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    • 专利摘要:
    Liquid crystal actuator dispersed in elastomer. The present invention relates to a material comprising a thermotropic-type liquid crystal dispersed in the form of drops in an elastomeric matrix and its production processes. In addition, the present invention relates to a dielectric elastomer actuator comprising the material and its uses for the manufacture of robotic, electronic, industrial devices and biomedical components. Likewise, the present invention relates to a dielectric elastomer generator that comprises the material and its uses for the manufacture of olamotroz or wave power generators. Therefore, the invention could fit into the sectors of robotics, electronics, industry and biomedicine. (Machine-translation by Google Translate, not legally binding)
    公开号:ES2564396A1
    申请号:ES201431248
    申请日:2014-08-22
    公开日:2016-03-22
    发明作者:Raquel VERDEJO MÁRQUEZ；Laura JIMENEZ ROMASANTA；Luis Ignacio MORA VALVO
    申请人:Consejo Superior de Investigaciones Cientificas CSIC；
    IPC主号:
    专利说明:

    The present invention relates to a material comprising a liquid crystal typethermotropic dispersed in the form of drops in an elastomeric matrix and itsprocurement procedures
    In addition, the present invention relates to a dielectric elastomer actuator comprising the material and its uses for the manufacture of robotic, electronic, industrial and biomedical components.
    Likewise, the present invention relates to a dielectric elastomer generator comprising the material and its uses for the manufacture of wave or wave power generators.
    Therefore, the invention could be framed in the robotics, electronics, industry and biomedicine sectors
    20 STATE OF THE TECHNIQUE
    Dielectric elastomers are essentially soft or flexible capacitors,
    composed of a thin elastomer membrane interspersed between two
    electrodes with elastic or malleable characteristics. The devices or transducers
    25 formed by these materials are capable of transducing electrical energy into mechanical energy, which are called actuators, and of transducing mechanical energy into electrical energy, which are referred to as generators.
    The actuators of dielectric elastomers or "DEA" for its acronym in English
    30 are a type of materials with great scientific and industrial interest today that are characterized by having a high degree of mechanical deformation through the application of an electric field. One of the problems they present is the need for high voltages (of the order of kV), which makes their application difficult.
    In general, the electro-mechanical response of dielectric elastomers is directly proportional to the permittivity of the material and the square of the field
    electrical applied and inversely proportional to the module. Therefore, the strategies for the development of effective dielectric actuators that have been followed in the state of the art are the decrease of the module and / or the increase of the dielectric constant of the material without adversely affecting the breaking potential or the 5 elastic properties of the system. This increase in dielectric permittivity has been the most studied route and can be done through the incorporation of metallic or ceramic charges within the elastomeric matrix to combine the high values of dielectric permittivity of these charges with the high dielectric breakdown value of the elastomers However, the incorporation of these charges produces
    10 a parallel increase in the component of dielectric losses, reducing the potential for rupture, as well as strengthening the elastomer, reducing the percentage of performance.
    Numerous disclosures about 15 dielectric elastomers based on polymeric matrices with conductive charges can be found in the state of the art. Some examples are:
    G. Gallone et al (Polymer International, Special Issue: Electromechanically Active Polymers, Volume 59, Issue 3, pages 400-406, March 2010) describing
    20 dielectric elastomers with improved transduction properties comprising at least one low dielectric constant polymer selected from polydimethylsiloxane (PDMS or dimethicone), polyurethane (PU) or combination thereof, and conductive modifiers such as barium titanate BaTi03, titanium dioxide TiO "Mg, nNb ~ 303.o.15PbTi03 (PMN-PT) and poly (3-hexylthiophene) (P3HT).
    LJ Romasanta et al (J. Mater. Ehem., 2012, 22, 24705-24712) which describes an actuator formed by a dielectric elastomer of copper and calcium titanate CaCu3Ti40 12 (CCTO) and polydimethylsiloxane (PDMS or dimethicone) that exhibits properties improved electromechanics with respect to those present to the state
    30 of art.
    And, the international patent application W02014049102, which describes a polymer composition having high electrical permittivity and good mechanical properties for use as a dielectric elastomer. The polymer composition is formed by an elastomeric polymer matrix of polydimethylsiloxane (continuous phase) and modifying particles encapsulated in the same elastomer used
    as matrix (discontinuous phase). Among the modifying particles encapsulated in the elastomeric matrix are mentioned an electrical conductive material (polyaniline or polypyridine conductive polymer, threads or fibers formed by cotton, polyester or polyamide and coated with metals), a magnetic substance (ferrocene, nanoparticles
    5 magnetic) or a biological plotter (copper, titanium, gold, silver a plotterluminescent or fluorescent).
    In addition, documents describing dielectric elastomers including a liquid crystal are also in the state of the art. The term liquid crystal (Cl)
    10 encompasses a state of intermediate aggregation between the crystalline solid and the amorphous liquid. Generally the substances in this state have a strong anisotropy in several of their properties (especially in the molecular geometry in the form of a rod or disk) but at the same time show a high degree of fluidity comparable to that of a common liquid.
