MXPA96004251A - Mixed material of liquid crystal and method to make my - Google Patents

Abstract

The present invention relates to a method for making a mixed liquid crystal material wherein varying volumes of a liquid crystal material are dispersed in an encapsulating material and the liquid crystal material is at least partially separated from the encapsulating material by a interfacial material placed therebetween, said method comprising the steps of: a) forming an emulsion comprising the encapsulating material, the interfacial material or a precursor thereof, the liquid crystal material, and an aqueous vehicle medium, under such that i) varying volumes of the liquid crystal material are contained by the encapsulating material and ii) the interfacial material or precursor thereof forms a homogeneous solution with the liquid crystal material and optionally a solvent in which the interfacial material or precursor same and liquid crystal material are mutually soluble b) make the interfacial material or precursor thereof is formed in separate phases from the liquid crystal material and deposited between the liquid crystal material and the encapsulating material either by evaporation of the solvent or by reduction of the temperature of the emulsion to a temperature lower to which the interfacial material or precursor thereof is insoluble in the liquid crystal material c) polymerize the interfacial material precursor to form the interfacial material, wherein said precursor is present and d) remove the aqueous vehicle medium

Description

MIXED MATERIAL OF LIQUID CRYSTAL AND METHOD TO DO THE SAME TECHNICAL FIELD OF THE INVENTION This invention relates to mixed liquid crystal materials, suitable for use in light valves, and methods for making them.

BACKGROUND OF THE INVENTION Liquid crystal light valves are known, wherein the electro-optically active element is a mixed liquid crystal material. The mixed material comprises varied volumes or droplets of a liquid crystal material dispersed, encapsulated, embedded, or otherwise contained within a polymer matrix. Illustrative descriptions include Fergason, U.S. Patent. 4,435,047 (1984) ("* 047 of Fergason"); West and others, patent of E.U.A. 4,685,771 (1987); Pearlman, patent of E.U.A. 4,992,201 (1991); Dainippon Ink, EP 0, 313.053 (1989). These light valves can be used in presentation and window or privacy panels. The prior art also describes the concept of having an additional material disposed between the polymer matrix and the liquid crystal material. See, for example, Fergason, '047; Fergason et al., E. U.A. 4, 950, 052 (1990) ("'052 of Fergason"); and Raychem, WO 93/1 8431 (1993) ("'431 by Raychem"). The purpose of having this additional material has been variously established to preserve the integrity of the volumes of liquid crystal material and to alter the electro-optical properties of the mixed material. However, the techniques described to form a mixed material with this intervention of the additional material, have been specialized and not generally applicable to a wide variety of materials. The present invention provides an improved and generally more applicable method for making such mixed materials.

