JP2016210917A - Liquid crystal gel, production method and design method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the liquid crystal gel volume change produced by conformational change of liquid crystal polymer in response to the photoisomerization reaction of photochromic molecule.SOLUTION: Provided is a liquid crystal gel or the like obtained by gelling a liquid crystal polymer having a photochromic molecule introduced into the side chain and capable of reversible change between a uniaxial orientation state and a non-oriented state, with solvent, and in which the photochromic molecule is a molecule which takes a zwitter ionic structure by a photoisomerization reaction, and the liquid crystal polymer is a molecule configured so that the volume change due to a conformational change which changes the orientation state in response to the photoisomerization reaction of the photochromic molecule, is increased by gelation.SELECTED DRAWING: Figure 4

Description

  The present invention is a liquid crystal gel in which a photochromic molecule having a zwitterionic structure is introduced into a side chain by a photoisomerization reaction, and a liquid crystal polymer capable of reversibly changing between a uniaxial alignment state and a non-alignment state is gelled with a solvent. In addition, the present invention relates to a liquid crystal gel having a huge volume expansion coefficient due to a photoisomerization reaction of photochromic molecules.

  Attention has been focused on research on the so-called photomechanical effect (PM effect), in which light energy is directly converted into mechanical energy using the volume change of the photochromic material accompanying the photoisomerization reaction. So far, research on the PM effect using azobenzene molecules and diarylethene derivatives as photochromic materials has been progressed with gels and elastomers centering on thin films, but most of them have been researched on polymer materials centering on acrylic resins. There are few examples of research using other polymer chains.

  Under such circumstances, in recent years, research on the photoresponsiveness of a photoresponsive polypeptide in which an azobenzene molecule, which is a typical photochromic molecule, is introduced into the side chain has been advanced. For example, when an azobenzene molecule is introduced into polyaspartate, the secondary structure of the polyaspartate main chain changes from a helix structure to a random coil structure due to the cis-trans photoisomerization reaction of the side chain azobenzene molecule accompanying ultraviolet irradiation. It has been reported to metastasize.

  In addition, when an azobenzene molecule is introduced into the side chain of polyglutamate or polylysine, the trans-conformation side chain azobenzene molecule forms a strong association between the side chains in the solution. Strong strain is generated in the structure. It has been reported that irradiation with ultraviolet light leads to relaxation (non-association) of the side chain association structure due to the cis-trans photoisomerization reaction of the azobenzene molecule, and the distortion of the helix structure is accordingly reduced. Yes.

  On the other hand, several reports are also known regarding polyglutamate (PSPLG) and polylysine (PSPLL) in which spiropyran (SP), which is one of typical photochromic molecules, is introduced into the side chain. When UV light is irradiated to a solution of PSPLG or PSPLL, the secondary structure of the main chain may be transferred from a helix structure to a random coil structure with the photoisomerization reaction of the side chain terminal SP to merocyanine (MC). Reported.

  However, so far, PSPLG and PSPLL have mostly been subjected to conformational analysis in solution, and there have been few studies on photoresponsiveness of solids (thin films) and gels.

  In the non-patent document 1, the present inventor created an alignment film of PSPLG cholesteric liquid crystal using shear stress. As a result, the film thickness increased by about 13% by irradiation with ultraviolet light, and the film thickness was based on the film thickness in the dark. I found it back. However, it has been revealed that the PSPLG alignment film takes about 40 minutes to reach the maximum displacement after irradiation with ultraviolet light, and that cracking occurs in the direction of shear stress when irradiation with ultraviolet light is repeated.

Toshihiro Hiejima, Ryofumi Akai, Shunichi Kawabata, “Photomechanical effects of photochromic polyglutamate with spiropyran introduced in the side chain upon UV irradiation”, polyimide / aromatic polymer Recent advances 2014, p. 128-131

  In order to avoid the above-mentioned problems, the present inventor has high molecular mobility in the liquid crystal polymer in order to easily change the shape by slight light stimulation while maintaining the high orientation of the liquid crystal polymer. We thought that it was necessary to give (flexibility). Therefore, it was decided to give flexibility to the liquid crystal polymer by impregnating the PSPLG liquid crystal with a solvent to form a liquid crystal gel.

  One embodiment of the present invention is a liquid crystal gel in which a photochromic molecule is introduced into a side chain and a liquid crystal polymer capable of reversibly changing between a uniaxially aligned state and an unaligned state is gelled with a solvent. The liquid crystal polymer is configured such that the volume change due to the conformational change that changes the alignment state according to the photoisomerization reaction of the photochromic molecule is increased by gelation. A liquid crystal gel which is a molecule is provided.

