A cellulose-based ion conductive gel film and a method for preparing the same

Abstract

This invention discloses a cellulose-based ion-conductive gel membrane and its preparation method, belonging to the technical field of flexible wearable electronic materials and sensors. Addressing the technical pain points of existing ion gels, such as easy dehydration and failure, insufficient mechanical properties, difficulty in film formation, and inability to synergistically optimize multiple performance indicators, this invention constructs a composite gel matrix by crosslinking sodium alginate and sodium carboxymethyl cellulose with calcium ions. The crosslinking density of the system is controlled by sodium carboxymethyl cellulose, and glycerol is used as a plasticizer to construct ion transport channels. A solid gel membrane free of free water is obtained through coating, crosslinking, room temperature equilibration, and drying dehydration. The raw materials of this invention are environmentally friendly, the preparation process is simple and controllable, and the resulting gel membrane possesses high tensile strength, high transparency, excellent ion conductivity, and environmental stability. It exhibits sensitive strain response and good linearity, and can be widely used in the field of flexible strain sensing.

Description

Technical Field

[0001] This invention relates to the field of flexible wearable electronic materials and sensor devices, specifically to a cellulose ion-conductive gel film and its preparation method. Background Technology

[0002] With the development of wearable electronics, human-computer interaction, and artificial intelligence, flexible strain sensors have attracted widespread attention. Traditional flexible sensors mostly use conductive polymers, carbon nanotubes, or metal nanomaterials as conductive layers. In recent years, ionogels have become a research hotspot in the field of flexible sensing due to their biomimetic, transparent, and biocompatible properties, similar to human skin.

[0003] In existing technologies, ion gels are mostly prepared by mixing synthetic polymers or single natural polysaccharides with water and conductive inorganic salts, and then cross-linking them. Among these, sodium alginate-based hydrogel systems are the most widely used.

[0004] This type of technical solution has the following shortcomings in practical applications:

[0005] The crosslinking density of a single sodium alginate system is difficult to control, resulting in insufficient mechanical properties, low tensile strain, poor toughness and fatigue resistance, and inability to adapt to repeated deformation application scenarios. Traditional hydrogels contain a large amount of free water, which is easy to evaporate quickly in normal environments, causing the material to dry out, deform, harden, lose flexibility and ionic conductivity, and have insufficient environmental stability and long-term performance.

[0006] Traditional calcium ion crosslinked sodium alginate hydrogels tend to form bulk structures, making it difficult to process into thin and flat films. They also lack sensitivity to capture minute strains, limiting their application scenarios. In order to improve conductivity, some composite systems add opaque nanofillers, which leads to a decrease in material transparency and makes them unsuitable for applications that require optical performance. Summary of the Invention

[0007] The purpose of this invention is to overcome the above-mentioned defects of the prior art and provide a cellulose-based ion-conductive gel membrane and its preparation method. While maintaining the high transparency, biocompatibility and green environmental protection characteristics of the all-natural polymer system, this invention solves the technical pain point of the inability to synergistically optimize multiple performance indicators in the prior art through component synergistic regulation and precise optimization of the preparation process. It simultaneously improves the tensile properties, ion conductivity, environmental stability and strain response sensitivity of the material, and prepares a solid thin gel membrane that can be used independently. At the same time, it simplifies the preparation process and adapts to the needs of industrial-scale production.

[0008] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0009] This invention provides a cellulose-based ion-conductive gel membrane. The gel membrane is a continuous, uniform, filler-free, phase-separated solid film structure. The continuous phase of the composite gel matrix consists of a physical hydrogen bond network formed by calcium ion crosslinking of sodium alginate and sodium carboxymethyl cellulose. Glycerol fills the gaps in the network of the physical hydrogen bond network. Free conductive ion components are dispersed in the system composed of the composite gel matrix and glycerol. The gel membrane system contains no free water, with a water content ≤5%. The gel membrane has a transmittance ≥90% at a wavelength of 550 nm, a tensile breaking strain ≥250%, and an electrical conductivity ≥8 mS / m.

[0010] Furthermore, the amount of sodium carboxymethyl cellulose added is 10wt% to 50wt% of the sodium alginate solution, with an optimal range of 30wt% to 45wt%; the amount of glycerol added is 10wt% to 35wt% of the sodium alginate solution, with an optimal range of 20wt% to 30wt%.

[0011] Furthermore, the conductive ionic components include free calcium ions, chloride ions, and sodium ions; the calcium ions are derived from calcium chloride, which is used to perform ionic crosslinking on the mixed system of sodium alginate and sodium carboxymethyl cellulose.

