Electronic skin and preparation method thereof

Abstract

The invention discloses electronic skin and a preparation method thereof.The method comprises the following steps that MXene dispersion liquid is treated through ultrasonic waves so as to increase the distance between MXene layered structures in the MXene dispersion liquid; the preparation method comprises the following steps: coating a PI thin film with an MXene dispersion liquid subjected to ultrasonic treatment, and then carrying out laser induction to obtain laser-induced MXene modified graphene; transferring the laser-induced MXene modified graphene onto the hydrogel by adopting a repeated freezing and thawing method to obtain a conductive layer; preparing a bionic layer; and assembling the conductive layer and the bionic layer to obtain the electronic skin. The electronic skin prepared by the method can realize high-linearity sensing response of resistance in a wide range and realize heat and humidity management of a human skin-electronic skin interface.

Description

Technical Field

[0001] The present invention belongs to the technical field of electronic skin, and specifically relates to an electronic skin and a preparation method thereof. Background Art

[0002] Electronic skin is a system that allows robots to sense touch. It has a simple structure and can be processed into various shapes. It can be attached to the surface of a device like clothes, allowing robots to sense the location, orientation, hardness and other information of an object. Electronic skin is actually a new type of sensor that imitates the perception function of human skin.

[0003] The existing electronic skin is prepared with high molecular polymer as the substrate, and the laser-induced graphene is transferred to these flexible substrates and then cured. For example, the invention patent with application number CN202410646332.0 discloses "an ultra-thin flexible pressure sensor based on graphene", which uses a laser-induced method to induce a graphene film on a carbon-rich substrate PI film, and then uses aerosol printing technology to punch the lead onto the graphene to form a circuit; finally, PDMS is cast on its surface or directly bonded to the PDMS film package, and the pressure sensing performance is obtained by calibrating and testing the sensor.

[0004] The existing method for preparing electronic skin has the following problems:

[0005] Since the curing process of laser-induced graphene transferred to these flexible substrates is usually irreversible, and laser-induced graphene itself is a porous and defective graphene, it is easy to cause the conductive network to be disconnected when stretched in a high strain range, thereby losing the linear sensing function or completely losing the sensing function. Therefore, the strain range and sensing linearity of existing electronic skins are poor. Summary of the invention

[0006] In order to solve the problem that electronic skin prepared by existing methods has poor strain range and sensing linearity, the present invention provides an electronic skin and a preparation method thereof, which can achieve a high linear sensing response of resistance in a wide range.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] The first aspect of the present invention provides a method for preparing electronic skin, comprising the following steps:

[0009] The MXene dispersion is treated with ultrasound to cause the MXene in the MXene dispersion to be layered and spread out;

[0010] The MXene dispersion treated with ultrasound is coated on the PI film and then laser induced to obtain laser-induced MXene-modified graphene;

[0011] The laser-induced MXene-modified graphene is transferred to the hydrogel by a freeze-thaw cycle method to obtain a conductive layer;

[0012] preparing a flexible layer;

[0013] The conductive layer and the flexible layer are assembled to obtain the electronic skin.

[0014] A second aspect of the present invention provides an electronic skin, which is prepared by using an electronic skin preparation method described in the first aspect.

[0015] Compared with the prior art, the present invention has at least the following advantages and beneficial effects:

[0016] 1. The present invention increases the unfolding state of MXene stratification by ultrasonic treatment of MXene, and performs laser induction together with PI film after ultrasonic treatment. The MXene derivative TiO2 nanospheres are embedded in the defects and pores of graphene, and the surface of the TiO2 nanospheres is covered with graphene, which can provide an additional electrical path when the graphene is about to break, thereby increasing the sensing range.

