Graphene oxide-based stimuli-responsive functional material and preparation method thereof

Abstract

Existing spherical graphene oxide aggregates are single in morphology and structure, and application scenes of the spherical graphene oxide aggregates are limited. And the problems that the existing spherical aggregate cannot realize reversible large-volume shrinkage and expansion after solvent desorption-adsorption, so that the actuating deformation degree is small, the sensing precision is poor, the aggregate is difficult to recycle and the like are caused. The invention provides a graphene oxide-based stimuli-responsive functional material, and the morphology and structure of the material can be customized as required, including but not limited to a four-leaf clover shape, a clover shape, a triangular cake shape, an ellipsoid shape, a tadpole shape and the like. The structure of the material comprises a core body and a shell, wherein the shell wraps the core body. The core body is of a network structure formed by overlapping graphene oxide sheet layers, the shell is formed by overlapping graphene oxide sheet layers, and each graphene oxide sheet layer has a wrinkle structure. On the basis of intrinsic characteristics of graphene oxide and in combination with structural design, regulation and control of the morphology structure of the aggregate and reversible large-volume shrinkage and expansion are realized.

Description

Technical Field

[0001] This invention relates to the field of functional materials technology, and in particular to a graphene oxide-based stimulus-responsive functional material and its preparation method. Background Technology

[0002] Graphene oxide is a graphene derivative with oxygen-containing functional groups such as hydroxyl, carboxyl, and epoxy groups modified on a single-layer carbon six-membered ring framework. It possesses excellent processability and mechanical properties. After processing and assembling, graphene oxide materials with specific structures and sizes ranging from sub-millimeter to millimeter can be prepared.

[0003] Stimulus-responsive functional materials, also known as "smart materials" or "environmentally sensitive materials," refer to a class of advanced materials that can sense minute changes in the external environment (such as temperature, pH value, light, electric / magnetic fields, chemical substances, mechanical stress, etc.) and respond to these changes by reversibly or irreversibly altering certain physical or chemical properties (such as shape, size, color, transparency, hydrophilicity / hydrophobicity, permeability, etc.).

[0004] Spherical graphene oxide aggregates are a type of stimulus-responsive functional material. However, the existing spherical graphene oxide aggregates have a single morphological structure, which limits their application scenarios. At the same time, the existing spherical aggregates cannot achieve reversible large volume shrinkage and expansion after solvent desorption-adsorption, resulting in problems such as small actuation deformation, poor sensing accuracy, and difficulty in recycling the aggregates. Summary of the Invention

[0005] This invention addresses the limitations of existing spherical graphene oxide aggregates, which have a single morphological structure that restricts their application scenarios, and the problems that existing spherical aggregates cannot achieve reversible large-volume shrinkage and expansion after solvent desorption-adsorption, resulting in small actuation deformation, poor sensing accuracy, and difficulty in recycling aggregates. It provides a graphene oxide-based stimulus-responsive functional material and its preparation method.

[0006] This invention utilizes the oxygen-containing functional groups of graphene oxide to perform specific structural design of graphene oxide, thereby obtaining stimulus-responsive functional materials. The presence of oxygen-containing functional groups makes graphene oxide highly sensitive to polar solvents; furthermore, they can act as defects to induce wrinkle formation. This invention effectively combines the above-mentioned characteristics of oxygen-containing functional groups with a core-shell structure design. Through the bulging and stretching of hill-like wrinkles, reversible three-dimensional contraction and expansion occur, enabling self-driving under the stimulation of polar solvents. This results in large actuation deformation, sensitive response, and long cycle life.

[0007] One of the technical solutions of the present invention is to provide a graphene oxide-based stimulus-responsive functional material, comprising a core and a shell, wherein the shell encapsulates the core, the core is formed by overlapping graphene oxide to form a network structure, and the shell is formed by overlapping graphene oxide sheets, wherein the graphene oxide sheets have a wrinkled structure.

[0008] When this core-shell aggregate is placed in a polar solvent, the wrinkled structure of the shell graphene oxide sheets unfolds, the core network structure expands, and the core-shell structure undergoes three-dimensional expansion. After the polar solvent is removed, the wrinkled structure of the shell graphene oxide shrinks, the core network structure tightens, and the core-shell structure shrinks three-dimensionally. It should be noted that by controlling the drying temperature and pressure of the aggregate, the degree of shrinkage of the shell graphene oxide wrinkled structure can be controlled by controlling the degree of removal of the polar solvent, forming a hilly structure with small shrinkage or a ridge structure with large shrinkage. Correspondingly, the network structure tightens to form a porous network structure or a dense structure. In some embodiments of the present invention, the volume change rate during the shrinkage and expansion process is ≥90%, the Young's modulus changes from 10 kPa to 10 GPa (spanning up to 6 orders of magnitude), and the multi-level shape recovery rate is ≥90%, which has extremely important application value in biomimetic machines, biological tissue engineering, and wastewater treatment.

