Solvent-mediated rigidity-adjustable material, preparation method and application

Abstract

The invention relates to the technical field of biomimetic materials, in particular to a solvent-mediated rigidity-adjustable material, a preparation method and application. The rigidity-adjustable material comprises a base material, wherein the base material comprises a hydrophobic main chain and a spatial cross-linked network structure formed by hydrophilic side chains grafted to the hydrophobic main chain in a comb shape; the base material forms a nanoscale hard domain under the triggering of a polar or non-polar solvent, and forms a polar hardened body material or a non-polar hardened body material respectively; in the hardened body material, the size of the hard domain is in positive correlation with the surface energy of the solvent, the modulus amplification of the hardened body material relative to the matrix material is directly determined by the size of the hard domain, and the modulus amplification can reach 9.9 times; and after multiple swelling-desolventizing cycles, the modulus attenuation is less than 5%. The material provided by the invention breaks through the defects that the modulus switching range of the existing material is mostly limited to be less than 5 times, and the rigidity is improved along with the obvious reduction of the toughness, and has a wide application prospect in the fields of wearable electronics, soft robots, anti-impact protection and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of biomimetic materials, and particularly relates to a solvent-mediated rigidity-adjustable material, a preparation method and application. BACKGROUND

[0002] Rigidity-adjustable materials are the core of intelligent materials that can reversibly switch between soft and hard states, and have strategic value in the fields of wearable electronics, soft robots and impact protection. Through the instantaneous switching between "compliant state" and "load-bearing state", these materials endow the system with adaptive deformation capability and dynamic impact resistance. In nature, sea cucumbers harden their dermis when in danger, longfin fish muscles cooperatively regulate skin rigidity, and plant vascular water regulation exhibits a high degree of reversible environmental adaptation, providing a biomimetic blueprint for artificial material design. However, the current biomimetic system faces three dilemmas: the modulus switching range is mostly limited to less than 5 times, making it difficult to cope with complex dynamic loads; the strong dependence on external stimuli such as heat, light and magnetism leads to response lag and system integration barriers; more importantly, rigidity enhancement is often accompanied by a significant decrease in toughness, severely degrading the material's impact resistance and durability in humid or extreme environments.

[0003] The solvent-mediated polymer rigidity adjustment system uses solvent as the dynamic control medium, and realizes the reversible switching of polymer modulus through the cyclic process of immersion swelling and volatilization desorption (Nature Communications 2024, 15, 1587). Its core mechanism of action is manifested in two paths: in the traditional scheme, solvent penetration induces plasticization, weakening intermolecular forces and causing the material to soften. Although the intermolecular distance decreases after desorption to increase rigidity, the incomplete recovery of the molecular network results in compromised mechanical integrity (Science Advances 2023, 9, eade3240); while the improved anti-plasticization strategy (such as solvent-induced microphase separation or structural rearrangement) can achieve rigidity enhancement through local ordering when the solvent is involved, it still faces systematic defects.

[0004] This technical system has three fundamental limitations: first, the modulus switching ratio is generally not more than 5 times, making it difficult to meet the needs of high dynamic load scenarios; second, the solvent plasticization effect irreversibly damages intermolecular forces, causing a cliff-like drop in toughness at high rigidity, and a substantial loss of impact resistance; more importantly, the repeated solvent mediation and structural reconstruction process induces continuous damage to the polymer chains, leading to cumulative performance degradation and recycling deterioration. Despite the anti-plasticization strategy, these defects still constitute insurmountable technical boundaries.

[0005] The present application realizes solution-mediated intelligent hardening through a double-mode solvent response by introducing a comb-like copolymer composed of a hydrophobic main chain and a hydrophilic polyethylene glycol (PEG) side chain: when a polar solvent is involved, it forms a high-strength hydrogen bond network with the PEG side chain, inducing the generation of 213.2 nm heterogeneous aggregation domains (P-BSM), triggering nanophase separation reinforcement; a non-polar solvent forces the hydrophobic main chain to pack densely (NP-BSM) by repelling the hydrophilic side chain, increasing the hydrogen bond density between the chains. Both modes achieve a significant modulus jump, and only heating to remove the solvent (60-80℃, 5min) is required to completely reset the performance, and the performance degradation is less than 5% after multiple cycle tests.