    An example of a dielectric elastomer comprising the can be found in international patent application W02011 / 0360BO. This patent application describes materials that result from the cross-linking of the mesogenic groups that constitute the el with the elastomeric chains. In these materials the groups
    The mesogenic 20 are part of the main chain or are anchored in the side chains of the elastomeric matrix. However, the problem with these materials is that they have a modest percentage of performance.
    Therefore, it is of interest to find new actuators of dielectric elastomers that have better performance percentages.
    DESCRIPTION OF THE INVENTION
    The present invention relates to a material comprising a liquid crystal (el)
    30 thermotropic type dispersed in drops in an elastomer matrix. These are actuators that respond in a reversible and controllable way to an external stimulus.
    The material of the present invention is an immiscible mixture of it and matrix
    35 elastomeric, where Cl does not react with the polymeric chains of the elastomeric matrix. He forms a second phase in the form of drops. The percentage of action is not affected by the presence of these drops, and is determined by the elastomeric matrix used. The separation of the two phases that make up the material does not adversely affect the electro-mechanical response of the system.
    The material of the present invention improves the percentage of performance thanks to, on the one hand, the increase in dielectric permittivity of the system and, on the other, the reduction of elastic modulus while maintaining or even increasing the potential for breaking of the system.
    10 Due to the high deformation values of these materials, they present direct applications of public interest in various sectors, such as robotics, industry, electronics and biomedical.
    In a first aspect, the present invention relates to a material comprising a liquid crystal dispersed in an elastomeric matrix.
    The term liquid Ucristal "(el) encompasses in the present invention a state of intermediate aggregation between the crystalline solid and the amorphous liquid.
    20 The existence of thousands of organic compounds capable of suffering from mesomorphism towards the state is known and depending on details in the molecular structure a certain compound may undergo various mesomorphic changes before reaching the state of isotropic liquid. The transition between
    25 these mesomorphic states may depend purely on temperature (thermotropic mesomorphism) or on the temperature and solvent effect (liotropic mesomorphism).
    the vast majority of liquid crystals belong to the compound thermotropic group
    30 per rod-shaped molecules. These types of liquid crystals are classified into three sub-groups: pneumatic, symetrical and cholesteric. The group of the nematic ones are identified by presenting an orientation of the long axes of the molecules approximately parallel to each other. The fluidity of this mesophase originates from the relative ease of sliding that exists between parallel molecules.
    In a preferred embodiment, the Cl comprising the material of the invention is a
    Therotropic Cl or a mixture of thermotropic liquid crystals. More preferably, the thermotropic Cl is a nematic Cl.
    In another preferred embodiment, the concentration of Cl in the material is between 1 and 30parts per hundred (ppc) with respect to the final material.
    In another preferred embodiment, the Cl has a dielectric anisotropy f1r. greater than 5. More preferably, the Cl has a dielectric anisotropy f1r. between 5 and 16. More 10 preferably between 8 and 12.
    In another preferred embodiment, Cl is selected from cyanobiphenyl (nCB) compounds, a eutectic mixture of 4-n-pentyl-4 · -cyanobiphenyl (5CB), 4-nheptyl-4'-cyanobiphenyl (7CB), 4- n-octyl-4'-cyanobiphenyl (80CB) and 4,4'-pentyl-cyanoterphenyl
    15 (51/25/16/8), and an eutectic mixture of three phenylcyclohexanes. More preferably the Cl is 4-n-pentyl-4 · -cyanobiphenyl.
    To the eutectic mixture of 4-n-pentyl-4 · -cyanobiphenyl (5CB), 4-n-heptyl-4'-cyanobiphenyl (7CB), 4-n-octyl-4'-cyanobiphenyl (80CB) and 4.4 '-pentyl-cyanoterphenyl (51/25/16/8) is
    20 known as E7.
    The eutectic mixture of three phenylcyclohexanes is known as ZL1083.
    In another preferred embodiment, the Cl is dispersed in the form of droplets of size between 5 and 15 ... 1m in the elastomeric matrix. More preferably of size between 5 and 10 ... 1m.
    In the present invention, "elastomeric matrix" is understood to mean that matrix formed by polymers that are characterized by their high elasticity, that is, they undergo considerable deformations at low stresses and quickly recover their shape and
    30 dimensions when the deforming force ceases. The origin of elasticity in elastomers is based on the formation of a three-dimensional network based on the creation of chemical bonds between the elastomer chains during the cross-linking or vulcanization process.
    The elastomeric matrix is selected from an acrylic, and a rubber in another preferred embodiment. More preferably, the rubber is selected from a silicone, a polyurethane (PU), poly (styrene-ethylene-butylene-styrene) (SEBS) and acrylonitrile butadiene rubber (NBR). Even more preferably the silicone is selected from polymethylsiloxane and fluorosilicones. Preferably it is polydimethylsiloxane.
