Liquid crystal oligomer and liquid crystal elastomer, material including same, and applications thereof

Abstract

The present disclosure provides an oligomer and a liquid crystal elastomer, a material including same, and applications thereof, the oligomer having an average molecular mass of 1,000 Da to 50,000 Da and being derived from a first mixture including a first monomer represented by chemical formula 1 below and a second monomer represented by chemical formula 2 below. [Chemical formula 1] [Chemical formula 2] The definitions of chemical formulas 1 and 2 are the same as those described in the specification.

Description

Liquid crystal oligomers and liquid crystal elastomers, materials containing the same, and applications thereof

[0001] The embodiments of the present disclosure relate to liquid crystal oligomers and liquid crystal elastomers, materials containing the same, and applications thereof; specifically, to artificial muscles or actuators derived from materials containing said liquid crystal elastomers. More specifically, the invention relates to oligomers and liquid crystal elastomers that actuate in response to irradiated light without the supply of an external power source, materials containing the same that have excellent mechanical properties and can be used independently without a separate support, and applications thereof.

[0002] Liquid crystal elastomers (LCEs) are polymers in which liquid crystal molecules are bonded to flexible polymer chains in the form of main chains or side chains and then weakly chemically cross-linked. Therefore, liquid crystal elastomers possess both the properties of liquid crystals (orientation, optical anisotropy, self-assembly characteristics, etc.) and the properties of elastomers (high strain and high elasticity).

[0003] In the case of liquid crystal elastomer monomers in which liquid crystal molecules are uniformly oriented at a macroscopic scale, applying heat, light, or chemical stimuli capable of reducing the order of the liquid crystal molecules can lead to macroscopic shape transformations, as changes in the order of the molecules can alter the surrounding polymer chain structure. Furthermore, if the applied stimulus is removed to increase the order of the liquid crystal molecules, the material possesses reversibility, allowing it to return to its original shape—similar to rubber—due to the entropy effect associated with the cross-linking structure. Due to these unique characteristics, liquid crystal elastomers can be utilized in actuators, artificial muscles, soft robots, flexible devices, and sensors, and are receiving significant attention from academia and industry for the development of next-generation flexible smart materials.

[0004] Meanwhile, an actuator refers to a component that functions as a switch, transducer, or driving source in mechanical or electrical devices by causing a change in its shape in response to externally input energy. Actuators can be broadly classified into metal actuators and polymer actuators.

[0005] However, regarding these conventional oligomers and liquid crystal elastomers, materials containing them, and their applications, liquid crystal elastomers derived from monomers of a single composition have had the problem of being difficult to control their physical properties.

[0006] The embodiments of the present disclosure aim to solve various problems, including those described above, by providing an oligomer and a liquid crystal elastomer that are driven in response to irradiated light without the supply of an external power source and possess excellent mechanical properties, allowing them to be used independently without a separate support, a material containing the same, and an application thereof, such as an artificial muscle or actuator. However, these problems are exemplary and the scope of the present disclosure is not limited by them.

[0007] According to one aspect of the present disclosure, an oligomer having an average molecular weight of 1,000 Da to 50,000 Da is provided, derived from a first mixture comprising a first monomer represented by the following chemical formula 1 and a second monomer represented by the following chemical formula 2.

[0008] [Chemical Formula 1]

[0009]

[0010] [Chemical Formula 2]

[0011]

[0012] In the above Chemical Formula 1 and the above Chemical Formula 2, L 1 to L 3 Each is independently a substituted or unsubstituted C1 to C20 alkylene group, and M 1is -O-, -C(=O)O-, a substituted or unsubstituted C6 to C20 arylene group, or a combination thereof, and n is one of integers from 1 to 7.

[0013] According to the present embodiment, the above chemical formula 1 can be represented by the following chemical formula 1-1:

[0014] [Chemical Formula 1-1]

[0015]

[0016] In the above chemical formula 1-1, L 11 and L 12 Each is independently a substituted or unsubstituted C1 to C10 alkylene group.

[0017] According to the present embodiment, a liquid crystal elastomer derived from a second mixture comprising the oligomer and a photoinitiator is provided.

[0018] According to the present embodiment, the glass transition temperature of the liquid crystal elastomer may be -10°C to 0°C.

[0019] According to the present embodiment, the melting temperature of the liquid crystal elastomer may be 50°C to 100°C.

[0020] According to the present embodiment, the nematic-isotropic transition temperature of the liquid crystal elastomer may be 90°C to 130°C.

[0021] According to the present embodiment, the Young's modulus of the liquid crystal elastomer may be 1 MPa to 300 MPa.

[0022] According to the present embodiment, the toughness of the liquid crystal elastomer may be 1 MPa to 200 MPa.

[0023] According to the present embodiment, the maximum tensile strength of the liquid crystal elastomer may be 1 MPa to 100 MPa.

[0024] According to the present embodiment, the fracture strain of the liquid crystal elastomer may be 100% to 1,000%.

[0025] According to the present embodiment, an artificial muscle comprising the liquid crystal elastomer described above is provided.

[0026] According to the present embodiment, an actuator comprising the liquid crystal elastomer described above is provided.

[0027] Other aspects, features, and advantages other than those described above will become clear from the following specific details, claims, and drawings for implementing the invention.