BRIEF DESCRIPTION OF THE INVENTION A method for making a mixed liquid crystal material is provided, wherein varied volumes of liquid crystal material are dispersed in an encapsulating material and the liquid crystal material is at least partially separated from the encapsulating material by an interfacial material. Arranged therebetween, the method comprises the steps of: a) forming an emulsion comprising the encapsulating material, the interfering material or a precursor thereof, the liquid crystal material, and an aqueous vehicle medium. , under conditions such that, (i) volumes of the liquid crystal material are contained by the encapsulation material and, (ii) the interfacial material or its precursor forms a homogeneous solution with the liquid crystal material and optionally a solvent, and wherein the interfacial material or its precursor, and the liquid crystal material are mutually soluble; b) causing the interfacial material or its precursor to separate the phase of the liquid crystal material and deposit it between the liquid crystal material and the encapsulating material, either by evaporating the solvent or reducing the temperature of the emulsion at a lower temperature , to which the interfacial material or its precursor is insoluble in the liquid crystal material; c) polymerizing the interfacial material precursor to form the interfacial material, wherein said precursor is present; and d) removing the aqueous vehicle medium. In a first preferred embodiment, the method comprises the steps of: a) forming an emulsion comprising the encapsulating material, the interfacial material, the liquid crystal material and the aqueous vehicle medium, under conditions such that, (i) Varied volumes of the liquid crystal material are contained by the encapsulating material, and (ii) the interfacial material forms a homogeneous solution with the liquid crystal material and a solvent, wherein the interfacial material and the liquid crystal material are mutually soluble.; b) cause the mixed material to separate the phase of the liquid crystal material and deposit between the liquid crystal material and the encapsulation material, evaporating the solvent; and c) removing the aqueous vehicle medium. In a second preferred embodiment the method comprises the steps of: a) forming an emulsion comprising the encapsulating material, the interfacial precursor, the liquid crystal material and the aqueous carrier medium, under conditions such that (i) ) varying volumes of the liquid crystal material are contained by the encapsulating material, and (ii) the interfacial material precursor forms a homogeneous solution with the liquid crystal material and a solvent, wherein the interfacial material precursor and the material liquid crystal are mutually soluble; b) causing the precursor of the interfacial material to separate the phase of the liquid crystal material and deposit between the liquid crystal material and the encapsulating material, evaporating the solvent; c) polymerizing the interfacial material precursor to form the interfacial material; and d) removing the aqueous vehicle medium. In a third preferred embodiment, the method comprises the steps of: a) forming an emulsion comprising the encapsulating material, the interfacial material, the liquid crystal material and the aqueous carrier medium, at or above a first Ti temperature , under conditions such that (i) varying volumes of the liquid crystal material are contained by the encapsulating material, and (ii) the interfacial material forms a homogeneous solution with the liquid crystal material; b) causing the metallic material to separate the phase of the liquid crystal material and deposit between the liquid crystal material and the encapsulating material, reducing the temperature of the emulsion to a second temperature T2, to or below which the material interfacial is insoluble in the liquid crystal material; and c) removing the aqueous vehicle medium. In a fourth preferred embodiment, the method comprises the steps of: a) forming an emulsion comprising the encapsulating material, a precursor of the interfacial material, the liquid crystal material and the aqueous carrier medium, at or above a first temperature T,, under conditions so that, (i) varying volumes of liquid crystal material are dispersed in the encapsulating material, and (ii) the precursor of the interfacial material forms a homogeneous solution with the liquid crystal material; b) causing the interfacial material precursor to separate the phase from the liquid crystal material and deposit between the liquid crystal material and the encapsulating material, reducing the temperature of the emulsion to a second temperature T2, at or below the which the precursor of the interfacial material is insoluble in the liquid crystal material; c) polymerizing the interfacial material precursor to form an interfacial material; and d) removing the aqueous vehicle medium. In another embodiment, a mixed liquid crystal material is provided which comprises varying volumes of the liquid crystal material dispersed in a matrix material, wherein the liquid crystal material is at least partially separated from the matrix material by means of an interfacial material and an encapsulation material successively disposed around the liquid crystal material. In a further embodiment, a method is provided for making a mixed liquid crystal material comprising varying volumes of the liquid crystal material dispersed in a matrix material, wherein the liquid crystal material is at least partially separated from the matrix material by means of an interfacial material and an encapsulating material successively arranged around the liquid crystal material, comprising the steps of: a) forming capsules in which the liquid crystal material is successively surrounded by the interfacial material and the encapsulating material; b) dispersing the capsules in a medium in which the matrix material or a precursor thereof is present; and c) causing the matrix material or its precursor to be fixed around the capsules, to form the mixed liquid crystal material.

BRIEF DESCRIPTION OF THE DRAWINGS Figures 1 to 1 b show a light valve made from a liquid crystal mixed material of the prior art. Figures 2a-2b show a preferred light valve made from a mixed liquid crystal material according to the present invention. Figure 3 shows a mixed liquid crystal material according to this invention. Figure 4 shows polarized optical microscope data for a mixed liquid crystal material of this invention. Figures 5a-5b and 6 show carbon-13 NMR data for mixed liquid crystal materials of this invention.

