A dynamic cross-linking polyurethane-based ionic gel material and a preparation method and application thereof

Abstract

This invention relates to a dynamically crosslinked polyurethane-based ionogel material, its preparation method, and its applications. The ionogel uses PCL and HMDI as the soft and hard segments of a polyurethane substrate, with ID and SS added as chain extenders to synthesize a polyurethane elastomer with a dynamically crosslinked structure. The ionogel prepared by mixing this material with EMIMTFSI exhibits excellent mechanical properties and conductivity. The ionogel sensor prepared according to this invention demonstrates excellent sensitivity, operating range, and fatigue resistance, and expands its application range in underwater and salt solutions, providing new ideas for next-generation high-performance flexible electronic materials.

Description

Technical Field

[0001] This invention relates to the field of flexible sensor technology, and more particularly to a dynamically cross-linked polyurethane-based ionogel material, its preparation method, and its applications. Background Technology

[0002] Flexible ionogels, as key materials for next-generation flexible electronic devices and human-computer interfaces, have attracted much attention due to their unique ionic conductivity, flexibility, and designability. However, existing ionogels still face insurmountable performance bottlenecks: the core contradiction lies in the mutual constraint between mechanical properties and ionic conductivity. High ionic conductivity often relies on flexible polymer segments, but this leads to a decrease in the material's mechanical strength, while mechanical reinforcement strategies limit ion migration efficiency. Simultaneously, most materials struggle to simultaneously achieve high strength, high conductivity, self-healing capabilities, and extreme temperature adaptability, exhibiting significant shortcomings in multifunctional integration requirements such as damage tolerance and sustainable recyclability, failing to fully meet the application requirements of complex scenarios. Achieving synergistic optimization of mechanical properties, conductivity, and environmental stability in ion-conductive systems remains a critical challenge to be addressed. Various theoretical and technological approaches have been explored, such as constructing hierarchical cross-linked networks through supramolecular engineering, utilizing dynamic non-covalent bonds such as multiple hydrogen bonds and π-π stacking to achieve energy dissipation and structural repair while preserving ion transport channels, and using biomimetic design to simulate the structural synergistic effects of natural materials to achieve the integration of mechanical properties and functional characteristics. However, these strategies still have room for improvement in terms of multifunctional synergy. Therefore, it is of great significance to develop a multifunctional biomimetic dynamic cross-linked ionogel material that can simultaneously possess high strength, high ionic conductivity, self-healing ability, resilience and tear resistance, and environmental tolerance. Summary of the Invention

[0003] The purpose of this invention is to solve the problems of the irreconcilable contradiction between mechanical properties and ionic conductivity, insufficient multifunctional integration, and poor environmental tolerance of existing ion gel materials. This invention aims to provide a multifunctional dynamic cross-linked ion gel material that can simultaneously possess high strength, high ionic conductivity, self-healing ability, resilience and tear resistance, and environmental tolerance.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: using polycaprolactone diol (PCL) as the soft segment and 4,4'-dicyclohexylmethane diisocyanate (HMDI) as the hard segment, introducing isophthalic acid dihydrazide (ID) as a chain extender to construct a multi-level hydrogen bond network, and simultaneously introducing dihydroxyphenyl disulfide (SS) as a dynamic crosslinking unit to form disulfide bonds, and preparing a dynamically crosslinked polyurethane elastomer through prepolymerization and chain extension reaction, which is named DCPU.

[0005] Dynamically crosslinked polyurethane elastomers were dissolved in DMF solution with different mass fractions of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMIMTFSI). After stirring, the solution was poured into a mold and vacuum dried to obtain an ionic gel, named DCPU-ILX, where X is the mass fraction of EMIMTFSI added to DCPU.

[0006] Specifically, a dynamically cross-linked polyurethane-based ionogel material and its preparation method include the following steps: Step 1: Place polycaprolactone diol (PCL) into a three-necked flask and heat to remove moisture; Step 2: Add 4,4'-dicyclohexylmethane diisocyanate (HMDI) dissolved in N,N-dimethylformamide (DMF) to a three-necked flask, and add dibutyltin dilaurate (DBTDL) as a catalyst, and stir to obtain polyurethane prepolymer; Step 3: Add isophthalic acid dihydrazide (ID) and dihydroxyphenyl disulfide (SS) dissolved in DMF respectively, and stir to obtain a light yellow transparent viscous polyurethane liquid; Step 4: Pour the liquid obtained in Step 3 into a mold and dry it until the solvent has completely evaporated. Step 5: Dissolve the polyurethane elastomer obtained in Step 4 with different mass fractions of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMIMTFSI) in DMF solution, stir, pour into a mold and vacuum dry to finally obtain ion gel.

