils (Brooks et al., Reynaert et al., Verwijlen et al.) or by a positioning magnet that remains fixed (Tajuelo et al.). The force due to this fixed potential well 10 can be represented as an elastic force characterized by a recovery constant that we will call kpos (elastic positioning constant). The equation of motion takes the form: ∫ ()
where F0 is the amplitude of the forcing. In operation, the expressions for the ratio of theoretical amplitudes and offset in the fd representation for a traditional RICAM device 15 can be calculated:
| | √ (∫ ([])) (∫ ([])) () (∫ ([]) ∫ ([]))

These two equations are the same as those obtained for the RICAM system of the present invention except for the presence in both of kpos, the elastic constant of the potential well that sets the equilibrium position of the needle.

That is, the theoretical model predicts that the dynamics that govern the new RICAM system is equivalent to that corresponding to traditional systems making the elastic constant kpos strictly zero. It should be remembered that in RICAM 25 devices
Traditional the value of the constant kpos can be reduced, but never completely annulled, since it is necessary to keep the needle aligned and with its equilibrium position in the center of the rheometer. Therefore, in traditional RICAM systems, a reduction in kpos is inevitably accompanied by a greater influence of any external disturbance (air currents, convective currents in the subphase, external vibrations, etc.) and consequently a growing difficulty in The experimental procedure. In the new RICAM device of the present invention, a zero kpos is achieved while maintaining a well-defined balance and needle alignment position. In addition, as will be seen later, a null value of kpos has great advantages in characterizing the rheological properties of thin films, especially at low frequencies.

Figure 11A shows a comparison of the ratio of amplitudes in the fp representation for a clean water-air interface for the two RICAM systems, the traditional and the new system object of the present invention. Continuous curves 15 represent the best adjustments resulting from the respective calibrations. As can be seen, both curves converge at high frequencies, but the traditional RICAM system has a plateau at low frequencies that is not observed in the new rheometer. Analyzing the theoretical equations that define each of the systems, it is demonstrated that for the traditional RICAM system it is verified: 20
       | |

Therefore, the differences at low frequencies have their origin in the strictly null value of kpos in the new RICAM system. These curves represent the response of the rheometer itself, in the absence of thin film or monolayer (in the absence of interfacial viscoelasticity). This response is determined by different contributions:
- Traditional RICAM system: inertia + subphase friction + positioning well (kpos).
- New RICAM system: inertia + subphase friction

The advantages that there is no positioning well in the new RICAM system can be seen in Figure 11B, which includes the ratio of amplitudes measured experimentally on a thin film 1 of silicone oil with both systems
RICAM This figure also shows the adjustment curves of Figure 11A that are the object of the calibration process. That is, the response that is measured in the presence of the thin film depends on the following contributions:
- Traditional RICAM system: inertia + subphase friction + positioning well (kpos) + interphase friction. 5
- New RICAM system: inertia + subphase friction + interphase friction.

The final resolution of the measures obtained in the RICAM systems depends on the ability to separate the contribution due to the interface from the global response measured experimentally. Such separation will be all the more precise the greater the contribution due to the interface with respect to the rest, that is, the greater the difference between the ratio of amplitudes for the clean interface and the ratio of amplitudes in the presence of the thin film. As can be seen in Figure 11B, at low frequencies the ratio of amplitudes measured with the traditional RICAM system for the thin film of silicone oil converges with the plateau mentioned in Figure 11A. That is, at low frequencies the potential positioner characterized by kpos dominates the dynamics of the system, even in the presence of the thin film 1. This causes that with a traditional RICAM system and at low frequencies, it is not possible to discriminate the contribution due to the interface, and therefore it is not possible to make significant measurements of the viscoelastic properties of the interface. On the contrary, in the new RICAM 20 system object of the present invention, the null value of kpos makes that, even at low frequencies, the ratio of amplitudes measured in the presence of the thin film is different from that measured with the interface clean, allowing the calculation of the viscoelastic properties of the interface.
The procedure for calculating viscoelastic modules from the data obtained in the presence of the thin film 1 that it is desired to characterize is analogous to that described in Verwijlen et al, 2011, adapted to the most convenient pp representation for the new RICAM system. First, the force balance equation is completed with the term corresponding to friction due to the interface: 30
() ∫ () ()