DESCRIPTION OF THE PREFERRED MODALITIES Figure 1 a shows a light valve of the prior art, made from a mixed liquid crystal material, such as that described in '047 of Fergason. The light valve 10 comprises a mixed liquid crystal material 1 1, in which drops or volumes 12 of a nematic liquid crystal material 13, having a positive dielectric anisotropy, are dispersed in an encapsulating material 14. The mixed material 1 1 is sandwiched between first and second electrodes 15a and 15b, made of a transparent conductor such as indium tin oxide ("ITO"). The application or not of a voltage across the electrodes 15a and 15b from a power source 16, is controlled by the switch 17, shown here in the open position ("off state"). As a result, no voltage is printed through the mixed material 1 1 and the electric field experienced by the liquid crystal material 13 is effectively zero. Due to the surface interactions, the liquid crystal molecules preferentially meet with their longitudinal axes parallel to the curved contact surface with the encapsulating material 14, resulting in a generally curvilinear alignment within each drop. In this particular embodiment, the encapsulation material 14 also acts as a matrix to contain the drops 12 of the liquid crystal material 13. The curvilinear shafts in different drops 12 are randomly oriented, as symbolizing the different orientations of the curvilinear patterns. The liquid crystal material 13 has a refractive index ne, which is different from the refractive index np of the encapsulation material 14 and an ordinary refractive index n0, which is substantially equal to np. (Here, two indices or refraction that are said to be substantially equal, or that coincide, if they differ by less than 0.05, preferably less than 0.02). The incident light beam 18, which travels through the mixed material 1 1, has a high statistical probability of finding at least one contact surface between the encapsulating material 14 and the liquid crystal material 13, wherein the index of refraction of the liquid crystal, with which it interacts operatively, is ne. Since ne is different from np, there is a refraction, or scattering of the ray of light 18, both forward and backward, making the mixed material 1 1 have a translucent or frosty appearance. Figure 1 b shows the light valve 10 in the on state, with the switch 17 closed. An electric field is applied between the electrodes 15a and 15b and through the mixed material 1 1, with a directionality indicated by the arrow 19. The liquid crystal material 13, being positive and dielectrically anisotropic, is aligned parallel to the direction of the electric field . (The required voltage depends, among other things, on the thickness of the mixed material, and typically is between 3 and 50 volts). In addition, alignment with the field occurs in each drop 12, so there is order among the managers drop by drop, as symbolically shown in Figure 1 b. When the molecules of the liquid crystal are aligned in this way, the refractive index of the liquid crystal, with which the incident light beam 18 interacts operatively, is n0. Since nD is substantially equal to np, there is no spreading at the contact surface of the liquid-encapsulating crystal material. As a result, the beam 18 is transmitted through the mixed material 1 1, which now appears transparent. Transmission rates of at least 50%, and preferably of the order of 70% or more, can be obtained. The electro-optical performance (e.g., switching voltage, off state spread, switching speed, and hysteresis) of the light valve 10 depends on the nature of the interactions of the surface between the encapsulation material 14 and the liquid crystal material 13. An encapsulation material, which is desirable with respect to characteristics such as mechanical properties, ability to protect against environmental contaminants, UV stability, etc. , it may be undesirable with respect to its surface interactions with the liquid crystal material, for example, by making the switching speed too slow or that the switching voltage is too high. In this way, it is desirable to be able to isolate the interactions of the surface from the other characteristics of the encapsulation material. Figures 2a and 2b (wherein repeated numbers of Figures 1 a-1 b denote similar elements) show a light valve 20 of this invention, in which the objective is achieved. The light valve 20 comprises a liquid crystal material 21, which is similar to the mixed material 1 1 of Figure 1 ab, except that the liquid crystal material 13 is separated from the encapsulating material 14 by means of an interfacial material. The light valve 20 appears frosty or translucent in the off state (Figure 2a) and transparent in the on state (Figure 2b), for the reasons given above. The surface interactions, which affect the alignment of the liquid crystal material 13, are predominantly with the interfacial material 22 and not with the encapsulating material 14. The interfacial material 22 can be selected based on its interactions with the glass material liquid 13, while the encapsulation material 14 can be selected based on its mechanical, optical, or other properties. In this way, the need for compromise with respect to a set of properties or another set of properties is avoided. The equalization of n0 of the liquid crystal material with the refractive index np of the interfacial material is important only if the thickness of the layer of the interfacial material is comparable with the wavelength of the light. Generally, the thickness is less than about 100 nm, much less than the wavelengths of 400 to 700 nm for visible light, so that equalization of the refractive indices is usually not necessary. However, if the layer of the interfacial material is thick or if the objective is to minimize optical clarity in the on state (e.g., in window applications), then equalization of the refractive indexes is desirable. A colored visual effect can be obtained by the inclusion of colorants, either pleochroic or isotropic, in the liquid crystal material.

