A method for preparing a non-planar nanocomposite liquid crystal elastomer

Abstract

The application discloses a preparation method of a non-planar nano-composite liquid crystal elastomer, and the method comprises the following steps: arranging silver nanowires into a highly oriented array by a Langmuir-Blodgett method and depositing the silver nanowires on a glass substrate, assembling a twist type liquid crystal box after drying; then, filling a mixture of liquid crystal molecules containing double-end acrylate groups, liquid crystal molecules containing single-end acrylate groups and an initiator into the assembled liquid crystal box by a heating melting method to polymerize; finally, taking out the polymerized liquid crystal elastomer from the liquid crystal box, and cutting the liquid crystal elastomer along different directions to obtain left-handed and right-handed helical drivers or non-handed circular ring drivers.

Description

Technical Field

[0001] This invention belongs to the field of liquid crystal elastomer actuators, and specifically relates to a method for preparing a non-planar nanocomposite liquid crystal elastomer. Background Technology

[0002] Flexible intelligent actuators refer to a class of materials that can autonomously change shape in response to external environmental stimuli, and the process is reversible. They have broad application prospects in fields such as flexible robots, artificial muscles, oscillators, and energy generators. Liquid crystal elastomers, due to their combination of the elasticity of rubber, the orderliness of crystals, and their inherent stimulus responsiveness, are often used in the design of intelligent actuators.

[0003] Surface morphology induction is the most classic technique for inducing liquid crystal molecule orientation. On a glass surface coated with polyimide or polyvinyl alcohol, grooves are formed through directional friction. To reduce the energy generated by elastic deformation, long, rod-shaped liquid crystal molecules align parallel to the grooves. However, during friction, polymer debris and static electricity are often generated, interfering with the orientation of the liquid crystal molecules; furthermore, the template function is relatively limited, only inducing the orderly alignment of liquid crystal molecules. Researchers have successfully induced liquid crystal molecule orientation by preparing highly oriented carbon nanotube arrays through chemical vapor deposition. The carbon nanotubes can also act as photothermal conversion agents, enabling the liquid crystal elastomer to respond to light. However, this method is currently only applicable to carbon nanotubes, mainly because it is difficult to obtain other high-performance inorganic nanomaterial arrays with similar groove structures.

[0004] The initial form of intelligent actuators is typically two-dimensional planar, capable of static deformations such as bending, twisting, and spiraling in response to stimuli such as light, heat, electricity, chemicals, and humidity. However, even when continuously altering external stimuli to achieve more valuable sustained movements like walking, crawling, and jumping, two-dimensional planar actuators are limited by their slow movement speed and low energy conversion efficiency. Compared to traditional actuators, three-dimensional non-planar actuators (such as spiral or toroidal actuators) store some elastic potential energy within their shape, enabling them to convert potential energy into kinetic energy when the external environment changes, greatly improving movement speed and energy conversion efficiency. However, the shape of these actuators is highly dependent on the mold, requiring the replacement of matching molds when manufacturing actuators with different shape parameters, leading to increased mold design complexity and resource waste. Furthermore, more complex mold structures imply more difficult demolding stages. Summary of the Invention

[0005] This invention addresses the shortcomings of existing liquid crystal elastomer technologies by innovating on the orientation of liquid crystal molecules and proposing a novel method for preparing non-planar nanocomposite liquid crystal elastomers.

[0006] This invention first uses the Langmuir-Blodgett method to orient silver nanowires into a highly oriented array and deposit them on a glass substrate. After drying, the array is assembled into a twisted liquid crystal cell. Next, a mixture containing liquid crystal molecules with double-ended acrylate groups, liquid crystal molecules with single-ended acrylate groups, and an initiator is melted and poured into the assembled liquid crystal cell for polymerization. Finally, the polymerized liquid crystal elastomer is removed from the liquid crystal cell and cut along different directions. The twisted liquid crystal cell induces a 90° angle between the upper and lower surfaces of the liquid crystal molecules. Therefore, during polymerization, the thermal expansion of the upper and lower surfaces is perpendicular to each other, forming a geometrically incompatible liquid crystal elastomer. The incompatible elasticity caused by this geometric incompatibility is further amplified by the silver nanowires distributed on the upper and lower surfaces of the elastomer, but due to the constraint of the liquid crystal cell, it still exhibits a planar shape. Once removed from the liquid crystal cell, the elastomer transforms into a saddle shape. Cutting this specially shaped elastomer in different directions yields left- or right-handed helical actuators or non-chiral annular actuators, respectively.

