Environment-responsive hydrogel and preparation method and application thereof

Abstract

This invention discloses an environmentally responsive hydrogel, its preparation method, and its applications, belonging to the field of intelligent hydrogels and microchannel control technology. The invention uses stimulus-responsive hydrogel monomers and an aqueous dispersant as raw materials. Linear molecular chains are formed under the action of a free radical thermal initiator. After generating free radicals, the aqueous dispersant polymerizes on the stimulus-responsive hydrogel monomer molecules due to the action of a cross-linking agent. During polymerization, the carbon-carbon double bonds of the cross-linking agent break, reacting with the aqueous dispersant and the stimulus-responsive hydrogel monomer to form a cross-linked structure, thus obtaining the environmentally responsive hydrogel. The environmentally responsive hydrogel prepared by this invention has a triple cross-linked network structure and exhibits dual-response functionality for pH and temperature, with fast response speed and high precision, while also demonstrating hysteresis during the response process.

Description

Technical Field

[0001] This invention relates to the field of smart hydrogels and microchannel control technology, specifically to an environmentally responsive hydrogel, its preparation method, and its applications. Background Technology

[0002] Miniature valves are miniaturized modern valves that operate on the same principle as conventional valves, primarily regulating the flow and control of fluid media through on / off actions. In recent years, environmentally responsive hydrogel microvalves have found wide application in many fields, including microfluidic control, portable diagnostics, and controlled drug release.

[0003] Environmentally responsive hydrogels can reversibly change their size or shape in response to external stimuli such as temperature, pH, and light. While the material properties of most stimulus-responsive hydrogels have a one-to-one relationship with the environmental stimulus, some stimulus-responsive hydrogels exhibit a hysteresis in their response process. Under the same environmental stimulus, the hydrogel material stores historical information from its previous environment and exhibits different properties. This hysteresis allows for the writing, storage, and retrieval of information, mimicking the operations of an electronic computing system, such as sensing input signals, storing and processing information, and outputting readable signals.

[0004] Currently, existing technologies disclose methods for preparing and applying temperature- and photosensitivity-sensitive environmentally responsive hydrogels. These hydrogels are used as microvalves, responding to external stimuli by adjusting their shape or size to meet flow control requirements. However, the responsiveness of these hydrogels is dependent on external stimuli; they only respond to external input and disappear once the stimulus is removed. The response behavior based on external stimuli (such as shape memory) cannot be sustained, thus hindering efficient flow control through microvalves. Furthermore, the hysteresis of hydrogels refers to the delay in their reaction to external stimuli. This characteristic allows the hydrogel to reach a swelling or contraction state after a certain time following stimulation, which can be used for precise flow control. However, existing hydrogels suffer from unstable hysteresis responses, meaning their reaction time and degree of response are delayed, leading to poor accuracy in flow control. Summary of the Invention

[0005] This invention provides an environmentally responsive hydrogel, its preparation method, and its application. It effectively solves the technical problems of hydrogels having a large correlation between response and stimulus, and the inability to maintain the response behavior independently; as well as the unstable response hysteresis of hydrogels. At the same time, it provides a heterogeneous hydrogel with excellent mechanical properties and multi-solvent responsiveness, and applies it to an intelligent micro-valve actuator to realize intelligent control that integrates sensing input signals, intelligent memory analysis, and output driving behavior.

[0006] The first objective of this invention is to provide a method for preparing an environmentally responsive hydrogel, comprising the following steps:

[0007] The photothermal conversion material is added to an aqueous solution of an aqueous dispersant and dispersed to obtain a suspension of the photothermal conversion material.

[0008] The stimulus-responsive hydrogel monomer is added to the photothermal conversion material suspension and dissolved. A free radical thermal initiator and a crosslinking agent are added, the mixture is stirred, cooled, and then a promoter is added. The polymerization reaction is carried out in a nitrogen atmosphere. During the polymerization process, the carbon-carbon double bonds of the crosslinking agent break and react with the aqueous dispersant and the stimulus-responsive hydrogel monomer under the action of the free radical thermal initiator and the promoter to form a crosslinked structure. The photothermal conversion material is then loaded into the crosslinked structure to obtain an environmentally responsive hydrogel.

