CN115894763A - Hydrogel strain sensing material and preparation method and application thereof - Google Patents
Hydrogel strain sensing material and preparation method and application thereof Download PDFInfo
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Abstract
The invention discloses a hydrogel strain sensing material and a preparation method and application thereof. Firstly soaking the polyampholyte preformed gel in a metal salt solution, then applying external force to stretch to a certain pre-stretching ratio, then soaking in deionized water to remove redundant ions by dialysis, and finally removing the external force to enable the gel to reach a balanced state. The obtained hydrogel material not only has good mechanical properties, but also has good mechanical responsiveness and electrical properties. The preparation process of the invention is not only simple and convenient to operate, but also has excellent product performance, and can be used in the fields of wearable electronic equipment, sensing technology, soft robots and the like.
Description
Technical Field
The invention relates to the technical field of high polymer materials, in particular to a hydrogel strain sensing material and a preparation method and application thereof.
Background
The high molecular hydrogel is a three-dimensional crosslinking hydrophilic polymer containing a large amount of moisture. Because of having physical properties of softness, wetness and the like, the hydrogel material shows attractive application prospects in the fields of biological tissue engineering, biomedicine, flexible electronics, soft robots and the like. Traditional synthetic hydrogels generally have non-uniform network structures or lack energy dissipation mechanisms, resulting in poor mechanical properties, severely limiting their practical applications.
In response to the problem of weak mechanical properties, in recent years, gong et al prepared a novel Polyampholyte (PA) hydrogel by radical solution polymerization using an anionic monomer and a cationic monomer based on the "sacrificial bond" principle (j.p.gong, "while double network hydrogels so tough.
To further improve the mechanical properties of PA hydrogels, huang et al recently prepared ion-bond and metal-coordinate bond synergistically reinforced and toughened PA hydrogels by introducing metal-coordinate bonds into the hydrogel network using a simple secondary equilibrium method (Y. Huang, et al, "Strong drug polymeric hydrogels of ionic and metal-ligand bonds", advanced Functional Materials 31 (2021) 2103917.). The method can effectively strengthen and toughen the PA hydrogel mainly due to the fact that polyvalent metal ions can form metal coordination bonds with anionic groups in a hydrogel network, so that the original PA hydrogel network based on ionic bonds is adjusted and optimized, and synergistic toughening is realized.
On the basis, the invention further utilizes a pre-stretching treatment means to induce the orientation of polymer chains in the PA hydrogel network, and the obtained hydrogel not only has good conductivity in a water balance state, but also shows excellent strain response capability, can be used as a strain sensor, and expands the application of the hydrogel in the fields of biological tissue engineering, flexible electronics and the like.
Disclosure of Invention
The invention aims to provide a hydrogel-based strain sensor which can show good conductivity and high-sensitivity strain signal transmission performance in a water balance state and a preparation method thereof, and has the advantages of simple process, easy operation control, easy obtainment of raw materials and short preparation period.
The scheme adopted by the invention for solving the technical problems is as follows:
a method for preparing a strain sensing material comprises the following steps:
1) Mixing and dissolving an anionic monomer, a cationic monomer, a cross-linking agent and an initiator in deionized water;
2) Injecting the mixed solution obtained in the step 1) into a mold, and initiating polymerization reaction of two monomers to obtain flexible preformed polyampholyte gel;
3) Soaking the preformed gel obtained in the step 2) in an aqueous solution containing metal ions to obtain supersaturated gel;
4) Applying external force to the supersaturated hydrogel obtained in the step 3) and stretching the supersaturated hydrogel to a certain pre-stretching ratio;
5) Keeping the pre-stretched hydrogel in the step 4) in a stretched state, and dialyzing to remove impurities in the hydrogel network structure to obtain the metal ion crosslinked oriented state polyampholyte hydrogel;
6) And (3) removing the external force from the oriented polyampholyte hydrogel crosslinked by the metal ions in the step 5) to obtain the strain sensing material.
