Temperature-strain-pressure self-decoupling self-powered electronic skin and preparation method thereof

Abstract

The invention provides a temperature-strain-pressure self-decoupling self-powered electronic skin and a preparation method thereof. The temperature-strain-pressure self-decoupling self-powered electronic skin sequentially comprises a thermoelectric layer, an insulating layer, a piezoelectric layer and a packaging layer from bottom to top, the thermoelectric layer is composed of conductive thermoelectric hydrogel and electrodes arranged on the upper surface and the lower surface of the conductive thermoelectric hydrogel. The piezoelectric layer is composed of a piezoelectric film and electrodes arranged on the upper surface and the lower surface of the piezoelectric film. According to the invention, the sensing layers with different sensing mechanisms are integrated, so that self-powered and self-decoupling sensing of various sensing signals is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of high polymer materials and flexible electronics, and particularly relates to a temperature-strain-pressure self-decoupling self-powered electronic skin and a preparation method thereof. BACKGROUND

[0002] Skin is the largest sensory organ of the human body, and plays an important role in biological perception and protection of the human body. It can convert various complex environmental stimuli from the outside world into bioelectric signals and feed them back to the brain to enable the human body to perceive the environment. Electronic skin can mimic the function of human skin, convert external stimuli into electrical signals and provide sensory feedback to achieve accurate perception of the external environment. It is widely concerned in the fields of motion monitoring, sign language recognition and health monitoring.

[0003] The development and integration of multi-modal sensors are essential for the realization of electronic skin functions. For example, the preparation method of a dual-mode flexible sensor for measuring temperature and strain is disclosed in CN113720386A. The invention is composed of a flexible substrate, electrodes, dielectric materials and strain-sensitive materials, which can realize temperature measurement of 20-200℃, strain measurement of 0-2000με, strain sensitivity of 1.635, temperature measurement error of 4.44%, and strain measurement error of 6.5%. However, the sensor has low sensitivity, narrow strain monitoring range, and the obtained sensing signals interfere with each other, limiting the application environment. CN118329079A discloses a self-driven dual-parameter decoupling sensor based on thermoelectric effect and a preparation method thereof. The invention uses laser-induced graphene technology to prepare a temperature and strain dual-parameter decoupling sensor with self-powering capability, achieving a Seebeck coefficient of 37.33μV / ℃ in temperature detection, a minimum temperature detection resolution of 0.2℃, and a strain sensitivity of 1401.5. However, the multi-modal sensors currently developed have insufficient sensing function integration and different sensing signals interfere with each other. Therefore, it is valuable to develop multi-modal sensors with higher integration and self-decoupling capability. SUMMARY

[0004] The present application provides a temperature-strain-pressure self-decoupling self-powered electronic skin and a preparation method thereof. By integrating sensing layers with different sensing mechanisms, the self-powered and self-decoupling sensing of multiple sensing signals is achieved.

[0005] To achieve the above-mentioned purpose, the specific technical solution is as follows: A temperature-strain-pressure self-decoupling self-powered electronic skin, comprising, from bottom to top, a thermoelectric layer, an insulating layer, a piezoelectric layer, and a packaging layer. The thermoelectric layer is composed of a conductive thermoelectric hydrogel and electrodes arranged on the upper and lower surfaces of the conductive thermoelectric hydrogel. The piezoelectric layer is composed of a piezoelectric film and electrodes arranged on the upper and lower surfaces of the piezoelectric film.