[0009] In a preferred embodiment, the aqueous solution of the aqueous dispersant has a mass concentration of 5 mg / mL, and the mass ratio of the photothermal conversion material to the aqueous solution of the aqueous dispersant is 5-9:325-450.

[0010] In a preferred embodiment, the mass ratio of the stimulus-responsive hydrogel monomer to the photothermal conversion material is 40-60:5-9.

[0011] In a preferred embodiment, the mass ratio of the free radical thermal initiator, crosslinking agent, and initiator is 10-15:5-10:15-20.

[0012] In a preferred embodiment, the stimulus-responsive hydrogel monomer is one or more of N-isopropylacrylamide, acrylic acid, N-propylacrylamide, or sodium alginate.

[0013] In a preferred embodiment, the photothermal conversion material is one or more of carbon nanotubes, silver nanowires, and carbon black.

[0014] In a preferred embodiment, the free radical thermal initiator is one or more of ammonium persulfate, azobisisobutyronitrile, and diacyl peroxide; the crosslinking agent is one or more of N,N-methylenebisacrylamide, dicumyl peroxide, butadiene, and vinylbenzene; and the initiating agent is one or more of N,N,N',N'-tetramethylethylenediamine, propylenediamine, and isopropylenediamine.

[0015] The second objective of this invention is to provide an environmentally responsive hydrogel prepared by the above-described preparation method.

[0016] A third objective of this invention is to provide an application of the aforementioned environmentally responsive hydrogel in a driver-driven smart microvalve.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] This invention utilizes stimulus-responsive hydrogel monomers, aqueous dispersants, photothermal conversion materials, free radical thermal initiators, crosslinking agents, and initiation promoters as raw materials to construct a heterogeneous environmentally responsive hydrogel with excellent mechanical properties and multi-solvent responsiveness. The invention uses stimulus-responsive hydrogel monomers and aqueous dispersants as raw materials. Under the action of a free radical thermal initiator, linear molecular chains are formed. After generating free radicals, the aqueous dispersant grafts and polymerizes onto the stimulus-responsive hydrogel monomer molecules due to the action of a crosslinking agent. During polymerization, the carbon-carbon double bonds of the crosslinking agent break, reacting with the aqueous dispersant and stimulus-responsive hydrogel monomers to form a crosslinked structure. The photothermal conversion material is then loaded into the crosslinked structure to obtain the environmentally responsive hydrogel. When the environmentally responsive hydrogel prepared by this invention is applied to a microvalve, it exhibits independent responsiveness and hysteresis. When an external stimulus is applied to the hydrogel, the microvalve is closed when the hydrogel expands to a certain extent, preventing liquid flow; or when the hydrogel shrinks to a certain extent, the microvalve is opened, allowing liquid flow. In applications, the micro-valve achieves three states—normally open, normally closed, and switching between open and closed—under the condition of changing only the pH value at the same temperature. It has dual response functions of pH and temperature, fast response speed, high precision, and exhibits hysteresis stability during the response process.

[0019] Since microvalve control systems need to memorize and analyze historical environmental information to make intelligent judgments and controls, the environmentally responsive hydrogel prepared in this invention is applied to the driver of intelligent microvalve. Because the hydrogel has a response hysteresis, which allows for writing, storing, and retrieving information, it mimics the operation of an electronic computing system to sense input signals, store and process information, and output readable signals. Therefore, the environmentally responsive hydrogel of this invention can realize intelligent hydrogel microvalve control that integrates sensing input signals, intelligent memory analysis, and output driving behavior, thereby storing historical environmental information and exhibiting different properties. Attached Figure Description

[0020] Figure 1 This is a schematic diagram illustrating the application of the environmentally responsive hydrogel of the present invention in an intelligent micro-valve actuator.

