Hydrogel-based self-powered smart pressure sensor

Abstract

The present invention relates to a pressure sensor comprising a first electrode, a pressure sensing unit, and a second electrode, wherein the pressure sensing unit includes a polymer hydrogel laminate, and the polymer hydrogel laminate includes a rigid polymer hydrogel layer, a polymer hydrogel layer laminated on the rigid polymer hydrogel layer and having ion selectivity, and a soft polymer hydrogel layer laminated on the polymer hydrogel layer having ion selectivity. The hydrogel-based self-powered smart pressure sensor can output, as an electrical signal (voltage and current), pressure applied without the introduction of an external power source, generate an electrical signal proportional to the magnitude of the external pressure applied to the sensor, distinguish the position to which the external pressure is applied, through the polarity of the output electrical signal, and detect changes in external pressure and the rate of the changes through variations in the electrical signal.

Description

Hydrogel-based self-powered smart pressure sensor

[0001] The present invention relates to a self-powered pressure sensor capable of outputting applied pressure as an electric signal without introducing an external power source.

[0002] Conventional pressure sensors or strain sensors are based on the principle that resistance or capacitance changes due to applied deformation (tension, compression, twisting, bending, etc.) after power is supplied from an external power supply.

[0003] Additionally, studies on self-powered pressure sensors utilizing triboelectric and piezoelectric phenomena have been reported recently.

[0004] However, pressure sensors or strain sensors according to conventional technology can only convert the size of the applied deformation into an electrical signal change, and no sensor has yet been developed that can simultaneously detect the size, position, and speed of the deformation applied to the sensor and convert them into an electrical signal without an additional electrical circuit.

[0005] The present invention aims to provide a self-powered smart pressure sensor capable of converting inputs such as the intensity of pressure, position, and deformation rate applied to an ion-conductive hydrogel into electrical signals without an external power supply and an additional electric circuit.

[0006] In order to achieve the above technical task, the present invention provides a pressure sensor comprising a first electrode, a pressure sensing unit, and a second electrode, wherein the pressure sensing unit comprises a polymer hydrogel laminate, and the polymer hydrogel laminate comprises a hard polymer hydrogel layer, a polymer hydrogel layer laminated on the hard polymer hydrogel layer and having ion selectivity, and a soft polymer hydrogel layer laminated on the polymer hydrogel layer having ion selectivity.

[0007]

[0008] When pressure is applied from the outside of the pressure sensor according to the present invention, since the degree of compression is greater for the soft polymer hydrogel than for the hard polymer hydrogel, the soft polymer hydrogel layer is selectively compressed, and cations or anions derived from the electrolyte dispersed inside the soft polymer hydrogel layer move toward the hard polymer hydrogel layer to output an electrical signal, and the pressure applied to the sensor can be detected in various aspects, such as its size, location, change, and change speed, through the size, sign, and change of the electrical signal.

[0009] At this time, the type of ion moving from the soft polymer hydrogel layer to the hard polymer hydrogel layer is determined depending on whether the polymer hydrogel layer interposed between the soft polymer hydrogel layer and the hard polymer hydrogel layer has cation selectivity or anion selectivity.

[0010]

[0011] In the hydrogel-based self-powered smart pressure sensor according to the present invention, the first electrode and the second electrode can be formed in an opposing form with the polymer hydrogel laminate interposed therebetween.

[0012] That is, the first electrode may be formed on the lower side of the hard polymer hydrogel layer of the polymer hydrogel laminate, and the second electrode may be formed on the upper side of the soft polymer hydrogel layer of the polymer hydrogel laminate.

[0013]

[0014] In addition, both the first electrode and the second electrode may be disposed on the surface of the hard polymer hydrogel layer of the polymer hydrogel laminate, and both the first electrode and the second electrode may be disposed on the surface of the soft polymer hydrogel layer of the polymer hydrogel laminate.

[0015] That is, the first electrode and the second electrode can be spaced apart from each other at a predetermined interval between the electrodes, either on the lower side of the hard polymer hydrogel layer or on the upper side of the soft polymer hydrogel layer of the polymer hydrogel laminate.

