Super-flexible bimodal nanocellulose ionic liquid gel as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of ionic liquid gel preparation, and particularly relates to super-flexible bimodal nanocellulose ionic liquid gel as well as a preparation method and application thereof. The nanocellulose ionic liquid gel is composed of covalent cross-linked polyacrylamide, a rod-like cellulose nanocrystal and an ionic liquid, the nanocellulose ionic liquid gel has dual modes of structural color and electric signal response at the same time. The nanocellulose ionic liquid gel combines dynamic structural color and ionic conductivity, has excellent mechanical properties, rapid electrical signal response and environmental stability, endows bionic ion skin with photoelectric dual-mode signal output capability, and can be used for real-time human motion tracking.

Description

Technical Field

[0001] This invention belongs to the technical field of ionic liquid gel preparation, specifically relating to an ultra-flexible bimodal nanocellulose ionic liquid gel, its preparation method, and its application. Background Technology

[0002] Ionic liquid gels, as functional materials that immobilize ionic liquids within a three-dimensional polymer network, have shown broad application prospects in flexible electronics, energy storage, and sensors in recent years. However, traditional ionic liquid gel systems are mostly limited to a single functional mode, unable to simultaneously integrate multiple advanced properties, particularly the dual-modal fusion of electrochemical and optical properties, which severely restricts their application potential in high-end technologies. Traditional ionic liquid gel materials are particularly inadequate in terms of optical functional integration. Most research focuses on improving the electrochemical performance or environmental stability of the materials, with very little attention paid to the introduction of optical properties. Although a few studies have recently attempted to introduce structural colors into ionic liquid gel systems, these attempts face numerous technical bottlenecks, such as optical signal distortion due to deformation and performance degradation under humid environments.

[0003] Research on CNC-based ionic liquid gel systems is still in its early stages. For example, the literature Shan C, Che M, Cholewinski A, et al. Multifunctional nanocrystalline cellulose ionogels towards tough and sustainable materials [J]. Cell Reports Physical Science, 2023, 4(8): 101511. describes the preparation of ionic liquid gels by forming a cross-linked polymer network of acrylamide and acrylic acid. Although a certain balance between rigidity and elasticity is achieved, the network brittleness problem still exists, and the traditional blending strategy makes it difficult to retain the chiral phase structure of CNC. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of current ionic liquid gels, such as insufficient flexibility and the fact that they only have a single mode, by providing an ultra-flexible bimodal nanocellulose ionic liquid gel, its preparation method, and its applications.

[0005] This invention is based on the unique rod-shaped crystal structure of cellulose nanocrystals (CNC), which exhibit excellent mechanical strength, significant optical anisotropy, and chiral liquid crystal self-assembly characteristics. Therefore, cellulose nanocrystals are innovatively introduced into ionic liquid gels to obtain nanocellulose ionic liquid gels. These gels have the function of simulating the dynamically tunable guanine crystal photon array and flexible dermal matrix in biological systems.

[0006] The technical solution of this invention is as follows: An ultra-flexible bimodal nanocellulose ionic liquid gel is composed of covalently cross-linked polyacrylamide, rod-shaped cellulose nanocrystals, and an ionic liquid.

[0007] This nanocellulose ionic liquid gel possesses a self-assembled core-shell structure. Cellulose nanocrystals form rigid cores with a chiral nematic structure, resembling Bouligand structures. Polyacrylamide chains are wound around the surface of these rigid cores, forming a soft matrix coating with a cross-linked network structure. The ionic liquid acts as a matrix, uniformly dispersed between the cellulose nanocrystal layers. The ionic liquid also acts as a lubricant, enhancing the interlayer flowability of the CNC (Cellular Nanocrystalline) gel.

[0008] The nanocellulose ionic liquid gel exhibits both structural color and electrical signal response in a dual-mode configuration.

[0009] In this nanocellulose ionic liquid gel, the dry weight ratio of cellulose nanocrystals:acrylamide monomer of polyacrylamide:ionic liquid is (15-20):(35-40):(50-60).

[0010] At the molecular level, hydrogen bonding and electrostatic interactions between cellulose nanocrystals (CNCs), polyacrylamide (PAM), and ionic liquids (ILs) drive the self-assembly of the core-shell structure. The rigid nuclei of the Bruggon structure formed by the oriented alignment of cellulose nanocrystals provide a rigid framework for the gel and also offer abundant interfacial hydrogen bonding sites. Combined with the strong hydrogen bonding tendency of the ionic liquids that permeate within and act as lubricants, the nanocellulose ionic liquid gel structure simultaneously incorporates chemical crosslinking and physical crosslinking mediated by multilevel hydrogen bonds.

[0011] This unique multi-level structure induces the polyacrylamide chains to slip under mechanical stress, triggering a rearrangement of cellulose nanocrystals, thereby achieving multi-level energy dissipation from the molecular to the macroscopic scale in the nanocellulose ionic liquid gel. Specifically: The physically cross-linked polyacrylamide network formed by chain entanglement restricts the initial network deformation. When the material is stretched, the polyacrylamide chains untangle and hydrogen bonds break, but the cross-linked domains of cellulose nanocrystals can still maintain strength and elasticity under small deformation along the direction of force. At the microscale, external force triggers the unwinding and reorientation of the Bouligand structured cellulose nanocrystals along the stress axis, followed by delamination, bridging, pull-out, and eventually fracture, forming a rough and loose layered fracture surface.