[0012] Furthermore, the thickness of the gel film is 20μm to 100μm, which can be precisely adjusted according to the application scenario.

[0013] This invention provides a method for preparing the above-mentioned cellulose ion-conductive gel membrane, comprising the following steps:

[0014] Step 1: Add sodium alginate powder and sodium carboxymethyl cellulose powder to deionized water and stir at room temperature until completely dissolved to obtain sodium alginate solution with a mass concentration of 1% to 4% and sodium carboxymethyl cellulose solution with a mass concentration of 3% to 5%, respectively. Stir at room temperature for 16 to 18 hours.

[0015] Step 2: Add sodium carboxymethyl cellulose solution to sodium alginate solution at 10wt% to 50wt% of the mass of sodium alginate solution, and stir for 1 to 2 hours until homogeneous to obtain sodium alginate / sodium carboxymethyl cellulose mixed solution.

[0016] Step 3: Add glycerol to the sodium alginate / sodium carboxymethyl cellulose mixed solution. The amount of glycerol added is 10wt% to 35wt% of the sodium alginate solution mass. Stir continuously for 1 to 2 hours, then degas by sonication for 1 to 2 minutes to obtain a uniform precursor solution.

[0017] Step 4: Coat the precursor solution onto the substrate surface with a coating thickness of 0.5 mm to 2 mm. Immerse the substrate coated with the precursor solution into a calcium chloride solution with a mass concentration of 1 wt% to 5 wt% for ionic cross-linking for 30 s to 180 s to obtain sodium alginate / sodium carboxymethyl cellulose / glycerol hydrogel.

[0018] Step 5: After sealing the cross-linked hydrogel, equilibrate it at room temperature for 22h to 36h.

[0019] Step 6: Place the hydrogel that has been equilibrated in an environment of 50℃~65℃ and continue to dry for 24h~36h to remove free water in the system until the weight of the gel membrane no longer changes, and obtain a cellulose ion-conductive gel membrane.

[0020] In this process, the ratio of the drying temperature in step 6 to the crosslinking time in step 4 is controlled between 0.5 and 1.0 to precisely regulate the microporous structure of the gel membrane.

[0021] Furthermore, in step 4, the precursor solution is coated by glass rod coating, blade coating, or spin coating, and the substrate is a plastic plate; after ionic crosslinking is completed, a room temperature equilibration treatment is performed.

[0022] This invention provides a cellulose-based ion-conductive gel membrane and its preparation method, which has the following beneficial effects:

[0023] First, a composite gel matrix was constructed by combining sodium alginate and sodium carboxymethyl cellulose. Sodium carboxymethyl cellulose can regulate the crosslinking density of the system, optimize the microstructure of the gel network, and improve the tensile properties and flexibility of the gel membrane, making it suitable for applications with repeated deformation.

[0024] Secondly, the free water in the system is removed by the drying process, while the high-boiling-point glycerol is retained to fill the gaps in the gel network. Glycerol can play a plasticizing and moisturizing role, avoiding the problems of water loss and shrinkage and performance degradation of traditional hydrogels, and improving the environmental stability and long-term performance of the material.

[0025] Meanwhile, this invention employs a coating-then-crosslinking preparation process, which can produce thin, flat solid films. Combined with uniformly dispersed free conductive ions within the system, it enhances the material's response sensitivity to strain and expands its application scenarios. The invention also uses all-natural polymer raw materials to construct the system, without the addition of additional opaque conductive fillers. The gel matrix forms a continuous and uniform phase structure, eliminating phase separation issues and ensuring the transparency of the material. Furthermore, the preparation process is simple, requires no expensive equipment, uses environmentally friendly raw materials, and is suitable for large-scale production needs. Attached Figure Description

[0026] Figure 1This is a graph showing the relationship between tensile strain and resistance change rate of the ion-conductive gel film of the present invention.

[0027] Figure 2 This is a diagram showing the electrical signal of the ion-conductive gel membrane of the present invention in response to a tapping event.

[0028] Figure 3 The graph shows the response time and recovery time of the ion-conductive gel membrane of the present invention.