  Further, as another aspect of the present invention, there is provided a method for producing a liquid crystal gel as described in the above aspect, wherein a photochromic molecule introduction process for introducing a photochromic molecule having a zwitterionic structure into a liquid crystal polymer by a photoisomerization reaction; A gelling process in which the liquid crystal polymer introduced with the photochromic molecule is impregnated with a solvent to gel the liquid crystal polymer to form a liquid crystal gel, and a crosslinking process in which the liquid crystal polymer in the liquid crystal gel is crosslinked with a crosslinking agent And a uniaxial alignment process for uniaxially aligning the liquid crystal polymer in the liquid crystal gel.

  Further, as another aspect of the present invention, in the method for producing a liquid crystal gel described in the above aspect, a cross-linking agent that uses the volume expansion coefficient of the liquid crystal gel to be produced for the cross-linking process or a solvent that is used for the gelation process is selected. Thus, a liquid crystal gel design method for designing a predetermined volume expansion coefficient is provided.

  In the liquid crystal gel of the present invention, the volume change of the liquid crystal gel obtained by the conformational change of the liquid crystal polymer according to the photoisomerization reaction of the photochromic molecule is enormous, and the volume change can be caused at high speed.

The figure which shows the outline | summary of the conformation change of the liquid crystal gel of this invention Figure comparing the volume change mechanism of the liquid crystal gel of the prior art and the present invention The figure which shows an example of the flow of a process of the manufacturing method of the liquid crystal gel of this invention The figure which shows the volume change at the time of ultraviolet light irradiation of the PSPLG gel created in the Example The figure which shows about the expansion coefficient of the orientation direction (helix axis | shaft: L) of the liquid crystal polymer at the time of ultraviolet light irradiation of the PSPLG gel produced in the Example, and its perpendicular direction (radius: r) The figure shown about the volume expansion coefficient at the time of ultraviolet light irradiation of the PSPLG gel created in the Example The figure which shows about the crosslinking agent density | concentration dependence of the volume expansion rate at the time of ultraviolet light irradiation of the PSPLG gel created in the Example The figure which shows the magnetic field application days dependence of the volume expansion rate at the time of ultraviolet light irradiation of the PSPLG gel created in the Example The figure shown about the volume expansion coefficient at the time of ultraviolet light irradiation of 1D-PSPLG gel and u-PSPLG gel which were created in the Example

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, this invention is not limited to description of these embodiment and drawing at all, In the range which does not deviate from the summary, it can implement with a various aspect.
<< Embodiment 1 >>
<Overview>

  FIG. 1 is a diagram showing an outline of the conformational change of the liquid crystal gel of the present invention. “Conformation” is also called “conformation” and indicates a spatial atomic arrangement, and “conformation change” indicates a structural change of a three-dimensional structure. FIG. 1A shows an outline of the helix coil transition of the liquid crystal polymer as an example of the conformational change of the liquid crystal gel of the present invention. The “helix coil transition” is a structural change between a “helix structure” (0101) in which the protein (0100) has a regular helical structure and a “random coil structure” (0102) that is randomly oriented. That is. If the protein (liquid crystal polymer) has a helix structure and the liquid crystal polymer is uniaxially oriented, when the structure of the liquid crystal polymer changes to a random coil structure due to the helical coil transition, The liquid crystal polymer is non-oriented. Since the helix coil transition is a reversible change, the liquid crystal polymer can reversibly change between a uniaxial alignment state and a non-alignment state. In addition, in FIG. 1, it demonstrates using the polypeptide as an example of protein, and in order to show the outline | summary, the chemical structural formula shown in the center of each structure is the structure except the side chain among chemical structural formulas of polypeptide. Show.

  Here, in this specification, “liquid crystal polymer” basically indicates one liquid crystal polymer chain. Therefore, “liquid crystal polymer is uniaxially aligned” indicates a state in which each liquid crystal polymer chain is aligned in a common direction in a liquid crystal gel, and “liquid crystal polymer is not aligned”. Shows a state in which the alignment directions of the liquid crystal polymer chains are dispersed in the liquid crystal gel. Note that uniaxial alignment is not limited to the state in which all the liquid crystal polymers in the liquid crystal gel are oriented in a common direction, but the liquid crystal polymers in the liquid crystal gel are aligned in one direction as a whole. It should be. Moreover, even if it says non-alignment, it is not limited to the state in which the liquid crystal polymers in the liquid crystal gel are completely oriented in different directions, for example, one direction in which the liquid crystal polymers in the liquid crystal gel are slightly in total. May be oriented.

  The helix coil transition can be induced by the kind of solvent, pH change, temperature change, etc., but can also be caused by a photoisomerization reaction of a photochromic molecule introduced into a side chain. “Photochromic” refers to a reversible change in the light physical properties of a substance by light, and “photochromic molecule” refers to a molecule that can reversibly change the light physical properties of the molecule by light. In addition, “photoisomerization” is a phenomenon in which the structure atom of a substance is not changed by light energy, and photochromic molecules are often caused by a photoisomerization reaction of molecules.

