CN114621497B - Preparation method of gradient macroporous conductive composite hydrogel for flexible strain sensor - Google Patents
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- G01L1/20—Measuring force or stress, in general by measuring variations in ohmic resistance of solid materials or of electrically-conductive fluids; by making use of electrokinetic cells, i.e. liquid-containing cells wherein an electrical potential is produced or varied upon the application of stress
- G01L1/22—Measuring force or stress, in general by measuring variations in ohmic resistance of solid materials or of electrically-conductive fluids; by making use of electrokinetic cells, i.e. liquid-containing cells wherein an electrical potential is produced or varied upon the application of stress using resistance strain gauges
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Abstract
The invention discloses a preparation method of gradient macroporous conductive composite hydrogel applied to a flexible strain sensor, belonging to the field of flexible electronic materials. Graphene and polyaniline are jointly used as conductive substances, polyacrylamide is used as a flexible substrate, and the gradient macroporous conductive composite hydrogel is obtained through preparation of graphene oxide/polyacrylamide-based composite hydrogel containing a foaming agent, preparation of graphene/polyacrylamide-based conductive composite hydrogel with a gradient macroporous structure and aniline in-situ polymerization. The gradient macroporous conductive composite hydrogel prepared by the invention has excellent mechanical property and sensing property, high sensitivity, wide strain detection range and good circulation stability, can be widely applied to wearable electronic equipment such as flexible sensors and the like, and has wide application prospect in the fields of human motion monitoring and the like.
Description
Technical Field
The invention belongs to the field of flexible electronic materials, relates to preparation of a flexible strain sensor, and particularly relates to a preparation method of gradient macroporous conductive composite hydrogel applied to the flexible strain sensor.
Background
Along with the development of wearable electronic equipment and the attention of people to body health, the application demand of the flexible strain sensor in the field of human motion monitoring is larger and larger. The traditional sensor cannot bear excessive deformation due to the brittleness of the sensor, the requirement of monitoring the motion of the human body cannot be met, and meanwhile, the development of the traditional sensor is further limited by the complex process and the expensive cost. Therefore, there is an urgent need to develop a flexible strain sensor having a wide strain detection range, high sensitivity, and low cost.
The hydrogel has high water content and good biocompatibility, and can be combined with a conductive substance to prepare the hydrogel-based flexible strain sensor with flexibility and conductivity. Polyaniline can be conductive after being doped, so that the conductivity is high, the raw materials are easy to obtain, and the synthesis process is simple, so that the introduction of polyaniline into hydrogel for preparing the flexible sensor is concerned. However, the general pore diameter of the hydrogel is small (usually less than 1 μm, and can reach several micrometers after pore formation), and the phenomenon of hydrogel pore channel blockage is easy to occur in the process of in-situ polymerization of adsorbed aniline, so that the utilization rate of aniline is low, and the sensitivity of the sensor is affected. In addition, polyaniline undergoes volume expansion when electrified for a long time, resulting in structural damage and performance degradation.
Disclosure of Invention
The invention aims to provide a preparation method of gradient macroporous conductive composite hydrogel applied to a flexible strain sensor aiming at the defects of the prior art.
In order to achieve the purpose, the invention adopts the following technical scheme:
a gradient macroporous conductive composite hydrogel applied to a flexible strain sensor is prepared by the following steps:
(1) Preparation of graphene oxide/polyacrylamide composite hydrogel (GPH) containing foaming agent
Adding 54 mu L of hydrophobic monomer into 10ml of sodium chloride/lauryl sodium sulfate solution, stirring for 3h, adding 15-30mg of Graphene Oxide (GO), then adding 5.3g of acrylamide (AAm), 17.2mg of N, N' -Methylene Bisacrylamide (MBA), 0.01-0.03g of foaming agent and 0.05g of ammonium persulfate, magnetically stirring to fully dissolve, and polymerizing for 6h at 45 ℃ to obtain GPH;
(2) Preparation of graphene/polyacrylamide conductive composite hydrogel (RGPH) with gradient macroporous structure
Immersing the prepared GPH into 0.1-0.2mol/L organic acid solution, standing for 5h, heating at 90 ℃ for reaction for 8h, and cleaning to remove impurities to obtain RGPH;
(3) Preparing gradient macroporous conductive composite hydrogel:
soaking the prepared RGPH into a mixed solution of phytic acid and aniline hydrochloride, sealing and storing for 12h, and then cooling in an environment at 0-5 ℃; adding ammonium persulfate into deionized water, mixing, cooling to below 5 ℃, quickly pouring into the solution, uniformly mixing, reacting for 24 hours, and cleaning the product with deionized water to obtain the gradient macroporous conductive composite hydrogel applied to the flexible strain sensor.