[0016] For example, the first electrode and the second electrode may be disposed at both ends of the lower portion of the hard polymer hydrogel layer of the polymer hydrogel laminate with a predetermined interval therebetween, or the first electrode and the second electrode may be disposed at both ends of the upper portion of the soft polymer hydrogel layer of the polymer hydrogel laminate with a predetermined interval therebetween.

[0017]

[0018] In addition, the first electrode and the second electrode of the hydrogel-based self-powered smart pressure sensor according to the present invention may include a metal plate and a metal nanowire layer formed on the metal plate.

[0019] At this time, the metal nanowire layer included in the first electrode and the second electrode is preferably provided between the metal thin plate and the polymer hydrogel layer to significantly improve the output of the sensor compared to a conventional flat electrode by increasing the interfacial contact area with the hydrogel layer constituting the pressure sensing unit.

[0020] That is, when the first electrode and the second electrode are arranged opposite each other with the polymer hydrogel laminate interposed therebetween, the metal nanowire layer included in the first electrode is preferably formed between the metal thin plate and the hard polymer hydrogel layer, and the metal nanowire layer included in the second electrode is preferably formed between the metal thin plate and the soft polymer hydrogel layer.

[0021] In addition, when the first electrode and the second electrode are spaced apart from each other on the lower side of the hard polymer hydrogel layer or on the upper side of the soft polymer hydrogel layer, the metal nanowire layer included in the first electrode and the second electrode can be formed between the metal plate and the hard polymer hydrogel layer or the soft polymer hydrogel layer.

[0022]

[0023] Meanwhile, the type of metal forming the metal nanowires included in the first electrode and the second electrode is not particularly limited, and for example, the metal nanowires may be core-shell structured gold-silver nanowires (Ag-Au nanowires) including a core formed of silver (Ag) nanowires and a shell layer formed of gold (Au) covering the outer surface of the silver nanowires.

[0024]

[0025] In the soft polymer hydrogel layer and the hard polymer hydrogel layer constituting the upper and lower portions of the polymer hydrogel laminate constituting the above pressure sensing portion, the soft polymer hydrogel and the hard polymer hydrogel refer to hydrogels having different rigidities, each being relatively soft or hard, due to the difference in the content of a crosslinking agent that reacts with the crosslinkable polymer during hydrogel synthesis.

[0026] That is, the soft polymer hydrogel refers to a polymer hydrogel that exhibits relatively lower rigidity than a hard polymer hydrogel by adding a relatively smaller amount of cross-linking agent during hydrogel synthesis compared to the case of synthesizing a hard polymer hydrogel, and the hard polymer hydrogel refers to a polymer hydrogel that exhibits relatively lower rigidity than a soft polymer hydrogel by adding a relatively larger amount of cross-linking agent during hydrogel synthesis compared to the case of synthesizing a soft polymer hydrogel.

[0027]

[0028] The above soft polymer may be, for example, polyamide, which has relatively soft properties due to the use of a relatively small amount of crosslinking agent during polymer synthesis, but is not necessarily limited thereto.

[0029] In addition, the above-mentioned rigid polymer may be, for example, polyamide, which has relatively soft properties due to the addition of a relatively large amount of crosslinking agent during polymer synthesis, but is not limited thereto.

[0030]

[0031] In addition, the ion-selective polymer included in the polymer hydrogel layer, which has ion selectivity that determines the type of ions that can move between the soft polymer hydrogel layer and the hard polymer hydrogel layer, may be, but is not necessarily limited to, polyacrylic acid (PAAc).

[0032]

[0033] For example, in a polymer hydrogel laminate constituting a pressure sensing unit of a pressure sensor according to the present invention, the hard polymer hydrogel layer may include a crosslinked hard polyacrylamide (PAAm) hydrogel and an electrolyte dispersed within the hydrogel, the polymer hydrogel layer having ion selectivity may include a crosslinked polyacrylic acid (PAAc) hydrogel, and the soft polymer hydrogel layer may include a crosslinked soft polyacrylamide (PAAm) hydrogel and an electrolyte dispersed within the hydrogel.