[0028] According to the exemplary embodiment of the present disclosure as described above, oligomers and liquid crystal elastomers can be realized that are efficiently formed, have various molecular weights, and possess various physical and mechanical properties, and that physical properties can be easily controlled and have various characteristics. Accordingly, materials comprising said liquid crystal elastomers capable of optimizing required characteristics, and applications thereof, such as artificial muscles or actuators, can be realized. Of course, the scope of the present disclosure is not limited by these effects.

[0029] FIG. 1 is an IR spectrum graph of an oligomer according to an exemplary embodiment of the present disclosure.

[0030] FIG. 2 is a graph of the GPC curve of an oligomer according to an exemplary embodiment of the present disclosure.

[0031] FIG. 3 is a graph of the molecular weight of an oligomer according to an exemplary embodiment of the present disclosure.

[0032] FIG. 4 is a graph showing the results of DSC analysis of a liquid crystal elastomer according to an exemplary embodiment of the present disclosure.

[0033] FIG. 5 is a graph showing the DSC analysis results during the first heating of a liquid crystal elastomer according to an exemplary embodiment of the present disclosure.

[0034] FIG. 6 is a graph showing the DSC analysis results during the first cooling of a liquid crystal elastomer according to an exemplary embodiment of the present disclosure.

[0035] FIG. 7 is a graph of the wide-angle X-ray diffraction pattern of a liquid crystal elastomer according to an exemplary embodiment of the present disclosure.

[0036] FIG. 8 is a two-dimensional wide-angle X-ray diffraction pattern figure according to temperature of a liquid crystal elastomer according to an exemplary embodiment of the present disclosure.

[0037] FIG. 9 is a graph of the X-ray diffraction pattern according to temperature of a liquid crystal elastomer according to an exemplary embodiment of the present disclosure.

[0038] FIG. 10 is a graph showing the storage modulus according to temperature of a liquid crystal elastomer according to an exemplary embodiment of the present disclosure.

[0039] FIG. 11 is a stress graph according to strain of a liquid crystal elastomer according to an exemplary embodiment of the present disclosure.

[0040] FIG. 12 is a polarized optical microscope image showing the double refraction of a liquid crystal elastomer according to an exemplary embodiment of the present disclosure.

[0041] FIG. 13 is a graph showing the relative light transmittance according to the rotation angle between cross polarizers of a liquid crystal elastomer according to an exemplary embodiment of the present disclosure.

[0042] FIG. 14 is a graph showing the change in dimensions of a liquid crystal elastomer according to temperature in accordance with an exemplary embodiment of the present disclosure.

[0043] FIG. 15 is a graph showing the strain and working capacity according to stress of a liquid crystal elastomer according to an exemplary embodiment of the present disclosure.

[0044] FIG. 16 is a graph showing the viscosity stability at room temperature of a liquid crystal oligomer according to an exemplary embodiment of the present disclosure.

[0045] The present disclosure is capable of various modifications and may have various embodiments; specific embodiments are illustrated in the drawings and described in detail in the detailed description. The effects and features of the present disclosure and the methods for achieving them will become clear by referring to the embodiments described below in detail together with the drawings. However, the present disclosure is not limited to the embodiments disclosed below and may be implemented in various forms.

[0046] In the following embodiments, terms such as first, second, etc. are used not in a limiting sense, but for the purpose of distinguishing one component from another component.

[0047] In the following examples, singular expressions include plural expressions unless the context clearly indicates otherwise.

[0048] In the following embodiments, terms such as "include" or "have" mean that the features or components described in the specification are present, and do not preclude the possibility that one or more other features or components may be added.

[0049] In the following embodiments, when a part such as a layer, region, or component is described as being on or above another part, it includes not only cases where it is directly on top of another part, but also cases where another region, component, etc. is interposed in between.

[0050] In the drawings, the size of components may be exaggerated or reduced for convenience of explanation. For example, the size and thickness of each component shown in the drawings are depicted arbitrarily for convenience of explanation, and therefore the present disclosure is not necessarily limited to what is depicted.

[0051] Where an embodiment can be implemented differently, a specific sequence of operations may be performed differently from the order described. For example, two steps described consecutively may be performed substantially simultaneously or proceed in the reverse order of the description.

[0052] In this specification, “A and / or B” indicates the case where it is A, B, or A and B. And, “at least one of A and B indicates the case where it is A, B, or A and B.”

[0053] In the following embodiments, when layers, regions, components, etc. are described as being connected, this includes cases where the layers, regions, components are directly connected, or / or cases where other layers, regions, components are interposed between the layers, regions, components to form an indirect connection. For example, when layers, regions, components, etc. are described as being electrically connected in this specification, it indicates cases where the layers, regions, components, etc. are directly electrically connected, and / or cases where other layers, regions, components, etc. are interposed between them to form an indirect electrical connection.

[0054] The x-axis, y-axis, and z-axis are not limited to the three axes of an orthogonal coordinate system but can be interpreted in a broader sense that includes them. For example, the x-axis, y-axis, and z-axis may be orthogonal to each other, but they may also refer to different directions that are not orthogonal to each other.

[0055] The advantages and features of the present disclosure and the methods for achieving them will become clear by referring to the embodiments described below in detail together with the accompanying drawings. However, the present disclosure is not limited to the embodiments disclosed below but may be implemented in various different forms. These embodiments are provided merely to ensure that the disclosure is complete and to fully inform those skilled in the art of the scope of the present disclosure, and the present disclosure is defined only by the scope of the claims.