Preferably, the anionic monomer of step 1) comprises sodium p-styrenesulfonate (NaSS); the cationic monomer is selected from methacryloyloxyethyl trimethyl ammonium chloride (MATAC), acryloyloxyethyl trimethyl ammonium chloride (DMAEA-Q), N, N, N-trimethyl-3- (2-methallylamido) -1-propanaminium chloride (MPTC), N, N, N-trimethyl-3- (2-methallylamido) -1-propanaminium chloride (DMAPAA-Q).
Preferably, the ratio of the molar amount of the anionic monomer to the total molar amount of the anionic monomer and the cationic monomer in the step 1) is (0.48 to 0.52): 1; the total molar concentration of the monomers in the mixed solution is 2.1-2.7 mol/L; the cross-linking agent and the initiator respectively account for 0.1 to 0.5 percent of the total molar weight of the monomers.
Preferably, the crosslinking agent of step 1) comprises N, N' -methylenebisacrylamide; the initiator comprises alpha-ketoglutaric acid.
Preferably, the metal ion in step 3) is selected from Fe 3+ 、Al 3+ 、Ca 2+ 、Zn 2+ 。
Preferably, the concentration of the metal ions in the metal ion solution in the step 3) is 0.3-2.0 mol/L; the soaking time is 48 to 72 hours.
Preferably, in step 4), the pre-stretching ratio is between 1.0 and 5.0m/m.
Preferably, after the external force is removed in the step 6), the water is kept for more than 1 hour in a water balance state, and further the water can be placed in deionized water for balancing for more than 1 hour.
The invention also provides a strain sensing material prepared by the method.
The invention also provides application of the strain sensing material, and strain sensing is realized through resistance response of the strain sensing material under different strain conditions. The strain sensing material can realize strain sensing under the condition of higher water content.
The invention obtains the metal coordination cooperative orientation structure reinforced polyampholyte hydrogel by firstly introducing polyvalent metal cations into the polyampholyte gel and pre-stretching the polyampholyte gel at the same time, and the hydrogel also shows good conductivity and high sensitivityThe signal transmission performance is changed. During the pre-stretching process, part of the-SO in the polymer 3 - The groups form coordination bonds under the action of metal ions, so that the ionic bonds and the metal coordination bonds are coordinated to fix a molecular chain in the pre-stretching direction, and the oriented structure reinforced polyampholyte hydrogel is achieved. Under the action of external stress, the dynamic bonds in the hydrogel network can effectively dissipate energy, so that the mechanical properties of the hydrogel are remarkably improved, and meanwhile, the dynamic bonds can be recombined in a short time, so that the hydrogel has excellent fatigue resistance. Meanwhile, the oriented structure reinforced polyampholyte hydrogel also has good conductivity and high-sensitivity strain signal transmission performance, and has the advantages of one-pot material feeding, one-time polymerization reaction, free forming, high strength, high toughness and the like. The method becomes a common method for preparing the metal coordination synergistic pre-stretching induced orientation reinforced and toughened polyampholyte hydrogel with high-sensitivity strain sensing.
Compared with the prior art, the invention has the following advantages and remarkable progress:
1) The preparation process is extremely simple, the production period is short, the process conditions are simple and convenient, the production cost is low, and the raw materials are easy to obtain.
2) In the method, two different forms of physical bonds are adopted to fix the molecular chain in the pre-stretching direction to obtain the oriented crosslinked hydrogel network, so that the tensile strength, young modulus and mechanical toughness of the hydrogel are obviously improved, and the hydrogel in a water balance state is endowed with high sensitivity as a strain sensor.
Drawings
The invention is further illustrated by means of the attached drawings, the examples of which are not to be construed as limiting the invention in any way.