[0007] The method for preparing the non-planar nanocomposite liquid crystal elastomer of the present invention includes the following steps:

[0008] Step 1: Fabrication of highly oriented silver nanowire liquid crystal cells

[0009] In a Langmuir-Blodgett membrane analyzer filled with subphase material, a silver nanowire dispersion was added dropwise to the subphase surface. After standing for a period of time, a nanofilm was pressed at a constant rate, and the silver nanowires were aligned along a direction parallel to the push rod. The highly oriented silver nanowires were deposited on the treated glass surface and assembled into a twisted liquid crystal cell after drying.

[0010] In step 1, the subphase is deionized water (18.2 MΩ·cm), and the amount used needs to exceed the edge of the Langmuir-Blodgett membrane analyzer by 1-2 mm.

[0011] In step 1, the silver nanowires are prepared as follows: 5g of polyvinylpyrrolidone is dissolved in 200mL of glycerol. To accelerate the dissolution rate, this process needs to be carried out in an oven at 120℃. After the solution cools, a solution containing 2.5g of silver nitrate (dissolved in 1.5mL of deionized water) and a solution containing 0.15g of sodium chloride (dissolved in 1mL of water) are added, and the solution is placed in an oven at 180℃ for 16 hours. After cooling to room temperature, the resulting silver nanowire solution is centrifuged and washed multiple times to remove excess polyvinylpyrrolidone and glycerol. Finally, the resulting silver nanowires are dispersed in deionized water for later use.

[0012] In step 1, the silver nanowire dispersion is prepared as follows: Take an appropriate amount of silver nanowire solution dispersed in deionized water, add three times the amount of N,N'-dimethylformamide (DMF), centrifuge at 5000 rpm / min for 5 min, discard the supernatant, redisperse the precipitate in DMF, centrifuge again at the same speed, disperse the obtained precipitate in 0.5 mL of DMF, and add 0.5 mL of chloroform. The final concentration of silver nanowires in the dispersion is 10-25 mg / mL.

[0013] In step 1, the constant speed is 20 cm. 2 / min, stop compressing when wrinkles appear parallel to the push rod.

[0014] In step 1, the glass is hydrophilic glass that has been treated with a plasma cleaner.

[0015] In step 1, the assembly method of the twisted liquid crystal cell is as follows: two glass sheets with highly oriented silver nanowires deposited on their surfaces are assembled in a manner that keeps the silver nanowires facing each other and their orientation directions perpendicular to each other. During assembly, the two surfaces with silver nanowires deposited on them face each other and are separated by spacers of 30-90 μm in the middle.

[0016] Step 2: Polymerization of nanocomposite liquid crystal elastomers

[0017] A mixture of liquid crystal molecules containing double-ended acrylate groups, liquid crystal molecules containing single-ended acrylate groups, and an initiator in different proportions is filled into the liquid crystal cell assembled in step 1 by heating and melting, and then heated and polymerized.

[0018] In step 2, the general structural formula of the liquid crystal molecule with double-terminated acrylate groups is as follows:

[0019]

[0020] Wherein, n takes the value in the range of 6-12; X represents the central unit of the liquid crystal molecule with double-terminated acrylate groups, and its general structural formula is shown in formula A or formula B below:

[0021]

[0022] In step 2, the general structural formula of the liquid crystal molecule with single-ended acrylate groups is as follows:

[0023]

[0024] Where p takes values ​​in the range of 6-12, and q takes values ​​in the range of 3-6.

[0025] In step 2, the initiator is a thermal initiator, preferably benzoyl peroxide.