[0006] To overcome the fundamental defects of solvent-mediated systems, the present application proposes a biomimetic stiffness-adjustable material (BSM) that simultaneously overcomes three major technical barriers: 1. Breakthrough modulus switching limit, achieve a record-breaking switching ratio of more than 9 times (measured up to 9.9 times), surpassing the 5 times ceiling of existing systems; 2. Overturn the traditional understanding that "stiffness improvement must compromise toughness", still maintain ultra-high toughness of 254.44 MJ·m -3 at a high modulus state of 262.78 MPa, ensuring structural integrity under impact load; 3. Give the material excellent environmental robustness, not only maintain long-term structural fidelity in humid / extreme conditions, but also achieve a performance degradation rate of less than 5% after multiple solvent cycles. SUMMARY

[0007] The purpose of the present application is to provide a solvent-mediated stiffness-adjustable material, a preparation method and an application, to solve the problem that the modulus switching range of existing stiffness-adjustable materials is mostly limited to less than 5 times, making it difficult to cope with complex dynamic loads; the strong dependence on external stimuli such as heat, light and magnetism leads to response delay and system integration barriers; more importantly, stiffness improvement often accompanies toughness collapse, making the material's impact resistance and durability in humid or extreme environments severely deteriorated.

[0008] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows: a solvent-mediated stiffness-adjustable material, comprising a base material;

[0009] The base material comprises a hydrophobic main chain, and a spatial cross-linking network structure composed of hydrophilic side chains grafted comb-like to the hydrophobic main chain; the hydrophobic main chain constitutes the mechanical skeleton of the stiffness-adjustable material, and the hydrophilic side chain provides the solvent response site;

[0010] The base material forms a nanoscale hard domain under the trigger of a polar or non-polar solvent, which is dispersed in the base material as a reversible reinforcing phase, forming a polar hardening body material or a non-polar hardening body material, respectively;

[0011] The solvent channel penetrates the entire space crosslinking network structure, and the nanoscale hard domain is reversibly connected to the hydrophobic main chain or the hydrophilic side chain through hydrogen bond as a heterogeneous aggregation domain.

[0012] Further, the polymer monomer in the hydrophobic main chain includes polycaprolactone PCL, Mn = 1000-2000 g / mol; and polylactic acid PLA, crystallinity 30-50%;

[0013] The polymer monomer in the hydrophobic main chain is linearly connected by urethane bond -NHCOO-; the crosslinking agent includes 4,4'-dicyclohexyl methane diisocyanate HMDI and hexamethylene diisocyanate HDI;

[0014] The polymer monomer in the hydrophilic side chain includes trimethylolpropane polyethylene glycol monomethyl ether Ymer N-120, Mn = 500-1500 g / mol.

[0015] Further, the polar solvent includes a protic solvent and an aprotic polar solvent, which ensures triggering the hydrophilic hard domain and hydrogen bond; the protic solvent includes water, methanol, ethanol and ethylene glycol; the aprotic polar solvent includes dimethylformamide DMF and dimethyl sulfoxide DMSO; the non-polar solvent includes alkanes or cycloalkanes, which ensures the penetration of the hydrophobic main chain and the formation of the hard domain; the alkanes include pentane, hexane and heptane; the cycloalkanes include cyclohexane and methylcyclohexane.

[0016] Further, in the hardening material, the hard domain size is positively correlated with the solvent surface energy, and the hard domain size directly determines the modulus increment of the hardening material relative to the matrix material, and the modulus increment can be up to 9.9 times; after multiple swelling-desolventization cycles, the modulus attenuation is less than 5%, and the heterogeneous aggregation domain is reversibly dissociated.

[0017] The preparation method of the solvent-mediated stiffness adjustable material comprises the following steps:

[0018] S1, polymerize the hydrophilic side chain polymer monomer and the crosslinking agent under the condition of a catalyst to obtain a polymerization product;

[0019] S2, continue to add the hydrophobic main chain polymer monomer to the polymerization product of S1, graft after completion, pour the reaction mixture into a mold, and solidify to obtain the matrix material of the application;

[0020] S3, immerse the matrix material obtained in S2 in a polar solvent to obtain the polar hardening material of the application, and immerse the BSM material obtained in S2 in a non-polar solvent to obtain the non-polar hardening material of the application.