[0034]

[0035] At this time, the electrolyte in the hard and / or soft polyacrylamide (PAAm) hydrogel may be one or a combination of two or more selected from the group consisting of NaCl, KCl, Na2HPO4, KH2PO4, Na2SO4, Li2SO4, MgSO4, PBS buffer, and Tris-HCl buffer, but is not necessarily limited thereto.

[0036] The hydrogel-based self-powered smart pressure sensor according to the present invention is an innovative hydrogel-based ion-conductive pressure sensor that can output pressure applied as an electric signal (voltage and current) without introducing an external power source, generate an electric signal proportional to the magnitude of the external pressure applied to the sensor, distinguish the location where the external pressure is applied through the sign of the output electric signal, and detect changes in the external pressure and the rate of change through changes in the electric signal.

[0037] Figure 1a is a schematic diagram showing the synthesis of Ag-Au nanowires (NWs) and the fabrication of a hydrogel device, Figure 1b is an FE-SEM image of Ag NWs, and Figures 1c and 1d are an FE-SEM image and EDX mapping results of Ag-Au NWs, respectively (Ag and Au are indicated in red and green, respectively).

[0038] Figures 2a to 2c are results showing the rheological properties of PAAm(S), PAAm(H) and PAAc hydrogels, and Figures 2d to 2f are FE-SEM images of freeze-dried PAAm(S), PAAm(H) and (f) PAAc hydrogels, respectively.

[0039] FIG. 3a is a schematic diagram showing the mechanical-electrical conversion process of a hydrogel device, FIG. 3b and FIG. 3c are results showing the potential difference and current density in the compressed and released states of the hydrogel device, respectively, FIG. 3d and FIG. 3e are results showing the open-circuit voltage and short-circuit current density during continuous compression-release cycles for hydrogel devices with or without Ag-Au NW electrodes, respectively, FIG. 3f is a cyclic voltammetry (CV) curve at a scan rate of 50 mV / s for hydrogel devices with or without Ag-Au NW electrodes, FIG. 3g and FIG. 3f are results measuring the open-circuit voltage and short-circuit current density changes according to the degree of compression for the hydrogel device, FIG. 3i is a result measuring the sensitivity of the hydrogel device, and FIG. 3j is a result of a durability test of the hydrogel device.

[0040] Figure 4 shows the results of comparing the electrical output of hydrogel devices having PAAm(S) / PAAc / PAAm(H), PAAm(S) / PAAc / PAAm(S), and PAAm(S) / PAAm(H) laminated structures, respectively (the total thickness of the laminated hydrogels in each hydrogel device is the same at 6 mm).

[0041] Figures 5a and 5b show the measurement results of the open circuit voltage and short circuit current density of a hydrogel device having a laminated structure of PAAm(H) / PAAc / PAAm(S), respectively.

[0042] FIG. 6a is a schematic diagram showing the structure of a hydrogel-based smart pressure sensor, FIG. 6b is a schematic diagram depicting a change in the sign of an output current according to the application of local pressure to a hydrogel-based smart pressure sensor, FIG. 6c is a result of measuring the output current according to the pressure application position of the hydrogel-based smart pressure sensor, FIGS. 6d and 6e are results of measuring the output current when drawing horizontal and vertical lines in both directions on the hydrogel-based smart pressure sensor, respectively, and FIGS. 6f to 6h are results of measuring the encoded output current obtained when drawing a square and a circle, playing the piano, and writing, respectively, on the hydrogel-based smart pressure sensor.

[0043] Figures 7a and 7b show the results of measuring the output current when drawing diagonal lines in opposite directions.

[0044] Figure 8a is a schematic diagram depicting drawing a line on a hydrogel device, and Figure 8b shows the results of measuring the output current while drawing a line at different speeds (arrows indicate the start and end times of drawing the line).