The sodium chloride/sodium dodecyl sulfate solution in the step (1) is prepared by dissolving 0.05-0.15g of sodium chloride and 0.1-0.3g of sodium dodecyl sulfate in 10ml of deionized water. The hydrophobic monomer is alkyl methacrylate, and the alkyl carbon chain length of the hydrophobic monomer is 8-18 carbon atoms. The foaming agent is any one of sodium carbonate, sodium bicarbonate, ammonium carbonate and ammonium bicarbonate.
The organic acid in the step (2) is any one of oxalic acid, ascorbic acid, valine, leucine and cysteine.
The molar ratio of the phytic acid to the aniline hydrochloride in the mixed solution in the step (3) is 0.15; the molar ratio of ammonium persulfate to aniline hydrochloride used was 1:1.
According to the invention, graphene and polyaniline are jointly used as conductive substances, and the structural integrity of polyaniline is enhanced through pi-pi conjugation of the graphene and the polyaniline, so that the circulation stability of the composite hydrogel is improved. And the polyacrylamide is used as a flexible substrate, and organic acid is utilized to react with a foaming agent to release CO 2 Constructing a gradient macroporous structure (pores) for the hydrogelThe diameter is from dozens of microns to 100 microns), the problem that aniline monomer and ammonium persulfate initiator are not easy to permeate into hydrogel during in-situ polymerization of hydrogel and pore channels are easy to block during in-situ polymerization of aniline is solved, and the specificity of the gradient structure of the aniline in-situ polymerization significantly improves the sensitivity of hydrogel, so that the flexible strain sensing material with strong mechanical property, high sensitivity and good cycling stability is prepared by a simple synthesis process.
Compared with the prior art, the invention has the following advantages:
(1) According to the invention, hydrophobic monomers enter the micelle under the action of a surfactant, and a hydrophobic association micro-region is formed by a micelle copolymerization method, so that a physical reversible crosslinking point is added to the hydrogel, and a large amount of hydrogen bond actions are formed between hydroxyl and carboxyl on the surface of graphene oxide and an amide group on a polyacrylamide chain, so that the mechanical property of the hydrogel is obviously enhanced.
(2) The invention constructs a macroporous structure with gradient pore diameter change (the pore diameter is from dozens of micrometers to 100 micrometers) for the hydrogel by using a foaming method, solves the problem that pore channels are easy to block due to too small pore diameter when the hydrogel is polymerized in situ, and obviously improves the sensitivity in a mode of synergistically increasing the resistance when the gradient macroporous structure is stretched;
(3) The organic acid adopted by the invention is reductive organic acid which is used as a foaming promoter to react with a foaming agent to control the release of CO 2 And the graphene oxide in the hydrogel is reduced as a reducing agent, so that the function of the organic acid is fully exerted, new impurities are not introduced, and the cost is reduced.
(4) According to the invention, graphene and polyaniline are jointly used as conductive fillers, and the strong pi-pi conjugated acting force of the graphene and the polyaniline can enable the polyaniline to be tightly attached to the surface of the graphene, so that the structural integrity of the polyaniline is improved, the structural damage caused by volume expansion of the polyaniline under long-time electrification is prevented, and the circulation stability is enhanced; and polyacrylamide is used as a flexible substrate to form a double-network hydrogel structure, and a large amount of hydrogen bonds between two networks have the effects of improving the mechanical property of the hydrogel, increasing a conductive path and improving the conductivity of the hydrogel.
(5) The invention has simple preparation process and low cost, and has application potential in the field of manufacturing wearable electronic devices such as flexible strain sensors and the like.