  FIG. 1 (b) shows an outline of helix coil transition of a polypeptide having spiropyran (0103) introduced as a photochromic molecule in the side chain. When spiropyran (0103) is introduced into the side chain of the polypeptide as a photochromic molecule and irradiated with ultraviolet light, spiropyran causes a photoisomerization reaction, that is, spiropyran is changed to merocyanine (0104). Merocyanine has a zwitterionic structure including a nitrogen atom having a positive charge and an oxygen atom having a negative charge in the molecule. A “zwitter ion” is a molecule that has both positive and negative charges in one molecule. Here, the nitrogen atom of the polypeptide is positively charged due to polarization, and the oxygen atom is negatively charged. Then, the nitrogen atom or oxygen atom of merocyanine and the nitrogen atom or oxygen atom of the polypeptide interact with each other by Coulomb force, thereby inducing a helix-coil transition of the polypeptide.

FIG. 1 (c) shows an outline of a liquid crystal gel in which a polypeptide having spiropyran introduced into the side chain is crosslinked. In the liquid crystal gel of the present invention, liquid crystal polymers are cross-linked with a cross-linking agent (0105), and the liquid crystal polymer is swollen with a solvent (0106) to form a liquid crystal gel. Then, high molecular mobility can be imparted to the liquid crystal polymer, and as a result, a huge and high-speed volume change of the liquid crystal gel can be caused by the photoisomerization reaction of spiropyran. Hereafter, each structure of the liquid crystal gel of this invention is demonstrated.
<Configuration>

(Liquid crystal polymer)
In the liquid crystal gel of the present invention, the liquid crystal polymer is configured to change the alignment state according to the photoisomerization reaction of the photochromic molecule. As will be described later, since the photochromic molecule of the present invention is a molecule having a zwitterion structure by a photoisomerization reaction, for example, a liquid crystal polymer is used for “changing the alignment state according to the photoisomerization reaction of the photochromic molecule”. May be composed of molecules having atoms that are positively charged and / or negatively charged by polarization within the molecule. That is, when a photochromic molecule has a zwitterion structure by a photoisomerization reaction, atoms having a positive charge and a negative charge in the zwitterion structure have a positive charge and / or a negative charge in the liquid crystal polymer. By interacting with the atoms, the liquid crystal polymer may cause a conformational change and change its alignment state. Note that “changing the alignment state” means, for example, changing from a uniaxial alignment state in which the liquid crystal polymer is uniaxially aligned to a non-alignment state in which the liquid crystal polymer is not aligned. Further, the change in the orientation state is preferably a reversible change. The liquid crystal gel of the present invention changes in volume due to a conformational change that changes the alignment state of the liquid crystal polymer.

  In addition, you may comprise the liquid crystal gel of this invention using the polypeptide shown to Formula (1) as an example of a liquid crystal polymer. Here, X in formula (1) represents an ester bond (—COO—) or an amide bond (—CONH—, or —NHCO—). R represents a photochromic molecule. N represents the number of methylene units, and n = 1, 2, and 4 are preferable. P represents the degree of polymerization of the polypeptide chain.

(Photochromic molecule)
In the liquid crystal gel of the present invention, the photochromic molecule is composed of a molecule having a zwitterionic structure by a photoisomerization reaction. As described above, the photochromic molecule is irradiated with light to induce a photoisomerization reaction of the photochromic molecule, thereby inducing a conformational change of the liquid crystal polymer. As an example of the photochromic molecule of the present invention, the liquid crystal gel of the present invention may be constituted using spiropyran represented by the formula (2). Here, m in the formula (2) represents the number of methylene units, and m = 1, 2 is preferable. Note that spiropyran represented by the formula (2) causes a photoisomerization reaction upon irradiation with ultraviolet rays, and changes to a merocyanine represented by the formula (3). Merocyanine has a positive nitrogen atom and a negative oxygen atom in its molecular structure.

(Crosslinking agent)
In the liquid crystal gel of the present invention, the liquid crystal polymers are preferably cross-linked with each other. By cross-linking the liquid crystal polymer in the liquid crystal gel, flexibility can be imparted to the liquid crystal polymer, and as a result, a liquid crystal gel capable of obtaining a large volume change by photoisomerization reaction of photochromic molecules can be obtained. . The cross-linking agent used for cross-linking the liquid crystal polymer is preferably a highly flexible substance in order to impart flexibility to the liquid crystal polymer. The “highly flexible substance” refers to a substance including a portion having a high degree of rotational freedom such as a carbon-carbon single bond.

  As examples of the crosslinking agent used in the liquid crystal gel of the present invention, diamine derivatives represented by the formulas (4) to (6) may be used. Here, p, q, and r in the formulas (4) to (6) each represent the number of units of the chain segment, and p = 4, 5 q = 1 to 3, and r = 5 to 12, respectively. It is preferable that

  The liquid crystal gel of the present invention can change the volume expansion coefficient depending on the concentration and type of the crosslinking agent used. For example, by changing the concentration of the crosslinking agent, the degree of crosslinking of the liquid crystal polymer in the liquid crystal gel can be changed, and the volume expansion coefficient of the liquid crystal gel can be changed according to the degree of crosslinking. Moreover, according to the kind of crosslinking agent, the magnitude | size of interaction of the solvent mentioned later and a crosslinking agent can be changed, and the volume expansion coefficient of liquid crystal gel can be changed.