[0026] In step 2, in the mixture containing liquid crystal molecules with double-ended acrylate groups, liquid crystal molecules with single-ended acrylate groups, and an initiator, the mass of the liquid crystal molecules with double-ended acrylate groups accounts for 20-85% of the total mass of the mixture, the mass of the liquid crystal molecules with single-ended acrylate groups accounts for 14-79.9% of the total mass of the mixture, and the mass of the initiator accounts for 0.1-1% of the total mass of the mixture.

[0027] In step 2, the heating process takes place on the hot plate.

[0028] In step 2, the heating and melting temperature is controlled at 85-105℃.

[0029] In step 2, the heating polymerization temperature is controlled at 70-85℃, and the polymerization time is 3-12h.

[0030] Step 3: Preparation of nonplanar nanocomposite liquid crystal elastomer

[0031] The silver nanowire composite liquid crystal elastomer polymerized in step 2 is removed from the liquid crystal cell and cut into different sizes along different directions. Depending on the cutting direction, left-handed or right-handed helical actuators or non-chiral annular actuators with different structural parameters are obtained.

[0032] In step 3, the method for removing the silver nanowire composite liquid crystal elastomer from the liquid crystal cell is as follows: use a sharp blade to pry open the liquid crystal cell along the gap between the two glass pieces, then immerse the side of the glass with the liquid crystal elastomer film adhering to it in a cyclohexane solution to remove unreacted liquid crystal molecules; after immersion for 8-12 hours, peel the silver nanowire composite liquid crystal elastomer off the glass.

[0033] In step 3, the cutting direction is 0° with the direction parallel to the orientation of the silver nanowires on the bottom side of the elastomer, and the cutting angle is from 0 to 180°.

[0034] In step 3, the cutting dimensions refer to a width of 0.1-7mm and a length of 5-30mm.

[0035] The beneficial effects of this invention are reflected in:

[0036] This invention provides a simple and convenient method for preparing non-planar nanocomposite liquid crystal elastomers. First, a large-scale, highly oriented array of silver nanowires induced by the Langmuir-Blodgett method is used as a substrate. The grooves formed between adjacent silver nanowires further induce the orientation of liquid crystal molecules. This orientation method not only avoids polymer debris or static electricity generated during traditional friction processes, but also, due to the surface plasmon resonance effect of the silver nanowires, enables the prepared composite liquid crystal elastomer to exhibit photoresponsiveness. Second, the Langmuir-Blodgett method can induce various one-dimensional inorganic nanomaterials to form highly oriented arrays, offering greater versatility compared to chemical vapor deposition. Finally, the liquid crystal elastomer prepared using a torsion-type liquid crystal cell exhibits perpendicular thermal expansion behavior of its upper and lower surfaces during polymerization, directly producing a non-planar saddle-shaped liquid crystal elastomer. Due to differences in cutting direction and size, the original saddle-shaped liquid crystal elastomer releases residual stress and transforms into helical or achiral ring-shaped liquid crystal elastomers with different structural parameters (left-handed or right-handed). Compared to traditional methods of preparing non-planar liquid crystal elastomers using molds, this method eliminates the need for complex mold design and difficult demolding processes.

[0037] In summary, this invention provides a method for preparing non-planar nanocomposite liquid crystal elastomers. It primarily utilizes a twisted liquid crystal cell composed of highly oriented silver nanowires to prepare a saddle-shaped nanocomposite liquid crystal elastomer with incompatible geometry. Then, through a simple cutting process, various left- or right-handed helical or non-chiral annular liquid crystal elastomer actuators with different structural parameters can be prepared. Based on the combination of the photothermal effect of silver nanowires and the inherent temperature response characteristics of liquid crystal elastomers, these non-planar actuators can respond to both light and heat stimuli. Furthermore, the motion mode of the actuator is related to its inherent shape; for example, the motion mode of the annular liquid crystal elastomer actuator is jumping, while the motion mode of the helical liquid crystal elastomer actuator is rolling, and the rolling speed and direction are related to the structural parameters and chirality of the helix, respectively. This invention provides a new approach to the induced orientation of liquid crystal molecules and a new method for preparing non-planar nanocomposite liquid crystal elastomers. Attached Figure Description

[0038] Figure 1 These are scanning electron microscope images of the silver nanowire array prepared according to this invention. From... Figure 1 As can be seen, the silver nanowires are highly oriented and are a single layer.