[0021] Figure 2 This is a diagram illustrating the synthesis mechanism of the environmentally responsive hydrogel of this invention.

[0022] Figure 3 This is a schematic diagram of a plastic model of the intelligent micro-valve driven by the present invention; wherein, (a) is a left view and (b) is a right view.

[0023] Figure 4 The diagram shows the working state of the environmentally responsive hydrogel of the present invention in the actuator smart microvalve at 45°C and pH values ​​of 4, 5 and 6.5. Detailed Implementation

[0024] To enable those skilled in the art to better understand and implement the technical solutions of this invention, the invention will be further described below with reference to specific embodiments and accompanying drawings. However, the embodiments described are not intended to limit the invention. Unless otherwise specified, the following test methods and detection methods are conventional methods; unless otherwise specified, the reagents and raw materials are commercially available.

[0025] In response to the issues mentioned in the background section of this invention, environmentally responsive hydrogel microvalves have found wide application in many fields such as microfluidic control, portable diagnostics, and controlled drug release in recent years. Hydrogels are used as microvalves, responding to external stimuli to meet corresponding regulatory needs. However, the responsiveness of microvalves prepared using existing hydrogels is correlated with external stimuli; a response only occurs upon input of external information, and the response cannot be maintained independently. Furthermore, the measurement time of hydrogel hysteresis is too fast, and the hydrogel system has not reached or approached equilibrium steady state, resulting in unstable hysteresis. Based on the above technical problems, this invention provides an environmentally responsive hydrogel, its preparation method, and its applications.

[0026] The technical solution of the present invention will be analyzed and explained below.

[0027] This invention provides a method for preparing the above-mentioned environmentally responsive hydrogel, comprising the following steps:

[0028] The photothermal conversion material is added to an aqueous solution of an aqueous dispersant and dispersed to obtain a suspension of the photothermal conversion material.

[0029] The stimulus-responsive hydrogel monomer is added to the photothermal conversion material suspension and dissolved. A free radical thermal initiator and a crosslinking agent are added, the mixture is stirred, cooled, and then a promoter is added. The polymerization reaction is carried out in a nitrogen atmosphere. During the polymerization process, the carbon-carbon double bonds of the crosslinking agent break and react with the aqueous dispersant and the stimulus-responsive hydrogel monomer under the action of the free radical thermal initiator and the promoter to form a crosslinked structure. The photothermal conversion material is then loaded into the crosslinked structure to obtain an environmentally responsive hydrogel.

[0030] In the above preparation method, the role of the free radical thermal initiator is to initiate the polymerization of free radicals. Stimulus-responsive hydrogel monomers form linear molecular chains under the action of the initiator. After generating free radicals, the aqueous dispersant molecules undergo graft polymerization on the stimulus-responsive hydrogel monomer molecules due to the action of the crosslinking agent, forming a crosslinked structure. The accelerator lowers the thermal initiation temperature of the free radical thermal initiator, meeting the polymerization requirement that stimulus-responsive hydrogel monomers need to polymerize at a lower temperature.

[0031] It should be noted that the aqueous solution of the aqueous dispersant has a mass concentration of 5 mg / mL, and the mass ratio of the photothermal conversion material to the aqueous dispersant is 5–9:325–450. The mass ratio of the stimulus-responsive hydrogel monomer to the photothermal conversion material is 40–60:5–9. Since the amount of photothermal conversion material affects the photothermal response rate of the hydrogel, if the proportion of photothermal conversion material is too small, the hydrogel valve's opening and closing response rate will decrease, and the overall sensitivity of the intelligent micro-valve will decrease. At the same time, more photothermal conversion material is not necessarily better; the proportion of photothermal conversion material has an upper limit on its impact on conversion efficiency, and an excessive proportion will affect the polymerization reaction. Furthermore, a too small proportion of methylcellulose will reduce the association effect of hydrophobic interactions on methylcellulose segments, thereby reducing the hydrophobic hysteresis of the hydrogel system. Conversely, a too large proportion of methylcellulose will reduce the concentration of other monomers, affecting the critical solution temperature and pH response. Therefore, the dosage ratio of the photothermal conversion material claimed in this invention can ensure that the environmentally responsive hydrogel prepared by this invention has a fast photothermal conversion efficiency while not having an adverse effect on the polymerization reaction of the system.