FIG. 1 is a schematic diagram of the design of a metal coordination cooperative pre-stretching induced orientation enhanced polyampholyte hydrogel with high-sensitivity strain sensing according to the present invention;
FIG. 2 is a scanning electron microscope image of the hydrogel prepared by the present invention, wherein (a) is a cross-sectional electron microscope image of the original hydrogel, and (b) is an axial cross-sectional electron microscope image of the pre-stretched induced oriented reinforced hydrogel;
FIG. 3 shows the results of mechanical properties in the orientation direction corresponding to different concentrations of iron ions in the hydrogel prepared according to the present invention, wherein the pre-stretching ratio is constant at 4.0m/m (which is 4 times of the initial hydrogel), (a) is the stress-strain curve, and (b) is the tensile breaking strength, elongation at break, young's modulus and tensile breaking work;
FIG. 4 shows the results of mechanical properties along the orientation direction corresponding to the pre-stretching ratio of the hydrogel prepared in accordance with the present invention, wherein the iron ion concentration is constant at 1.0mol/L, (a) is the stress-strain curve, and (b) is the tensile breaking strength, elongation at break, young's modulus and tensile breaking work;
FIG. 5 shows the results of electrical properties in the orientation direction for hydrogels prepared according to the present invention with different iron ion concentrations, wherein the pre-stretching ratio is constant at 4.0m/m (i.e., 4 times the initial hydrogel), (a) the conductivity, (b) the relative resistance-strain change, (c) the GF value;
FIG. 6 shows the results of electrical properties along the orientation direction corresponding to the pre-stretching ratio of the hydrogel prepared according to the present invention, wherein the iron ion concentration is constant at 1.0mol/L, (a) the conductivity, (b) the relative resistance-strain change, (c) the GF value;
FIG. 7 shows the results of the fatigue performance test of the hydrogel prepared according to the present invention as a strain sensor, wherein (a) the relative resistance changes at 50%, 100%, 150%, 200%, 250%, 300% strain, (b) the 50% strain 300 cycles fatigue test;
fig. 8 is a schematic diagram and a physical diagram of a pneumatic gripper for indicating an object by using the hydrogel prepared by the invention as a strain sensor, wherein (a) is a physical diagram of the pneumatic gripper, (b) is a physical diagram of fruit with different sizes, and (c) is a diagram for monitoring resistance change of the hydrogel caused by different deformation generated by gripping different fruits.
Detailed Description
The following examples are provided to further illustrate the present invention for better understanding, but the present invention is not limited to the following examples.
Example 1
1) Weighing 2.34558g of sodium p-styrenesulfonate, 2.3244g of N, N-trimethyl-3- (2-methyl allyl propionyl) -1-propylamine chloride, 0.0039g of N, N' -methylene bisacrylamide and 0.0037g of alpha-ketoglutaric acid at room temperature, and adding deionized water to prepare 10mL of mixed solution; the concentration of sodium p-styrene sulfonate is 1.13mol/L, the concentration of N, N, N-trimethyl-3- (2-methyl allyl propionyl) -1-propyl ammonium chloride is 1.20mol/L, the concentration of N, N' -methylene bisacrylamide is 0.0025mol/L, and the concentration of alpha-ketoglutaric acid is 0.0025mol/L;
2) Placing the beaker filled with the mixed solution in the step 1) in a water bath at 60 ℃ and stirring for 10 minutes until the mixed solution is completely dissolved;
3) Injecting the mixed solution obtained in the step 2) into a glass mold, reacting for 12 hours at room temperature, performing ultraviolet-initiated polymerization to obtain a binary copolymer of sodium styrene sulfonate and N, N, N-trimethyl-3- (2-methyl allyl propionyl) -1-propyl ammonium chloride, and performing co-crosslinking through chemical bonds and ionic bonds to obtain a flexible preformed hydrogel;
4) Weighing 4.86g of anhydrous ferric chloride, adding the anhydrous ferric chloride into deionized water to prepare a ferric chloride solution with the concentration of 0.3mol/L, and soaking the preformed hydrogel obtained in the step 3) in the ferric chloride solution for 48 hours, wherein ferric ions can destroy ionic bonds in a network of the preformed hydrogel to obtain a supersaturated hydrogel with certain strength;
5) Pre-stretching the supersaturated hydrogel obtained in the step 4) by 4.0 times;
6) Soaking the pre-stretched hydrogel obtained in the step 5) in deionized water, wherein the water changing frequency is 12 hours/time; dialyzing in water to remove residual unreacted monomers and cross-linking agent initiators in the hydrogel, and simultaneously removing sodium ions, chloride ions and uncoordinated iron ions to obtain the iron ion cross-linked oriented polyampholyte high-strength hydrogel;
7) Removing external force from the hydrogel obtained in the step 6) to obtain iron ion crosslinked free-state polyampholyte high-strength hydrogel;
the test shows that the tensile breaking strength of the hydrogel material prepared in the embodiment is 3.05MPa, the breaking elongation is 514 percent, the Young modulus is 0.63MPa, and the tensile breaking work is 4.38MJ/m 3 。
Examples 2 to 5
The preparation procedure was the same as in example 1; except that in the step 4), the concentrations of the ferric chloride solution are respectively 0.5mol/L, 0.7mol/L, 1.0mol/L and 2.0mol/L.