    A second aspect of the invention relates to the method of obtaining thematerial described above by conventional methods of processingrubbers
    In a preferred embodiment, the process comprises the following steps:
    10 a) mixing the elastomeric matrix with at least one crosslinking agent, the liquid crystal and, optionally, an additive, in an extruder or an open or closed mixer. b) carry out the vulcanization of the resulting mixture in a), at a temperature of between 80 and 160 oC, at a pressure of between 150 and 250 bars and at an optimum time of
    15 Iop curing in a hydraulic press.
    In another preferred embodiment, the method comprises the following steps:
    a) mixing the elastomeric matrix with at least one crosslinking agent, the
    liquid crystal and an additive, in an extruder or an open or closed mixer.
    20 b) carry out the vulcanization of the resulting mixture in a), at a temperature of between 80 and 160 oC, at a pressure of between 150 and 250 bars and at an optimum cure time Iop in a hydraulic press.
    The purpose of step a) of the procedure is to mix all the ingredients in one
    Extruder, for example a twin screw extruder, or an open or closed mixer until a homogeneous dispersion is achieved and subsequently the vulcanization of the mixture obtained in step a) is carried out.
    In the present invention the term "vulcanization process, curing or
    Cross-linking "or simply the term" vulcanization, curing or cross-linking "is understood as that chemical process for the conversion of plastic materials into elastic or elastomeric materials through the addition of sulfur or other equivalents, other cross-linking agents. These additives modify. the polymer by forming crosslinks (bridges) between the
    35 different polymer chains. The "vulcanized, cured or crosslinked" material has superior mechanical properties.
    In this sense, the term "crosslinking agent" or "agent of
    vulcanization "as that compound that creates covalent bonds between
    elastomeric chains of the matrix.
    In a preferred embodiment, the crosslinking agent of step a) is selected from organic peroxide, inorganic peroxide, sulfur, diazide, ionizing radiation or any combination thereof.
    In the present invention, the term "additive" is understood as those substances that are conventionally included in rubber technology, such as fillers, plasticizers, accelerators and activators, pigments, or antidegradants.
    In a preferred embodiment, the additive of step a) is selected from pigments, antidegradants, stabilizers, and accelerators.
    15 Step b) of the process refers to the vulcanization of the mixture obtained in stage a) at a temperature of between 80 and 160 oC, at a pressure of between 150 and 250 bars and at an optimum curing time in a " hydraulic press.
    In the present invention, the "optimum cure time lop" is understood as the time to reach 90% of the maximum torque during the vulcanization or cross-linking process.
    A third aspect of the invention relates to the method of obtaining the
    25 material described above by casting elastomer processing methods whose English term is casting.
    In the present invention, "casting elastomer processing methods" is understood as the pouring of a polymeric material into a mold to harden or
    30 polymerize.
    In a preferred embodiment, the process described above comprises the following steps: a) mixing an elastomeric matrix, a liquid crystal and, optionally, an organic solvent, crosslinking agents and / or a catalyst by mechanical stirring or ultrasound,
    b) degassing the mixture obtained in a) by vacuum or ultrasound,c) pour the mixture obtained in b) into the mold,d) optionally evaporate the solvent containing the mixture obtained in c),e) cure the mixture obtained in c) or d) at a temperature between 10 and 100 oC,in the presence or absence of a magnetic field.
    When the elastomeric matrix is SEBS, TPU or NBR it is necessary to dissolve the matrix in the organic solvent mentioned in step a) of the process. The solvent is preferably organic and should be such that it can dissolve the elastomer that forms the elastomeric matrix by mechanical agitation or ultrasound.
    Preferably the solvent of step a) is selected from the list comprising ethyl acetate, acetone, chloroform, dichloromethane, dimethylformamide, tetrahydrofuran, toluene and xylene.
    When the elastomeric matrix has a viscosity between 40 mPa.s and 15,000 mPa.s, it is not necessary to dissolve the matrix in the solvent. Examples of
    elastomeric matrices with this low viscosity are some silicones and those polyurethanes formed by polyols and isocyanates with visions between 40 mPa.s and 15,000 mPa.s.
    In another preferred embodiment, when a silicone elastomeric matrix is used, step a) of the process is performed in the presence of a PI catalyst.
    The addition of the components of the mixture of step a) is carried out under constant stirring or by ultrasound, in order to obtain a homogeneous dispersion of Cl in the elastomeric matrix.
    The mixture obtained in step a) is degassed in step b) by subjecting the solution to vacuum or ultrasound. For this, the mixture obtained in step a) can be introduced into a vacuum oven or a vacuum hood. On an industrial level the degassing described in step b) would be carried out in an autoclave or in an ultrasonic bath.
    Step c) of the process refers to the casting stage where the mixture obtained in step b) is poured into a mold. This operation is preferably performed at a temperature between 10 and 100 oC.
    5 Step d) of the process refers to the evaporation of the solvent. This stageit's optional.
    In the event that the elastomeric matrix has a viscosity between 40 mPa.s and 15,000 mPa.s, it is not necessary to dissolve the matrix in the solvent, so it is not necessary to carry out step d) of the evaporation process of the solvent.
    Stage e) of the process refers to the stage of the mixture obtained in stage c) or stage d). This stage e) of curing is carried out at a temperature of between 10 and 100 oC in the presence or absence of a magnetic field.
