CN114716779B - Ionic gel based on multiple physical crosslinking, preparation method and strain sensor - Google Patents

Ionic gel based on multiple physical crosslinking, preparation method and strain sensor Download PDF

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CN114716779B
CN114716779B CN202210427935.2A CN202210427935A CN114716779B CN 114716779 B CN114716779 B CN 114716779B CN 202210427935 A CN202210427935 A CN 202210427935A CN 114716779 B CN114716779 B CN 114716779B
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ionic liquid
ionic gel
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CN114716779A (en
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吕晓林
张浩琦
邹志刚
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Mindu Innovation Laboratory
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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J3/00—Processes of treating or compounding macromolecular substances
    • C08J3/24—Crosslinking, e.g. vulcanising, of macromolecules
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F220/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical or a salt, anhydride ester, amide, imide or nitrile thereof
    • C08F220/02—Monocarboxylic acids having less than ten carbon atoms; Derivatives thereof
    • C08F220/10—Esters
    • C08F220/12—Esters of monohydric alcohols or phenols
    • C08F220/14—Methyl esters, e.g. methyl (meth)acrylate
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F8/00—Chemical modification by after-treatment
    • C08F8/44—Preparation of metal salts or ammonium salts
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
    • G01B7/16—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring the deformation in a solid, e.g. by resistance strain gauge
    • G01B7/18—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring the deformation in a solid, e.g. by resistance strain gauge using change in resistance
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2333/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides, or nitriles thereof; Derivatives of such polymers
    • C08J2333/04—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides, or nitriles thereof; Derivatives of such polymers esters
    • C08J2333/06—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides, or nitriles thereof; Derivatives of such polymers esters of esters containing only carbon, hydrogen, and oxygen, the oxygen atom being present only as part of the carboxyl radical
    • C08J2333/10—Homopolymers or copolymers of methacrylic acid esters
    • C08J2333/12—Homopolymers or copolymers of methyl methacrylate
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/50—Improvements relating to the production of bulk chemicals
    • Y02P20/54—Improvements relating to the production of bulk chemicals using solvents, e.g. supercritical solvents or ionic liquids

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Abstract

The invention discloses an ionic gel based on multiple physical crosslinking, a preparation method and a strain sensor. The ionic gel exhibits good mechanical properties (maximum tensile stress 610KPa, strain 1160%), and a low ionic liquid loading (60 wt%) can achieve the desired ionic conductivity (> 0.12mS/cm at room temperature). The sensor can still keep a gel state in a wider temperature range (20 to 180 ℃), is suitable for severe environments, and has long-term electrical signal stability. In addition, the strain sensor can be used for detecting movements of different parts of a human body, including bending of fingers, wrists and elbows, and slight throat shake during swallowing and sounding, and shows quick response, high sensitivity and good repeatability, so that the ionic gel has potential of being applied to flexible electronic equipment.

Description

Ionic gel based on multiple physical crosslinking, preparation method and strain sensor
Technical Field
The invention relates to the field of polymer gel and sensors, in particular to application of high mechanical property ionic liquid gel in wearable equipment such as a flexible sensor and the like, and particularly relates to ionic gel based on multiple physical crosslinking, a preparation method and a strain sensor. The device has the characteristics of portability, thinness, softness, flexibility and the like, has higher flexibility, extensibility, flexibility and sensitivity, and is mainly used for detecting the fields of human body movement and the like.
Background
Ionic liquids are ionic compounds that are entirely composed of anions and cations and are in a liquid state at 100 ℃. Most ionic liquids exhibit a liquid state at or near room temperature. The ionic liquid has the advantages of good stability, incombustibility, small vapor pressure, difficult volatilization and excellent solubility, and is a good substitute for the traditional organic solvent. Meanwhile, the ionic liquid has unique advantages in the aspects of thermal stability, conductivity and the like.