[0021] Further, in the S1, the catalysts include tertiary amines and organic metals; the tertiary amines include triethylamine and triethylene diamine; the organic metals include organic bismuth, dibutyl tin dilaurate and stannous octoate; the -NCO / -OH reaction conversion rate is maintained to be greater than 95% and toxic residues are avoided.

[0022] Further, in the S1, the polymerization methods include bulk polymerization and solution polymerization; the bulk polymerization is carried out in a protective atmosphere; the solution polymerization, the solvent includes tetrahydrofuran THF, and the solid content is 30±5%.

[0023] Further, in the S1-S2, the hydrophilic side chain polymer monomers and the hydrophobic main chain polymer monomers need to be vacuum dried to remove water before being added.

[0024] Further, in the S3, the matrix material is immersed in a polar solvent and a non-polar solvent for not less than 24 hours.

[0025] Application of solvent-mediated stiffness-adjustable material in the field of wearable electronics, soft robots and impact-resistant protection.

[0026] The beneficial effects of the present application are:

[0027] 1. Breakthrough in modulus switching ratio bottleneck

[0028] The modulus switching ratio of traditional solvent-responsive materials is less than or equal to 5 times; through the synergistic reinforcement of the double-mode heterogeneous aggregation domain, the modulus of the present application is increased from 26.58 MPa (original state) to 262.78 MPa (water phase hardened state), and the switching ratio is 9.9 times, which breaks the record in the field;

[0029] 2. Resolving the contradiction between stiffness and toughness

[0030] Traditional stiffness increase leads to a sharp decrease in toughness; the dynamic energy consumption mechanism of the present application synchronously improves the stiffness and toughness: the pentane hardened body (NP-BSM) and the water phase hardened body (P-BSM) realize the synchronous improvement of stiffness and toughness through micro-domain sliding energy consumption and hydrogen bond reversible recombination;

[0031] 3. Solving the problem of cycle stability

[0032] Traditional solvent soaking easily causes structural damage; based on the design of covalent cross-linked network, the modulus attenuation of the present application is less than 5% after multiple swelling-desolventization cycles, which lays the foundation for engineering application. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 It is the synthesis flow chart of the BSM of the present application;

[0034] Figure 2A. Hydrogen bond transition of BSM, NP-BSM and P-BSM; B. FTIR spectra of carbonyl (C=O) and ether (C-O-C) functional groups of BSM, NP-BSM and P-BSM;

[0035] Figure 3 A-C. AFM phase diagrams of BSM, NP-BSM and P-BSM, respectively.

[0036] Figure 4 A. Tensile stress-strain curves of BSM, NP-BSM and P-BSM, and watermelon load-bearing experiment diagrams; B. Comparison diagrams of Young's modulus between BSM, NP-BSM and P-BSM (error bar: standard deviation SD, n=5); C. Comparison diagrams of toughness between BSM, NP-BSM and P-BSM (error bar: standard deviation SD, n=5); D. Demonstration photos changing with time, showing the softening, non-polar solvent hardening (NP-BSM) and polar solvent hardening (P-BSM) processes of BSM, NP-BSM and P-BSM; E. Photomechanical verification diagrams of multi-solvent enhanced load capacity (thin film size: 80mm*12mm*2mm); F. Diagrams of reversible mechanical strength of polymers in continuous hardening-softening cycles, with the soaking time fixed at 6 hours.

[0037] Figure 5 A. Force-time curve diagrams of BSM, NP-BSM and P-BSM in impact tests (steel ball falling from a height of 30 centimeters); B. Statistical data diagrams of maximum impact force (Fmax) and buffer time (buffer time) of BSM, NP-BSM and P-BSM in impact tests; C. Comparison diagrams of maximum impact force (Fmax) and buffer time (buffer time) across materials, BSM material vs. traditional smart materials.

[0038] Figure 6 A. Recycling process of BSM-based materials through a hot-pressing process; B. Mechanical property test of BSM-based materials recycled through a hot-pressing process; C. Impact property test of BSM-based materials recycled through a hot-pressing process. DETAILED DESCRIPTION

[0039] The technical solutions of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application.