[0017] 2. The present invention realizes transfer through repeated and reversible freeze-thaw method, forming a strong mechanical interlock between graphene and hydrogel, and combining with TiO2 nanospheres that provide additional electrical pathways to achieve a highly linear sensing response of resistance in a wide range. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0019] Figure 1 Schematic diagram of the products obtained in each step of the preparation process of the conductive layer;

[0020] Figure 2 for Figure 1 Schematic diagram of the middle section A;

[0021] Figure 3 for Figure 1 The enlarged view of the middle B part, the ruler is 2 microns;

[0022] Figure 4 This is a scanning electron microscope image of MXene before layering and unfolding, with a scale of 2 microns;

[0023] Figure 5This is a scanning electron microscope image of MXene after layering and unfolding, with a scale of 1 micron;

[0024] Figure 6 This is a scanning electron microscope image of titanium dioxide nanospheres embedded in graphene pores, with a scale of 2 microns;

[0025] Figure 7 This is a transmission electron microscopy image of titanium dioxide nanospheres embedded in graphene pores, with the ruler being 100 nanometers;

[0026] Figure 8 This is a scanning electron microscope side view of graphene transferred to hydrogel, with the ruler being 30 μm;

[0027] Fig. 9 is a curve diagram showing the linear change of the resistance of the electronic skin with strain;

[0028] Fig.10 It is a schematic diagram of the structure of the 3D printed microneedle array template;

[0029] Fig.11 The schematic diagram of the bionic wedge-shaped channel structure for the bird's beak;

[0030] Fig.12 is a flow chart for the preparation of the biomimetic layer;

[0031] Fig.13 This is an enlarged view of a lizard's foot. The rulers are 200 microns and 5 microns.

[0032] Fig.14 A schematic diagram of the prepared electronic skin being attached to human skin;

[0033] Fig.15 The output response of the electronic skin when saying "he l lo graphene";

[0034] Fig.16 Section A in the middle shows the output response of the electronic skin when the finger is half-bent, and section B shows the output response of the electronic skin when the finger is fully bent;

[0035] Fig.17 The output response of the electronic skin when the wrist is bent;

[0036] Fig.18 Output response of the electronic skin when walking;

[0037] Fig.19 This is the output response of the electronic skin when the elbow is bent;

[0038] Fig. 20 The upper arrow segment in the middle represents the output response of the electronic skin when sitting down, and the lower arrow segment represents the output response of the electronic skin when standing up;

[0039] Fig.21 This is the result of the experiment on unidirectional transport of droplets.

[0040] Fig. 22 This is an application diagram of the cooling function of electronic skin, compared with commercial polyester. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0042] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0043] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features of the embodiments may be combined with each other.

[0044] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0045] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inside", "outside", etc. indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, or the positions or positional relationships in which the product of the invention is usually placed when in use, or the positions or positional relationships commonly understood by those skilled in the art, which are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0046] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0047] The present invention discloses an electronic skin and a preparation method thereof. The electronic skin is prepared by the preparation method. Specifically, the preparation method comprises steps S1 to S3. It should be noted that the sequence numbers of the steps in the present invention do not limit the order of the steps. The order of the steps is subject to the description of the steps.

[0048] Step S1, preparing a conductive layer. Specifically, this step includes steps S11 to S13, and the products obtained in each step are as follows: Figure 1 shown.

[0049] Step S11: Treat the MXene dispersion liquid with ultrasound to increase the spacing between the MXene layered structures in the MXene dispersion liquid 51.

[0050] MXene is Ti3C2T x , is a multi-layered accordion-like structure with a layered structure, such as Figure 4 The scanning electron microscope image shown in the figure. Ultrasonic treatment is used to increase the spacing between the MXene layered structures in the MXene dispersion, that is, to increase the layered expansion state to increase the contact area and thus increase the effective reaction area during the laser induction process in the subsequent steps.

[0051] In this step, an ultrasonic cleaner or other ultrasonic equipment can be used to treat the MXene dispersion. The ultrasonic power is 30-40W and the treatment time is greater than 10 hours. This will make the MXene appear in a clear layered state to increase the contact area and thus increase the effective reaction area in the laser induction process in the subsequent steps. The scanning electron microscope image of the MXene after ultrasonic treatment is as follows: Figure 5 shown.

[0052] The concentration of the MXene dispersion in this step is related to the effect of laser-induced MXene modification of graphene and the growth effect of graphene in the subsequent steps. According to the test, the concentration of the MXene dispersion is preferably greater than or equal to 10 mg / ml and less than or equal to 20 mg / ml. Preferably, the concentration is set between 15 mg / ml and 20 mg / ml.