[0045] In describing the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the gist of the present invention, the detailed description will be omitted.

[0046]

[0047] Embodiments according to the concept of the present invention may be modified in various ways and take various forms. Therefore, specific embodiments are illustrated in the drawings and described in detail in this specification or application. However, this is not intended to limit embodiments according to the concept of the present invention to specific disclosed forms, and it should be understood that all modifications, equivalents, and alternatives included within the spirit and technical scope of the present invention are included.

[0048]

[0049] The terminology used herein is for the purpose of describing specific embodiments only and is not intended to limit the present invention. The singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, it should be understood that the terms "comprises" or "has" indicate the presence of a described feature, number, step, operation, component, part, or combination thereof, but do not preclude the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0050]

[0051] Hereinafter, the present invention will be described in more detail with reference to preferred embodiments. The presented embodiments are merely specific examples of the present invention and are not intended to limit the scope of the present invention.

[0052]

[0053] <Example>

[0054] In this example, core-shell structured Ag-Au nanowires (NWs) and a hydrogel laminate were manufactured as electrode and sensing materials, respectively, and a device and a pressure sensor including an electrode and a hydrogel laminate made of the Ag-Au NWs were fabricated.

[0055]

[0056] 1. Fabrication of Ag-Au nanowire electrodes

[0057] Figure 1a is a schematic diagram showing the process of synthesizing Ag-Au nanowires (NWs) with a core-shell structure.

[0058] First, silver nanowires (Ag NWs) were synthesized using a one-pot polyol process using polyvinylpyrrolidone (PVP) as a capping agent and ethylene glycol (EG) as a reducing agent and solvent according to a publicly known method. That is, 0.2 g of polyvinylpyrrolidone (PVP) was dissolved in 25 mL of ethylene glycol (EG) with stirring at room temperature overnight, and then 0.25 g of silver nitrate (AgNO3) was added. Subsequently, 3.5 g of 0.6 mM iron (III) chloride (FeCl3) in ethylene glycol was added, stirred for 2 minutes, and then immediately transferred to a three-necked round-bottom flask preheated to 130 °C, where the reaction was carried out for 5 hours at 130 °C without stirring. The synthesized Ag NWs were cooled to room temperature and purified by diluting with a mixture of acetone (30 mL) and ethanol (10 mL). Then, the mixture was centrifuged at 4000 rpm for 10 minutes and redispersed in ethanol for further use.

[0059] Ag NW electrodes were fabricated via a vacuum-transfer method. The prepared Ag NW solution (5 mL, 350 mg / mL) was gradually deposited onto a polytetrafluoroethylene (PTFE) membrane filter through a circular mold (diameter 2 mm) under vacuum to form a thin layer of Ag NWs. The Ag NW layer was then transferred to a glass substrate by suction from the opposite side of the PTFE membrane filter. Next, the PTFE membrane filter was removed, leaving a thin layer of Ag NWs on the glass substrate, which was then annealed in an oven at 220 °C for 2 h.

[0060] Au-coated Ag NWs were synthesized by immersing Ag NWs in a reducing solution containing water (10.2 mL), 2% PVP aqueous solution (8 mL), 0.5 M ascorbic acid (0.96 mL), and diethylamine (200 μL) for 60 min and then immersing the Ag NWs in a 0.25 mM chloroauric acid (HAuCl) aqueous solution (10 mL) for 30 min. Finally, the Ag-Au NW electrodes were rinsed with deionized water and dried at room temperature.

[0061] The synthesized Ag NWs were confirmed to have an average diameter of approximately 75 nm and a length of several tens of micrometers (Fig. 1b). In addition, the Au-coated Ag NWs exhibited a uniform and smooth surface morphology (Fig. 1c). The Au coating on the Ag NWs was further confirmed by energy-dispersive X-ray spectroscopy (EDX) mapping results, which clearly showed characteristic Ag and Au signals (Fig. 1d).

