Liquid crystal elastomer, liquid crystal elastomer fiber comprising same, and manufacturing method thereof

Abstract

The present invention relates to a method for controlling the driving direction and physical properties of a liquid crystal elastomer fiber and, more specifically, to a method for manufacturing a liquid crystal elastomer fiber in which the degree of contraction and expansion can be controlled according to the extrusion temperature and other conditions.

Description

Liquid crystal elastomer, liquid crystal elastomer fiber including the same, and method for producing the same

[0001] The present invention relates to a liquid crystal elastomer and a liquid crystal elastomer fiber including the same, and more particularly, to a liquid crystal elastomer and a liquid crystal elastomer fiber having the property of expanding when heat is applied.

[0002] Macroscopically aligned liquid crystal elastomers (LCEs) are soft, actuating materials that can be programmably and reversibly shaped in response to external stimuli. Macroscopic shape changes, including shrinkage and elongation upon heating and cooling, respectively, can be induced by various means, including direct or indirect heating, as well as other stimuli such as light and chemicals.

[0003] Recently, liquid crystal elastomer fibers have attracted attention due to their similarity to the human body's own muscles, their flexible design that allows for complex operations, and their large surface area for fast operation. All liquid crystal elastomer fibers reported in the literature so far have mesogens aligned along the fiber axis, resulting in an isotropic temperature (T i ) undergoes shrinkage when heated above this temperature.

[0004] Despite the significant potential for commercialization of these materials across various industries, current liquid crystal elastomer fibers only shrink along the fiber axis when heated. To enhance the practicality and functionality of liquid crystal elastomer fibers, the development of liquid crystal elastomer fibers capable of a wider range of actuations is essential.

[0005] The present invention has been devised to solve the above problems, and the purpose of the present invention is to provide a method for controlling the driving direction and physical properties of a liquid crystal elastic body.

[0006] The technical problems to be solved by the invention are not limited to the technical problems mentioned above, and other technical problems not mentioned can be clearly understood by a person having ordinary skill in the technical field to which the present invention belongs from the description below.

[0007] In order to achieve the above object, the present invention provides a method for producing a liquid crystal elastomer, comprising: a first step of producing a liquid crystal mixture by mixing a first liquid crystal monomer, a second liquid crystal monomer, a chain extender, and a photoinitiator; a second step of producing a liquid crystal oligomer by performing oligomerization on the liquid crystal mixture; a third step of extruding the liquid crystal oligomer using a 3D printer; and a fourth step of performing UV curing on the extruded liquid crystal oligomer.

[0008] The first liquid crystal monomer may be a nematic mesogen, and the second liquid crystal monomer may be a smectic mesogen.

[0009] In the first step, the first liquid crystal monomer and the second liquid crystal monomer can be mixed in a molar ratio of 10:90 to 40:60.

[0010] In the first step, a mixture of the first liquid crystal monomer and the second liquid crystal monomer and the chain extender can be mixed in a molar ratio of 1 to 2:1.

[0011] In the first step, the photoinitiator can be mixed in an amount of 1 to 2 parts by weight per 100 parts by weight of the liquid crystal mixture.

[0012] In the third step, the liquid crystal oligomer can be extruded at a pressure of 300 to 700 kPa.

[0013] In the third step, the extrusion temperature may be 30 to 60°C.

[0014] In the fourth step, the extruded liquid crystal oligomer is exposed to a wavelength of 300 to 600 nm and a power of 20 to 40 mW cm -1 UV curing can be performed by exposing it to ultraviolet rays.

[0015] In addition, the present invention provides a liquid crystal elastomer comprising a first liquid crystal monomer; a second liquid crystal monomer; a chain extender; and a photoinitiator, wherein the first liquid crystal monomer is a nematic mesogen and the second liquid crystal monomer is a smectic mesogen.

[0016] The first liquid crystal monomer and the second liquid crystal monomer may be included in a molar ratio of 10:90 to 40:60.

[0017] The mixture of the first liquid crystal monomer and the second liquid crystal monomer and the chain extender may be included in a molar ratio of 1 to 2:1.

[0018] The photoinitiator may be included in an amount of 1 to 2 parts by weight, respectively, per 100 parts by weight of a mixture comprising the first liquid crystal monomer, the second liquid crystal monomer, the chain extender, and the photoinitiator.

[0019] The tensile strength of the above liquid crystal elastic body may be 0.5 to 10 MPa.

[0020] The glass transition temperature (T) of the above liquid crystal elastic body g ) can be between -10 and -30 ℃.

[0021] The isotropy temperature (T) of the above liquid crystal elastic body i ) can be between 40 and 70°C.

[0022] In addition, the present invention can provide a liquid crystal elastomer fiber including a liquid crystal elastomer manufactured according to the above manufacturing method.

[0023] By means of solving the above problem, the present invention can produce liquid crystal elastomer fibers in large quantities using 3D printing and photocuring.

[0024] In particular, when the temperature is increased, a liquid crystal elastic fiber can be provided that can exhibit not only the characteristic of shrinking in the longitudinal direction but also the characteristic of expanding by up to 30% in the longitudinal direction, depending on the type and composition of the liquid crystal monomer.