Examples 6 to 11
The preparation procedure was the same as in example 4; the difference is that in the step 5), the pre-stretching times of the supersaturated hydrogel are respectively as follows: 1.5 times, 2.0 times, 2.5 times, 3.0 times, 3.5 times, 5.0 times.
Example 12
1-3) the preparation steps are the same as in example 1;
4) Weighing 13.33g of anhydrous aluminum chloride, adding the anhydrous aluminum chloride into deionized water to prepare an aluminum chloride solution with the concentration of 0.5mol/L, and soaking the preformed hydrogel obtained in the step 3) in the aluminum chloride solution for 48 hours, wherein ionic bonds in the preformed hydrogel can be destroyed by aluminum ions, so that a supersaturated hydrogel with a certain strength is obtained;
5) Pre-stretching the supersaturated hydrogel obtained in the step 4) by 4.0 times;
6) Soaking the pre-stretched hydrogel obtained in the step 5) in deionized water, wherein the water changing frequency is 12 hours/time; dialyzing in water to remove residual unreacted monomers, cross-linking agents and initiators in the hydrogel, and simultaneously removing sodium ions, chloride ions and uncoordinated aluminum ions to obtain the aluminum ion cross-linked oriented polyampholyte high-strength hydrogel;
7) Removing external force from the hydrogel obtained in the step 6) to obtain the aluminum ion crosslinked free-state polyampholyte high-strength hydrogel.
Example 13
1-3) the preparation steps are the same as in example 1;
4) Weighing 11.11g of anhydrous calcium chloride, adding the anhydrous calcium chloride into deionized water to prepare a calcium chloride solution with the concentration of 0.5mol/L, and soaking the preformed hydrogel obtained in the step 3) in the calcium chloride solution for 48 hours, wherein the ionic bonds in the preformed hydrogel can be damaged by calcium ions, so that a supersaturated hydrogel with a certain strength is obtained;
5) Pre-stretching the supersaturated hydrogel obtained in the step 4) by 4.0 times;
6) Soaking the pre-stretched hydrogel obtained in the step 5) in deionized water, wherein the water changing frequency is 12 hours/time; dialyzing in water to remove residual unreacted monomers, cross-linking agents and initiators in the hydrogel, and simultaneously removing sodium ions, chloride ions and uncoordinated calcium ions to obtain the calcium ion cross-linked oriented polyampholyte high-strength hydrogel;
7) Removing external force from the hydrogel obtained in the step 6) to obtain the calcium ion crosslinked free-state polyampholyte high-strength hydrogel.
Example 14
1-3) the preparation steps are the same as in example 1;
4) Weighing 13.63g of anhydrous zinc chloride, adding the anhydrous zinc chloride into deionized water to prepare a zinc chloride solution with the concentration of 1.0mol/L, and soaking the preformed hydrogel obtained in the step 3) in the zinc chloride solution for 48 hours, wherein the zinc ions can destroy ionic bonds in the preformed hydrogel to obtain a supersaturated hydrogel with certain strength;
5) Pre-stretching the supersaturated hydrogel obtained in the step 4) by 4.0 times;
6) Soaking the pre-stretched hydrogel obtained in the step 5) in deionized water, wherein the water changing frequency is 12 hours/time; dialyzing in water to remove residual unreacted monomers, cross-linking agents and initiators in the hydrogel, and simultaneously removing sodium ions, chloride ions and uncoordinated zinc ions to obtain the zinc ion cross-linked oriented polyampholyte high-strength hydrogel;
7) Removing external force from the hydrogel obtained in the step 6) to obtain the iron ion crosslinked free-state polyampholyte high-strength hydrogel.
