ITO and calcium alginate double-layer coated hollow glass microsphere, flexible multi-parameter sensor and preparation method thereof
Patent Information
- Application Number
- CN202610973765.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-07-01
- Publication Date
- 2026-08-21
AI Technical Summary
[0004]本发明的第一个目的是提供一种ITO和海藻酸钙双层包覆空心玻璃微珠以解决现有基于空心玻璃微珠的柔性传感器作用机制单一，难以满足现代科技对多参数协同感知的复合需求的技术问题
柔性适配性与机械稳定性显著提升：传统柔性传感器中，ITO薄膜因脆性高，在基材弯曲时易因拉伸或压缩产生微裂纹，导致传感器的导电性能急剧衰减。本发明通过将ITO包覆于空心玻璃微珠表面，形成离散的导电单元，构建了“微珠接触导电”机制。当硅橡胶基材弯曲时，空心玻璃微珠可自由滚动或滑动，将局部应力分散至整个导电网络，避免ITO层直接受力断裂。
Smart Images
Figure SMS_1
Abstract
Description
Technical Field
[0001] This invention belongs to the field of flexible electronics technology, specifically relating to a hollow glass microsphere double-coated with ITO and calcium alginate, a flexible multi-parameter sensor, and its preparation method. Background Technology
[0002] With the rapid development of flexible electronics and wearable devices, flexible multi-parameter sensors capable of simultaneously sensing multiple physical signals such as temperature, humidity, and pressure have become a research hotspot. These sensors have broad application prospects in fields such as electronic skin, human-computer interfaces, intelligent medical monitoring, and structural health monitoring. The core performance of flexible sensors largely depends on the design of their composite system of conductive fillers and flexible substrates. Transparent conductive oxides are among the commonly used conductive materials in flexible sensors. Indium tin oxide (ITO), due to its high transmittance and low sheet resistance, has been widely used in touchscreens, displays, and solar cells. However, the intrinsic brittleness of ITO makes it prone to microcracks when bent or stretched, leading to conductive network failure, which severely limits its application in flexible devices. Regarding humidity-sensitive materials, calcium alginate, as a natural high-molecular-weight polysaccharide, has received widespread attention in recent years. Sodium alginate is cross-linked with calcium ions to form calcium alginate, which is insoluble in water. Its fibers have ionic conductivity and can be directly used as humidity sensing materials. It also has the advantage of being biodegradable and is suitable for green electronics and sensing fields. However, calcium alginate has poor conductivity, is sensitive to the environment, and has low preparation precision, resulting in poor sensor repeatability and failing to meet the requirements for high-precision multi-parameter detection.
[0003] Hollow glass microspheres are micron-sized, lightweight spherical materials made of borosilicate. Their low thermal conductivity and high compressive strength make them ideal functional fillers for applications such as thermal insulation coatings, deep-sea buoyancy materials, and aerospace composites. Existing technologies prepare conductive fillers by silver plating on the surface of hollow glass microspheres; however, this only achieves conductivity, and the sensor's response mechanism is singular, making it difficult to meet the complex demands of modern technology for multi-parameter collaborative sensing. Therefore, there is an urgent need to develop flexible multi-parameter sensors based on hollow glass microspheres to break through the performance limitations of traditional materials. Summary of the Invention
[0004] The first objective of this invention is to provide a hollow glass microsphere double-coated with ITO and calcium alginate to solve the technical problem that the existing flexible sensors based on hollow glass microspheres have a single working mechanism and are difficult to meet the complex requirements of modern technology for multi-parameter collaborative sensing.
[0005] The second objective of this invention is to provide a method for preparing hollow glass microspheres with a double layer of ITO and calcium alginate coating.
[0006] The third objective of this invention is to provide a flexible multi-parameter sensor.
[0007] The fourth objective of this invention is to provide a method for fabricating a flexible multi-parameter sensor.
[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: Hollow glass microspheres are double-coated with ITO and calcium alginate. An ITO layer and a calcium alginate layer are coated on the surface of the hollow glass microspheres. The ITO layer is located between the hollow glass microspheres and the calcium alginate layer. The thickness of the ITO layer is 60-110 nm, and the degree of crosslinking of the calcium alginate layer is 30-85%.
[0009] The preparation method of ITO and calcium alginate double-layer coated hollow glass microspheres includes: S1: ITO layer was coated on the surface of hollow glass microspheres by chemical vapor deposition, followed by heat treatment to obtain ITO coated hollow glass microspheres; S2: Hollow glass microspheres with ITO and calcium alginate double-layer coating were obtained by coating the surface of ITO-coated hollow glass microspheres with a calcium alginate layer using a microfluidic method.