[0025] Additionally, depending on the type and composition of the liquid crystal monomer, the mechanical and thermal properties can be controlled, and the degree of shrinkage and expansion can also be controlled.

[0026] The effects of the present invention are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the description of the claims.

[0027]

[0028] Figure 1 illustrates the manufacturing process of liquid crystal elastomer (LCE) fibers. (a) Schematic diagram of the manufacturing process of liquid crystal elastomer fibers (including extrusion, UV curing, and winding), (b) Photograph showing the manufacturing of liquid crystal elastomer fibers.

[0029] Figure 2 shows the diameter of the liquid crystal elastic fiber according to the speed of pulling out the fiber.

[0030] Figure 3 (a) LCE at 120°C (R0C 100 ) POM image, (b) LCE(R0C 100 ) This is a photo of fiber extruded to a length of 10 m.

[0031] Figure 4 shows a liquid crystal oligomer (R 100 C0) 1 This is the H-NMR spectrum.

[0032] Figure 5 is a size exclusion chromatography (SEC) graph of a liquid crystal oligomer.

[0033] Figure 6 shows the FT-IR spectra of a liquid crystal mixture (LCM), a liquid crystal oligomer (LCO), and a liquid crystal elastomer (LCE).

[0034] Figure 7 shows the results of gel content analysis of liquid crystal elastic fibers extracted from CHCl3.

[0035] Figure 8 is a DSC thermogram of a liquid crystal oligomer.

[0036] Figure 9 shows (a) the liquid crystal oligomer LCO(R) in the nematic (91°C) and isotropic (91°C) phases. 100 C0) and (b) smectic (45°C) and isotropic (50°C) liquid crystal oligomer LCO(R0C) 100 ) is a POM image.

[0037] Fig. 10 is 10°C / min -1 DSC thermogram of the liquid crystal elastomer during the second heating cycle at a rate of .

[0038] Figure 11 shows the behavior of liquid crystal elastomer fibers upon heating. (a) Photographs of liquid crystal elastomer fibers at 30°C (left) and 120°C (right), (b) Changes in length of liquid crystal elastomer fibers with temperature, (c) Strain behavior of liquid crystal elastomer fibers.

[0039] Figure 12 shows (a) a schematic of the WAXS measurement setup of a liquid crystal elastomer fiber, (b) a 2D-WAXS pattern, (c) an azimuthal plot, (d) the calculated order parameter, and (e) the order parameter as a function of temperature of the liquid crystal elastomer fiber.

[0040] Figure 13 (a) Liquid crystal elastic fiber LCE(R 100 C0) and (b) liquid crystal elastomer fiber LCE(R0C) 100 ) is a cross-sectional POM image.

[0041] Figure 14 is a stress-strain curve of a liquid crystal elastomer fiber.

[0042] Figure 15 shows a schematic diagram of mesogen orientation and thermal actuation for (a) shrinkable and (b) expanded liquid crystal elastomer fibers.

[0043]

[0044] The terms used in this invention have been selected from widely used, current terms, taking into account the functions of the invention. However, these terms may vary depending on the intentions of those skilled in the art, precedents, the emergence of new technologies, etc. Furthermore, in certain cases, terms may be arbitrarily selected by the applicant, in which case their meanings will be described in detail in the relevant description of the invention. Therefore, the terms used in this invention should not be defined simply as names, but rather based on their inherent meanings and the overall content of the invention.

[0045] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Terms defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and shall not be interpreted in an idealized or overly formal sense unless explicitly defined herein.

[0046] When a part of a specification is said to “include” a component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise stated.

[0047] Below, with reference to the attached drawings, embodiments of the present invention are described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0048]

[0049] Hereinafter, the present invention will be described in detail.

[0050]

[0051] The present invention provides a method for producing a liquid crystal elastomer, comprising: a first step of producing a liquid crystal mixture by mixing a first liquid crystal monomer, a second liquid crystal monomer, a chain extender, and a photoinitiator; a second step of producing a liquid crystal oligomer by performing oligomerization on the liquid crystal mixture; a third step of extruding the liquid crystal oligomer using a 3D printer; and a fourth step of performing UV curing on the extruded liquid crystal oligomer.

[0052] The above liquid crystal oligomer can be synthesized by an Aza-Michael addition reaction between the first liquid crystal monomer and the second liquid crystal monomer mixture and the chain extender. More specifically, an Aza-Michael addition reaction is performed through chain extension in the liquid crystal monomer and chain extender present in the liquid crystal mixture, and the liquid crystal monomer and chain extender can be oligomerized through the addition reaction.

[0053] The first liquid crystal monomer may be a nematic mesogen, and the second liquid crystal monomer may be a smectic mesogen. Preferably, the first liquid crystal monomer may be 1,4-bis-[4-(6-acryloyloxyhexyloxy)benzoyloxy]-2-methylbenzene (1,4-bis-[4-(6-acryloyloxyhexyloxy)benzoyloxy]-2-methylbenzene, RM82), and the second liquid crystal monomer may be 4-(6-(acryloyloxy)hexyloxy)-phenyl-4-(6-(acryloyloxy)hexyloxy)benzoate (4-(6-(acryloyloxy)hexyloxy)benzoate, C6BAPE), but is not limited thereto.