[0009] In a preferred embodiment of the present invention, the network structure is a porous network structure or a dense network structure.

[0010] Those skilled in the art will foresee that, based on the core-shell structure design of this invention, the network structure of the core portion can be either dense or porous. The higher the density of the network structure in the core portion, the greater the expandability of the network structure, and the more pronounced the stimulus response.

[0011] In a preferred embodiment of the invention, a polar solvent is dispersed within the porous network structure. This graphene oxide-solvent composite system can achieve structural shrinkage directly through solvent removal. In this case, the solvent removal process directly induces the shrinkage of the graphene oxide sheets in the core portion, pulling the shell to form a smaller core-shell structure. In contrast to porous networks, dense networks do not contain solvent.

[0012] In a preferred embodiment of the present invention, the graphene oxide has the wrinkled structure. That is, the graphene oxide core has a wrinkled structure, and when placed in a polar solvent, the wrinkled structure of the core expands, expanding in conjunction with the wrinkles of the graphene oxide shell, resulting in a more pronounced stimulus response. Similarly, those skilled in the art should understand that the initial state of the wrinkled structure of the graphene oxide core can also be a hilly, low-wrinkle structure or a ridge-like, high-wrinkle structure. High-wrinkle structures exhibit greater expansion in polar solvents compared to low-wrinkle structures; however, in this invention, both low-wrinkle and high-wrinkle structures can achieve a solvent-responsive reaction.

[0013] In a preferred embodiment of the present invention, the folded structure is a hilly structure with small contractions or a ridge structure with large contractions.

[0014] Therefore, those skilled in the art should understand that in this invention, the initial state of the wrinkled structure of the shell graphene oxide can be either a hill-like low-wrinkle structure or a ridge-like high-wrinkle structure. High-wrinkle structures have a greater degree of expansion in polar solvents compared to low-wrinkle structures; however, in this invention, both low-wrinkle and high-wrinkle structures can achieve a solvent-responsive reaction.

[0015] As is common knowledge in this field, the wrinkles in graphene oxide refer to the bending or folding of its two-dimensional sheets caused by factors such as uneven distribution of oxygen-containing functional groups on the surface, stress shrinkage during drying, or interlayer interactions. Smaller wrinkles and a flatter structure are called hill-like low wrinkles; conversely, larger wrinkles and obvious three-dimensional bending or folding in the structure are called ridge-like high wrinkles.

[0016] The present invention also provides a driving body comprising multiple of the aforementioned stimulus-responsive functional materials. The driving body is an amorphous graphene oxide aggregate, and the driving body is clover-shaped, trefoil-shaped, triangular, beaded, ellipsoidal, or tadpole-shaped to adapt to different application scenarios.

[0017] In a preferred embodiment of the present invention, the driving body includes a first stimulus-responsive functional material and a second stimulus-responsive functional material connected to each other, and the first stimulus-responsive functional material and the second stimulus-responsive functional material have different expansion amounts in at least one direction in the same polar solvent, wherein the second stimulus-responsive functional material is one or more.

[0018] The expansion of the aforementioned stimulus-responsive functional material is uniform, representing an equal increase or decrease in volume. When two stimulus-responsive functional materials with different expansion amounts are joined together, the first stimulus-responsive functional material exerts a traction effect on the second stimulus-responsive functional material, causing uneven deformation of the second stimulus-responsive functional material and resulting in deformation of the driving body. A typical driving morphology is tadpole-shaped, with the first stimulus-responsive functional material forming the tadpole's head and the second stimulus-responsive functional material forming the tadpole's tail.

[0019] When the driving body comprises a first stimulus-responsive functional material and multiple consecutive second stimulus-responsive functional materials, the expansion of each individual stimulus-responsive functional material is uniform, representing an equal increase or decrease in volume. When two stimulus-responsive functional materials with different expansion amounts are connected together, the first stimulus-responsive functional material exerts a traction effect on the two second stimulus-responsive functional materials. Under the traction of the same first stimulus-responsive functional material, the driving body deforms. Typical driving morphologies are clover-shaped and trefoil-shaped structures, with the first stimulus-responsive functional material forming the middle part of the clover or trefoil shape, and the second stimulus-responsive functional materials forming the petals of the clover or trefoil shape.