The value of ki is already known from the calibration described above, so the only unknown term in this equation is Bo *, the complex Boussinesq number. As mentioned in the description of the velocity profile calculation, the function g depends on Bo * through the Boussinesq-Scriven boundary condition. Therefore, no 5 is possible to clear Bo * directly from the last equation. To find the correct value of Bo *, that is, the value that adjusts the theoretical equation to the experimentally obtained result, the following iterative procedure is carried out:
    {} () () {} {}
where the numerator is the ratio of amplitudes measured experimentally in the presence 10 of the thin or monolayer film 1, and the denominator is the ratio of amplitudes calculated from the theoretical equation by entering Bo * {i}, the complex Boussinesq number from step i of the iterative procedure. After a number of iterations, which generally depends on the distance between the initial value given to Bo and the stationary final value obtained in the iterative procedure, convergence is reached and the value of Bo * is obtained which adjusts the experimental data to The theoretical equation. Once this is done, the elastic module G’s, the viscous module G’’s and the complex viscosity are calculated as: [] []
where µ is the viscosity of subphase 1 ’and is the radius of magnetic needle 3.
Figure 12 shows the final result of an experiment on a thin film 1 of silicone oil for three different interface-magnet heights, that is, for three different values of ki.

权利要求:
Claims (19)
[1]

1. Needle drive system of an interfacial magnetic shear rheometer, characterized in that it comprises:
- two permanent magnets (13) with magnetization axes perpendicular to the plane of the interface where the magnetic needle (3) of the rheometer (30) is located, the magnets (13) being located at the same distance (h) from said plane and with its polarities reversed with respect to each other;
- drive means (15) configured to move the magnets (13) in a longitudinal direction parallel to the plane of the interface, keeping constant the distance 10 between the magnets (d).

[2]
2. Drive system according to claim 1, characterized in that it comprises support means (14) for the magnets in charge of supporting the magnets (13) at a distance (h) from the interface plane and transmitting the longitudinal movement from the 15 drive means (15) to the magnets (13).

[3]
3. Drive system according to claim 2, characterized in that the support means (14) comprise a plate with an intermediate groove (21) between both magnets (13) to allow the capture of the movement of the magnetic needle (3) by part of the chamber (12) of the rheometer (30).

[4]
4. Drive system according to claim 2, characterized in that the support means (14) comprise a plate of transparent material.
[5]
5. Drive system according to any one of the preceding claims, characterized in that the drive means (15) comprise a motor with a linear encoder for determining at every moment the longitudinal position of movement of the magnets (13).
[6]
6. Drive system according to any of the preceding claims, characterized in that the drive means (15) are configured to move the magnets (13) in the longitudinal direction of the channel (16) of the rheometer (30).

[7]
7. Drive system according to any of the preceding claims, characterized in that it comprises a positioning system of the magnets (13) in the longitudinal direction parallel to the plane of the interface, configured to modify the distance between the magnets (d).
[8]
8. Drive system according to any of the preceding claims, characterized in that it comprises a positioning system of the magnets (13) in the direction perpendicular to the plane of the interface, configured to modify the distance (h) of the magnets (13) to that plane.
[9]
9. Drive system according to any of the preceding claims, characterized in that it comprises a control unit (22) responsible for controlling the drive means (15).