[0040] The present application is a stiffness-adjustable material (BSM), the core of which is composed of the following components:

[0041] Hydrophobic backbone: linearly connected by polycaprolactone (PCL, Mn = 2000 g / mol) through urethane bond (-NHCOO-), forming the mechanical skeleton of the material; Hydrophilic side chain: trimethylolpropane polyethylene glycol monomethyl ether (Ymer N-120, Mn = 1000 g / mol) is grafted in a comb-like manner to the backbone, providing solvent-responsive sites; Polar or non-polar solvent triggers the formation of nanoscale hard domains (P-BSM: 213 nm, NP-BSM: 35 nm), which are reversibly dispersed in the matrix as reinforcing phases.

[0042] Connection relationship: the backbone and the side chain are connected by covalent bond, the solvent channel penetrates the network, and the heterogeneous aggregation domain is dynamically connected with the backbone / side chain through hydrogen bond.

[0043] (1) Molecular structure design

[0044] The present application adopts a comb-like copolymer architecture:

[0045] Hydrophobic backbone: linearly connected by polycaprolactone (PCL, Mn = 2000 g / mol) through urethane bond (-NHCOO-), forming the mechanical skeleton of the material;

[0046] Hydrophilic side chain: trimethylolpropane polyethylene glycol monomethyl ether (Ymer N-120, Mn = 1000 g / mol) provides solvent-responsive sites;

[0047] Connection mode: the backbone is covalently grafted through urethane bond (-NHCOO-), realizing nanoscale microphase separation of rigid and flexible segments.

[0048] (2) Dual-mode solvent response mechanism

[0049] Polar channel (P-BSM): water molecules penetrate into the PEG side chain and form an O-H···O hydrogen bond network with ether oxygen; Trigger directional migration of hydrophilic segments, inducing ordered stacking of hard segments into large-size hydrophilic hard domains.

[0050] Non-polar channel (NP-BSM): pentane penetrates into the hydrophobic backbone and excludes the PEG side chain through solvent locking effect, driving the enrichment of cyclic / alkyl chains and reconfiguring the hydrogen bond network to form hydrophobic dense-packed hard domains.

[0051] (3) Precise regulation of heterogeneous aggregation domains

[0052] Size control: the size of the hard domain is positively correlated with the surface energy of the solvent (water: 213 nm, pentane: 35 nm); Performance correlation: the domain size directly determines the modulus increase (213 nm domain: 9.9 times, 35 nm domain: 6.8 times).

[0053] (4) Stiff and tough synergistic dynamic energy dissipation mechanism

[0054] The rigidity enhancement of the present application is derived from solvent-triggered nanoscale heterogeneous aggregate reconstruction. In a polar aqueous solution environment, water molecules penetrate into the polyethylene glycol side chain region and form a high-density hydrogen bond network with ether oxygen atoms. This process drives the directional migration of hydrophilic segments and induces the ordered stacking of hard segments along the main chain, forming rigid aggregate domains. The strengthening of the hydrogen bond network significantly restricts molecular chain movement, building a rigid backbone. In a non-polar pentane environment, pentane molecules penetrate into the hydrophobic main chain and exclude polyethylene glycol side chains through solvent locking effect, forcing the enrichment of cyclic and alkyl segments to reconstruct the hydrogen bond network, forming a dense hard zone. Both modes achieve rigidity enhancement through hydrogen bond rearrangement and heterogeneous aggregate formation, and the aggregate size is positively correlated with the surface energy of the solvent, ultimately breaking through the upper limit of the modulus switching ratio of traditional materials and achieving a reversible rigidity enhancement of up to 9.9 times.

[0055] The toughness enhancement of the present application relies on the synergy of dynamic energy dissipation mechanism and multi-level deformation behavior. In the non-polar mode induced by pentane, the hydrophobic hard domain serves as a slidable physical crosslinking point, and micro-zone slip and segment relaxation occur between hard domains during stretching, converting external force into interfacial friction energy. The aggregation of the hydrophobic main chain maintains the integrity of the hydrogen bond network. In the polar mode mediated by water, the hydrophilic hard domain builds a rigid backbone, while the reversible rupture and recombination of hydrogen bonds act as an energy dissipation valve; after stretching to the yield point, the dynamic dissociation of hydrogen bonds buffers stress concentration, followed by continuous energy dissipation through crystalline zone slip. This mechanism enables the material to have impact strength enhancement under ultra-high modulus, completely avoiding the embrittlement problem caused by rigidity enhancement. Both modes rely on the unified contradictory performance of the rigid-soft interphase nanoscale structure: micro-zone slip and crystalline zone slip provide plastic deformation channels, dynamic recombination of hydrogen bonds and segment relaxation achieve continuous energy dissipation, and heterogeneous aggregate reversible dissociation ensures the stability of toughness in cyclic use. This study can be used for soft robot design and impact protection fields.