[0020] Different expansion amounts can be controlled by setting the internal density of the aggregates; the higher the density, the greater the expansion amount in a solvent of the same polarity.

[0021] The actuators in this invention can be applied to biomimetic machines, biological tissue engineering, wastewater treatment, sensing, and drug delivery. For example, when the aggregates have a tadpole-like appearance, solvent-driven actuation can achieve large local expansion of the tadpole, enabling point-to-point actuation, and holds promise for applications in soft robot joints and other areas.

[0022] This invention proposes a method for preparing a driving body with different densities and an integral structure, comprising the following steps: using a nozzle with one or more nozzles arranged in a specific pattern, fixing the nozzle on a robotic arm, controlling the movement of the nozzle, dripping a graphene oxide dispersion through the nozzle into a non-ionic coagulation bath to form a graphene oxide gel, controlling the spacing between the nozzles to allow the interface between the graphene oxide droplets to fuse, thereby transforming the fluid shape into various complex shapes to form a heteromorphic graphene oxide gel with different densities but an integral structure; filtering and drying the heteromorphic graphene oxide gel to form a dried material, and soaking and swelling the dried material with a polar solvent to obtain the driving body.

[0023] The nozzle allows for the design of multiple nozzle topologies. Simultaneously, the nozzle can move programmatically. With only one nozzle, controlling its movement creates tadpole-shaped aggregates. With two or more nozzles, the nozzle can remain stationary to create complex structures such as four-leaf clover shapes, three-leaf clover shapes, triangular disc shapes, beaded shapes, and ellipsoids. Furthermore, with two or more nozzles, the nozzle moves to create even more complex shapes.

[0024] In some embodiments of the present invention, the graphene oxide gel is dried at a temperature generally between 10 ℃ and 60 ℃, and at a pressure of 0.1 kPa to 101 kPa. This avoids the reduction reaction of graphene oxide at high temperatures, maintains its oxygen content, and ensures that the carbon-oxygen ratio after drying is ≤5. This ensures the affinity between the aggregates and the solvent, and guarantees that the aggregates can undergo large expansion after adsorbing the solvent.

[0025] In some embodiments of the present invention, the dried gel is also soaked and swollen with a polar solvent, on the one hand replacing the residual coagulation bath components, and on the other hand forming solvent components inside the aggregate.

[0026] The present invention also includes the removal of polar solvents, which involves placing the material in a vacuum oven and drying it at 20°C to 60°C under a pressure of 0.1 kPa to 101 kPa. The degree of removal is controlled by adjusting the drying temperature and pressure. Higher drying temperatures and lower pressures result in more thorough removal and a denser structure.

[0027] With the polar solvent removed, the network structure is dense; without removing the polar solvent, it is porous. By repeatedly removing and adsorbing the solvent, the network structure can be shrunk and expanded, thus driving deformation.

[0028] By combining the topological design of multiple nozzles in the nozzle, gels with structures resembling figures-eight, cloverleaf, beads, and four-leaf clover are formed. The gel density is higher at the nozzle locations and lower at the droplet fusion points, creating a driving body with different densities and an integrated structure. The nozzle topological design includes adjusting the number, arrangement, and spacing of the nozzles to match the size and droplet velocity of the extruded graphene oxide droplets. Droplets extruded from different nozzles undergo interfacial fusion under surface tension, thereby transforming the fluid shape into various complex shapes.

[0029] A graphene oxide dispersion is dripped into a non-ionic coagulation bath using a nozzle. The local morphology and density of the gel particles are controlled by adjusting the nozzle's movement speed and displacement. Higher movement speeds result in lower density. In embodiments of this invention, a tadpole-shaped drive body is constructed using a slow-then-fast approach. Generally, the initial height of the nozzle from the coagulation bath surface is ≥1 mm. The nozzle can achieve programmed spatial displacement in the x, y, and z directions, with a displacement speed ≥0.1 mm / s and a displacement accuracy ≥1 μm.

[0030] Based on this, those skilled in the art can combine the topological design of multiple nozzles and the programmed movement of the nozzles to fabricate more complex drive structures. Matching the nozzle topology with the movement and the flow of the spinning solution produces different complex fluid shapes. This solves the problem that when a single nozzle is used in a fixed position, the fluid shape is limited to a near-spherical shape due to surface tension constraints, preventing the formation of complex shapes. Furthermore, the poor adjustability of the shearing effect of the coagulation bath on the fluid hinders the complex and precise design of the aggregate structure. Combining these two adjustment methods significantly improves the structural tunability of graphene oxide aggregates.