[0006] The preparation method of the temperature-strain-pressure self-decoupling self-powered electronic skin comprises the following steps: (1) Preparation of the thermoelectric layer: crosslinking monomers and crosslinking agents are dispersed in deionized water and stirred uniformly, and then an initiator is added and stirred uniformly to obtain a precursor solution; The precursor solution is heated and left to form a gel; The gel is soaked in deionized water for complete swelling, then demolded and immersed in an ionic liquid with a concentration of 0.1-0.5 mol / L to obtain a conductive thermoelectric hydrogel; the conductive thermoelectric hydrogel is cut and electrodes are attached to the upper and lower surfaces to prepare a thermoelectric layer; (2) Preparation of the insulating layer and the packaging layer: polydimethylsiloxane and a crosslinking agent are mixed uniformly at a mass ratio of 10:1, heated and cured, and then demolded to obtain a material used as the insulating layer and the packaging layer material; (3) Preparation of the piezoelectric layer: polydimethylsiloxane and a crosslinking agent are mixed at a mass ratio of 10:1, and inorganic piezoelectric particles are added and mixed to obtain a mixed solution; the mixed solution is heated and cured to obtain a piezoelectric film; the piezoelectric film is cut and electrodes are arranged on the upper and lower surfaces to obtain a piezoelectric layer; (4) Assembly of the electronic skin: the thermoelectric layer is placed on the bottom layer, a layer of insulating layer is laid on the upper surface of the thermoelectric layer, and a layer of glycerol is covered; the piezoelectric layer is placed on the insulating layer to obtain a sensor; finally, the upper surface and the lower surface of the sensor are packaged with the packaging layer material.

[0007] Preferably, the crosslinking monomers include one or more of acrylamide, polyvinyl alcohol, acrylic acid, and hydroxyethyl acrylate; and the crosslinking agents include one or more of N,N'-methylenebisacrylamide, dimethylacrylamide, and polyethylene glycol diacrylate.

[0008] Preferably, the concentration of the crosslinking monomers in the precursor solution is 2-6 mol / L, and the concentration of the crosslinking agent is 0.025-0.05 mol / L.

[0009] Preferably, the amount of the initiator added in step (1) accounts for 0.2% of the mass of the crosslinking monomers; and the initiator is one or more of ammonium persulfate, potassium persulfate, azobisisobutyronitrile, and benzoyl peroxide.

[0010] Preferably, the ionic liquid in step (1) is at least one of a mixed solution of ferric chloride and ferrous chloride, a mixed solution of potassium ferricyanide and potassium ferrocyanide, a mixed solution of sodium sulfate and sodium sulfite, a mixed solution of ferric perchlorate and ferrous perchlorate, or a mixed solution of iodine ions and triiodide.

[0011] Preferably, the mass fraction of the inorganic piezoelectric particles in the mixed solution in step (3) is 4-20 wt%; the inorganic piezoelectric particles are one or more of lead zirconate titanate, tetragonal barium titanate, lead magnesium niobate, zinc oxide, silicon dioxide, and lead titanate.

[0012] Preferably, the electrode is a graphite paper electrode, a carbon cloth electrode, or a gel electrode.

[0013] Compared with the prior art, the present application has the following beneficial effects: (1) The present application can adjust the voltage under a constant temperature difference by soaking the gel in an ionic liquid, thereby preparing a conductive thermoelectric hydrogel, and realizing self-powered detection of temperature.

[0014] (2) The present application can adjust the piezoelectric voltage of the piezoelectric film when a constant pressure is applied by adding inorganic piezoelectric particles to the piezoelectric layer, thereby realizing self-powered detection of external pressure.