(solvent)
The liquid crystal gel of the present invention is constituted by gelation by impregnating a liquid crystal polymer in a solvent. That is, by impregnating a liquid crystal polymer in a solvent and gelling, the liquid crystal polymer can be given high flexibility, and the volume expansion coefficient of the liquid crystal gel due to the conformational change of the liquid crystal polymer can be increased. I can do it.

  As a solvent used for gelation of the liquid crystal polymer, an aqueous solvent, an alcohol solvent, a chlorinated organic solvent, an aprotic polar solvent, or the like may be used. Specifically, water or the like as an aqueous solvent, methanol or ethanol as an alcohol solvent, dichloroethane or chloroform as a chlorinated organic solvent, dimethylacetamide or the like as an aprotic polar solvent can be used.

  In addition, the liquid crystal gel of this invention can change a volume expansion coefficient according to the kind of solvent used for gelatinization of a liquid crystal polymer. That is, by changing the type of the solvent, the magnitude of the interaction between the solvent and the liquid crystal polymer can be changed, and the volume expansion coefficient of the liquid crystal gel due to the conformation change can be changed.

  In addition, the liquid crystal gel of the present invention can change the color tone of the liquid crystal gel depending on the type of solvent used for gelation of the liquid crystal polymer. The mechanism is known as “solvatochromism”. By changing the polarity of the solvent, the electronic state in the substance is changed, and the color tone of the liquid crystal gel is changed. Specifically, the color of the liquid crystal gel can be made shallower as the polarity of the solvent is made negative, and the color of the liquid crystal gel can be made deeper as the polarity is made positive.

(Comparison with prior art)
FIG. 2 is used to compare the volume change mechanism of the liquid crystal gel of the prior art and the present invention. Shown in (a) is the outline of the crystal structure of the alignment film of the PSPLG cholesteric liquid crystal prepared by using the shearing stress which is the prior art. In the case of an alignment film, adjacent polypeptides (0200) form strong associations to form an aggregate. Therefore, the photoisomerization reaction of the photochromic molecule (0201) is less likely to occur by ultraviolet irradiation, and it is difficult to induce the helical coil transition of the polypeptide even when the photoisomerization reaction occurs. The change in the thickness of the alignment film was small, and the time required for the change was also long. Furthermore, since the alignment film is formed by the formation of polypeptide aggregates, when the helix-coil transition of the polypeptide is induced, the aggregates dissociate, which causes a problem that the alignment film cracks. It was.

  Therefore, as shown in (b), the present inventor swelled the polypeptide (liquid crystal polymer) with a solvent (0204) in a state of being crosslinked with a crosslinking agent (0203), thereby preparing a liquid crystal gel. In this case, since the liquid crystal polymer is bonded at an appropriate distance by the crosslinking agent, the association of the liquid crystal polymer can be inhibited. Moreover, since the liquid crystal polymer is gelled by the solvent, flexibility can be imparted to the liquid crystal polymer. As a result, the volume change of the liquid crystal gel due to the change in the conformation of the liquid crystal polymer increases, and the volume change can be caused at high speed. Specifically, a liquid crystal gel having a volume expansion coefficient of 100% or more due to a photoisomerization reaction of photochromic molecules can be provided. Here, the volume expansion coefficient indicates the ratio of the increase in volume after the photoisomerization reaction to the volume of the liquid crystal gel before the photoisomerization reaction of the photochromic molecule.

  Furthermore, in the liquid crystal gel of the present invention, the photochromic molecule introduced into the side chain of the liquid crystal polymer has a zwitterionic structure by a photoisomerization reaction as described above. Then, the adjacent photochromic molecules in the liquid crystal gel are repelled by Coulomb force (0205), and the liquid crystal polymer in which the photochromic molecules are introduced into the side chain is also affected, and the polypeptide chain in the liquid crystal gel is The distance from each other increases, that is, the volume of the liquid crystal gel increases. As described above, since the liquid crystal polymer of the present invention is gelled by a solvent and given flexibility, it is considered that the liquid crystal gel is easily affected by the Coulomb force of the photochromic molecule and the volume change of the liquid crystal gel is increased. .