[0054] In the first step, the first liquid crystal monomer and the second liquid crystal monomer may be mixed in a molar ratio of 10:90 to 40:60. According to one embodiment of the present invention, when the second liquid crystal monomer is mixed in the above range, the liquid crystal elastomer may exhibit an expansion characteristic upon heating. More specifically, depending on the relative composition between the first liquid crystal monomer and the second liquid crystal monomer, the liquid crystal elastomer may exhibit a shrinkage or expansion characteristic upon heating. The mesogen of the shrinkable liquid crystal elastomer fiber may be aligned along the fiber axis, whereas the mesogen of the expandable liquid crystal elastomer fiber may be aligned perpendicular to the fiber axis. The alignment of the mesogen is determined solely by the type of liquid crystal phase during the extrusion process, and nematic phase extrusion may produce shrinkable fibers, and smectic phase extrusion may produce stretchable fibers. Additionally, order parameters and operating performance including strain and temperature can be systematically controlled by adjusting the relative composition between the nematic mesogen and smectic mesogen monomers.

[0055] In the first step, the chain extender may be n-butylamine (n-BA), which is a component that connects the liquid crystal monomer.

[0056] In the above first step, the photoinitiator may be 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1 (I-369), which is a composition for photocrosslinking by UV curing performed in the above fourth step.

[0057] In the first step, the mixture of the first liquid crystal monomer and the second liquid crystal monomer and the chain extender can be mixed in a molar ratio of 1 to 2:1, preferably in a molar ratio of 1.1:1, but is not limited thereto.

[0058] In the first step, the photoinitiator can be mixed in an amount of 1 to 2 parts by weight per 100 parts by weight of the liquid crystal mixture, preferably 1.5 parts by weight, but is not limited thereto.

[0059] The mechanical and thermal properties of the liquid crystal elastomer produced may vary depending on the mixing ratio of the above liquid crystal monomer, chain extender, and photoinitiator. When the molar ratio is within the above range, the mechanical and thermal properties may be improved, and thus the molar ratio within the above range is preferable. In addition, by controlling the molar ratio, the desired physical properties can be controlled.

[0060] The second step may be comprised of a second step of mixing the liquid crystal mixture by putting it into an extrusion barrel and applying heat of 110 to 130° C. with a heat gun; and a second step of performing oligomerization on the mixed liquid crystal mixture at 60 to 70° C. for 12 to 48 hours to produce a liquid crystal oligomer. Preferably, the second step may be comprised of a second step of mixing the liquid crystal mixture by putting it into an extrusion barrel and applying heat of 120° C. with a heat gun; and a second step of performing oligomerization on the mixed liquid crystal mixture at 65° C. for 24 hours to produce a liquid crystal oligomer, but is not limited thereto.

[0061] In the third step, a liquid crystal elastomer can be manufactured through a melt spinning process in which the liquid crystal oligomer is extruded using a 3D printer equipped with a high-pressure extruder and a 6.0 mm diameter nozzle and then wound around a rotating mandrel.

[0062] The third step may extrude the liquid crystal oligomer at a pressure of 300 to 700 kPa, preferably at a pressure of 500 kPa, but is not limited thereto.

[0063] In the third step, the extrusion temperature may be 30 to 60°C. Preferably, it may be 40 to 45°C, but is not limited thereto.

[0064] In the above third step, the winding speed is 200 to 600 mm min -1 It could be.

[0065] Before being wound on a winding device, the extruded liquid crystal oligomer can be exposed to strong ultraviolet light for photopolymerization to produce a liquid crystal elastic fiber (Fig. 1).

[0066] The diameter of the above liquid crystal elastomer fibers can be adjusted through process parameters such as extrusion temperature and winding speed (Fig. 2). Using the above process, uniformly aligned liquid crystal elastomer fibers with a diameter of 50 to 400 μm and a length exceeding 10 m can be easily produced (Fig. 3).

[0067] The fourth step is to extrude the liquid crystal oligomer at a wavelength of 300 to 600 nm and a power of 20 to 40 mW cm -1 UV curing can be performed by exposure to ultraviolet light of a wavelength of 320 to 500 nm and a power of 35 mW cm -1 UV curing can be performed by exposure to ultraviolet rays, but is not limited thereto.

[0068] In addition, the present invention provides a liquid crystal elastomer comprising a first liquid crystal monomer; a second liquid crystal monomer; a chain extender; and a photoinitiator, wherein the first liquid crystal monomer is a nematic mesogen and the second liquid crystal monomer is a smectic mesogen.

[0069] The first liquid crystal monomer may be 1,4-bis-[4-(6-acryloyloxyhexyloxy)benzoyloxy]-2-methylbenzene (RM82), and the second liquid crystal monomer may be 4-(6-(acryloyloxy)hexyloxy)-phenyl-4-(6-(acryloyloxy)hexyloxy)benzoate (C6BAPE), but is not limited thereto.