    In the case of using polymeric matrices of SEBS, TPU or NBR it is necessary to dissolve the matrix in the organic solvent mentioned in step a) of the process, so it is also necessary to evaporate this solvent. Therefore, in another embodiment
    20, the method described above comprises the following steps: a) mixing an elastomeric matrix, a liquid crystal and an organic solvent, and, optionally, crosslinking agents and / or a catalyst by mechanical stirring or ultrasound, b) degassing the mixture obtained in a) by vacuum or ultrasound,
    C) pour the mixture obtained in b) into the mold, d) evaporate the solvent containing the mixture obtained in c), e) cure the mixture obtained in d) at a temperature between 10 and 100 oC, in the presence or absence of a magnetic field.
    Preferably, step d) of the process is carried out at a temperature capable of evaporating the solvent used in step a) of the process.
    In another preferred embodiment, the process described above comprises an additional stage c '), between stage c) and stage d) or e) consisting of degassing the mixture obtained in c).
    The mold with the mixture obtained in step c) of the process can be subjected to
    new to the degassing process to eliminate possible bubbles generated
    during the pouring of the mixture.
    In another preferred embodiment, the curing of step e) is carried out at atemperature between 25 and 100 oC.
    In another preferred embodiment, the curing of step e) is performed in the absence of a magnetic field.
    In another preferred embodiment, the curing of step e) is performed in the presence of a magnetic field.
    When stage e) of curing is carried out in the presence of a magnetic field,
    15 induces an alignment of the mesophase of the thermotropic Cl with the applied magnetic field. The acting capacity is drastically improved with the Cl content, being especially evident for the sample with application of a magnetic field during the curing or cross-linking process as a consequence of the greater molecular orientation of the Cl.
    The fourth aspect of the invention relates to a dielectric elastomer actuator comprising the material described above.
    The term "dielectric elastomer actuator ~ in the present invention refers to
    25 devices or transducers formed by dielectric elastomers capable of transducing electrical energy into mechanical energy. In the present invention, dielectric elastomers are formed by a thin membrane of the material of the present invention sandwiched between two electrodes of elastic and malleable characteristics.
    The fifth aspect of the invention refers to the use of the dielectric elastomer actuator for the manufacture of robotic devices. Preferably the robotic device is a mimetic robot.
    The sixth aspect of the invention relates to the use of the dielectric elastomer actuator for the manufacture of electronic devices. Preferably the electronic device is a touch interface, ultra-flat speakers or a lens position.
    The seventh aspect of the invention relates to the use of the elastomer actuator.5 dielectric for the manufacture of industrial devices. Preferably theIndustrial device is a microvalve or articulated arm.
    The eighth aspect of the invention relates to the use of the dielectric elastomer actuator for the manufacture of biomedical components. Preferably a prosthesis or an active bandage.
    The ninth aspect of the invention relates to a dielectric elastomer generator comprising the material described above.
    The term "dielectric elastomer generator" in the present invention refers to devices or transducers formed by dielectric elastomers capable of transducing mechanical energy into electrical energy. In the present invention, the dielectric elastomers are formed by a thin membrane of the material of the present invention sandwiched between two electrodes of elastic characteristics and
    20 malleable.
    The last aspect of the invention relates to the use of the dielectric elastomer generator, according to the preceding claim, for the manufacture of wave or wave power generators, preferably for the manufacture of devices.
    25 articulated mobiles.
    Throughout the description and claims the word "comprises" and its
    variants are not intended to exclude other technical characteristics, additives, components or
    Steps. For experts in the field, other objects, advantages and characteristics of the
    The invention will be derived partly from the description and partly from the practice of the invention. The following examples and figures are provided by way of illustration, and are not intended to be limiting of the present invention.
    BRIEF DESCRIPTION OF THE FIGURES
    FIG. 1 Stress-strain curves for PDMS mixtures: (above) MF620U solid silicone mixtures; (below) RTV liquid silicone mixtures.
    FIG. 2 Dielectric permittivity (E ') as a function of the frequency applied to: (above)5 solid silicone mixtures MF620U, (below) RTV liquid silicone mixtures.
    FIG. 3 Percentage of action depending on the time for sample MF620U Cl-O.
    FIG. 4: Percentage of action depending on the electric field applied for 10 actuators of solid silicone MF620U.
    FIG. 5 Percentage of action depending on the electric field applied to RTV liquid silicone actuators.
    15 FIG. 6 SEM 250x images of RTV mixes: Cl-1; Cl-5; Cl-20
    EXAMPLES
    The invention will now be illustrated by tests carried out by the 20 inventors, which demonstrates the effectiveness of the product of the invention.
    materials
    Two commercial grades of polydimethylsiloxane (PDMS) and the liquid crystal 25 specified below were used:
    PDMS Rhodosil MF-620U (Rhodia). This commercial grade of solid physical appearance is presented with a vulcanizing system based on peroxide (dimethyl copolymer, methylhydrogen siloxane) and activated by
    30 high temperature application (approximately 10 min at 110 ° C).