[0056] The terms used in this disclosure are for describing the embodiments and are not intended to limit this disclosure. In this disclosure, the singular form may include the plural form unless specifically stated otherwise in the text. The terms “comprises” and / or “comprising” used in this disclosure do not exclude the presence or addition of one or more other components in addition to the components mentioned. Throughout the disclosure, the same reference numerals refer to the same components, and “and / or” may include each of the mentioned components and all combinations of one or more. Although terms such as “first,” “second,” etc., are used to describe various components, these components are not limited by these terms. These terms are used merely to distinguish one component from another. Accordingly, the first component mentioned below may be the second component within the technical scope of this disclosure.

[0057] The word "exemplary" is used in this disclosure to mean "used as an example or illustration." Any embodiment described as "exemplary" in this disclosure should not be interpreted as being preferred or having an advantage over other embodiments.

[0058] Unless otherwise defined, all terms used in this disclosure (including technical and scientific terms) may be used in a meaning commonly understood by those skilled in the art to which this disclosure pertains. Additionally, terms defined in commonly used dictionaries are not to be interpreted ideally or excessively unless explicitly and specifically defined otherwise.

[0059] Hereinafter, the oligomer, liquid crystal elastomer, and materials comprising the above according to the present invention, and applications thereof, such as artificial muscles or actuators, are described.

[0060] An oligomer according to one embodiment of the present invention is derived from a first mixture comprising a first monomer represented by the following chemical formula 1 and a second monomer represented by the following chemical formula 2, and has an average molecular weight of 1,000 Da to 50,000 Da.

[0061] [Chemical Formula 1]

[0062]

[0063] [Chemical Formula 2]

[0064]

[0065] In the above Chemical Formula 1 and the above Chemical Formula 2, L 1 to L 3 Each is independently a substituted or unsubstituted C1 to C20 alkylene group, and M 1 is -O-, -C(=O)O-, a substituted or unsubstituted C6 to C20 arylene group, or a combination thereof, and n is one of integers from 1 to 7.

[0066] L of the above chemical formula 1 1 and L 2 Each may independently be a substituted or unsubstituted C1 to 20 alkylene group, for example, a substituted or unsubstituted C1 to C15 alkylene group, for example, a substituted or unsubstituted C1 to C10 alkylene group, for example, a substituted or unsubstituted C1 to C5 alkylene group.

[0067] M of the above chemical formula 1 1 It is -O-, -C(=O)O-, substituted or unsubstituted C6 to C20 arylene groups, or a combination thereof, for example -O-, -C(=O)O-, substituted or unsubstituted C6 to C10 arylene groups, or a combination thereof, for example -O-, -C(=O)O-, substituted or unsubstituted phenylene groups, or a combination thereof.

[0068] The above n is one of an integer from 1 to 7, for example, one of an integer from 1 to 5, and for example, one of an integer from 2 to 5.

[0069] The above chemical formula 1 can be represented by the following chemical formula 1-1:

[0070] [Chemical Formula 1-1]

[0071]

[0072] In the above chemical formula 1-1, L 11 and L 12 Each is independently a substituted or unsubstituted C1 to C10 alkylene group, and may be, for example, a substituted or unsubstituted C1 to C5 alkylene group.

[0073] L of the above chemical formula 2 3 is a substituted or unsubstituted C1 to 20 alkylene group, for example, a substituted or unsubstituted C1 to C15 alkylene group, for example, a substituted or unsubstituted C1 to C10 alkylene group, for example, a substituted or unsubstituted C2 to C8 alkylene group.

[0074] The second monomer represented by the above chemical formula 2 may be, for example, 1,6-hexanedithol, 1,2-ethanedithol, 1,2-propanedithol, 1,3-propanedithol, 1,3-butanedithol, 1,4-butanedithol, 2,3-butanedithol, 1,3-pentanedithol, 1,5-pentanedithol, 1,6-hexanedithol, or 1,3-dimercapto-3-methylbutane, and may be, for example, 1,6-hexanedithol.

[0075] The above oligomer is derived from a first mixture comprising a first monomer represented by Chemical Formula 1 and a second monomer represented by Chemical Formula 2. That is, the above oligomer can be obtained by reacting the first mixtures at room temperature.

[0076] The first mixture may further include a catalyst and / or a chloroform (CHCl3) solvent in addition to the first monomer and the second monomer. The catalyst may be, for example, n-butylamine, tripropylamine, diisopropylethylamine, 1,4-dihydropyridine, methyldiphenylphosphane, tetramethylguanidine, 2-allyl-N-alkylimidazoline, tetra-t-butylammonium hydroxide, potassium methoxide, sodium methoxide, or sodium hydroxide, and may be, for example, n-butylamine.

[0077] The average molecular weight of the above oligomer is 1,000 Da to 50,000 Da, for example, 2,000 Da to 50,000 Da, for example, 3,000 Da to 50,000 Da, for example, 4,000 Da to 50,000 Da, for example, 5,000 Da to 50,000 Da, for example, 1,000 Da to 40,000 Da, for example, 2,000 Da to 40,000 Da, for example, 3,000 Da to 40,000 Da, for example, 4,000 Da to 40,000 Da, for example, 5,000 Da to 40,000 Da, for example, 1,000 Da to 30,000 Da, for example It may be 2,000 Da to 30,000 Da, for example, 3,000 Da to 30,000 Da, for example, 4,000 Da to 30,000 Da, for example, 5,000 Da to 30,000 Da, for example, 5,000 Da to 25,000 Da, for example, 5,000 Da to 20,000 Da, for example, 5,000 Da to 15,000 Da. The oligomer according to the present invention can be obtained by selectively controlling the average molecular weight within the above range, and accordingly, a liquid crystal elastomer having the required characteristics, a material including the same, and applications thereof, for example, an artificial muscle or an actuator can be realized.