Drawings
FIG. 1 is an electron microscope image of the graphene/polyacrylamide conductive composite hydrogel RGPH with a gradient macroporous structure in example 1;
FIG. 2 is a graph comparing the mechanical properties of hydrogel materials prepared in example 1 with those of comparative examples 1, 2 and 3;
FIG. 3 is an electron microscope image of the graphene/polyacrylamide conductive composite hydrogel RGPH with a uniform porous structure prepared in comparative example 5;
FIG. 4 is a graph comparing the sensitivity of hydrogel materials prepared in example 1 and comparative examples 4 and 5;
FIG. 5 is a graph showing the intermittent loading-unloading response test of the conductive composite hydrogel prepared in example 1;
FIG. 6 is a graph showing the rate of change in resistance of the conductive composite hydrogel prepared in example 1 after 500 cycles of stretching at a stretching speed of 200mm/min and a 50% tensile strain;
FIG. 7 is a graph comparing the conductivity of the conductive composite hydrogel materials prepared in examples 1-5.
Detailed Description
In order to make the present invention more comprehensible, the technical solutions of the present invention are further described below with reference to specific embodiments, but the present invention is not limited thereto.
Example 1
(1) 0.05g of sodium chloride and 0.1g of lauryl sodium sulfate are dissolved in 10ml of deionized water, 54 mu L of lauryl methacrylate is added, 30mg of Graphene Oxide (GO) is added after stirring for 3h, 5.3g of acrylamide (AAm), 17.2mg of N, N' -Methylene Bisacrylamide (MBA), 0.02g of sodium carbonate and 0.05g of Ammonium Persulfate (APS) are added, and after full dissolution by magnetic stirring, the mixture is polymerized for 6h at 45 ℃ to prepare the GPH.
(2) Soaking the prepared GPH into 80ml of 0.2mol/L ascorbic acid solution, standing for 5h, heating at 90 ℃ for reaction for 8h, then soaking in deionized water for 48h (changing the deionized water every 4 h), and cleaning to remove impurities to obtain RGPH.
(3) Placing the prepared RGPH in 80ml 0.1mol/L aniline hydrochloride solution containing 1.6mmol phytic acid, sealing and storing for 12h, and then placing in 0-5 deg.C environment for cooling; adding 1.824g of ammonium persulfate into 5ml of deionized water, mixing, cooling to below 5 ℃, quickly pouring into the solution, uniformly mixing, reacting for 24 hours, and cleaning the product with deionized water to obtain the gradient macroporous conductive composite hydrogel.
Comparative example 1
Dissolving 0.05g of sodium chloride and 0.1g of lauryl sodium sulfate in 10ml of deionized water, adding 54 mu L of lauryl methacrylate, stirring for 3h, adding 5.3g of acrylamide (AAm), 17.2mg of N, N' -Methylene Bisacrylamide (MBA) and 0.05g of Ammonium Persulfate (APS) after stirring is finished, and polymerizing for 6h at 45 ℃ after magnetic stirring is fully dissolved to obtain the LMA-PAAm hydrogel.
Comparative example 2
Dissolving 0.05g of sodium chloride and 0.1g of lauryl sodium sulfate in 10ml of deionized water, adding 54 mu L of lauryl methacrylate, stirring for 3h, adding 30mg of Graphene Oxide (GO), adding 5.3g of acrylamide (AAm), 17.2mg of N, N' -Methylene Bisacrylamide (MBA) and 0.05g of Ammonium Persulfate (APS), fully dissolving by magnetic stirring, and polymerizing for 6h at 45 ℃ to obtain the GO/PAAm composite hydrogel.
Comparative example 3
(1) Dissolving 0.05g of sodium chloride and 0.1g of lauryl sodium sulfate in 10ml of deionized water, adding 54 mu L of lauryl methacrylate, stirring for 3 hours, adding 30mg of Graphene Oxide (GO), then adding 5.3g of acrylamide (AAm), 17.2mg of N, N' -Methylene Bisacrylamide (MBA) and 0.05g of Ammonium Persulfate (APS), and after the materials are fully dissolved by magnetic stirring, polymerizing for 6 hours at 45 ℃ to obtain the GO/PAAm composite hydrogel.
(2) And soaking the prepared GO/PAAm composite hydrogel into 80ml of 0.2mol/L ascorbic acid solution, standing for 5h, heating at 90 ℃ for reaction for 8h, and soaking with deionized water for 48h (4 h is replaced by deionized water once) to obtain the graphene-based conductive hydrogel.