[0010] Furthermore, the chemical vapor deposition method described in S1 has a temperature of 300–350 °C, an air vacuum of 0.1–10 Pa, metal precursors of trimethylindium and tetramethyltin, carrier gas of argon, and deposition time of 15–45 min.
[0011] Furthermore, the deposition times were 15, 20, 25, 30, 35, and 40 minutes.
[0012] Furthermore, the molar ratio of trimethylindium to tetramethyltin is 1:(7-11), and the gas flow rate of argon is 40-60 sccm, preferably 50 sccm.
[0013] Furthermore, the heat treatment temperature in S1 is 300–350 °C, the time is 8–12 min, and oxygen is introduced during the heat treatment, with an oxygen flow rate of 15–25 sccm, preferably 20 sccm.
[0014] Furthermore, the steps of the microfluidic method are as follows: dissolving ITO-coated hollow glass microspheres in water to obtain a dispersed phase, dissolving sodium alginate in water to obtain a continuous phase, passing the dispersed phase and the continuous phase into a Y-type microfluidic chip respectively, collecting the hollow glass microspheres coated with sodium alginate, and then mixing them with calcium chloride solution, crosslinking them, and drying them.
[0015] Furthermore, the mass ratio of the ITO-coated hollow glass microspheres to sodium alginate is (2-3):10, preferably 2.5:10; the flow rate ratio of the dispersed phase to the continuous phase is 1:(1.5-2.5), preferably 1:2; the concentration of the calcium chloride solution is 0.05-0.5 mol / L; and the crosslinking time is 3-7 min, preferably 5 min.
[0016] Furthermore, the hollow glass microspheres coated with the ITO layer need to undergo pretreatment. The pretreatment steps include: ultrasonically cleaning the hollow glass microspheres sequentially with acetone, ethanol, and water, drying them to obtain dried hollow glass microspheres, and then subjecting the dried hollow glass microspheres to plasma treatment to obtain pretreated hollow glass microspheres. The plasma treatment power is 80-120 W, preferably 100 W, the time is 3-7 min, preferably 5 min, and the atmosphere is oxygen.
[0017] A flexible multi-parameter sensor includes a flexible substrate and hollow glass microspheres double-coated with ITO and calcium alginate. The ITO and calcium alginate double-coated hollow glass microspheres account for 20-30% of the total mass of the flexible multi-parameter sensor. The flexible substrate is Sylgard 184 type silicone rubber.
[0018] A method for preparing a flexible multi-parameter sensor includes: mixing a flexible substrate and a solvent to obtain a mixture one; removing air bubbles from the mixture one; then adding the ITO and calcium alginate double-layer coated hollow glass microspheres as described in claim 1 and stirring until homogeneous to obtain a mixture two; pouring the mixture two into a mold and curing to obtain the sensor; wherein the flexible substrate is Sylgard 184 type silicone rubber, the solvent is n-hexane, the solvent is 5-10% of the volume of the flexible substrate, and the ITO and calcium alginate double-layer coated hollow glass microspheres are 20-30% of the total mass of the flexible multi-parameter sensor.
[0019] Furthermore, the solvent is 5, 6, 7, 8, 9, or 10% of the volume of the flexible substrate.
[0020] Furthermore, the hollow glass microspheres double-coated with ITO and calcium alginate account for 20, 22, 24, 26, 28, and 30% of the total mass of the flexible multi-parameter sensor.
[0021] Furthermore, the thickness of mixture two in the mold is 1 to 3 mm.
[0022] Furthermore, the curing temperature in S3 is 70 ℃, and the curing time is 2 h.
[0023] The beneficial effects of this invention are: Significantly Improved Flexibility and Mechanical Stability: In traditional flexible sensors, the ITO film is highly brittle and prone to microcracks due to stretching or compression when the substrate is bent, leading to a sharp decline in the sensor's conductivity. This invention constructs a "microbead contact conductivity" mechanism by coating ITO onto the surface of hollow glass microspheres to form discrete conductive units. When the silicone rubber substrate is bent, the hollow glass microspheres can roll or slide freely, dispersing local stress throughout the conductive network and preventing the ITO layer from breaking under direct stress.
