A liquid-type flexible strain sensor for a fluorescent electronic skin based on liquid gallium

Abstract

The present invention relates to the field of flexible strain sensing, and discloses a liquid-type flexible strain sensor for fluorescent electronic skin based on liquid gallium. First, reduced graphene oxide is prepared. In order to improve the mechanical, electrical, and thermal properties of chitosan fibers, chitosan is blended and modified with graphene, and RGO / chitosan conductive fibers are prepared by spinning. Considering that the conductivity of the graphene chitosan conductive fibers is not ideal enough, silver nanowires are then dip-coated to improve the conductivity and increase the sensitivity of the sensor. Then, the RGO / chitosan / Ag nanowire conductive fibers are encapsulated with a fluorescent polymer to prepare a liquid-type flexible strain sensor for fluorescent electronic skin.

Description

Technical Field

[0001] The present invention relates to the field of flexible strain sensing, and particularly to a liquid-type flexible strain sensor for a fluorescent e-skin based on liquid gallium. Background Art

[0002] With the development of society and the progress of technology, wearable devices have received more and more extensive attention from people and are gradually changing people's lives. Wearable devices mainly refer to electronic devices that can be directly worn on the human body and are electronic products that can be integrated into clothes or similar clothing. Next-generation wearable electronic products require the system to be directly worn on the human body with highly extensible, soft and bendable skin. However, most of the wearable products currently on the market are mainly for wearing, mainly including smart watches, bracelets, glasses, etc., while there are very few products that can be directly worn. In order to obtain smart textiles, one method is to attach functional materials to a flat fabric in a stacked manner to achieve its functions. However, this method of stacking functional materials on the fabric surface greatly reduces the inherent properties of the fabric such as softness, breathability, and mechanical properties. As a component of the fabric, fibers have been manufactured and used by humans for thousands of years due to their softness, deformability, breathability, durability, and washability. Therefore, the research and preparation of functionalized flexible fibers are of great significance to the development of wearable devices.

[0003] Chitosan is the second most abundant natural polymer on earth. Its chemical name is (1,4)-2-amino-2-deoxyglucose. For decades, due to its good biocompatibility, biodegradability, hemostasis, antibacterial and other multifunctional properties, it has been widely studied in drug release, molecular separation, artificial skin, sensors, bone substitutes, etc. In addition, in many applications such as textiles, it can be easily made into fibers, films, hollow fibers and membranes. Fibers themselves have the characteristics of light weight, flexibility and easy weaving, and flexible fibrous devices can be constructed to achieve wearable applications. Therefore, fibrous flexible devices have been widely studied. Main energy devices, such as fibrous solar cells, supercapacitors, lithium-ion batteries, etc. However, the ultimate purpose of these energy devices is to provide energy for the corresponding wearable electronic devices to make them work properly. In addition to the strategy of constructing fibrous flexible devices and weaving them into clothes to achieve wearability, e-skin can be directly attached to the human skin because of its advantages of high flexibility and lightness, thus realizing the wearable application of electronic devices. Summary of the Invention

[0004] To solve the above technical problems, the present invention provides a liquid-type flexible strain sensor for a fluorescent electronic skin based on liquid gallium. First, reduced graphene oxide is prepared in the present invention. To improve the mechanical, electrical, and thermal properties of chitosan fibers, chitosan and graphene are blended and modified, and RGO / chitosan conductive fibers are prepared by spinning. Considering that the conductivity of the graphene chitosan conductive fibers is not ideal enough, silver nanowires are then dip-coated to improve the conductivity and increase the sensitivity of the sensor. Then, the RGO / chitosan / Ag nanowire conductive fibers are encapsulated with a fluorescent polymer to prepare a liquid-type flexible strain sensor for a fluorescent electronic skin.

[0005] The specific technical solution of the present invention is: a liquid-type flexible strain sensor for a fluorescent electronic skin based on liquid gallium, and the preparation method includes the following steps:

[0006] Step 1: Preparation of graphene oxide (GO): Graphite nanosheets are added to chromic acid cleaning solution for ultrasonic dispersion; then stirred, poured into water, filtered by suction, washed, baked, and cooled to room temperature.

[0007] GO has rich carboxyl active sites on its surface and at the same time increases the dispersibility of the solution.

[0008] Step 2: Preparation of reduced graphene oxide (RGO): The suspension of the obtained graphene oxide and the homogeneous mixture of HI solution are reacted, centrifuged and washed to obtain a reduced graphene oxide suspension.

[0009] Step 3: Preparation of RGO / chitosan composite slurry: The reduced graphene oxide suspension is dispersed in a phosphate buffer solution, Triton X-100 is added as a surfactant, ultrasonic treatment is carried out, glacial acetic acid solution is added, and stirred to form a uniform RGO acetic acid solution; chitosan is added to the RGO acetic acid solution and stirred until completely dissolved; the obtained RGO / chitosan solution is centrifuged, the supernatant is poured out to obtain RGO / chitosan slurry; the RGO / chitosan slurry is transferred to a spinning container for degassing treatment.