[0012] This dominant mechanism, in conjunction with the multiple hydrogen bond breaking-recombination process as secondary sacrificial bonds, contributes to the gel's superior mechanical properties.

[0013] Under natural light, the nanocellulose ionic liquid gel appears translucent. Polarized optical microscopy (POM) images show strong birefringence and a distinct fingerprint structure, indicating the preservation of the chiral nematic phase structure of the cellulose nanocrystals within the ionic liquid gel. The nanocellulose ionic liquid gel exhibits vibrant structural colors, and cross-sectional SEM images show that the long axes of the nanocrystals rotate counterclockwise around a vector perpendicular to the surface. The chiral nematic phase is uniformly and clearly defined throughout the fracture edges.

[0014] During the research process, this invention also discovered that while increasing the content of acrylamide monomer in polyacrylamide can improve the hydrogen bond density between polyacrylamide, cellulose nanocrystals, and ionic liquids in the gel network to some extent, the rigidity and brittleness of the gel network increase when the acrylamide monomer content exceeds 40%. During stretching, the lubricating effect of the ionic liquid on molecular chain slippage within the gel weakens, resulting in a decrease in the fracture strain of the ionic liquid gel with further increases in acrylamide content.

[0015] Although the Brugon structure formed by the self-assembly of cellulose nanocrystals can enhance the rigidity of ionic liquid gels, and the internal support of the ionic liquid gel network increases with the increase of cellulose nanocrystal content, thereby improving the Young's modulus of the ionic liquid gel, the study found that when the concentration of cellulose nanocrystals exceeds 20%, the structure of the ionic liquid gel becomes porous, causing a simultaneous decrease in Young's modulus and elongation at break. Furthermore, the electrostatic repulsion between the negatively charged cellulose surface and the ionic liquid also contributes to a decrease in the density of the gel structure.

[0016] An appropriate amount of ionic liquid can enhance the mechanical strength of ionic liquid gels by improving chain lubrication. However, excessive ionic liquid as a solvent can lead to overstretching of the polymer network, causing some areas of the internal network structure of the gel to loosen, triggering the disentanglement of polyacrylamide chains, and ultimately resulting in increased gel rigidity and decreased flexibility.

[0017] In this invention, the ultra-flexible bimodal nanocellulose ionic liquid gel has a microstructure of a left-handed helical layered structure with a pitch of 1.2-1.4 μm.

[0018] In this invention, the ultra-flexible bimodal nanocellulose ionic liquid gel has an elongation at break of 435%-2400%; when the tensile strain is ≤140%, the nanocellulose ionic liquid gel exhibits a dynamic structural color change from deep red to yellow to green.

[0019] In this invention, the ultraflexible bimodal nanocellulose ionic liquid gel has an electrical conductivity of 0.35-0.40 mS·cm. ﹣1 Under tensile strain of 200%-400%, the response time of the electrical signal is ≤380ms and the recovery time is ≤500ms.

[0020] like Figure 4 As shown, when the strain increases from 50% to 250% at a rate of 20%, the resistance increases accordingly, and the response curves for the five cycles are basically consistent. This result indicates that the nanocellulose ionic liquid gel exhibits highly sensitive and stable response characteristics in both small and large strain detection ranges.

[0021] The strain factor of the nanocellulose ionic liquid gel is 0.53 in the strain range where the tensile strain is less than 75%; 0.17 in the strain range where the tensile strain is greater than or equal to 75% and less than 150%; and 0.28 in the strain range where the tensile strain is greater than or equal to 150% and less than or equal to 200% (e.g., ...). Figure 3 (As shown). This multi-level sensitivity characteristic enables it to simultaneously detect subtle physiological signals and large joint movements.

[0022] The ultra-flexible bimodal nanocellulose ionic liquid gel exhibits a reversible change in relative resistance, enabling quantitative strain sensing via electrical signals. The strain factor (GF) of the strain sensor can be calculated using the following formula: GF = (∆R / R0) / ε, where R0 is the initial resistance, R is the test resistance, and ε is the tensile strain. It is evident that this ionic liquid gel demonstrates excellent electrochemical response characteristics.

[0023] Traditional methods for preparing ionic liquid gels involve directly mixing the ionic liquid with a matrix material. In this method, the ionic liquid gel is obtained by expanding the matrix material to form a network that confines the ionic liquid. However, the compatibility between ionic liquids and commercially available polymers limits the use of this method. The preparation method described in this invention solves the problem of monomer molecules not dissolving in ionic liquids and effectively avoids complex gelation reactions within the ionic liquid.

[0024] A method for preparing an ultra-flexible bimodal nanocellulose ionic liquid gel includes the following steps: (1) The cellulose nanocrystal suspension, acrylamide and crosslinking agent were mixed and stirred at room temperature (20-35℃) for at least 12 hours. After adding the photoinitiator and stirring evenly, the mixture was evaporated and concentrated. It was then sealed and equilibrated for at least 7 days and cured by ultraviolet light to obtain an ordered hydrogel. The evaporation, concentration and sealing equilibration were carried out in the dark to prevent the precursor solution from polymerizing prematurely under natural light.

[0025] The CNC suspension used is obtained by acid hydrolysis of cellulose. The acid hydrolysis process is as follows: the cellulose raw material is acid hydrolyzed, and after completion, a large amount of deionized water is added to terminate the reaction. After standing and centrifugation, the resulting precipitate is dialyzed until the pH is close to neutral, and then ultrasonically concentrated to obtain a CNC suspension of a certain concentration. The cellulose raw material is cotton fiber or filter paper pulp, more preferably filter paper pulp. The acid used for acid hydrolysis is hydrochloric acid or sulfuric acid, more preferably sulfuric acid; during operation, the acid hydrolysis temperature is 50-55℃, and the acid hydrolysis time is 25-35 min.

