CN115322419B - Preparation method and application of polarized light-responsive liquid crystal polymer network film based on gold nanorod doping - Google Patents

Abstract

The invention discloses a liquid crystal elastic body film based on gold nanorod doping and its preparation method and application. The gold nanorod is formed by first preparing a gold seed liquid and a growth liquid through reaction. And by using the dichroism of gold nanorods, doping them into the liquid crystal polymer network realizes the oscillation of the above-mentioned liquid crystal polymer network film under the stimulation of polarized light. The liquid crystal elastomer film doped with gold nanorods can effectively realize polarized light-driven oscillation, and provide material and principle support for soft drives, bionic robots, 3D printing and other biological materials.

Description

A polarized light-responsive liquid crystal polymer network film based on gold nanorod doping The preparation method and its application

technical field

The invention relates to the technical field of liquid crystal elastomers, in particular to a preparation method and application of a polarized light-responsive liquid crystal polymer network film based on gold nanorod doping.

Background technique

In nature, changes in the environment usually cause changes in the adaptability of some animals and plants, such as the opening and closing of the scales of pine cones after soaking in water and drying, and the skin color of chameleons will change with changes in the external environment, imitating natural organisms The environmental responsiveness of the environment becomes a fascinating and challenging job.

In recent years, most light-driven liquid crystal elastomers rely on the reversible trans-cis photoisomerization of azobenzene derivatives excited by ultraviolet and visible light. The change of molecular configuration during cis-isomerization can lead to the transition from liquid crystal phase to isotropic phase (LC-isotropic) (see Advanced Materials, 2022, 34(3): 2105758), making the polymer exhibit macroscopic deformation and related sports. However, ultraviolet light can be harmful to the human body and cannot be widely used, especially in some biological applications, because the penetration depth of ultraviolet light is limited, it will damage healthy cells and cause side reactions in the photochemical reaction process. Therefore, in the face of this defect, people hope to synthesize gold nanorods whose long-axis absorption is distributed in the range of visible light to near-infrared light, which can convert light energy into heat energy, and by doping it in liquid crystal polymer films, so as to achieve Liquid crystal polymer films have a certain degree of reversible deformation effect under visible light/near-infrared light stimulation, and thus have potential application value in many fields.

Contents of the invention

The technical solution discloses a gold nanorod whose long-axis absorption is distributed in the range of visible light to near-infrared light, which can convert light energy into heat energy, and by doping it in the liquid crystal polymer film, the realization of liquid crystal polymer The film has a certain degree of reversible deformation effect under the stimulation of visible light/near-infrared light. The technical solution is expected to have potential application value in fields such as liquid crystal actuators, soft robots, and oscillators.

One object of the present invention is to provide a kind of preparation method based on gold nanorod doping polarized light response type liquid crystal polymer network film, it comprises the steps:

S1. Preparation of gold nanorods: adding the gold seed solution into the growth solution to grow, obtaining the gold nanorods, and removing water;

S2, the preparation of the liquid crystal cell of splay (splay) orientation: prepare the glass substrate with parallel alignment layer and the glass substrate with vertical alignment layer respectively, then described glass substrate with parallel alignment layer and the glass substrate with vertical alignment layer The substrate is adhered, and the splay-oriented liquid crystal cell is obtained after photocuring;

S3. Doping the gold nanorods into a solvent including a liquid crystal monomer material and a catalyst, heating and stirring, and volatilizing the solvent, and filling it into the splay-oriented liquid crystal cell; then UV curing to obtain a film;

S4. Cutting and stretching the film to obtain a product.

Further, the preparation method of the gold seed solution is as follows: mix auric acid chloride and cetyltrimethyl, add sodium borohydride, and let stand to grow.

Further, the preparation method of the growth liquid is as follows: adding the chloroauric acid solution into the CTAB solution and stirring, adding the silver nitrate solution, L-ascorbic acid, and hydrochloric acid, and standing for growth.