[0062]

[0063] 2. Synthesis of polyacrylamide (PAAm) and polyacrylic acid (PAAc) hydrogels

[0064] Polyacrylamide (PAAm) hydrogels were synthesized by free-radical crosslinking polymerization of acrylamide monomers in aqueous solution. The amount of hydrogel crosslinker was adjusted during synthesis to control the stiffness of the hydrogel.

[0065] Under typical conditions, acrylamide (AAm) monomer (3 g) and N,N'-methylenebisacrylamide (MBAA) cross-linker (10 mg) were dissolved in 2 M NaCl aqueous solution (12 mL) to prepare a soft PAAm gel. The mixture was degassed at 60 °C for 30 min and then cooled to room temperature. APS initiator (100 μL, 20 wt% in water) and N,N,N',N'-tetramethylethylenediamine (TEMED) accelerator (10 μL) were sequentially added to the mixture solution. The homogeneous mixture was rapidly transferred onto a glass substrate containing Ag-Au NWs through a circular silicone mold (inner diameter 16 mm, thickness 2 mm). The mold was carefully covered with a glass slide, and polymerization was performed at room temperature for 30 min. The synthesized soft PAAm gel was separated from the glass substrate. At this stage, the Ag-Au NWs were transferred to the bottom of the hydrogel.

[0066] A rigid PAAm gel was prepared using a larger amount of MBAA cross-linker (150 mg) while maintaining all other conditions described above. Furthermore, polyacrylic acid (PAAc) hydrogels were synthesized by dissolving acrylic acid (AAc) monomer (3 g) and MBAA cross-linker (20 mg) in deionized water (12 mL). Using the same procedure as described above, the monomer solution was degassed at 60 °C for 30 min and then cooled to room temperature. The mixed solution was sequentially added with APS initiator (100 μL, 20 wt% in water) and TEMED accelerator (10 μL), then transferred to a circular mold and polymerized in an oven at 70 °C for 1 h.

[0067] The rheological properties of the hydrogel synthesized as described above were evaluated using a rotational rheometer (MCR 302e, Anton Paar, Austria). The hydrogel was subjected to a strain of 1% at a strain rate of 0.05–500 rad s -1Dynamic frequency sweep measurements were performed over a range of angular frequencies (ω). The linear and nonlinear viscoelastic regimes of each hydrogel were measured at 1 rad s. -1 This was confirmed by conducting a dynamic strain sweeping test while increasing the shear strain (0.05–1000%) at a constant frequency.

[0068] Figure 2a is 1 rad s -1The storage modulus (G') of each hydrogel as a function of shear strain at each frequency is shown. The G' values ​​of all hydrogels remain constant in the linear viscoelastic region, whereas they gradually decrease beyond their respective critical yield strains in the nonlinear viscoelastic region. In particular, the G' value (6.5 kPa) of the more crosslinked PAAm hydrogel (PAAm(H)) in the linear viscoelastic region is higher than that (1.5 kPa) of the less crosslinked PAAm hydrogel (PAAm(S)). The higher the G' value, the higher the hydrogel stiffness and mechanical strength. In addition, PAAm(H) exhibits a smaller critical yield strain than PAAm(S), which is because the stiffer hydrogel with a higher crosslinking density undergoes nonlinear failure at a lower strain. PAAc hydrogels exhibited a G' value of 3.5 kPa, which is intermediate between the values ​​above, and a larger linear viscoelastic region. The frequency dependence of the storage (G') and loss (G'') moduli of each hydrogel by dynamic frequency sweep tests at 1% strain showed that G' was significantly larger than G'' throughout the investigated frequency range (Fig. 2b), indicating that these hydrogels are solid-like and elastic. In addition, the G' curves showed a plateau-like curve, which is a typical tendency of stiff hydrogels. The elastic mechanical behavior was also evidenced by the frequency dependence of the complex viscosity (η*). Figure 2c shows that the η* values ​​for the PAAm(S), PAAm(H), and PAAc hydrogels, respectively, initially decreased linearly with increasing frequency, indicating typical Bingham behavior observed in hydrogel structures.The η* value decreased significantly and reached a minimum, after which it continued to increase. This increase in η* was mainly due to the re-establishment of cross-links between molecules, which transformed the hydrogel into a more solid-like material as it was compressed at high angular frequencies. For the PAAm hydrogel, the η* value also increased with increasing cross-linker concentration, indicating that entanglement within the hydrogel was enhanced.