[0026] (2) Immerse the ordered hydrogel obtained in step (1) into the ionic liquid for solvent exchange twice, each time for 12 hours. After the solvent exchange is completed, place it at room temperature until the water evaporates to obtain the ionic liquid gel.

[0027] (3) The ionic liquid gel obtained in step (2) is subjected to isothermal heat treatment at 50-90℃ for 6 hours; or placed in a room temperature (20-35℃) environment for 0.5-2 months to obtain the ultra-flexible bimodal nanocellulose ionic liquid gel. After isothermal heat treatment or room temperature environment treatment, the ionic liquid gel can improve energy dissipation efficiency through the rigid support provided by the CNC crystal nucleus, the uniform dispersion promoted by the ionic liquid, and the dynamic hydrogen bond network. The unique triple synergistic effect significantly changes the mechanical properties of the ionic liquid gel, thereby achieving the control of its flexibility.

[0028] Furthermore, the dry weight ratio of the cellulose nanocrystals:acrylamide:ionic liquid is (15-20):(35-40):(50-60).

[0029] Furthermore, the dry weight ratio of the cellulose nanocrystals:acrylamide:ionic liquid is 15:40:60.

[0030] Furthermore, the amount of crosslinking agent added is 2% of the mass of acrylamide; the amount of photoinitiator used is 1% of the mass of acrylamide.

[0031] Furthermore, the crosslinking agent is polyethylene glycol diacrylate; the photoinitiator is 2-hydroxy-2-methylphenylacetone.

[0032] Furthermore, the ionic liquid is 1-butyl-3-methylimidazolium acetate ([Bmim]OA). The ionic liquid can be selected from any one of pyridine ionic liquids, imidazole ionic liquids, quaternary phosphonium ionic liquids, or quaternary ammonium salt ionic liquids. Imidazole ionic liquids or quaternary ammonium salt ionic liquids are preferred; imidazole ionic liquids are more preferred.

[0033] Applications of the above-mentioned ultra-flexible bimodal nanocellulose ionic liquid gel or the ultra-flexible bimodal nanocellulose ionic liquid gel prepared by the above preparation method in biomimetic ionic skin and human motion dual sensing.

[0034] The nanocellulose ionic liquid gel described in this invention combines dynamic structural color with ionic conductivity, endowing biomimetic ionic skin with photoelectric dual-modal signal output capability, which can be used for real-time human motion tracking.

[0035] This nanocellulose ionic liquid gel possesses excellent mechanical properties, rapid electrical signal response, and environmental stability, while maintaining conductivity and sensing capabilities under large strain. It can be used as a bio-based functional material, such as flexible electronic skin, large strain sensors, and wearable devices.

[0036] The strain sensor based on the aforementioned nanocellulose ionic liquid gel can detect human movement in real time and exhibits excellent temperature tolerance. By fixing the nanocellulose ionic liquid gel to different body parts, such as fingers, wrists, and elbows, motion signals can be detected. The gel responds differently to deformations in different areas. Furthermore, due to the excellent mechanical properties of the ionic liquid gel, the sensor maintains excellent sensitivity and stability during continuous stretching and recovery. Simultaneously, the nanocellulose ionic liquid gel displays dynamic changes in structural color as the fingers bend. This multimodal sensing of the nanocellulose ionic liquid gel opens up new directions for intelligent flexible sensing technology. By simultaneously capturing the dual signals of structural color changes and resistance changes, holographic monitoring of human movement can be achieved.

[0037] High ionic conductivity, sensitivity, and strong adhesion are key characteristics of ionic liquid gels as strain sensors. The nanocellulose ionic liquid gel described in this invention possesses universal adhesive capabilities. It can easily and tightly adhere to various substrate materials, including skin, polymers, glass, metals, and paper, by forming interactions such as van der Waals forces, hydrogen bonds, electrostatic attraction, and coordination bonds with polar groups on the substrate surface. Figure 1 (As shown).

[0038] The adhesion strength of nanocellulose ionic liquid gel on various substrates (including PVC, rubber, copper, glass, and paper) was quantitatively characterized using the overlap shear test method. Figure 2 As shown, the ionic liquid gel exhibits the highest adhesion strength on the paper surface, reaching 89.5 kPa. Such excellent adhesion properties are crucial for the application of ionic liquid gels, especially in the field of flexible sensors.

[0039] The beneficial effects of the present invention are as follows: The nanocellulose ionic liquid gel of the present invention combines dynamic structural color with ionic conductivity, and has excellent mechanical properties, fast electrical signal response and environmental stability, giving the biomimetic ionic skin photoelectric dual-modal signal output capability, which can be used for real-time human motion tracking.

[0040] When the aforementioned nanocellulose ionic liquid gel is connected to the circuit, the LED light immediately illuminates. As the CNC cholesteric phase structure unwinds during the stretching process of the nanocellulose ionic liquid gel, the light intensity gradually decreases. This phenomenon stems from the narrowing of the ion conduction channels and the elongation of the ion migration path, which in turn increases the resistance of the ionic liquid gel. Thanks to the excellent self-healing properties of this ionic liquid gel, broken fragments spontaneously rebuild the conductive path upon contact, thus achieving instantaneous switching of the bulb's illumination. The corresponding electrical response time and recovery time were quantified as 20 milliseconds and 30 milliseconds, respectively, demonstrating ultra-fast circuit repair capabilities.

