Synthesis method and application of double-layer thermochromic deformation hydrogel

Abstract

The invention relates to a synthesis method and application of a double-layer thermochromic deformation hydrogel, according to the double-layer thermochromic deformation hydrogel, CMC is adopted to perform mechanical enhancement on original PNIPAm, LAP is adopted to perform photo-initiation on a monomer, and the price of CMC and LAP is far lower than that of functionalized silicon dioxide nanoparticles and AIBA in the prior art under the same usage amount. Meanwhile, drugs used in the process are free of volatility and corrosivity, and the safety degree is higher than that of acrylic monomers used in the prior art. Besides, the use temperature of a hydrogel device in the prior art is 60 DEG C and is high, while the double-layer temperature-sensitive hydrogel in the invention can be curled only at 40 DEG C, so that the hydrogel has more advantages in temperature. By adding CMC, the volume change of the hydrogel in the heating process is remarkably reduced, meanwhile, the mechanical property of the hydrogel is greatly improved, the mechanical property of the hydrogel is further improved through impregnation of zirconium ions, and the hydrogel has a wider application scene.

Description

A method for synthesizing a bilayer thermochromic degradable hydrogel and its application Technical Field

[0001] This invention relates to the field of novel hydrogel materials, specifically a method for synthesizing a bilayer thermochromic deformable hydrogel and its application. Background Technology

[0002] In fields such as intelligent soft robots, flexible grippers, and wearable devices, the demand for flexible materials that can autonomously deform, reversibly drive, and operate under low-energy conditions is rapidly increasing. Traditional mechanical actuators typically rely on motors, pneumatic or magnetic field structures, which are not only bulky and energy-intensive but also difficult to use in humid or flexible conditions. Therefore, developing a hydrogel actuator material that can autonomously deform under changes in external temperature and possesses high flexibility and safety is of great significance for the lightweighting and low-energy consumption of intelligent devices.

[0003] Poly(N-isopropylacrylamide) (PNIPAm) is a typical thermosensitive hydrogel that exhibits a distinct volumetric phase transition behavior around 32 °C: hydrophilic swelling below the LCST and hydrophobic shrinkage above the LCST. This phase transition characteristic, requiring no additional energy input, makes it an ideal candidate for smart responsive materials. However, pure PNIPAm hydrogels suffer from weak mechanical strength, brittleness, and insufficient driving force; furthermore, the volume shrinkage of monolayer PNIPAm is uniform, preventing directional bending or curling deformation, thus limiting its application in actuators.

[0004] To address the aforementioned shortcomings, this invention proposes a method based on the PNIPAm active layer and CMC-Zr. 4 ⁺ A bilayer thermosensitive hydrogel with coordination-enhanced passive layer. The framework structure was constructed by introducing carboxymethyl cellulose (CMC) into PNIPAm, and Zr was utilized. 4 The strong coordination between the ⁺ and CMC carboxylic acid groups constructs a passive layer with high modulus and low volume change, achieving significant mechanical strengthening and volume stability. Simultaneously, low-crosslinked pure PNIPAm is used as the active layer, causing it to exhibit greater volume shrinkage upon heating than the passive layer. This creates differential stress at the bilayer interface, driving the gel to achieve rapid and reversible bending and curling. The resulting bilayer thermosensitive hydrogel exhibits characteristics such as fast response speed, large deformation amplitude, high cycle durability, and stable interfacial bonding. It can autonomously curl and achieve flexible clamping in water at 40 ℃, possessing grasping, lifting, and programmable deformation functions, making it suitable for novel applications such as flexible actuators, soft robots, and adaptive shape control materials. Summary of the Invention

[0005] This invention addresses the shortcomings of existing technologies by providing a method for synthesizing a bilayer thermochromic hydrogel and its applications.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for synthesizing a bilayer thermochromic degradable hydrogel includes the following steps:

[0008] Step 1: N-isopropylacrylamide, carboxymethyl cellulose, N,N'-methylenebisacrylamide and lithium 2,4,6-trimethylbenzoylphenylphosphonate were added to a solvent, mixed, poured into a mold, and subjected to UV photoinitiated polymerization to prepare B-layer hydrogel.

[0009] Step 2: N-isopropylacrylamide, N,N'-methylenebisacrylamide and lithium 2,4,6-trimethylbenzoylphenylphosphonate are added to a solvent and mixed. The mixture is poured onto the B-layer hydrogel in the mold and UV photoinitiated polymerization is performed. The A-layer hydrogel is then condensed on the B-layer hydrogel to obtain an AB bilayer thermosensitive hydrogel.