[0010] Chitosan has strong intra- and intermolecular hydrogen bonds, poor solubility, and a very high viscosity of the spinning dope after dissolution, which limits the concentration of the spinning dope, resulting in too low fiber strength to meet wide applications. Chitosan molecules contain a large number of amino and hydroxyl groups, so it has active chemical properties, and other functional groups can be introduced to increase its functionality. To improve the mechanical, electrical, and thermal properties of chitosan fibers, chitosan and graphene are blended and modified.

[0011] Step 4: Preparation of RGO / chitosan conductive fibers by wet-dry spinning: Using the degassed RGO / chitosan syrup as the spinning solution for spinning. The spinning solution is extruded through the spinneret, enters the coagulation bath through the air, and the coagulation bath is a mixed solution of sodium hydroxide solution and ethanol; it is cured in the coagulation bath, washed with water, stretched, and dried to obtain RGO / chitosan conductive fibers.

[0012] Step 5: Preparation of RGO / chitosan / Ag nanowire conductive fiber sensor: Immerse the obtained RGO / chitosan conductive fibers into the silver nanowire solution, extract and dry them, immerse again, and then take them out and dry them. Repeat the above steps multiple times and set aside.

[0013] The conductive properties of the fibers obtained with different dipping times are different. The conductivity increases with the increase of the dipping times. Considering that the conductivity of graphene chitosan conductive fibers is not as good as that of silver nanowires, silver nanowires are dipped to improve the conductivity and increase the sensitivity of the sensor.

[0014] Step 6: Preparation of fluorescent polymer composites: First, stir and dissolve AIEgens in toluene, add tetraethyl orthosilicate to the obtained AIEgens solution and stir; then evacuate the obtained mixture until all the solvents are volatilized; add sulfur for cross-linking, mix, degas the mixture under vacuum, and perform pre-curing.

[0015] Step 7: Encapsulation of RGO / chitosan / Ag nanowire conductive fibers with fluorescent polymer: Straighten the RGO / chitosan / Ag nanowire conductive fibers and fix them at both ends of the paper rack with copper foil conductive tape. Wrap the fibers with a paper rack, pour the fluorescent polymer into the paper rack, and after curing, realize the encapsulation of the middle section of the fibers, without encapsulating both ends.

[0016] In the present invention, a layer of fluorescent polymer is coated on the fiber surface for encapsulation. On the one hand, it can protect the silver nanowires and the sensor. On the other hand, considering that the existing functional devices require rich and colorful appearances to meet people's diverse aesthetic needs and advanced optical application requirements.

[0017] Step 8: Preparation of liquid channel mold: Mix tetraethyl orthosilicate and platinum catalyst, stir evenly, degas under vacuum and pour it into the sensor mold, let it stand and cure to obtain a cured polymer; suck the liquid metal Ga with a syringe and inject it into the liquid metal mold, press it with a glass slide, and cool the liquid metal to solid state; obtain a cuboid gallium metal, take it out and use it as the liquid channel mold.

[0018] In the present invention, a cooling spray is sprayed on the surface of the glass slide to cool the liquid metal. When the temperature reaches 0 °C, the liquid metal becomes solid.

[0019] Step 9: Assembly of the sensor: Take both ends of the unencapsulated fiber obtained in Step 7 as electrodes and place them on the polymer cured in Step 8 respectively. Then place the liquid channel mold on the cured polymer and press both ends of the fiber. Mix tetraethyl orthosilicate and platinum catalyst evenly by stirring, degas under vacuum and then pour them into the sensor mold to wrap the electrodes and the liquid channel mold. After standing and curing, a liquid-type flexible strain sensor for skin is prepared.

[0020] Preferably, Step 1 specifically includes: adding 100 - 120 mg of graphite nanosheets into 560 - 600 ml of chromic acid cleaning solution and ultrasonically dispersing for 30 - 40 min; then mechanically stirring at 35 - 40 °C for 10 - 20 min, pouring into 1 - 2 L of deionized water, filtering by suction, washing with water 3 - 5 times and washing with ethanol 2 - 3 times; baking at 110 - 120 °C for 3 - 3.5 h, and storing for use after cooling to room temperature.

[0021] Preferably, Step 2 specifically includes: reacting a homogeneous mixture of the obtained graphene oxide suspension and 40 - 50 wt% HI solution at a volume ratio of 8 - 12:1 at 85 - 90 °C for 2 - 2.5 h to obtain a reduced graphene oxide suspension; centrifuging and washing the reduced graphene oxide suspension at 8000 - 9000 r / min for 3 - 5 times, and storing for use.

[0022] Preferably, Step 3 specifically includes: dispersing 3 - 4 ml of the reduced graphene oxide suspension in 8 - 12 ml of 0.1 M phosphate buffer solution, adding 1 - 2 ml of 1 wt% Triton X - 100 as a surfactant, ultrasonically treating with an ultrasonic cell disruptor for 30 - 35 min, then adding 1 - 2 ml of 2 - 3% glacial acetic acid solution and stirring for 10 - 15 min to form a uniform RGO acetic acid solution; adding 1 - 2 g of chitosan into the RGO acetic acid solution and stirring in a constant temperature water bath at 40 - 50 °C for 50 - 60 min until completely dissolved; finally, centrifuging the obtained RGO / chitosan solution at 13000 - 17000 r / min, pouring out the supernatant to obtain an RGO / chitosan syrup; transferring the RGO / chitosan syrup to a spinning container with a volume of 10 ml, and then placing the spinning container in a vacuum box at 45 - 55 °C for defoaming overnight.