[0032] It is important to note that the concentration of the free radical thermal initiator is 10% wt, the concentration of the crosslinking agent is 2.5% wt, and the mass ratio of the free radical thermal initiator, crosslinking agent, and initiator is 5–15:5–10:15–20. The free radical thermal initiator affects the polymerization rate; a lower content reduces the polymerization rate, while a higher content leads to more chain transfer, a decrease in polymer molecular weight, and a wider molecular weight distribution. Insufficient crosslinking agent prevents the hydrogel network from forming a complete crosslinked structure, resulting in poor hydrogel polymer stability; excessive crosslinking agent leads to too many crosslinking sites, forming numerous crosslinked structures, causing polymer structural inhomogeneity, affecting the hydrogel's volume change response, resulting in a low swelling ratio, hindering micro-valve control, and also contributing to polymer structural inhomogeneity. The main function of initiators is to lower the initiation temperature of free radical thermal initiators, which meets the polymerization conditions of stimulus-responsive hydrogel monomers. Therefore, a low content of initiators will result in a high polymerization temperature, causing the stimulus-responsive hydrogel to lose its temperature-responsive function; an excessive content of initiators will result in a low polymerization temperature, making room temperature polymerization impossible and increasing the difficulty of the reaction.

[0033] The present invention also provides an environmentally responsive hydrogel, which is made from the following raw materials in parts by weight: 40-60 parts of stimulus-responsive hydrogel monomer, 325-450 parts of aqueous dispersant, 5-9 parts of photothermal conversion material, 5-15 parts of free radical thermal initiator, 5-10 parts of crosslinking agent, and 15-20 parts of initiator.

[0034] The stimulus-responsive hydrogel monomer is one or more of N-isopropylacrylamide, acrylic acid, N-propylacrylamide, or sodium alginate. The photothermal conversion material is one or more of carbon nanotubes, silver nanowires, and carbon black. The free radical thermal initiator is one or more of ammonium persulfate, azobisisobutyronitrile, and diacyl peroxide; the crosslinking agent is one or more of N,N-methylenebisacrylamide, dicumyl peroxide, butadiene, and vinylbenzene; and the initiator is one or more of N,N,N',N'-tetramethylethylenediamine, propylenediamine, and isopropyldiamine.

[0035] In the above technical solution, a heterogeneous environmentally responsive hydrogel with excellent mechanical properties and multi-solvent responsiveness is constructed using stimulus-responsive hydrogel monomers, aqueous dispersants, photothermal conversion materials, free radical thermal initiators, crosslinking agents, and initiators as raw materials. The hydrogel has a triple crosslinked network structure and exhibits dual-response functionality for pH and temperature, with fast response speed and high precision, while also displaying hysteresis during the response process.

[0036] This invention also provides an application of the above-mentioned environmentally responsive hydrogel in an actuator-driven intelligent microvalve, specifically including the following steps:

[0037] Preparation of pH buffer solutions: Prepare acetate-sodium acetate buffer solutions with a concentration of 0.01 mol / L and a pH value of 4; prepare disodium hydrogen phosphate-sodium dihydrogen phosphate buffer solution with a concentration of 0.01 mol / L and a pH value of 6.5.

[0038] Construct a plastic model of the actuator for the intelligent micro-valve, with dimensions such as Figure 3 As shown, the cavity dimensions are 16mm×17mm×15mm and 16mm×16mm×15mm respectively, and the dimensions of the central groove are 3mm×10mm×8mm. A U-shaped plastic mold for curing Ecoflex was printed using a 3D printer.