Comparative example 1
1) 3) the preparation steps are the same as in example 6;
4) Pre-stretching the hydrogel obtained in the step 3) by 4 times, soaking the hydrogel in deionized water, dialyzing the hydrogel in water to remove residual unreacted monomers, cross-linking agents and initiators in the hydrogel, and removing sodium ions and chloride ions to obtain the ion-crosslinked oriented polyampholyte hydrogel;
5) Removing external force from the hydrogel obtained in the step 4) to obtain the ionic bond crosslinked free-state polyampholyte high-strength hydrogel.
Comparative example 2
1) 4) the preparation steps are the same as in example 6;
5) Weighing 16.20g of anhydrous ferric chloride, adding 100mL of deionized water, adding the deionized water into the deionized water to prepare a ferric chloride solution with the concentration of 1.0mol/L, soaking the polyampholyte hydrogel obtained in the step 4) in the ferric chloride solution for 48 hours, and performing ion coordination crosslinking on the preformed hydrogel in the ferric ion solution to obtain the supersaturated hydrogel with certain strength.
6) The procedure is as in example 6.
Comparative example 3
1-3) the preparation steps are the same as in example 1;
4) Weighing 5.84g of anhydrous sodium chloride, adding the anhydrous sodium chloride into deionized water to prepare a sodium chloride solution with the concentration of 1.0mol/L, and soaking the preformed hydrogel obtained in the step 3) in the sodium chloride solution for 48 hours, wherein the ionic bonds in the preformed gel can be damaged by sodium ions, so that the supersaturated hydrogel with certain strength is obtained;
5) Pre-stretching the supersaturated hydrogel obtained in the step 4) by 4.0 times;
6) Soaking the pre-stretched hydrogel obtained in the step 5) in deionized water, wherein the water changing frequency is 12 hours/time; dialyzing in water to remove residual unreacted monomers, cross-linking agents and initiators in the hydrogel, and simultaneously removing sodium ions, chloride ions and uncoordinated sodium ions to obtain the oriented polyampholyte high-strength hydrogel;
7) Removing external force from the hydrogel obtained in the step 6) to obtain the free-state polyampholyte high-strength hydrogel.
Comparative example 4
1-3) the preparation steps are the same as in example 1;
4) Weighing 7.46g of anhydrous potassium chloride, adding the anhydrous potassium chloride into deionized water to prepare a potassium chloride solution with the concentration of 1.0mol/L, and soaking the preformed hydrogel obtained in the step 3) in the potassium chloride solution for 48 hours, wherein the potassium ions can destroy ionic bonds in the preformed gel to obtain a supersaturated hydrogel with certain strength;
5) Pre-stretching the supersaturated gel obtained in the step 4) by 4.0 times;
6) Soaking the pre-stretched gel obtained in the step 5) in deionized water, wherein the water changing frequency is 12 hours/time; dialyzing in water to remove residual unreacted monomers, cross-linking agents and initiators in the hydrogel, and simultaneously removing sodium ions, chloride ions and uncoordinated potassium ions to obtain the oriented polyampholyte high-strength hydrogel;
7) Removing external force from the hydrogel obtained in the step 6) to obtain the free-state polyampholyte high-strength hydrogel.
Performance testing
1, mechanical Property test
The hydrogel samples obtained in the examples were subjected to tensile testing using a universal tensile testing machine, and the test results are shown in table 1 below.