[0015] (3) The self-powered electronic skin of the present application generates a continuous thermoelectric voltage sensing signal when a temperature difference exists, generates a resistance change when stretched, causing a change in loop current, and generates an instantaneous piezoelectric voltage signal when subjected to vertical pressure, thereby realizing self-decoupling sensing of temperature / strain / pressure stimulation through the difference in sensing signals and the single sensing ability which is not disturbed by other external stimuli. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 Structure diagram of the temperature-strain-pressure self-decoupling self-powered electronic skin; Figure 2 Thermoelectric voltage change of the self-powered electronic skin prepared in Example 1 of the present application under a temperature difference of 0-40 ℃; Figure 3 Thermoelectric voltage of the self-powered electronic skin prepared in Example 1 of the present application under a temperature difference of 2K, 5K, 10K, and 15K during a strain of 0-350%; Figure 4 Thermoelectric voltage of the self-powered electronic skin prepared in Example 1 of the present application under a temperature difference of 2K, 5K, 10K, and 15K during a pressure of 0-200 kPa; Figure 5 Change in normalized current in the loop of the self-powered electronic skin prepared in Example 1 of the present application during a strain of 0-200%. Figure 6 The normalized current change in the circuit of the self-powered electronic skin prepared in Example 1 of the present application during the process of strain from 0-350% at temperature differences of 5K, 10K, 15K, respectively; Figure 7 The normalized current change in the circuit of the self-powered electronic skin prepared in Example 1 of the present application during the process of strain from 0-200% at pressures of 0 kPa, 40 kPa, 80 kPa, 120 kPa, respectively; Figure 8 The piezoelectric voltage change of the self-powered electronic skin prepared in Example 1 of the present application during the process of pressure from 0-200 kPa; Figure 9 The piezoelectric voltage change of the self-powered electronic skin prepared in Example 1 of the present application during the process of pressure from 0-200 kPa at temperatures of 25℃, 30℃, 35℃, 40℃, respectively; Figure 10 The piezoelectric voltage of the self-powered electronic skin prepared in Example 1 of the present application when pressed with the same size of pressure at strains of 0, 50%, 100%; Figure 11 The change trend of the Seebeck coefficient and the electrical conductivity of the thermoelectric layer of the self-powered electronic skin in Example 2 with the concentration of the ionic liquid immersed; Figure 12 The change of the piezoelectric voltage of the piezoelectric film in the piezoelectric layer in Example 3 with the concentration of inorganic piezoelectric particles added under the same pressure size. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical scheme and advantages of the present application clearer, the preferred embodiments of the present application will be further described in detail below in combination with examples. All other examples obtained by those skilled in the art without creative labor on the basis of the examples in the present application belong to the scope of protection of the present application.

[0018] Example 1

[0019] A temperature-strain-pressure self-decoupling self-powered electronic skin is prepared by the following steps: Step one, monomer acrylamide and crosslinking agent N,N'-methylene bisacrylamide are added to deionized water, a magnetic stirrer is used to stir at a speed of 1200 rpm for 15 min, 0.2% of initiator ammonium persulfate based on the mass of acrylamide is added, and the magnetic stirrer is continued to be used to stir at a speed of 1200 rpm for 15 min, so that it is completely dissolved and uniformly mixed to obtain a precursor solution; the concentration of acrylamide in the precursor solution is 5 mol / L, and the concentration of N,N'-methylene bisacrylamide is 0.05 mol%; The precursor solution is poured into a first mold made of glass, which is composed of two opposite glass sheets with a 1 mm thick spacer glass strip in between, and kept at 60°C for 1 h to shape the hydrogel. The hydrogel is then demolded and soaked in deionized water for 24 h to fully swell.

[0020] An aqueous solution of potassium ferricyanide with a concentration of 0.4 mol / L and an aqueous solution of potassium ferrocyanide with a concentration of 0.4 mol / L are mixed in equal volumes to obtain an ionic liquid; The swelled hydrogel is soaked in the ionic liquid for 24 h to fully exchange ions, and a conductive gel with thermoelectric ability is obtained; Step two, polydimethylsiloxane (PDMS) and curing agent are mixed at a mass ratio of 10:1, and a magnetic stirrer is used to stir at a speed of 1200 rpm for 30 min. Tetragonal barium titanate particles with a particle size of 200 nm are added to the PDMS mixed solution, and then the magnetic stirrer is used to continue stirring the solution at a speed of 1200 rpm for 1 h to mix uniformly, obtaining a mixed solution; the concentration of tetragonal barium titanate particles in the mixed solution is 12 wt%; the mixed solution is placed in a vacuum drying box for vacuum treatment for 30 min, thereby forming a white and bubble-free uniform solution, obtaining a precursor solution for preparing a piezoelectric film.

[0021] The precursor solution of the piezoelectric film is transferred to a glass substrate, and a glass rod with 100 μm thick adhesive tape wound at both ends is used for blade coating, and then cured in a 60°C oven for 3 h, obtaining a piezoelectric film with piezoelectric properties.