To achieve the advantages of the present invention, it is not necessary for the interfacial material 22 to completely separate the encapsulating material 14 from the liquid crystal material 13. It is sufficient that the interfacial material 22 at least partially separate the last two materials, so that the switching characteristics (speed, voltage, hysteresis, etc.) of the light valve 20 are characteristic of a contact surface of the interfacial material-liquid crystal material and not of a contact surface of the encapsulation material-material of liquid crystal. Preferably, the interfacial material 22 effectively separates the encapsulating material 14 and the liquid crystal material 13, which means that the contact surfaces of the glass material 13 are mainly with the material! interfacial 22 and not with the encapsulation material 14. In the previous figures, the drops or volumes 12 of the liquid crystal material 13 have been shown to have a spherical shape for convenience. Other shapes are possible, for example Oblate spheroid, irregular shapes, or type of weights, where two or more drops are connected by channels. Also, the thickness of the interfacial material layer 22 and the size of the drops 12 have been greatly exaggerated for clarity. The experimental support for the deposition of the interfacial material between the liquid crystal material and the encapsulation material is provided by the electronic scanning microscope ("MEE"). The cross sections, in which the thickness of the wall between the drops is measured, show an increase in thickness after deposition and polymerization (if said step is applicable) of the interfacial material. The increase corresponds closely to that predicted, should a uniform deposition of the interfacial material occur at the contact surface. Additional experimental supports are provided by electro-optical data. For a mixed material, in which the encapsulation material is polyvinyl alcohol ("PVA") and the interfacial material is acrylate, the field of operation is 0.7 volts / μm. This value is much closer to that of a mixed material of the prior art shown in Figures 1 a-1 b, wherein the encapsulation material 14 is acrylate (approximately 0.5 volts / μm), than one in which the material of encapsulation 14 is PVA (approximately 6.1 volts / μm). In the method of the present invention, an emulsion is initially prepared in an aqueous vehicle, wherein droplets of the liquid crystal material are dispersed in the encapsulating material and in the presence of the interfacial material or a precursor thereof. The interfacial material (or its precursor) is made of a material which is, under the conditions of emulsification, initially soluble in the liquid crystal material or a combination of the liquid crystal material and a mutually compatible solvent, and is therefore in a homogeneous phase together with the liquid crystal material. The interfacial material is then induced to separate the phase from the liquid crystal material, by removing the mutually compatible solvent (where present) or by reducing the temperature (if the emulsion was originally prepared above a temperature at which the interfacial material is soluble in the liquid crystal material). An emulsion can be prepared by rapidly stirring a mixture of liquid crystal material, interfacial material (or precursor thereof), encapsulating material, and a vehicle medium, typically water. Optionally, an emulsifier, a wetting agent, or other surfactants may be added. Suitable emulsification techniques are described in '047 by Fergason,' 052 by Fergason, '431 by Raychem, and Andrews et al., E.U.A. 5,202,063 (1993), the descriptions of which are incorporated herein by reference. Suitable encapsulation materials include polyvinyl alcohol, pofi (vinylpyrrolidone), polyethylene glycol, poly (acrylic) acid, and its copolymers, poly (hydroxy-acrylate), cellulose derivatives, epoxies, silicones, acrylates, polyesters, styrene-acrylic acid acrylate terpolymers, and mixtures of the same. Particularly preferred is a combination of an aqueous carrier medium and an encapsulating material, which is soluble or colloidally dispersible in the aqueous carrier medium. Although surfactants may be employed, it is generally preferred that the encapsulating material be capable of forming capsules containing the liquid crystal material without its addition. In such cases, the encapsulation material itself must have good surfactant properties (ie, be a good emulsifier). One class of polymers having such characteristics are amphiphilic polymers, which contain both hydrophilic and lipophilic segments. Examples of this class include partially hydrolyzed polyvinyl acetates (e.g., Airvol ™ 205 from Air Products), ethylene-acrylic acid copolymers (e.g., Adcote ™ from Dow Chemical), and styrene-acid acrylate terpolymers -acrílico (e.g., Joncryl ™ by SC Johnson). As noted above, initially the emulsion can be formed not in the presence of the ifacial material, but of a precursor thereof, which can finally be polymerized to form the ifacial material. The phase separation between the liquid crystal material and the ifacial material precursor can be effected by removing the solvent or changing the temperature, as described above. Next, the precursor of the ifacial material is converted to the ifacial material by polymerization. The polymerization of the ifacial material precursor can be initiated by heating (wherein the phase separation is effected by removal of the solvent) or, preferably, photomechanically, for example, by irradiation with UV light. Since the solubility characteristics of the ifacial material will be different from those of the ifacial material precursor, it may not be necessary, where temperature change methods are used, to perform the emulsification at a temperature above the ordinary service temperature of the material mixed final. It has been discovered that by causing the deposition of the ifacial material