[0056] (5) Cycle stability technology

[0057] Anti-solvent erosion design: covalent crosslinking network inhibits main chain degradation; performance durability: modulus attenuation <5% after multiple swelling-desolventization cycles, heterogeneous aggregate reversible dissociation.

[0058] Example 1

[0059] S1, Preparation of BSM

[0060] Under the protection of nitrogen atmosphere, 2 grams of trimethylolpropane polyglycol monomethyl ether (Ymer N-120, Mn = 1000 g / mol) was first placed in a three-necked flask and vacuum dried at 100 °C for 2 hours; then 2 milliliters of 4,4'-dicyclohexylmethane diisocyanate (HMDI, Mn = 262.35 g / mol) and 2-5 drops of organic bismuth catalyst were added successively, and the reaction was continuously stirred at 70 °C for 2 hours; then 12 grams of 2-[2-(6-hydroxyhexanoyloxy)ethoxy]ethyl-6-hydroxyhexanoate (PCL, Mn = 2000 g / mol) monomer, which was previously vacuum dried at 110 °C for 2 hours, was added to the reaction system, and the grafting was completed by keeping the stirring for 2 hours; finally, the reaction mixture was poured into a polytetrafluoroethylene mold and cured in a 100 °C oven for 6 hours to obtain the base BSM material.

[0061] S2, solvent phase change treatment to realize double-mode hardened sample preparation

[0062] Through the solvent phase change treatment to realize double-mode hardened, the BSM sample was immersed in deionized water for at least 24 hours to obtain a water phase hardened body (P-BSM), or immersed in n-pentane solvent for at least 24 hours to obtain an oil phase hardened body (NP-BSM).

[0063] The performance tests of the BSM, P-BSM and NP-BSM obtained by the present application are as follows:

[0064] As shown in Figures 1-2 BSM has a comb copolymer structure composed of a hydrophobic main chain and a suspended hydrophilic polyethylene glycol (PEG) side chain. This molecular design enables BSM to exhibit obvious double-mode hydrogen bond lock-mediated heterogeneous aggregation behavior when encountering polar or non-polar solvent molecules. Compared with the original BSM, the BSM mediated by polar molecules (P-BSM) and the BSM mediated by non-polar molecules (NP-BSM) have significantly enhanced modulus, thereby realizing a double-mode hardening mechanism.

[0065] The double-mode adjustment mechanism shows that the microstructure of the BSM is adjusted according to the polarity of the solvent Figure 2 A) significantly different micro-path: under the condition of polar aqueous solution, P-BSM undergoes structural reorganization, which starts from the formation of strong hydrogen bonds between water molecules and ether oxygen atoms on the suspended PEG side chain. This interaction promotes the directional migration and aggregation of hydrophilic fragments, thereby mediating heterogeneous aggregation and promoting the ordered stacking of hard segments along the main chain. Red shift and enhancement of C-O-C absorption band Figure 2B) demonstrates this. In contrast, in the nonpolar pentane environment, the NP-BSM mechanism is driven by the affinity between the hydrophobic backbone and the nonpolar solvent interface. Pentane does not disrupt the existing hydrogen bonds, it induces the enrichment of cyclic and alkyl segments to the solvent phase through a solvent locking effect, thus promoting segment aggregation and hydrogen bond reorganization. The enhanced C=0 absorption supports the formation of denser and stable hard domains.

[0066] As shown in Figure 3 , micro-characterization further reveals distinct morphological features under polar and nonpolar solvent conditions. AFM images Figure 3 A) show that the pristine BSM surface is smooth and uniform, lacking distinct phase contrast, indicating uniform molecular distribution. In sharp contrast, P-BSM Figure 3 C) and NP-BSM Figure 3 B) both exhibit nanoscale hetero-phase aggregation, with significantly different aggregate sizes. The aggregate size of P-BSM is 213 nm, while that of NP-BSM is only 35 nm, indicating that polar and nonpolar hydrogen bond locking modes trigger different hetero-phase aggregation behaviors. The high surface energy of water leads to larger aggregation domains rich in C-O-C and H2O hydrogen bonds, while the low surface energy of pentane leads to smaller aggregation domains that exclude PEG side chains and promote hydrogen bond formation between urethane bonds in the backbone.