    PDMS RTV R31-2186 (Sigma Aldrich). This commercial grade of liquid physical appearance (high viscosity, 80,000 mPa.s) and bicomponent (part A and part B) is presented with a vulcanizing system based on a platinum complex 35 found in part B. Crosslinking is achieved when mixing
    both parts A and B in a 1: 1 ratio at room temperature in a minimum time of 24 hours.
    4-n-pentyl-4'-cyanobiphenyl (5GB) (Sigma Aldrich), Polymeric Gristalliquido (Gl)5 of the pneumatic thermotropic type with transition at 35 ° C.
    Preparation of mixtures by conventional methods based on solid PDMS
    iMF620Ul
    The mixtures based on solid silicone MF620U with two liquid crystal contents were prepared: O and 1 part per cent (ppc), called Cl-O and Cl-l respectively. No higher concentration of Cl was applied in this type of silicon because of a moderate reduction in torque during cross-linking at higher concentrations. The development of the mixtures was carried out by kneading in
    15 rollers (Comerio Ercole MGN-300S), at room temperature for 18 min.
    Vulcanization curves were then obtained using a Rheometer to
    rubber analysis (Alpha Technologies RPA-2000). Of the curves obtained,
    determined too much that is defined as the time to reach 90% of the torque
    20 maximum obtained during the vulcanization process. Said too was used as the optimal cure time for the vulcanization of the plates.
    Then the vulcanized plates of different thicknesses were obtained in a hydraulic press (Gumiz TP 300/450/1) applying a pressure of
    25 200 bar with a temperature of 100 oC and a time too. It should be noted that for mixing with it, the plates obtained showed poor mechanical properties, so it was decided to use for all samples an optimal cure time defined as last optimal = 1.7 X too. After the correct obtaining of the plates, the corresponding test pieces were punched for mechanical, dielectric conductivity and
    30 electro-mechanics.
    Preparation of mixtures by laundry processing based on PDMS RTV (R31
    The casting method or "casting" was chosen as the most suitable method for obtaining defect-free plates (air bubbles, etc ...). By this technique, mixtures based on RTV PDMS with four liquid crystal contents were prepared: 0, 1, 5 and 20 ppc, called Cl-O, Cl-1, Cl-5, Cl-20 respectively.
    Additionally, for mixtures with higher Cl contents (5 and 20 ppc),
    5 prepared samples with application of a magnetic field during theevaporation of the solvent, in order to achieve a greater degree of orientation inthe liquid crystal molecules and thereby facilitate the increase of the permittivitydielectric of the final mixture (called Cl-5 and Cl-20 mag).
    10 The procedure for preparing these types of materials was carried out by weighing 1.7 grams of each part of the liquid silicone in individual containers. Then, each part was dissolved in approximately 10 ml of chloroform by magnetic stirring at room temperature for 2 hours, after which the contents of both were mixed in a vessel submerged in a bath with ultrasound to remove
    15 possible bubbles for 1 minute. Finally, the mixture was poured into a circular Teflon mold and the chloroform was evaporated at room temperature for a period of 24 hours during which the silicone crosslinking occurs. the realization of the mixtures with Cl was produced by adding the necessary amount of liquid crystal in the container with the part of the
    20 silicone without the catalyst (Part A) during the stirring step and subsequently proceeding as described above.
    After evaporation of the solvent plates were obtained with a final thickness between 250¡1m and 350¡1m. These plates were punched to obtain the specimens
    25 corresponding for mechanical, dielectric and electromechanical conductivity tests.
    Analysis of mechanical properties
    30 For the performance of the axial tensile tests, a universal Instron 3366 mechanical test equipment was used. The tests were carried out at room temperature, approximately 23 ° C with a test speed of 200mm / min initial separation between jaws of 20mm and using halter type specimens with the dimensions and specifications of DIN-53504. They were tested between 9 and 14
    35 test pieces of each mixture to ensure reproducibility of the results.
    In FIG. 1. The stress-strain curves obtained for the different developed mixtures are presented. Observing the mechanical behavior for mixtures of solid silicone MF620U with different Cl content (O and 1 ppc), a drastic decrease in the values of the elastic modulus can be seen
    5 different deformations with the content of CL modifier. This behaviourshows the plasticizing effect that this organic modifier brings to the elastomerused, thus producing materials with less mechanical resistance for the samedeformation value
    10 Similarly, in the case of mixtures with RTV liquid silicone, it can be seen in FIG. 1. a decrease in the elastic modulus at different deformations with the Cl content, in this case the tendency is slightly less pronounced compared to the solid mixtures MF620U.
    15 In the case of the cured sample while applying a magnetic field (Cl-5 mag), the values of the elastic modulus are not far from that observed in Cl-5 since the orientation of the Cl occurs at the molecular level and, therefore, does not affect the conformation of phases at larger scales
    20 Given the elastic nature of rubbers, it is not correct to talk about Young's module in this type of actuator, however, we will refer to module 50 (Y so) and module 100 (Y100) to the efforts recorded at 50% and the 100% deformation respectively.
    25 Table 1 shows the values obtained from Yso and Y100 for the silicone mixtures developed. You can see a decrease of both modules with the Cl content, this decrease being similar for both deformations.