[0039] Figure 2 This is a scanning image of the nanocomposite liquid crystal elastomer prepared according to the present invention. From... Figure 2As can be seen, the silver nanowires are encapsulated in a liquid crystal elastomer matrix, and the polymerization process does not disrupt the orientation of the silver nanowires.

[0040] Figure 3 This is an optical photograph of the saddle-shaped nanocomposite liquid crystal elastomer prepared according to the present invention, before it was cut.

[0041] Figure 4 This is an optical photograph of the non-planar nanocomposite liquid crystal elastomer prepared according to the present invention. From... Figure 4 As can be seen, cutting the initial saddle-shaped nanocomposite liquid crystal elastomer at 0° or 90° yields a ring-shaped liquid crystal elastomer; when the cutting angle is 15°, 30°, 45°, 60°, or 75°, a right-handed spiral liquid crystal elastomer is obtained. The pitch and diameter of the spiral change with the cutting angle, showing an overall symmetrical trend around a cutting angle of 45°. All samples in the photographs have a cutting length of 25 mm and a width of 2 mm.

[0042] Figure 5 This describes the driving behavior of the non-planar nanocomposite liquid crystal elastomer prepared in this invention under near-infrared light. Figure 5 As can be seen, a right-handed spiral-shaped liquid crystal elastomer cut at a cutting angle of 45°, a length of 20mm, and a width of 3mm, exhibits performance at a light intensity of 1.4W / cm². 2 Under near-infrared light scanning, it can undergo a parallel displacement to the right from its initial position, moving 4.1 cm within 24 seconds. Detailed Implementation

[0043] The present invention will be further described below with reference to specific embodiments, so that those skilled in the art can better understand and implement the present invention, but the embodiments are not intended to limit the present invention.

[0044] Example 1: Fabrication of a highly oriented silver nanowire liquid crystal cell

[0045] 1. Preparation of silver nanowires. 5g of polyvinylpyrrolidone was dissolved in 200mL of glycerol. To accelerate the dissolution rate, this process was carried out in an oven at 120℃. After the solution cooled, 2.5g of silver nitrate (dissolved in 1.5mL of deionized water) and 0.15g of sodium chloride (dissolved in 1mL of water) were added, and the mixture was placed in an oven at 180℃ for 16 hours. After cooling to room temperature, the resulting silver nanowire solution was centrifuged and washed multiple times to remove excess polyvinylpyrrolidone and glycerol. Finally, the obtained silver nanowires were dispersed in deionized water for later use.

[0046] 2. Preparation of silver nanowire dispersion. Take 2 mL of silver nanowires with a concentration of 10 mg / mL, add 6 mL of DMF, and centrifuge at 5000 rpm / min for 5 min. Discard the supernatant, redisperse the precipitate in 8 mL of DMF, and centrifuge again at 5000 rpm / min for 5 min. Disperse the precipitate in 0.5 mL of DMF, and then slowly add 0.5 mL of chloroform dropwise. A silver nanowire dispersion with a final concentration of 20 mg / mL is finally obtained.

[0047] 3. Preparation of highly oriented silver nanowire arrays. Deionized water was poured into a Langmuir-Blodgett membrane analyzer until the liquid level was 2 mm above the edge of the cell. The silver nanowire dispersion was added dropwise to the surface of the deionized water. After standing for 1 hour, the nanowires were added at 20 cm⁻¹. 2 The liquid surface is compressed at a constant rate of / min until wrinkles appear parallel to the push rod direction, at which point compression is stopped. Then, a highly oriented silver nanowire array is deposited onto a hydrophilic glass substrate using a lifting method.

[0048] 4. Fabrication of twisted silver nanowire liquid crystal cells. Glass layers with highly oriented silver nanowires on their surfaces are assembled with the silver nanowires facing each other and perpendicular to each other, and the two glass layers are separated by 50 μm spacers.