precursor by reducing the temperature, followed by the polymerization, it unexpectedly leads to a reduction in the field of operation. In the case of a UV curable monomer (see Example 1 below) this results in a reduction in the field of operation from 2.7 volts / μm to 1.1 volts / μm. The polymerization of the ifacial material precursor can be carried out in a single step, or it can be carried out via a sequence of steps. For example, a single exposure to UV light may not be sufficient to effect a complete polymerization of the precursor, due to the reduction of molecular mobility as the polymerization proceeds. Therefore, a partial polymerization initiated with UV light of the precursor can be performed, raise the temperature of the mixed material to move any molecules of the unpolymerized precursor, and then complete the polymerization with further exposure to UV light. As used herein, "polymerize" and "polymerization" include the reaction of the iphase material (or its precursor) with the encapsulation material to fix the ifacial material between the liquid crystal material and the encapsulation material. Suitable precursors of the ifacial material include mono- or difunctional acrylates, mono- or difunctional methacrylates, epoxies (for example, those cured with thiols, amines, or alcohols), isocyanates (for example, those cured with alcohols or amines), and silanes . Preferred are precursors with branched alkyl units, for example, 2-ethylhexyl acrylate. Suitable ifacial materials are the corresponding polymers and oligomers, derivatives of the precursors listed above, mainly acrylates, methacrylates, epoxies, polyurethanes, polyureas, siloxanes and mixtures thereof. The method of the invention can be combined with the method of the patent application of E.U.A. by Reamey et al, entitled "Method of Making Liquid Crystal Composite", ("Method for Making a Mixed Liquid Crystal Material"), series no. 08/217581, filed March 24, 1994, the description of which is incorporated herein by reference, to make novel mixed liquid crystal materials. The liquid crystal material, the encapsulating material, and the interfacial material (or a precursor thereof) can be emulsified in a vehicle medium to form an intermediate, in which the liquid crystal material and the interfacial material (or a precursor thereof) are contained within the encapsulation material; cooling to separate the interfacial material (or precursor) and depositing it between the encapsulating material and the liquid crystal material; wherein a precursor of the interfacial material was used, curing the precursor (e.g., photochemically); separating the vehicle medium, for example, by centrifugation, to form capsules, in which the liquid crystal material is successively surrounded by the interfacial material and the encapsulating material. The capsules are then dispersed in a medium, in which a matrix material (or a precursor thereof) is present. The matrix material is then made to be fixed around the capsules to be fixed around the capsules to form a mixed liquid crystal material. By "fix", it is meant that the matrix material hardens in a continuous resinous phase, capable of containing, dispersed therein, various volumes of the liquid crystal material, with the intervention of the layers of the encapsulation material. and interfacial. The matrix material can be fixed by evaporating a solvent or vehicle medium, such as water, or by polymerizing a precursor monomer. Suitable matrix materials include polyurethane, polyvinyl alcohol, epoxies, poly (vinylpyrrolidone), polyethylene glycol, poly (acrylic) acid and its copolymers, poly (hydroxy-acrylate), cellulose derivatives, silicones, acrylates, polyesters, acrylate terpolymers of styre-acrylic acid, and mixtures thereof. In Figure 3 a mixed material produced by this modality is shown. The mixed liquid crystal material 30 comprises a liquid crystal material 13, which is first surrounded by an interfacial material 22a and then by an encapsulating material 22b, and finally by the matrix material 14. In this embodiment, in contrast to the embodiment shown in Figures 2a-2b, the encapsulation material serves only as an encapsulation function and the function of the matrix is served by the matrix material. A preferred combination of the interfacial material, encapsulation material, and matrix material is poly (2-ethylhexyl) acrylate, poly (vinyl alcohol), and polyurethane, respectively. Said mixed material was unexpectedly found to have a relatively low field of operation and superior dissemination out of the field, in addition to a wide range of operating temperature, high quality coatings, and good voltage support performance. It may be advantageous to entangle, physically entangle molecular chains, or otherwise ensure that the encapsulation material is fixed in place, whereby displacement by the matrix material is minimized. The above discussion has been in the context of nematic liquid crystals that have a positive dielectric anisotropy, but other types of liquid crystals can be encapsulated by the method of this invention. The techniques of this invention can be applied to mixed liquid crystal materials, wherein the liquid crystal material is a chiral nematic (also known as cholesteric), such as that described by Crooker et al., E. U.A. 5,200,845 (1993), and the commonly assigned, co-pending, Jones application, entitled "Chiral Nematic Liquid Crystal Composition and Devices Comprising the Same" ("Chiral Nematic Liquid Crystal Composition and Devices Comprising It"), No. 08/139382 , filed on October 18, 1993. Mixed materials are also contemplated wherein the liquid crystal material is a smectic liquid crystal, as described in E. U.A. 5,216,530, Pearlman et al. (1993). The practice of this invention may be further understood by reference to the following examples, which are provided by way of illustration and not limitation. All relative amounts are by weight, unless otherwise indicated.