[0039] Preparation of Ecoflex film: The U-shaped groove is immersed in isopropanol, the silicone rubber Ecoflex prepolymer solution is poured into the U-shaped groove, excess liquid on the surface is scraped off, and after being covered with a glass slide, it is cured in an oven at 60°C for 1 hour to obtain a U-shaped Ecoflex hydrophobic film with a thickness of 200 mm.

[0040] Since microvalves are controlled by the swelling and contraction of hydrogels, simple hydrogels cannot perfectly fit or precisely control the flow. Furthermore, the switching process only involves two points: on and off. Adding this hydrophobic film extends and complements the hydrogel switching function of the microvalves, enabling them to achieve different degrees of on / off switching in addition to the basic on / off function, thereby controlling variations in flow rate. This enhances the precision and accuracy of hydrogel control.

[0041] The environmentally responsive hydrogel prepared in this invention is used as the "switch" for an actuator-driven intelligent microvalve. The actuator-driven intelligent microvalve model is the main body of the intelligent microvalve, such as... Figure 3 As shown.

[0042] An environmentally responsive hydrogel is placed in an actuator-controlled smart microvalve containing a U-shaped Ecoflex hydrophobic film. Environmental changes are used as input signals, and the expansion and contraction of the hydrogel are used as output signals. When the hydrogel expands, the microvalve closes; when the hydrogel contracts, the microvalve opens.

[0043] The technical effects of the present invention will be described below with reference to specific embodiments and comparative examples.

[0044] Example 1

[0045] An environmentally responsive hydrogel is composed of the following raw materials in parts by weight: 55 parts of stimulus-responsive hydrogel monomer (N-isopropylacrylamide and acrylic acid), 400 parts of aqueous dispersant (methylcellulose), 6 parts of photothermal conversion material (carbon nanotubes), 10 parts of free radical thermal initiator (ammonium persulfate: APS), 7.5 parts of crosslinking agent (N,N-methylenebisacrylamide: MBAA), and 20 parts of initiator (N,N,N',N'-tetramethylethylenediamine: TMEDA).

[0046] The weight ratio of the above-mentioned N-isopropylacrylamide, acrylic acid, methylcellulose aqueous solution, CNT, APS aqueous solution, MBAA aqueous solution, and TMEDA is 50:5:400:6:10:7.5:20.

[0047] The preparation method of the above-mentioned environmentally responsive hydrogel includes the following steps:

[0048] S1. Carbon nanotubes were added to an aqueous solution of methylcellulose with a mass concentration of 5 mg / mL, ultrasonically dispersed for 5 min and stirred for 1 h to obtain a uniformly dispersed photothermal conversion suspension.

[0049] S2, add N-isopropylacrylamide and acrylic acid to the photothermal conversion material suspension and stir for 2 hours, then ultrasonically disperse for 5 minutes and stir for 20 minutes to fully dissolve.

[0050] S3, add 10% wt APS aqueous solution and 2.5% wt MBAA aqueous solution, continue stirring for 20 min, then transfer to a 0℃ ice-water bath. After the solution cools, add TMEDA and continue stirring for 5 min. Purge with nitrogen and let stand for 24 h to obtain an environmentally responsive hydrogel. The reaction process is as follows. Figure 2 As shown.

[0051] Example 2

[0052] An environmentally responsive hydrogel is composed of the following raw materials in parts by weight: 40 parts of stimulus-responsive hydrogel monomer (N-isopropylacrylamide and acrylic acid), 325 parts of aqueous dispersant (methylcellulose), 5 parts of photothermal conversion material (carbon nanotubes), 5 parts of free radical thermal initiator (ammonium persulfate), 5 parts of crosslinking agent (N,N-methylenebisacrylamide), and 15 parts of initiator (N,N,N',N'-tetramethylethylenediamine).

[0053] The weight ratio of the above-mentioned N-isopropylacrylamide, acrylic acid, methylcellulose aqueous solution, CNT, APS aqueous solution, MABA aqueous solution, and TMEDA is 35:5:325:5:5:5:15.