[0070] The above chain extender may be n-butylamine (n-BA), which is a component that connects the above liquid crystal monomer.

[0071] The photoinitiator may be 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1 (2-Benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1, I-369).

[0072] The first liquid crystal monomer and the second liquid crystal monomer may be included in a molar ratio of 10:90 to 40:60.

[0073] The mixture of the first liquid crystal monomer and the second liquid crystal monomer and the chain extender may be included in a molar ratio of 1 to 2:1.

[0074] The photoinitiator may be included in an amount of 1 to 2 parts by weight, respectively, per 100 parts by weight of a mixture comprising the first liquid crystal monomer, the second liquid crystal monomer, the chain extender, and the photoinitiator.

[0075] The tensile strength of the above liquid crystal elastic body may be 0.5 to 10 MPa.

[0076] The glass transition temperature (T) of the above liquid crystal elastic body g ) can be between -10 and -30 ℃.

[0077] The isotropy temperature (T) of the above liquid crystal elastic body i ) can be between 40 and 70°C.

[0078] In addition, the present invention can provide a liquid crystal elastomer fiber including a liquid crystal elastomer manufactured according to the above manufacturing method.

[0079]

[0080] Hereinafter, the present invention will be described in detail using examples. However, the examples according to the present invention may be modified in various ways, and the scope of the present invention is not limited to the examples described below. The examples in this specification are provided to more fully explain the present invention to those of ordinary skill in the art.

[0081]

[0082] Example 1. Preparation of liquid crystal oligomer 1

[0083] Liquid crystal oligomers were synthesized by the Aza-Michael Addition reaction between liquid crystal monomers (RM82 and C6BAPE) and n-BA. RM82 and C6BAPE were mixed in a molar ratio of 10:90. The liquid crystal monomer mixture (RM82 and C6BAPE) and n-butylamine (n-BA) were mixed in a molar ratio of 1.1:1, and I-369 was added in an amount of 1.5 parts by weight per 100 parts by weight of the liquid crystal mixture. The liquid crystal mixture containing RM82, C6BAPE, n-BA, and I-369 was placed in an extrusion barrel and thoroughly mixed using a vortex while applying heat (120°C) using a heat gun. Afterwards, the liquid crystal mixture was placed in a convection oven at 65°C for 24 hours to perform an oligomerization reaction, thereby synthesizing the liquid crystal oligomer.

[0084]

[0085] Example 2. Preparation of liquid crystal oligomer 2

[0086] RM82 and C6BAPE were prepared in the same manner as in Example 1, except that they were mixed in a molar ratio of 30:70.

[0087]

[0088] Example 3. Preparation of liquid crystal elastic fiber 1

[0089] Liquid crystal oligomer 1 (RM82: C6BAPE = 10:90, R) prepared in Example 1 above10 C 90 ) were used to manufacture liquid crystal elastomer fibers. The liquid crystal elastomer fibers were manufactured using a 3D printer (Doctor Invivo, Rocket Healthcare) equipped with a pneumatic extruder and a 0.6 mm diameter nozzle. The liquid crystal oligomer was extruded at a constant pressure of 500 kPa at high temperature. The extrusion temperature was 40°C, and the winding speed was 390 mm min. -1 was extruded. The extrusion temperature varies depending on the oligomer composition, but is generally extruded at a temperature a few degrees lower than the isotropic temperature to maintain the liquid crystal phase. The extruded oligomer was carefully pulled and placed on a rotating mandrel (BLDC motor 30W, DISSOL) covered with a Teflon sheet. After that, the oligomer was exposed to ultraviolet light (OmniCure S1500, λ = 320-500 nm and 30 mW cm) for photopolymerization. -1 ) was exposed to produce a liquid crystal elastic fiber.

[0090]

[0091] Example 4. Preparation of liquid crystal elastic fiber 2

[0092] The above liquid crystal oligomer 2 (RM82: C6BAPE = 30:70, R 30 C 70 ) was used, and the extrusion temperature was 45°C, and the same method as in Example 3 was used.

[0093]

[0094] Comparative Example 1. Preparation of liquid crystal oligomer 3

[0095] RM82 and C6BAPE were prepared in the same manner as in Example 1, except that they were mixed in a molar ratio of 0:100.

[0096]

[0097] Comparative Example 2. Preparation of Liquid Crystal Oligomer 4

[0098] RM82 and C6BAPE were prepared in the same manner as in Example 1, except that they were mixed in a molar ratio of 50:50.

[0099]

[0100] Comparative Example 3. Preparation of Liquid Crystal Oligomer 5

[0101] RM82 and C6BAPE were prepared in the same manner as in Example 1, except that they were mixed in a molar ratio of 70:30.

[0102]

[0103] Comparative Example 4. Preparation of Liquid Crystal Oligomer 6

[0104] RM82 and C6BAPE were prepared in the same manner as in Example 1, except that they were mixed in a molar ratio of 90:10.