[0024] Multi-parameter integrated detection: In traditional hybrid sensors, the direct mixing of ITO, calcium alginate, and hollow glass microspheres can lead to crosstalk in the functional layers. For example, the swelling of calcium alginate, which is relied upon for humidity detection, can disrupt the continuity of the outer ITO layer, causing uneven conductivity or breakage, resulting in unstable signal transmission. This invention employs a double-layer coating structure of ITO and calcium alginate around hollow glass microspheres. When the outer calcium alginate layer absorbs moisture and swells, it only changes the spacing between the hollow glass microspheres without disrupting the ITO conductive network. This achieves independent decoupled detection of pressure, temperature, and humidity. This structure enables the flexible multi-parameter sensor of this invention to simultaneously detect pressure, temperature, and humidity.
[0025] Material cost and resource utilization optimization: Traditional flexible sensors require ITO to cover the entire surface to form a continuous conductive path, resulting in low material utilization and high cost. This invention coats the surface of hollow glass microspheres with an ITO layer, requiring only sufficient contact points between the hollow glass microspheres to construct a three-dimensional conductive network, significantly reducing the amount of ITO used. The discrete conductive units also have high tolerance for local defects. Even if there are defects in the ITO layer on some hollow glass microspheres, the three-dimensional conductive network can still maintain conductivity through the multi-path contact design between the hollow glass microspheres. Detailed Implementation
[0026] The present invention will be further described below with reference to embodiments.
[0027] Example 1 The preparation method of ITO and calcium alginate double-layer coated hollow glass microspheres in Example 1 includes the following steps: S1: Pretreatment: 10 g of hollow glass microspheres were sequentially washed with 200 mL of analytical grade acetone, ethanol, and deionized water. Each ultrasonic cleaning was performed at a power of 100 W, a frequency of 40 kHz, and a time of 15 min to remove surface organic contaminants and dust. Subsequently, the microspheres were dried in an oven at 100 ℃ for 2 h to remove moisture, resulting in dried hollow glass microspheres. The dried hollow glass microspheres were then treated with a plasma cleaner for 5 min to obtain pretreated hollow glass microspheres. The plasma cleaner had a power of 100 W and was used in an oxygen atmosphere.
[0028] S2: ITO Coating: Pretreated hollow glass microspheres were placed in the heating zone of a tube furnace. High-purity argon gas was introduced to purge the air from the tube until the air vacuum reached 8 Pa. The temperature was then raised to 320 °C. Trimethylindium and tetramethyltin were used as metal precursors and carried to the reaction zone via a bubbling method, where deposition was carried out for 30 min. After deposition, high-purity oxygen was introduced for 10 min to convert the amorphous ITO into a transparent conductive oxide, resulting in ITO-coated hollow glass microspheres. The flow rate of high-purity argon was 50 sccm, and the molar ratio of trimethylindium to tetramethyltin was 1:9. The argon carrier gas flow rate for the bubbling method was 50 sccm. The flow rate of high-purity oxygen was 20 sccm. The thickness of the ITO layer was 85 nm.
[0029] S3: Coating with calcium alginate layer: 2.5 g of ITO-coated hollow glass microspheres were dispersed in 250 mL of deionized water and ultrasonically dispersed for 30 min to obtain the dispersed phase; 10 g of sodium alginate solution was dispersed in 500 mL of deionized water and magnetically stirred for 2 h, and the insoluble matter was removed by filtration to obtain the continuous phase; laminar coating was performed using a Y-type microfluidic chip, and the dispersed phase and the continuous phase were respectively introduced into the two inlet channels of the Y-type microfluidic chip, with a flow rate ratio of 1:2 between the dispersed phase and the continuous phase. The coated hollow glass microspheres flowed into the collection tank from the chip outlet and were allowed to stand for 5 min to precipitate the unadsorbed sodium alginate solution. The sodium alginate-coated hollow glass microsphere suspension in the collection tank was poured into 250 mL of 0.1 mol / L calcium chloride solution and crosslinked under magnetic stirring for 5 min. The mixture was washed three times with deionized water to remove residual crosslinking solution, and then dried in a vacuum oven at 40 ℃ for 12 h to obtain ITO and calcium alginate double-layer coated hollow glass microspheres. The degree of cross-linking of the calcium alginate layer is 58%.
[0030] Example 2 The preparation method of ITO and calcium alginate double-layer coated hollow glass microspheres in Example 2 includes the following steps: S1: The pretreatment steps for hollow glass microspheres are the same as in Example 1.
[0031] S2: ITO Coating: Pretreated hollow glass microspheres were placed in the heating zone of a tube furnace. High-purity argon gas was introduced to purge the air from the tube until the air vacuum reached 8 Pa. The temperature was then raised to 320 °C. Trimethylindium and tetramethyltin were used as metal precursors and carried to the reaction zone via a bubbling method, where deposition was carried out for 15 min. After deposition, high-purity oxygen was introduced for 10 min to convert the amorphous ITO into a transparent conductive oxide, resulting in ITO-coated hollow glass microspheres. The flow rate of high-purity argon was 50 sccm, and the molar ratio of trimethylindium to tetramethyltin was 1:9. The nitrogen carrier gas flow rate for the bubbling method was 50 sccm. The flow rate of high-purity oxygen was 20 sccm. The thickness of the ITO layer was 65 nm.