[0007] Specifically, in the synthesis step, the sum of the molar masses of polycaprolactone diol, diisophthalic acid dihydrazide, and dihydroxyphenyl disulfide is equal to the molar mass of 4,4'-dicyclohexylmethane diisocyanate, wherein the molar mass of polycaprolactone diol is half that of 4,4'-dicyclohexylmethane diisocyanate, and the molar ratio of diisophthalic acid dihydrazide and dihydroxyphenyl disulfide is 3:1.

[0008] Specifically, in step two, the heating temperature is 80°C, and the mixture is stirred for 3 hours.

[0009] Specifically, in step three, the heating temperature is 40°C, and the mixture is stirred for 12 hours.

[0010] Specifically, in step five, the mass fractions of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide are 40%, 60%, 80%, 100%, and 120%, respectively.

[0011] The present invention also characterized the synthesis and properties of the ionogel.

[0012] Specifically, the molecular structure of the material was characterized using attenuated total reflection Fourier transform infrared spectroscopy (FT-IR).

[0013] Specifically, it characterizes the tensile properties and electrical conductivity of the material.

[0014] The present invention also discloses a strain sensor prepared from an ion gel obtained by the above method.

[0015] Specifically, it characterizes the sensor's sensitivity, relative resistance change under different strains, fatigue resistance, and stability in complex environments.

[0016] Compared with the prior art, the present invention has the following beneficial effects: (1) DCPU-IL100 has excellent comprehensive mechanical properties: at room temperature, the tensile strength is as high as 37.09 MPa, the elongation at break is 1940%, and the ultra-high toughness (119.05 kJ / m²) is also high. -2 ).

[0017] (2) DCPU-IL100 has high ionic conductivity: the ionic conductivity at room temperature reaches 7.49 × 10⁻⁶. -4 S cm -1 .

[0018] (3) The DCPU-IL100 has high sensitivity: a stable sensitivity of 0.95 in the low strain range and an improved sensitivity of 1.49 in the high strain range.

[0019] (4) DCPU-IL100 has fatigue resistance: the sensor maintains signal stability after being repeatedly stretched for 4000s at 100% strain to complete 800 cycles.

[0020] (5) DCPU-IL100 has the ability to adapt to complex environments: it maintains signal stability in underwater and in solutions with a certain salt concentration. Attached Figure Description

[0021] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 It is the FT-IR plot of DCPU-ILX; Figure 2 This is a diagram showing the mechanical properties of the DCPU-ILX. Figure 3 This is a stress and toughness diagram of DCPU-ILX; Figure 4This is a diagram showing the conductivity of DCPU-ILX; Figure 5 This is a sensitivity diagram based on the DCPU-IL100 sensor; Figure 6 Relative resistance change rate graph based on DCPU-IL100 sensor under different strains Figure 7 Relative resistance change rate diagram based on DCPU-IL100 sensor during cyclic stretching Figure 8 underwater finger bending relative resistance rate graph based on DCPU-IL100 sensor Figure 9 Plot of relative resistance change rate of finger bending in saline solution of different concentrations based on DCPU-IL100 sensor Detailed Implementation

[0023] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0024] The term "an embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the invention. The phrase "in one embodiment" appearing in different places throughout this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0025] Unless otherwise specified, all materials used in the embodiments of this invention are commercially available.

[0026] Example 1 This embodiment provides a method for preparing dynamically cross-linked polyurethane-based ionogel (DCPU-IL), the specific steps of which are as follows: -PCL (Mn = 2000 g mol) -112.0 g of DMF was added to a three-necked flask and stirred under vacuum at 110 °C for 1 h to completely remove moisture. The reaction system was then cooled to 80 °C, and HMDI (12 mmol) dissolved in DMF was added to the three-necked flask along with 5 drops of DBTBL as a catalyst. The reaction was continued at 80 °C for 3 h to obtain a polyurethane prepolymer. The reaction system was then cooled to 40 °C, and ID (3.75 mmol) and bis(4-hydroxyphenyl) disulfide (SS, 1.25 mmol) dissolved in DMF were added. The mixture was stirred at 40 °C for 12 h to obtain a light yellow, transparent, viscous polyurethane liquid. The resulting viscous liquid was poured into a polytetrafluoroethylene (PTFE) mold and transferred to a vacuum drying oven to dry at 80 °C for 24 h. DCPU and different mass fractions of EMIMTFSI (40%, 60%, 80%, 100%, and 120% by mass) were dissolved in DMF solution. Then, the mixture was stirred at 40°C for 6 hours to obtain a viscous and transparent solution. This solution was poured into a petri dish and transferred to a vacuum drying oven at 80°C to dry until the solvent was completely evaporated, thus obtaining the DCPU-ILX ion gel.