  The liquid crystal gel of the present invention may have different expansion coefficients when the liquid crystal gel is irradiated with light in the alignment direction of the liquid crystal polymer and the vertical direction thereof. For example, the expansion coefficient in the direction perpendicular to the alignment direction of the liquid crystal polymer may be larger than the expansion coefficient in the alignment direction of the liquid crystal polymer, in which case the volume expansion of the liquid crystal gel of the present invention is different. It can be said that

In addition, the liquid crystal gel of the present invention can expand its volume by light irradiation, but the photochromic molecules are changed to the state before light irradiation under light shielding conditions or by heating, and accordingly the volume and shape of the liquid crystal gel are changed. It is preferable that the state before light irradiation can be restored. That is, the liquid crystal gel of the present invention preferably has a self-repairing property and a shape memory property with respect to volume and shape.
<Manufacturing method>

  The liquid crystal gel of the present invention can be produced by a known method using the above-described liquid crystal polymer, crosslinking agent, solvent and the like, and the production method is not particularly limited. An example of the flow of the process of the manufacturing method of liquid crystal gel is shown. For example, the liquid crystal gel of the present invention includes a photochromic molecule introduction process, a gelation process, a crosslinking process, and a uniaxial alignment process. Note that the order of these processes is not particularly limited, and for example, a configuration in which a crosslinking process and a uniaxial orientation process are simultaneously performed may be employed.

(Photochromic molecule introduction process)
In the photochromic molecule introduction process (S0301), photochromic molecules having a zwitterionic structure are introduced into the liquid crystal polymer by a photoisomerization reaction. The introduction of the photochromic molecule into the liquid crystal polymer can be performed using, for example, a dehydration esterification reaction between the liquid crystal polymer and the photochromic molecule.

(Gelation process)
In the gelation process (S0302), a liquid crystal polymer into which photochromic molecules are introduced is impregnated in a solvent to gel the liquid crystal polymer to obtain a liquid crystal gel. As described above, the volume expansion coefficient of the liquid crystal gel can be changed according to the type of the solvent impregnated in the liquid crystal polymer. That is, by selecting a solvent to be impregnated into the liquid crystal polymer, the liquid crystal gel can be designed to have a predetermined volume expansion coefficient.

(Crosslinking process)
In the crosslinking process (S0303), the liquid crystal polymer in the liquid crystal gel is crosslinked with a crosslinking agent. That is, the liquid crystal polymer in the liquid crystal gel can be crosslinked by mixing the liquid crystal gel and the crosslinking agent. Here, the degree of crosslinking of the liquid crystal polymer can be adjusted not only by the type and concentration of the crosslinking agent but also by the crosslinking time and the crosslinking temperature. That is, the volume expansion coefficient of the liquid crystal gel can be designed to a predetermined volume expansion coefficient by selecting the type and concentration of the crosslinking agent, the crosslinking time, the crosslinking temperature, and the like.

(Uniaxial orientation process)
In the uniaxial alignment process (S0304), the liquid crystal polymer in the liquid crystal gel is uniaxially aligned. Uniaxial alignment of the liquid crystal polymer can be performed by applying a shear stress to the liquid crystal gel, but may be performed uniaxially using a magnetic field. That is, by leaving the liquid crystal gel in a magnetic field, the liquid crystal polymer is uniaxially aligned in the magnetic field application direction. When the liquid crystal polymer is uniaxially aligned in a magnetic field, the degree of alignment of the liquid crystal polymer can be improved, and as a result, the volume expansion coefficient of the liquid crystal gel can be increased.

The liquid crystal gel manufacturing process described above is simple, highly safe, and can be carried out using inexpensive and recyclable resources as a material for the liquid crystal gel, which is suitable for a recycling society.
<Application>

  The liquid crystal gel of the present invention described above is suitable as an actuator because it can cause a huge and high-speed volume change by light irradiation. Specifically, the actuator can be applied to devices such as a micro robot, a micro manipulator, and an active catheter.

In this example, a uniaxially oriented PSPLG liquid crystal gel (1D-PSPLG gel) was synthesized and its swelling and shrinkage behavior was verified. The results are shown below.
<Experiment>

(Preparation of poly (methyl-L-glutamate) (PMLG) mixed solution)
PMLG swollen in dichloroethane (DCE) was finely pulverized, and DCE was completely blown off by vacuum drying. The following operations were all performed in the draft. In an eggplant flask, 1 ml of 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP): 5 ml was added to 1 g of PMLG, and light-shielded with aluminum foil and stirred overnight. About 40 ml of chloroform was gradually added to this solution, and the mixture was further vigorously stirred for 1 hour or more. Thereafter, 100 ml of DCE was added and concentrated with an evaporator set at 40 ° C. to obtain a PMLG mixed solution. In addition, Formula (7) shows the outline.

(Synthesis of poly (chloroethylene-L-glutamate) (PC1ELG))
Ethylene chlorohydrin and p-toluenesulfonic acid were added to the DCE solution of PMLG and reacted at 70 ° C. for 2 hours. Then, methanol generated during the reaction was distilled off while slightly reducing the pressure with an evaporator set at 40 ° C. did. The polymer solution was dropped into methanol, and the precipitated polymer was collected. Further, reprecipitation was performed in a DCE / methanol system, followed by vacuum drying. In addition, Formula (8) shows the outline.