Ionic gels are a class of soft material that holds ionic liquid matrices in a network backbone structure. Ionic gels represent an important class of sensing materials that contain ionic liquid-containing polymers, both solid and liquid, with the polymer network backbone providing an elastic solid structure that prevents ionic liquid leakage while ionic liquid ensures conductivity. The ionic gel retains the main properties of the ionic liquid, is easy to form, and greatly expands the application range of the ionic liquid. Therefore, ionic gels can be developed for wide application in the field of wearable electronics, in particular electronic skin. Notably, the non-conductive polymer in the ionic gel affects conductivity, thereby reducing sensitivity. Although multifunctional high-sensitivity ion gel pressure sensors have been developed so far, they face significant challenges due to material limitations.
High-performance ionic gel based on double-network structure, although great progress is made in gel performance and preparation flow, the mechanical properties of the obtained ionic gel are still unavoidable compared with many high-performance hydrogels, and chemical crosslinking bond formation inevitably increases preparation difficulty. Although "one pot" gel rapid preparation strategies have been developed, it is also necessary to perform the post-heat curing reaction. More importantly, because some dual-network systems require the design of monomers, the preparation of unconventional polymer monomers with special structures, while being able to introduce functionality well, increases the difficulty and cost of mass production and manufacture. Therefore, the polymer structure design is considered, the gel performance is further improved, the difficulties in molecular synthesis and gel preparation are reduced, and the possibility of rapid preparation and large-scale application of the high-performance ionic gel is expected to be improved.
Corresponding to chemical crosslinking is physical crosslinking, which generally results in the formation of a gel bulk structure through non-covalent interactions. Non-covalent interactions refer to interactions in which the intermolecular or single intramolecular forces are subjected to a dispersed variation to maintain a certain spatial structure, including electrostatic interactions, van der Waals forces, hydrogen bonding, hydrophobic interactions, etc. Ionic liquids are most distinguished from other conventional liquids in that they consist of a large number of charged ions. Many of the non-covalent interactions associated with such a charged ion are involved, such as pi-cation interactions, ion-dipole interactions, and most commonly coulombic forces, among others. Therefore, through polymer structure design, the single-network ionic gel can be prepared by utilizing the non-covalent interaction, and the ionic gel which is simple to prepare, excellent in performance and capable of being produced in large scale can be realized.
The strain sensor based on the ionic gel has wide application prospect in the aspect of motion monitoring. The ionic gel film is used as a sensor to be attached to the skin of a joint because the deformation of the gel can be caused by the motions such as bending and rotating of the joint, and the tiny changes can be displayed on a test instrument in real time through the change of the conductivity, so that the precise and rapid monitoring of the joint motion is realized. Has a certain application prospect in the fields of human health monitoring, intelligent robots and the like.
Disclosure of Invention
Based on the theory and the problems, the invention aims to provide an ionic gel based on multiple physical crosslinking, a preparation method and a strain sensor. The invention provides a design and preparation method of a physical cross-linking type ionic gel, and the physical cross-linking type ionic gel is used in the field of strain sensors. The self-supporting physical crosslinking composite polymer is prepared by introducing multiple ionic bonds; the strength of the polymer network is regulated and controlled by designing a proper molecular structure, the molecular weight of the polymer is regulated and controlled by optimizing the polymerization condition, the content of ionic liquid with proper mass fraction is selected, and the prepared ionic gel has excellent mechanical and electrochemical properties and good thermal stability. And because the construction of the whole network does not need any post-crosslinking, the preparation process is simple and is expected to be produced in a large scale. The material has great potential in the fields of flexible strain sensors and the like.
In particular, the invention aims to improve the sensing performance of a flexible device, design and optimize the chemical composition structure of a polymer, and adopt a novel method for ionizing a copolymer to regulate and control the monomer proportion, the ionization degree and the ionic liquid content of the copolymer so as to prepare an ideal sensor material.
The components composing the ionic gel have different synergistic regulation and control effects.