Comparative example 4
(1) 0.05g of sodium chloride and 0.1g of lauryl sodium sulfate are dissolved in 10ml of deionized water, 54 mul of lauryl methacrylate is added, 30mg of Graphene Oxide (GO) is added after stirring for 3h, 5.3g of acrylamide (AAm), 17.2mg of N, N' -Methylene Bisacrylamide (MBA) and 0.05g of Ammonium Persulfate (APS) are added, and polymerization is carried out for 6h at 45 ℃ after magnetic stirring and full dissolution. Obtaining the GO/PAAm composite hydrogel.
(2) The prepared GO/PAAm composite hydrogel is immersed into 80ml of 0.2mol/L ascorbic acid solution and placed for 5 hours, then the heating reaction is carried out for 8 hours at 90 ℃, and then deionized water is used for immersion for 48 hours (4 hours is replaced by once deionized water). Obtaining the graphene-based conductive hydrogel.
(3) Placing the prepared graphene-based conductive hydrogel in 80ml of 0.1mol/L aniline hydrochloride solution containing 1.6mmol phytic acid, sealing and storing for 12h, and then placing in an environment at 0-5 ℃ for cooling; adding 1.824g of ammonium persulfate into 5ml of deionized water, mixing, cooling to below 5 ℃, quickly pouring into the solution, uniformly mixing, reacting for 24 hours, and cleaning the product with deionized water to obtain the non-foamed and pore-formed conductive composite hydrogel.
Comparative example 5
(1) 0.05g of sodium chloride and 0.1g of lauryl sodium sulfate are dissolved in 10ml of deionized water, 54 mul of lauryl methacrylate is added, 30mg of Graphene Oxide (GO) is added after stirring for 3h, 5.3g of acrylamide (AAm), 17.2mg of N, N' -Methylene Bisacrylamide (MBA), 0.02g of white granulated sugar and 0.05g of Ammonium Persulfate (APS) are added, and polymerization is carried out for 6h at 45 ℃ after magnetic stirring and full dissolution. Obtaining the GO/PAAm composite hydrogel.
(2) And soaking the prepared GO/PAAm composite hydrogel in deionized water for 48h (replacing the deionized water for 4 h). And then putting the graphene-based conductive hydrogel into 80ml of 0.2mol/L ascorbic acid solution, heating and reacting for 8 hours at 90 ℃, then putting the graphene-based conductive hydrogel into deionized water for soaking for 48 hours (replacing the deionized water every 4 hours), and cleaning and removing impurities to obtain the graphene-based conductive hydrogel.
(3) Placing the prepared graphene-based conductive hydrogel in 80ml of 0.1mol/L aniline hydrochloride solution containing 1.6mmol phytic acid, sealing and storing for 12h, and then placing in an environment at 0-5 ℃ for cooling; adding 1.824g of ammonium persulfate into 5ml of deionized water, mixing, cooling to below 5 ℃, quickly pouring into the solution, uniformly mixing, reacting for 24 hours, and cleaning the product with deionized water to obtain the non-foamed and pore-formed conductive composite hydrogel.
FIG. 1 is an electron microscope image of the gradient macroporous conductive composite hydrogel prepared in example 1. As can be seen from the figure, the pore diameter of the porous material changes in a gradient manner, and the overall pore diameter is distributed within 20 to 100 μm. The macroporous structure can solve the problem that the pore channel is easy to block during the in-situ polymerization of the aniline.