[0022] Step three, polydimethylsiloxane (PDMS) and curing agent are mixed at a mass ratio of 10:1, and a magnetic stirrer is used to stir at a speed of 1200 rpm at room temperature for 30 min, and then the mixture is vacuum treated in a vacuum drying box for 30 min; the defoamed mixture is placed in a second mold, which is composed of a glass slide with a thickness of 100 μm spacer on both sides and a cover glass on the upper layer, and cured in a 60°C oven for 3 h, obtaining an elastic polymer film for the insulating layer and the packaging layer.

[0023] Step four, preparation of a temperature-strain-pressure self-decoupling self-powered electronic skin, specifically including: Step 4.1 Preparation of a thermoelectric layer: the conductive thermoelectric gel prepared above is cut into the desired target shape and size, and graphite paper electrodes are used as thermoelectric layer electrodes, which are placed on the upper and lower sides of the conductive thermoelectric gel to obtain a thermoelectric layer; Step 4.2 Preparation of piezoelectric layer: The piezoelectric film prepared above is cut into the desired target shape and size, and graphite paper electrodes are used as piezoelectric layer electrodes, which are placed on the upper and lower sides of the piezoelectric film. The film and the electrodes are naturally adsorbed to obtain the piezoelectric layer.

[0024] Step 4.3 Preparation of self-decoupled self-powered electronic skin: The thermoelectric layer is placed at the bottom layer. In order to avoid signal interference caused by the contact between different sensing layers and the influence of strain stimulation on the piezoelectric layer, an insulating layer is introduced on the surface of the thermoelectric layer, and a layer of glycerol is coated for lubrication. The piezoelectric layer is placed on the insulating layer. After placing the piezoelectric layer, a double-layer PDMS film is used as packaging to avoid the decrease of sensing effect caused by water loss of hydrogel in dry environment, and to protect the entire sensor.

[0025] As shown in Figure 1 , it is a structure diagram of the temperature-strain-pressure self-decoupled self-powered electronic skin prepared in this embodiment. It includes packaging, thermoelectric layer, insulating layer and piezoelectric layer; the packaging is an elastomer film, which is arranged at the top layer; the piezoelectric layer is a piezoelectric film, which is arranged below the packaging; the thermoelectric layer is a conductive hydrogel, which is arranged at the bottom layer; the insulating layer is arranged between the thermoelectric layer and the piezoelectric layer.

[0026] The temperature-strain-pressure self-decoupled self-powered electronic skin prepared in Example 1 of the present application has different output voltages for different temperature differences, as shown in Figure 2 , it is the voltage generated across the sensor under a temperature difference of 0-40 ℃. The greater the temperature difference across the sensor, the greater the output voltage. Through linearity fitting, it is found that the self-decoupled self-powered electronic skin of the present application has a high Seebeck coefficient, about 1.05 mV / K.

[0027] The temperature sensing function of the electronic skin prepared in Example 1 of the present application is decoupled from strain and pressure, as shown in Figure 3 , it is the thermoelectric voltage generated when the temperature difference between the upper and lower layers is 2K, 5K, 10K, 15K during the process of strain from 0-200%. It remains consistent in a large strain range, proving that its temperature sensing is not affected by strain. As shown in Figure 4 , it is the thermoelectric voltage generated when the temperature difference between the upper and lower layers is 2K, 5K, 10K, 15K during the process of applying pressure from 0-200 kPa. It remains consistent in a large pressure range, proving that its temperature sensing is not affected by pressure.

[0028] The self-powered electronic skin prepared in Example 1 of the present application produces varying normalized current in the circuit under different strain stimuli, as shown in Figure 5 , it is the change of normalized current in the circuit during the process of strain from 0-200%. The current change trend can be divided into three sections, each of which has a high linearity.

