Azobenzene fiber as well as preparation method and application thereof

Abstract

The invention discloses an azobenzene fiber as well as a preparation method and application thereof, belongs to the technical field of functional polymer materials, and solves the problems of low photoresponse rate, weak photodeformation output and single motion mode of an azobenzene material in the prior art. According to the preparation method of the azobenzene fiber, provided by the invention, an azobenzene monomer containing a long flexible terminal hydroxyl group and polyacrylic acid are subjected to an esterification reaction to synthesize a high-molecular-weight azo polymer with a photoresponse characteristic, then the high-molecular-weight azo polymer and polyvinyl alcohol are used for constructing a hydrogen bond cross-linked network, and the high-orientation azobenzene fiber is prepared by combining wet spinning and a 100%-200% pre-stretching process. According to the invention, molecular orientation design and hydrogen bond network construction are changed into light-force coupling mechanism innovation, and a programmable and high-response material solution is provided for a high-performance flexible light-driven actuator.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of functional polymer materials, and more particularly to an azobenzene fiber and a preparation method and application thereof. BACKGROUND

[0002] With the rapid development of flexible electronics and bionic engineering technology, intelligent driving material systems show important application potential in emerging fields such as light-controlled microfluids, soft robots and energy generators. Such functional materials can trigger reversible deformation through external stimuli (such as light, temperature, humidity, electric field, etc.), and complete the directional conversion from energy capture to mechanical action. Among the many driving modes, light-responsive driving systems stand out with non-contact precise control, high spatiotemporal resolution and clean energy characteristics, overcoming the physical contact limitation of traditional mechanical transmission systems and providing an ideal platform for building bionic motion systems. Azobenzene-based materials, as a typical light-responsive system, can induce macroscopic deformation (such as bending, rolling, oscillation, twisting, etc.) through intramolecular trans-cis photoisomerization, showing unique potential in light-controlled actuation.

[0003] However, the existing azobenzene driving system still faces multiple restrictions in molecular structure design, network topology optimization and processing technology, including the following aspects: first, the complex molecular side chain design limits the molecular weight of the polymer, and the fiber-forming performance is poor and the mechanical strength is insufficient; second, the disordered distribution of azobenzene groups significantly reduces the ultraviolet light absorption efficiency, and the photoisomerization rate is limited; third, the isotropic cross-linked network and low orientation degree make it difficult to effectively accumulate and amplify the photo-induced strain into macroscopic mechanical output. The above bottlenecks seriously restrict the practical application of azobenzene materials in high-speed response, high-strength output and complex motion control scenarios, and it is urgent to optimize the molecular arrangement, network construction and microstructure from multiple dimensions to break through the performance boundaries.

[0004] At present, azobenzene photo-driven researches are mostly focused on thin films or liquid crystal phase change materials, while the development of fiber-shaped driving materials is severely lagging behind. The existing azobenzene fibers are limited by poor fiber-forming performance and insufficient orientation degree, and can only achieve simple light-bending, lacking controllable regulation of complex light-mechanical motion (such as spiral rolling, self-propelled motion, etc.). Therefore, it is urgent to develop a preparation method of azobenzene fiber with high orientation structure and asymmetric stress gradient, to unlock the application potential of fiber materials in programmable, high-response actuators through the coordinated design of molecule-microstructure-macroscopic morphology. SUMMARY

[0005] To solve the above problems, the present application provides an azobenzene fiber and a preparation method and application thereof.

[0006] In a first aspect, the present application provides a preparation method of azobenzene fiber, comprising the following steps: dissolving 4-[4-(trifluoromethylthio) phenylazo] phenol, 8-bromo-1-hexanol, potassium carbonate and potassium iodide in N,N-dimethylformamide, refluxing reaction, and obtaining azobenzene monomer after purification; dissolving polyacrylic acid and the azobenzene monomer in dimethyl sulfoxide, adding 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride / 4-dimethylamino pyridine catalyst, and sufficiently reacting under argon protection, and then the product is precipitated by ethyl acetate, filtered and washed to obtain an azo polymer; dissolving the azo polymer and polyvinyl alcohol in dimethyl sulfoxide, mixing uniformly under argon protection, standing until defoaming, and preparing a spinning solution; wet spinning the spinning solution to form a nascent fiber, and after 100% to 200% axial stretching, cooling and setting the nascent fiber to obtain the azobenzene fiber.