[0069] The freeze-dried hydrogels were analyzed by field emission scanning electron microscopy (FE-SEM) to compare the polymer network structures of the hydrogels, and the results are shown in Figures 2d to 2f. The hydrogels exhibited a hollow porous structure, with average pore sizes of 9.7, 4.6, and 5.5 μm for PAAm(S), PAAm(H), and PAAc, respectively. Although the porous structure in the FE-SEM images is not the actual polymer structure of the hydrated hydrogels, the denser and smaller pores in the order of PAAm(H) > PAAc > PAAm(S) support the rheological properties.

[0070]

[0071] 3. Fabrication of hydrogel-based devices and pressure sensors

[0072] As illustrated in Fig. 1a, a hydrogel device having a stacked structure of Ag-Au NW / PAAm(S) / PAAc / PAAm(H) / Ag-Au NW was fabricated by co-assembling Ag-Au NW electrodes with PAAm and PAAc hydrogel layers. In the hydrogel device, the Au-Ag NW electrodes are positioned on top of the PAAm(S) layer and on the bottom of the PAAm(H) layer, and strong intermolecular hydrogen bonds are formed between the PAAm and PAAc layers, ensuring the physical stability of the stacked hydrogel. At this time, each hydrogel layer had a thickness of 2 mm, a diameter of 16 mm, and a thickness of the entire hydrogel stack of 6 mm.

[0073] The above-described laminated hydrogels were aged overnight in a Ziploc bag and then assembled with two acrylic plates and copper (Cu) foil. The Cu foil (5 x 6 cm) was attached to the surface of the acrylic plate (5 x 5 x 0.5 cm) using Kapton tape. The positive and negative terminals of a Keithley 6514 electrometer were connected to the lower and upper Cu foils, respectively.

[0074] A three-layer hydrogel-based smart pressure sensor was fabricated using PAAm(S) / PAAc / PAAm(H). First, NW-Cu electrodes were attached to both ends of the lower PAAm(H) layer, and a rectangular hydrogel (3.5 cm × 1 cm × 1 mm) was laminated in the sequence of PAAm(S) / PAAc / PAAm(H) to create a laminate. Next, a thin PET film (3.5 cm × 3 cm) wider than the hydrogel surface (3.5 cm × 1 cm) was placed on the PAAm(S) hydrogel layer to protect the device from mechanical failure and minimize pen friction during drawing and writing. To stabilize the entire assembly when various pressures were applied throughout the sensor testing, the hydrogel pressure sensor was fixed to the table using double-sided VHB tape, and the excess PET film that protruded from the hydrogel layer was also taped.

[0075]

[0076] <Experimental Example>

[0077] Using a PMC-1 / 2HS series linear motor, the hydrogel devices fabricated in the above examples were subjected to repeated compression / release cycles at a frequency of 0.25 Hz within a compression range of 25% of the total thickness. During the cycle, PAAm(S) experienced a larger volume change than PAAm(H) due to the difference in stiffness. Therefore, the different degrees of volume reduction during compression resulted in the dissolution of Na from the PAAm(S) layer at the top of the device to the PAAm(H) layer at the bottom. + and Cl -A convective flow of ions is induced. However, due to the cation-selective nature of the PAAc layer between the PAAm(S) and PAAm(H) layers, Na + Transport is facilitated while Cl - Transport is greatly hindered, resulting in a charge imbalance between the upper and lower PAAm hydrogel layers (Fig. 3a). The PAAm(S) layer on the upper part of the device is Cl - The anion is enriched, and the lower PAAm(H) layer is Na + The cations become abundant. This charge imbalance creates a potential difference between the two electrodes, and the potential of the lower electrode becomes higher. Figure 3b shows the potential generated when the hydrogel device is compressed. The generated potential slightly decreased and then maintained during continued compression, which is due to the selective Na + The charge configuration achieved through ion flow is shown to be stable. The excess Na in the lower PAAm(H) hydrogel due to the concentration gradient + Although ions tend to diffuse toward the upper PAAm(S) hydrogel, the diffusion process is inherently slow. It takes several hours to re-establish the equilibrium concentration that explains the stable potential under compression, whereas when the pressure is removed at any time (indicated by the arrow in Figure 3b), the volume of the compressed hydrogel quickly expands to its original state. This is due to the excess Na + This creates a convective flow that returns the charge imbalance to its initial equilibrium state, ultimately returning the potential to the baseline. The potential generates a current flow that is generated and removed during the compression and release processes (Fig. 3c).