(Synthesis of poly (L-glutamic acid) (PLGA))
The prepared polymer was fined with tweezers and saponified by dipping in a 75 vol% methanol aqueous solution having a sodium hydroxide concentration of 1.8 wt% for 15 hours. Thereafter, it was filtered off, washed with methanol and dried. The obtained sodium poly-L-glutamate was dissolved in water, hydrochloric acid was added to precipitate poly-L-glutamic acid (PLGA), filtered, centrifuged, and vacuum dried. In addition, Formula (9) shows the outline.

(Synthesis of poly (L-glutamic acid) spiropyran introduced product (PSPLG))
PLGA (0.10 g, 0.774 mmol) was dissolved in 10 ml of N, N-dimethylformamide (DMF) and stirred overnight. 1- (2-hydroxyethyl) -3,3-dimethylindolino-6-nitrobenzopyrospirane (SP) 1.365 g (3.87 mmol) (manufactured by Tokyo Chemical Industry), 1-hydroxybenzotriazole (HOBt) 0 .228 g (1.49 mmol) and dicyclohexylcarbodiimide (DCC) 0.307 g (1.49 mmol) were added and the reaction was carried out in an incubator at 30 ° C. for 2 weeks. After dicyclohexylurea in the solution was removed by filtration with Kiriyama filter paper, it was dropped into methanol and the precipitated polymer was recovered. Further, recrystallization was repeated in a chloroform / methanol system, followed by vacuum drying. In addition, Formula (10) shows the outline.

(Synthesis of 1D-PSPLG gel)
PSPLG was synthesized from the dehydration esterification reaction of poly (L-glutamic acid) and N-hydroxyethyl spiropyran (Sp). The introduction rate of spiropyran was estimated to be about 71% from the absorbance at 355 nm in a hexafluoro-2-propanol solution. After mixing 10 mol% of pentaethylenehexamine (PEHA) and 55 mol% of 2-hydroxypyridine per monomer residue in a 25 wt% PSPLG dimethylacetamide (DMAc) solution that expresses a cholesteric liquid crystal phase, in a magnetic field of 11.74 T The uniaxially oriented PSPLG liquid crystal gel (1D-PSPLG gel) was prepared by allowing to stand for 3 days. As a reference material, an unoriented PSPLG liquid crystal gel (u-PSPLG gel) in which the PSPLG liquid crystal polymer was not oriented was prepared under the same conditions under no magnetic field. Irradiation with ultraviolet light was performed for 10 minutes using an LED lamp having a center wavelength of 365 nm.

(DFT calculation)
The structure optimization and molecular volume estimation of PSPLG and PMCLG monomers were performed from density functional theory (DFT) calculations at the B3LYP / 3-21G level. Here, the molecular volume was defined as a volume in which the electron density of each monomer whose structure was optimized was within 0.001 electron / bohr ³ .
<Result>

FIG. 4 shows the volume change of the prepared PSPLG gel when irradiated with ultraviolet light. Each numerical value indicates the volume change rate after solvent impregnation ((b), (c)) and after ultraviolet irradiation. FIG. 4 shows a PSPLG gel impregnated with three types of solvents, (a) dimethylacetamide (DMAc) solvent, (b) chloroform (CHCl ₃ ) solvent, and (c) dichloroethane (DCE). ) PSPLG gel impregnated with solvent. First, in the state before irradiating with ultraviolet light (UV), the so-called solvatochromism in which the PSPLG gel changes its color tone when the type of the impregnating solvent is changed was observed ((a) is the left figure, (b) ), (C) is the center figure). The color change almost reflects the characteristics in the solution.

In addition, when the PSPLG gel is impregnated with the DMAc solvent used for the crosslinking reaction, the volume is most swollen, and when impregnated with other solvent, water or methanol (MeOH), which is a poor solvent for the PSPLG, is used. Needless to say, the volume was greatly shrunk even when DCE or CHCl ₃ as good solvents was used. Among the solvents used in this example, MeOH contracted the volume most, and the contraction rate was about 50% with respect to the PSPLG gel in DMAc solvent.

When each of the prepared PSPLG gels was irradiated with ultraviolet light (UV ₃₆₅ ) having a wavelength of 365 nm, the color of the sample surface was instantaneously changed and the volume was expanded without changing the shape of the gel. The change in color indicates that spiropyran in the PSPLG gel has undergone a photoisomerization reaction with merocyanine. Here, each numerical value represents the volume expansion coefficient, that is, the volume expansion coefficient when the PSPLG gel impregnated with the DMAc solvent shown in (a) is irradiated with ultraviolet light is 128%, and CHCl ₃ shown in (b). The volume expansion coefficient of the PSPLG gel impregnated with the solvent was 160%, and the volume expansion coefficient of the PSPLG gel impregnated with the DCE solvent shown in (c) was 144%. Here, the “volume expansion coefficient” indicates the expansion ratio of the volume after ultraviolet light irradiation to the volume of each PSPLG gel before ultraviolet light irradiation. In addition, the expanded PSPLG gel can be returned to the volume and shape before ultraviolet light irradiation under light shielding conditions or by heating.