TABLE 1 mechanical Property data for hydrogel samples
| Tensile strength | Elongation at break | Tensile modulus | Work of tensile failure | |
| Example 1 | 3.05 | 514 | 0.63 | 4.38 |
| Example 2 | 3.13 | 420 | 0.67 | 4.26 |
| Example 3 | 4.97 | 535 | 0.88 | 7.53 |
| Example 4 | 6.60 | 325 | 1.84 | 6.42 |
| Example 5 | 7.35 | 387 | 3.95 | 9.46 |
| Example 6 | 3.41 | 500 | 0.73 | 5.70 |
| Example 7 | 3.59 | 361 | 1.00 | 5.12 |
| Example 8 | 3.91 | 380 | 1.1 | 4.85 |
| Example 9 | 4.2 | 365 | 1.36 | 5.38 |
| Example 10 | 4.70 | 369 | 1.77 | 5.72 |
| Example 4 | 6.60 | 325 | 1.84 | 6.42 |
| Example 11 | 7.90 | 372 | 1.95 | 8.03 |
| Example 12 | 4.61 | 715 | 0.23 | 9.05 |
| Example 13 | 3.43 | 705 | 0.18 | 4.99 |
| Example 14 | 2.96 | 707 | 0.17 | 5.47 |
| Comparative example 1 | 2.1 | 740 | 0.19 | 3.14 |
| Comparative example 2 | 1.92 | 670 | 0.35 | 5.76 |
| Comparative example 3 | 2.19 | 650 | 0.21 | 3.52 |
| Comparative example 4 | 1.93 | 705 | 0.18 | 3.52 |
2, electrical property test:
2.1 conductivity test
The electrical conductivity of the hydrogels prepared in examples 1-5 and comparative example 1, respectively, was first tested, as shown in fig. 5 a; the hydrogels prepared in examples 7,9,4, 11 and comparative example 2 were again tested for electrical conductivity, as shown in figure 6 a.
2.2 resistance Strain responsiveness test
First, the hydrogel samples prepared in examples 1 to 5 and comparative example 1 were tested for the change in relative resistance with strain, respectively, as shown in fig. 5 b; and calculating the ratio of the relative resistance to strain of the sample, abbreviated as GF value (GF = (Delta R/R) 0 ) /epsilon), wherein the calculated GF value in the smaller strain range of epsilon =0-100% is labeled GF S Values whereas GF values calculated over a larger strain range of e =100-350% are labeled GF L Values, as shown in fig. 5 c. The hydrogels prepared in examples 7,9,4, 11 and comparative example 2 were again tested for resistance as a function of strain, as shown in FIG. 6b; and calculating GF in the lower strain range of ε =0-100% S Values and GF over a large strain range of ε =100-350% L The values are shown in figure 6c.
2.3 fatigue test
The hydrogels prepared in example 4 were first tested for resistance change corresponding to 10 cycles of stretching at 50%, 100%, 150%, 200%, 250% and 300% strain, as shown in figure 7 a. The hydrogel prepared in example 4 was again tested for a change in resistance corresponding to 300 cycles of stretching at 50% strain, as shown in figure 7 b.
The hydrogel sample prepared in the embodiment 4 of the invention is further used as a strain sensor to carry out a flexible pneumatic hand-grasping monitoring experiment, and the method specifically comprises the following steps:
1) Attaching a strain sensor to one finger of the pneumatically flexible grip as shown in FIG. 8 a;
2) Driving the gripper to continuously grip different fruits such as pears, apples, oranges, bananas, mangos and the like, as shown in fig. 8 b;
3) Recording the relative resistance changes when picking different fruits such as pear, apple, orange, banana, mango and the like, as shown in fig. 8 c; the experimental results show that the prepared hydrogel with the high GF value can be used as a high-sensitivity strain sensor to be applied to real-time monitoring and tracking of the motion of a human body or a soft robot.
Table 2: electrical property data of the hydrogel samples.