[0054] The preparation method of the above-mentioned environmentally responsive hydrogel includes the following steps:

[0055] S1. Carbon nanotubes were added to an aqueous solution of methylcellulose with a mass concentration of 5 mg / mL, ultrasonically dispersed for 10 min and stirred for 2 h to obtain a uniformly dispersed photothermal conversion suspension.

[0056] S2, add N-isopropylacrylamide and acrylic acid to the photothermal conversion material suspension and stir for 2 hours, then ultrasonically disperse for 10 minutes and stir for 30 minutes to fully dissolve.

[0057] S3, add 10% wt APS aqueous solution and 2.5% wt MBAA aqueous solution, continue stirring for 20 min, then transfer to 0℃ ice water bath. After the solution cools, add TMEDA and continue stirring for 5 min. Purge with nitrogen and let stand for 24 h to obtain an environmentally responsive hydrogel.

[0058] Example 3

[0059] An environmentally responsive hydrogel is composed of the following raw materials in parts by weight: 60 parts of stimulus-responsive hydrogel monomer (N-isopropylacrylamide and acrylic acid), 450 parts of aqueous dispersant (methylcellulose), 9 parts of photothermal conversion material (carbon nanotubes), 15 parts of free radical thermal initiator (ammonium persulfate), 10 parts of crosslinking agent (N,N-methylenebisacrylamide), and 18 parts of initiator (N,N,N',N'-tetramethylethylenediamine).

[0060] The weight ratio of the above-mentioned N-isopropylacrylamide, acrylic acid, methylcellulose aqueous solution, CNT, APS aqueous solution, MBAA aqueous solution, and TMEDA is 55:5:450:9:15:10:18.

[0061] The preparation method of the above-mentioned environmentally responsive hydrogel includes the following steps:

[0062] S1. Carbon nanotubes were added to an aqueous solution of methylcellulose with a mass concentration of 5 mg / mL, ultrasonically dispersed for 8 min, and stirred for 1.5 h to obtain a uniformly dispersed photothermal conversion suspension.

[0063] S2, add N-isopropylacrylamide and acrylic acid to the photothermal conversion material suspension and stir for 2 hours, then ultrasonically disperse for 8 minutes and stir for 25 minutes to fully dissolve.

[0064] S3, add 10% wt APS aqueous solution and 2.5% wt MBAA aqueous solution, continue stirring for 20 min, then transfer to 0℃ ice water bath. After the solution cools, add TMEDA and continue stirring for 5 min. Purge with nitrogen and let stand for 24 h to obtain an environmentally responsive hydrogel.

[0065] Example 4

[0066] An environmentally responsive hydrogel is composed of the following raw materials in parts by weight: 50 parts of stimulus-responsive hydrogel monomer (N-isopropylacrylamide and acrylic acid), 350 parts of aqueous dispersant (methylcellulose), 7 parts of photothermal conversion material (carbon nanotubes), 8 parts of free radical thermal initiator (ammonium persulfate), 7 parts of crosslinking agent (N,N-methylenebisacrylamide), and 16 parts of initiator (N,N,N',N'-tetramethylethylenediamine).

[0067] The weight ratio of the above-mentioned N-isopropylacrylamide, acrylic acid, methylcellulose aqueous solution, CNT, APS aqueous solution, MBAA aqueous solution, and TMEDA is 45:5:350:7:8:7:16.

[0068] The preparation method of the above-mentioned environmentally responsive hydrogel includes the following steps:

[0069] S1. Carbon nanotubes were added to an aqueous solution of methylcellulose with a mass concentration of 5 mg / mL, ultrasonically dispersed for 5 min, and stirred for 2 h to obtain a uniformly dispersed photothermal conversion suspension.

[0070] S2, add N-isopropylacrylamide and acrylic acid to the photothermal conversion material suspension and stir for 2 hours, then ultrasonically disperse for 10 minutes and stir for 20 minutes to fully dissolve.