[0041] The preparation method utilizes the property of ionic liquids to dissolve cellulose. By controlling the solvation temperature and time, in-situ surface solvation of CNC within the gel is achieved, thereby constructing an ultra-flexible nanocellulose ionic liquid gel. The in-situ solvation strategy significantly improves the elongation at break of the gel (up to 2400%), realizing a transformation from tough to ultra-flexible mechanical properties.

[0042] During solvation, the chiral nematic phase structure of the nanocellulose ionic liquid gel transforms from long-range ordered to short-range ordered, while the reconstruction of the hydrogen bond network enhances its conductivity. The ultraflexibility of the nanocellulose ionic liquid gel is mainly attributed to a triple synergistic enhancement mechanism: CNC crystal nuclei provide rigid support, ionic liquids promote uniform dispersion, and dynamic hydrogen bond networks improve energy dissipation efficiency.

[0043] The coordination of ionic liquid anions with cellulose hydroxyl groups promotes the breaking of β-1,4 glycosidic bonds on the surface, leading to the layer-by-layer exfoliation of short-chain cellulose on the CNC surface. Simultaneously, the regenerated molecular chains form a dynamic sacrificial bond network and flexible molecular chain segments with the host network through hydrogen bonds and van der Waals forces, increasing the gel's flexibility. The ultra-flexible nanocrystalline cellulose ionic liquid gel retains the ordered structure of cellulose nanocrystals while achieving a maximum elongation at break of 2400%. The gel exhibits excellent electrical response characteristics, and as a strain sensor, its signal transmission is stable under high strains of 200%-400% (e.g., ...). Figure 5 (As shown).

[0044] Meanwhile, the ultra-flexible nanocellulose ionic liquid gel exhibits rapid response capability, with a response time of only 380ms and a recovery time of 500ms (e.g., Figure 6 (As shown). The shorter response time is beneficial for the practical application of ultra-flexible ionic liquid gel strain sensors.

[0045] The ultra-flexible ionic liquid gel sensor described in this invention exhibits good stability, reliability, and large strain detection capability, and has application potential in the field of flexible electronics that requires high stretchability.

[0046] This invention creatively constructs an ionic liquid gel network using renewable and biodegradable cellulose nanocrystals (CNCs) as the core, improving the preparation method of traditional petroleum-based polymer ionic liquid gels and significantly reducing environmental pollution. It develops an ionic liquid gel with both electro-optical dual-modal responses, solving the technical challenge of synergistically optimizing the mechanical properties and electrical response characteristics of bio-based functional materials. Utilizing the optical anisotropy of CNCs and the conductivity of ionic liquids, it achieves synchronous output of electrical signals (such as resistance changes) and optical signals (such as structural color changes). The obtained ionic liquid gel possesses comprehensive advantages such as structural order, mechanical tunability, rapid electrical response, and environmental stability, demonstrating significant industrial application value in fields such as flexible electronic skin, large strain sensing devices, and wearable smart devices. This technical solution provides a new environmentally friendly manufacturing paradigm for the development of high-performance bio-based functional materials, exhibiting significant technological advancements in green manufacturing and performance optimization.

[0047] Therefore, the ultra-flexible ionic liquid gel described in this invention has good mechanical properties, adhesion properties, and electrical conductivity, and shows application potential in the field of flexible strain sensors. Attached Figure Description

[0048] Figure 1 This is a schematic diagram illustrating the adhesive properties of the nanocellulose ionic liquid gel of the present invention to different materials.

[0049] Figure 2 The adhesion strength of the nanocellulose ionic liquid gel described in this invention to various materials.

[0050] Figure 3 The strain-resistance response curve of the nanocellulose ionic liquid gel described in this invention is given by the strain factor GF.

[0051] Figure 4 The relative resistivity of the nanocellulose ionic liquid gel described in this invention under different tensile strains (50-200%) change.

[0052] Figure 5 The present invention relates to the tensile electrical signal sensing of the nanocellulose ionic liquid gel under strains of 200% (a), 300% (b), and 400% (c).

[0053] Figure 6 The electrical signal response and recovery time of the nanocellulose ionic liquid gel described in this invention.

[0054] Figure 7 The images are POM and SEM images of the nanocellulose ionic liquid gels of Examples 1-2 and Comparative Examples 1-3.

[0055] Figure 8 Fourier transform infrared (FT-IR) spectra of the gels of Example 1 and Comparative Example 6.

[0056] Figure 9 The X-ray diffraction (XRD) patterns of the gels of Example 1 and Comparative Example 6 are shown.

[0057] Figure 10 This is the EDS spectrum of the nanocellulose ionic liquid gel described in this invention.

[0058] Figure 11 The tensile stress-strain curves of the ionic liquid gels in Examples 1, 3 and Comparative Example 4 without heat treatment or at room temperature are shown.

[0059] Figure 12 The tensile stress-strain curves are shown for the ionic liquid gels in Examples 1-2 and Comparative Examples 1-3 when they were not heat-treated or placed at room temperature.

[0060] Figure 13 The tensile stress-strain curves of the ionic liquid gels in Examples 1, 4 and Comparative Example 5 without heat treatment or at room temperature are shown.

[0061] Figure 14 The diagram shows the toughness and Young's modulus of the ionic liquid gels in Examples 1, 3 and Comparative Example 4 when they were not heat-treated or placed at room temperature.