FIG. 5 shows the expansion rate in the alignment direction (helix axis: L) and the vertical direction (radius: r) of each PSPLG gel when the liquid crystal molecules are irradiated with ultraviolet light. The PSPLG gel impregnated with good solvents DCE, CHCl ₃ , and DMAc with respect to the PSPLG gel was suppressed from expanding in the direction parallel to the magnetic field, and changed greatly in the vertical direction. This result shows that the molecular mobility of the polypeptide chain in the 1D-PSPLG gel is suppressed in the direction parallel to the magnetic field. In addition, the expansion coefficient shown on the vertical axis | shaft of a graph has shown about the ratio of the increase after ultraviolet light irradiation with respect to each length L and r before ultraviolet light irradiation of each PSPLG gel. On the other hand, the PSPLG gel impregnated with MeOH as a poor solvent reduced the lengths L and r by irradiation with ultraviolet light.

In FIG. 6, it shows about the volume expansion rate at the time of ultraviolet light irradiation of each PSPLG gel. As shown in FIG. 6, when the PSPLG gel was impregnated with CHCl ₃ , the volume was expanded most, followed by DCE and DMAc in this order. On the other hand, the volume of the PSPLG gel impregnated with MeOH, which is a poor solvent, was shrunk by irradiation with ultraviolet light. That is, the liquid crystal gel of the present invention can control the volume expansion coefficient by the solvent to be impregnated. Here, the “volume expansion coefficient” shown on the vertical axis in FIG. 6 indicates the ratio of the increase in volume after ultraviolet light irradiation to the volume of each PSPLG gel before ultraviolet light irradiation.

The molar extinction coefficient ([ε] ₃₆₅ ) of ₃₆₅ nm UV in a hexafluoro-2-propanol solution of PSPLG and PMCLG (polyglutamate in which spiropyran is changed to merocyanine) is 1.54 × 10 ⁴ Lmol ⁻¹ cm ^{−. 1} and 0.83 × 10 ⁴ Lmol ⁻¹ cm ⁻¹ . (Note that the solvent to be impregnated into the PSPLG gel is not a hexafluoro-2-propanol solution, but the molar extinction coefficient has been reported in papers and the like, so this value was used as a reference.) Is approximately 0.51 mol L ⁻¹ , the penetration length of the ultraviolet light having a wavelength of 365 nm into the PSPLG gel is estimated to be about 1.3 to 2.4 μm at most. (Invasion length indicates the depth from the sample surface where the intensity of the incident ultraviolet light attenuates to 1/10.) Then, when the PSPLG gel is irradiated with ultraviolet light, It is considered that spiropyran is converted to merocyanine by the photoisomerization reaction and causes volume expansion of the PSPLG gel. Specifically, when the PSPLG gel is irradiated with ultraviolet light, the PSPLG from the surface of the PSPLG gel up to 2 microns changes to PMCLG, and as a result, expands by 100 microns in the direction perpendicular to the magnetic field (radius: r). it is conceivable that. Then, it is considered that 2 micron PSPLG changed to 100 micron PMCLG, that is, 2 micron PSPLG was considered to have expanded about 5000% in the direction perpendicular to the magnetic field.

When the PSPLG gel prepared in this experiment is irradiated with ultraviolet light having a wavelength of 365 nm, the volume of PMCLG generated by the photoisomerization reaction of spiropyran is only about 5% of the entire sample. Here, the molecular volumes of PSPLG and PMCLG monomer calculated from the DFT calculation are 209.8 cm ³ mol ⁻¹ and 238.5 cm ³ mol ⁻¹ , respectively. Then, even if the spiropyran photoisomerization reaction proceeds in monomer units in the PSPLG gel, the volume expansion coefficient obtained from the DFT calculation is only 14%. That is, the volume expansion caused by the photoisomerization reaction of spiropyran induced on the surface of the PSPLG gel corresponds to a very large change.

  FIG. 7 shows the dependency of the volume expansion coefficient of the PSPLG gel upon irradiation with ultraviolet light on the concentration of the crosslinking agent. As shown in the figure, when the concentration of the cross-linking agent is changed to 6 mol%, 8 mol%, and 10 mol%, the volume change increases as the concentration of the cross-linking agent increases. That is, the volume expansion coefficient of the PSPLG gel can be controlled by the concentration of the crosslinking agent.

  FIG. 8 shows the dependency of the volume expansion rate upon irradiation with ultraviolet light of the PSPLG gel on the number of days of magnetic field application. As the number of days of magnetic field application increases, the degree of orientation of the polypeptide in the PSPLG gel can be increased. When the data is confirmed, it can be seen that the volume change amount increases as the number of magnetic field application days increases. That is, the degree of orientation of the polypeptide in the PSPLG gel can be changed according to the number of days of application of the magnetic field to the PSPLG gel, and the volume expansion coefficient of the PSPLG gel when irradiated with ultraviolet light can be controlled.