The pre-stretching ratio in the metal coordination pre-stretching induction orientation enhanced polyampholyte hydrogel prepared in examples 1-5 is constant at 4.0m/m, and only the concentration of iron ions changes. Comparative example 1 the pre-stretching ratio of the hydrogel sample prepared was 4.0m/m and the iron ion concentration was 0mol/L. Table 1 shows the mechanical property data of the hydrogel samples prepared in examples 1 to 5 and comparative example 1 in an equilibrium state in water. As can be seen from the data in the table, the tensile breaking strength of the hydrogel is increased from 2.10MPa to 7.35MPa with the increase of the iron ion concentration, and the tensile breaking strength is improved by 2.5 times. The concentration of iron ions in the hydrogel samples prepared in examples 6 to 11 was constant at 1.0mol/L, and only the pre-stretching ratio was changed, while the concentration of iron ions in the hydrogel sample prepared in comparative example 2 was 1.0mol/L and no pre-stretching external force was applied. Table 1 shows the mechanical property data of the hydrogel samples prepared in examples 6 to 11 and comparative example 2 in an equilibrium state in water. As can be seen from the data in the table, the tensile breaking strength of the hydrogel increased from 1.92MPa to 7.90MPa with an increase in the pre-stretching ratio by a factor of 3.1. The reason is mainly that the orientation degree of polymer chains in a hydrogel network is improved through the pre-stretching effect, and the formed metal coordination bonds can lock an orientation structure, so that the mechanical property is enhanced cooperatively. Examples 12 to 14 hydrogel samples prepared with a constant metal ion concentration of 1.0mol/L and a constant draw-down ratio of 4.0m/m, only of polyvalent metal ion species (Al) 3+ 、Ca 2+ 、Zn 2+ ) In contrast, comparative examples 3 and 4 were prepared in which only monovalent metal ions (Na) having no coordinating ability were selected for the hydrogel samples having a constant metal ion concentration of 1.0mol/L and a constant pre-stretching ratio of 4.0m/m + 、K + ). Table 1 also shows the mechanical properties of the hydrogels obtained in examples 12 to 14 and comparative examples 3 and 4. ByAs can be seen from the data in the tables, although the hydrogels of examples 12-14 all exhibited enhanced mechanical properties compared to the original polyampholyte hydrogel, the enhanced effect was different, probably due to the fact that the metal ions and-SO in the hydrogel network 3 - The strength of coordinate bonds between groups. Al with same charge and similar radius 3+ Ionic (8 e-configuration) phase comparison, fe 3+ Ions (18 e-configuration) tend to have some covalent properties, so Fe 3+ with-SO 3 - Coordination bond ratio between groups Al 3+ Is more stable. Zn 2+ And Ca 2+ The radius of the ion is 0.74 and
is slightly larger than Fe 3+ Ions. In addition, zn 2+ And Ca 2+ The charge of the ion being less than Fe 3+ The ions, and thus the relatively weak reinforcing effect, indicates that the strength of the coordinate bonds formed in the hydrogel can be significantly affected by the number of charges of the metal ions. From the data of comparative examples 3 and 4, it can be further seen that the metal coordinate bonds play an important role in the pre-stretch induced orientation-enhanced polyampholyte hydrogel.