[0031] Furthermore, the polar solvent includes one or more of water, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, ethylene glycol, trifluoroacetic acid, and acetonitrile, with a swelling time ≥1 min. After gel drying-swelling, its morphology and structural stability are further improved, enabling the aggregates to exhibit reversible large shrinkage-swelling capacity during solvent desorption and adsorption cycles. When the polar solvent is water, after solvent replacement, freeze-drying can be performed to obtain a solvent-free driven body that maintains the gel morphology.

[0032] Based on the above method, the length of the prepared driving body is 1 mm to 10 mm, the volume change rate of the driving body during contraction and expansion is ≥90%, the Young's modulus of the driving body varies from 10 kPa to 10 GPa, and the multi-level shape recovery rate of the driving body is ≥90%.

[0033] In this invention, a coagulation bath system without metal ions can be used to coagulate graphene oxide dispersion droplets to prepare graphene oxide aggregates. This process preserves the complex fluid shape while preventing the introduction of additional chemical interactions between the layers, thus avoiding the loss of interlayer ionic cross-linking and reversible large-volume change capability caused by metal ion coagulation bath preparation. The stability of the complex shape of the aggregates is achieved through near-room temperature drying and solvent swelling.

[0034] Generally, the concentration of the graphene oxide dispersion is 1–10 mg / g, and the dispersion solvent is a polar organic solvent, including one or more of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), N-methylpyrrolidone, ethylene glycol, trifluoroacetic acid, and acetonitrile.

[0035] Furthermore, the nonionic coagulation bath includes one or more of ethyl acetate, dichloromethane, ethanol, isopropanol, methanol, acetic acid, acetone, tetrahydrofuran, carbon disulfide, n-hexane, cyclohexane, petroleum ether, benzene, and toluene. The nonionic coagulation bath does not contain metal ions, allowing the graphene oxide fluid to solidify and maintain a specific shape without introducing additional chemical reactions, ensuring that the solidified aggregates maintain reversible large shrinkage-expansion capabilities during solvent desorption-adsorption.

[0036] Compared with the prior art, the present invention has the following advantages: 1) The graphene oxide-based stimulus-responsive functional material of the present invention, based on the intrinsic properties of graphene oxide and combined with structural design, realizes the regulation of aggregate morphology and structure and reversible large volume shrinkage and expansion.

[0037] 2) Based on the large volume shrinkage and expansion characteristics, a drive body with sensitive response to solvent stimulation, large actuation deformation, and long cycle life was realized.

[0038] 3) By designing the topology and programmed movement of multiple nozzles in the nozzle, the limitations of poor adjustability of aggregate structure when a single nozzle is used in a fixed position in the existing technology are overcome. By utilizing the controllable droplet fusion and the shearing action of the coagulation bath, complex and precise aggregates are generated, which greatly improves the designability and precision of the aggregate structure.

[0039] 4) The non-ionic coagulation bath does not contain metal ions and does not introduce additional chemical reactions, ensuring that the layers inside the aggregate can be repeatedly attached and opened, guaranteeing that the aggregate can undergo reversible large shrinkage and expansion during solvent desorption-adsorption, and the coagulation bath can be repeatedly recycled, which is beneficial for energy saving and efficiency improvement.

[0040] 5) The near-room temperature drying conditions are mild and energy-efficient, maintaining the carbon-to-oxygen ratio of graphene oxide to ≤5 to the greatest extent possible, thus ensuring the affinity between the aggregates and the solvent and the solvent-driven reversible large shrinkage-expansion capability. The entire preparation process can be scaled up for mass production.

[0041] 6) The aggregates (i.e. the material) have a wrinkled core-shell structure network, which ensures that the aggregates can achieve large reversible shrinkage and expansion during solvent desorption and adsorption, thereby realizing ultra-wide range of volume and modulus adjustability and multi-level shape recovery. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of the preparation method. Figure 1 a is a schematic diagram of the preparation apparatus; Figure 1 b is a schematic diagram of a typical nozzle topology; Figure 1 c is a schematic diagram of the droplet fusion process when a four-nozzle nozzle (arranged 1) is used to prepare clover-shaped graphene oxide aggregates.

[0043] Figure 2 The images show the preparation process of Examples 1-3 and polarized light microscope images of the reversible large shrinkage-expansion of the aggregates. Figure 2 Photo a shows the preparation process of four-leaf clover-shaped, tadpole-shaped, and triangular disc-shaped graphene oxide aggregates. Figure 2 b is a polarized light microscope image of the reversible large contraction-expansion of aggregates of three shapes during solvent desorption-adsorption.