[0105]

[0106] Comparative Example 5. Preparation of Liquid Crystal Oligomer 7

[0107] RM82 and C6BAPE were prepared in the same manner as in Example 1, except that they were mixed in a molar ratio of 100:0.

[0108]

[0109] Comparative Example 6. Manufacturing of Liquid Crystalline Elastic Fiber 3

[0110] The above liquid crystal oligomer 3 (RM82: C6BAPE = 0:100, R0C 100 ) is used, and the winding speed is 260 mm min -1 It was manufactured in the same manner as Example 3 except that

[0111]

[0112] Comparative Example 7. Manufacturing of Liquid Crystalline Elastic Fiber 4

[0113] The above liquid crystal oligomer 4 (RM82: C6BAPE = 50:50, R 50 C 50 ) is used, the extrusion temperature is 45℃, and the winding speed is 260mm min. -1 It was manufactured in the same manner as Example 3 except that

[0114]

[0115] Comparative Example 8. Manufacturing of Liquid Crystalline Elastic Fiber 5

[0116] The above liquid crystal oligomer 5 (RM82: C6BAPE = 70:30, R 70 C 30 ) is used, the extrusion temperature is 50℃, and the winding speed is 260mm min. -1 Except that, it was manufactured in the same manner as in Example 3.

[0117]

[0118] Comparative Example 9. Manufacturing of Liquid Crystalline Elastic Fiber 6

[0119] The above liquid crystal oligomer 6 (RM82: C6BAPE = 90:10, R 90 C 10 ) was used, and the extrusion temperature was 50°C, and the same method as in Example 3 was used to manufacture the product.

[0120]

[0121] Comparative Example 10. Manufacturing of Liquid Crystalline Elastic Fiber 7

[0122] The above liquid crystal oligomer 7 (RM82: C6BAPE = 100: 0, R 100 C0) is used, the extrusion temperature is 60℃, and the winding speed is 520mm min. -1 Except that, it was manufactured in the same manner as in Example 3.

[0123]

[0124] Experimental Example 1. Material Characteristics Analysis

[0125] 1-1. 1 H NMR spectra

[0126] In order to determine the number average molecular weight of the liquid crystal oligomer according to the present invention, the liquid crystal oligomer (R 100 C0) was measured using a Bruker Ascend 400 MHz spectrophotometer using CDCl3 as solvent. 1 H NMR was measured and is shown in Figure 4.

[0127] Referring to Figure 4, the number average molecular weight (M n ) is 4,400 g mol-1 calculated by final group analysis. 1 The peak appearing at 5.8-6.5 ppm in the peak spectrum (bd) of H-NMR corresponds to the six protons of the terminal acrylate group.

[0128] The integration value of this peak was used to correct other peaks and was set to one. The peak at 8.1-8.2 ppm (a) corresponds to the four protons in the benzene of RM82, and its integration value is 3.98. Therefore, the degree of polymerization (DP) was calculated as follows: (3.98 / 4 × 6) = 5.9, since the terminal group is composed of RM82, M n Silver (DP-1) × M of repeating units n (4.9 × 745.9 g mol -1 ) + M of RM82 n (672.76 g mol -1 ) = 4,400 g mol -1 was calculated as

[0129] As above 1 It can be confirmed through the H NMR spectrum that the liquid crystal oligomer according to the present invention was manufactured, and the liquid crystal oligomer was 4,400 g mol -1 It can be confirmed that it has a number average molecular weight.

[0130]

[0131] 1-2. Size exclusion chromatography (SEC)

[0132] In order to determine the number average molecular weight of the liquid crystal oligomer according to the present invention, the liquid crystal oligomers prepared in the above examples and comparative examples were analyzed using an Agilent 1260 Infinity II LC system equipped with a refractive index detector and a PSS SDV (PLgel 5 μm MIXED D, 7.5 × 300 mm) column. The eluent was 1 mL / min at 40°C. -1 THF was used at a flow rate of . A calibration curve was created using polystyrene standards. The texture and alignment of the liquid crystal oligomers and liquid crystal elastomers were characterized using a polarizing optical microscope (POM, Nikon Eclipse LV100N POL) equipped with a heating stage (Linkam LTS420), and are shown in Fig. 2 and Table 1.

[0133] [Table 1]

[0134]

[0135] Referring to Figure 2 and Table 1, the M of the liquid crystal oligomer determined by SEC analysis n It has a wide molecular weight distribution (2.0–3.3) of 1500–2800 g mol -1 are in the range. Liquid crystal oligomers and liquid crystal elastomers are respectively LCO(R x C y ) and LCE(R x C y ), where R and C represent RM82 and C6BAPE, and x and y represent the relative molar ratio between RM82 and C6BAPE.

[0136]

[0137] Experimental Example 2. Analysis of molecular properties and thermal characteristics

[0138] 2-1. Fourier transform infrared (FT-IR) analysis

[0139] In order to monitor the change in functional groups during the synthesis of the liquid crystal oligomer and liquid crystal elastomer according to the present invention, the liquid crystal oligomer and liquid crystal elastomer prepared in the above examples and comparative examples were analyzed using a Jasco FTIR-4600 spectrometer at 4000 to 650 cm -1 was recorded. The background spectrum was obtained by scanning a clean ATR crystal (4 cm -1 (32 scans at resolution) is shown in Fig. 6.