[0078] Conventionally, the reaction between a compound containing diacrylate and a compound containing dithiol is based on click chemistry, which is fast, highly selective, proceeds with high yield, and has few side reactions; however, it is difficult to control the termination of the reaction, making it difficult to obtain a product of the desired molecular weight. The present invention solves the above problem and enables the efficient production of oligomers having an average molecular weight within the above range. Since oligomers with a desired average molecular weight can be obtained by controlling the reaction as described above, the physical and mechanical properties of the liquid crystal elastomer derived therefrom can be controlled. In other words, since the liquid crystal elastomer according to the present invention and the materials derived therefrom allow for easy control of physical and mechanical properties, applications such as artificial muscles and actuators can be easily implemented to meet the required characteristics.

[0079] A liquid crystal elastomer according to one embodiment of the present invention is derived from a second mixture comprising the oligomer and a photoinitiator. That is, the liquid crystal elastomer can be obtained by reacting the second mixture comprising the oligomer and the photoinitiator at room temperature. The physical properties, mechanical properties, or crystallinity properties of the liquid crystal elastomer according to the present invention may be influenced by the properties of the oligomer, such as the average molecular weight of the oligomer.

[0080] The above photoinitiator can be represented, for example, by the following chemical formula 3:

[0081] [Chemical Formula 3]

[0082]

[0083] The glass transition temperature of the liquid crystal elastomer according to the present invention may be -10°C to 0°C, for example -9°C to 0°C, -8°C to 0°C, -10°C to -0.5°C, -9°C to -0.5°C, or -8°C to -0.5°C.

[0084] The melting temperature of the liquid crystal elastomer may be 50°C to 100°C, for example, 50°C to 95°C, 50°C to 90°C, or 50°C to 88°C.

[0085] The nematic-isotropic transition temperature of the liquid crystal elastomer may be 90°C to 130°C, for example, 95°C to 130°C, 98°C to 130°C, or 90°C to 127°C. The nematic-isotropic transition temperature (T ni ) refers to the temperature at which the liquid crystal elastomer changes from a nematic state (aligned state) to an isotropic state (randomly arranged state).

[0086] The melting enthalpy (Heat of Melting, △H) of the above liquid crystal elastomer m ) may be 1 J / g to 50 J / g, for example, 2 J / g to 50 J / g, 1 J / g to 45 J / g, 2 J / g to 45 J / g, 2 J / g to 40 J / g, or 2 J / g to 37 J / g. The melting enthalpy refers to the amount of heat absorbed when the liquid crystal elastomer changes from a solid to a liquid, and the higher the crystallinity of the liquid crystal elastomer, the greater the value of the melting enthalpy, while in the amorphous state, the melting enthalpy is small or does not appear.

[0087] Nematic-Isotropic Transition Enthalpy of the above liquid crystal elastomer (Heat of Nematic-Isotropic Transition, △H ni) may be 0.05 J / g to 5.0 J / g, for example, 0.05 J / g to 4.5 J / g, for example, 0.05 J / g to 4.0 J / g, for example, 0.05 J / g to 3.5 J / g, for example, 0.05 J / g to 3.0 J / g, for example, 0.05 J / g to 3.5 J / g, for example, 0.05 J / g to 3.0 J / g, for example, 0.05 J / g to 2.5 J / g, for example, 0.05 J / g to 2.0 J / g. The nematic-isotropic transition enthalpy refers to the absorption or release of heat generated by the liquid crystal elastomer during the nematic-isotropic transition.

[0088] The Young's modulus of the liquid crystal elastomer may be 1 MPa to 300 MPa, for example, 1 MPa to 270 MPa, for example, 1 MPa to 250 MPa, for example, 1 MPa to 230 MPa, for example, 1 MPa to 200 MPa, for example, 1 MPa to 170 MPa, for example, 1 MPa to 150 MPa, for example, 1 MPa to 120 MPa. The Young's modulus is the ratio between stress and strain, and the Young's modulus of the liquid crystal elastomer refers to a value indicating the stiffness or flexibility of the liquid crystal elastomer. The higher the Young's modulus, the stronger and harder the liquid crystal elastomer is, and the lower the Young's modulus, the more flexible it is.

[0089] The toughness of the liquid crystal elastomer may be 1 MPa to 200 MPa, for example, 1 MPa to 170 MPa, for example, 1 MPa to 150 MPa, for example, 1 MPa to 120 MPa, for example, 1 MPa to 100 MPa, for example, 1 MPa to 80 MPa, for example, 1 MPa to 60 MPa. The toughness of the liquid crystal elastomer refers to the total amount of energy that the liquid crystal elastomer can absorb before it is destroyed. If the toughness is high, the liquid crystal elastomer absorbs a large amount of energy and has the characteristic of not being easily destroyed even after deformation.