[0044] Figure 3 The volume of the aggregates prepared in Example 2 changes with solvent desorption and adsorption time.

[0045] Figure 4 The Young's modulus of the aggregates prepared in Example 2 changes with solvent desorption and adsorption time.

[0046] Figure 5 The shape recovery rate of the aggregates prepared in Example 2 varies with the number of shrinkage-expansion cycles. Detailed Implementation

[0047] The following examples are provided to further illustrate the present invention and are intended to explain the invention, not to limit its scope. Unless otherwise specified, all figures are expressed in parts by weight and weight percentages.

[0048] Unless otherwise specified, the raw materials used in this invention are all conventional commercially available products; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0049] The embodiments of the present invention will be further described below with reference to several examples.

[0050] It should be understood that the described embodiments are merely some, not all, of the embodiments in this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0051] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0052] Methods for adjusting the morphology of graphene oxide aggregates typically involve changing the position of the needle, immersing it in or above the coagulation bath, to obtain fibrous or spherical aggregates. However, this method offers very limited control and cannot produce complex and diverse aggregate structures. Furthermore, the metal ion-containing coagulation bath causes interlayer ionic cross-linking after solvent desorption and drying. When the solvent is re-adsorbed, the aggregates cannot reversibly expand, with a volume change rate of less than 40%, Young's modulus variation limited to 1 GPa-10 GPa, and shape recovery rate less than 10%. This severely impacts the structural diversity and adsorption actuation performance of graphene oxide aggregates, hindering their application in various scenarios.

[0053] This invention utilizes the controlled movement, number, topological arrangement, and spinning solution concentration of nozzles to drip graphene oxide spinning solution into a coagulation bath, resulting in graphene oxide gels of various shapes. The batch-spun gels are then filtered, dried, and swollen in solvent to obtain shape-stable heteromorphic graphene oxide aggregates. These aggregates exhibit shapes including cloverleaf, trefoil, triangular, ellipsoidal, and tadpole-shaped aggregates. During solvent desorption-adsorption, these aggregates show a volume change rate as high as 96%, a Young's modulus change spanning six orders of magnitude, and a shape recovery rate as high as 98%. In the mass production process, the ingenious nozzle design and non-ionic coagulation bath significantly enrich the topological morphology of the aggregates and endow them with multi-level morphological stability after large contraction-expansion, overcoming the problems of traditional aggregates' difficulty in shape control and reversible large volume changes. This has significant value for applications in sensing, drug delivery, and biomimetic robotics.

[0054] See Figures 1-5 The preparation of aggregates in this invention includes the following steps: (1) A graphene oxide dispersion is dripped into a non-ionic coagulation bath through a nozzle. The nozzle is fixed on a robotic arm and can achieve programmed displacement. The number of nozzles in the nozzle is ≥1, the inner diameter of a single nozzle is ≥60 μm, and when the number of nozzles is ≥2, they are arranged in a straight line, triangle, triangular support, quadrilateral and other characteristic structures to obtain a heteromorphic graphene oxide gel; (2) The above-mentioned heteromorphic graphene oxide gel is filtered through a plastic mesh and dried at 10 ℃~60 ℃. The pressure during drying is 0.1 kPa~101 kPa; (3) The dried gel is soaked and swollen with a polar solvent to obtain a heteromorphic graphene oxide aggregate. The aggregate has a reversible large shrinkage-expansion capability.

[0055] The initial height of the nozzle from the surface of the coagulation bath is ≥1 mm. The nozzle can achieve programmed spatial displacement in the x, y, z directions, with a displacement speed ≥0.1 mm / s and a displacement accuracy ≥1 μm.

[0056] Example 1: 1. Take 18 mL of a 3 mg / g graphene oxide DMF dispersion and transfer it into a 20 mL syringe. The syringe is fitted with a four-nozzle nozzle. The four nozzles are positioned at a 2:1 angle. The syringes were arranged in a 2-way configuration, with each nozzle having an inner diameter of 400 μm and a spacing of 3 mm between adjacent nozzles. The syringes were mounted on a programmed robotic arm, with the nozzles initially positioned 5 mm above the coagulation bath surface. The coagulation bath consisted of a 7:3 volume ratio mixture of ethyl acetate and dichloromethane. The dispersion was extruded at a rate of 2.5 mL / min. Droplets extruded from the four nozzles coalesced at the contact interface, forming a four-leaf clover shape upon falling onto the coagulation bath surface. The material was then immersed in the coagulation bath for 1 h to allow for complete solidification, yielding a four-leaf clover-shaped graphene oxide gel.