[0062] Figure 15 The diagram shows the toughness and Young's modulus of the ionic liquid gels in Examples 1-2 and Comparative Examples 1-3 when they were not heat-treated or placed at room temperature.

[0063] Figure 16 The diagram shows the toughness and Young's modulus of the ionic liquid gels in Examples 1, 4 and Comparative Example 5 when they were not heat-treated or placed at room temperature.

[0064] Figure 17 This is a stretched optical image of the nanocellulose ionic liquid gel described in this invention.

[0065] Figure 18 The tensile stress-strain curves are shown for the ultra-flexible bimodal nanocellulose ionic liquid gels obtained after being left to stand at room temperature in Examples 1, 5, and 6, and for the ionic liquid gel obtained in Comparative Example 7.

[0066] Figure 19 The tensile stress-strain curves are shown for the ultra-flexible bimodal nanocellulose ionic liquid gels obtained after isothermal heat treatment in Examples 7, 8, and 9, and the ionic liquid gel obtained in Comparative Example 7.

[0067] Figure 20 Mechanochromatic optical photographs and ultraviolet reflectance spectra of the nanocellulose ionic liquid gel prepared in Example 1 under different strains.

[0068] Figure 21 The images show motion electrical signal sensing of the nanocellulose ionic liquid gel prepared in Example 1 at different parts of the body; where (a) is the finger; (b) is the wrist; and (c) is the elbow.

[0069] Figure 22 This is an optical photograph showing the structural color change of the nanocellulose ionic liquid gel at a joint during tensile motion in a multimodal sensing application of the nanocellulose ionic liquid gel prepared in Example 1. Detailed Implementation

[0070] The technical solution of the present invention will now be described in detail with reference to the accompanying drawings.

[0071] 1. Monomers: Acrylamide (AM) was purchased from Aladdin; all were of analytical grade. Ionic liquid: 1-Butyl-3-methylimidazolium acetate ([Bmim]OA) was purchased from the Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences; purity was 98%. Photoinitiator: 2-hydroxy-2-methylphenylacetone and crosslinking agent: polyethylene glycol diacrylate (PEGDA) were purchased from Shanghai Maclean Biochemical Technology Co., Ltd. All chemicals were used without further purification. Deionized water was used in all experimental procedures.

[0072] 2. The process flow for preparing cellulose nanocrystals (CNCs) suspension by sulfuric acid hydrolysis is as follows: First, the cellulose raw material (such as cotton fiber or filter paper pulp) is pretreated. Under constant temperature water bath conditions of 50-55℃, the raw material is mixed with 64wt% concentrated sulfuric acid in a certain proportion and mechanically stirred for 30 min. Then, excess deionized water is quickly added to quench the reaction. After standing precipitation to promote phase separation, the precipitate is collected and subjected to gradient centrifugation. The centrifuged product is purified by dialysis until the pH of the system is close to neutral. Finally, a CNCs suspension of a certain concentration is obtained by ultrasonic treatment. The suspension is stored at a low temperature of 4℃ to maintain its stability.

[0073] 3. Polarized light images: taken using an Axioscope 5 microscope (Zeiss, Germany).

[0074] 4. Cross-sectional scanning electron microscope images: Characterization was performed using a Regulus 8220 field emission scanning electron microscope (FE-SEM, Hitachi, Japan).

[0075] 5. Ultraviolet-Vis Spectroscopy: C2600 UV-Vis spectrophotometer (Shimadzu, Japan) was used in reflectance mode for C2600 UV-Vis spectrophotometry. x Py I z The ionic liquid gel was tested.

[0076] 6. Mechanical property testing: The tensile stress and strain of the ionic liquid gel were recorded on a WDW-05J universal testing machine (Jinan Tianchen, China) at a tensile speed of 10 mm / min.

[0077] 7. Electrical signal sensing performance test: Tested using a CHI760E electrochemical workstation (Shanghai Chenhua).

[0078] Example 1 The ultra-flexible bimodal nanocellulose ionic liquid gel is composed of covalently cross-linked polyacrylamide, rod-shaped cellulose nanocrystals, and ionic liquid.

[0079] This nanocellulose ionic liquid gel has a self-assembled core-shell structure; wherein, cellulose nanocrystals form rigid crystal nuclei with chiral nematic structures; polyacrylamide chains are wrapped around the surface of the rigid crystal nuclei of cellulose nanocrystals to form a soft matrix coating shell with a cross-linked network structure; and ionic liquid is uniformly dispersed between the layers of cellulose nanocrystals as a matrix.

[0080] In this nanocellulose ionic liquid gel, the dry weight ratio of cellulose nanocrystals:acrylamide monomer of polyacrylamide:ionic liquid is 15:40:60.

[0081] The specific steps for preparing the ultra-flexible bimodal nanocellulose ionic liquid gel are as follows: (1) First, 4.41 g of cellulose nanocrystal suspension with a mass fraction of 6.8 wt% was mixed with 0.8 g of acrylamide and stirred at room temperature for 2 h.

[0082] Then, add 0.16 g of a 10 wt% crosslinking agent polyethylene glycol diacrylate solution and continue stirring for 10 h.

[0083] Add 0.008g of the photoinitiator 2-hydroxy-2-methylphenylacetone and stir for 3h to obtain the hydrogel precursor solution.

[0084] The obtained hydrogel precursor solution was placed in a dark chamber at room temperature (35°C) for evaporation-induced self-assembly until the concentration of CNC in the hydrogel precursor solution was 10 wt%, thus obtaining the hydrogel precursor.