[0071] S3, add 10% wt APS aqueous solution and 2.5% wt MBAA aqueous solution, continue stirring for 20 min, then transfer to 0℃ ice water bath. After the solution cools, add TMEDA and continue stirring for 5 min. Purge with nitrogen and let stand for 24 h to obtain an environmentally responsive hydrogel.

[0072] Example 5

[0073] An environmentally responsive hydrogel is composed of the following raw materials in parts by weight: 50 parts of stimulus-responsive hydrogel monomer (N-isopropylacrylamide and acrylic acid), 425 parts of aqueous dispersant (methylcellulose), 8 parts of photothermal conversion material (carbon nanotubes), 12 parts of free radical thermal initiator (ammonium persulfate), 6 parts of crosslinking agent (N,N-methylenebisacrylamide), and 17 parts of initiator (N,N,N',N'-tetramethylethylenediamine).

[0074] The weight ratio of the above-mentioned N-isopropylacrylamide, acrylic acid, methylcellulose aqueous solution, CNT, APS aqueous solution, MBAA aqueous solution, and TMEDA is 45:5:425:8:12:6:17.

[0075] The preparation method of the above-mentioned environmentally responsive hydrogel includes the following steps:

[0076] S1. Carbon nanotubes were added to an aqueous solution of methylcellulose with a mass concentration of 5 mg / mL, ultrasonically dispersed for 5 min, and stirred for 2 h to obtain a uniformly dispersed photothermal conversion suspension.

[0077] S2, add N-isopropylacrylamide and acrylic acid to the photothermal conversion material suspension and stir for 2 hours, then ultrasonically disperse for 10 minutes and stir for 20 minutes to fully dissolve.

[0078] S3, add 10% wt APS aqueous solution and 2.5% wt MBAA aqueous solution, continue stirring for 20 min, then transfer to 0℃ ice water bath. After the solution cools, add TMEDA and continue stirring for 5 min. Purge with nitrogen and let stand for 24 h to obtain an environmentally responsive hydrogel.

[0079] The performance testing of the environmentally responsive hydrogel using the above embodiments in an actuator-driven smart microvalve is detailed below:

[0080] The environmentally responsive hydrogel prepared in this invention was placed in a buffer solution at room temperature or 45°C with pH values ​​of 4, 5 and 6.5 for proton exchange, and then placed in a plastic model of an actuator for a smart microvalve.

[0081] When the acetic acid-sodium acetate buffer solution has a pH of 4, the entire actuator intelligent microvalve system is placed in a room temperature environment. Both side grooves contain buffer solutions with a pH of 4, and the hydrogel expands to its maximum in the middle groove. Initially, the hydrogel compresses the Ecoflex membrane at the front, sealing the circular opening, and the valve is in the closed state. Blue dye is added to the left tank, and after 30 minutes, the right tank shows no color change, indicating good valve sealing. Then, the hydrogel is irradiated with near-infrared light (808nm, 2W), and the hydrogel visibly begins to shrink, the Ecoflex membrane returns to its original shape, opening the circular opening, and the blue liquid gradually flows to the right tank. When the near-infrared emitter is turned off, the hydrogel gradually expands. Yellow dye is then added to the left tank; as shown in the image, the water in the left tank has turned green, while the right tank remains blue. This demonstrates that applying the hydrogel prepared in this invention to a microvalve enables good control of fluid flow and exhibits excellent control stability.

[0082] When the pH of the disodium hydrogen phosphate-sodium dihydrogen phosphate buffer solution is 6.5, the entire microvalve system is placed on a heating platform. Both side grooves contain buffer solutions with a pH of 6.5 and a temperature of 45°C. The hydrogel expands to its maximum in the middle groove. Initially, the hydrogel compresses the Ecoflex membrane in front, sealing the circular opening, and the valve is in the closed state. Blue dye is added to the left tank, and after 30 minutes, there is no color change in the right tank, indicating that the valve is properly closed. Next, the hydrogel is irradiated with near-infrared light; the hydrogel shows no significant change, the circular opening remains closed, and the blue liquid cannot flow into the right tank. It can be seen that the hydrogel microvalve is normally closed at this point. Therefore, the hydrogel has a good control effect on the microvalve.