[0029] The strain sensing function of the electronic skin prepared in Example 1 of this invention is decoupled from temperature and pressure: as follows Figure 6 As shown, the normalized current in the strain-to-strain loop changes under temperature differences of 5K, 10K, and 15K. The normalized current remains constant when there are different temperature differences between the upper and lower surfaces, proving that its strain sensing capability is not affected by temperature. Figure 7 As shown, the normalized current change during the strain from 0 to 200% under pressures of 0 kPa, 40 kPa, 80 kPa, and 120 kPa proves that its strain sensing is not affected by pressure.

[0030] The self-powered electronic skin described in Embodiment 1 of this invention exhibits different piezoelectric voltage responses under different pressure stimuli, such as... Figure 8 As shown, the piezoelectric voltage variation trend is observed during the application of pressure from 0 to 200 kPa. The piezoelectric voltage curve is divided into two segments, at 9.76 mV / kPa and 4.67 mV / kPa, respectively, and exhibits good linearity.

[0031] The pressure sensing function of the electronic skin prepared in Example 1 of this invention is decoupled from temperature and strain: as follows Figure 9 As shown, the piezoelectric voltage changes when the sensor temperature is 25℃, 30℃, 35℃, and 40℃ respectively, during the application of 0-100 kPa, proving that its pressure sensing capability is not affected by external temperature. Figure 10 As shown, the piezoelectric voltage is the same under the same pressure when the strain is 0%, 50%, and 100%, respectively, proving that its pressure sensing capability is not affected by strain.

[0032] Example 2

[0033] The self-powered electronic skin with temperature-strain-pressure self-decoupling in this embodiment is basically the same as that in Example 1. The difference between the two lies in the different concentrations of ionic liquid added in step one.

[0034] This embodiment describes an ionic liquid obtained by mixing equal volumes of potassium ferricyanide and potassium ferrocyanide aqueous solutions of equal concentrations. The concentrations of the potassium ferricyanide and potassium ferrocyanide aqueous solutions are 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, and 0.5 mol / L, respectively. This embodiment obtains thermoelectric gel layers with different Seebeck coefficients and thermoelectric capabilities by changing the ion concentration.

[0035] like Figure 11As shown in the process of the concentration of potassium ferricyanide and potassium ferrocyanide from 0.1 mol / L to 0.5 mol / L, the Seebeck coefficient first increases and then decreases, and the conductivity first increases obviously and then remains unchanged. By soaking the ion solution with different concentrations, the conductivity and the Seebeck coefficient of the gel can be regulated.

[0036] As can be seen from Figure 11 , at first, the increase of ion concentration makes more redox ions enter the hydrogel to participate in electrochemical reactions, thereby increasing the Seebeck coefficient. When the ion concentration is further increased, the ion circulation in the interior is hindered due to the excessive ion concentration, and the Seebeck coefficient decreases.

[0037] Example 3

[0038] The preparation method of the temperature-strain-pressure self-decoupling self-powered electronic skin of the present embodiment is basically the same as that of Example 1, and the difference between the two is that the concentration of the inorganic piezoelectric particles added in step two is different. In the present embodiment, by changing the concentration of the inorganic piezoelectric particles, a piezoelectric film with different piezoelectric voltages under the same pressure is obtained. In step two, the concentration of the barium titanate particles in the mixed solution is 4 wt%, 8 wt%, 12 wt%, 16 wt%, and 20 wt%.

[0039] As shown in Figure 12 , with the increase of the concentration of inorganic piezoelectric particles, the piezoelectric voltage of the piezoelectric film first increases and then decreases, and has the maximum piezoelectric voltage at 12 wt%.

[0040] As can be seen from Figure 12 , the increase of the concentration of inorganic piezoelectric particles in the piezoelectric film is conducive to the polarization of the dipole moment in the polymer film, thereby increasing the piezoelectric voltage. When the concentration reaches a certain value, the addition of inorganic piezoelectric particles will cause the interaction between the barium titanate particles and the agglomeration phenomenon, resulting in uneven electric field in the local area, thereby reducing the piezoelectric response effect.