[0090] The ultimate strength of the liquid crystal elastomer may be 1 MPa to 100 MPa, for example, 1 MPa to 170 MPa, for example, 1 MPa to 150 MPa, for example, 1 MPa to 130 MPa, for example, 1 MPa to 100 MPa, for example, 1 MPa to 80 MPa, for example, 1 MPa to 50 MPa, for example, 1 MPa to 30 MPa, for example, 1 MPa to 15 MPa. The ultimate strength of the liquid crystal elastomer refers to the maximum stress that the liquid crystal elastomer can withstand, meaning the maximum load that the liquid crystal elastomer can withstand until just before it breaks.

[0091] The failure strain of the liquid crystal elastomer may be 100% to 1,000%, for example, 100% to 900%, for example, 100% to 800%, for example, 100% to 700%, for example, 200% to 1,000%, for example, 200% to 800%, for example, 200% to 700%. The failure strain of the liquid crystal elastomer refers to the strain before the material is fractured, and is a value indicating how much the material can be deformed before it is fractured.

[0092] The present invention provides an artificial muscle comprising the aforementioned liquid crystal elastomer.

[0093] In addition, the present invention provides an actuator comprising the aforementioned liquid crystal elastomer.

[0094] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the attached drawings. When describing with reference to the drawings, identical or corresponding components are given the same reference numerals, and redundant descriptions thereof will be omitted.

[0095]

[0096] Preparation of oligomers

[0097] Example 1

[0098] A mixture is prepared containing LC mesogen, a compound represented by the chemical formula 1-2 below, and 1,6-hexanedithiol in a weight ratio of 1.1:1. To this, n-butylamine and chloroform (CHCl3) are added as catalysts and reacted at room temperature. After carrying out the reaction for 5 minutes, methanol is added to terminate the reaction, thereby obtaining the oligomer 5m (LCO_5m) according to Example 1.

[0099] [Chemical Formula 1-2]

[0100]

[0101]

[0102] Example 2

[0103] Oligomer 30m (LCO_30m) according to Example 2 is obtained in the same manner as Example 1, except that the reaction was carried out for 30 minutes.

[0104]

[0105] Example 3

[0106] Oligomer 4h (LCO_4h) according to Example 3 is obtained in the same manner as Example 1, except that the reaction is carried out for 4 hours.

[0107]

[0108] Example 4

[0109] Oligomer 24h (LCO_24h) ​​according to Example 4 is obtained in the same manner as Example 1, except that the reaction is carried out for 24 hours.

[0110]

[0111] Characteristics of oligomers

[0112] Each sample is prepared comprising the respective oligomer obtained in Examples 1 to 4 above, the compound represented by Chemical Formula 1-2 (RM82 in FIG. 1), and 1,6-hexanedithiol (HDT in FIG. 1). Infrared light is transmitted through the sample using an FT-IR device to obtain a wavelength (cm²).-1 IR spectra showing the relationship between ) and absorbance are obtained. Each of the above IR spectra is as shown in FIG. 1, and it can be seen that LCO_5m, LCO_30m, LCO_4h, and LCO_24h all formed oligomers through the polymerization reaction of the reactants.

[0113] In addition, the average molecular weight of each of the above oligomers was measured by gel permeation chromatography (GPC), as shown in Fig. 2. Fig. 2 shows graphs corresponding to the oligomers LCO_24h (red line), LCO_4h (black line), LCO_30m (green line), and LCO_5m (blue line), respectively, from left to right. Furthermore, Fig. 3 shows a graph obtained by transforming Fig. 2 so that the vertical axis represents the average molecular weight. In Fig. 3, the points are in order of proximity to the vertical axis and correspond to LCO_5m, LCO_30m, LCO_4h, and LCO_24h, respectively, and it can be confirmed that the average molecular weights are 6,000 Da, 12,000 Da, 21,000 Da, and 30,000 Da, respectively. From this, it was confirmed that a larger molecular weight can be obtained as the synthesis time of the oligomer increases.

[0114] In addition, each oligomer obtained in Examples 1 to 4 was left at room temperature, and the viscosity of each oligomer was measured at 5-day intervals, and the results are as shown in FIG. 16. Referring to FIG. 16, it can be seen that each oligomer obtained in Examples 1 to 4 showed a constant viscosity even when left at room temperature, indicating viscosity stability.

[0115]

[0116] Synthesis of liquid crystal elastomers

[0117] Example 5

[0118] 5 m of the oligomer obtained in Example 1 above is dissolved in chloroform to prepare a solution containing 30 wt% of the oligomer. 5 wt% of a compound represented by Chemical Formula 3 below is added to this solution, and the solution is vortexed to uniformly mix and dissolve the compounds. The mixed solution is irradiated with UV light at 365 nm at an intensity of 250 mW / cm² for 10 minutes to perform photocrosslinking. After photocrosslinking, the solution is post-cured for 12 hours under a vacuum at 60°C. Subsequently, the solution is stored at room temperature for at least 12 hours to obtain the liquid crystal elastomer 5 m (LCE_5m) according to Example 5.

[0119] [Chemical Formula 3]

[0120]

[0121] Example 6

[0122] Liquid crystal elastomer 30m (LCE_30m) according to Example 6 is obtained in the same manner as in Example 5, except that oligomer 30m obtained in Example 2 is used instead of oligomer 5m.

[0123]

[0124] Example 7

[0125] Liquid crystal elastomer 4h (LCE_4h) according to Example 7 is obtained in the same manner as in Example 5, except that the oligomer 4h obtained in Example 3 is used instead of the oligomer 5m.