[0007] As a possible implementation manner, the purification comprises operations of water washing, dichloromethane extraction and ethanol recrystallization; and / or, the washing comprises operations of washing several times with distilled water and methanol; and / or, the wet spinning comprises an operation of extruding the spinning solution into a 20±2℃ methanol coagulation bath at an injection speed of 0.45 mL / min by using a stainless steel wet spinning needle, and hydrogen bond reconstruction to form the nascent fiber.

[0008] As a possible implementation manner, the mass ratio of the 4-[4-(trifluoromethylthio) phenylazo] phenol, the 8-bromo-1-hexanol, the potassium carbonate and the potassium iodide is 9:10:10:0.75; and / or, the molecular weight of the polyacrylic acid is 450,000; and / or, the mass ratio of the polyacrylic acid and the azobenzene monomer is 1:1.4; and / or, the molecular weight of the polyvinyl alcohol is 205,000; and / or, the mass ratio of the azo polymer and polyvinyl alcohol is 2:1; and / or, the total mass concentration of solutes in the spinning solution is 0.18±0.005 g / mL.

[0009] As a possible implementation manner, the refluxing reaction is under the condition of a temperature of 130℃ and a time length of 10 hours; and / or, the uniform mixing is achieved by stirring for 1 hour; and / or, the standing time length is 48 hours; and / or, the axial stretching is performed at 100℃.

[0010] In a second aspect, the present application provides the azobenzene fiber prepared by the preparation method of any one of the possible implementation manners of the first aspect.

[0011] As a possible implementation, the fiber has axially arranged azobenzene groups and a directional hydrogen bond network, and a photo-induced shrinkage stress gradient microstructure is formed from the fiber surface to the core. The axial high orientation promotes the ordered arrangement of azobenzene groups and the formation of a directional hydrogen bond network; the cross section is composed of an asymmetric stress gradient structure of a surface photo-induced shrinkage layer and a core rigid constraint layer, realizing efficient light-force coupling transmission.

[0012] In a third aspect, the application provides an application of the azobenzene fiber in the light-driven system according to any possible implementation of the second aspect.

[0013] In a fourth aspect, the application provides a light-driven actuator prepared based on the azobenzene fiber according to any possible implementation of the second aspect.

[0014] As a possible implementation, the preparation method comprises the following steps: winding the azobenzene fiber around a metal rod at 60-80 DEG C to form a left / right spiral structure, and cooling and setting to obtain a left / right spiral light-driven actuator.

[0015] As a possible implementation, in the left / right spiral structure, the ratio of the pitch to the diameter is 3:1.

[0016] The application breaks through the traditional design paradigm of azobenzene materials and proposes a high-orientation light-driven fiber system based on dynamic hydrogen bond network regulation. By introducing a flexible spacer group (C8 hydroxyl segment) into the azobenzene monomer through molecular engineering, the light isomerization degree and the molecular chain entanglement effect are effectively balanced, and the material is given high ductility. At the same time, combined with the hydrogen bond crosslinking network construction and the wet spinning-pre-stretching synergistic process, the directional arrangement of the polymer main chain along the fiber axis is realized. The optimization of this structure not only enhances the absorption efficiency of the azobenzene fiber to ultraviolet light, but also improves the trans-cis isomerization reaction rate of the azobenzene group. The surface photo-induced shrinkage strain and the core rigid constraint are coupled by directional transmission of photo-induced deformation to form an asymmetric light-force gradient, and then the macroscopic deformation output of the light-driven is synergistically amplified, so as to realize the high-response light-driven performance. This systematic solution from molecular conformation regulation, network topology design to processing technology innovation provides a new way for the development of programmable and high-response azobenzene fiber-based light-driven systems. The innovative process based on hydrogen bond crosslinking and pre-stretching induced orientation realizes the spiral rapid directional motion of the azobenzene fiber for the first time, and provides a new material platform for flexible light-driven systems.