[0140] Referring to Figure 6, the acrylate group of the liquid crystal oligomer is 815 cm after photopolymerization. -1 , indicating that the liquid crystal elastomer was successfully synthesized.

[0141]

[0142] 2-2. Gel fraction characteristics of liquid crystal elastomers

[0143] To confirm the gel fraction characteristics of the liquid crystal elastomer according to the present invention, the liquid crystal elastomer fiber according to the present invention was soaked in calcium chloride (CHCl3) at room temperature for 72 hours to extract the uncrosslinked portion. The sample was then dried in a vacuum oven at room temperature for 72 hours.

[0144] The gel fraction (G) was calculated according to the following mathematical formula 1 and is shown in Figure 7.

[0145]

[0146] [Mathematical Formula 1]

[0147]

[0148]

[0149] (here m i is the initial mass of the fiber before immersion, and m f is the mass of dry extracted fiber.)

[0150] Referring to Figure 7, a representative liquid crystal elastomer fiber (LCE(R0C) 100)) The gel fraction value is approximately 87%, which means that sufficient cross-linking has occurred.

[0151]

[0152] 2-3. Differential Scanning Calorimetry (DSC)

[0153] In order to confirm the thermal properties of the liquid crystal oligomer and liquid crystal elastomer according to the present invention, differential scanning calorimetry (DSC) was performed on the liquid crystal oligomer and liquid crystal elastomer prepared in the above examples using a TA Instruments Discovery DSC 25 instrument. The samples were heated at a temperature of -50 to 150°C under a nitrogen atmosphere at a rate of 10°C / min. -1 It went through a heat-cool-heat cycle at a rate of . This is shown in Fig. 8, Fig. 10 and Table 3.

[0154] [Table 3]

[0155]

[0156] Referring to Figure 8 and Table 3, the liquid crystal oligomer has a glass transition temperature (T g ) and isotropic temperature (T i ) is shown. As the C6BAPE content in the liquid crystal oligomer increases, T g (-17 ℃ to -30 ℃) and T i (from 100 ℃ to 40 ℃) both gradually decrease. The decrease in the two transition temperatures is related to the unique molecular structure of C6BAPE. Unlike the three phenyl groups of RM82, C6BAPE contains only two phenyl groups in its molecular structure, which reduces the π-π interaction in the mesogenic core. The weaker the molecular interaction, the more flexible the liquid crystal oligomer chains become, and less thermal energy is needed to disrupt the liquid crystal phase. On the other hand, as the C6BAPE content increases, the T i The enthalpy of is from 0.5 to 6.8 Jg -1tends to increase. This result is also due to the different molecular properties of RM82 and C6BAPE (i.e., RM82 is a nematogen and C6BAPE is a smectogen).

[0157] In liquid crystal oligomers composed of sufficient amounts of nematogen and smectogen, both nematic and smectic phases were detected. The coexistence of these two phases is prominent when the ratios of the two liquid crystal monomers are similar, as summarized in the phase diagram (Fig. 8b).

[0158] When a chain network is formed by photopolymerization, all thermal transition temperatures (T) of the liquid crystal elastomer g and T i ) increases by about 10℃. In particular, T i It is observed that the enthalpy value is significantly reduced (Fig. 10). The smectic-nematic transition (T SN ) and nematic-isotropic transition (T NI ) are no longer distinguishable, unlike liquid crystal oligomers. All these results result from the cross-linked structure restricting chain mobility and limiting the degree of freedom for the transition between liquid crystal order and disorder.

[0159]

[0160] 2-4. Polarizing optical microscope (POM)

[0161] In order to confirm the texture and alignment of the liquid crystal oligomer and liquid crystal elastomer according to the present invention, the liquid crystal oligomer and liquid crystal elastomer manufactured in the above examples and comparative examples were measured using a polarizing optical microscope (POM, Nikon Eclipse LV100N POL), and the results are shown in Fig. 9.

[0162] Referring to Fig. 9, the liquid crystal oligomer LCO(R 100 C 0)shows the schlieren texture commonly observed in the nematic phase, whereas the liquid crystal oligomer LCO (R0C 100 ) exhibits a fiber-like texture, suggesting a smectic phase. Since the smectic phase is of higher order than the nematic phase, the associated thermal energy to disrupt the liquid crystal order is also greater, reflecting a higher enthalpy.

[0163]

[0164] Experimental Example 3. Thermal actuation characteristics of liquid crystal elastomers

[0165] To verify the thermal operating characteristics of the liquid crystal elastomer according to the present invention, the liquid crystal elastomer fibers prepared in the above examples and comparative examples were repeatedly heated and cooled over several cycles between 30 and 130°C. Dimensional changes were monitored using a POM equipped with a heating step at 10°C intervals.