[0053] In the above concentration range, the higher the concentration, the better the effect of laser-induced MXene modification of graphene. However, when the concentration is greater than 20 mg / ml, it will affect the growth of graphene and prevent it from growing. Therefore, the optimal concentration of MXene dispersion is 20 mg / ml.

[0054] Step S12, coating the ultrasonically treated MXene dispersion on the PI film and then performing laser induction to obtain laser-induced MXene-modified graphene 52.

[0055] In this step, when the PI film coated with the MXene dispersion is laser-induced, an infrared nanosecond laser or other lasers with better thermal effects, such as ultraviolet nanosecond lasers, can be used. When performing laser induction, an infrared nanosecond laser is used with a power of 8-9.5W, a scanning speed of 30-45mm / s, and a scanning line interval of 0.02-0.04mm.

[0056] PI film is a polyimide film, and laser-induced graphene can be obtained by laser induction, which is a porous carbon nanomaterial.

[0057] like Figure 6 and Figure 7 As shown, after laser induction on the PI film coated with MXene dispersion, the C-Ti-O chemical bonds of the laser-induced MXene-modified graphene are coated with graphene, and the titanium dioxide nanospheres are embedded in the porous structure of the conductive network of graphene.

[0058] Step S13: transferring the laser-induced MXene-modified graphene to the hydrogel by repeated freezing and thawing to obtain a conductive layer 53.

[0059] Specifically, in this step, the laser-induced MXene-modified graphene and the hydrogel are stacked and placed in an environment with a temperature of -35 degrees to -55 degrees Celsius for half an hour to an hour, and then placed in a room temperature environment to thaw, and the above freezing-thawing steps are repeated at least 3 times.

[0060] The hydrogel here can be cross-linked with polyvinyl alcohol, phytic acid, honey, and propylene glycol as raw materials, or can be made by using polyvinyl alcohol and other cross-linking agents rich in monosaccharides. As long as the curing process of the hydrogel can be repeatedly frozen and thawed, it can be used. When used close to the skin, it is preferably cross-linked with polyvinyl alcohol, phytic acid, honey, and propylene glycol as raw materials, and the cross-linking agents are basically natural complexes and are harmless to the skin.

[0061] This step can form a bond between graphene and hydrogel through repeated freeze-thaw processes. Figures 1 to 3 Very strong mechanical interlock, such as Figure 8 As shown, graphene is uniform and smooth on the hydrogel.

[0062] The conductive layer prepared by the above steps is subjected to ultrasonic treatment on the MXene dispersion to make the MXene spread out in layers, and then coated on the PI film for laser induction and then transferred by repeated freezing and thawing. The MXene derivative TiO2 nanospheres are embedded in the defects and pores of the graphene, and the surface of the TiO2 nanospheres is covered by graphene, which can provide an additional electrical path when the graphene is about to break, thereby increasing the sensing range; and the transfer is achieved by repeated and reversible freezing and thawing, and a strong mechanical interlock is formed between the graphene and the hydrogel. The combination of the TiO2 nanospheres that provide an additional electrical path can achieve a high linear sensing response of resistance in a wide range, wherein the wide range is a strain range of 0-366%, and the sensing response R 2 =0.9948, the linear sensing diagram of the electronic skin's resistance versus strain is shown in Fig. 9 shown.

[0063] Step S2: preparing a flexible layer.

[0064] The flexible layer in contact with the skin can be prepared by existing methods, such as heat curing the high molecular weight polymer polydimethylsiloxane. However, the flexible layer prepared by the existing method has poor adhesion and heat dissipation, and cannot discharge sweat on the skin. In severe cases, it may cause local inflammation of the skin. In this regard, a bionic structure can be further added to the flexible layer. Specifically, the method of adding a bionic structure to the flexible layer can be adopted from step S21 to step S23. The products obtained in each step are detailed in Fig.12 shown.

[0065] Step S21, pouring a hydrogel precursor solution onto a microneedle array plate for transfer printing, and forming a hydrogel 2 having a wedge-shaped bionic channel after solidification.

[0066] The microneedle array plate in this step can be made by 3D printing. The microneedle array template 1 is a template having a triangular cone microneedle array 12 on the template 11, and its structure is as follows: Fig.10 shown.