FIG. 2 is a graph comparing the mechanical properties of hydrogel materials prepared in example 1 with those of comparative examples 1, 2 and 3. As can be seen from the figure, the gradient macroporous conductive composite hydrogel prepared in example 1 has an elongation at break of 510% and a stress at break of 0.65MPa, and exhibits excellent mechanical properties. The hydrogel material prepared in comparative example 1 has an elongation at break of 470% and a stress at break of 0.23MPa, which is because the hydrogel material of comparative example 1 does not contain graphene oxide, and only contains hydrophobic association physical crosslinking and slight chemical crosslinking of MBA in the internal network, resulting in a material strength significantly lower than that of example 1. The hydrogel material prepared in comparative example 2 has elongation at break of 571% and stress at break of 0.84MPa, which is 3.65 times that of the hydrogel without graphene oxide in comparative example 1. The graphene oxide is mainly characterized in that the surface of the graphene oxide is rich in oxygen-containing groups such as hydroxyl groups and carboxyl groups, and can form a large number of hydrogen bonds with amino groups on polyacrylamide, so that a large number of physical crosslinking points are provided for the overall network structure of the hydrogel, a large number of energy dissipation can be provided for the hydrogel during stretching, and the mechanical properties of the hydrogel are remarkably enhanced. This shows that the addition of graphene oxide can provide excellent mechanical properties for the material. Compared with the comparative example 2, the mechanical property of the hydrogel material prepared by the comparative example 3 is reduced, and the stress is almost recovered to the level of the graphene oxide without addition of the graphene oxide, wherein the elongation at break is 388%, the stress at break is 0.27MPa, and the conductivity is 9.63 mS/m. The graphene oxide is reduced, so that a large number of original oxygen-containing groups on a sheet layer of the graphene oxide are removed, and a large number of hydrogen bonds can not be formed, so that the mechanical property is reduced to be close to that of the comparative example 1; however, after reduction, the hydrogel material also has conductivity, and compared with example 1, as comparative example 3 does not contain polyaniline, a large number of hydrogen bonds can be formed between polyaniline segments and polyacrylamide chains, and polyaniline and graphene have pi-pi effect, polyaniline can be attached to the surface of graphene to form a plurality of cross-linking points, the mechanical property of comparative example 3 is also obviously lower than that of example 1.
FIG. 3 is an electron micrograph of the conductive composite hydrogel prepared in comparative example 5. As can be seen from the figure, the hydrogel material prepared using white granulated sugar had a uniform pore size of 10 μm, compared to example 1.
FIG. 4 is a graph comparing the sensitivity of the hydrogel flexible strain sensing materials prepared in example 1 and comparative examples 4 and 5. It can be seen from the figure that the gradient macroporous conductive composite hydrogel prepared in example 1 has a resistance change rate of 2835% under a strain of 400%, has a wide strain sensing range and high sensitivity, is subjected to sensitivity fitting within a strain range of 150% -400%, has a sensitivity factor as high as 8.86, and is a very effective flexible strain sensor material. This is mainly due to the fact that the hydrogel of example 1 is subjected to controlled foaming, the inner macropores are in gradient distribution, which not only solves the problem that the polyaniline blocks the pore channels, but also increases the sensitivity due to the fact that the number of polyaniline attached to the pore walls is large because of the special structure of the gradient macropores, and the deformation of the macropores is different among different gradients during stretching, which is a synergistic effect. Compared with the embodiment 1, the conductive composite hydrogel obtained in the comparative example 4 is not added with a foaming agent, so that the internal pore diameter is small, aniline is difficult to permeate into hydrogel during in-situ polymerization of the adsorbed aniline, and the phenomenon that polyaniline blocks hydrogel pore channels is easy to occur, so that the utilization rate of polyaniline is low, the polyaniline is not uniformly dispersed, and finally the resistance change is small, so that the resistance change rate is only 768% under 400% strain and is 3.7 times smaller than that of the embodiment 1. The conductive composite hydrogel prepared in the comparative example 5 has a resistance change rate of 1363% under 400% strain, which is 2.1 times smaller than that of the conductive composite hydrogel in the example 1, and it can be seen that the problem of pore blocking during in-situ polymerization of aniline is improved through uniform pore-forming treatment, so that the sensitivity of the hydrogel is improved, but the hydrogel has a smaller sensitivity than that of the conductive composite hydrogel in the example 1 because a gradient macroporous structure is not formed inside the hydrogel. Thus, the gradient macroporous structure obtained through foaming can remarkably enhance the sensitivity of the hydrogel sensor.
Fig. 5 is a resistance change rate curve of the gradient macroporous conductive composite hydrogel prepared in example 1 under different tensile strains when intermittently loaded and unloaded. As can be seen from the figure, the electrical signal of the gradient macroporous conductive composite hydrogel is kept stable in the intermittence, and the electrical signal is restored to the initial state in the unloading process, which shows that the strain response of the sensing material has strong stability and reversibility.
FIG. 6 is a graph of the rate of change of resistance of the conductive composite hydrogel flexible strain sensing material prepared in example 1 after 500 stretching cycles at a stretching speed of 200mm/min and 50% tensile strain. As can be seen from the figure, the gradient macroporous conductive composite hydrogel can keep the stability and repeatability of an electric signal in 500 continuous stretching cycles, and the cycle stability is good.