The monomer A is methyl methacrylate with good compatibility with ionic liquid and polar groups on side groups, the mass ratio of more than 80wt% gives the polymer a high glass transition temperature, and hydrogen bond crosslinking is carried out among the groups;
the monomer B is acrylic acid, so that a second heavy hydrogen bond network is formed, and phase separation can not occur in a small proportion;
the ionized alkali solution is methanol solution of NaOH, and carboxyl of polyacrylic acid can react to increase dipole moment of the polyacrylic acid, and has ion and dipole cross-linking effect with ionic liquid.
The ionic liquid is [ EMIM ] [ TFSI ], provides conductivity of gel, has ion and dipole cross-linking effect with polymer, and can reduce the robustness of the polymer so as to increase the flexibility of polymer chains.
In conclusion, the flexibility and the rigidity of the conductive gel are balanced through the design of a certain degree of flexibility and a main chain structure and the microscopic multiple physical crosslinking effect, so that better performance is obtained; in particular, it is proposed that the room temperature co-solvent evaporation process greatly simplifies the gel preparation steps.
In order to achieve the above purpose, the technical scheme adopted by the invention is as follows.
An ionic gel based on multiple physical crosslinking, which comprises a copolymer and an ionic liquid, wherein a physical crosslinking system is formed by ion-dipole interaction, hydrogen bonds and ion clusters between the copolymer and the ionic liquid, so as to obtain the conductive ionic gel.
Further, the structure of the copolymer is shown as a formula (I):
in the formula (I), M + Is an alkali metal cation of group IA, x, y and z respectively represent each monomer inThe molar ratio of x+y+z=1 in the copolymer, where x is 0.83 to 0.875, y is 0 to 0.09, and z is 0.063 to 0.17. For example, x is 0.83, 0.835, 0.84, 0.845, 0.85, 0.855, 0.86, 0.865, 0.87, or 0.875. For example, y is 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08 or 0.09. For example, z is 0.063, 0.065, 0.07, 0.075, 0.08, 0.085, 0.09, 0.095, 0.1, 0.105, 0.11, 0.115, 0.12, 0.125, 0.13, 0.135, 0.14, 0.145, 0.15, 0.155, 0.16, 0.165, or 0.17.
Further, the mass percentage of the copolymer is 40% -60% based on the total mass of the ionic gel, and the mass percentage of the ionic liquid is 40% -60%. For example, the mass percent of the copolymer is 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, or 60%. For example, the ionic liquid comprises 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59% or 60% by mass.
Further, the ionic liquid is room temperature ionic liquid which is formed by taking alkyl imidazole salts as cations and anions. Preferably, the ionic liquid is [ EMIM][TFSI]、[BMIM][TFSI]、[BMIM][BF 4 ]Or [ BMIM ]][PF 6 ]。
A method of preparing an ionic gel according to any one of the preceding claims, comprising the steps of:
step 1, preparing an ionized copolymer precursor, wherein the precursor is prepared by free radical polymerization of two monomers;
step 2, completely dissolving the prepared precursor by an organic solvent, and then adding alkali to ionize the precursor to obtain an ionized polymer solution;
step 3, adding an ionic liquid into the ionized polymer solution, and stirring to mix the polymer solution with the ionic liquid to obtain a mixed solution;
and 4, standing the mixed solution at normal temperature to volatilize and remove the cosolvent, and drying.
Further, in step 1, the two monomers used for the precursor are a monomer a and a monomer B, respectively, wherein the monomer a is at least one selected from the group consisting of acrylamide, methyl methacrylate, methyl acrylate, n- (iso) butyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate and 2-hydroxypropyl acrylate. Preferably, monomer B is acrylic acid. Preferably, the molar ratio of monomer a to monomer B is 5, 6 or 7.
Further, in step 2, the organic solvent is selected from one, two, three, four or five of methanol, toluene, acetone, dichloromethane and dimethyl sulfoxide.