[0017] The application significantly improves the performance of photo-driven azobenzene fibers through multi-scale structure innovation. First, based on the esterification reaction of azobenzene monomer with flexible chain modification (C8 hydroxyl segment) and polyacrylic acid, a photoresponsive polymer with high molecular weight characteristics and hydrogen bond crosslinking network is constructed, which synergistically enhances the mechanical stability and fiber forming performance of the material. Second, through the wet spinning and pre-stretching process, the polymer main chain is highly oriented in the axial direction, which promotes the ordered arrangement of azobenzene groups, improves the ultraviolet light absorption efficiency, and accelerates the trans-cis isomerization dynamic response. Further, through the construction of an asymmetric stress gradient structure with a surface light-induced shrinkage layer and a core rigid constraint layer, efficient transfer of photo-force coupling is realized, significantly amplifying the axial photo-driven strain output. The azobenzene fiber spiral actuator prepared based on this can realize multi-parameter programming control of the motion direction and photoresponsive force, breaking through the limitations of existing photo-driven systems in terms of directional motion ability and response sensitivity. This technology provides an innovative material platform for the development of intelligent flexible actuators, and has broad application prospects in the fields of flexible robots, adaptive biomimetic devices, etc. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, below the drawings needed to be used in the embodiment or prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0019] Figure 1 The spinning process flowchart provided for the embodiments of the present application.

[0020] Figure 2 The scanning electron microscope (SEM) images of the unstretched azobenzene fiber and the 200% pre-stretched azobenzene fiber provided for the embodiments of the present application, wherein a is the plan view of the unstretched fiber, b is the cross-sectional view of the unstretched fiber (cross-sectional diameter d=0.97mm), c is the plan view of the 200% pre-stretched fiber, and d is the cross-sectional view of the 200% pre-stretched fiber (cross-sectional diameter d=0.82mm).

[0021] Figure 3 The polarized light microscope images of the 200% pre-stretched azobenzene fiber provided for the embodiments of the present application, wherein a represents 0=0°, b represents 0=45°, and c represents 0=90°.

[0022] Figure 4 The 50~100 mW / cm 2 Comparison chart of photoresponsive force of 200% pre-stretched azobenzene fiber under ultraviolet light irradiation.

[0023] Figure 5The light response stress contrast diagram of 100% and 200% pre-stretching azobenzene fibers provided by the embodiment of the present application is provided.

[0024] Figure 6 The light driving behavior of 200% pre-stretching azobenzene fibers wound into a right helix structure and irradiated by ultraviolet light from left to right and from right to left is provided by the embodiment of the present application.

[0025] Figure 7 The light driving behavior of 200% pre-stretching azobenzene fibers wound into a left helix structure and irradiated by ultraviolet light from left to right and from right to left is provided by the embodiment of the present application. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0027] In view of the technical bottlenecks of low photo-mechanical energy conversion efficiency, slow dynamic response and insufficient structural stability of the light response material in the prior art, the present application develops an azobenzene fiber with an asymmetric stress gradient through molecular orientation design and hydrogen bond crosslinking network regulation. The embodiments of the present application solve the problems of low light response rate, weak light-induced deformation output and single motion mode of the existing azobenzene material through the synergistic effect of molecular orientation design, hydrogen bond network regulation and asymmetric light-force gradient, and provide a programmable and high-response material solution for a high-performance flexible light-driven system.

[0028] The preparation method of the azobenzene fiber provided by the present application performs esterification reaction on azobenzene monomers containing long flexible terminal hydroxyl groups and polyacrylic acid to synthesize a high molecular weight azo polymer with light response characteristics, and then constructs a hydrogen bond crosslinking network with polyvinyl alcohol, and finally prepares a highly oriented azobenzene fiber through wet spinning and 100%-200% pre-stretching process. Wet spinning and pre-stretching treatment induce the axial high orientation arrangement and microstructure reconstruction of the azo polymer main chain, realize the significant improvement of light driving performance, and the azobenzene groups are orderly distributed along the orientation direction, thereby enhancing the ultraviolet light absorption efficiency and trans-cis isomerization reaction rate. The hydrogen bond crosslinking network transmits the photo-induced strain in a directional manner, and constructs an asymmetric stress gradient structure by combining the surface photo-induced shrinkage layer and the core rigid constraint layer, and cooperatively amplifies the macroscopic deformation output. The helical actuator of the high orientation azobenzene fiber has a deformation output of 0.5% under the irradiation of 100 mW / cm 2The controllable movement is output under ultraviolet light irradiation, the direction of which is cooperatively regulated by the helical chirality and the light irradiation direction, and the light response force size is accurately programmed by the light irradiation intensity and the stretching degree.