[0032] S3: Coating with calcium alginate layer: 2.5 g of ITO-coated hollow glass microspheres were dispersed in 250 mL of deionized water and ultrasonically dispersed for 30 min to obtain the dispersed phase; 10 g of sodium alginate solution was dispersed in 500 mL of deionized water and magnetically stirred for 2 h, and the insoluble matter was removed by filtration to obtain the continuous phase; laminar coating was performed using a Y-type microfluidic chip, and the dispersed phase and the continuous phase were respectively introduced into the two inlet channels of the Y-type microfluidic chip, with a flow rate ratio of 1:2 between the dispersed phase and the continuous phase. The coated hollow glass microspheres flowed into the collection tank from the chip outlet and were allowed to stand for 5 min to precipitate the unadsorbed sodium alginate solution. The sodium alginate-coated hollow glass microsphere suspension in the collection tank was poured into 250 mL of 0.1 mol / L calcium chloride solution and crosslinked under magnetic stirring for 5 min. The mixture was washed three times with deionized water to remove residual crosslinking solution, and then dried in a vacuum oven at 40 ℃ for 12 h to obtain ITO and calcium alginate double-layer coated hollow glass microspheres.
[0033] Example 3 The preparation method of ITO and calcium alginate double-layer coated hollow glass microspheres in Example 3 includes the following steps: S1: The pretreatment steps for hollow glass microspheres are the same as in Example 1.
[0034] S2: ITO Coating: Pretreated hollow glass microspheres were placed in the heating zone of a tube furnace. High-purity argon gas was introduced to purge the air from the tube until the air vacuum reached 8 Pa. The temperature was then raised to 320 °C. Trimethylindium and tetramethyltin were used as metal precursors and carried to the reaction zone via a bubbling method, where deposition was carried out for 45 min. After deposition, high-purity oxygen was introduced for 10 min to convert the amorphous ITO into a transparent conductive oxide, resulting in ITO-coated hollow glass microspheres. The flow rate of high-purity argon was 50 sccm, and the molar ratio of trimethylindium to tetramethyltin was 1:9. The nitrogen carrier gas flow rate for the bubbling method was 50 sccm. The flow rate of high-purity oxygen was 20 sccm. The thickness of the ITO layer was 105 nm.
[0035] S3: Coating with calcium alginate layer: 2.5 g of ITO-coated hollow glass microspheres were dispersed in 250 mL of deionized water and ultrasonically dispersed for 30 min to obtain the dispersed phase; 10 g of sodium alginate solution was dispersed in 500 mL of deionized water and magnetically stirred for 2 h, and the insoluble matter was removed by filtration to obtain the continuous phase; laminar coating was performed using a Y-type microfluidic chip, and the dispersed phase and the continuous phase were respectively introduced into the two inlet channels of the Y-type microfluidic chip, with a flow rate ratio of 1:2 between the dispersed phase and the continuous phase. The coated hollow glass microspheres flowed into the collection tank from the chip outlet and were allowed to stand for 5 min to precipitate the unadsorbed sodium alginate solution. The hollow glass microsphere suspension in the collection tank was poured into 250 mL of 0.1 mol / L calcium chloride solution and crosslinked under magnetic stirring for 5 min. The mixture was washed three times with deionized water to remove the residual crosslinking solution, and then dried in a vacuum oven at 40 ℃ for 12 h to obtain ITO and calcium alginate double-layer coated hollow glass microspheres.
[0036] Example 4 The preparation method of ITO and calcium alginate double-layer coated hollow glass microspheres in Example 4 includes the following steps: S1: The pretreatment steps for hollow glass microspheres are the same as in Example 1.
[0037] S2: ITO Coating: Pretreated hollow glass microspheres were placed in the heating zone of a tube furnace. High-purity argon gas was introduced to purge the air from the tube until the air vacuum reached 8 Pa. The temperature was then raised to 320 °C. Trimethylindium and tetramethyltin were used as metal precursors and carried to the reaction zone via a bubbling method, where deposition was carried out for 30 min. After deposition, high-purity oxygen was introduced for 10 min to convert the amorphous ITO into a transparent conductive oxide, resulting in ITO-coated hollow glass microspheres. The flow rate of high-purity argon was 50 sccm, and the molar ratio of trimethylindium to tetramethyltin was 1:9. The nitrogen carrier gas flow rate for the bubbling method was 50 sccm, and the high-purity oxygen flow rate was 20 sccm.