[0085] The hydrogel precursor was sealed and stored horizontally in a light-proof environment for 7 days to equilibrate. After equilibration, it was placed under a 100W UV lamp and irradiated for 10 seconds to carry out photopolymerization, thus obtaining an ordered hydrogel.

[0086] (2) The ordered hydrogel obtained in step (1) was immersed in 1.2 g of 40 wt% ionic liquid 1-butyl-3-methylimidazolium acetate solution for solvent exchange. The solvent exchange was performed twice, each time for 12 h. The gel after solvent exchange was placed at room temperature until the water evaporated completely to obtain the ionic liquid gel.

[0087] (3) The ionic liquid gel obtained in step (2) is placed in a room temperature environment of 35°C for 2 months to obtain the ultra-flexible bimodal nanocellulose ionic liquid gel.

[0088] The nanocellulose ionic liquid gel obtained in this embodiment can lift a 500g weight with only 0.3g of the gel, reaching 1600 times its own weight.

[0089] The nanocellulose ionic liquid gel has a strength of 0.8 MPa, a Young's modulus of 1.1 MPa, an elongation at break of 437%, and a toughness of 900 kJ / m. 3 Compared to the nanocellulose-polyacrylamide hydrogel of Comparative Example 6, the strength was increased by 3.9 times; the elongation at break was increased by 2.0 times; and the toughness was increased by 9.8 times.

[0090] Figure 8 In the middle, at 2900cm ﹣1 A CH stretching vibration peak of the -CH2 group appears at 1057 cm⁻¹. ﹣1 The CO stretching vibration peak at 1147 cm⁻¹, and the peak at 1147 cm⁻¹. ﹣1 The COC framework vibration peaks at 1563 cm⁻¹ are characteristic absorption peaks of cellulose nanocrystals (CNC). ﹣1 The absorption peak at that point corresponds to the imidazole ring vibration of the ionic liquid cation.

[0091] pass Figure 8 It can be seen that in the nanocellulose ionic liquid gel described in this invention, the -OH absorption peak of CNC is from 3341 cm⁻¹. ﹣1 (Comparative Example 6 hydrogel) shifted to 3336cm ﹣1 This indicates that intramolecular / intermolecular hydrogen bonds partially dissociate, subsequently forming a strong hydrogen bond network between the hydroxyl groups, ionic liquid functional groups, and PAM amide groups on the CNC surface. Simultaneously, the C=O stretching vibration peak of the amide increases from 1665 cm⁻¹. ﹣1 (Comparative Example 6 hydrogel) Blue shifted to 1672 cm⁻¹ ﹣1 This indicates that the hydrogen bonds originally formed between the amide groups on the PAM chains and hydroxyl or other groups have been broken or weakened. This change in the hydrogen bonding environment forces the PAM molecular chains to adjust their spatial arrangement to achieve a new energy-stable state, resulting in conformational rearrangement. These dynamic hydrogen bond interactions not only maintain structural stability but also endow the gel network with excellent energy dissipation capabilities.

[0092] exist Figure 9 In this invention, the nanocellulose ionic liquid gel exhibits characteristic crystallization peaks of cellulose type I at 22.6° (200), 16.4° (110) and 14.8° (110), confirming that the integrity of its crystal structure is maintained despite the introduction of polyacrylamide (PAM) and ionic liquid (IL).

[0093] pass Figure 10 It can be seen that carbon (C), oxygen (O), nitrogen (N), and sulfur (S) are spatially uniformly distributed in the nanocellulose ionic liquid gel. This uniform distribution contributes to improving the conductivity of the ionic liquid gel. Furthermore, the elemental spectra show a chiral nematic phase distribution, further confirming the successful introduction of an ordered structure into the gel.

[0094] pass Figure 18 As can be seen, the ultra-flexible bimodal nanocellulose ionic liquid gel described in this embodiment, after being solvated for 2 months, can achieve a strain rate of 2400%.

[0095] from Figure 20 Observations revealed that the ultra-flexible bimodal nanocellulose ionic liquid gel exhibited a unique strain-dependent structural color response during tensile testing. In uniaxial tensile testing, as the strain increased from 0% to 140%, the CPI showed a dynamic structural color change from deep red through yellow to green, with the UV-Vis reflection peak continuously blue-shifting from 670 nm to 520 nm. Furthermore, the width of the reflection peak increased with increasing strain.

[0096] from Figure 21 Observations show that when the ultra-flexible bimodal nanocellulose ionic liquid gel is fixed to different body parts, such as fingers, wrists, and elbows, it can detect human motion signals. The gel responds to different electrical signals in response to deformation at different locations.

[0097] Example 2 In the ultra-flexible bimodal nanocellulose ionic liquid gel, the dry weight ratio of cellulose nanocrystals:acrylamide monomer of polyacrylamide:ionic liquid is 15:35:60.

[0098] The difference from Example 1 is that in step (1) of the preparation method, 4.41 g of cellulose nanocrystal suspension with a mass fraction of 6.8 wt% is mixed with 0.7 g of acrylamide.

[0099] Add 0.14 g of a 10 wt% crosslinking agent, polyethylene glycol diacrylate solution.

[0100] The others are the same as in Example 1.

[0101] Example 3 In the ultra-flexible bimodal nanocellulose ionic liquid gel, the dry weight ratio of cellulose nanocrystals: acrylamide monomer of polyacrylamide: ionic liquid is 20:40:60.