[0023] Preferably, Step 4 specifically includes: using the defoamed RGO / chitosan syrup as a spinning solution for spinning, with a spinning speed of 0.2 - 0.4 m / min -1 , the spinning solution is extruded from the spinneret, enters the coagulation bath through the air, and the coagulation bath is a mixed solution of 3 - 7 wt% sodium hydroxide solution and 93 - 97 wt% ethanol with a volume ratio of 0.8 - 1.2:1; curing in the coagulation bath for 30 - 35 min, washing with water 2 - 3 times, stretching, vr 1= 3.6 cm / s, vr 2 = 3.8 cm / s, and the RGO / chitosan conductive fibers were obtained by drying at room temperature.

[0024] Preferably, step 5 specifically includes: immersing the obtained RGO / chitosan conductive fibers into a silver nanowire solution of 8 - 12 mg / ml, then extracting and drying at 40 - 50 °C, immersing again, taking out and drying, repeating the above steps 2 - 3 times and then setting aside. -1

[0025] Preferably, step 6 specifically includes: first, stirring and dissolving 2 - 3 g of AIEgens in toluene, adding 9 - 10 g of tetraethyl orthosilicate to the obtained AIEgens solution and stirring for 10 - 15 min; then subjecting the obtained mixture to vacuum treatment at 60 - 70 °C until all the solvent evaporates; adding 1 - 1.2 g of sulfur for crosslinking, mixing for 2 - 3 min, placing the mixture in a vacuum box at 37 - 40 °C for vacuum degassing, and pre-curing at 50 - 60 °C for 13 - 15 min.

[0026] Preferably, step 7 specifically includes: straightening the RGO / chitosan / Ag nanowire conductive fibers and fixing them at both ends of the paper rack with copper foil conductive tape, wrapping the fibers with a paper rack, pouring the fluorescent polymer into the paper rack, and curing at 90 - 100 °C for 10 - 12 h to achieve the encapsulation of the middle section of the fibers, without encapsulating the two ends.

[0027] Preferably, step 8 specifically includes: mixing 20 - 25 ml of tetraethyl orthosilicate and 20 - 25 ml of platinum catalyst, stirring for 3 - 5 min, vacuum degassing at 37 - 40 °C for 10 - 15 min and then pouring into the sensor mold, standing at room temperature for 1 - 15 h; sucking 2 - 3 g of liquid metal Ga with a syringe and injecting it into the liquid metal mold, pressing with a glass slide, spraying a cooling spray on the surface of the glass slide to cool the liquid metal, when the temperature reaches 0 °C, the liquid metal becomes solid, obtaining a cuboid gallium metal with a length of 40 - 50 mm, a width of 5 - 7 mm, and a thickness of 0.8 - 1.2 mm, taking it out and using it as the liquid channel mold.

[0028] Preferably, step 9 specifically includes: using the non-encapsulated two ends of the fibers obtained in step 7 as electrodes and placing them on the polymer cured in step 8 respectively, then placing the liquid channel mold on the cured polymer and pressing the two ends of the fibers; mixing 20 - 25 ml of tetraethyl orthosilicate and 20 - 25 ml of platinum catalyst and stirring evenly, vacuum degassing at 37 - 40 °C for 10 - 15 min and then pouring into the sensor mold to wrap the electrodes and the liquid channel mold, standing at room temperature for curing for 3 - 4 h to obtain a liquid-type flexible strain sensor for skin; the overall size of the sensor is 60 - 70 mm in length, 25 - 35 mm in width, and 3 - 5 mm in thickness

[0029] Compared with the prior art, the present invention has the following technical effects:

[0030] (1) The surface of GO in the present invention is rich in carboxyl active sites, and at the same time, the dispersibility of the solution is increased.

[0031] (2) Chitosan has strong intra- and intermolecular hydrogen bonds, poor solubility, and a very high viscosity of the spinning dope after dissolution, which limits the concentration of the spinning dope, resulting in too low fiber strength to meet extensive applications. Chitosan molecules contain a large number of amino and hydroxyl groups, so it has active chemical properties, and thus other functional groups can be introduced to increase its functionality. In order to improve the mechanical, electrical, and thermal properties of chitosan fibers, chitosan is blended and modified with graphene.

[0032] (3) The fiber conductivity obtained with different dipping times is different, and the conductivity increases with the increase of the dipping times. Considering that the conductivity of the graphene-chitosan conductive fiber is not as good as that of silver nanowires, silver nanowires are dipped to improve the conductivity and increase the sensitivity of the sensor.