In addition, the gradient macroporous conductive composite hydrogel prepared in the embodiment 1 can accurately respond to human motion signals, such as large deformation caused by bending of finger wrists and small deformation caused by breathing and swallowing.
The gradient macroporous conductive composite hydrogel has the advantages of strong mechanical property, high sensitivity and good cycling stability, and is suitable for flexible strain sensors.
Example 2
(1) 0.1g of sodium chloride and 0.1g of sodium dodecyl sulfate are dissolved in 10ml of deionized water, 54 mu L of hexadecyl methacrylate is added, 30mg of Graphene Oxide (GO) is added after stirring for 3h, 5.3g of acrylamide (AAm), 17.2mg of N, N' -Methylene Bisacrylamide (MBA), 0.02g of sodium bicarbonate and 0.05g of Ammonium Persulfate (APS) are added, and after the materials are fully dissolved by magnetic stirring, the materials are polymerized for 6h at 45 ℃ to prepare the GPH.
(2) The prepared GPH is soaked in 80ml of 0.2mol/L valine for 5 hours, then heated to 90 ℃ for reaction for 8 hours, and then soaked in deionized water for 48 hours (the deionized water is replaced every 4 hours) to be cleaned and removed to obtain RGPH.
(3) Placing the prepared RGPH in 80ml 0.05mol/L aniline hydrochloride solution containing 1.0mmol phytic acid, sealing and storing for 12h, and then placing in an environment of 0-5 ℃ for cooling; and adding 0.912g of ammonium persulfate into 5ml of deionized water, mixing, cooling to below 5 ℃, quickly pouring into the solution, uniformly mixing, reacting for 24 hours, and cleaning the product with deionized water to obtain the gradient macroporous conductive composite hydrogel.
Example 3
(1) 0.15g of sodium chloride and 0.3g of sodium dodecyl sulfate are dissolved in 10ml of deionized water, 54 mu L of octadecyl methacrylate is added, 20mg of Graphene Oxide (GO) is added after stirring for 3h, 5.3g of acrylamide (AAm), 17.2mg of N, N' -Methylene Bisacrylamide (MBA), 0.03g of sodium bicarbonate and 0.05g of Ammonium Persulfate (APS) are added, and after the materials are fully dissolved by magnetic stirring, the materials are polymerized for 6h at 45 ℃ to prepare the GPH.
(2) Soaking the prepared GPH into 80ml of 0.2mol/L cysteine, standing for 5h, heating at 90 ℃ for reacting for 8h, then soaking in deionized water for 48h (changing the deionized water every 4 h), and cleaning to remove impurities to obtain RGPH.
(3) Placing the prepared RGPH in 80ml 0.15mol/L aniline hydrochloride solution containing 2.4mmol phytic acid, sealing and storing for 12h, and then placing in an environment of 0-5 ℃ for cooling; 2.738g ammonium persulfate is added into 5ml deionized water to be mixed, after the mixture is cooled to below 5 ℃, the mixture is quickly poured into the solution to be uniformly mixed, and after the reaction is carried out for 24 hours, a product is washed by the deionized water to obtain the gradient macroporous conductive composite hydrogel.
Example 4
(1) 0.15g of sodium chloride and 0.2g of sodium dodecyl sulfate are dissolved in 10ml of deionized water, 54 mu L of hexadecyl methacrylate is added, 30mg of Graphene Oxide (GO) is added after stirring for 3h, 5.3g of acrylamide (AAm), 17.2mg of N, N' -Methylene Bisacrylamide (MBA), 0.03g of ammonium carbonate and 0.05g of Ammonium Persulfate (APS) are added, and after the materials are fully dissolved by magnetic stirring, the materials are polymerized for 6h at 45 ℃ to prepare the GPH.
(2) The prepared GPH is soaked in 80ml of 0.1mol/L leucine for 5 hours, then heated to 90 ℃ for reaction for 8 hours, and then soaked in deionized water for 48 hours (the deionized water is replaced every 4 hours) to be cleaned and decontaminated to prepare RGPH.