[0067] As shown in Figure 4 , stress-strain curves clearly show the hardening behavior mediated by the dual-mode Figure 4 A). BSM behaves as a typical soft elastomer with a continuously rising stress-strain curve and no yield platform. Its fracture strain exceeds 870%, but the initial modulus is low, at 26.49 ± 2.31 MPa. In contrast, NP-BSM exhibits a plastic mechanical behavior with an initial yield platform followed by stress hardening. Its modulus sharply rises to 230.96 ± 5.69 MPa (8.7 times higher than that of BSM), with a fracture strain of 746.1%. P-BSM shows a similar plastic stress-strain response to NP-BSM, with a modulus of 262.78 ± 3.47 MPa (9.9 times higher than that of BSM) Figure 4 B), indicating that the dual-mode hydrogen bond locking-mediated hetero-phase aggregation strategy significantly enhances hardness. Notably, P-BSM can bear the weight of a watermelon (10 kg), demonstrating excellent load-bearing ability. A hanging clip weighing 1.5 grams significantly bends the BSM strip, with a bending angle of 30°, indicating its low stiffness. For NP-BSM strips, the bending angle is less than 10°, while P-BSM strips (only 2 millimeters thick) are almost not bent, proving the excellent deformation resistance of P-BSM and NP-BSM Figure 4 D). In the load-bearing test,Figure 4 E), 200 grams of weight can be stably placed on P-BSM and NP-BSM without deformation, while BSM deforms immediately. All these excellent performances highlight the significant modulus enhancement achieved by the heterogeneous aggregation mediated by dual-mode hydrogen bonding lock. The reversibility of modulus transition was investigated by repeatedly treating polar or nonpolar solvents and heating. The modulus of the material was tested after each treatment, and it was found that the material could recover to the same modulus level regardless of the type of solvent, with almost no decline in mechanical properties Figure 4 F), demonstrating the outstanding performance of BSM in terms of repeatable adjustment of stiffness. The dual-mode modulus transition greatly improves the toughness capability of BSM Figure 4 C), perfectly solving the dilemma in traditional polymers.

[0068] As Figure 5 shown, in addition to high tensile modulus and toughness, hydrogen bonding-mediated aggregation endows BSM with outstanding impact energy absorption performance. In a series of drop ball impact tests, the impact force of BSM film is significantly reduced from 3800 N to 200 N. Notably, NP-BSM and P-BSM exhibit more excellent cushioning performance Figure 5 A). Unusually, the impact force signal of NP-BSM and P-BSM presents a clear plateau region, indicating the presence of an abnormal energy absorption mechanism. The reduction in impact force is accompanied by an increase in the cushioning time of dual-mode BSM, which means its superior energy dissipation capability. Notably, the cushioning time is significantly prolonged from 0.23 milliseconds of the blank control to 1.1 milliseconds of P-BSM Figure 5 B). Compared with other metal and plastic impact absorbing materials, dual-mode BSM stands out significantly, especially P-BSM Figure 5 C).

[0069] As Figure 6 shown, the parameters of the hot pressing process are temperature 160℃, pressure 4000bar; the recovered BSM can be easily repaired by using polar or nonpolar solvents to obtain P-BSM or NP-BSM Figure 6 A). After two rounds of recovery, the tensile and impact performance of dual-mode BSM was tested and compared with its original value. Surprisingly, the tensile performance (tensile strength, modulus and toughness) Figure 6 B) and impact performance (impact force and cushioning time) Figure 6C) Remained at the same level before and after recycling (about 99% performance remained unchanged), indicating that the dual-mode BSM has long-term structural integrity and functional durability. The mechanical performance consistency of P-BSM and NP-BSM before and after recycling further highlights the reversibility of the dual-mode hydrogen bond lock-mediated heterophase aggregation behavior. In summary, the dual-mode BSM provides a rare combination of reversible stiffness adjustment, outstanding modulus, toughness, impact resistance, and excellent recycling ability, making it a powerful and sustainable protective material.

[0070] The present application is not limited to the above best mode, and anyone can derive other various forms of products under the inspiration of the present application, but regardless of any changes in shape or structure, any technical solution with the same or similar to the present application falls within the scope of the present application.