The alkali is at least one selected from LiOH, naOH and KOH.
Preferably, the amount of the base added is 50mol%, 60mol%, 70mol%, 80mol%, 90mol% or 100mol% to the molar percentage of carboxyl groups in the monomer B in the precursor.
Further, in step 3, the ionic liquid is composed of anions and cations; preferably, the anions are: hexafluorophosphate, acetate, trifluoroacetate, sulfate, bisulfate, alkyl sulfate, nitrate, dicyandiamide [ N (CN) 2 ] – Triflate [ CF 3 SO 3 ] – Bis-trifluoromethanesulfonyl imide [ N (CF) 3 SO 2 ) 2 ] – And tris [ (trifluoromethyl) sulfonyl ]]Methane [ C (CF) 3 SO 2 ) 3 ] – At least one of (a) and (b); the cation is at least one of alkyl quaternary ion and pyrrolidinium; preferably, the mass percentage of the ionic liquid in the whole mixed liquid is 50wt% or 60wt%.
An ionic gel flexible strain sensor comprising an ionic gel as claimed in any one of the preceding claims or an ionic gel prepared by a method as claimed in any one of the preceding claims.
The PMMA copolymer forming the ionic gel strain sensor has a structure shown in a formula (I):
in the formula (1), M + Including but not limited to group IA alkali metal cations, in addition to Li + 、Na + 、K + In addition, any cation that can produce a large dipole moment can be selected. The polymers x, y, z are preferably divided by 10:1: 1. 50:3: 7. 5:1: and 0, the ionization proportion can be freely regulated and controlled according to the actual application environment of the sensor.
The initial polymer synthesized in the formula (1) has a molar ratio of initial monomer charge to methyl methacrylate to acrylic acid of 5, 7, etc., but not less than 4, otherwise the ionic liquid becomes less compatible, and the weight average force of the polymer is not less than 150000 Da. The molecular weight can be regulated and controlled, and is generally controlled between 150000 Da and 300000 Da.
In the ionic gel, the mass percentage of the ionic liquid serving as a matrix is 40% -60%, and the mass percentage of P (MMA-AA) forming a physical cross-linked network is 40% -60%.
The ionic liquid can be room temperature ionic liquid composed of alkyl imidazole salt as cation and anion, such as [ EMIM ]][TFSI]、[BMIM][TFSI]、[BMIM][BF 4 ]、[BMIM][PF 6 ]Etc. The ionic liquid structure of the invention is shown as a formula (II):
the preparation method of the ionic gel strain sensor for physical crosslinking comprises the following steps:
step one, dissolving the binary copolymer P (MMA-AA) by using a methanol/toluene mixed solvent with a certain mass ratio at room temperature, and stirring until the binary copolymer P (MMA-AA) is completely dissolved to obtain a methanol toluene solution of poly (methyl methacrylate-acrylic acid).
And step two, adding a quantitatively calculated NaOH methanol solution into the mixed solution according to the selected z value, and stirring until the ionization reaction is complete.
And thirdly, adding quantitative ionic liquid 1-ethyl-3-methylimidazole bis (trifluoromethanesulfonyl imide) salt ([ EMIM ] [ TFSI ]) into the mixed solution, and uniformly stirring.
Pouring the mixed solution prepared in the step three into a polytetrafluoroethylene mold, wrapping an aluminum foil, uniformly punching holes, volatilizing in a fume hood, and continuously drying in a vacuum drying oven to obtain the ionic gel.
The stirring time of the methanol/toluene solution of poly (methyl methacrylate-acrylic acid) (P (MMA-co-AA)) in the first step should be 4h to 6h, the mass ratio of methanol to toluene should be 5, and the mass to be added should be determined according to the mass of the polymer to be added.