[0010] Furthermore, in step 1, the mass ratio of N-isopropylacrylamide, carboxymethyl cellulose, N,N'-methylenebisacrylamide and lithium 2,4,6-trimethylbenzoylphenylphosphonate is 90-100:25-35:1.5-2.5:1.

[0011] Furthermore, in step 2, the mass ratio of N-isopropylacrylamide, N,N'-methylenebisacrylamide, and lithium 2,4,6-trimethylbenzoylphenylphosphonate is 90-100:0.8-1.2:0.8-1.2.

[0012] Furthermore, the thickness ratio of the A-layer hydrogel to the B-layer hydrogel is 1-2:1-2.

[0013] The above-mentioned synthesis method of bilayer thermochromic deformable hydrogel has applications in flexible actuators, soft robots, or adaptive shape control materials.

[0014] The beneficial effects of this invention are as follows:

[0015] The bilayer thermosensitive hydrogel of this invention uses CMC to mechanically enhance the original PNIPAm and LAP to photoinitiate the monomer. Both, used in the same amounts, are significantly cheaper than functionalized silica nanoparticles and AIBA in existing technologies. Furthermore, the chemicals used in this invention are non-volatile and non-corrosive, offering a higher level of safety than the acrylic monomers used in existing technologies. Additionally, existing hydrogel devices operate at a relatively high temperature of 60°C, while the bilayer thermosensitive hydrogel of this invention curls at only 40°C, providing a significant temperature advantage. The addition of CMC significantly reduces the volume change of the hydrogel during heating and greatly improves its mechanical properties. The impregnation with zirconium ions further enhances the mechanical properties of the hydrogel.

[0016] In addition, the invention uses fewer types of pharmaceuticals, and both A and B double membranes use PNIPAm as the main hydrogel, which greatly simplifies the synthesis of the double-layer hydrogel.

[0017] Compared to existing temperature-sensitive bilayer hydrogels, the hydrogel synthesis route of this invention is simpler. Furthermore, it replaces polyacrylic acid (PAA) + ferric ion impregnation with a PNIPAm + CMC + zirconium ion impregnation method, significantly improving experimental safety without complicating the synthesis steps. The synthesis process avoids the use of traditional toxic and explosive acrylic monomers. Additionally, the bilayer temperature-sensitive hydrogel of this invention can begin to curl at 40°C, a lower bending temperature than existing methods, thus offering better application prospects.

[0018] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. Attached Figure Description

[0019] Figure 1 shows the front, side and fully rolled-up images of the AB double-layer hydrogel of the present invention.

[0020] Figure 2 shows the time relationship of the AB bilayer hydrogel in Example 1 from flat to completely rolled up;

[0021] Figure 3 shows the interface microstructure of the AB bilayer thermosensitive hydrogel; the large image on the left is a SEM image of the bilayer hydrogel, in which a clear interface can be observed; the right side, from top to bottom, shows the distribution of zirconium, oxygen, and carbon elements, with the green diagonal line in the zirconium distribution map representing the interface of the bilayer hydrogel.

[0022] Figure 4 shows the infrared spectra of PNIPAm and PNIPAm / CMC;

[0023] Figure 5 shows the thermogravimetric curves of pure PNIPAm and PNIPAm / CMC-Zr4+.

[0024] Figure 6 shows PNIPAAm / CMC-Zr 4+Stress-strain curves of PNIPAm / CMC. Detailed Implementation

[0025] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0026] This invention proposes a method based on the PNIPAm active layer and CMC-Zr 4 ⁺ A bilayer thermosensitive hydrogel with coordination-enhanced passive layer. The framework structure was constructed by introducing carboxymethyl cellulose (CMC) into PNIPAm, and Zr was utilized. 4 The strong coordination between the ⁺ and CMC carboxylic acid groups constructs a passive layer with high modulus and low volume change, achieving significant mechanical strengthening and volume stability. Simultaneously, low-crosslinked pure PNIPAm is used as the active layer, causing it to exhibit greater volume shrinkage upon heating than the passive layer. This creates differential stress at the bilayer interface, driving the gel to achieve rapid and reversible bending and curling. The resulting bilayer thermosensitive hydrogel exhibits characteristics such as fast response speed, large deformation amplitude, high cycle durability, and stable interfacial bonding. It can autonomously curl and achieve flexible clamping in water at 40 ℃, possessing grasping, lifting, and programmable deformation functions, making it suitable for novel applications such as flexible actuators, soft robots, and adaptive shape control materials.