[0033] (4) A layer of fluorescent polymer is coated on the surface of the fiber of the present invention for encapsulation. On the one hand, it can protect the silver nanowires and the sensor. On the other hand, considering that the existing functional devices require a rich and colorful appearance to meet people's diverse aesthetic needs and advanced optical application requirements. Detailed implementation manners

[0034] The present invention will be further described below in conjunction with embodiments.

[0035] Embodiment 1

[0036] Step 1: Preparation of graphene oxide (GO): Add 100 mg of graphite nanosheets to 560 ml of chromic acid cleaning solution and ultrasonically disperse for 30 min; then mechanically stir at 35 °C for 10 min, pour into 1 liter of deionized water, filter by suction, wash with water 3 times, and wash with ethanol 2 times; bake at 110 °C for 3 hours, and reserve after cooling to room temperature;

[0037] Step 2: Preparation of reduced graphene oxide (RGO): React the GO suspension and the uniform mixture of HI (40 wt%) (volume ratio: GO suspension: HI = 10:1) in an oven at 85 °C for 2 h; centrifuge (8000 r / min) and wash the RGO suspension 3 times, and reserve;

[0038] Step 3: Preparation of RGO / chitosan composite slurry: Disperse 3 ml of RGO in 10 ml of 0.1 M phosphate buffer solution (PBS, pH 7.4), add 1 - 2 ml of Triton X-100 (1 wt%) as a surfactant, and ultrasonically treat it with an ultrasonic cell disruptor for 30 min. Then add 1 ml of 2% glacial acetic acid solution and stir for 10 min to form a uniform RGO acetic acid solution; add 1 g of chitosan to the RGO acetic acid solution and stir in a 40°C constant temperature water bath for 50 min until completely dissolved; finally, centrifuge the RGO / chitosan solution (15000 r / min), pour out the supernatant to obtain the RGO / chitosan slurry; transfer the RGO / chitosan slurry to a spinning container with a volume of 10 ml (medical syringe), and then place the spinning container in a 45°C vacuum box for degassing overnight;

[0039] Step 4: Preparation of RGO / chitosan conductive fibers by wet-dry spinning: Fix the spinning container on a peristaltic pump, set the spinning speed to (0.3 m min -1 ), the spinning solution is extruded from the spinneret, enters the coagulation bath through the air, and the composition of the coagulation bath is 5% sodium hydroxide solution and 95% ethanol (volume ratio 1:1); cure in the coagulation bath for 30 min, wash with water twice, stretch (vr 1 = 3.6 cm / s, vr 2 = 3.8 cm / s), and dry at room temperature to obtain RGO / chitosan conductive fibers;

[0040] Step 5: Preparation of RGO / chitosan / Ag nanowire conductive fiber sensor: Immerse the prepared RGO / chitosan conductive fiber in the silver nanowire solution (10 mg ml -1 ), then slowly take it out and quickly dry it in a 40°C oven, immerse it again, then take it out and dry it, repeat the above steps 2 times for standby;

[0041] Step 6: Preparation of fluorescent polymer composite: First, dissolve 2 g of AIEgens by stirring in toluene, add 9 g of the prepolymer of Dow Corning 184 (Part A, the main component is tetraethyl orthosilicate) to the AIEgens solution and stir for 10 min; then place the mixture in a 60°C vacuum box for vacuum treatment until all the solvents are completely volatilized; add 1 g of curing agent (Part B, the main component is sulfur) for crosslinking, manually mix for 2 min, place the mixture in a 37°C vacuum box for degassing overnight, and place the mixture in a 50°C forced air drying oven for pre-curing for 13 min;

[0042] Step 7: Encapsulating the RGO / chitosan / Ag nanowire conductive fiber with fluorescent polymer: Straighten the RGO / chitosan / Ag nanowire conductive fiber and fix it to both ends of the paper holder with copper foil conductive tape. Wrap the fiber with a paper holder, pour a thin layer of fluorescent polymer resin into the paper holder, cure it at 90 °C for 10 h, and do not encapsulate both ends.

[0043] Step 8: Preparation of the liquid channel mold: Mix 20 ml of the prepolymer of Ecoflex0050 (the main component is tetraethyl orthosilicate) and 20 ml of the curing agent (platinum catalyst) in an equal volume ratio, stir evenly with a glass rod for 3 min, degas under vacuum at 37 °C for 10 min, pour it into the sensor mold, and wait for 1 h at room temperature; suck 2 g of liquid metal Ga with a syringe, inject it into the liquid metal mold, press it tightly with a glass slide, spray a cooling spray on the surface of the glass slide to cool the liquid metal, and when the temperature reaches 0 °C, the liquid metal becomes solid; Take out the low-temperature formed cuboid gallium metal (length: 45 mm, width: 6 mm, thickness: 1 mm), and use it as the liquid channel mold.

[0044] Step 9: Assembly of the fluorescent e-skin: Take the unencapsulated ends of the fluorescent conductive fiber in Step 7 as electrodes and place them on the Ecoflex0050 cured for 1 h respectively, then place the liquid channel mold on the Ecoflex0050 and press the fluorescent conductive fibers on both sides; Mix 20 ml of the prepolymer of Ecoflex0050 and 20 ml of the curing agent in an equal volume ratio, stir evenly with a glass rod for 3 min, degas under vacuum at 37 °C for 10 min, pour it into the sensor mold to wrap the electrodes and the liquid channel mold, and wait at room temperature for 3 h. After Ecoflex0050 is completely cured, the liquid-type flexible strain sensor is prepared. The overall size of the sensor is 65 mm in length, 30 mm in width, and 4 mm in thickness.