(3) Placing the prepared RGPH in 80ml 0.1mol/L aniline hydrochloride solution containing 2.0mmol phytic acid, sealing and storing for 12h, and then placing in an environment of 0-5 ℃ for cooling; adding 1.824g of ammonium persulfate into 5ml of deionized water, mixing, cooling to below 5 ℃, quickly pouring into the solution, uniformly mixing, reacting for 24 hours, and cleaning the product with deionized water to obtain the gradient macroporous conductive composite hydrogel.
Example 5
(1) 0.05g of sodium chloride and 0.3g of sodium dodecyl sulfate are dissolved in 10ml of deionized water, 54 mu L of hexadecyl methacrylate is added, 30mg of Graphene Oxide (GO) is added after stirring for 3 hours, 5.3g of acrylamide (AAm), 17.2mg of N, N' -Methylene Bisacrylamide (MBA), 0.02g of ammonium bicarbonate and 0.05g of Ammonium Persulfate (APS) are added, and after the materials are fully dissolved by magnetic stirring, the materials are polymerized for 6 hours at 45 ℃ to prepare GPH.
(2) The prepared GPH is immersed into 80ml of 0.15mol/L oxalic acid and placed for 5h, then the mixture is heated and reacted for 8h at 90 ℃, and then the mixture is immersed into deionized water for 48h (the deionized water is replaced every 4 h), and the RGPH is prepared after cleaning and impurity removal.
(3) Placing the prepared RGPH in 80ml 0.2mol/L aniline hydrochloride solution containing 2.4mmol phytic acid, sealing and storing for 12h, and then placing in an environment of 0-5 ℃ for cooling; adding 3.651g ammonium persulfate into 5ml deionized water, mixing, cooling to below 5 ℃, quickly pouring into the solution, uniformly mixing, reacting for 24 hours, and cleaning the product with deionized water to obtain the gradient macroporous conductive composite hydrogel.
FIG. 7 is a graph comparing the conductivity of the conductive composite hydrogel materials prepared in examples 1-5. As shown in the figure, the conductivity of the hydrogel materials prepared in examples 1-5 was 2.7S/m, 1.56S/m, 0.91S/m, 0.96S/m, and 1.61S/m, respectively, and it can be seen that the hydrogel material prepared in example 1 has the best conductivity.
Example 6
(1) 0.05g of sodium chloride and 0.3g of sodium dodecyl sulfate are dissolved in 10ml of deionized water, 54 mu L of stearyl methacrylate is added, after stirring for 3 hours, 15mg of Graphene Oxide (GO) is added, 5.3g of acrylamide (AAm), 17.2mg of N, N' -Methylene Bisacrylamide (MBA), 0.01g of sodium bicarbonate and 0.05g of Ammonium Persulfate (APS) are added, and after the materials are fully dissolved by magnetic stirring, the materials are polymerized for 6 hours at 45 ℃ to prepare GPH.
(2) Soaking the prepared GPH into 80ml of 0.2mol/L ascorbic acid solution, standing for 5h, heating at 90 ℃ for reaction for 8h, then soaking in deionized water for 48h (changing the deionized water every 4 h), and cleaning to remove impurities to obtain RGPH.
(3) Placing the prepared RGPH in 80ml 0.1mol/L aniline hydrochloride solution containing 1.2mmol phytic acid, sealing and storing for 12h, and then placing in an environment of 0-5 ℃ for cooling; adding 1.824g of ammonium persulfate into 5ml of deionized water, mixing, cooling to below 5 ℃, quickly pouring into the solution, uniformly mixing, reacting for 24 hours, and cleaning the product with deionized water to obtain the gradient macroporous conductive composite hydrogel.
Example 7
(1) 0.1g of sodium chloride and 0.2g of sodium dodecyl sulfate are dissolved in 10ml of deionized water, 54 mu L of n-decyl methacrylate is added, 20mg of Graphene Oxide (GO) is added after stirring for 3h, 5.3g of acrylamide (AAm), 17.2mg of N, N' -Methylene Bisacrylamide (MBA), 0.03g of ammonium bicarbonate and 0.05g of Ammonium Persulfate (APS) are added, and after the materials are fully dissolved by magnetic stirring, the materials are polymerized for 6h at 45 ℃ to prepare the GPH.