[0027] The method of the present invention includes the following steps:

[0028] Step (1): Synthesis of layer B (passive layer) in AB bilayer thermosensitive hydrogel

[0029] The polymerization was initiated by UV light using N-isopropylacrylamide (NIPAm) and carboxymethyl cellulose (CMC) as the main raw materials. The main steps are as follows:

[0030] ① Add 0.3 g of carboxymethyl cellulose (CMC, DS=0.7, 50-100 mPa.s) to 10 mL of deionized water (DI);

[0031] ② Stir for 10 minutes to obtain a homogeneous solution;

[0032] ③ Add 1g N-isopropylacrylamide (NIPAm), 0.02g N,N'-methylenebisacrylamide (MBA), and 0.01g 2,4,6-trimethylbenzoylphenylphosphonate lithium (LAP) sequentially to the above solution.

[0033] ④ Stir for 10 minutes to obtain a homogeneous solution;

[0034] ⑤ Take about 3 mL of the final homogeneous solution and pour it into a glass pool with a length, width and height of 6 cm, 6 cm and 0.5 mm respectively, and cover it with a glass plate with a thickness of about 2 mm (to ensure that the liquid overflows slightly after covering with the glass plate).

[0035] ⑥ Place the above-mentioned instrument under a UV (ultraviolet light) lamp (power 20W, wavelength 365nm), with the lamp about 35cm away from the instrument, and irradiate for about 15 minutes to obtain the unimpregnated B-layer hydrogel.

[0036] ⑦ Immerse the obtained hydrogel membrane in a 0.1 mol / L solution of zirconium oxychloride octahydrate and let it stand for 1 hour to obtain layer B hydrogel.

[0037] Step (2), Synthesis of AB bilayer thermosensitive hydrogel

[0038] UV (ultraviolet light) initiated polymerization was carried out using N-isopropylacrylamide (NIPAm) as the main raw material. The main steps are as follows:

[0039] ① Add 1g NIPAM, 0.01g MBA, and 0.01g LAP sequentially to 10mL DI;

[0040] ② Stir for 10 minutes to obtain a homogeneous solution;

[0041] ③ Take about 3 mL of the obtained homogeneous solution and pour it into a glass pool with a length, width and height of 5 cm, 5 cm and 0.5 mm respectively;

[0042] ④ Place the B membrane onto a 2mm thick glass slide and align the B membrane with the glass pool from step ③, so that the B membrane covers the glass pool and the uniform solution in the glass pool overflows slightly.

[0043] ⑤ Place the above-mentioned instrument under a UV lamp (power 20W, wavelength 365nm), with the lamp about 35cm away from the instrument, and irradiate for about 15 minutes to obtain AB double-layer thermosensitive hydrogel.

[0044] By controlling the thickness variation of the glass pool in steps (1) and (2), AB double-layer thermosensitive hydrogels with different thickness ratios can be obtained. The time required for AB double-layer thermosensitive hydrogels with different thickness ratios to go from flat to completely rolled up in water at 40°C is different.

[0045] Example 1: Both layers A and B are 0.5mm thick, with a thickness ratio of 1:1, and the required time is 150 seconds.

[0046] Example 2: Layer A is 1mm thick, layer B is 0.5mm thick, thickness ratio 2:1, required time is 90 seconds.

[0047] Example 3: Layer A is 0.5mm thick, layer B is 1mm thick, thickness ratio 1:2, required time is 300 seconds.

[0048] This invention utilizes the different volume shrinkage capabilities of bilayer hydrogels after heating to successfully prepare temperature-responsive AB bilayer thermosensitive hydrogels.

[0049] The internal structure of the hydrogel was determined using SEM technology to understand the impact of CMC addition on the original hydrogel's microstructure from a microscopic perspective, and to explain its effect on mechanical properties. Simultaneously, EDS technology was used to observe the distribution of tetravalent zirconium ions in the hydrogel at the microscopic level, to understand how CMC and tetravalent zirconium ions jointly alter the hydrogel's microstructure. The layering of the hydrogel interface can be clearly observed in the large SEM image on the left of Figure 3, with layer B on the left and layer A on the right. The fine porous structure helps the hydrogel in layer A to better expel water and shrink. The three smaller images on the right are EDS images of the gel, showing the distribution of zirconium, oxygen, and carbon from top to bottom. It can be seen that oxygen and carbon are evenly distributed, while zirconium is more densely distributed on the left due to the active addition of zirconium ions to the B membrane. The zirconium on the right side of the A membrane is due to the permeation of zirconium ions from the B membrane, so there is also zirconium on the right side, but in a smaller quantity.