[0049] Example 2: Polymerization of nanocomposite liquid crystal elastomers

[0050] 1. The selected liquid crystal molecule with double-terminated acrylate groups has the following structural formula:

[0051]

[0052] The selected liquid crystal molecule with a single acrylate group is as follows:

[0053]

[0054] 2. Preparation of liquid crystal molecule mixture. 24 mg (40% of total mass) of liquid crystal molecule I with double acrylate groups, 12 mg (20% of total mass) of liquid crystal molecule II with double acrylate groups, 23.4 mg (39% of total mass) of liquid crystal molecule with single acrylate groups, and 0.6 mg of benzoyl peroxide were mixed together, and dichloromethane was added to completely dissolve them. The mixture was then placed in an oven at 30°C until the dichloromethane completely evaporated, resulting in a homogeneous liquid crystal molecule mixture.

[0055] 3. Polymerization of nanocomposite liquid crystal elastomers. A mixture of liquid crystal molecules is uniformly spread at the junction of the upper and lower glass panes of the liquid crystal cell. The mixture is placed on a 90°C hot plate and heated until it melts. Then, it is poured into the liquid crystal cell under capillary force. After the liquid crystal cell is filled with the molten material, the hot plate temperature is lowered to 75°C, and polymerization is carried out for 8 hours.

[0056] Example 3: Preparation of nonplanar nanocomposite liquid crystal elastomer

[0057] 1. Using a sharp blade, pry open the liquid crystal cell along the gap between the two glass panes. Then, immerse the side of the glass with the liquid crystal elastomer film adhering to it in a cyclohexane solution to remove unreacted liquid crystal molecules. After immersion for 10 hours, peel the silver nanowire composite liquid crystal elastomer off the glass to obtain a saddle-shaped nanocomposite liquid crystal elastomer.

[0058] 2. By determining the orientation direction of the silver nanowires parallel to the bottom side of the elastomer as 0°, the cutting direction as 45°, and the cutting size as a strip with a length of 20 mm and a width of 2 mm, a right-handed spiral liquid crystal elastomer actuator with a pitch of 6 mm and a diameter of 1.5 mm was prepared.

[0059] In summary, this invention provides a method for preparing non-planar nanocomposite liquid crystal elastomers. It primarily utilizes a twisted liquid crystal cell composed of highly oriented silver nanowires to prepare a saddle-shaped nanocomposite liquid crystal elastomer with incompatible geometry. Then, through a simple cutting process, various left- or right-handed helical or non-chiral annular liquid crystal elastomer actuators with different structural parameters can be prepared. Based on the combination of the photothermal effect of silver nanowires and the inherent temperature response characteristics of liquid crystal elastomers, these non-planar actuators can respond to both light and heat stimuli. Furthermore, the motion mode of the actuator is related to its inherent shape; for example, the motion mode of the annular liquid crystal elastomer actuator is jumping, while the motion mode of the helical liquid crystal elastomer actuator is rolling, and the rolling speed and direction are related to the structural parameters and chirality of the helix, respectively. This invention provides a new approach to the induced orientation of liquid crystal molecules and a new method for preparing non-planar nanocomposite liquid crystal elastomers.