The preparation method first prepares gold seed liquid and growth liquid, and then reacts to generate gold nanorods; the surface plasmon resonance absorption peak of the gold nanorod-doped liquid crystal polymer network film is still in the range of 840-1100nm, when the temperature is heated to various When the temperature of the isotropic state is above, the liquid crystal molecules change from an ordered arrangement to a disordered state, which in turn causes the liquid crystal elastomer to shrink, and when the temperature drops back to the liquid crystal state, the film elongates and returns to its original shape.

Dichroism refers to the fact that a substance has optical anisotropy that depends on polarization. When a small amount of dichroic dye is mixed with liquid crystal and filled into the aligned liquid crystal cell, the dye molecules will spontaneously align along the alignment direction of the liquid crystal molecules. This phenomenon is called the guest-host effect (Guest-Host). Dichroic dyes are generally small molecular organic compounds, which are prone to fluorescence quenching and are unstable when used for a long time. Similar to dichroic dye molecules, gold nanorods are also rod-shaped molecules with optical anisotropy, and the light scattering and other effects of gold nanorods will not cause failure of fluorescence quenching and other similar phenomena, so they have high stability. , can effectively replace dichroic dyes in optical devices based on liquid crystal systems, and has potential applications in oscillators and other fields.

The dichroism of gold nanorods makes the absorption maximum when the polarization direction is parallel to the long axis of gold nanorods, that is, the heat generated by absorbing infrared light in this direction is the highest; conversely, when the polarization direction is parallel to the gold nanorods When the long axis is vertical, it absorbs the least and generates the least heat. In order to obtain the shape change in the three-dimensional direction of the liquid crystal film doped with gold nanorods and their composite materials, the present invention prepares a liquid crystal polymer network (LCN) film with a splay orientation, and the film macroscopically behaves as a film when the temperature changes Bending occurs.

When the anisotropic LCN film is stimulated by the outside world, it will shrink along the direction of the director, and expand in the direction perpendicular to the direction of the director. The bending occurs in three dimensions, and the film bends toward the parallel-oriented side, thereby realizing polarized light driving.

Further, the liquid crystal monomer material is selected from one or more of HCM-021, HCM-020, and HCM-008.

Further, the content of the gold nanorods is 0.1-1.0 wt% of the liquid crystal monomer material.

Further, the long-axis absorption peak of the gold nanorods is 580-840nm.

In some embodiments of the present invention, gold nanorods whose long axis absorbs at 740nm are selected to prepare gold nanorod-doped polarized light-responsive liquid crystal polymer network films, and cause photothermal oscillation due to their dichroism. Dichroism means that a certain substance has optical anisotropy dependent on polarization. When a small amount of dichroic dye is mixed with liquid crystal and filled into an aligned liquid crystal cell, gold nanorods will spontaneously follow the alignment of liquid crystal molecules. This phenomenon is called the guest-host effect.

The invention successfully prepares the polarization-responsive liquid crystal polymer network film doped with splay-oriented gold nanorods, and successfully realizes the bending and oscillation of the film driven by polarized light. The anisotropic liquid crystal polymer network film will shrink along the direction of the director when it is stimulated by the outside world, and it will expand in the direction perpendicular to the director. Therefore, it is different from the shrinkage or expansion in the two-dimensional direction. The liquid crystal polymer network film can be bent in the three-dimensional direction, and the film is bent toward one side of the parallel orientation, so as to realize polarized light driving.

Further, in step S2, the preparation of the splay-oriented liquid crystal cell includes: using polyvinyl alcohol as a parallel alignment agent to prepare a glass substrate with a parallel alignment layer, and using polyimide as a vertical alignment agent to prepare a glass substrate with a vertical alignment layer The glass substrate, and then the spacer is mixed into the UV glue to configure the mixed glue, and the glass substrate with the parallel alignment layer and the glass substrate with the vertical alignment layer are adhered with the mixed glue, and the splay is obtained after photocuring. Oriented liquid crystal cell.