In the second step, naOH is accurately weighed in the methanol solution of NaOH, and the method is calculated as follows. Let the relative atomic mass of chain A be M A The relative atomic mass of chain B is M B The mass of NaOH added is calculated as follows: { [ M ] B / (M A +M B )]* Ionization degree }. Times.M NaOH . The ionization degree is 50% -100%. The amount of methanol is generally greater than 0.3mmol/mL as long as it dissolves NaOH.
In the third step, the mass fraction of the added ionic liquid can be 40%, 50% and 60%. The stirring time is at least 6 hours.
In step four, the mold size of polytetrafluoroethylene is selected according to the thickness of the film to be produced, and typically a mold film of 40 x 60mm for 600mg of polymer is approximately 0.4mm thick. The time for volatilizing and removing the solvent at normal temperature is 12-18 h. The temperature of the vacuum drying oven is 65 ℃ and the heating time is at least 24 hours.
The ionic gel provided by the invention has certain self-repairing property, and the self-repairing speed is more than 2 hours. The specific implementation method is that after the complete gel is cut off, the fracture is contacted together, and if necessary, a certain external force and auxiliary solvent can be implemented. Its self-repair is achieved by the reformation of broken non-covalent bonds. The self-repairable gel provides a guarantee for the accidental use of the strain sensor. The ionic liquid is fixed by multiple non-covalent actions to form a network skeleton structure, so that the advantages of easily available comprehensive monomers, simple and convenient preparation, excellent performance, mass production and the like are realized, and the sensor is endowed with practical significance; the prepared sensor can be attached to the surface of the skin, can sense and identify the movement of muscles at any time, can avoid measurement deviation generated by the movement of the muscles to the greatest extent, can measure accurate data, and is used in the fields of human health detection and the like.
In conclusion, the single-network ionic gel strain sensor with the simple structure provided by the invention has excellent mechanical property, thermal stability and ionic conductivity, and can be widely applied to aspects such as human motion detection.
The invention has the beneficial effects that:
the invention prepares a stretchable ionic gel strain sensor composed of a physically cross-linked poly (methyl methacrylate-acrylic acid-sodium acrylate) (P (MMA-co-AA-co-AANa)) elastomer network. The ionic gel shows good mechanical properties (maximum tensile stress 610KPa, strain 1160%), a low ionic liquid loading (60 wt%) can achieve the required ionic conductivity (room temperature >0.12mS/cm. the sensor can still maintain a gel state in a wide temperature range (20 to 180 ℃) and is suitable for harsh environments and has long-term electrical signal stability.
1) The selected polymer has cheap and easily obtained raw materials, simple structure and is expected to be produced in large scale;
2) The single-network ionic gel has excellent mechanical properties, and solves the problem of complex technology in preparation compared with complex double-network gel;
3) The single network ionic gel can realize certain self-repairing at room temperature due to the recombination of non-covalent bonds;
4) The single-network ion gel sensor has low delay time, namely high sensitivity in detection, and good contact with human skin, and is expected to be applied to the fields of human health detection and the like.
Drawings
FIG. 1 is a schematic diagram of an ionic gel prepared in example 2 in a mixed solution of deuterated methanol/deuterated chloroform at a mass ratio of 5 1 H NMR spectrum.
FIG. 2 is a gel permeation chromatography graph of the polymer prepared in example 1.
FIG. 3 is an infrared plot of the polymer films, ionized polymer films, and ionic gels prepared in example 1, example 2.
FIG. 4 is a thermal weight loss curve of the ionic gel prepared in example 2.
Fig. 5 is an SEM image of the ionic gel prepared in example 2.
FIG. 6 is a SAXS/WAXS plot of the ionic gels prepared in example 1, example 2.
FIG. 7 is a stress-strain plot of the ionic gels prepared in example 2 with varying degrees of ionization.
FIG. 8 is a temperature swing dynamic rheology curve of the ionic gel prepared in example 2.
Fig. 9 is a graph of normal temperature conductivity for the ionic gels prepared in example 2 with varying degrees of ionization and a graph of temperature change conductivity for one of the samples.