FIG. 9 shows the volume expansion coefficient of the 1D-PSPLG gel and the u-PSPLG gel when irradiated with ultraviolet light. In the case of the PSPLG gel impregnated with CHCl ₃ and DMAc, the volume expansion coefficient of the 1D-PSPLG gel in which the PSPLG liquid crystal polymer is uniaxially aligned is higher than that of the u-PSPLG gel in which the PSPLG liquid crystal polymer is not aligned. It was big. On the other hand, in the case of a PSPLG gel impregnated with DCE and MeOH, conversely, the u-PSPLG gel in which the PSPLG liquid crystal polymer is not aligned is larger in volume expansion than the 1D-PSPLG gel in which the PSPLG liquid crystal polymer is uniaxially aligned. The rate was large. In addition, the volume expansion coefficient (Volume Ratio) shown on the vertical axis | shaft of FIG. 9 has shown about the ratio of the increase or decrease | decrease of the volume after ultraviolet light irradiation with respect to the volume before ultraviolet light irradiation of each PSPLG gel.

0100: Polypeptide, 0101: Helix structure, 0102: Random coil structure, 0103: Spiropyran, 0104: Merocyanine, 0105: Crosslinker, 0106: Solvent, 0201: Polypeptide, 0202: Photochromic molecule, 0203: Crosslinker, 0204 : Solvent, 0205: Coulomb force, S0301: Photochromic molecule introduction process, S0302: Gelation process, S0303: Crosslinking process, S0304: Uniaxial orientation process

Claims (14)

A liquid crystal gel in which a photochromic molecule is introduced into a side chain and a liquid crystal polymer capable of reversibly changing between a uniaxial alignment state and a non-alignment state is gelled with a solvent,
The photochromic molecule is a molecule that takes a zwitterionic structure by a photoisomerization reaction,
The liquid crystal polymer is a liquid crystal gel in which a volume change due to a conformational change that changes an alignment state according to a photoisomerization reaction of the photochromic molecule is increased by gelation.   The liquid crystal gel according to claim 1, wherein the liquid crystal polymers are cross-linked with each other. The liquid crystal gel according to claim 1, wherein the liquid crystal polymer contains a polypeptide represented by the following formula (1).
(X in Formula (1) represents an ester bond (—COO—) or an amide bond (—CONH—, or —NHCO—), R represents a photochromic molecule, n represents the number of methylene units, and p represents a number of methylene units. Indicates the degree of polymerization of the polypeptide chain.) The liquid crystal gel according to any one of claims 1 to 3, wherein the photochromic molecule is spiropyran represented by the following formula (2).
(M in the formula (2) represents the number of methylene units.)   The liquid crystal gel according to any one of claims 1 to 4, wherein a volume expansion coefficient of the liquid crystal gel by a photoisomerization reaction of the photochromic molecules is 100% or more. A method for producing a liquid crystal gel according to any one of claims 1 to 5,
A photochromic molecule introduction process for introducing a photochromic molecule having a zwitterionic structure into a liquid crystal polymer by a photoisomerization reaction;
A gelation process in which the liquid crystal polymer introduced with the photochromic molecule is impregnated with a solvent to gel the liquid crystal polymer to form a liquid crystal gel;
A crosslinking process of crosslinking the liquid crystal polymer in the liquid crystal gel with a crosslinking agent;
A uniaxial alignment process for uniaxially aligning the liquid crystal polymer in the liquid crystal gel;
A method for producing a liquid crystal gel comprising:   The method for producing a liquid crystal gel according to claim 6, wherein the liquid crystal polymer contains a polypeptide represented by the formula (1).   The method for producing a liquid crystal gel according to claim 6 or 7, wherein the photochromic molecule is spiropyran represented by the formula (2). The method for producing a liquid crystal gel according to any one of claims 6 to 8, wherein the crosslinking agent is a diamine derivative represented by the following formulas (4) to (6).
(In formulas (4) to (6), p, q, and r each represent the number of units of chain segments.)   The method for producing a liquid crystal gel according to claim 6, wherein the uniaxial alignment process is a process of uniaxially aligning a liquid crystal polymer in a magnetic field.   A liquid crystal gel designed to have a predetermined volume expansion coefficient by selecting a cross-linking agent that uses a volume expansion coefficient of the liquid crystal gel to be manufactured in the method for manufacturing a liquid crystal gel according to any one of claims 6 to 10 in a cross-linking process. Design method.   A liquid crystal gel that is designed to have a predetermined volume expansion coefficient by selecting a solvent used in the gelation process for the volume expansion coefficient of the liquid crystal gel to be manufactured in the method for manufacturing a liquid crystal gel according to any one of claims 6 to 10. Design method.   An actuator using the liquid crystal gel according to any one of claims 1 to 5.   An apparatus using the actuator according to claim 13.