    Analysis of dielectric properties
    The dielectric permittivity of the elastomeric samples was determined by Broadband Dielectric Spectroscopy using an impedance analyzer (Alpha Novocontrol Technologies). the tests were carried out at room temperature and in a frequency range of 10. 1 to 107 Hz. Cylindrical samples were used with
    35 thicknesses between 200-250 J.1m and a diameter of 2 and 3 cm for RTV and MF620U samples respectively. From each sample, 3 specimens were measured to ensure
    Reproducibility of results.
    FIG. 2. shows the average curves of the dielectric permittivity (E ') as a function of
    5 the frequency for the developed mixtures.
    From the solid mixtures MF620U a decrease in the dielectric permittivity with the CL content can be observed. the most likely cause of the decrease in the permittivity value could be related to the curing system of this type of
    10 silicone Somehow, the peroxide may be reacting with the added Cl producing a deactivation of its efficiency as a polar modifier.
    In FIG. 2 The results obtained for mixtures with liquid RTV silicone are also observed. the curves show increased dielectric permittivity with
    15 the concentration of Cl being the Cl-5 mag sample the one with the highest permittivity. This fact can be explained taking into account the highly polar character of the liquid crystal, so that the application of a magnetic field produces a certain degree of orientation and polarization in its structure during the curing process, which translates into an increase in the permittivity of the composite material.
    Analysis of electro-mechanical properties
    To determine the performance capacity of the developed samples, electro-mechanical tests were performed where the dimensional expansion of a membrane was studied as a function of the applied voltage. For this, plates of 4 x 4 cm in size and thicknesses between 250 and 350 Jlm were punched out. These plates were pre-stretched
    biaxially in a 50% acrylic frame. Then circular electrodes of 1 cm in diameter were deposited in the center of the membrane on both sides by spray gun using a dispersion of graphite in ethanol (2mg / ml).
    30 Finally, for the test an image recognition program developed in labview (National Instruments) was used, whose function is to measure and detect the diameter of a circumference (electrode) of an image obtained with the help of a digital camera. For the determination of the electro-mechanical properties of
    35 the developed mixtures were applied periods of voltage interspersed with periods of relaxation (voltage O kV) of one minute each, increasing the potential by 0.5 kV for each interval until reaching the dielectric breakage of the actuator or a maximum of 9.5
    kV In FIG. 3 a typical curve of the electrode expansion can be observed for the different voltages applied.
    5 Dividing the values of the degree of deformation of the base material and itscorresponding mixtures, it is possible to qualitatively determine the capacityof performance of the different mixtures developed. This value is called a factor.electro-mechanical t and is given by the expression:
    F
    where Se and So are the degree of electro-mechanical deformation of the mixture and the matrix
    base, respectively, e 'is the dielectric permittivity, and Y is the resistance to
    traction.
    15 In this way, for values of t greater than the unit, an increase in the elastomer's performance capacity is expected (greater degree of deformation for the same electric field), the degree of deformation being greater the higher the factor value electro-mechanical f.
    20 Otherwise, if values of the electro-mechanical factor t lower than the
    unit, it is expected deficiency in the ability of the mixture to act.
    Below are the values of electro-mechanical factor f obtained both
    25 for the solid silicone MF620U as for the liquid RTV when modified with eL.
    Table 1: Electro-mechanical factor t and values of Yso and Y100 for mixtures
    developed.
    , '(10' Hz) And., (M Pa)f (Y.,)And ,,,, (MPa)f (Y ,,,,)
    MW620U CL-O 2.900.31-0.42-
    MF620U CL-1 2.600.221.30.291.3
    RTV CL-O 4.130.47-0.65-
    RTV CL-1 4.370.441.10.611.1
    RTV CL-5 4.880.351.60.471.6
    RTV CL-5 mag 5.500.312.00.422.0
    All calculated electro-mechanical factor values f exceed the unit so that, a priori, an increase in the degree of performance of all developed mixtures can be expected.
    In the case of liquid silicones, the increase in the degree of action is more pronounced for high concentrations of Cl, with special consideration being given to mixing with 5 ppc of the modifier and applying the magnetic field during the curing process due to the combined effect of the increase in permittivity and decrease
    10 of module Y.
    In FIG. 4 shows the percentage of performance depending on the electric field applied for the solid silicone samples MF620U. A significant increase in the ability to act is observed with the addition of Cl as an organic modifier even at low electric field values. Thus, for a 50 V / lJm electric field, the Cl-1 sample shows a degree of deformation approximately 2 times higher than that obtained with the base matrix (10% deformation versus 5%), while for an electric field of 75 V / lJm reaches a performance deformation approximately 3 times greater (30% deformation versus 10%). He
    20 result demonstrates a high effectiveness of Cl as a modifier to improve properties as an actuator.
    Gallone et al [G. Gallone, F. Galantini and F. Carpi, Polymer International, 2010, 59, 400-406.], Obtain performance deformation percentages of maximum 3.5% for
    25 raw PDMS and up to 8% in the most promising mix of their work based on the same PDMS with poly (3-hexylthiophene) (P3HT) as an organic modifier.