In some embodiments of the present invention, the glass substrate of the parallel alignment layer is prepared by using polyvinyl alcohol as a parallel alignment agent, preparing ordinary glass, and then ultrasonically cleaning it in acetone solution, ethanol solution, and deionized water for 30 minutes, and then drying it. The glass was irradiated in an ultraviolet ozone machine for 10 minutes to further clean the glass surface and improve hydrophilicity. Prepare a polyvinyl alcohol layer solution with a concentration of 5wt% in advance, and spin-coat it on the glass at 2000rpm for 30s, then transfer it to a hot stage at 60°C for 1h to evaporate the solvent, and finally cool it down to room temperature to obtain A glass substrate coated with a PVA layer on the surface; then the side with the polyvinyl alcohol layer is placed on a black velvet cloth and directional rubbed along the vertical direction to obtain a polyvinyl alcohol film layer with parallel grooves, that is, to obtain a polyvinyl alcohol film layer with a parallel orientation layer. Glass base board.

In some embodiments of the present invention, the glass substrate of the vertical alignment layer is prepared by using polyimide as the vertical alignment agent. The polyimide stored in the refrigerator is taken out two hours in advance and returned to room temperature. The final glass plate was spin-coated at 2500rpm for 60s, then heated on a hot stage at 90°C for 60s, then immediately transferred to a hot stage at 105°C in a nitrogen atmosphere and heated for 30 minutes, and finally heated to 230°C for 90 minutes. After cooling down to room temperature, after a series of treatments, the polyimide is completely imidized, that is, a glass substrate with a vertical alignment layer is obtained.

In some embodiments of the present invention, in the preparation process of the mixed glue, in order to obtain a film with a certain thickness, when using the ultraviolet curing glue to adhere the glass substrate, the spacer is mixed into the UV glue according to the ratio of 1:99 , Stir at room temperature until the spacers are evenly mixed in the UV glue.

Further, the size of the spacer is 10-50 μm.

Preferably, the size of the spacer is selected from 10 μm, 20 μm, 30 μm, 40 μm, or 50 μm.

Another object of the present invention is to provide an elastomer film prepared based on a method for preparing a gold nanorod-doped polarized light-responsive liquid crystal polymer network film.

Another object of the present invention is to disclose the application of the above-mentioned elastomer film in bionic robots, drivers, 3D printing, and biomaterials.

The present invention has the following beneficial effects: the long axis absorption peak of gold nanorods is at 580-840nm, and a splay orientation-based polarized light-responsive liquid crystal polymer network film doped with gold nanorods is successfully prepared, and the doping concentrations of gold nanorods are respectively 0.1wt%, 0.2wt%, 0.5wt%, 1wt%, the bending and oscillation of the film driven by polarized light are realized. The results show that when L//M, the degree of bending of the film is the largest. The bending degree of the film increases with the increase of the power of the polarized light. When the power increases to a certain extent, the film presents an oscillation frequency with an average value of about 0.26Hz.

Description of drawings

1 is a schematic diagram of the preparation process of gold nanorod-doped liquid crystal polymer network film in Example 1;

Fig. 2 is the mechanism diagram of polarized light irradiation gold nanorod-doped liquid crystal polymer network film in embodiment 1, wherein L represents the vibration direction of polarized light, M represents the liquid crystal molecular orientation on the parallel alignment plane, and θ refers to the clip between L and M horn;

Fig. 3 is the curve of bending angle and temperature variation with θ of gold nanorod doped liquid crystal polymer network film in embodiment 1;

Fig. 4 (a)-(b) respectively is the bending angle change curve (a) and the film bending physical figure (b) in the polymer network film oscillation process in embodiment 1;

Figure 5(a)-(c) are the L⊥M and L∥M absorbance curves in Example 12(a), Example 11(b), and Example 10(c) in parallel examples, respectively.

Detailed ways

In order to illustrate the technical solutions of the present invention more clearly, the following examples are listed. The raw materials, reactions and post-treatment means presented in the examples, unless otherwise stated, are common raw materials on the market and technical means well known to those skilled in the art.