Claims

1. A solvent-mediated stiffness-tunable material, characterized in that: The base material comprises a hydrophobic main chain and a spatial cross-linking network structure formed by hydrophilic side chains grafted on the hydrophobic main chain in a comb shape; the hydrophobic main chain forms a mechanical skeleton of the stiffness-adjustable material, and the hydrophilic side chains provide solvent response sites; The nanoscale hard domains formed by the base material under the triggering of polar or non-polar solvents are reversibly dispersed in the base material as a reversible reinforcing phase to form polar or non-polar hardening materials; In the polar or non-polar hardening materials, solvent channels pass through the entire spatial cross-linking network structure, and the nanoscale hard domains are dynamically connected to the hydrophobic main chain or the hydrophilic side chain through hydrogen bonds as a heterogeneous aggregation domain. The polymer monomers in the hydrophobic main chain comprise polycaprolactone PCL with Mn being 1000-2000 g / mol and polylactic acid PLA with a crystallinity of 30-50%.

2. The solvent-mediated stiffness-tunable material of claim 1, wherein: The polymer monomers in the hydrophobic main chain are linearly connected by urethane bonds -NHCOO-; and the cross-linking agent comprises 4,4'-dicyclohexyl methane diisocyanate HMDI and hexamethylene diisocyanate HDI. The polymer monomers in the hydrophilic side chain comprise trimethylolpropane polyethylene glycol monomethyl ether Ymer N-120 with Mn being 500-1500 g / mol. The polar solvent comprises a protic solvent and an aprotic polar solvent to ensure triggering of the hydrophilic hard domain and hydrogen bonds; the protic solvent comprises water, methanol, ethanol and ethylene glycol; the aprotic polar solvent comprises dimethylformamide DMF and dimethyl sulfoxide DMSO; the non-polar solvent comprises alkanes or cycloalkanes to ensure penetration of the hydrophobic main chain and formation of the hard domain; the alkanes comprise pentane, hexane and heptane; and the cycloalkanes comprise cyclohexane and methylcyclohexane.

3. The solvent-mediated stiffness-tunable material of claim 1, wherein: In the hardening material, the hard domain size is positively correlated with the solvent surface energy, and the hard domain size directly determines the modulus increase of the hardening material relative to the base material, and the modulus increase can be up to 9.9 times; 4. The solvent-mediated stiffness-tunable material of any one of claims 1-3, wherein: After multiple swelling-deswelling cycles, the modulus attenuation is less than 5%, and the heterogeneous aggregation domain is reversibly dissociated. The method comprises the following steps:

5. The method of claim 1-4, wherein the solvent-mediated stiffness-tunable material is prepared by the steps of: S1, polymerizing the hydrophilic side chain polymer monomers and the cross-linking agent under the action of a catalyst to obtain a polymerization product; S2, continuously adding the hydrophobic main chain polymer monomers to the polymerization product of S1, pouring the reaction mixture into a mold after grafting is completed, and solidifying to obtain the base material of the application; S3, immersing the base material obtained in S2 in a polar solvent to obtain the polar hardening material of the application, and immersing the BSM material obtained in S2 in a non-polar solvent to obtain the non-polar hardening material of the application. In S1, the catalyst comprises tertiary amines and organometallics; the tertiary amines comprise triethylamine and triethylene diamine; and the organometallics comprise organobismuth, dibutyltin dilaurate and stannous octoate; the -NCO / -OH reaction conversion rate is maintained to be greater than 95% and toxic residues are avoided.

6. The method of claim 5, wherein: ​ 7. The method of claim 5, wherein: The S1, the polymerization mode includes bulk polymerization and solution polymerization; the bulk polymerization is carried out under a protective atmosphere; the solution polymerization, the solvent includes tetrahydrofuran THF, and solid content is 30±5%.

8. The method of claim 5, wherein: In the S1-S2, the hydrophilic side chain polymer monomer and the hydrophobic main chain polymer monomer need to be vacuum dried to remove water before adding.

9. The method of claim 5, wherein: In the S3, the matrix material is immersed in a polar solvent and a non-polar solvent for not less than 24 hours.

10. The use of the solvent-mediated stiffness-tunable material according to any one of claims 1-9 in the field of wearable electronics, soft robots and impact protection.

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