[0166] Referring to Figure 11, a liquid crystal elastomer fiber (i.e., LCE(R)) composed of a relatively high nematogen content 100 C0), LCE(R 90 C 10 ), LCE(R 70 C 30 )) undergoes thermal shrinkage along the fiber axis. Liquid crystal elastomer fibers (i.e., LCE(R0C)) containing relatively high smectogen content 100 ), LCE(R 10 C90), LCE(R 30 C 70 ) is T i When heated above this temperature, spontaneous elongation is observed. The reason for this completely opposite operational behavior is related to the different orientation of the mesogens with respect to the fiber axis.

[0167] In general, the operating temperature of liquid crystal elastomer fibers gradually decreases with increasing C6BAPE content, regardless of the operating direction. This decrease in operating temperature is associated with a decrease in π-π interactions. Furthermore, the operating strain is significantly influenced by the relative ratio between RM82 and C6BAPE in the liquid crystal elastomer fibers. In particular, a higher symmetry ratio between the two liquid crystal monomers reduces the operating strain, regardless of the operating direction.

[0168]

[0169] Experimental Example 4. Morphological Analysis of Liquid Crystalline Elastic Fibers

[0170] To confirm the morphological analysis of the liquid crystal elastomer according to the present invention, WAXS analysis was performed on the liquid crystal elastomers prepared in the above examples and comparative examples at the 9A U-SAXS beamline of the Pohang Accelerator Laboratory (PAL), Korea. A 2D charge-coupled device area detector (Rayonix MX170-HS) with an X-ray wavelength (λ) of 0.6258 Å (E = 19.81 keV) was used to acquire a two-dimensional scattering pattern. The distance between the sample and the detector for the WAXS measurement was set to 0.38 m.

[0171] Thermoresolved WAXS analysis involved heating the liquid crystal elastomer fiber with a hot wire, and the order parameter (S) was calculated from the azimuthal plot using the following mathematical expression 2.

[0172]

[0173] [Equation 2]

[0174]

[0175]

[0176]

[0177] As shown in Fig. 12a, the aligned optical cable specimen is mounted on a sample holder whose temperature can be controlled by a heating device. The sample is then exposed to an X-ray beam at various temperatures, and 2D-WAXS patterns are recorded.

[0178] Nematogen-rich liquid crystal elastomer fibers (i.e., LCE(R) 90 C 10 ), LCE(R 70 C 30 ), LCE(R 50 C 50 )) have mesogens aligned along the fiber axis and exhibit a small-angle, four-point "eyebrow" pattern characteristic of nematic-phase cytotactic packing (Fig. 12b). In contrast, smectogen-rich liquid crystal elastomer fibers (i.e., LCE(R 30 C 70 ) and LCE(R 10 C 90 )) The mesogenic alignment is orthogonal to the fiber axis and exhibits sharp internal reflections at small angles, suggesting a smectic A phase. qo = 1.41 Å. -1 The order parameter calculated based on the azimuthal scan profile in is greatly influenced by the relative composition of the liquid crystal monomers in the liquid crystal elastomer fibers (Figs. 12c and 12d). The order parameter gradually decreases with increasing smectogen content, reaching a negative value when the liquid crystal phase transforms from the nematic phase to the smectic phase. And upon heating, the order parameter gradually decreases, eventually reaching a value of T i At this temperature, it becomes 0 (Fig. 12e).

[0179] In addition, the cross-sections of nematic and smectic liquid crystal elastomer optical fibers were investigated using POM together with microtome specimens, and are shown in Fig. 13. Nematic liquid crystal elastomer optical fibers, LCE(R 100 In the case of C0), birefringence does not appear at all observation angles, indicating orientation similar to isotropy.

[0180] In contrast, LCE (R0C), a smectic liquid crystal elastomer fiber 100) shows distinct birefringence at 45 degrees and appears dark at 0 or 90 degrees. Based on this observation, LCE(R0C 100 ) can be assumed to adopt a bipolar or monodomain-like orientation.

[0181]

[0182] Experimental Example 5. Mechanical Properties of Liquid Crystalline Elastic Fibers

[0183] In order to confirm the mechanical properties of the liquid crystal elastomer according to the present invention, the mechanical properties of the liquid crystal elastomer fibers manufactured in the examples and comparative examples were measured by stress-strain using a dynamic mechanical analyzer (DMA Q850) from TA Instruments using a tensile film clamp. For the stress-strain analysis, the sample (5 mm in length, 0.3 mm in width, and 0.3 mm in thickness) was equilibrated at 25°C under a preload of 1 mN and strained at a rate of 0.05 N / min. -1 Increased power at the rate of .

[0184] Referring to Figure 14 and Table 2, nematogen-rich liquid crystal elastomer fibers (i.e., LCE(R 100 C0), LCE(R 90 C 10 ), LCE(R 70 C 30 )) Elastic modulus and tensile strength of smectogen-rich LCE fibers (i.e., LCE(R 30 C 70 ), LCE(R 10 C 90 ), LCE(R0C 100 )) is significantly higher than that of the smectogen-rich LCE fibers. In particular, the tensile strength of the nematogen-rich LCE fibers was almost three times higher than that of the smectogen-rich liquid crystal elastomer fibers, yet no cases of these fibers breaking occurred during DMA measurements. The significantly weaker mechanical properties of the smectogen-rich liquid crystal elastomer fibers are due to the orthogonal alignment of the mesogens along the fiber axis, which is consistent with the WAXS results.