Fig. 10 is a time-resistance change rate curve of the ion gel strain sensor prepared in example 3 when monitoring human body movement.
Detailed Description
The invention is further described below by means of specific examples.
The synthesis of poly (methyl methacrylate-acrylic acid) of example 1, formula iii, is as follows:
taking the case where the molar ratio of the monomer A to the monomer B is 5 as an example.
(1) 5.60g (0.56 mmol) of monomer A Methyl Methacrylate (MMA), 0.80g (0.112 mmol) of monomer B Acrylic Acid (AA), 8.0mg of initiator Azobisisobutyronitrile (AIBN) and 12ml of dioxane were weighed into a polymerization tube and stirred uniformly.
(2) And (3) under the state of introducing high-purity argon, putting the solution in the polymerization tube in the step (1) into liquid nitrogen, after the solution is completely frozen, converting the ventilation ports of the double calandria into an air extraction state, vacuumizing the interior of the polymerization tube, then carrying out three times of ventilation-re-air extraction, and then hydrolyzing and freezing at normal temperature under the ventilation state.
(3) Repeating the step (2) at least three times to ensure that no oxygen or oxygen is not dissolved in the mixed solution in the polymerization tube.
(4) Finally, in the state that the liquid in the pipe is frozen, vacuumizing and burning the pipe orifice by using an alcohol burner, and sealing the polymerization pipe. Then the liquid in the tube was thawed and reacted in an oil bath at 65℃for about 15 hours.
(5) After the reaction is finished, after the reaction liquid is cooled to room temperature, the reaction liquid is slowly poured into 150mL of normal hexane for precipitation after the polymerization tube is broken up, and the precipitate is taken out. The precipitate was then placed again in 150mL of n-hexane solvent and sonicated in an sonicator for 30 minutes to remove the high boiling dioxane entrapped in the precipitate. Finally, the precipitate is placed in a vacuum oven to be dried for 24 hours at 65 ℃ to obtain the copolymer.
Example 2, the preparation of the ionic gel, comprises the following specific steps:
(1) 600mg of the copolymer prepared in example 1 was dissolved in a mixed solvent of 6g of methanol and 1.2g of toluene, respectively, and then 20.7mg (ionization degree: 50%), 29.0mg (ionization degree: 70%), 41.4mg (ionization degree: 100%) of sodium hydroxide was added thereto, followed by stirring for about 4 hours until ionization was completed. The structure is shown as a formula III, wherein M=Na.
(2) 900mg of ionic liquid [ EMIM ] [ TFSI ] is added into each solution, and stirred for 6 hours, and the solutions are named as 50-60%, 70-60% and 100-60% respectively. Further, the solution was poured into a mold. Volatilizing at room temperature for 12h, removing the solvent, and then drying in a vacuum oven at 65 ℃ for 24h to obtain the conductive ionic gel.
Example 3, the preparation and testing method of the ion gel strain sensor comprises the following specific steps:
(1) The gel material of the ion gel strain sensor to be tested prepared in example 2 was cut into a rectangle with a cutter. And connecting two copper wires to two ends of the conductive gel fixed at the mechanical motion joint by using a conductive adhesive tape, and then connecting to a source meter of the Jili 2601B system to assemble the flexible strain sensor.
(2) And selecting a measurement R-T mode in a control software system, wherein after the initial resistance is stable, the mechanical movement drives the conductive gel at the joint movement to change in strain, so that the resistance of the conductive gel is changed. According to different amplitudes of the motion, the change of the resistance is also different, so that the monitoring purpose of the strain sensor for detecting the motion is achieved.
Analysis of results:
FIG. 1 is a schematic diagram of an ionic gel prepared in example 2 in a mixed solution with a deuterated methanol/deuterated chloroform mass ratio of 5 1 H NMR spectrum. And (3) checking chemical displacement and calculating the corresponding peak area to prove that the copolymer consistent with the feeding ratio is synthesized.