[0045] Example 2

[0046] Step 1: Preparation of graphene oxide (GO): Add 110 mg of graphite nanosheets to 580 ml of chromic acid cleaning solution and ultrasonically disperse for 35 min; then mechanically stir at 37 °C for 15 min, pour it into 1 liter of deionized water, filter by suction, wash with water 4 times, and wash with ethanol 2 times; Bake at 115 °C for 3 h, and set aside after cooling to room temperature.

[0047] Step 2: Preparation of reduced graphene oxide (RGO): React the GO suspension and the uniform mixture of HI (45 wt%) (volume ratio: GO suspension: HI = 10:1) in an oven at 85 °C for 2 h; Centrifuge (8500 r / min) and wash the RGO suspension 4 times, and set aside.

[0048] Step 3: Preparation of RGO / chitosan composite slurry: Disperse 3 ml of RGO in 10 ml of 0.1 M phosphate buffer solution (PBS, pH 7.4), add 1 ml of Triton X-100 (1 wt%) as a surfactant, and ultrasonically treat it with an ultrasonic cell disruptor for 33 min. Then add 1.5 ml of 2% glacial acetic acid solution and stir for 12 min to form a uniform RGO acetic acid solution; add 1.5 g of chitosan to the RGO acetic acid solution and stir in a 45°C constant temperature water bath for 55 min until completely dissolved; finally, centrifuge the RGO / chitosan solution (15000 r / min), pour out the supernatant to obtain the RGO / chitosan slurry; transfer the RGO / chitosan slurry to a spinning container with a volume of 10 ml (medical syringe), and then place the spinning container in a vacuum box at 50°C for degassing overnight;

[0049] Step 4: Preparation of RGO / chitosan conductive fibers by wet-dry spinning: Fix the spinning container on a peristaltic pump and set the spinning speed to (0.3 m min -1 ), the spinning solution is extruded from the spinneret, enters the coagulation bath through the air, and the composition of the coagulation bath is 5% sodium hydroxide solution and 95% ethanol (volume ratio 1:1); cure in the coagulation bath for 30 min, wash twice with water, and stretch (vr 1 = 3.6 cm / s, vr 2 = 3.8 cm / s), and dry at room temperature to obtain RGO / chitosan conductive fibers;

[0050] Step 5: Preparation of RGO / chitosan / Ag nanowire conductive fiber sensor: Immerse the prepared RGO / chitosan conductive fiber in the silver nanowire solution (10 mg ml -1 ), then slowly take it out and quickly dry it in an oven at 45°C, immerse it again, then take it out and dry it, repeat the above steps 3 times for standby;

[0051] Step 6: Preparation of fluorescent polymer composite: First, stir and dissolve 2.5 g of AIEgens in toluene, add 10 g of the prepolymer of Dow Corning 184 (Part A, the main component is tetraethyl orthosilicate) to the AIEgens solution and stir for 13 min; then place the mixture in a vacuum box at 65°C for vacuum treatment until all the solvents are completely volatilized; add 1.2 g of curing agent (Part B, the main component is sulfur) for crosslinking, manually mix for 3 min, place the mixture in a vacuum box at 40°C for degassing overnight, and place the mixture in a forced-air drying oven at 55°C for pre-curing for 14 min;

[0052] Step 7: Encapsulating RGO / chitosan / Ag nanowire conductive fiber with fluorescent polymer: Straighten the RGO / chitosan / Ag nanowire conductive fiber and fix it at both ends of the paper holder with copper foil conductive tape. Wrap the fiber with a paper holder, pour a thin layer of fluorescent polymer resin into the paper holder, and cure it at 95 °C for 11 h without encapsulating the two ends.

[0053] Step 8: Preparation of liquid channel mold: Mix 23 ml of prepolymer of Ecoflex0050 (the main component is tetraethyl orthosilicate) and 23 ml of curing agent (platinum catalyst) in an equal volume ratio, stir evenly with a glass rod for 4 min, degas under vacuum at 38.5 °C for 13 min, pour it into the sensor mold, and wait for 7 h at room temperature; suck 2.5 g of liquid metal Ga with a syringe, inject it into the liquid metal mold, press it tightly with a glass slide, spray a cooling spray on the surface of the glass slide to cool the liquid metal, when the temperature reaches 0 °C, the liquid metal becomes solid; Take out the low-temperature formed cuboid gallium metal (length: 45 mm, width: 6 mm, thickness: 1 mm), and use it as the liquid channel mold.