[0029] Figure 4 This is a Morse code application test diagram of the ion-conductive gel film of the present invention. Detailed Implementation

[0030] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0031] Example

[0032] 1. Preparation of the basic solution, as follows:

[0033] Crosslinking can be achieved with sodium alginate solution concentrations ranging from 1% to 4%. In this example, a 3wt% sodium alginate solution and a 4wt% sodium carboxymethyl cellulose solution were used. 9g of sodium alginate powder and 3.2g of sodium carboxymethyl cellulose powder were weighed and added to 291mL and 76.8mL of deionized water, respectively. The solutions were stirred with a magnetic stirrer at room temperature for 16-18 hours to obtain transparent and homogeneous sodium alginate and sodium carboxymethyl cellulose solutions.

[0034] 2. The experimental group setup is as follows:

[0035] Experiments were conducted using the mass ratio of sodium carboxymethyl cellulose solution as the independent variable to investigate the system performance of sodium carboxymethyl cellulose solution relative to sodium alginate solution at different mass ratios.

[0036] Experiment 1: Take 25g of sodium alginate solution, add 2.5g of sodium carboxymethyl cellulose solution and 6.25g of glycerol, stir for 1h and then sonicate to degas for 1min to obtain a precursor solution; coat the precursor solution onto the surface of a plastic plate and immerse it in a 3wt% calcium chloride solution for crosslinking for 60 seconds to obtain a hydrogel; seal the hydrogel and equilibrate at room temperature for 24h, then dry it in a 55℃ forced-air drying oven for 24h to obtain an ion-conductive gel membrane.

[0037] Experiment 2: Take 25g of sodium alginate solution, add 5.0g of sodium carboxymethyl cellulose solution and 6.25g of glycerol, and the rest of the steps are the same as in Experiment 1.

[0038] Experiment 3: Take 25g of sodium alginate solution, add 7.5g of sodium carboxymethyl cellulose solution and 6.25g of glycerol, and the remaining steps are the same as in Experiment 1.

[0039] Experiment 4: Take 25g of sodium alginate solution, add 10g of sodium carboxymethyl cellulose solution and 6.25g of glycerol, and follow the same steps as in Experiment 1.

[0040] Experiment 5: Take 25g of sodium alginate solution, add 12.5g of sodium carboxymethyl cellulose solution and 6.25g of glycerol, and the remaining steps are the same as in Experiment 1.

[0041] Experiment 6: Take 25g of sodium alginate solution, add 7.5g of sodium carboxymethyl cellulose solution and 6.25g of glycerol, and immerse the precursor solution in 2wt% calcium chloride solution for crosslinking for 60 seconds. The remaining steps are the same as in Experiment 1.

[0042] Experiment 7: Take 25g of sodium alginate solution, add 7.5g of sodium carboxymethyl cellulose solution and 6.25g of glycerol, and immerse the precursor solution in 4wt% calcium chloride solution for crosslinking for 60 seconds. The remaining steps are the same as in Experiment 1.

[0043] Experiment 8: Take 25g of sodium alginate solution, add 7.5g of sodium carboxymethyl cellulose solution and 6.25g of glycerol, and immerse the precursor solution in 3wt% calcium chloride solution for crosslinking for 120 seconds. The remaining steps are the same as in Experiment 1.

[0044] 3. The control group was set up as follows:

[0045] Control group 1: Based on Experiment 1, without adding sodium carboxymethyl cellulose solution, the remaining steps are exactly the same.

[0046] Control group 2: Based on Experiment 1, without the addition of glycerol and sodium carboxymethyl cellulose solution, the remaining steps are exactly the same.

[0047] Control group 3: Based on Experiment 1, without the addition of sodium carboxymethyl cellulose solution, and without the cross-linking of calcium chloride solution in the precursor solution, the remaining steps were exactly the same.

[0048] 4. Performance testing methods, including:

[0049] Transparency verification: The transmittance of the sample was measured at a wavelength of 550 nm using a UV-vis spectrometer.

[0050] Mechanical property verification: The tensile strain and fracture stress of the samples were measured using a tensile-compression testing machine.

[0051] Conductivity test: The conductivity of the sample was measured using an electrochemical workstation.

[0052] Electrical signal performance verification: Wearable strain sensors were prepared by attaching copper foil electrodes to both ends of the sample. Dynamic mechanical deformation was applied using a universal tensile testing machine equipped with insulating clamps. The resistance change was monitored in real time using a digital multimeter, and strain-resistance data were collected simultaneously to determine the sensitivity, response time, and recovery time of the sample.

[0053] The performance test results of each experimental group and the control group are shown in the table below:

[0054]

[0055] The ion-conductive gel membrane prepared by this invention has a sensitivity of 0.72, a response time of 0.04207s, and a recovery time of 0.14522s, and can be applied to strain sensing scenarios such as Morse code signal transmission.