[0029] The high-orientation azobenzene fiber suitable for the application realizes high-efficiency conversion of photo-mechanical energy through the synergistic effect of hydrogen bond cross-linking network and molecular orientation. The design of the flexible spacer group introduces C8 hydroxyl segments in the azobenzene monomer, which provides the site for polyacrylic acid grafting and reduces the molecular chain entanglement through the long flexible chain to improve the isomerization degree of freedom. The hydrogen bond cross-linking network further enhances the mechanical stability and fiber-forming performance of the material, and cooperatively amplifies the macroscopic deformation output through the asymmetric photo-force gradient formed by the surface layer light contraction stress and the core rigid constraint. The wet spinning process promotes the preliminary arrangement of the polymer main chain along the fiber axis. The pre-stretching reinforcement makes the molecular chain further stretch, the hydrogen bond reconfigure along the axial direction, significantly improves the ordered distribution of the azobenzene group along the orientation direction, and enhances the ultraviolet light absorption efficiency and the trans-cis isomerization response rate.

[0030] The high-orientation azobenzene fiber provided by the embodiment of the application has a 200% pre-stretching rate and can output a macroscopic deformation of 0.5% under 365 nm ultraviolet light irradiation with an intensity of 100 mW / cm 2The output controllable motion of the helical azobenzene fiber is realized under the irradiation of light intensity, and the direction is cooperatively regulated by the helical chirality and the light irradiation direction. Specifically, when the pre-stretched azobenzene fiber is irradiated by the ultraviolet light obliquely, the light intensity decays exponentially along the thickness direction of the fiber, resulting in the cis-trans isomerization in the surface layer near the light source and the shrinkage stress. The shrinkage layer and the rigid core form an asymmetric stress gradient structure, which is equivalent to generating a bending moment pointing to the light source to drive the fiber to bend towards the light. The macroscopic rolling motion direction is precisely controlled by the combination of the helical geometric chirality and the light irradiation direction. When the right-handed helical azobenzene fiber is placed horizontally, if the ultraviolet light is obliquely irradiated from right to left, the light-induced shrinkage is concentrated on the right side (near the light source), and the clockwise geometric constraint makes the local curvature of the side decrease. The asymmetric strain is converted into a counterclockwise torque (observed along the axis) through the screw lever effect, driving the helical fiber to roll along the contact surface away from the light source (retreat); if the light irradiation direction is changed to obliquely irradiate from left to right, the shrinkage is concentrated on the left side, and the geometric constraint converts the strain into a clockwise torque, driving the helical fiber to roll towards the light source (advance). On the contrary, under the same conditions, when the ultraviolet light is obliquely irradiated from right to left, the counterclockwise geometric chirality of the left-handed helical fiber makes the shrinkage strain distribution (compared with the right-handed helical fiber) symmetrically inverted, and the curvature of the side near the light source (right side) increases to generate a clockwise torque, driving the helical fiber to roll towards the light source (advance); when the ultraviolet light is obliquely irradiated from left to right, the strain distribution is inverted to generate a counterclockwise torque, driving the helical fiber to roll away from the light source (retreat). The programmable motion direction is due to the directional amplification of the helical chirality to the light-induced strain distribution. The core of the motion behavior lies in the dynamic coupling of the helical geometric curvature and the light gradient field: the helical chirality determines the conversion direction of the strain-torque, and the light irradiation direction controls the spatio-temporal distribution of the curvature change. The dual regulation mechanism of "chirality coding-light control triggering" makes it possible to realize programmable motion (phototaxis / photophobic x advance / retreat) by simply changing the helical winding direction (right / left) and the light irradiation path (left / right).

[0031] The technical solutions of the application will be further described below with reference to specific embodiments.

[0032] Embodiment 1

[0033] The embodiment provides a preparation of an azobenzene fiber.

[0034] The 4-[4-(trifluoromethylthio)phenylazo]phenol (18.0 mmol), 8-bromo-1-hexanol (20.0 mmol), potassium carbonate (20.0 mmol) and potassium iodide (1.5 mmol) were dissolved in N,N-dimethylformamide (100 mL) and refluxed at 130°C for 10 hours. After the reaction was completed, the reaction was cooled to room temperature, the crude product was added to a beaker containing 400 mL of water, filtered, washed with distilled water several times, extracted with dichloromethane, and finally recrystallized with ethanol to obtain a bright yellow powder of azobenzene monomer, and the structural formula is shown as formula I;

[0035]

[0036] Formula I

[0037] The polyacrylic acid (5.0 mmol, molecular weight Mw: 450,000), the prepared azobenzene monomer (7.0 mmol), 4-dimethylamino pyridine (1 mmol) and 1-ethyl-(3-dimethylamino propyl) carbonyl diimide hydrochloride (8.0 mmol) were dissolved in dimethyl sulfoxide (150 mL). After the above reaction was subjected to three times of freezing-vacuum-purging with argon to remove oxygen, the reaction was carried out at 110°C under argon protection for 72 hours. After the reaction was completed, the product was precipitated with ethyl acetate, filtered, and washed with distilled water and methanol several times to obtain an azo polymer, and the structural formula is shown as formula II;