[0054] Step 9: Assembly of fluorescent e-skin: Take the unencapsulated ends of the fluorescent conductive fiber in Step 7 as electrodes and place them on the Ecoflex0050 cured for 1 h respectively, then place the liquid channel mold on the Ecoflex0050 and press the fluorescent conductive fibers on both sides; Mix 23 ml of prepolymer of Ecoflex0050 and 23 ml of curing agent in an equal volume ratio, stir evenly with a glass rod for 4 min, degas under vacuum at 39 °C for 13 min, pour it into the sensor mold to wrap the electrodes and the liquid channel mold. After waiting at room temperature for 3.5 h, the Ecoflex0050 is completely cured, and at this time, the liquid-type flexible strain sensor is prepared. The overall size of the sensor is 65 mm in length, 30 mm in width, and 4 mm in thickness.

[0055] Example 3

[0056] Step 1: Preparation of graphene oxide (GO): Add 120 mg of graphite nanosheets to 600 ml of chromic acid cleaning solution and ultrasonically disperse for 40 min; then mechanically stir at 40 °C for 20 min, pour it into 2 liters of deionized water, filter by suction, wash with water 5 times, and wash with ethanol 3 times; Dry at 120 °C for 3.5 h and set aside after cooling to room temperature.

[0057] Step 2: Preparation of reduced graphene oxide (RGO): React the GO suspension and the uniform mixture of HI (50 wt%) (volume ratio: GO suspension: HI = 10:1) in an oven at 90 °C for 2.5 h; Centrifuge (9000 r / min) and wash the RGO suspension 5 times and set aside.

[0058] Step 3: Preparation of RGO / chitosan composite slurry: Disperse 4 ml of RGO in 10 ml of 0.1 M phosphate buffer solution (PBS, pH 7.4), add 2 ml of Triton X-100 (1 wt%) as a surfactant, and ultrasonically treat it with an ultrasonic cell disruptor for 35 min. Then add 2 ml of 3% glacial acetic acid solution and stir for 15 min to form a uniform RGO acetic acid solution; add 2 g of chitosan to the RGO acetic acid solution and stir in a 50 °C constant temperature water bath for 60 min until completely dissolved; finally, centrifuge the RGO / chitosan solution (15000 r / min), pour out the supernatant to obtain the RGO / chitosan slurry; transfer the RGO / chitosan slurry to a spinning container with a volume of 10 ml (medical syringe), and then place the spinning container in a vacuum box at 55 °C for degassing overnight;

[0059] Step 4: Preparation of RGO / chitosan conductive fibers by wet-dry spinning: Fix the spinning container on a peristaltic pump and set the spinning speed to (0.3 m min -1 ), the spinning solution is extruded from the spinneret, enters the coagulation bath through the air, and the composition of the coagulation bath is 5% sodium hydroxide solution and 95% ethanol (volume ratio 1:1); cure in the coagulation bath for 35 min, wash with water 3 times, stretch (vr 1 = 3.6 cm / s, vr 2 = 3.8 cm / s), and dry at room temperature to obtain RGO / chitosan conductive fibers;

[0060] Step 5: Preparation of RGO / chitosan / Ag nanowire conductive fiber sensor: Immerse the prepared RGO / chitosan conductive fiber in the silver nanowire solution (10 mg ml -1 ), then slowly take it out and quickly dry it in an oven at 50 °C, immerse it again, then take it out and dry it, repeat the above steps 3 times for standby;

[0061] Step 6: Preparation of fluorescent polymer composite: First, stir and dissolve 3 g of AIEgens in toluene, add 10 g of prepolymer of Dow Corning 184 (part A, the main component is tetraethyl orthosilicate) to the AIEgens solution and stir for 15 min; then place the mixture in a vacuum box at 70 °C for vacuum treatment until all the solvents are completely evaporated; add 1.2 g of curing agent (part B, the main component is sulfur) for crosslinking, manually mix for 3 min, place the mixture in a vacuum box at 40 °C for degassing overnight, and place the mixture in a forced-air drying oven at 60 °C for pre-curing for 15 min;

[0062] Step 7: Encapsulating RGO / chitosan / Ag nanowire conductive fiber with fluorescent polymer: Straighten the RGO / chitosan / Ag nanowire conductive fiber and fix it at both ends of the paper holder with copper foil conductive tape. Wrap the fiber with a paper holder, pour a thin layer of fluorescent polymer resin into the paper holder, and cure it at 100 °C for 12 h without encapsulating the two ends.

[0063] Step 8: Preparation of the liquid channel mold: Mix 25 ml of the prepolymer of Ecoflex0050 (the main component is tetraethyl orthosilicate) and 25 ml of the curing agent (platinum catalyst) in an equal volume ratio, stir evenly with a glass rod for 5 min, degas under vacuum at 40 °C for 15 min, and pour it into the sensor mold, and wait at room temperature for 15 h; suck 3 g of liquid metal Ga with a syringe and inject it into the liquid metal mold, press it tightly with a glass slide, and spray a cooling spray on the surface of the glass slide to cool the liquid metal. When the temperature reaches 0 °C, the liquid metal becomes solid; Take out the low-temperature formed cuboid gallium metal (length: 45 mm, width: 6 mm, thickness: 1 mm) and use it as the liquid channel mold.