[0050] As shown in Figure 4, the changes in various chemical bonds in the hydrogel were determined by using FT-IR technology. At the same time, the changes in hydrogen bonds in the hydrogel were analyzed by the peak changes of chemical bonds in the FT-IR spectrum. The mechanism of enhanced mechanical properties of hydrogel was explained from the perspective of hydrogen bonds. The mechanism of the influence of zirconium ion infiltration on hydrogel properties was also understood, and the significance of zirconium ion impregnation was explored. It can be seen that the peak value of PNIPAm / CMC in the FT-IR spectrum is much larger than that of PNIPAm.

[0051] As shown in Figure 5, the thermal stability of the AB bilayer hydrogel was understood through TG-DTG testing, and the applicable temperature range of the AB bilayer hydrogel was further understood. The minimum bending temperature of the AB bilayer hydrogel was determined through DSC testing, so that it can be better put into use. It can be seen that the bending temperature of PNIPAm / CMC is much lower than that of PNIPAm.

[0052] As shown in Figure 6, a tensile testing machine was used to determine the differences in mechanical properties between the B-layer hydrogel without zirconium ions, the B-layer hydrogel with zirconium ions, and the AB double-layer hydrogel. From a mechanical perspective, the necessity of adding CMC and impregnating zirconium ions for improving the mechanical properties of the hydrogel was analyzed. Figure 6 shows the stress-strain curves of PNIPAm hydrogel after the addition of CMC and the dual effect of CMC and zirconium ions. It can be seen that CMC and zirconium ions have a mechanical strengthening effect on the hydrogel.

[0053] The experimental results above demonstrate that the addition of CMC significantly reduces the volume change of the hydrogel during heating, while greatly improving its mechanical properties. The impregnation with zirconium ions further enhances the mechanical properties of the hydrogel, enabling it to be used in a wider range of applications. Furthermore, this invention uses fewer types of pharmaceuticals, and both A and B double membranes utilize PNIPAm as the hydrogel matrix, greatly simplifying the synthesis of the bilayer hydrogel.

[0054] Compared to existing temperature-sensitive bilayer hydrogels, the hydrogel synthesis route of this invention is simpler. Furthermore, it replaces polyacrylic acid (PAA) + ferric ion impregnation with a PNIPAm + CMC + zirconium ion impregnation method, significantly improving experimental safety without complicating the synthesis steps. The synthesis process avoids the use of traditional toxic and explosive acrylic monomers. Additionally, the bilayer temperature-sensitive hydrogel of this invention can begin to curl at 40°C, a lower bending temperature than existing methods, thus offering better application prospects.

[0055] The above description provides examples of the preferred embodiments of the present invention. Parts not detailed herein are common knowledge to those skilled in the art. The scope of protection of the present invention is determined by the claims. Any equivalent modifications based on the technical teachings of the present invention are also within the scope of protection of the present invention.

Claims

1. A method for synthesizing a bilayer thermochromic hydrogel, characterized in that, Includes the following steps: Step 1: N-isopropylacrylamide, carboxymethyl cellulose, N,N'-methylenebisacrylamide, and lithium 2,4,6-trimethylbenzoylphenylphosphonate are mixed in a solvent and poured into a mold. UV photoinitiated polymerization is then performed to prepare layer B hydrogel. Step 2: N-isopropylacrylamide, N,N'-methylenebisacrylamide, and lithium 2,4,6-trimethylbenzoylphenylphosphonate are mixed in a solvent. The mixture is poured onto layer B hydrogel in the mold and UV photoinitiated polymerization is performed. Layer A hydrogel is then formed on layer B hydrogel to obtain AB bilayer thermosensitive hydrogel.

2. The method for synthesizing a bilayer thermochromic hydrogel according to claim 1, characterized in that, In step 1, the mass ratio of N-isopropylacrylamide, carboxymethyl cellulose, N,N'-methylenebisacrylamide and lithium 2,4,6-trimethylbenzoylphenylphosphonate is 90-100:25-35:1.5-2.5:

1.

3. The method for synthesizing a bilayer thermochromic hydrogel according to claim 1, characterized in that, In step 2, the mass ratio of N-isopropylacrylamide, N,N'-methylenebisacrylamide and lithium 2,4,6-trimethylbenzoylphenylphosphonate is 90-100:0.8-1.2:0.8-1.

2.

4. The method for synthesizing a bilayer thermochromic hydrogel according to claim 1, characterized in that, The thickness ratio of the A-layer hydrogel to the B-layer hydrogel is 1-2:1-2.

5. The method for synthesizing the bilayer thermochromic deformable hydrogel according to any one of claims 1-3, and its application in flexible actuators, soft robots, or adaptive shape control materials.

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