[0102] The difference from Example 1 is that in step (1) of the preparation method, 5.88g of cellulose nanocrystal suspension with a mass fraction of 6.8wt% is mixed with 0.8g of acrylamide.

[0103] The others are the same as in Example 1.

[0104] Example 4 In the ultra-flexible bimodal nanocellulose ionic liquid gel, the dry weight ratio of cellulose nanocrystals:acrylamide monomer of polyacrylamide:ionic liquid is 15:40:50.

[0105] The difference from Example 1 is that in step (2) of the preparation method, solvent exchange is performed by immersing the sample in a 1.0 g solution of 1-butyl-3-methylimidazolium acetate with a mass fraction of 40 wt%.

[0106] The others are the same as in Example 1.

[0107] Example 5 The difference from Example 1 is that in step (3) of the preparation method, the obtained ionic liquid gel is placed in a room temperature environment of 35°C for 0.5 months to obtain the ultra-flexible bimodal nanocellulose ionic liquid gel.

[0108] The others are the same as in Example 1.

[0109] Example 6 The difference from Example 1 is that in step (3) of the preparation method, the obtained ionic liquid gel is placed in a room temperature environment of 35°C for 1 month to obtain the ultra-flexible bimodal nanocellulose ionic liquid gel.

[0110] The others are the same as in Example 1.

[0111] Example 7 The difference from Example 1 is that in step (3) of the preparation method, the obtained ionic liquid gel is subjected to constant temperature heat treatment at 50°C for 6 hours to obtain the ultra-flexible bimodal nanocellulose ionic liquid gel.

[0112] The others are the same as in Example 1.

[0113] Example 8 The difference from Example 1 is that in step (3) of the preparation method, the obtained ionic liquid gel is subjected to constant temperature heat treatment at 70°C for 6 hours to obtain the ultra-flexible bimodal nanocellulose ionic liquid gel.

[0114] The others are the same as in Example 1.

[0115] Example 9 The difference from Example 1 is that in step (3) of the preparation method, the obtained ionic liquid gel is subjected to constant temperature heat treatment at 90°C for 6 hours to obtain the ultra-flexible bimodal nanocellulose ionic liquid gel.

[0116] The others are the same as in Example 1.

[0117] pass Figure 19 As can be seen, the ultra-flexible bimodal nanocellulose ionic liquid gel obtained by constant temperature heat treatment at 90℃ described in this embodiment can achieve a strain rate of 1300%.

[0118] Comparative Example 1 In this comparative example of nanocellulose ionic liquid gel, the dry weight ratio of cellulose nanocrystals: acrylamide monomer of polyacrylamide: ionic liquid is 15:25:60.

[0119] The difference from Example 1 is that in step (1) of this comparative preparation method, 4.41 g of cellulose nanocrystal suspension with a mass fraction of 6.8 wt% is mixed with 0.5 g of acrylamide.

[0120] Add 0.10 g of a 10 wt% crosslinking agent, polyethylene glycol diacrylate solution.

[0121] The others are the same as in Example 1.

[0122] Comparative Example 2 In this comparative example of nanocellulose ionic liquid gel, the dry weight ratio of cellulose nanocrystals: acrylamide monomer of polyacrylamide: ionic liquid is 15:30:60.

[0123] The difference from Example 1 is that in step (1) of this comparative preparation method, 4.41 g of cellulose nanocrystal suspension with a mass fraction of 6.8 wt% is mixed with 0.6 g of acrylamide.

[0124] Add 0.12 g of a 10 wt% crosslinking agent, polyethylene glycol diacrylate solution.

[0125] The others are the same as in Example 1.

[0126] Comparative Example 3 In this comparative example of nanocellulose ionic liquid gel, the dry weight ratio of cellulose nanocrystals: acrylamide monomer of polyacrylamide: ionic liquid is 15:45:60.

[0127] The difference from Example 1 is that in step (1) of this comparative preparation method, 4.41 g of cellulose nanocrystal suspension with a mass fraction of 6.8 wt% is mixed with 0.9 g of acrylamide.

[0128] Add 0.18g of a 10wt% crosslinking agent, polyethylene glycol diacrylate solution.

[0129] The others are the same as in Example 1.

[0130] Comparative Example 4 In this comparative example of nanocellulose ionic liquid gel, the dry weight ratio of cellulose nanocrystals: acrylamide monomer of polyacrylamide: ionic liquid is 10:40:60.

[0131] The difference from Example 1 is that in step (1) of this comparative preparation method, 2.94 g of cellulose nanocrystal suspension with a mass fraction of 6.8 wt% is mixed with 0.8 g of acrylamide.

[0132] The others are the same as in Example 1.

[0133] Comparative Example 5 In this comparative example of nanocellulose ionic liquid gel, the dry weight ratio of cellulose nanocrystals: acrylamide monomer of polyacrylamide: ionic liquid is 15:40:70.

[0134] The difference from Example 1 is that in step (2) of this comparative preparation method, 1.4 g of 40 wt% [amount of substance] is immersed. Solvent exchange was carried out in a solution of the ionic liquid 1-butyl-3-methylimidazolium acetate.

[0135] The others are the same as in Example 1.

[0136] Comparative Example 6 In this comparative example, the dry weight ratio of cellulose nanocrystals to acrylamide monomer in polyacrylamide hydrogel is 15:40.

[0137] The difference from Example 1 is that the preparation method for this comparative example is as follows: (1) Mix 4.41 g of cellulose nanocrystal suspension with a mass fraction of 6.8 wt% with 0.8 g of acrylamide and stir at room temperature for 2 h.