EXAMPLE 1 A precursor of the interfacial material was prepared by mixing 100 parts of a UV-curable acrylate (PN393 ™ from EM Industries) with two portions of 1,1,1-trimethylol propane trimethacrylate (from PolysCiences). An isotropic mixture of 100 parts of liquid crystal material (TL205, a liquid crystal material having a positive dielectric anisotropy, EM Industries) and 20 parts of the interfacial material precursor was prepared at room temperature and emulsified to an average diameter of volume of 1.89 μm in an aqueous PVA solution (Airvol ™ 205, from Air Products). After defoaming at room temperature for several hours, the emulsion was divided into four samples. Three of the samples were cooled in a stream of nitrogen at 2 ° C for several times to cause phase separation of the interfacial material precursor. A fourth sample was maintained at 30 ° C and served as a control. The samples were then exposed to a UV lamp at an intensity of 11 mW / cm2, for 5 minutes without changing the temperature to polymerize the precursor. The irradiated emulsion capsules were then separated from the aqueous vehicle medium by centrifugation, and redispersed in an aqueous suspension of polyurethane latex (Neorez ™ from ICI Resins) at a solids level of 40%. Then, an ITO bombarded glass was coated with the emulsion, dried, and laminated with an ITO glass counter electrode. The amount of the polyurethane matrix material in the dry film was 10% by weight. The results for the four samples are presented in Table I. E90 is the electric field (in V / μm) required to turn on a device at 90% of its maximum transmission. The opposite ratio by thickness (CR / t) is the ratio of the saturated transmission to the transmission without any applied electric field, normalized for the thickness of the sample. CR / t provides a measure of the effectiveness of dissemination of the samples. Since a low £ 90 and a high CR / t are advantageous for presentation applications, exposure to a low temperature before and during UV treatment shows a clear benefit in relation to the control sample. a Values that are an average of five measurements for each condition The results of polarized optical microscopy suggest that the low temperature exposure of the emulsion, prior to UV treatment, causes the phase separation of the precursor from the interfacial material of the liquid crystal material. Figure 4 shows the experimental data for the sample, before the UV treatment, mixed as described above. The aqueous emulsion with a volume-average drop size of 1.9 μm was placed in a temperature-controlled stage between crossed polarizers in an optical microscope. At temperatures above 25 ° C, the liquid crystal and the interfacial precursor form a homogeneous solution, which is not birefringent, and therefore, negligible light is transmitted through the crossed polarizers. However, as the temperature is reduced, the droplets begin to acquire bi-refringency, as the nematic domes of the liquid crystals form within the droplets and the precursor phase is separated from the interfacial material. This results in an increase in transmission. When the temperature decreases below about 14 ° C, as seen in Figure 4, a loss of birefringence begins to occur. It is believed that this results from the phase separation of the interfacial precursor to the droplet wall, initiating a change in the alignment of the nematic liquid crystal material to a configuration exhibiting less birefringence and therefore a lower intensity of transmitted light. through crossed polarizers. At temperatures below 0 ° C, the birefringence stabilizes at a higher level than that initially present above 25 ° C in the isotropic solution of the liquid crystal and the interfacial precursor. The results of nuclear magnetic resonance (NMR) also indicate that a low-temperature exposure of the emulsion, before the UV treatment, causes the phase separation of the precursor of the interfacial material of the liquid crystal. Figures 5a-5b show 50 MHz carbon-13 spectra as a function of the temperature recorded for the emulsion samples before the UV treatment, as described above. The results in Figure 5a were accumulated using single pulse excitation with high energy proton decoupling for the static samples. As is well known to those skilled in the art, these conditions preferentially improve the mobile components of the sample, and the acute resonance at 130 ppm arises from the aromatic carbons of liquid crystal mesogens. In the isotropic state at 25 ° C, this peak is relatively intense, and, as the temperature is reduced, the intensity decreases rapidly. This behavior suggests that the mesogen becomes less mobile as the temperature decreases. Simultaneously, there is an increase in peak intensity at 150 ppm, which is assigned to relatively rigid mesogens when they are in the liquid crystalline state. These data support the phase separation of the interfacial material precursor and the transmission of an isotropic state to a liquid crystalline state as the temperature is reduced in these emulsions. Additional evidence is presented in Figure 5b, where cross polarization (CP) spectra corroborate the results of a single pulse. Cross polarization is a way to improve the relatively rigid components of a sample, since it relies on dipole interactions between protons and carbons, which are not averaged by molecular motions in the time scale of kHz. At 25 ° C, there is a relatively weak resonance at 130 ppm, corresponding to highly mobile aromatic mesogens in the isotropic state. As the temperature is reduced, this peak decreases in intensity, and the peak at 150 ppm, characteristic of the crystalline liquid nematic state, grows. The phase separation of the precursor from the interfacial material results in the generation of this nematic component, at approximately the same temperature at which the birefringence arising in the optical microscope results is observed. The NMR intensities, as measured by the peak height, are shown in Figure 6. The CP data correspond to the peak of 150 ppm characteristic of the nematic component. The data of a single pulse correspond to the peak of 130 ppm characteristic of the mobile isotropic component. This phase separation induced by temperature, before and during UV exposure of the emulsion, produces devices with appreciably improved electro-optical properties.