Example 1

A method for preparing a polarized light-responsive liquid crystal polymer network film based on gold nanorod doping, comprising the steps of:

S1. Preparation of gold nanorods: adding the gold seed solution into the growth solution to grow, obtaining the gold nanorods, and removing water;

Wherein, the preparation method of the gold seed solution is: use a pipette gun to take 25 μL of chloroauric acid solution (0.01M) and 975 μL of CTAB solution (0.1M) and mix them evenly, and the solution is bright yellow at this time. Then, 60 μL of NaBH ₄ solution (0.01 M) was quickly added dropwise under high-speed stirring, and the solution changed from yellow to dark brown after vigorous stirring for 2 minutes. Since NaBH ₄ has a strong reducing property, the solution needs to be prepared and used immediately, and stored under ice water to inhibit its activity. Finally, let it stand for 2 hours in an incubator at 27°C to allow the seeds to grow, and then obtain a well-reacted seed solution;

The preparation method of the growth solution is: take 500 μL of chloroauric acid solution (0.01M) and add it into 10 mL of CTAB solution (0.1M) and stir rapidly, and the solution turns bright yellow. Add 10-100 μL of AgNO ₃ solution (0.01M) to obtain gold nanorods with different aspect ratios, ie, different long-axis absorption peaks. Then, 80 μL of L-ascorbic acid solution (0.1M) was quickly added under slow stirring. Under the action of the reduction reaction, the solution changed from yellow to colorless, and the well-reacted growth solution was obtained;

Preparation of gold nanorods: 200 μL of dilute HCl (1.0 M) and 24 μL of seed solution were added to the above growth solution, stirred evenly, and left to grow for 6 hours to obtain a CTAB-coated gold nanorod solution. In order to avoid crystallization of CTAB at low temperature, the above solution addition process was carried out in a water bath at 27°C and then transferred to a constant temperature box until the reaction was completed; the gold nanorod solution was prepared immediately.

Before doping, it is necessary to remove water from the gold nanorod solution by solvent replacement. Tetrahydrofuran (THF) was selected as the solvent to redisperse gold nanorods for the synthesis of liquid crystal polymer network film materials. The specific operation is: take 10mL of gold nanorod solution and rotate at 9500rpm for 10min, remove the supernatant, then redisperse the concentrated solution in 10mL of THF, centrifuge again at 9500rpm for 10min, and repeat the operation twice.

S2, the preparation of the liquid crystal cell of splay orientation:

The glass substrate preparation of parallel alignment layer: utilize polyvinyl alcohol (PVA) as parallel alignment agent, configure the PVA aqueous solution of 5wt%, then put the side that has PVA layer on the black velvet cloth and carry out orientation rubbing along vertical direction to obtain parallel alignment layer. Grooved PVA film layer, that is, to obtain a glass substrate with parallel orientation layers;

The glass substrate of the vertical alignment layer is prepared by using polyimide (PI) as the vertical alignment agent. The PI stored in the refrigerator is taken out 2 hours in advance and returned to room temperature. Spin-coating under the conditions of 90°C for 60s, then transfer to 105°C and nitrogen atmosphere for 30min, then heat up to 230°C, heat for 90min, then cool down to room temperature, after a series of treatments After that, the polyimide is completely imidized, that is, a glass substrate with a vertical alignment layer is obtained;

Preparation of mixed glue: When using ultraviolet (UV) curing glue to adhere to the glass substrate, mix the spacers into the UV glue at a ratio of 1:99, and stir at room temperature until the spacers (40 μm in size) are evenly mixed in the UV glue middle;

Preparation of splay-oriented liquid crystal cell: Adhere the PVA layer glass substrate and PI layer glass substrate obtained above with a mixed glue, and cure under UV light for 60s to obtain a liquid crystal cell capable of splay-oriented liquid crystal.

S3. Weigh 244.5mg of HCM-021, 81.5mg of HCM-020, 163mg of HCM-008 and 11mg of Irg-819, place the above-mentioned liquid crystal material and photoinitiator in a 5mL brown bottle, and add dispersing 2 ml of a gold nanorod solution in THF was placed on a magnetic stirring table at 70° C. for thorough mixing, and the solvent was evaporated to obtain a 1 wt % gold nanorod-doped mixture. Then fill the liquid crystal box, UV curing, disassemble the liquid crystal box and cut the film into a size of 28mm×10mm along the direction parallel to the liquid crystal molecules, and stretch it slightly to obtain a gold nanorod-doped film with splay Oriented liquid crystal polymer network films;