[0064] Step 9: Assembly of the fluorescent e-skin: Use the two unencapsulated ends of the fluorescent conductive fiber in Step 7 as electrodes and place them on the Ecoflex0050 that has been solidified for 1.5 h, then place the liquid channel mold on the Ecoflex0050 and press down on the fluorescent conductive fibers on both sides; Mix 25 ml of the prepolymer of Ecoflex0050 and 25 ml of the curing agent in an equal volume ratio, stir evenly with a glass rod for 5 min, degas under vacuum at 40 °C for 15 min, and pour it into the sensor mold to wrap the electrodes and the liquid channel mold. After waiting at room temperature for 4 h, the Ecoflex0050 is completely cured, and at this time, the liquid-type flexible strain sensor is prepared. The overall size of the sensor is 65 mm in length, 30 mm in width, and 4 mm in thickness.

[0065] In the present invention, the raw materials and equipment used, unless otherwise specified, are all common raw materials and equipment in the art; the methods used in the present invention, unless otherwise specified, are all conventional methods in the art.

[0066] The above description is only a preferred embodiment of the present invention and does not impose any limitation on the present invention. Any simple modification, change, and equivalent transformation made to the above embodiments according to the technical essence of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A liquid-type flexible strain sensor for a fluorescent electronic skin based on liquid gallium, Characterized in that: The preparation method comprises the following steps: Step 1: Preparation of graphene oxide: Graphite nanosheets are added to chromic acid cleaning solution and ultrasonically dispersed; then stirred, poured into water, filtered by suction, washed, baked, and cooled to room temperature; Step 2: Preparation of reduced graphene oxide: A uniform mixture of the obtained graphene oxide suspension and HI solution is reacted, centrifuged and washed to obtain a reduced graphene oxide suspension; Step 3: Preparation of RGO / chitosan composite slurry: The reduced graphene oxide suspension is dispersed in a phosphate buffer solution, Triton X-100 is added as a surfactant, ultrasonically treated, acetic acid solution is added, and stirred to form a uniform RGO acetic acid solution; Chitosan is added to the RGO acetic acid solution and stirred until completely dissolved; The obtained RGO / chitosan solution is centrifuged, and the supernatant is poured out to obtain RGO / chitosan slurry; The RGO / chitosan slurry is transferred to a spinning container and degassed; Step 4: Preparation of RGO / chitosan conductive fibers by wet-dry spinning: Using the degassed RGO / chitosan slurry as a spinning solution for spinning, the spinning solution is extruded from the spinneret, enters the coagulation bath through the air, and the coagulation bath is a mixed solution of sodium hydroxide solution and ethanol; Cured in the coagulation bath, washed with water, stretched, and dried to obtain RGO / chitosan conductive fibers; Step 5: Preparation of RGO / chitosan / Ag nanowire conductive fiber sensor: The obtained RGO / chitosan conductive fibers are immersed in silver nanowire solution, drawn out and dried, immersed again, taken out and dried, and the above steps are repeated multiple times and then set aside; Step 6: Preparation of fluorescent polymer composite: First, AIEgens are stirred and dissolved in toluene, and tetraethyl orthosilicate is added to the obtained AIEgens solution and stirred; Then the obtained mixture is evacuated until all the solvent volatilizes; Sulfur is added for crosslinking, mixed, and the mixture is vacuum degassed and pre-cured; Step 7: Encapsulation of RGO / chitosan / Ag nanowire conductive fibers with fluorescent polymer: Straighten the RGO / chitosan / Ag nanowire conductive fibers and fix them at both ends of the paper frame with copper foil conductive tape, wrap the fibers with a paper frame, pour the fluorescent polymer into the paper frame, and after curing, the middle section of the fiber is encapsulated, and the two ends are not encapsulated; Step 8: Preparation of liquid channel mold: Tetraethyl orthosilicate and platinum catalyst are mixed, stirred evenly, vacuum degassed and then poured into the sensor mold, left to stand and cure to obtain a cured polymer; A syringe is used to suck in liquid metal Ga and inject it into the liquid metal mold, pressed tightly with a glass sheet, and the liquid metal is cooled to solid state; A cuboid gallium metal is obtained, taken out and used as the liquid channel mold; Step 9: Assembly of the sensor: Use the two ends of the non-encapsulated fiber obtained in Step 7 as electrodes and place them on the polymer cured in Step 8 respectively. Then place the liquid channel mold on the cured polymer and press the two ends of the fiber. Mix and stir tetraethyl orthosilicate and platinum catalyst evenly, degas under vacuum and pour it into the sensor mold to wrap the electrodes and the liquid channel mold. After standing and curing, a flexible strain sensor of liquid type for skin is obtained.

2. The flexible strain sensor according to claim 1, wherein: Step 1 specifically includes: adding 100 - 120 mg of graphite nanosheets into 560 - 600 ml of chromic acid cleaning solution, ultrasonically dispersing for 30 - 40 min; then mechanically stirring at 35 - 40 °C for 10 - 20 min, pouring into 1 - 2 L of deionized water, filtering by suction, washing with water 3 - 5 times and washing with ethanol 2 - 3 times; baking at 110 - 120 °C for 3 - 3.5 h, and storing at room temperature after cooling.