EXAMPLE 2 This example describes the use of a solvent to compatibilize liquid crystal material and interfacial material, followed by phase separation induced by solvent removal. The interfacial material was a copolymer of 2-ethylhexyl acrylate, with a low molecular weight (approximately 7,400), and hydroxyethyl acrylate (1: 1 molar ratio), which is not soluble in the liquid crystal material at a 4% level without the addition of a solvent (toluene). In a small beaker, 2.033 g of the liquid crystal material (RY1007, from Chisso), 0.2185 g of a solution at 36.7% w / w of the copolymer in toluene, and 4.1383 g of a 9.9% aqueous solution p / w were added. p of polyvinyl alcohol (Airvol ™ 205, Air Products). The contents were swirled to mix and then combined with a propeller blade for 3 minutes at approximately 4200 rpm. After filtration, through a 3.0 μm filter, the volume droplet size in volume was 2.23 μm. The emulsion was allowed to stand overnight and then coated on polyethylene terephthalate coated with ITO (ITO / PET) with a knife. After standing for 30 minutes, a second piece of ITO / PET was laminated onto the film to give a device. Two of these devices, designated as Device I and Device I I, were prepared. These devices were electro-optically tested and compared to a control, which did not contain any interfacial material. The results, in Table II below, show that the devices where interfacial material is present require a lower field to activate.