[0027] Example 2 The DCPU-ILX ion-conductive gel was cut into 30.0mm × 10.0mm × 0.6mm pieces. Conductive copper foil was attached to both ends of the DCPU-ILX, and two wires were led out for direct measurement.

[0028] Performance testing Infrared spectroscopy was performed on the ion gel sensor prepared in Example 1 of this invention, as follows: Figure 1 As shown, the -NH- stretching vibration occurs at 3317 cm⁻¹. -1 -NH- bending vibration at 1540 cm -1 The NCO characteristic peak disappears at 2260 cm⁻¹, indicating that the polyurethane prepolymer has completely reacted. The urethane group and the ASCZ group show a peak at 1730 cm⁻¹. -1 A C=O stretching vibration peak appears nearby. Due to the ion-dipole interaction between EMIM⁺ and oxygen atoms, the peak position changes from 1731 cm⁻¹ after the addition of EMIMTFSI. -1 Redshifted to 1724cm -1 Furthermore, the peak intensity gradually decreases, indicating that EMIMTFSI was successfully introduced into the elastomer. Additionally, the peak intensity at 1186 cm⁻¹ increased after the addition of EMIMTFSI. -1 and 740 cm -1 A distinct peak appears at this point, indicating TFSI. - The vibrational peak of CF in anions.

[0029] The mechanical properties of the ionogel prepared in Example 1 of this invention were tested, such as... Figure 2As shown in Figure 3, pure DCPU without added ionic liquid exhibits excellent mechanical properties, with a tensile strength as high as 57.56 MPa, an elongation at break of 1075%, and a toughness of 252.89 MJ / m. -3 This is mainly attributed to the robust network constructed by strong intermolecular hydrogen bonding interactions. With increasing EMIMTFSI concentration, the system exhibits a typical trade-off effect, with the overall tensile strength showing a decreasing trend. DCPU-IL100, however, maintains a high tensile strength of 37.09 MPa and a tensile strength of 243.25 MJ / m². -3 It exhibits extremely high toughness, with an elongation at break reaching 1940%. However, when the concentration of the ionic liquid further increases to 120%, the excess liquid causes excessive swelling of the polymer network, resulting in a decrease in both tensile strength and elongation at break. This performance evolution is closely related to the precise control of the dynamic cross-linked network within the system and the mediating effect of the ionic liquid.

[0030] The conductivity of the ionogel prepared in Example 1 of this invention was tested, such as... Figure 4 As shown, the conductivity gradually increases with increasing ionic liquid concentration; DCPU-100 exhibits a conductivity of 7.49 × 10⁻⁶. -4 S cm -1 Its excellent ionic conductivity achieves a balance between mechanical properties and electrical conductivity.

[0031] The strain sensitivity of the ionogel sensor prepared in Example 2 of this invention was tested, such as... Figure 5 As shown, the sensitivity (GF) is characterized by the ratio of strain to resistance change rate. The DCPU-ILX exhibits a stable sensitivity of GF=0.95 in the low strain range, while the sensitivity increases to GF=1.49 in the high strain range. This change is due to the dissociation of dynamic bonds and the directional reconstruction of ion channels under high strain, which enables the material to have excellent response recognition for both small deformations and large-scale stretching.

[0032] The relative resistance change rate of the ion gel sensor prepared in Example 2 of this invention was tested under different strains, such as... Figure 6 The ionogel was tested at a constant strain rate, and the resistance change rate (ΔR / R0) from 5% to 150% strain was measured. It showed a wide strain operating range and maintained good sensing characteristics even under large strain.

[0033] The relative resistance change rate of the ionogel sensor prepared in Example 2 of this invention was tested during cyclic stretching. Figure 7 As shown, the sensor was subjected to repeated stretching for 4000 seconds at 100% strain to complete 800 cycles. Throughout the process, the rate of change of resistance remained basically stable, demonstrating excellent fatigue resistance.

[0034] Application Example 1: Underwater Finger Bending Detection The ionogel sensor prepared in Example 2 was worn on a finger joint, and the finger was immersed in water and bent to monitor signal changes in real time. Figure 7 As shown, the signal remains stable in water.