[0038]

[0039] Formula II

[0040] The prepared azo polymer (0.6 g) and polyvinyl alcohol (0.2 g, molecular weight: Mw=205,000) were dissolved in dimethyl sulfoxide (5 mL), stirred at 80°C under argon protection for 1 hour, and stood for 48 hours to defoam, and prepared into a 18±0.5 wt% spinning solution;

[0041] The spinning solution was extruded into a 20±2°C methanol (concentration 99.8%) coagulation bath at a speed of 0.45 mL / min using a 14# stainless steel wet spinning needle, and the as-spun fiber was taken out after staying in the coagulation bath for 5 minutes, and dried at room temperature for 48 hours, and the spinning process flow is shown as Figure 1 The SEM scanning of the unstretched and 200% pre-stretched azobenzene fibers was carried out, and the results are shown as Figure 2 a and b in Figure 2 respectively present the plane and the cross-sectional view (cross-sectional diameter d=0.97 mm) of the unstretched fiber, and Figure 2Figures c and d show the plan and cross-sectional views of 200% pre-stretched fibers (cross-sectional diameter d = 0.82 mm). By comparison, the unstretched azobenzene fibers form an axially grooved planar morphology and a densified cross-sectional structure after stretching, achieving the coordinated evolution of enhanced surface orientation and radial dimensional compression.

[0042] Example 2

[0043] This embodiment provides a performance test of azobenzene fibers with a highly oriented structure.

[0044] The azobenzene fiber prepared according to the method of Example 1 was axially stretched by 100% to 200% at 100° C. and then cooled to set the fiber, thereby obtaining an azobenzene fiber with a highly oriented structure.

[0045] The orientation of azobenzene fibers after 200% pre-stretching was tested using a polarizing microscope. By changing the angle (θ) between the arrangement direction of the azobenzene fibers and the analyzer, the orientation of the fibers was observed, and the following results were obtained: Figure 3 The results shown. Figure 3 As can be seen from a in the figure, when θ is 0°, the eyepiece field of view is very dark, almost completely black; as the azobenzene fiber rotates around the center, the fiber in the eyepiece gradually becomes brighter until the angle between the fiber arrangement direction and the analyzer is 45°, at which point the fiber in the field of view reaches its brightest ( Figure 3 b in the figure); then rotate the fiber clockwise, and the fiber in the field of view gradually becomes darker. When the angle between the fiber arrangement direction and the analyzer becomes 90°, the field of view reaches its darkest again ( Figure 3 c). The light and dark changes that occur at every 45° angle prove that the azobenzene fibers prepared in this example have a high degree of orientation.

[0046] The mechanical properties of azobenzene fibers (100% and 200% strain) were measured. First, the azobenzene fibers (100% and 200% strain) prepared in this example were fixed on a tensile testing machine (UTM2203X, China), and then irradiated with 365 nm ultraviolet light at 100 mW / cm 2 The light intensity is irradiated on the sample, and the contraction force generated is detected, and the results are as follows: Figure 4 The results shown. Figure 4 It can be seen that the photoresponse force of the 200% pre-stretched azobenzene fiber (close to 3.3 MPa) is at least twice that of the 100% pre-stretched azobenzene fiber (close to 1.6 MPa). When the UV light is removed, the photoresponse force drops rapidly, but does not drop to the initial value and retains a significant stress. By controlling the on and off of the UV light, this force generation and reduction cycle can be repeated many times. At the same time, the 200% pre-stretched azobenzene fiber was subjected to 50~100 mW / cm 2 The intensity of ultraviolet light is irradiated to obtainFigure 5 The results shown, Figure 5 Showed that higher UV light intensity can produce greater shrinkage force.

[0047] Example 3

[0048] This example provides an application experiment of a high-orientation structure of an azobenzene fiber.

[0049] The 200% pre-stretched azobenzene fiber prepared according to the method of Example 2 was wound to the right (left) around a metal rod with a diameter of 1 mm at 60°C to form a right (left) helical structure with a length of 2.6 cm (the ratio of the pitch to the diameter is 3:1), and a right (left) helical actuator was obtained after cooling and setting.