[0038] S3: Coating with calcium alginate layer: 2.5 g of ITO-coated hollow glass microspheres were dispersed in 250 mL of deionized water and ultrasonically dispersed for 30 min to obtain the dispersed phase; 10 g of sodium alginate solution was dispersed in 500 mL of deionized water and magnetically stirred for 2 h, and the insoluble matter was removed by filtration to obtain the continuous phase; laminar coating was performed using a Y-type microfluidic chip, and the dispersed phase and the continuous phase were respectively introduced into the two inlet channels of the Y-type microfluidic chip, with a flow rate ratio of 1:2 between the dispersed phase and the continuous phase. The coated hollow glass microspheres flowed into the collection tank from the chip outlet and were allowed to stand for 5 min to precipitate the unadsorbed sodium alginate solution. The hollow glass microsphere suspension in the collection tank was poured into 250 mL of 0.05 mol / L calcium chloride solution and crosslinked under magnetic stirring for 5 min. The mixture was washed three times with deionized water to remove the residual crosslinking solution, and then dried in a vacuum oven at 40 ℃ for 12 h to obtain ITO and calcium alginate double-layer coated hollow glass microspheres. The degree of cross-linking of the calcium alginate layer is 32%.
[0039] Example 5 The preparation method of ITO and calcium alginate double-layer coated hollow glass microspheres in Example 5 includes the following steps: S1: The pretreatment steps for hollow glass microspheres are the same as in Example 1.
[0040] S2: ITO Coating: Pretreated hollow glass microspheres were placed in the heating zone of a tube furnace. High-purity argon gas was introduced to purge the air from the tube until the air vacuum reached 8 Pa. The temperature was then raised to 320 °C. Trimethylindium and tetramethyltin were used as metal precursors and carried to the reaction zone via a bubbling method, where deposition was carried out for 30 min. After deposition, high-purity oxygen was introduced for 10 min to convert the amorphous ITO into a transparent conductive oxide, resulting in ITO-coated hollow glass microspheres. The flow rate of high-purity argon was 50 sccm, and the molar ratio of trimethylindium to tetramethyltin was 1:9. The nitrogen carrier gas flow rate for the bubbling method was 50 sccm, and the high-purity oxygen flow rate was 20 sccm.
[0041] S3: Coating with calcium alginate layer: 2.5 g of ITO-coated hollow glass microspheres were dispersed in 250 mL of deionized water and ultrasonically dispersed for 30 min to obtain the dispersed phase; 10 g of sodium alginate solution was dispersed in 500 mL of deionized water and magnetically stirred for 2 h, and the insoluble matter was removed by filtration to obtain the continuous phase; laminar coating was performed using a Y-type microfluidic chip, and the dispersed phase and the continuous phase were respectively introduced into the two inlet channels of the Y-type microfluidic chip, with a flow rate ratio of 1:2 between the dispersed phase and the continuous phase. The coated hollow glass microspheres flowed into the collection tank from the chip outlet and were allowed to stand for 5 min to precipitate the unadsorbed sodium alginate solution. The hollow glass microsphere suspension in the collection tank was poured into 250 mL of 0.5 mol / L calcium chloride solution and crosslinked under magnetic stirring for 5 min. The mixture was washed three times with deionized water to remove the residual crosslinking solution, and then dried in a vacuum oven at 40 ℃ for 12 h to obtain ITO and calcium alginate double-layer coated hollow glass microspheres. The degree of cross-linking of the calcium alginate layer is 81%.
[0042] Example 6 The fabrication method of the flexible multi-parameter sensor in Example 6 includes the following steps: Weigh the silicone rubber (Sylgard 184) matrix and curing agent at a mass ratio of 10:1, then add 8% hexane by volume. Stir at 500 rpm for 5 min using a magnetic stirrer to obtain mixture one. Place mixture one in a vacuum degassing machine and evacuate to -80 kPa for 10 minutes to remove air bubbles. Weigh 25% of the total mass of the flexible multi-parameter sensor, consisting of ITO and calcium alginate double-layer coated hollow glass microspheres, and slowly add them to mixture one in three portions. Stir for 10 min to obtain mixture two. Pour mixture two into a PDMS mold, filling it to a thickness of 2 mm. Gently tap the edges of the mold to remove residual air bubbles. Place the mold in a constant temperature oven and cure at 70 ℃ for 2 h. Allow it to cool naturally to room temperature and demold to obtain a flexible multi-parameter sensor based on ITO and calcium alginate double-layer coated hollow glass microspheres. Example 6 uses the ITO and calcium alginate double-layer coated hollow glass microspheres from Example 1.