Specifically, the film preparation process is shown in Fig. 1 . Place the prepared splay-oriented liquid crystal cell (cell thickness: 40 μm) on a hot stage at 80°C for 5 minutes and keep it warm for 5 minutes. At 80°C, the liquid crystal mixture is in a clear state, that is, an isotropic state. Take a small amount of the volatilized mixture and drop it on one side of the opening of the liquid crystal box, and the mixture will fill the entire liquid crystal box under capillary action. Keep warm at 80°C for 10 minutes, then cool down to 45°C, that is, cool down to the liquid crystal phase and keep warm for 10 minutes, then irradiate for 30 minutes under the ultraviolet exposure condition of 4mW/cm ² , disassemble the box with a blade, carefully remove the film, and follow the The film was cut to a size of 28mm×10mm in the direction parallel to the liquid crystal molecules.

The chemical structures of the above mentioned liquid crystal monomer materials and photoinitiators are as follows:

Figure 1 shows a method for preparing a polarized light-responsive liquid crystal polymer network film based on gold nanorod doping; Figure 2 is a mechanism diagram of gold nanorod doped liquid crystal polymer network film irradiated with polarized light in the above embodiment.

parallel embodiment

Referring to the preparation method of polarized light-responsive liquid crystal polymer network film based on gold nanorod doping in Example 1, a series of examples are set up, mainly to change some relevant experimental parameters, so as to explore the preparation of different response times and bending degrees. Liquid crystal elastomer film. The changes in the experimental parameters are shown in Table 1.

Each embodiment in the parallel embodiment of table 1 and its corresponding experimental parameter

test case

In the embodiment of the present invention, the LCN liquid crystal elastomer film with splay orientation is prepared by doping gold nanorods, and the bending and oscillation of the film driven by polarized light are successfully realized.

Among them, the test method of test example 1 is: use a 740nm laser source to generate laser light with a laser intensity of 50mW/cm ² . area, changing the angle between the polarization direction of the polarized light and the orientation of the liquid crystal molecules on the parallel orientation plane of the film, and using a thermal imager to record the corresponding temperature changes of the film.

Test example 2, the test optical path is similar to test example 1, the difference is that the laser power is 116mW/cm ² , the angle θ between the vibration direction of the vibrating light and the orientation of liquid crystal molecules parallel to the orientation plane is 0°, and the bending angle of the film is recorded by a protractor Angle, the film oscillation frequency is calculated from the number of oscillations and time.

Test example 3, the test optical path is similar to test example 1, the difference is that the angle θ between the vibration direction of polarized light and the orientation of liquid crystal molecules parallel to the orientation plane is 0° and 90°, and the ultraviolet-visible-near-infrared spectrophotometer is used to test the Prepare the polarized light absorbance curve of the film.

Table 2 Test experimental parameters and test items in the test case

In Test Example 1, the long-axis absorption peak is at 740nm, the box thickness is 40 μm, the gold nanorod doping concentration is 1wt%, and the excitation power of the 740nm laser is about 50mW/ ^cm2 . When θ=0, the film The bending angle is the largest, about 17°; when θ = 45° and 90°, respectively, the bending angle is about 12° and 10°; correspondingly, the film temperature changes are about 57°C, 54°C, and 52°C , the test results are shown in Figure 3.

In Test Example 2, in order to observe the oscillation phenomenon of the thin film more clearly, the laser power was continued to be increased to 116mW/cm ² , and the oscillation times of the thin film within 23s were recorded. It is defined here that the film reaches the maximum or minimum bending angle twice as one cycle, as shown in Figure 4(a), the film oscillates back and forth for six cycles within 23s, and it is observed that the maximum bending angle of the film is between 110° and 113° during the oscillation process. floating between. As shown in Figure 4(b), the minimum bending angle fluctuates between 99° and 102°, but the oscillation frequency of the film is unstable, and the average oscillation frequency is about 0.26Hz.