(2) Soaking the prepared GPH into 80ml of 0.2mol/L ascorbic acid solution, standing for 5h, heating at 90 ℃ for reaction for 8h, then soaking in deionized water for 48h (changing the deionized water every 4 h), and cleaning to remove impurities to obtain RGPH.
(3) Placing the prepared RGPH in 80ml 0.1mol/L aniline hydrochloride solution containing 1.6mmol phytic acid, sealing and storing for 12h, and then placing in an environment of 0-5 ℃ for cooling; adding 1.824g of ammonium persulfate into 5ml of deionized water, mixing, cooling to below 5 ℃, quickly pouring into the solution, uniformly mixing, reacting for 24 hours, and cleaning the product with deionized water to obtain the gradient macroporous conductive composite hydrogel.
The above description is only a preferred embodiment of the present invention, and all equivalent changes and modifications made in accordance with the claims of the present invention should be covered by the present invention.
Claims (5)
1. A preparation method of gradient macroporous conductive composite hydrogel applied to a flexible strain sensor is characterized by comprising the following steps: the method comprises the following steps:
(1) Preparing graphene oxide/polyacrylamide composite hydrogel containing a foaming agent;
(2) Preparing graphene/polyacrylamide conductive composite hydrogel with a gradient macroporous structure;
(3) Absorbing aniline by using graphene/polyacrylamide conductive composite hydrogel with a gradient macroporous structure, and then initiating in-situ polymerization to obtain the gradient macroporous conductive composite hydrogel applied to the flexible strain sensor;
adding 54 mu L of hydrophobic monomer into 10ml of sodium chloride/lauryl sodium sulfate solution, stirring for 3 hours, adding 15-30mg of graphene oxide, adding 5.3g of acrylamide, 17.2mg of N, N' -methylene-bisacrylamide, 0.01-0.03g of foaming agent and 0.05g of ammonium persulfate, magnetically stirring to fully dissolve, and polymerizing for 6 hours at 45 ℃ to obtain the graphene oxide/polyacrylamide composite hydrogel containing the foaming agent;
the hydrophobic monomer is alkyl methacrylate, and the length of an alkyl carbon chain of the hydrophobic monomer is 8-18 carbon atoms; the foaming agent is any one of sodium carbonate, sodium bicarbonate, ammonium carbonate and ammonium bicarbonate;
step (2) specifically, the prepared graphene oxide/polyacrylamide composite hydrogel containing the foaming agent is immersed in 0.1-0.2mol/L organic acid solution and placed for 5 hours, then the graphene oxide/polyacrylamide composite hydrogel is heated and reacted for 8 hours at 90 ℃, and the graphene oxide/polyacrylamide conductive composite hydrogel with the gradient macroporous structure is prepared after cleaning and impurity removal; the organic acid is any one of oxalic acid, ascorbic acid, valine, leucine and cysteine.
2. The preparation method of the gradient macroporous conductive composite hydrogel applied to the flexible strain sensor, according to claim 1, is characterized in that: the sodium chloride/sodium dodecyl sulfate solution is prepared by dissolving 0.05-0.15g of sodium chloride and 0.1-0.3g of sodium dodecyl sulfate in 10ml of deionized water.
3. The preparation method of the gradient macroporous conductive composite hydrogel applied to the flexible strain sensor, according to claim 1, is characterized in that: the step (3) is to immerse the prepared graphene/polyacrylamide conductive composite hydrogel with the gradient macroporous structure into a mixed solution of phytic acid and aniline hydrochloride, store the mixture for 12 hours in a sealing way, and then place the mixture into an environment with the temperature of 0-5 ℃ for cooling; adding ammonium persulfate into deionized water, mixing, cooling to below 5 ℃, quickly pouring into the solution, uniformly mixing, reacting for 24 hours, and cleaning the product with deionized water to obtain the gradient macroporous conductive composite hydrogel applied to the flexible strain sensor.
4. The preparation method of the gradient macroporous conductive composite hydrogel applied to the flexible strain sensor, according to claim 3, is characterized in that: the molar ratio of the phytic acid to the aniline hydrochloride in the mixed solution is 0.15-0.25; the molar ratio of ammonium persulfate to aniline hydrochloride used was 1:1.
5. A gradient macroporous conductive composite hydrogel applied to a flexible strain sensor prepared by the method of any one of claims 1 to 4.
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