[0067] Exemplarily, the template is 4 cm long and 2 cm wide, the distance between two adjacent rows of microneedles is 1500 um, the distance between two adjacent columns of microneedles is 0.4 cm, the cone height of the microneedles is 1200 um, and the bottom diameter is 800 um.

[0068] After this step, the bionic object of the obtained bionic wedge-shaped channel is a bird's beak, and the structure of the bionic wedge-shaped channel is as follows: Fig.11 As shown. Because when a bird drinks water, the process of the droplet moving from the front end of the beak to the mouth is precisely due to the Laplace pressure difference formed by the wedge-shaped channel.

[0069] Step S22, hydrophobically modifying the central area of ​​one side of the hydrogel having the wedge-shaped bionic channel to form a wettability water contact angle gradient structure, wherein the water contact angle gradient structure includes a water contact angle in a hydrophilic region and a water contact angle in a hydrophobic region, and the angles of the water contact angle in the hydrophilic region and the water contact angle in the hydrophobic region differ by at least 60 degrees.

[0070] For example, the water contact angle of the hydrophobic area after hydrophobic treatment is greater than 70 degrees, and the water contact angle of the hydrophilic area is preferably close to 0 degrees. The hydrophobic treatment area is the central area 3, that is, Fig.12 The green area in the figure realizes the unidirectional transport of droplets in the wedge-shaped channel.

[0071] One side of the hydrogel is the side that directly contacts the skin, and the other side is the side that is connected and assembled with the conductive layer.

[0072] The hydrophobic modified side is the side that directly contacts the skin. Through the hydrophobic modification, the purpose of unidirectional transport of sweat can be achieved.

[0073] In this step, the area of ​​the central region can be adjusted according to usage requirements.

[0074] Step S23, performing femtosecond laser processing on the two side regions of the hydrophobicity modification region of the hydrogel to process a bionic structure in the region to improve the adhesion of the region.

[0075] In step S22, the hydrophobic modification is performed on the central area of ​​the hydrogel close to the skin, which will cause it to lose its adhesiveness. In this regard, femtosecond laser processing is performed on the non-hydrophobic modified area 4 on the same side, that is, the areas on both sides of the original hydrophilic area, to further improve its adhesiveness and enhance wearability. Fig.12 The arrows in the figure represent the femtosecond laser operation.

[0076] In this step, the bionic object of the bionic structure is the lizard's foot, such as Fig.13 shown.

[0077] The bionic layer prepared by this step has a wedge-shaped bionic channel and a micro-nano bionic groove structure, which can realize unidirectional transport of sweat and good adhesion contact with the skin, and has the function of cooling the skin, thereby enhancing wearability and comfort.

[0078] Step S3: Fig.14 The conductive layer 6 and the flexible layer 7 are assembled to obtain the electronic skin.

[0079] The hydrogel precursor solution is coated onto the edge of the adjacent side of the conductive layer and the flexible layer, and solidified by repeated freezing and thawing method.

[0080] The repeated freezing and thawing method of this step is the same as the method of step S13, that is, the sample is placed in an environment of -35°C to -55°C for half an hour to one hour and then thawed at room temperature, and the above freezing-thawing steps are repeated at least three times. Fig.12 shown.

[0081] The schematic diagram of the prepared electronic skin attached to human skin 8 is shown in Fig.14 shown.

[0082] Indicative 1:

[0083] The electronic skin prepared by the above method can be divided into three sensing areas according to the different muscle deformation amounts, namely small sensing area, medium sensing area and large sensing area. Due to its excellent linear sensing response, the electronic skin can be divided into different working areas according to the different resistance change rates, including Fig.15 and 16 Small sensing area, Fig.17 and 18 The middle sensing area, Fig.19 and 20 The electronic skin has a large sensing area and can achieve accurate muscle deformation detection under different degrees of tensile strain, with good distinction between muscle movements, thanks to its excellent linear sensing response.

[0084] in,

[0085] Fig.15 The output response of the electronic skin when saying "he l lo graphene";

[0086] Fig.16 Section A in the middle shows the output response of the electronic skin when the finger is half-bent, and section B shows the output response of the electronic skin when the finger is fully bent;

[0087] Fig.17 The output response of the electronic skin when the wrist is bent;

[0088] Fig.18 Output response of the electronic skin when walking;

[0089] Fig.19 This is the output response of the electronic skin when the elbow is bent;

[0090] Fig. 20 The upper middle arrow segment represents the output response of the electronic skin when sitting down, and the lower middle arrow segment represents the output response of the electronic skin when standing up.