[0126]

[0127] Example 8

[0128] Liquid crystal elastomer 24h (LCE_24h) ​​according to Example 8 is obtained in the same manner as in Example 5, except that the oligomer 24h obtained in Example 4 is used instead of the oligomer 5m.

[0129]

[0130] Measurement of gel fraction of liquid crystal elastomer

[0131] Approximately 20 mg of each liquid crystal elastomer film obtained in Examples 5 to 8 was immersed in chloroform for 24 hours and then dried in a vacuum oven at 60°C for 24 hours. The gel fraction was calculated by measuring the mass before immersion in chloroform and after drying. The gel fraction refers to the ratio of components included in the cross-linked network, and as shown in FIG. 3, the gel fractions of the liquid crystal elastomers LCE_5m, LCE_30m, LCE_4h, and LCE_24h according to Examples 5 to 8 were all found to be 90% or higher. From this, it can be seen that the oligomers form a cross-linked network through the synthesis to form each liquid crystal elastomer.

[0132]

[0133] Measurement of thermal properties of liquid crystal elastomers

[0134] Differential Scanning Calorimetry (DSC) analysis was performed on each of the liquid crystal elastomers LCE_5m, LCE_30m, LCE_4h, and LCE_24h obtained in Examples 5 to 8 above. Each of the liquid crystal elastomers was heated to an isotropic state at a rate of 20°C / min (1st heating), then cooled to -50°C at a rate of -10°C / min (1st cooling). Subsequently, it was heated again at a rate of 20°C / min (2nd heating). The graphs of heat flow (W / mg) as a function of temperature (°C) for the liquid crystal elastomers LCE_5m, LCE_30m, LCE_4h, and LCE_24h measured under the above conditions are as shown in Figures 4 (a) to (d). The glass transition temperature (T) of the liquid crystal elastomer g ), melting temperature (T m ), and nematic-isotropic transition temperature (T ni) was measured. Figure 5 is a graph in which each graph during the first heating of Figure 4 is plotted simultaneously, showing the glass transition temperature, melting temperature, and nematic-isotropic transition temperature according to the liquid crystal elastomer. Additionally, Figure 6 is a graph in which each graph during the first cooling of Figure 4 is plotted simultaneously, showing the heat released as the liquid crystal elastomer crystallizes through the exo thermal peak in the temperature-decreasing region.

[0135] The glass transition temperature (T) measured through the above DSC analysis g ), melting temperature (T m ), and nematic-isotropic transition temperature (T ni ), enthalpy of melting (Heat of Melting, △H m ), Nematic-Isotropic Transition Enthalpy (Heat of Nematic-Isotropic Transition, △H ni The values ​​are as shown in Table 1 below.

[0136] Tg(℃)Tm(℃)T ni (℃)△H m (J / g)△H ni (J / g) Example 5 - 0.56 - 126.29 - 0.71 Example 6 - 1.435 2.95 119.14 2.20 0.65 Example 7 - 3.057 6.85 110.03 22.14 0.58 Example 8 - 7.148 6.749 8.04 35.40 0.13

[0137] As shown in FIGS. 4 to 6 and Table 1 above, it was confirmed that each liquid crystal elastomer derived from the oligomer exhibits different thermal properties. Specifically, the liquid crystal elastomer derived from the oligomer with a large molecular weight has a glass transition temperature (T g ), melting temperature (T m ), and nematic-isotropic transition temperature (T niIt can be seen that ) is lower. In addition, the melting temperature and melting enthalpy were measured only in Examples 6 to 8, excluding Example 5, which indicates that the liquid crystal elastomer according to Example 5 is completely amorphous, while the liquid crystal elastomers according to Examples 6 to 8 are crystalline. Referring to the melting enthalpy of Examples 6 to 8, it can be seen that the liquid crystal elastomer derived from a large molecular weight oligomer exhibits increased crystallinity. In other words, it can be seen that the crystallinity of the liquid crystal elastomer according to the present invention can be controlled by adjusting the characteristics of the oligomer forming it.

[0138]

[0139] X-ray diffraction pattern measurement of liquid crystal elastomers

[0140] Wide-angle X-ray scattering (WAXS) of the liquid crystal elastomers according to Examples 5 to 8 was measured using an X-ray diffractometer. The measured results are shown in Fig. 7. In Fig. 7, the graphs corresponding to the wide-angle X-ray diffraction patterns of the liquid crystal elastomers according to Examples 5 to 8 are arranged sequentially from bottom to top. In addition, the temperature dependence of the X-ray diffraction patterns of the liquid crystal elastomers according to Examples 5 to 8 was measured. As a result of the measurement, Fig. 8 shows the two-dimensional wide-angle X-ray diffraction pattern according to temperature, and Fig. 9 shows the case where q is 0.5 Å. -1 to 2.5 Å -1 This is a graph of the X-ray diffraction pattern according to temperature within the range.

[0141] Referring to FIG. 8, the two-dimensional wide-angle X-ray diffraction patterns of liquid crystal elastomers according to Examples 5 to 8 are shown in order from top to bottom. When observing the ring pattern below the melting temperature in each case, it can be confirmed that the ring pattern is most distinct and crystallinity is present below the melting temperature (86.74°C) of the liquid crystal elastomer according to Example 8.