    FIG. 5 shows the electro-mechanical results obtained from the RTV liquid silicone mixtures. the curves show the efficiency of Cl to increase the
    The actuator capacity of the silicone used, observing not only an increase in the percentage of action but also the potential for rupture, thus increasing its resistance to dielectric rupture.
    In particular, the application of magnetic field during the curing processhelps to substantially improve the actuator's ability to actelastomeric, becoming approximately 10 times greater than that obtained with the5 base matrix for an electric field of 50 V / l-lm (35% deformation vs. 3.5%).This phenomenon is probably due to the combination of the orientation of thePolymeric liquid crystal molecules (improves degree of polarization of the materialcompound), together with the decrease of the elastic modulus to different deformations,thus producing a material where Maxwell's tension is greater, and therefore, with
    10 greater deformability even at low voltages.
    Morphological analysis
    The morphology of the obtained mixtures was observed by means of a scanning electron microscope (ESEM, Philips Xl30). The fracture surface was observed after the deposition of a 3-4 nm thin layer of an Au / Pd alloy (80/20).
    The study of morphology for RTV mixtures by scanning electron microscopy (SEM) shows how the increase in modifier induces a separation of 20 phases. Thus, in FIG. 6, in the case of a sample with higher Cl content (Cl-5 and Cl-20) it is possible to visualize the presence of said minor phase in the form of drops
    spherical with an approximate diameter of 4.5 Ilm.
    权利要求:
    Claims (33)
    [1]
    1. Material comprising a liquid crystal dispersed in an elastomeric matrix.
    2. Material according to claim 1, wherein the liquid crystal is a thermotropic liquid crystal or a mixture of thermotropic liquid crystals.
    [3]
    3. Material according to the preceding claim, wherein the thermotropic liquid crystal is
    a nematic liquid crystal. 10
    [4]
    4. Material according to claims 1 to 3, wherein the concentration of liquid crystal in the material is between 1 and 30 parts per hundred (ppc) with respect to the final material.
    Material according to any one of claims 1 to 4, wherein the liquid crystal has a dielectric anisotropy l1r. greater than 5.
    [6]
    6. Material according to the preceding claim, wherein the liquid crystal has a dielectric anisotropy 8.r. between 5 and 16.
    [7]
    7. Material according to the preceding claim, wherein the liquid crystal has a dielectric anisotropy 8.r. between 8 and 12.
    [8]
    8. Material according to any one of claims 1 to 7, wherein the liquid crystal is
    25 selects from among cyanobiphenyl (neB) compounds, a eutectic mixture of 4-n-pentyl-4'-cyanobiphenyl (5GB), 4-n-heptyl-4'-cyanobiphenyl (7GB), 4-n-octyl-4 'cyanobiphenyl (80GB) and 4,4'-pentyl-cyanoterphenyl (51/25/16/8), and a eutectic mixture of three phenylcyclohexanes.
    Material according to the preceding claim, wherein the liquid crystal is 4-pentyl-4'-cyanobiphenyl.
    [10]
    10. Material according to any one of claims 1 to 9, wherein the liquid crystal
    It is dispersed in the form of drops of size between 5 and 15 ... 1m in the elastomeric matrix 35.
    [11]
    11. Material according to the preceding claim, wherein the liquid crystal is dispersed in the form of drops of size between 5 and 10 11m.
    [12]
    12. Material according to any of claims 1 to 11, wherein the matrix5 elastomer is selected from an acrylic, and a rubber.
    [13]
    13. Material according to the preceding claim, wherein the rubber is selected from a silicone, a polyurethane (PU), poly (styrene-ethylene-butylene-styrene) (SEBS) and acrylonitrile butadiene rubber (NBR).
    [14]
    14. Material according to the preceding claim, wherein the silicone is selected from polymethylsiloxane and fluorosilicones.
    [15]
    fifteen. Material according to the preceding claim, wherein the silicone is polydimethylsiloxane.
    [16]
    16. Procedure for obtaining the material according to any of claims 1 to 15, by conventional methods of processing rubbers.
    [17]
    17. Procedure for obtaining the material according to the preceding claim, which
    20 comprises the following steps: a) mixing the elastomeric matrix with at least one crosslinking agent, the liquid crystal and, optionally, an additive, in an extruder or an open or closed mixer. b) carry out the vulcanization of the mixture obtained in step a), at a
    25 temperature between 80 and 160 oC, at a pressure of between 150 and 250 bars and at an optimum time of curing Iop in a hydraulic press.
    [18]
    18. Method of obtaining the material according to any of claims 16 or 17, comprising the following steps:
    30 a) mixing the elastomeric matrix with at least one crosslinking agent, the liquid crystal and an additive, in an extruder or an open or closed mixer. b) carry out the vulcanization of the mixture obtained in step a), at a temperature of between 80 and 160 oC, at a pressure of between 150 and 250 bars and at an optimum cure time Iop in a hydraulic press.
    [19]
    19. Process for obtaining the material according to any of claims 16 to 18, wherein the cross-linking agent of step a) is selected from organic peroxide, inorganic peroxide, sulfur, diazide, ionizing radiation or any combination thereof.