[0091] Example 2:

[0092] The electronic skin prepared by the above method was attached to the arm to conduct an experiment on the unidirectional transport of droplets. Fig.21 As shown, after 32 seconds, it can be seen that the droplets can only be transported in one direction, which proves the ability of the bionic layer to transport droplets in one direction.

[0093] When the electronic skin is placed on a sweaty area and then removed, the part with sweat becomes dry, proving its ability to transport sweat.

[0094] Example 3:

[0095] The electronic skin prepared by the above method was attached to the arm under the irradiation of the sun at 38 degrees outdoors, and a piece of commercial polyester was used as a comparison. Fig. 22 As shown, it can be seen that the temperature of the area with electronic skin always remained below 36 degrees after being exposed to the sun for a few minutes, the temperature of the area with commercial skin remained at 35.2℃ to 35.7℃, and the temperature of the area with commercial polyester rose sharply, reaching a maximum of 38.9℃. One minute after taking them away, the area originally with electronic skin also maintained a lower temperature.

[0096] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing electronic skin, characterized in that: The following steps are involved: The MXene dispersion is treated with ultrasound to increase the spacing between MXene layered structures in the MXene dispersion; the MXene dispersion treated with ultrasound is coated on a PI film and then laser induced to obtain laser induced MXene modified graphene; The laser-induced MXene-modified graphene is transferred to the hydrogel by a freeze-thaw cycle method to obtain a conductive layer; preparing a flexible layer; The conductive layer and the flexible layer are assembled to obtain the electronic skin.

2. The method for preparing electronic skin according to claim 1, characterized in that: The concentration of the MXene dispersion is greater than or equal to 10 mg / ml and less than or equal to 20 mg / ml.

3. The method for preparing electronic skin according to claim 1, characterized in that: The concentration of the MXene dispersion is 20 mg / ml.

4. The method for preparing electronic skin according to claim 1, characterized in that: When the MXene dispersion is treated with ultrasound, The ultrasonic power is 30W-40W, and the treatment time is more than 10 hours.

5. The method for preparing electronic skin according to claim 1, characterized in that: The method of transferring the laser-induced MXene-modified graphene to the hydrogel by repeated freezing and thawing comprises: The laser-induced MXene-modified graphene and hydrogel are stacked and placed in an environment with a temperature of -35 to -55 degrees Celsius for half an hour to one hour, and then placed in a room temperature environment to thaw, and this step is repeated at least 3 times.

6. The method for preparing electronic skin according to claim 1, characterized in that: The hydrogel is prepared by cross-linking polyvinyl alcohol, phytic acid, honey and propylene glycol as raw materials.

7. The method for preparing electronic skin according to claim 1, characterized in that: The preparation of the flexible layer comprises: The hydrogel precursor solution is poured onto a microneedle array plate for transfer printing, and after curing, a hydrogel having a wedge-shaped bionic channel is formed; a central area of ​​one side of the hydrogel having the wedge-shaped bionic channel is hydrophobically modified to form a wettability water contact angle gradient structure, wherein the water contact angle gradient structure includes a hydrophilic region contact angle and a hydrophobic region contact angle, and the angles of the hydrophilic region water contact angle and the hydrophobic region water contact angle differ by at least 60 degrees; Femtosecond laser processing is performed on the two side areas of the hydrophobic modification area of ​​the hydrogel to process a bionic structure in the area to improve the adhesion of the area.

8. The method for preparing electronic skin according to claim 7, characterized in that: The bionic object of the bionic channel is a bird's beak, and / or the bionic object of the bionic structure is a lizard's paw.

9. The method for preparing electronic skin according to claim 1, characterized in that: The step of assembling the conductive layer and the flexible layer to obtain the electronic skin comprises: The heated hydrogel precursor solution is coated on the edge of the adjacent side of the conductive layer and the flexible layer, and solidified by repeated freezing and thawing method.

10. An electronic skin, characterized in that: The electronic skin is prepared by using an electronic skin preparation method as described in any one of claims 1 to 9.

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