[0142] Referring to FIG. 9, FIG. 9(a) to FIG. 9(d) are X-ray diffraction pattern graphs of liquid crystal elastomers according to Examples 5 to 8, respectively. FIG. 9(a) is the liquid crystal elastomer according to Example 5 with a q of 0.5 Å. -1 to 2.5 Å -1 This is a graph of the X-ray diffraction pattern as a function of temperature in the range, where the q value is 1.43 Å. -1 A nematic hollow centered at was observed, indicating that it does not possess a crystal structure. On the other hand, Fig. 9(d) shows the liquid crystal elastomer according to Example 8 with a q of 0.5 Å. -1 to 2.5 Å -1 This is a graph of the X-ray diffraction pattern according to temperature in the range, where 5 to 6 peaks were observed, and the d-spacing (Å) is 6.88 Å to 2.62 Å, indicating that it has a crystal structure.

[0143] In FIG. 9 above, the q-values ​​and d-interval values ​​of the graphs according to Examples 5 to 8 are as shown in Table 2 below.

[0144] q (Å -1 )d-spacing (Å)Example 51.4334(broad peak)4.38Example 61.45(broad peak)4.331.72(sharp peak, small)3.65Example 71.37(sharp peak, small)4.601.48(sharp peak, small)4.251.60(sharp peak) 3.941.70 (sharp peak) 3.68 Example 81.34 (sharp peak) 4.701.48 (sharp peak) 4.251.58 (sharp peak) 3.961.70 (sharp peak) 3.68

[0145] Referring to Figures 7 to 9 and Table 2 above, it can be seen that the crystallinity of the liquid crystal elastomer according to the present invention is influenced by the characteristics of the oligomer forming it.

[0146] Measurement of mechanical properties of liquid crystal elastomers

[0147] Changes in the thermomechanical properties of the liquid crystal elastomers according to Examples 5 to 8 were measured using Dynamic Mechanical Analysis (DMA). FIG. 10 is a graph showing the storage modulus of the liquid crystal elastomers according to Examples 5 to 8 as a function of temperature. Referring to FIG. 10, graphs (b to d) according to Examples 6 to 8 show a significant decrease in storage modulus as the temperature increases, and a rapid decrease in storage modulus occurred above the melting temperature. In contrast, graph (a) according to Example 5 shows a rapid decrease in storage modulus above the glass transition temperature. This indicates that the temperature at which the rapid decrease in storage modulus occurs differs due to the difference in that the liquid crystal elastomers according to Examples 6 to 8 are crystalline, whereas the liquid crystal elastomer according to Example 5 is amorphous. Furthermore, in all graphs (a to d) according to Examples 5 to 8, the storage modulus increased as the temperature increased above the nematic-isotropic transition temperature.

[0148] FIG. 11 is a stress graph according to strain of liquid crystal elastomers according to Examples 5 to 8. Referring to FIG. 11, graph (a) according to Example 5 shows a relatively low slope, meaning it has a relatively low modulus, is relatively soft, and can deform significantly under small forces. In addition, graphs (b to d) according to Examples 6 to 8 show high yielding behavior, and the stress remained relatively flat in the necking region. That is, it can be seen that the liquid crystal elastomers according to Examples 6 to 8, which have crystallinity, possess excellent characteristics of both strength and ductility.

[0149] The Young's modulus (MPa), toughness (Mpa), ultimate strength (MPa), and failure strain (%) of the liquid crystal elastomers according to Examples 5 to 8, measured using the dynamic mechanical analysis (DMA) above, are as shown in Table 3 below.

[0150] Young's modulus (MPa) Toughness (MPa) Ultimate Strength (MPa) Failure strain (%) Example 5 2.37 1.69 1.57 236.23 Example 6 5.38 4.95 2.94 322 Example 7 8 6.71 32.71 7.45 46 2.91 Example 8 117.55 0.66 10.40 620.45

[0151] Referring to Table 3 above, it can be seen that the Young's modulus of the liquid crystal elastomer according to Example 8 is 50 times greater than that of the liquid crystal elastomer according to Example 5, and the toughness of the liquid crystal elastomer according to Example 8 is 30 times greater than that of the liquid crystal elastomer according to Example 5. This can be interpreted as being due to the high crystallinity of the liquid crystal elastomer derived from an oligomer having a larger molecular weight.

[0152] Measurement of optical properties of liquid crystal elastomers

[0153] The liquid crystal elastomers according to Examples 5 to 8 were all shortened to 150% in the nematic state and then stored at room temperature for 12 hours. The samples obtained above were observed using a polarizing optical microscope (Scale bar = 500 μm). Figure 12, obtained as a result, is a photograph showing the double refraction of the aligned liquid crystal elastomer under a polarizing optical microscope. In addition, Figure 13 is a graph showing the relative light transmittance of the liquid crystal elastomers of Examples 5 to 8 according to the rotation angle between cross polarizers.

[0154] Referring to FIG. 12, dark or bright optical characteristics resulting from uniform double refraction when rotated between cross polarizers were observed. From the above, it can be seen that the liquid crystal elastomers according to Examples 5 to 8 can be aligned in the short axis direction through a mechanical stretching process.

[0155] Referring to FIG. 13, the difference between the liquid crystal elastomers of Examples 5 to 8 according to the rotation angle between the cross polarizers can be approximated by the measured brightness of the light. It can be confirmed that the liquid crystal elastomers according to Examples 5 to 8 all exhibit clear uniaxial alignment. That is, it can be seen that the molecular alignment within the liquid crystal elastomer may differ depending on the molecular weight, even when stretched with the same strain, and that liquid crystal elastomers with smaller molecular weights have relatively shorter chains, so they can align more easily when stretched with the same strain.