[0185]

[0186] [Table 2]

[0187]

[0188]

[0189] Based on the results of WAXS, POM, and mechanical property analyses, the mesogen alignment and working principle of nematic and smectic liquid crystal elastomer fibers are shown in Fig. 15. Meanwhile, the mesogens of nematic liquid crystal elastomer fibers are aligned along the fiber axis, resulting in a homeotropic cross-section. As a result, nematic liquid crystal elastomer fibers exhibit T similar to conventional uniaxially aligned liquid crystal elastomers. i When heated above this, it shrinks and T i When cooled below this temperature, it becomes elongated. On the other hand, the mesogens of smectic liquid crystal elastomer fibers are aligned perpendicular to the fiber axis, resulting in a cross-section like anodes. Consequently, smectic LCE fibers have a T i When heated and cooled beyond , they exhibit spontaneous elongation and contraction, respectively.

[0190]

[0191] We have discussed specific embodiments of the present invention. Those skilled in the art will appreciate that the present invention can be implemented in modified forms without departing from its essential characteristics. Therefore, the disclosed embodiments should be considered illustrative rather than restrictive. The scope of the present invention is set forth in the claims, not the foregoing description, and all differences within the scope equivalent thereto should be construed as being encompassed by the present invention.

Claims

1. A first step of preparing a liquid crystal mixture by mixing a first liquid crystal monomer, a second liquid crystal monomer, a chain extender, and a photoinitiator; A second step of producing a liquid crystal oligomer by performing oligomerization on the above liquid crystal mixture; A third step of extruding the liquid crystal oligomer using a 3D printer; and A method for manufacturing a liquid crystal elastomer, comprising a fourth step of performing UV curing on the extruded liquid crystal oligomer.

2. In paragraph 1, A method for manufacturing a liquid crystal elastomer, characterized in that the first liquid crystal monomer is a nematic mesogen and the second liquid crystal monomer is a smectic mesogen.

3. In paragraph 1, A method for producing a liquid crystal elastic body, characterized in that in the first step, the first liquid crystal monomer and the second liquid crystal monomer are mixed in a molar ratio of 10:90 to 40:

60.

4. In paragraph 1, A method for producing a liquid crystal elastomer, characterized in that in the first step, a mixture of the first liquid crystal monomer and the second liquid crystal monomer and the chain extender are mixed in a molar ratio of 1 to 2:

1.

5. In paragraph 1, A method for producing a liquid crystal elastic body, characterized in that in the first step, the photoinitiator is mixed in an amount of 1 to 2 parts by weight per 100 parts by weight of the liquid crystal mixture.

6. In paragraph 1, The third step is a method for producing a liquid crystal elastomer, characterized in that the liquid crystal oligomer is extruded at a pressure of 300 to 700 kPa.

7. In paragraph 1, A method for manufacturing a liquid crystal elastic body, characterized in that the extrusion temperature in the third step is 30 to 60°C.

8. In paragraph 1, The fourth step is to extrude the liquid crystal oligomer at a wavelength of 300 to 600 nm and a power of 20 to 40 mW cm -1 A method for manufacturing a liquid crystal elastomer characterized by performing UV curing by exposing to strong ultraviolet rays 9. First liquid crystal monomer; Second liquid crystal monomer; chain extender; and Contains a photoinitiator, A liquid crystal elastomer characterized in that the first liquid crystal monomer is a nematic mesogen and the second liquid crystal monomer is a smectic mesogen.

10. In paragraph 9, A liquid crystal elastic body characterized in that the first liquid crystal monomer and the second liquid crystal monomer are included in a molar ratio of 10:90 to 40:

60.

11. In paragraph 9, A liquid crystal elastomer characterized in that the mixture of the first liquid crystal monomer and the second liquid crystal monomer and the chain extender are included in a molar ratio of 1 to 2:

1.

12. In paragraph 9, A liquid crystal elastic body characterized in that the photoinitiator is included in an amount of 1 to 2 parts by weight per 100 parts by weight of a mixture of the first liquid crystal monomer, the second liquid crystal monomer, the chain extender, and the photoinitiator.

13. In paragraph 9, The liquid crystal elastomer is characterized in that the tensile strength of the liquid crystal elastomer is 0.5 to 10 MPa.

14. In paragraph 9, The glass transition temperature (T) of the above liquid crystal elastic body g ) is a liquid crystal elastic body characterized by a temperature of -10 to -30 ℃.

15. In paragraph 9, The isotropy temperature (T) of the above liquid crystal elastic body i ) is a liquid crystal elastic body characterized by a temperature of 40 to 70 ℃.

16. A liquid crystal elastomer fiber comprising a liquid crystal elastomer manufactured according to the method of the above-mentioned first paragraph.

Images