FIG. 2 is a gel permeation chromatograph of the carboxymethylesterified polymer prepared in example 1. As can be seen from FIG. 1, M of P (MMAA-co-AA) polymerized by ordinary free radicals w The polydispersity was around 4 at around 150,000 Da. In the later stage of the polymerization reaction, the viscosity of the system is observed to be large, the polymer chain diffusion is not facilitated, the diradical coupling is difficult to terminate, and therefore, the dispersion degree of the obtained polymer is wider.
FIG. 3 is an infrared plot of the polymer prepared in example 1, the ionized polymer prepared in example 2, and an ionic gel having V 1580 、V 1360 、V 1060 Is a characteristic peak of (2).
Fig. 4 is a graph of thermal weight loss of the ion gel strain sensor prepared in example 2. About 10mg of ionic gel was taken and tested for thermal stability by using a German X/STA 449C/6/G thermogravimetric analyzer, and the temperature was raised at a rate of 10 ℃/min within 0-600 ℃. The results showed that the 5% thermal decomposition temperature was about 273℃under a nitrogen atmosphere, and the thermal stability was good.
Fig. 5 is an SEM image of the ionic gel prepared in example 2, the ionic gel in a being x (y+z) =5:1, y: z=1:1; the ionic gel in b is x (y+z) =5:1, y: z=3:7; the ionic gel in c is x (y+z) =5:1, y: z=0:10; the ionic gel in d is x (y+z) =7:1, y: z=1:1; the ionic gel in e is x (y+z) =7:1, y: z=3:7; the ionic gel in f is x (y+z) =7:1, y: z=0:10. All showed a smooth film surface without macroscopic phase separation.
FIG. 6 is a SAXS/WAXS plot of the ionic gels prepared in example 1, example 2. When the molar ratio of monomer MMA to AA is 5, the SAXS curve in a is at q=1.1 nm at different degrees of ionization -1 The peak at b indicates the presence of ionic clusters in the ionic gel, the WAXS curve in b at q=10 and 15nm -1 The peaks at these points further demonstrate the presence of ionic clusters.
FIG. 7 is a stress-strain graph of the ionic gel strain sensor prepared in example 2. A dumbbell-shaped specimen having a length of 3.5cm and a width of 8mm was produced from a film having a thickness of 0.2mm to 0.5mm, and tensile test was performed at a rate of 8mm/min or 10mm/min on a multifunctional tester. When the molar ratio of the monomer MMA to the monomer AA is 5, the tensile rate of the film with different ionization degrees is 920-1170% and the tensile strength is 608Kpa-371Kpa when the ionic liquid content is 60wt%.
FIG. 8 is a temperature change dynamic rheological profile of the ionic gel strain sensor prepared in example 2. An ionic gel having a thickness of 1mm was heated from room temperature to 170℃at 2℃per minute using a DHR-2 rheometer from Waters, USA, using a 1Hz oscillation mode. The results show that the storage modulus (about 20000 Pa) is always greater than the loss modulus (about 8000 Pa), i.e. no sol-gel transition occurs and is always solid. The prepared ionic gel has good thermal stability at high temperature.
FIG. 9 is a conductivity test of ionic gel strain sensors of varying degrees of ionization with a molar ratio of monomer MMA to AA of 5 and an ionic liquid content of 60wt%. Cutting a film with the thickness of about 0.3mm into a 16mm wafer film by using a cutter, clamping the wafer film by using a stainless steel sheet, testing impedance spectrum on a Shanghai Chenhua CHI760e system by adopting an AC-impedance mode, and calculating by using a conductivity formula delta=L/(R.s) after the impedance value is obtained, wherein L is the film thickness, R is the impedance, and S is the cross-sectional area of the film. It can be seen from the normal-temperature electrochemical impedance spectrum a and the conductivity chart b that the conductivity is slightly reduced with the increase of the ionization degree, and the follow-up stability is unchanged. From the variable-temperature electrochemical impedance spectrum c and the conductivity graph d, the conductivity increases along with the temperature rise, the numerical induction effect of the temperature on the conductivity is obvious, and the temperature increases from 0.27mS/cm to 1.11mS/cm at normal temperature.