    [20]
    twenty. Method of obtaining the material according to any of claims 16 to 19, wherein the additive of step a) is selected from pigments, antidegradants, stabilizers, and accelerators.
    [21]
    twenty-one. Method of obtaining the material according to any of claims 1 to 15, by methods of processing elastomers in laundry.
    [22]
    22 Procedure for obtaining the material according to the preceding claim, which
    It comprises the following steps: a) mixing an elastomeric matrix, a liquid crystal and, optionally, an organic solvent, crosslinking agents and / or a catalyst by mechanical stirring or ultrasound, b) degassing the mixture obtained in a) by vacuum or ultrasonic , c) pour the mixture obtained in b) into the mold, d) optionally evaporate the solvent containing the mixture obtained in c), e) cure the mixture obtained in c) od) at a temperature between 10 and 100 oC, in the presence or absence of a magnetic field.
    [23]
    2. 3. Method of obtaining according to any of claims 21 or 22, which
    It comprises the following steps: a) mixing an elastomeric matrix, a liquid crystal and an organic solvent, and, optionally, crosslinking agents and / or a catalyst by mechanical stirring or ultrasound, b) degassing the mixture obtained in a) by vacuum or ultrasound, c) pour the mixture obtained in b) into the mold, d) evaporate the solvent containing the mixture obtained in c), e) cure the mixture obtained in d) at a temperature between 10 and 100 oC, in the presence or absence of a magnetic field.
    [24]
    24. Method of obtaining, according to any of claims 21 to 23, wherein between stage e) and stage d) or e) there is an additional stage c ') consisting of degassing the mixture obtained in c).
    25. Method of obtaining according to any of claims 21 to 24, wherein the solvent of step a) is selected from the list comprising ethyl acetate, acetone, chloroform, dichloromethane, dimethylformamide, tetrahydrofuran, toluene and xylene.
    10 26. Method of obtaining according to any of claims 21 to 25, wherein step e) of curing is carried out at a temperature between 25 and 100
    oC.
    [27]
    27. Method of obtaining according to any of claims 21 to 26, 15 wherein step e) of curing is carried out in the absence of a magnetic field.
    [28]
    28. Method of obtaining according to any of claims 21 to 26, wherein step e) of curing is carried out in the presence of a magnetic field.
    20 29. Dielectric elastomer actuator comprising the material according to any one of claims 1 to 15.
    [30]
    30. Use of the dielectric elastomer actuator according to the preceding claim for the manufacture of robotic devices.
    [31 ]
    31. Use of the dielectric elastomer actuator according to the preceding claim wherein the robotic device is a mimetic robot.
    [32]
    32 Use of the dielectric elastomer actuator according to claim 29 for the manufacture of electronic devices.
    [33]
    33. Use of the dielectric elastomer actuator according to the preceding claim wherein the electronic device is a touch interface, ultra-flat speakers or a lens positioner.
    [34]
    3. 4. Use of the dielectric elastomer actuator according to claim 29 for the manufacture of industrial devices.
    [35]
    35 Use of the dielectric elastomer actuator according to the preceding claim wherein the industrial device is a micro valve or an articulated arm.
    [36]
    36. Use of the dielectric elastomer actuator according to claim 29 for the manufacture of biomedical components
    Use of the dielectric elastomer actuator according to the preceding claim wherein the biomedical component is a prosthesis or an active bandage.
    [38]
    38. Dielectric elastomer generator comprising the material according to any one of claims 1 to 15.
    [39]
    39. Use of the dielectric elastomer generator, according to the preceding claim, for the manufacture of wave or wave power generators.
    [40]
    40. Use of the dielectric elastomer generator according to the preceding claim for the manufacture of articulated mobile devices.
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    同族专利:
    公开号 | 公开日
    WO2016026995A1|2016-02-25|
    ES2564396B1|2016-12-30|
    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    US4869847A|1987-03-16|1989-09-26|Hoechst Celanese Corp.|Microdisperse polymer/liquid crystal composite|
    CN1871326A|2003-11-03|2006-11-29|陶氏康宁公司|Silicone composition and polymer dispersed liquid crystal|
    US9260570B2|2012-04-10|2016-02-16|William Marsh Rice University|Compression induced stiffening and alignment of liquid crystal elastomers|IT201600118202A1|2016-11-22|2018-05-22|Atom Spa|COMPOSITE MATERIAL WITH ELECTROSTRICTIVE PROPERTIES FOR A MECHANICAL ENERGY RECOVERY DEVICE|
    CN107603047B|2017-10-31|2019-11-05|江汉大学|The preparation method of polymer blending gradient function composite material|
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    优先权:
    申请号 | 申请日 | 专利标题
    ES201431248A|ES2564396B1|2014-08-22|2014-08-22|LIQUID CRYSTAL ACTUATOR DISPERSED IN ELASTÓMERO|ES201431248A| ES2564396B1|2014-08-22|2014-08-22|LIQUID CRYSTAL ACTUATOR DISPERSED IN ELASTÓMERO|
    PCT/ES2015/070621| WO2016026995A1|2014-08-22|2015-08-12|Actuator of liquid crystals dispersed in elastomer|
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