[0057] 2. The bottom of a glass filter cup is wrapped with an 80-mesh nylon mesh. A coagulation bath containing graphene oxide gel is poured into the filter cup, allowing the coagulation bath to filter out, while the gel is retained on the nylon mesh. The apparatus is placed at 25 °C and atmospheric pressure for 2 days to allow the residual solvent in the coagulation bath to fully evaporate, resulting in dried graphene oxide aggregates. The carbon-to-oxygen ratio of the dried graphene oxide is 1.8.

[0058] 3. The dried graphene oxide aggregates obtained in step 2 were soaked in water to swell for 1 hour. The aggregates gradually swelled into a regular four-leaf clover shape, resulting in four-leaf clover-shaped graphene oxide aggregates with a side length of 4 mm. The aggregates have a four-leaf clover-shaped outline with smooth edges, and the center is slightly concave, with a concavity depth of 1.5 mm. The interior exhibits the characteristic liquid crystal texture of graphene oxide, with a carbon-to-oxygen ratio of 1.8. Further, the aggregates were placed in a vacuum oven at 60 °C and 0.1 kPa to completely remove water. Figure 2 As shown, during water molecule desorption, the aggregates shrink in volume, with a volume change rate as high as 90%, and the Young's modulus increases dramatically from 10 kPa to 10 GPa. The shape shrinks from a regular four-leaf clover shape to an irregular, multi-folded shape. However, when water molecules are adsorbed, the aggregates undergo a reversible large expansion, returning to their initial regular four-leaf clover shape, volume, and modulus.

[0059] 4. After 10 cycles of water molecule desorption-adsorption, the aggregates maintained a shape recovery rate of 95%, with no significant structural damage or deformation.

[0060] 5. When the pressure for water removal from the aggregates in step 3 remains constant, and the temperatures are 40 ℃ and 20 ℃ respectively, the degree of water removal gradually decreases, with the volume change rates during shrinkage being 86% and 81% respectively, and the Young's modulus increasing to 7 GPa and 3 GPa respectively. When the temperature for water removal from the aggregates in step 3 remains constant, and the pressures are 10 kPa and 101 kPa respectively, the degree of water removal gradually decreases, with the volume change rates during shrinkage being 88% and 85% respectively, and the Young's modulus increasing to 8 GPa and 4 GPa respectively.

[0061] Comparative Example 1 This comparative example is the same as Example 1, except that in the four-nozzle nozzle, the distance between adjacent nozzles is 1 cm.

[0062] 1. Take 18 mL of a 3 mg / g graphene oxide DMF dispersion and load it into a 20 mL syringe. Extrude the dispersion through a four-nozzle nozzle into a coagulation bath. The distance between adjacent nozzles in the nozzle is 1 cm. After the dispersion is extruded simultaneously from the four nozzles, because the distance between adjacent droplets is greater than the diameter of the droplets themselves, the droplets do not come into contact and merge, but instead form four independent droplets. After the four droplets have been immersed in the coagulation bath for 1 h, four separate spherical graphene oxide gels are obtained.

[0063] 2. The spherical gel obtained in step 1 was filtered through a nylon filter and dried at 25 °C and normal pressure for 2 days to obtain dried graphene oxide aggregates, consistent with step 2 of Example 1.

[0064] 3. The dried graphene oxide aggregates obtained in step 2 were immersed in water to swell for 1 hour, resulting in spherical graphene oxide aggregates with a diameter of 1.9 mm. The aggregates exhibited a monochromatic spherical shape, similar to spherical aggregates prepared by conventional methods, but with significantly lower shape complexity than those in Example 1. During water molecule desorption-adsorption, the volume change rate was 88%, the Young's modulus ranged from 10 kPa to 10 GPa, and the shape recovery rate after 10 adsorption-desorption cycles was 92%.

[0065] Comparative Example 2 This comparative example is the same as Example 1, except that the dispersion solvent for graphene oxide is water, and a coagulation bath system containing calcium ions is used.

[0066] 1. Take 3 mg / g of graphene oxide aqueous dispersion and put it into a syringe. Squeeze it out from the four-nozzle nozzle and drip it into a 5 wt.% calcium chloride aqueous solution coagulation bath to obtain a four-leaf clover-shaped graphene oxide gel.