In Test Example 3, from the absorption curves in Fig. 5 (a), (b), (c), we can get: the A/ / is 0.47, A⊥ is 0.43, that is, the maximum absorption is about 1.09 times of the minimum absorption; the A// of the polarized light-responsive liquid crystal polymer network film doped with 0.2wt% gold nanorods is 0.21, and A⊥ is 0.19 , that is, the maximum absorption is about 1.11 times of the minimum absorption; the A// of the polarized light-responsive liquid crystal polymer network film doped with 0.1wt% gold nanorods is 0.16, and A⊥ is 0.12, that is, the maximum absorption is about the minimum absorption 1.3 times. Although the difference in absorbance of the polarized light-responsive liquid crystal polymer network film doped with gold nanorods is improved at the doping concentration of 0.1wt%, the difference is not obvious enough.

It will be apparent to those skilled in the art that the invention is not limited to the details of the above-described exemplary embodiments, but that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Accordingly, the embodiments should be regarded in all points of view as exemplary and not restrictive, the scope of the invention being defined by the appended claims rather than the foregoing description, and it is therefore intended that the scope of the invention be defined by the appended claims rather than by the foregoing description. All changes within the meaning and range of equivalents of the elements are embraced in the present invention.

In addition, it should be understood that although this specification is described according to implementation modes, not each implementation mode only includes an independent technical solution, and this description in the specification is only for clarity, and those skilled in the art should take the specification as a whole , the technical solutions in the various embodiments can also be properly combined to form other implementations that can be understood by those skilled in the art.

Claims (7)

1. A method for preparing a polarized light-responsive liquid crystal polymer network film based on gold nanorod doping, characterized in that, the preparation method of a polarized light-responsive liquid crystal polymer network film based on gold nanorod doping comprises Follow the steps below: S1. Preparation of gold nanorods: adding the gold seed solution into the growth solution to grow, obtaining the gold nanorods, and removing water; S2. Preparation of liquid crystal cells with splay orientation: prepare glass substrates with parallel alignment layers and glass substrates with vertical alignment layers respectively, and then adhere the glass substrates with parallel alignment layers and the glass substrates with vertical alignment layers , obtain the liquid crystal cell of the splay orientation after photocuring; S3. Doping the gold nanorods into a solvent including a liquid crystal monomer material and a catalyst, heating and stirring, and volatilizing the solvent, and filling it into the splay-oriented liquid crystal cell; then UV curing to obtain a film; S4, cutting and stretching the film to obtain a product; The preparation method of the growth liquid is: adding the chloroauric acid solution into the CTAB solution and stirring, adding the silver nitrate solution, L-ascorbic acid, hydrochloric acid, and standing to grow; The liquid crystal monomer material is selected from one or more of HCM-021, HCM-020, and HCM-008; The content of the gold nanorods is 0.1-1.0 wt% of the liquid crystal monomer material. 2. according to the preparation method of the polarized light-responsive liquid crystal polymer network film based on gold nanorod doping according to claim 1, it is characterized in that, the preparation method of described gold seed liquid is: get chloroauric acid, hexadecane Base trimethyl mixed, adding sodium borohydride, static growth. 3. The method for preparing a polarized light-responsive liquid crystal polymer network film based on gold nanorod doping according to claim 1, wherein the long-axis absorption peak of the gold nanorod is 580-840 nm. 4. according to claim 1, based on the preparation method of the polarized light-responsive liquid crystal polymer network film doped with gold nanorods, it is characterized in that, in step S2, the preparation of the liquid crystal cell of the splay orientation comprises: using polyethylene Alcohol is used as a parallel alignment agent to prepare a glass substrate with a parallel alignment layer, and polyimide is used as a vertical alignment agent to prepare a glass substrate with a vertical alignment layer, and then the spacers are mixed into the UV glue to form a mixed glue. The glass substrate with the parallel alignment layer and the glass substrate with the vertical alignment layer are adhered with the mixed glue, and the liquid crystal cell with the splay alignment is obtained after photocuring. 5 . The method for preparing a polarized light-responsive liquid crystal polymer network film based on gold nanorod doping according to claim 4 , wherein the spacer has a size of 10-50 μm. 6. The elastic body film prepared based on the preparation method of the polarized light responsive liquid crystal polymer network film doped with gold nanorods according to any one of claims 1-5. 7. The application of the elastomer film according to claim 6 in bionic robots, drivers, 3D printing, and biomaterials.