3. The flexible strain sensor according to claim 1, wherein: Step 2 specifically includes: reacting a homogeneous mixture of the obtained graphene oxide suspension and 40 - 50 wt% HI solution in a volume ratio of 8 - 12:1 at 85 - 90 °C for 2 - 2.5 h to obtain a reduced graphene oxide suspension; centrifuging and washing the reduced graphene oxide suspension at 8000 - 9000 r / min for 3 - 5 times for standby.

4. The flexible strain sensor according to claim 1, wherein: Step 3 specifically includes: dispersing 3 - 4 ml of the reduced graphene oxide suspension in 8 - 12 ml of 0.1 M phosphate buffer solution, adding 1 - 2 ml of 1 wt% Triton X - 100 as a surfactant, ultrasonically treating with an ultrasonic cell disruptor for 30 - 35 min, then adding 1 - 2 ml of 2 - 3% glacial acetic acid solution, and stirring for 10 - 15 min to form a uniform RGO acetic acid solution; adding 1 - 2 g of chitosan into the RGO acetic acid solution, stirring in a 40 - 50 °C constant temperature water bath for 50 - 60 min until completely dissolved; finally, centrifuging the obtained RGO / chitosan solution at 13000 - 17000 r / min, pouring out the supernatant to obtain RGO / chitosan syrup; transferring the RGO / chitosan syrup to a spinning container with a volume of 10 ml, and then placing the spinning container in a vacuum box at 45 - 55 °C for defoaming overnight.

5. The flexible strain sensor according to claim 1, wherein: Step 4 specifically includes: using the defoamed RGO / chitosan syrup as a spinning solution for spinning, with a spinning speed of 0.2 - 0.4 m / min -1 , extruding the spinning solution through a spinneret, passing through air and entering a coagulation bath. The coagulation bath is a mixed solution of 3 - 7 wt% sodium hydroxide solution and 93 - 97 wt% ethanol with a volume ratio of 0.8 - 1.2:1; curing in the coagulation bath for 30 - 35 min, washing with water 2 - 3 times, stretching, and drying at room temperature to obtain RGO / chitosan conductive fibers.

6. The flexible strain sensor according to claim 1, wherein: Step 5 specifically includes: immersing the obtained RGO / chitosan conductive fibers into a silver nanowire solution of 8 - 12 mg / ml -1 , then taking them out and drying at 40 - 50 °C, immersing them again, taking them out and drying again. After repeating the above steps 2 - 3 times, they are reserved for use.

7. The flexible strain sensor according to claim 1, wherein: Step 6 specifically includes: First, 2-3 g of AIEgens is stirred and dissolved in toluene, and 9-10 g of tetraethyl orthosilicate is added to the obtained AIEgens solution and stirred for 10-15 min; then the obtained mixture is subjected to vacuum treatment at 60-70 °C until all the solvent evaporates; 1-1.2 g of sulfur is added for cross-linking, and the mixture is mixed for 2-3 min. The mixture is placed in a vacuum oven at 37-40 °C for vacuum degassing, and pre-cured at 50-60 °C for 13-15 min.

8. The flexible strain sensor according to claim 1, characterized in that: Step 7 specifically includes: Straighten the RGO / chitosan / Ag nanowire conductive fiber and fix it at both ends of the paper holder with copper foil conductive tape. Wrap the fiber with a paper holder, pour the fluorescent polymer into the paper holder, and cure it at 90-100 °C for 10-12 h to achieve the encapsulation of the middle section of the fiber, and the two ends are not encapsulated.

9. The flexible strain sensor according to claim 1, characterized in that: Step 8 specifically includes: Mix 20-25 ml of tetraethyl orthosilicate and 20-25 ml of platinum catalyst, stir for 3-5 min, vacuum degas at 37-40 °C for 10-15 min, then pour it into the sensor mold, and let it stand at room temperature for 1-15 h; suck 2-3 g of liquid metal Ga with a syringe and inject it into the liquid metal mold, press it with a glass slide, spray a cooling spray on the surface of the glass slide to cool the liquid metal. When the temperature reaches 0 °C, the liquid metal becomes solid, and a cuboid gallium metal with a length of 40-50 mm, a width of 5-7 mm, and a thickness of 0.8-1.2 mm is obtained. Take it out and use it as a liquid channel mold.

10. The flexible strain sensor according to claim 1, characterized in that: Step 9 specifically includes: Use the unencapsulated two ends of the fiber obtained in Step 7 as electrodes and place them on the polymer cured in Step 8 respectively, then place the liquid channel mold on the cured polymer and press the two ends of the fiber; Mix 20-25 ml of tetraethyl orthosilicate and 20-25 ml of platinum catalyst and stir evenly, vacuum degas at 37-40 °C for 10-15 min, then pour it into the sensor mold to wrap the electrodes and the liquid channel mold, and let it stand at room temperature for curing for 3-4 h to prepare a liquid-type flexible strain sensor for skin; The overall size of the sensor is 60-70 mm in length, 25-35 mm in width, and 3-5 mm in thickness.