[0043] Examples 7-10 The fabrication methods of the flexible multi-parameter sensors in Examples 7-10 are largely the same as those in Example 6. The difference between the fabrication methods of the flexible multi-parameter sensors in Examples 7-10 and Example 6 is that Example 7 uses ITO and calcium alginate double-layer coated hollow glass microspheres from Example 2; Example 8 uses ITO and calcium alginate double-layer coated hollow glass microspheres from Example 3; Example 9 uses ITO and calcium alginate double-layer coated hollow glass microspheres from Example 4; and Example 10 uses ITO and calcium alginate double-layer coated hollow glass microspheres from Example 5.
[0044] Comparative Example 1 The preparation method of ITO-coated hollow glass microspheres in Comparative Example 1 includes the following steps: S1: The pretreatment steps for hollow glass microspheres are the same as in Example 1.
[0045] S2: ITO Coating: Pretreated hollow glass microspheres were placed in the heating zone of a tube furnace. High-purity argon gas was introduced to purge the air from the tube until the air vacuum reached 8 Pa. The temperature was then raised to 320 °C. Trimethylindium and tetramethyltin were used as metal precursors and carried to the reaction zone via a bubbling method, where deposition was carried out for 30 min. After deposition, high-purity oxygen was introduced for 10 min to convert the amorphous ITO into a transparent conductive oxide, resulting in ITO-coated hollow glass microspheres. The flow rate of high-purity argon was 50 sccm, and the molar ratio of trimethylindium to tetramethyltin was 1:9. The nitrogen carrier gas flow rate for the bubbling method was 50 sccm, and the high-purity oxygen flow rate was 20 sccm.
[0046] Comparative Example 2 The preparation method of calcium alginate-coated hollow glass microspheres in Comparative Example 2 includes the following steps: S1: The pretreatment steps for hollow glass microspheres are the same as in Example 1.
[0047] S2: Coating with calcium alginate layer: 2.5 g of pretreated hollow glass microspheres were dispersed in 250 mL of deionized water and ultrasonically dispersed for 30 min to obtain the dispersed phase; 10 g of sodium alginate solution was dispersed in 500 mL of deionized water and magnetically stirred for 2 h, and the insoluble matter was removed by filtration to obtain the continuous phase; laminar coating was performed using a Y-type microfluidic chip, and the dispersed phase and the continuous phase were respectively introduced into the two inlet channels of the Y-type microfluidic chip, with a flow rate ratio of 1:2 between the dispersed phase and the continuous phase. The coated hollow glass microspheres flowed into the collection tank from the chip outlet and were allowed to stand for 5 min to precipitate the unadsorbed sodium alginate solution. The hollow glass microsphere suspension in the collection tank was poured into 250 mL of 0.1 mol / L calcium chloride solution and crosslinked under magnetic stirring for 5 min. The mixture was washed three times with deionized water to remove the residual crosslinking solution, and then dried in a vacuum oven at 40 ℃ for 12 h to obtain calcium alginate coated hollow glass microspheres.
[0048] Comparative Examples 3-4 The fabrication methods of the flexible multi-parameter sensors in Comparative Examples 3 and 4 are largely the same as those in Example 6. The difference between Comparative Examples 3 and 4 and Example 6 is that Comparative Example 3 uses ITO-coated hollow glass microspheres from Comparative Example 1, while Comparative Example 4 uses calcium alginate-coated hollow glass microspheres from Comparative Example 2.
[0049] The performance of the flexible multi-parameter sensors in Examples 6-10 and Comparative Examples 3-4 is shown in Table 1.