[0067] 2. The filtration and drying process is the same as step 2 in Example 1.

[0068] 3. The dried graphene oxide aggregates obtained in step 2 were immersed in water to swell for 1 hour. The volume expansion rate of the aggregates was only 33%, failing to expand into a regular four-leaf clover shape. The final graphene oxide aggregates were approximately 2 mm wide, with irregular shapes, numerous surface wrinkles, and indistinct internal graphene oxide liquid crystal texture. During water molecule desorption-adsorption, the aggregates showed minimal shrinkage and expansion, with a volume change rate of only 33%, a Young's modulus variation ranging from 1.2 GPa to 10 GPa, and a shape recovery rate as low as 2%.

[0069] Example 2: 1. Take 9 mL of 5 mg / g graphene oxide (DMAc) dispersion and load it into a 10 mL syringe. The syringe is fitted with a single nozzle with an inner diameter of 210 μm. Mount the syringe on a programmed robotic arm, with the nozzle initially 4 mm above the coagulation bath surface. The coagulation bath is a 9:1 volume ratio mixture of acetone and isopropanol. Extrude the dispersion at a rate of 0.3 mL / min. During the preparation of a tadpole-shaped gel, the nozzle movement is programmed and controlled by the robotic arm. First, pause at the initial height for 1 s to allow the nozzle to extrude the head droplet of the tadpole. Then, move downwards by 7 mm at a speed of 10 mm / s, immersing the nozzle with the head droplet below the coagulation bath surface. Next, move upwards by 7 mm at a speed of 10 mm / s, allowing the nozzle to uniformly leave the coagulation bath and rise to the initial height. As the nozzle moves upwards, the dispersion is extruded while being sheared by the fluid in the coagulation bath, creating a tail-like trail above the head droplet, forming a complete tadpole shape. As the nozzle moves upwards away from the coagulation bath surface, the tadpole-shaped gel automatically falls from the nozzle and is completely submerged in the coagulation bath. This programmed nozzle displacement process is repeated to achieve batch preparation of the tadpole-shaped gel. The fallen tadpole-shaped gel is then immersed in the coagulation bath for 30 minutes to allow it to fully solidify, yielding tadpole-shaped graphene oxide gel.

[0070] 2. A 100-mesh nylon mesh was used to wrap the bottom of a glass filter cup. A coagulation bath containing graphene oxide gel was poured into the filter cup, allowing the coagulation bath to filter out, while the gel was retained on the nylon mesh. The apparatus was placed in a vacuum oven at 60 °C and vacuumed (pressure 0.1 kPa) for 6 h to allow the residual solvent in the coagulation bath to fully evaporate, resulting in dried graphene oxide aggregates. The carbon-to-oxygen ratio of the dried graphene oxide was 2.1.

[0071] 3. The dried graphene oxide aggregates obtained in step 2 are immersed in DMF for swelling for 30 minutes. The aggregates gradually swell into a regular tadpole shape, resulting in tadpole-shaped graphene oxide aggregates with a width and length of 2 mm, as shown below. Figure 2As shown, the aggregates have a tadpole-shaped outline with smooth edges, and the interior exhibits the characteristic liquid crystal texture of graphene oxide, with a carbon-to-oxygen ratio of 2.1. Further, the aggregates were placed in a vacuum oven at 60 °C and 0.1 kPa to completely remove DMF. During the desorption-adsorption of DMF molecules, the volume change rate of the aggregates reached as high as 96%, the Young's modulus changed from 13 kPa to 4 GPa, and the shape recovery rate reached as high as 92%. Figure 3-5 As shown.

[0072] Example 3: 1. Take 40 mL of a 4 mg / g graphene oxide DMSO dispersion and load it into a 50 mL syringe equipped with a three-nozzle nozzle. The three nozzles are arranged in an equilateral triangle, with an inner diameter of 200 μm for each nozzle and a spacing of 2 mm between adjacent nozzles. Mount the syringe on a programmed robotic arm, with the nozzles initially positioned 4 mm above the surface of the coagulation bath. The coagulation bath is a 5:5 volume ratio mixture of ethanol and methanol. Extrude the dispersion at a rate of 1 mL / min. The droplets extruded from the three nozzles coalesce at the contact interface, forming triangular discs upon landing on the coagulation bath surface. Immerse the material in the coagulation bath for 40 min to allow it to fully solidify, yielding a triangular disc-shaped graphene oxide gel.