[0041] Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0042] The above described embodiments are a part of the embodiments of the present application, rather than all the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the claimed application, but only represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

Claims

1. A self-powered electronic skin self-decoupled in temperature-strain-pressure, characterized in that, From bottom to top, the thermal layer, the insulating layer, the piezoelectric layer and the packaging layer are included in turn; The thermal layer is composed of conductive thermal hydrogel and electrodes arranged on the upper and lower surfaces of the conductive thermal hydrogel; The piezoelectric layer is composed of a piezoelectric film and electrodes arranged on the upper and lower surfaces of the piezoelectric film.

2. The method for preparing the temperature-strain-pressure self-decoupled self-powered electronic skin as described in claim , characterized in that, The method comprises the following steps: (1) Preparation of the thermal layer: disperse the cross-linking monomer and the cross-linking agent in deionized water and stir until uniform, then add the initiator and continue to stir until uniform to obtain a precursor solution; Heat and stand the precursor solution to form a gel; Completely swell the gel in deionized water, then demold and immerse in an ionic liquid with a concentration of 0.1-0.5 mol / L to obtain a conductive thermal hydrogel; cut the conductive thermal hydrogel and attach electrodes on its upper and lower surfaces to prepare the thermal layer; (2) Preparation of the insulating layer and the packaging layer: mix polydimethylsiloxane and a cross-linking agent in a mass ratio of 10:1, then heat and solidify, and demold to obtain a material used as the insulating layer and the packaging layer material; (3) Preparation of the piezoelectric layer: mix polydimethylsiloxane and a cross-linking agent in a mass ratio of 10:1, then add inorganic piezoelectric particles to obtain a mixed solution; heat and solidify the mixed solution to obtain a piezoelectric film; cut the piezoelectric film and arrange electrodes on its upper and lower surfaces to obtain the piezoelectric layer; (4) Assembly of the electronic skin: place the thermal layer on the bottom layer, lay an insulating layer on the upper surface of the thermal layer and cover a layer of glycerol; place the piezoelectric layer on the insulating layer to obtain a sensor; finally, use the packaging layer material to package the upper and lower surfaces of the sensor.

3. The method for preparing the temperature-strain-pressure self-decoupled self-powered electronic skin as described in claim 2, characterized in that, The cross-linking monomer includes one or more of acrylamide, polyvinyl alcohol, acrylic acid and hydroxyethyl acrylate; the cross-linking agent includes one or more of N,N'-methylene bisacrylamide, dimethyl acrylamide and polyethylene glycol diacrylate.

4. The method for preparing the temperature-strain-pressure self-decoupled self-powered electronic skin as described in claim 2, characterized in that, The concentration of the cross-linking monomer in the precursor solution is 2-6 mol / L; the concentration of the cross-linking agent is 0.025-0.05 mol / L.

5. The method for preparing the temperature-strain-pressure self-decoupled self-powered electronic skin as described in claim 2, characterized in that, The amount of the initiator added in step (1) accounts for 0.2% of the mass of the cross-linking monomer; the initiator is one or more of ammonium persulfate, potassium persulfate, azobisisobutyronitrile and benzoyl peroxide.

6. The method for preparing the temperature-strain-pressure self-decoupled self-powered electronic skin as described in claim 2, characterized in that, The ionic liquid in step (1) is at least one of a mixed solution of iron chloride and ferrous chloride, a mixed solution of potassium ferricyanide and potassium ferrocyanide, a mixed solution of sodium sulfate and sodium sulfite, a mixed solution of iron perchlorate and ferrous perchlorate, or a mixed solution of iodine ions and triiodide.

7. The method for preparing the temperature-strain-pressure self-decoupled self-powered electronic skin as described in claim 1, characterized in that, The mass fraction of the inorganic piezoelectric particles in the mixed solution in step (3) is 4-20 wt%; the inorganic piezoelectric particles are one or more of lead zirconate titanate, tetragonal barium titanate, lead magnesium niobate, zinc oxide, silicon dioxide and lead titanate.

8. The method for preparing the temperature-strain-pressure self-decoupled self-powered electronic skin as described in claim 1, characterized in that, The electrode is a graphite paper electrode, a carbon cloth electrode or a gel electrode.

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