[0056] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A cellulose ion-conductive gel membrane, characterized in that, The gel membrane is a continuous and uniform unfilled phase-separated solid film structure. The composite gel matrix is ​​a continuous phase composed of a physical hydrogen bond network formed by calcium ion crosslinking of sodium alginate and sodium carboxymethyl cellulose. Glycerol fills the gaps in the physical hydrogen bond network. Free conductive ion components are dispersed in the system composed of the composite gel matrix and glycerol. The gel membrane system contains no free water and has a water content of ≤5%. The gel film has a transmittance of ≥90% at a wavelength of 550nm, a tensile fracture strain of ≥250%, and an electrical conductivity of ≥8mS / m.

2. The cellulose ion-conductive gel membrane according to claim 1, characterized in that, The amount of sodium carboxymethyl cellulose added is 10wt% to 50wt% of the sodium alginate solution, and the amount of glycerol added is 10wt% to 35wt% of the sodium alginate solution.

3. The cellulose ion-conductive gel membrane according to claim 2, characterized in that, The amount of sodium carboxymethyl cellulose added is 30wt% to 45wt% of the sodium alginate solution, and the amount of glycerol added is 20wt% to 30wt% of the sodium alginate solution.

4. The cellulose ion-conductive gel membrane according to claim 1, characterized in that, The conductive ionic components include free calcium ions, chloride ions, and sodium ions; the calcium ions are derived from calcium chloride, which is used to perform ionic crosslinking on the mixed system of sodium alginate and sodium carboxymethyl cellulose.

5. The cellulose ion-conductive gel membrane according to claim 1, characterized in that, The thickness of the gel membrane is 20 μm to 100 μm.

6. A method for preparing the cellulose-based ion-conductive gel membrane according to any one of claims 1 to 5, characterized in that, Includes the following steps: Step 1: Add sodium alginate powder and sodium carboxymethyl cellulose powder to deionized water and stir at room temperature until completely dissolved to obtain sodium alginate solution with a mass concentration of 1% to 4% and sodium carboxymethyl cellulose solution with a mass concentration of 3% to 5%, respectively. Step 2: Add sodium carboxymethyl cellulose solution to sodium alginate solution at 10wt% to 50wt% of the mass of sodium alginate solution, stir and mix evenly to obtain sodium alginate / sodium carboxymethyl cellulose mixed solution. Step 3: Add glycerol to the sodium alginate / sodium carboxymethyl cellulose mixed solution. The amount of glycerol added is 10wt% to 35wt% of the sodium alginate solution mass. After continuous stirring, ultrasonic degassing is performed to obtain a uniform precursor solution. Step 4: Coat the precursor solution onto the substrate surface with a coating thickness of 0.5 mm to 2 mm. Immerse the substrate coated with the precursor solution into a calcium chloride solution with a mass concentration of 1 wt% to 5 wt% for ionic cross-linking for 30 s to 180 s to obtain sodium alginate / sodium carboxymethyl cellulose / glycerol hydrogel. Step 5: After sealing the cross-linked hydrogel, equilibrate it at room temperature for 22h to 36h. Step 6: Place the hydrogel that has been equilibrated in an environment of 50℃~65℃ and continue to dry for 24h~36h to remove free water in the system until the weight of the gel membrane no longer changes, and obtain a cellulose ion-conductive gel membrane. In this process, the ratio of the drying temperature in step 6 to the crosslinking time in step 4 is controlled between 0.5 and 1.0, and this ratio is used to regulate the microporous structure of the gel membrane.

7. The preparation method according to claim 6, characterized in that, In step 2, the amount of sodium carboxymethyl cellulose solution added is 30wt% to 45wt% of the mass of sodium alginate solution; in step 3, the amount of glycerol added is 20wt% to 30wt% of the mass of sodium alginate solution.

8. The preparation method according to claim 6, characterized in that, In step 4, the mass concentration of the calcium chloride solution is 2wt% to 4wt%, and the crosslinking time is 60s to 120s; in step 6, the drying temperature is 55℃ to 65℃, and the drying time is 24h to 30h.

9. The preparation method according to claim 6, characterized in that, In step 4, the precursor solution is coated by glass rod coating, blade coating, or spin coating, and the substrate is a plastic plate; after ionic crosslinking is completed, a room temperature equilibration treatment is performed.

10. The application of the cellulose ion-conductive gel membrane according to any one of claims 1 to 5 in flexible strain sensor devices.

Images