C u a d r I I Sample "Thickness Size of v90 Ego (μm) drop (μm) (volts) (V / μm) Control 9.6 2.36 38.1 3.97 Device 1 8.0 2.16 20.2 2.55 Device I I 7.8 2.16 19.9 2.55 The data are averaged for 5 measurements.

The above detailed description of the invention includes passages, which briefly or exclusively refer to particular parts or aspects of the invention. It should be understood that it is for clarity and convenience, that a particular aspect may be relevant in more than one passage, in which it is described, and that the description herein includes all appropriate combinations of information found in the different passages.

Similarly, although the various figures and descriptions thereof refer to specific embodiments of the invention, it should be understood that where a specific aspect is described in the context of a particular figure, said aspect may also be used, to an appropriate degree. , in the context of another figure, in combination with another aspect, or in the invention in general.

Claims (15)

1. CLAIMING IS 1 .- A method for making a liquid crystal mixed material, wherein varying volumes of liquid crystal material are dispersed in an encapsulating material, and the liquid crystal material is at least partially separated from the encapsulating material by an interfacial material disposed therebetween, said method comprises the steps of: a) forming an emulsion comprising the encapsulating material, the interfacial material or a precursor thereof, the liquid crystal material, and an aqueous vehicle medium, under conditions such that, (i) varying volumes of the liquid crystal material are contained by the encapsulating material and, (ii) the interfacial material or its precursor forms a homogeneous solution with the liquid crystal material and optionally a solvent, and wherein the interfacial material or its precursor, and the liquid crystal material are mutually soluble; b) causing the interfacial material or its precursor to be formed in separate phases of the liquid crystal material and deposited between the liquid crystal material and the encapsulating material, either by evaporating the solvent or reducing the temperature of the emulsion to a lower temperature, at which the interfacial material or its precursor is insoluble in the liquid crystal material; c) polymerizing the interfacial material precursor to form the interfacial material, wherein said precursor is present; and d) removing the aqueous vehicle medium.
2. 2. A method according to claim 1, wherein the interfacial material is separated from the liquid crystal material deposited between the liquid crystal material and the epcapsulation material, by evaporating the solvent.
3. 3. A method according to claim 1, wherein the precursor of the interfacial material is caused to separate the phase of the liquid crystal material and to be deposited between the liquid crystal material and the encapsulating material by evaporating the solvent, and The precursor of the interfacial material is then polymerized to form the interfacial material.
4. 4. A method according to claim 1, wherein an emulsion comprising the encapsulating material, the interfacial material, the liquid crystal material, and an aqueous carrier medium, is formed at or above a first Ti temperature. , under conditions such that, (i) the varied volumes of the liquid crystal material are contained by the encapsulation material and, (ii) the interfacial material forms a homogeneous solution with the liquid crystal material and then the interfacial material causes the The phase is separated from the liquid crystal material and deposited between the liquid crystal material and the encapsulating material by reducing the temperature of the emulsion to a second temperature T2 to or below where the interfacial material is insoluble in the liquid crystal material.
5. 5. - A method according to claim 1, wherein an emulsion comprising the encapsulating material, a precursor of the interfacial material, the liquid crystal material, and an aqueous vehicle medium, is formed at or above a first temperature Ti, under conditions such that, (i) the varied volumes of the liquid crystal material are dispersed in the encapsulating material and, (ii) the precursor of the interfacial material forms a homogeneous solution with the liquid crystal material; then the precursor of the interfacial material causes the phase to separate from the liquid crystal material and to deposit between the liquid crystal material and the encapsulating material by reducing the temperature of the emulsion to a second temperature T2 to or below where the material interfacial is insoluble in the liquid crystal material; and still later the precursor of interfacial material is polymerized to form the interfacial material.
6. 6. A method according to claim 3 or 5, wherein the precursor of the interfacial material is polymerized by exposure to ultraviolet light.
7. 7. A mixed liquid crystal material comprising varying volumes of a liquid crystal material dispersed in a matrix material, wherein the liquid crystal material is at least partially separated from the matrix material by an interfacial material and a material of encapsulation successively arranged around the liquid crystal material.
8. 8. - A mixed liquid crystal material according to claim 7, wherein the encapsulating material is fixed in place by entanglement or physical entanglement of the molecular chains.
9. 9. A method for making a mixed liquid crystal material comprising varying volumes of liquid crystal material dispersed in a matrix material, wherein the liquid crystal material is at least partially separated from the matrix material by an interfacial material and an encapsulating material successively arranged around the liquid crystal material, comprising the steps of: a) forming capsules in which the liquid crystal material is successively surrounded by the interfacial material and the encapsulating material; b) dispersing the capsules in a medium in which the matrix material or a precursor thereof is present; and c) causing the matrix material or its precursor to be fixed around the capsules, to form the mixed liquid crystal material.
10. 10. A method or a mixed liquid crystal material according to any of the preceding claims, wherein the liquid crystal material is a nematic liquid crystal material having a positive dielectric anisotropy. 1.
11. A method or a mixed liquid crystal material according to claim 10, wherein the liquid crystal material contains a pleochroic dye.
12. 12. - A method or a mixed liquid crystal material according to any of the preceding claims, wherein the encapsulating material is selected from the group consisting of polyvinyl alcohol, poly (vinylpyrrolidone), polyethylene glycol, poly (acrylic acid) and its copolymers, poly (hydroxy-acrylate), cellulose derivatives, epoxies, silicones, acrylates, polyesters, styrene-acrylic acid acrylate terpolymers and mixtures thereof.
13. 13. A method or a liquid crystal mixed material according to any of the preceding claims, wherein the interfacial material is selected from the group consisting of acrylates, methacrylates, epoxies, polyurethanes, polyureas, siloxanes, and mixtures thereof. .
14. 14. A method or a liquid crystal mixed material according to any of the preceding claims, wherein the matrix material is selected from the group consisting of polyurethanes, polyvinyl alcohol, poly (vinylpyrrolidone), polyethylene glycol, poly ( acrylic) and its copolymers, poly (hydroxy-acrylate), cellulose derivatives, epoxies, silicones, acrylates, polyesters, styrene-acrylic acid acrylate terpolymers, and mixtures thereof.
15. 15. A method or a liquid crystal mixed material according to any of the preceding claims, wherein the interfacial material, the encapsulating material, and the matrix material are poly (2-ethylhexyl) acrylate, polyvinyl alcohol , and polyurethane, respectively.