Claims

1. A method for preparing a non-planar nanocomposite liquid crystal elastomer, characterized in that: first, silver nanowires are arranged in a highly oriented array by a Langmuir-Blodgett method and deposited on a glass substrate, and after drying, a twisted liquid crystal cell is assembled; second, a mixture containing liquid crystal molecules with double-ended acrylate groups, liquid crystal molecules with single-ended acrylate groups and an initiator is filled into the assembled liquid crystal cell by heating and melting, and then polymerized; finally, the polymerized liquid crystal elastomer is taken out of the liquid crystal cell, and cut along different directions to obtain left-handed and right-handed helical actuators or non-handed circular ring actuators, respectively; comprising the following steps: Step 1: Preparation of a highly oriented silver nanowire liquid crystal cell In a Langmuir-Blodgett film analyzer filled with subphase, silver nanowire dispersion is added dropwise to the surface of the subphase; After standing for a period of time, the nanofilm is pressed at a constant rate, and the silver nanowires are arranged in a direction parallel to the push rod; the highly oriented silver nanowires are deposited on the treated glass surface, and after drying, a twisted liquid crystal cell is assembled; Step 2: Polymerization of the nanocomposite liquid crystal elastomer A mixture containing liquid crystal molecules with double-ended acrylate groups, liquid crystal molecules with single-ended acrylate groups and an initiator in different proportions is filled into the liquid crystal cell assembled in step 1 by heating and melting, and then polymerized; In step 2, the structure of the liquid crystal molecule with double-ended acrylate groups is as follows: wherein n is in the range of 6-12; X represents the central element of the liquid crystal molecule with double-ended acrylate groups, and its structure is as shown in formula A or formula B: In step 2, the structure of the liquid crystal molecule with single-ended acrylate groups is as follows: wherein p is in the range of 6-12, and q is in the range of 3-6; Step 3: Preparation of a non-planar nanocomposite liquid crystal elastomer The silver nanowire composite liquid crystal elastomer polymerized in step 2 is taken out of the liquid crystal cell, cut into different sizes along different directions, and according to the different cutting directions, left-handed and right-handed helical actuators or non-handed circular ring actuators with different structure parameters are obtained; In step 1, the twisted liquid crystal cell is assembled in a manner that the two glass surfaces with highly oriented silver nanowires deposited thereon are opposite to each other and the orientation directions are perpendicular to each other, and the two surfaces are separated by a spacer with a thickness of 30-90 μm; In step 2, in the mixture containing liquid crystal molecules with double-ended acrylate groups, liquid crystal molecules with single-ended acrylate groups and an initiator, the mass of the liquid crystal molecule with double-ended acrylate groups accounts for 20-85% of the total mass of the mixture, the mass of the liquid crystal molecule with single-ended acrylate groups accounts for 14-79.9% of the total mass of the mixture, and the mass of the initiator accounts for 0.1-1% of the total mass of the mixture.

2. The method according to claim 1, characterized in that: In step 1, the subphase is deionized water with a resistance of 18.2 MΩ·cm.

3. The method according to claim 1, characterized in that: ​ In step 1, the silver nanowire is prepared as follows: 5 g of polyvinylpyrrolidone is dissolved in 200 mL of glycerol at 120°C; after the solution is cooled, a solution containing 2.5 g of silver nitrate and a solution containing 0.15 g of sodium chloride are added, and the mixture is placed in an oven at 180°C for 16 h; after cooling to room temperature, the obtained silver nanowire solution is washed by centrifugation multiple times to remove excess polyvinylpyrrolidone and glycerol, and the obtained silver nanowire is finally dispersed in deionized water for use.

4. The preparation method of claim 3, wherein: In step 1, the silver nanowire dispersion liquid is prepared as follows: an appropriate amount of silver nanowire solution dispersed in deionized water is taken, three times the amount of N,N'-dimethylformamide is added, and centrifugation is performed at 5000 rpm / min for 5 min, the supernatant is discarded, and the precipitate is redispersed in DMF, and centrifugation is performed again at the same speed, the obtained precipitate is dispersed in 0.5 mL of DMF, and 0.5 mL of chloroform is added, and the final silver nanowire concentration in the dispersion liquid is 10-25 mg / mL.

5. The preparation method of claim 1, wherein: In step 1, the constant rate is 20 cm 2 / min, and the compression is stopped when a wrinkle line parallel to the pushrod appears.

6. The preparation method of claim 1, wherein: In step 2, the heating and melting temperature is controlled at 85-105°C, the heating and polymerization temperature is controlled at 70-85°C, and the polymerization time is 3-12 h.

7. The preparation method of claim 1, wherein: In step 3, the silver nanowire composite liquid crystal elastomer is removed from the liquid crystal cell by using a sharp blade to pry the liquid crystal cell along the gap between the two glasses, and then the glass with the liquid crystal elastomer film adhered to one side is soaked in a cyclohexane solution to remove the unreacted liquid crystal molecules; after soaking for 8-12 h, the silver nanowire composite liquid crystal elastomer is peeled off from the glass.

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