[0083] When the pH of the acetate-sodium acetate buffer solution is 5, the entire microvalve system is placed on a heating platform. Both side grooves contain buffer solutions at pH 5 and a temperature of 45°C. The hydrogel expands to its maximum in the middle groove. Initially, the hydrogel compresses the Ecoflex film at the front, sealing the circular opening, and the valve is closed. Blue dye is added to the left tank, and after 30 minutes, there is no color change in the right tank, indicating that the valve is properly closed. Next, near-infrared light is used to irradiate the hydrogel. The hydrogel volume shrinks slightly, the circular opening opens, and blue liquid slowly flows into the right tank. When the near-infrared emitter is turned off, the hydrogel still cannot expand. At this point, yellow dye is added to the left tank, and the water in the right tank turns green. This shows that the shape of the hydrogel during contraction is remembered. Even without near-infrared irradiation, the hydrogel microvalve remains open, thus fully demonstrating that the environmentally responsive hydrogel prepared in this invention has excellent response hysteresis stability.

[0084] In summary, the environmentally responsive hydrogel prepared by this invention has a triple cross-linked network structure and exhibits dual-response functionality for pH and temperature. It has a fast response speed and high precision, while also demonstrating hysteresis during the response process. This effectively solves the technical problems of current hydrogels where the response is highly correlated with the stimulus, the response cannot be maintained independently, and the hysteresis of hydrogels is unstable. By applying the environmentally responsive hydrogel to the actuator of an intelligent micro-valve, intelligent control integrating sensing input signals, intelligent memory analysis, and output driving behavior is achieved.

[0085] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for preparing an environmentally responsive hydrogel, characterized in that, Includes the following steps: The photothermal conversion material was added to an aqueous solution of methylcellulose as an aqueous dispersant and dispersed to obtain a suspension of the photothermal conversion material. Stimulus-responsive hydrogel monomers are added to the photothermal conversion material suspension and dissolved. A free radical thermal initiator and a crosslinking agent are added, the mixture is stirred, cooled, and then a promoter is added. Polymerization is carried out under a nitrogen atmosphere. During polymerization, the carbon-carbon double bonds of the crosslinking agent break, reacting with the aqueous dispersant and the stimulus-responsive hydrogel monomers under the action of the free radical thermal initiator and the promoter to form a crosslinked structure. The photothermal conversion material is then loaded into the crosslinked structure to obtain an environmentally responsive hydrogel. The mass ratio of the stimulus-responsive hydrogel monomers to the photothermal conversion material is 40~60:5~9. The stimulus-responsive hydrogel monomer is N-isopropylacrylamide and acrylic acid; the photothermal conversion material is one or more of carbon nanotubes, silver nanowires, and carbon black.

2. The method for preparing the environmentally responsive hydrogel according to claim 1, characterized in that, The aqueous solution of the aqueous dispersant has a mass concentration of 5 mg / mL, and the mass ratio of the photothermal conversion material to the aqueous dispersant is 5~9:325~450.

3. The method for preparing the environmentally responsive hydrogel according to claim 1, characterized in that, The mass ratio of the free radical thermal initiator, crosslinking agent, and initiator is 10~15:5~10:15~20.

4. The method for preparing the environmentally responsive hydrogel according to claim 1, characterized in that, The free radical thermal initiator is one or more of ammonium persulfate, azobisisobutyronitrile, and diacyl peroxide; the crosslinking agent is one or more of N,N-methylenebisacrylamide, dicumyl peroxide, butadiene, and vinylbenzene; and the initiator is one or more of N,N,N',N'-tetramethylethylenediamine, propylenediamine, and isopropyldiamine.

5. An environmentally responsive hydrogel prepared by the preparation method according to any one of claims 1 to 4.

6. The application of the environmentally responsive hydrogel of claim 5 in an actuator smart microvalve.

Images