[0138] Then, add 0.16 g of a 10 wt% crosslinking agent polyethylene glycol diacrylate solution and continue stirring for 10 h.

[0139] Then add the photoinitiator 2-hydroxy-2-methylphenylacetone and stir for 3 hours to obtain the hydrogel precursor solution.

[0140] (2) The obtained hydrogel precursor solution was placed in a dark box at room temperature (35°C) for evaporation-induced self-assembly until the concentration of CNC in the hydrogel precursor solution was 10 wt%, and the hydrogel precursor was obtained.

[0141] (3) The hydrogel precursor was sealed and stored in a light-proof environment and allowed to stand horizontally for 7 days to reach equilibrium. After the equilibrium was reached, it was placed under a 100W UV lamp and irradiated for 10 seconds to carry out photopolymerization to obtain an ordered hydrogel.

[0142] Comparative Example 7 The difference from Example 1 is that, in the preparation method steps of this comparative example, the ionic liquid gel obtained in step (2) was not placed in a room temperature (35°C) environment for 2 months.

Claims

1. A super-flexible bimodal nanocellulose ionic liquid gel, characterized in that, This nanocellulose ionic liquid gel is composed of covalently cross-linked polyacrylamide, rod-shaped cellulose nanocrystals, and ionic liquid. This nanocellulose ionic liquid gel has a self-assembled core-shell structure; wherein, cellulose nanocrystals form rigid crystal nuclei with chiral nematic structures; polyacrylamide chains are wrapped around the surface of the rigid crystal nuclei of cellulose nanocrystals to form a soft matrix coating shell with a cross-linked network structure; and ionic liquid is uniformly dispersed between the layers of cellulose nanocrystals as a matrix. The nanocellulose ionic liquid gel exhibits both structural color and electrical signal response in a dual-mode configuration. In this nanocellulose ionic liquid gel, the dry weight ratio of cellulose nanocrystals:acrylamide monomer of polyacrylamide:ionic liquid is (15-20):(35-40):(50-60).

2. The super-flexible bimodal nanocellulose ionic liquid gel of claim 1, wherein, The nanocellulose ionic liquid gel has a left-handed helical layered structure with a pitch of 1.2-1.4 μm.

3. The super-flexible bimodal nanocellulose ionic liquid gel of claim 1, wherein, The elongation at break of the nanocellulose ionic liquid gel is 435%-2400%; When the tensile strain is ≤140%, the nanocellulose ionic liquid gel exhibits a dynamic structural color change from deep red to yellow to green.

4. The ultra-flexible bimodal nanocellulose ionic liquid gel according to claim 1, characterized in that, The conductivity of the nanocellulose ionic liquid gel is 0.35-0.40 mS·cm ﹣1 ; the response time of the electrical signal under the tensile strain of 200%-400% is ≤380 ms, and the recovery time is ≤500 ms; The strain factor of the nanocellulose ionic liquid gel is 0.53 in the strain range where the tensile strain is less than 75%; 0.17 in the strain range where the tensile strain is greater than or equal to 75% and less than 150%; and 0.28 in the strain range where the tensile strain is greater than or equal to 150% and less than or equal to 200%.

5. A method for preparing an ultra-flexible bimodal nanocellulose ionic liquid gel, characterized in that, Includes the following steps: (1) Mix cellulose nanocrystal suspension, acrylamide and crosslinking agent, stir at room temperature for at least 12 hours, add photoinitiator and stir evenly, then evaporate and concentrate, seal and equilibrate for at least 7 days, and cure with ultraviolet light to obtain ordered hydrogel; (2) Immerse the ordered hydrogel obtained in step (1) in an ionic liquid for solvent exchange twice, each time for 12 hours; After the solvent exchange is complete, place it at room temperature until the water evaporates to obtain an ionic liquid gel. (3) The ionic liquid gel obtained in step (2) is subjected to constant temperature heat treatment at 50-90℃ for 6 hours; or placed in a room temperature environment for 0.5-2 months to obtain the ultra-flexible bimodal nanocellulose ionic liquid gel.

6. The method for preparing the ultra-flexible bimodal nanocellulose ionic liquid gel according to claim 5, characterized in that, The dry weight ratio of the cellulose nanocrystals:acrylamide:ionic liquid is (15-20):(35-40):(50-60); Preferably, the dry weight ratio of the cellulose nanocrystals:acrylamide:ionic liquid is 15:40:

60.

7. The method for preparing the ultra-flexible bimodal nanocellulose ionic liquid gel according to claim 5, characterized in that, The amount of crosslinking agent added is 2% of the mass of acrylamide; the amount of photoinitiator is 1% of the mass of acrylamide.

8. The method for preparing the ultra-flexible bimodal nanocellulose ionic liquid gel according to claim 5 or 7, characterized in that, The crosslinking agent is polyethylene glycol diacrylate; the photoinitiator is 2-hydroxy-2-methylphenylacetone.

9. The method for preparing the ultra-flexible bimodal nanocellulose ionic liquid gel according to claim 5, characterized in that, The ionic liquid is 1-butyl-3-methylimidazolium acetate.

10. The application of an ultra-flexible bimodal nanocellulose ionic liquid gel as described in any one of claims 1-4 or an ultra-flexible bimodal nanocellulose ionic liquid gel prepared by the preparation method described in any one of claims 5-9 in biomimetic ionic skin and human motion dual sensing.

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