The pre-stretching ratio in the metal coordination pre-stretching induction orientation enhanced polyampholyte hydrogel prepared in examples 1-5 was constant at 4.0m/m and only the concentration of iron ions was changed, and the pre-stretching ratio in the hydrogel sample prepared in comparative example 1 was 4.0m/m and the concentration of iron ions was 0mol/L. Table 2 shows the electrical property test data of the hydrogel samples prepared in examples 1 to 5 and comparative example 1 in the equilibrium state in water, including the electrical conductivity and the relative resistance to strain ratio (GF) of the samples over the smaller and larger strain ranges S And GF L ). As can be seen from the data in the table, the conductivity of the hydrogel is increased from 0.002 to 0.123 and is improved by 60.5 times along with the increase of the concentration of iron ions; GF S And GF L The increase from 1.00 and 1.62 to 5.26 and 9.00, respectively, is 4.3 and 4.6 times. Table 2 also shows the equilibrium state in water of the hydrogels prepared in examples 7 (2 times), 9 (3 times), 4 (4 times), 11 (5 times) and comparative example 2 (without pre-stretching)Electrical performance data. As can be seen from the data in the table, as the pre-stretching ratio is increased, the conductivity of the hydrogel is increased from 0.069 to 0.107, which is increased by 0.55 times; GF S And GF L The electrical performance is improved by 2.8 and 1.3 times from 1.49 and 5.68 to 7.41 and 13.0 respectively, and the remarkable improvement of the electrical performance is mainly attributed to that when the pre-stretching ratio is increased, polymer chains in the prepared hydrogel network are oriented along the pre-stretching direction, the hydrogel shrinks in the corresponding vertical pre-stretching direction, and the oriented structure is possibly more beneficial to the transmission of free ions in the hydrogel network, so that the conductivity of a sample is increased; when the pre-stretching force is released, the hydrogel sample will retract to some extent, which may make the resistance strain response more sensitive, as shown in fig. 1. The result shows that the pre-stretching ratio is increased, and the mechanical property, the conductivity and the resistance strain response sensitivity of the prepared hydrogel are also obviously improved.
Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention and not for limiting the protection scope of the present invention, and although the present invention is described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions can be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.
Claims (10)
1. A preparation method of a strain sensing material is characterized by comprising the following steps:
1) Mixing and dissolving an anionic monomer, a cationic monomer, a cross-linking agent and an initiator in deionized water;
2) Injecting the mixed solution obtained in the step 1) into a mold, and initiating polymerization reaction of two monomers to obtain flexible preformed polyampholyte gel;
3) Soaking the preformed gel obtained in the step 2) in an aqueous solution containing metal ions to obtain supersaturated gel;
4) Applying external force to the supersaturated hydrogel obtained in the step 3) and stretching the supersaturated hydrogel to a certain pre-stretching ratio;
5) Keeping the pre-stretched hydrogel in the step 4) in a stretched state, and dialyzing to remove impurities in the hydrogel network structure to obtain the metal ion crosslinked oriented state polyampholyte hydrogel;
6) And (5) removing the external force from the oriented polyampholyte hydrogel crosslinked by the metal ions in the step 5) to obtain the strain sensing material.
2. The method of claim 1, wherein the anionic monomer of step 1) comprises sodium p-styrenesulfonate (NaSS); the cationic monomer is selected from methacryloyloxyethyl trimethyl ammonium chloride (MATAC), acryloyloxyethyl trimethyl ammonium chloride (DMAEA-Q), N, N, N-trimethyl-3- (2-methallylamido) -1-propanaminium chloride (MPTC), N, N, N-trimethyl-3- (2-methallylamido) -1-propanaminium chloride (DMAPAA-Q).
3. The method according to claim 1, wherein the ratio of the molar amount of the anionic monomer to the total molar amount of the anionic monomer and the cationic monomer in step 1) is (0.48 to 0.52): 1; the total molar concentration of the monomers in the mixed solution is 2.1-2.7 mol/L; the cross-linking agent and the initiator respectively account for 0.1 to 0.5 percent of the total molar weight of the monomers.
4. The method of claim 1, wherein the crosslinking agent of step 1) comprises N, N' -methylenebisacrylamide; the initiator comprises alpha-ketoglutaric acid.
5. The method according to claim 1, wherein the metal ion in step 3) is selected from Fe 3+ 、Al 3+ 、Ca 2+ 、Zn 2+ 。
6. The production method according to claim 1, wherein the concentration of the metal ions in the metal ion solution in the step 3) is 0.3 to 2.0mol/L.
7. The production method according to claim 1, wherein the pre-stretching ratio in the step 4) is 1.0 to 5.0m/m.
8. The method of claim 1, wherein the external force is removed in step 6), and the mixture is maintained in a water-balanced state for 1 hour or more.
9. A strain sensing material prepared by the method of any one of claims 1 to 8.
10. Use of a strain sensing material according to claim 9, wherein strain sensing is achieved by the resistive response of the strain sensing material under different strain conditions.
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