[10]
10. Interfacial rheometer for magnetic needle shears, comprising:
- a cuvette (23) in which the subphase (1 ’) is deposited;
- a camera (12) for capturing the movement of the magnetic needle (3);
- a channel (16) within which the movement of the magnetic needle (3) occurs;
characterized in that the rheometer (30) additionally comprises a needle drive system according to any one of claims 1 to 6. 20

[11]
11. Interfacial magnetic shear rheometer according to claim 10, characterized in that it comprises a control unit (22) responsible for controlling the chamber (12) and the actuating means (15) of the needle actuation system.
[12]
12. Magnetic needle shear interfacial rheometer according to claim 11, characterized in that the control unit (22) is configured to:
- activating the actuation means (15) to move the two magnets (13) oscillatingly at a frequency ω in the longitudinal direction of the channel (16);
- obtain the position of the magnets (pi) from the information of the drive means (15);
- obtain the position of the magnetic needle (pa) from the images captured by the camera (12);
- get the offset (δpp) and the ratio of amplitudes (ARpp) between the position of the
magnets (pi) and the position of the magnetic needle (pa);
- obtain, in a previous calibration procedure, the elastic constant ki of the potential well created by the magnets (13) on the magnetic needle (3);
- calculate, using the elastic constant ki and the offset (δpp) and amplitude ratio (ARpp), the dynamic modules and the complex interfacial viscosity of the film (1) for the frequency ω.

[13]
13. Magnetic needle shear interfacial rheometer according to claim 12, characterized in that the control unit (22) is additionally configured to perform frequency sweeps ω within a frequency range and obtain dynamic modules 10 and complex interfacial viscosity of the film (1) for said frequency range.

[14]
14. Interfacial magnetic needle shear rheometer according to any of claims 10 to 13, characterized in that it additionally comprises a transparent lower window (17), practiced at the base of the cuvette (23), and a light source (19 ) to illuminate the magnetic needle through the lower window (17).

[15]
15. Interfacial magnetic needle shear rheometer according to any of claims 10 to 14, characterized in that it additionally comprises movable barriers (18) for controlling the spatial extent of the film (1) within the cuvette (23).

[16]
16. Method of actuating the needle of a magnetic shear interfacial rheometer, characterized in that it comprises moving, in a longitudinal direction parallel to the plane of the interface in which the magnetic needle (3) of the rheometer is located (30) , Two permanent magnets (13) with magnetization axes perpendicular to said plane, the magnets (13) being located at the same distance (h) from said plane and with their polarities reversed with respect to each other.

[17]
17. Method of actuating the needle of a magnetic shear interfacial rheometer 30 according to claim 16, characterized in that the displacement is performed in an oscillatory manner.

[18]
18. Method of measuring the viscosity of a film using an interfacial rheometer
of shear by magnetic needle, which employs the method of actuation of the rheometer needle (30) according to any of claims 16 to 17, characterized in that it comprises:
- move the two magnets (13) oscillatingly at a frequency ω in the longitudinal direction of the channel (16); 5
- get the position of the magnets (pi);
- obtain the position of the magnetic needle (pa);
- obtain the offset (δpp) and the ratio of amplitudes (ARpp) between the position of the magnets (pi) and the position of the magnetic needle (pa);
- obtain, in a previous calibration procedure, the elastic constant ki of the potential well 10 created by the magnets (13) on the magnetic needle (3);
- calculate, using the elastic constant ki and the offset (δpp) and amplitude ratio (ARpp), the dynamic modules and the complex interfacial viscosity of the film (1) for the frequency ω.
[19]
19. Method of measuring the viscosity of a film using a magnetic needle shear interfacial rheometer according to claim 18, characterized in that it comprises performing frequency scans ω within a frequency range and obtaining the dynamic modules and the complex interfacial viscosity of the film (1) for said frequency range. twenty

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同族专利:

公开号 | 公开日

WO2017017299A1|2017-02-02|

ES2603603B1|2017-12-12|

EP3330695A1|2018-06-06|

EP3330695A4|2018-08-29|

EP3330695B1|2020-09-09|

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CN112704910B|2021-01-14|2021-10-22|青岛理工大学|Organic liquid membrane interface shearing updating extraction device and use method|

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