[0050] When the obtained right helical actuator was irradiated from left to right at an oblique angle, it rolled at a speed of 0.28 cm / s towards the light source (forward) (a) in FIG. 1; Figure 6 When the obtained right helical actuator was irradiated from right to left, it rolled at a speed of 0.11 cm / s away from the light source (backward) (b) in FIG. 1. Figure 6

[0051] When the obtained left helical actuator was irradiated from left to right at an oblique angle, it rolled at a speed of 0.11 cm / s away from the light source (backward) (a) in FIG. 2; When the obtained left helical actuator was irradiated from right to left, it rolled at a speed of 0.28 cm / s towards the light source (forward) (b) in FIG. 2. Figure 7 Figure 7

[0052] While the preferred embodiments of the application have been described, those skilled in the art will readily devise their own additional changes and modifications of the preferred embodiments, without departing from the spirit and scope of the application. Accordingly, the appended claims are intended to encompass all such changes and modifications as fall within the scope of the application.

[0053] Obviously, many modifications and changes can be made to the present application without departing from the spirit and scope of the application. Accordingly, it is intended that all such modifications and changes be included within the scope of the application as long as the modified and changed forms fall within the scope of the claims and their equivalents.​​​

Claims

1. A method for preparing azobenzene fiber, characterized in that: The following steps are involved: 4-[4-(trifluoromethylthio)phenylazo]phenol, 8-bromo-1-hexanol, potassium carbonate and potassium iodide are dissolved in N,N-dimethylformamide, refluxed and purified to obtain an azobenzene monomer; Dissolving polyacrylic acid and the azobenzene monomer in dimethyl sulfoxide, adding 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride / 4-dimethylaminopyridine catalyst, and fully reacting under argon protection, the product is precipitated with ethyl acetate, filtered, and washed to obtain an azo polymer; The azo polymer and polyvinyl alcohol are dissolved in dimethyl sulfoxide, mixed evenly under argon protection, and allowed to stand until defoamed to prepare a spinning solution; The spinning solution is wet-spun to form nascent fibers, and the nascent fibers are axially stretched by 100% to 200% and then cooled and shaped to obtain the azobenzene fibers.

2. The preparation method according to claim 1, characterized in that The purification includes the following operations: water washing, dichloromethane extraction and ethanol recrystallization; And / or, the washing comprises the operation of: washing with distilled water and methanol several times; And / or, the wet spinning includes the operation of: using a stainless steel wet spinning needle to squeeze the spinning solution into a 20±2° C. methanol coagulation bath at an injection speed of 0.45 mL / min, and reconstructing hydrogen bonds to form the nascent fibers.

3. The preparation method according to claim 1, characterized in that The molar ratio of the 4-[4-(trifluoromethylthio)phenylazo]phenol, the 8-bromo-1-hexanol, the potassium carbonate, and the potassium iodide is 9:10:10:0.75; And / or, the molecular weight of the polyacrylic acid is 450,000; And / or, the molar ratio of the polyacrylic acid to the azobenzene monomer is 1:1.4; and / or, the molecular weight of the polyvinyl alcohol is 205,000; And / or, the mass ratio of the azo polymer to polyvinyl alcohol is 2:1; And / or, the total mass concentration of solutes in the spinning solution is 0.18±0.005 g / mL.

4. The preparation method according to claim 1, characterized in that The reflux reaction conditions are: temperature 130° C., duration 10 hours; And / or, the uniform mixing is achieved by stirring for 1 hour; And / or, the standing time is 48 hours; And / or, the axial stretching is performed at 100°C.

5. Azobenzene fiber prepared by the preparation method according to any one of claims 1 to 4.

6. The azobenzene fiber according to claim 5, characterized in that It has axially arranged azobenzene groups and a directional hydrogen bond network, and a photoinduced shrinkage stress gradient microstructure is formed from the fiber surface to the core.

7. Use of the azobenzene fiber according to any one of claims 5 to 6 in a light-driven system.

8. An optical drive brake, characterized in that: The azobenzene fiber is prepared based on any one of claims 5 to 6.

9. The optical drive brake according to claim 8, wherein: The preparation method comprises the following steps: The azobenzene fiber is wound around a metal rod at 60-80° C. to form a left / right spiral structure, and the structure is cooled and fixed to obtain a left / right spiral optical drive actuator.

10. The optical drive brake according to claim 9, wherein: In the left / right helical structure, the ratio of pitch to diameter is 3:1.

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