[0050] Table 1 Performance of the flexible multi-parameter sensors in Examples 6-10 and Comparative Examples 3-4
[0051] ITO coating improves the surface roughness of hollow glass microspheres and increases the contact area between calcium alginate and hollow glass microspheres, thereby enhancing interfacial adhesion. The flexible network of calcium alginate disperses stress and absorbs energy through plastic deformation, preventing crack propagation to the ITO layer and silicone rubber matrix. The ITO layer provides initial strength, while calcium alginate buffers stress; together, they synergistically delay crack initiation and propagation, significantly improving the flexural durability and tensile strength of the flexible multi-parameter sensor of this invention. Therefore, the flexural durability and tensile strength of the flexible multi-parameter sensors in Examples 6-10 are significantly higher than those in Comparative Examples 3-4. Appropriately increasing the crosslinking degree of the calcium alginate layer can provide better rigidity and strength, contributing to improved flexural durability and tensile strength of the flexible multi-parameter sensor. Therefore, the mechanical properties of the flexible multi-parameter sensor in Example 6 are superior to those in Example 9. However, excessively high crosslinking can also lead to material brittleness, reducing its impact resistance and toughness; therefore, the mechanical properties of Example 10 show a loss. Example 7 used a short deposition time of 15 min to obtain an ultrathin ITO layer. Although the outer layer of calcium alginate can improve the overall tensile strength and flexural durability of the film, the ultrathin ITO film has a large number of grain boundary defects and a low carrier concentration. At the same time, the calcium alginate layer provides deformation buffering damping, resulting in poor electrical sensing performance. The ultrathin ITO has poor continuity of conductive pathways, and the reconstruction of conductive pathways after pressure takes longer, resulting in a prolonged pressure response time. During cyclic pressurization, the film is prone to irreversible microcracks, and the resistance change rate is high after 10,000 cycles. The insufficient thickness of the ITO layer leads to a small number of effective carriers, weakening the temperature-dependent control effect on resistance. The temperature coefficient of resistance is only -80 ppm / ℃, resulting in low temperature sensitivity.
[0052] In terms of pressure sensing performance, the flexible multi-parameter sensor of Example 8 achieves a sensitivity of 0.15 kPa. -1 The response time is only 100 ms, after 10 4 After one cycle, the rate of change in resistance was only 2.5%. This is because the conductive network of the thick ITO layer is denser, and the resistance change caused by deformation under pressure is more significant, accelerating charge conduction and dispersing stress. The sensitivity of the monolayer ITO in Comparative Example 3 decreased to 0.09 kPa. -1The response time increased to 150 ms, and the cycle stability was 6.7%, resulting in a performance decrease. This is because the ITO layer lacks synergy with the calcium alginate layer. The three-dimensional network structure of the calcium alginate layer can form a mechanical interlock with the ITO layer. When the hollow glass microspheres are under pressure, the elastic deformation of the calcium alginate layer can be effectively transferred to the ITO layer, avoiding signal attenuation caused by interface slippage. For the low cross-linking degree calcium alginate layer, the porosity change is more significant under pressure, leading to an increase in the rate of change of resistance. Therefore, the sensitivity of the flexible multi-parameter sensor in Example 9 is higher than that in Example 10.
[0053] Regarding temperature sensing performance, an excessively thin ITO layer reduces carrier concentration and weakens the temperature coefficient of resistance (TCR) effect. Therefore, Example 8 exhibits the highest absolute TCR value of -150 ppm / ℃. The ITO and calcium alginate layers exhibit synergy. The calcium alginate layer, acting as an auxiliary structure for temperature sensing, allows its thermal expansion effect to be transferred to the ITO layer through interfacial stress, thus affecting the TCR. Consequently, Comparative Example 3 shows a lower absolute TCR value (95 ppm / ℃). Low-crosslinked calcium alginate layers have low elastic modulus and large deformation during thermal expansion, while high-crosslinked calcium alginate layers exhibit enhanced rigidity and smaller deformation during thermal expansion. Therefore, Example 9 shows a higher absolute TCR value than Example 6, and Example 6 shows a higher absolute TCR value than Example 10, further validating the crucial role of the bilayer structure in optimizing thermosensitive properties.
[0054] Regarding humidity sensing performance, an excessively thin ITO layer leads to increased surface defects, resulting in significant humidity interference, increased hysteresis, and reduced sensor stability. A thick, continuous, and dense ITO layer effectively blocks water molecule penetration and reduces the impact of fluctuations in the cross-linking degree of the calcium alginate layer on humidity sensitivity. The calcium alginate layer detects humidity through hygroscopic expansion. At low cross-linking degrees, it has high porosity and strong hygroscopicity, making it prone to dimensional expansion in humid environments and exhibiting poor stability. Excessive cross-linking significantly inhibits humidity-induced dimensional changes, reducing humidity sensitivity. Example 8 achieves 0.10% RH by combining a thick ITO layer with a medium-cross-linked calcium alginate layer. -1 The highest sensitivity indicates that moderate cross-linking degree and double-layer mechanical interlocking effect have a significant effect on reducing hysteresis and extending service life. However, single-layer calcium alginate has insufficient moisture absorption and slow deformation recovery, highlighting the necessity of the synergistic design of calcium alginate layer and ITO layer.