[0073] 2. A 40-mesh nylon mesh was used to cover the bottom of a glass filter cup. A coagulation bath containing graphene oxide gel was poured into the filter cup, allowing the coagulation bath to filter out, while the gel was retained on the nylon mesh. The apparatus was placed in a vacuum oven at 10 °C under vacuum (1 kPa pressure) for 12 h to allow the residual solvent in the coagulation bath to fully evaporate, resulting in dried graphene oxide aggregates. The carbon-to-oxygen ratio of the dried graphene oxide was 1.9.

[0074] 3. The dried graphene oxide aggregates obtained in step 2 were immersed in ethylene glycol for swelling for 2 hours. The aggregates gradually swelled into regular triangular disc shapes, resulting in triangular disc-shaped graphene oxide aggregates with a side length of 3 mm, as shown below. Figure 2 As shown, the aggregates have a triangular disc-shaped profile with smooth edges and a cross-sectional thickness of 1 mm. The interior exhibits a characteristic liquid crystal texture of graphene oxide, with a carbon-to-oxygen ratio of 1.9. Further, the aggregates were placed in a vacuum oven at 60 °C and 0.1 kPa to completely remove ethylene glycol. During the desorption-adsorption of ethylene glycol molecules, the aggregates underwent reversible large shrinkage and expansion, with a volume change rate of 94% during the shrinkage and expansion process, a Young's modulus change range of 40 kPa to 8 GPa, and a shape recovery rate of 94%.

[0075] The above embodiments describe in detail the structure, features, and effects of the present invention. The above description is only a preferred embodiment of the present invention. Any changes made in accordance with the concept of the present invention, or equivalent embodiments modified to have equivalent changes, shall still fall within the scope of protection of the present invention if they do not exceed the scope covered by the specification.

[0076] Although embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, variations, and modifications are possible without departing from the spirit and scope of the invention and the appended claims. Therefore, the scope of the invention is not limited to the contents disclosed in the embodiments.

Claims

1. A graphene oxide-based stimulus-responsive functional material, characterized in that, It includes a core and a shell, the shell enclosing the core, the core being a network structure formed by overlapping graphene oxide sheets, and the shell being formed by overlapping graphene oxide sheets having a wrinkled structure.

2. The stimulus-responsive functional material according to claim 1, characterized in that, The network structure is a porous network structure or a dense network structure.

3. The stimulus-responsive functional material according to claim 2, characterized in that, The porous network structure contains a polar solvent.

4. The stimulus-responsive functional material according to claim 3, characterized in that, The folded structure is either a hilly structure with small contractions or a ridge structure with large contractions.

5. A driving body, characterized in that, The invention includes a plurality of stimulus-responsive functional materials according to any one of claims 1 to 4, wherein the driving body is an amorphous graphene oxide aggregate, and the driving body is clover-shaped, trefoil-shaped, triangular, beaded, ellipsoidal, or tadpole-shaped.

6. The driving body according to claim 5, characterized in that, The driving body includes a first stimulus-responsive functional material and a second stimulus-responsive functional material connected to each other, and the first stimulus-responsive functional material and the second stimulus-responsive functional material have different expansion amounts in at least one direction in the same polar solvent, and the second stimulus-responsive functional material is one or more.

7. The driving body according to claim 6, characterized in that, The actuators can be applied to biomimetic machines, biological tissue engineering, wastewater treatment, sensing, and drug delivery.

8. A method for preparing the driving body according to any one of claims 5 to 7, characterized in that, The method includes the following steps: using a nozzle with one or more nozzles arranged in a specific pattern, fixing the nozzle on a robotic arm, controlling the movement of the nozzle, dripping graphene oxide dispersion into a non-ionic coagulation bath through the nozzle to form graphene oxide gel, controlling the spacing between the nozzles to allow the interface between the graphene oxide droplets to fuse, thereby transforming the fluid shape into various complex shapes, forming heteromorphic graphene oxide gels with different densities but an integral structure; filtering and drying the heteromorphic graphene oxide gel to form a dry material, and soaking and swelling the dry material with a polar solvent to obtain the driving body.

9. The method according to claim 8, characterized in that, It also includes the removal of polar solvents, which involves placing the material in a vacuum oven and drying it at 20 ℃ to 60 ℃, with a drying pressure of 0.1 kPa to 101 kPa. The degree of removal is controlled by controlling the drying temperature and pressure.

10. The method according to claim 9, characterized in that, The length of the driving body is 1 mm to 10 mm, the volume change rate of the driving body during contraction and expansion is ≥90%, the Young's modulus of the driving body varies from 10 kPa to 10 GPa, and the multi-level shape recovery rate of the driving body is ≥90%.

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