[0156] The deformation behavior of the liquid crystal elastomers according to Examples 5 to 8, aligned in parallel and perpendicular directions, was observed due to heat. When the aligned liquid crystal elastomers were heated, they contracted along the nematic orientation and expanded in a direction perpendicular to it. Here, the change in shape was quantified as the contracted length or increased width (L / L0) at the changed temperature relative to the length (L) or width (W) of the liquid crystal elastomer at room temperature. As a result, FIG. 14 is a graph regarding the dimensional change of the liquid crystal elastomers according to Examples 5 to 8, aligned in parallel and perpendicular directions, according to temperature.

[0157] Referring to FIG. 14, the liquid crystal elastomer graph (d) of Example 8 showed maximum strain behavior beyond the phase transition from nematic to isotropic state. The normalized dimension parallel to the nematic orientation was 1 at room temperature and decreased to 0.38 at 110°C, while the normalized dimension perpendicular to the nematic orientation was 1 at room temperature and increased to 1.63 at 110°C. Meanwhile, the liquid crystal elastomer graph (a) of Example 5 showed that the normalized dimension parallel to the nematic orientation was 1 at room temperature and decreased to 0.64 at 110°C, while the normalized dimension perpendicular to the nematic orientation was 1 at room temperature and increased to 1.31 at 110°C.

[0158] Referring to Figure 14, it was confirmed that the liquid crystal elastomer derived from larger oligomers exhibits significant dimensional changes with temperature. This suggests that the higher the molecular weight, the lower the crosslinking density. In other words, liquid crystal elastomers that are crosslinked at a low density may exhibit greater dimensional changes with temperature.

[0159] FIG. 15 is a graph showing the strain and working capacity according to stress of the liquid crystal elastomers according to Examples 5 to 8. Referring to FIG. 15, it was confirmed that the liquid crystal elastomer (d) according to Example 8 exhibited higher strain and working capacity compared to other liquid crystal elastomers (a to c). Specifically, the maximum working capacity of the liquid crystal elastomer according to Example 8 was 327 kJ / m³, which is higher than the maximum working capacity of the liquid crystal elastomer according to Example 5, which was 40.8 kJ / m³.

[0160] As described above, it can be confirmed that the liquid crystal elastomer according to the present invention can control thermal properties, mechanical properties, mechanical driving performance, and crystallinity characteristics depending on the oligomer with controlled molecular weight. As demonstrated in the above examples, the artificial muscle and actuator according to the present invention can be utilized as an artificial muscle and actuator by manufacturing a liquid crystal elastomer having the necessary driving performance and mechanical properties according to conventional methods.

[0161] Although the present disclosure has been described with reference to the embodiments illustrated in the drawings, this is merely illustrative, and those skilled in the art will understand that various modifications and equivalent alternative embodiments are possible therefrom. Accordingly, the true technical scope of protection of the present disclosure should be determined by the technical spirit of the appended claims.

Claims

1. An oligomer having a weight-average molecular weight of 1,000 Da to 30,000 Da, derived from a first mixture comprising a first monomer represented by the following chemical formula 1 and a second monomer selected from the group consisting of 1,6-hexanedithol, 1,2-ethanedithol, 1,2-propanedithol, 1,3-propanedithol, 1,3-butanedithol, 1,4-butanedithol, 2,3-butanedithol, 1,3-pentanedithol, 1,5-pentanedithol, or 1,3-dimercapto-3-methylbutane: [Chemical Formula 1] In the above chemical formula 1, L 1 to L 2 Each is independently a substituted or unsubstituted C1 to C20 alkylene group, and M 1 is -O-, -C(=O)O-, a substituted or unsubstituted C6 to C20 arylene group, or a combination thereof, and n is one of the integers from 1 to 7.

2. In claim 1, the above chemical formula 1 is an oligomer represented by the following chemical formula 1-1: [Chemical Formula 1-1] In the above chemical formula 1-1, L 11 and L 12 Each is independently a substituted or unsubstituted C1 to C10 alkylene group.

3. A liquid crystal elastomer derived from a second mixture comprising an oligomer according to claim 1 and a photoinitiator.

4. A liquid crystal elastomer according to paragraph 3, wherein the glass transition temperature of the liquid crystal elastomer is -10℃ to 0℃.

5. A liquid crystal elastomer according to paragraph 3, wherein the melting temperature of the liquid crystal elastomer is 50°C to 100°C.

6. A liquid crystal elastomer according to paragraph 3, wherein the nematic-isotropic transition temperature of the liquid crystal elastomer is 90°C to 130°C.

7. A liquid crystal elastomer according to paragraph 3, wherein the Young's modulus of the liquid crystal elastomer is 1 MPa to 300 MPa.

8. A liquid crystal elastomer according to paragraph 3, wherein the toughness of the liquid crystal elastomer is 1 MPa to 200 MPa.

9. A liquid crystal elastomer according to paragraph 3, wherein the maximum tensile strength of the liquid crystal elastomer is 1 MPa to 100 MPa.

10. A liquid crystal elastomer according to paragraph 3, wherein the fracture strain of the liquid crystal elastomer is 100% to 1,000%.

11. An artificial muscle comprising a liquid crystal elastomer according to paragraph 3.

12. An actuator comprising a liquid crystal elastomer according to paragraph 3.

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