FIG. 10 is a resistance-strain curve of the ion gel strain sensor prepared in example 3. The sensors are respectively arranged on the throat a, the wrist b, the elbow c, the index finger d and the knee e and are applied to human body movement detection. Experimental results prove that the ionic gel has the advantages of good durability, good stability, high response speed and the like when being used as a strain sensor, and can be used for rapid motion detection.
The present invention is not described in detail in part as being well known to those skilled in the art. The above examples are merely illustrative of preferred embodiments of the invention, which are not exhaustive of all details, nor are they intended to limit the invention to the particular embodiments disclosed. Various modifications and improvements of the technical scheme of the present invention will fall within the protection scope of the present invention as defined in the claims without departing from the design spirit of the present invention.

Claims (2)

1. The preparation method of the ionic gel based on the multiple physical crosslinking effect is characterized in that the ionic gel comprises a copolymer and an ionic liquid, and a physical crosslinking system is formed through ion-dipole interaction, hydrogen bonds and ion clusters between the copolymer and the ionic liquid to obtain conductive ionic gel;
the structure of the copolymer is shown as a formula (I):
in the formula (I), M + X, y, z represent the molar ratio of the monomers in the copolymer, x+y+z=1, wherein x is 0.835 to 0.875, y is 0 to 0.09, and z is 0.063 to 0.17;
the mass percentage of the copolymer is 41-60% based on the total mass of the ionic gel, and the mass percentage of the ionic liquid is 41-60%;
the IA group alkali metal cation is Li + 、Na + Or K + ；
The method comprises the following steps:
step 1, preparing an ionized copolymer precursor, wherein the precursor is prepared by free radical polymerization of two monomers;
step 2, completely dissolving the prepared precursor by an organic solvent, and then adding alkali to ionize the precursor to obtain an ionized polymer solution;
step 3, adding an ionic liquid into the ionized polymer solution, and stirring to mix the polymer solution with the ionic liquid to obtain a mixed solution;
step 4, placing the mixed solution at normal temperature to volatilize and remove the cosolvent, and drying;
in the step 1, the two monomers used by the precursor are a monomer A and a monomer B respectively, wherein the monomer A is methyl methacrylate; monomer B is acrylic acid; the molar ratio of the monomer A to the monomer B is 5, 6 or 7;
in the step 2, the organic solvent is selected from at least one of toluene, acetone, methylene dichloride and dimethyl sulfoxide; the alkali is at least one selected from LiOH, naOH and KOH; the addition amount of the alkali and the mole percentage of carboxyl in the monomer B in the precursor are 60mol%, 70mol%, 90mol% or 100mol%;
the ionic liquid is room-temperature ionic liquid which is formed by taking alkyl imidazole salts as cations and anions.
2. An ionic gel flexible strain sensor comprising an ionic gel prepared according to the method of claim 1.
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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN105153338A (en) * 2015-10-18 2015-12-16 长春工业大学 Preparation method of polymethyl methacrylate conductive gel
CN113061266A (en) * 2021-03-22 2021-07-02 北京大学 High-strength ionic gel based on multiple non-covalent crosslinking effects

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CN1934212B (en) * 2004-04-19 2010-12-22 Lg化学株式会社 Gel polymer electrolyte containing ionic liquid and electrochromic device using the same

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Publication number Priority date Publication date Assignee Title
CN105153338A (en) * 2015-10-18 2015-12-16 长春工业大学 Preparation method of polymethyl methacrylate conductive gel
CN113061266A (en) * 2021-03-22 2021-07-02 北京大学 High-strength ionic gel based on multiple non-covalent crosslinking effects

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