[0035] Application Example 2: Finger Bending Detection in Salt Water The ionogel sensor prepared in Example 2 was worn on a finger joint, and the finger was immersed in 1% wt NaCl aqueous solution and 3.5 wt% NaCl aqueous solution to simulate the average salt concentration of sweat and seawater environments. Signal changes were monitored by bending the finger. Figure 8 As shown, the resistance in NaCl solution decreases with finger bending, and the rate of change of resistance decreases with increasing NaCl concentration. This phenomenon can be analyzed from three aspects: the synergistic effect of ion transport competition, the coupling effect of network deformation, and the parallel resistance effect of the circuit. On the one hand, as previous experiments have shown, bending deformation stretches the elastomer network, widening the molecular chain spacing. Theoretically, this would lead to the elongation and narrowing of the internal EMIMTFSI ion transport channels, increasing ion migration resistance and causing an increase in resistance. On the other hand, the NaCl ionization in the NaCl aqueous solution produces Na+... + Cl - The NaCl solution acts as an external conductive charge carrier in the ion transport process, and the conductive NaCl solution forms a parallel circuit with the sensor, increasing the overall conductivity. These two components synergistically cancel each other out and reverse the increasing resistance trend, resulting in a resistance reduction phenomenon. As the NaCl concentration increases, the solution's ionic conductivity further improves, and the parallel resistance effect formed with the sensor becomes stronger, increasing its proportion in regulating the overall conductivity. This significantly weakens the interference of bending deformation on ion transport efficiency, thus gradually reducing the magnitude of resistance change.

Claims

1. A dynamically cross-linked polyurethane-based ionogel material, its preparation method, and its application, characterized in that: The material comprises a polyurethane-based elastomer and an ionic liquid.

2. The dynamically cross-linked polyurethane-based ionogel material according to claim 1, characterized in that: The polyurethane-based elastomer is composed of polycaprolactone diol (PCL, Mn = 2000 g mol) -1 The ionic liquid is prepared by prepolymerization and chain extension reaction of 4,4'-dicyclohexylmethane diisocyanate (HMDI), isophthalic acid dihydrazide (ID), dihydroxyphenyl disulfide (SS) and catalyst dibutyltin dilaurate (DBTDL); the ionic liquid is 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMIMTFSI), and its mass fraction relative to the polyurethane-based elastomer is 40% to 120%.

3. The dynamically cross-linked polyurethane-based ionogel material according to claim 1 or 2, characterized in that: The material has a tensile strength of at least 37.09 MPa, an elongation at break of at least 1940%, and a tensile strength of at least 119.05 kJ / m² at room temperature. -2 It has toughness and excellent resilience and tear resistance.

4. The dynamically cross-linked polyurethane-based ionogel material according to claim 1 or 2, characterized in that: The material exhibits an ionic conductivity of 7.49 × 10⁻⁶ at room temperature. -4 S cm -1 .

5. The dynamically cross-linked polyurethane-based ionogel material according to claim 1 or 2, characterized in that: The material exhibits a stable sensitivity of 0.95 in the low strain range and a sensitivity of 1.49 in the high strain range.

6. The dynamically cross-linked polyurethane-based ionogel material according to claim 1 or 2, characterized in that: The material exhibits excellent fatigue resistance; after repeated tensile testing at 100% strain for 4000 seconds to complete 800 cycles, the rate of change in resistivity remains essentially stable.

7. The dynamically cross-linked polyurethane-based ionogel according to claim 1 or 2, characterized in that: The material maintains stable sensing performance in complex environments such as underwater and in simulated sweat and seawater (NaCl solution).

8. A method for preparing a dynamically crosslinked polyurethane-based ionogel material as described in any one of claims 1-7, characterized in that, Includes the following steps: Step 1: Prepare the polyurethane-based elastomer; Step 2: Mix the polyurethane-based elastomer with the ionic liquid to prepare the ionic gel.

9. The preparation method according to claim 8, characterized in that: Step 1 includes adding PCL to a flask, stirring under vacuum to remove moisture; cooling the reaction system, then adding HMDI and DBTDL to react; cooling again, then adding ID and SS and stirring; pouring the resulting viscous liquid into a polytetrafluoroethylene mold and drying. Step 2 involves dissolving the polyurethane-based elastomer and EMIMTFSI in a DMF solution, stirring, pouring the solution into a petri dish, and drying it under vacuum.

10. The application of the dynamically crosslinked polyurethane-based ionogel material according to any one of claims 1-7 in underwater and aqueous solutions with high salt concentrations.

Images