[0055] The comprehensive performance comparison and optimization direction show that the flexible multi-parameter sensor of Example 8 performs best in pressure, temperature and humidity detection. The synergistic effect of its thick ITO layer and highly cross-linked calcium alginate layer achieves high sensitivity and high stability detection of pressure, temperature and humidity. The limitations of the single-layer structure in terms of sensitivity, stability and anti-interference ability further verify the necessity of the double-layer design.
Claims
1. Hollow glass microspheres double-coated with ITO and calcium alginate, characterized in that, An ITO layer and a calcium alginate layer are coated on the surface of hollow glass microspheres. The ITO layer is located between the hollow glass microspheres and the calcium alginate layer. The thickness of the ITO layer is 60-110 nm, and the degree of crosslinking of the calcium alginate layer is 30-85%.
2. The preparation method of hollow glass microspheres double-layered with ITO and calcium alginate as described in claim 1, characterized in that, include: S1: ITO layer was coated on the surface of hollow glass microspheres by chemical vapor deposition, followed by heat treatment to obtain ITO coated hollow glass microspheres; S2: Hollow glass microspheres with ITO and calcium alginate double-layer coating were obtained by coating the surface of ITO-coated hollow glass microspheres with a calcium alginate layer using a microfluidic method.
3. The method for preparing ITO and calcium alginate double-layer coated hollow glass microspheres according to claim 2, characterized in that, The chemical vapor deposition method described in S1 has a temperature of 300–350 °C, an air vacuum of 0.1–10 Pa, a metal precursor of trimethylindium and tetramethyltin, a carrier gas of argon, and a deposition time of 15–45 min.
4. The method for preparing ITO and calcium alginate double-layer coated hollow glass microspheres according to claim 3, characterized in that, The molar ratio of trimethylindium to tetramethyltin is 1:(7-11), and the gas flow rate of argon is 40-60 sccm.
5. The method for preparing hollow glass microspheres double-layered with ITO and calcium alginate according to claim 2, characterized in that, The heat treatment described in S1 is performed at a temperature of 300–350 °C for 8–12 min, with oxygen introduced during the heat treatment at a flow rate of 15–25 sccm.
6. The method for preparing ITO and calcium alginate double-layer coated hollow glass microspheres according to claim 2, characterized in that, The steps of the microfluidic method are as follows: dissolve ITO-coated hollow glass microspheres in water to obtain a dispersed phase, dissolve sodium alginate in water to obtain a continuous phase, pass the dispersed phase and the continuous phase into a Y-type microfluidic chip respectively, collect the hollow glass microspheres coated with sodium alginate, and then mix with calcium chloride solution, crosslink and dry.
7. The method for preparing ITO and calcium alginate double-layer coated hollow glass microspheres according to claim 6, characterized in that, The mass ratio of ITO-coated hollow glass microspheres to sodium alginate is (2-3):10; the flow rate ratio of the dispersed phase to the continuous phase is 1:(1.5-2.5); the concentration of the calcium chloride solution is 0.05-0.5 mol / L; and the crosslinking time is 3-7 min.
8. The method for preparing ITO and calcium alginate double-layer coated hollow glass microspheres according to claim 2, characterized in that, The hollow glass microspheres coated with the ITO layer need to undergo pretreatment. The pretreatment steps include: ultrasonically cleaning the hollow glass microspheres sequentially with acetone, ethanol and water, drying them to obtain dried hollow glass microspheres, and then subjecting the dried hollow glass microspheres to plasma treatment to obtain pretreated hollow glass microspheres. The plasma treatment power is 80-120 W, the time is 3-7 min, and the atmosphere is oxygen.
9. A flexible multi-parameter sensor, characterized in that, The sensor includes a flexible substrate and hollow glass microspheres double-coated with ITO and calcium alginate as described in claim 1, wherein the ITO and calcium alginate double-coated hollow glass microspheres account for 20-30% of the total mass of the flexible multi-parameter sensor, and the flexible substrate is Sylgard 184 type silicone rubber.
10. A method for fabricating a flexible multi-parameter sensor, characterized in that, include: The flexible substrate and solvent are mixed to obtain mixture one. After removing air bubbles from mixture one, ITO and calcium alginate double-layer coated hollow glass microspheres as described in claim 1 are added and stirred evenly to obtain mixture two. Mixture two is poured into a mold and cured to obtain the final product. The flexible substrate is Sylgard 184 type silicone rubber, the solvent is n-hexane, the solvent is 5-10% of the volume of the flexible substrate, and the ITO and calcium alginate double-layer coated hollow glass microspheres are 20-30% of the total mass of the flexible multi-parameter sensor.