[0078] The experimental results described above show that when a linear motor is used to perform compression and release cycles on a hydrogel device, the back and forth movement of mobile ions occurs through convection flow, which is reflected in the open circuit voltage (V ) as shown in Figs. 3d and 3e. OC ) and short-circuit current density (JSC ) is converted into electrical output, which is represented by V OC and J SC The changes are synchronized with the compression and release of the hydrogel, and V OC and J SC The maximum and minimum values ​​were observed in the fully compressed and released states, respectively, and the average peak-to-valley values ​​were 20.6 mV and 226 μAcm, respectively. -2 For comparison, the same hydrogel device was fabricated using only Cu electrodes without Ag-Au NWs. Under the same operating conditions, the device exhibited V OC and J SC are 9.0 mV and 40 μAcm, respectively. -2 , which showed significantly lower values ​​(black lines in Figures 3d and 3e), due to the smaller hydrogel-electrode interface.

[0079] Additionally, cyclic voltammetry (CV) was performed on the hydrogel devices using a Bio-Logic VSP300 potentiostat in the range of -30 to 30 mV at a scan rate of 50 mV / s (Fig. 3f). The hydrogel devices with NW-Cu electrodes (indicated in red) showed significantly higher current densities than the hydrogel devices with only Cu electrodes (indicated in blue). From the CV data, the current densities were 2.36 and 0.29 mFcm for the hydrogel devices with and without NWs, respectively. -2 The calculated capacitance values ​​were obtained. These results suggest that introducing Ag-Au NWs into the electrode significantly increases the interfacial area between the hydrogel and the electrode, which can accommodate more ions and improve the electrical output.

[0080] Additional experiments were performed on hydrogel devices with hydrogel stacking structures (PAAm(S) / PAAc / PAAm(S) or PAAm(S) / PAAm(H)) without controlling the stiffness, including NW-Cu electrodes (Fig. 4). However, these hydrogel devices exhibited minimal electrical output, demonstrating the important role of the stiffness and ion selectivity provided by the PAAm and PAAc hydrogels, respectively. In addition, adjusting the hydrogel stacking order from PAAm(S) / PAAc / PAAm(H) to PAAm(H) / PAAc / PAAm(S) resulted in Na + The direction of movement changes from the lower PAAm(S) layer to the upper PAAm(H) layer, thereby changing the sign of the electrical output signal, thereby reducing the external pressure to Na + It can be confirmed that it induces convective flow of ions (Fig. 5).

[0081] Since the electrical output is closely related to the number of ions moving under external pressure, V OC and J SC It all depends on the degree of compression of the layered hydrogel. When the layered hydrogel is compressed to different degrees in the range of 5 to 30% of its total thickness, V is as expected. OC and J SC All increased with increasing degree of compression (Fig. 3g and h). 30% compression is considered as the upper limit where inelastic deformation and / or destruction of the PAAm(H) hydrogel occurs, limiting the mechanoelectric conversion process. Figure 3i shows that the current density (red) and potential difference (blue) linearly responded to the applied pressure, with a detection range of 7.8–50.9 kPa and a current density of 5.8 μAcm, respectively. -1 kPa -1 and 0.5 mVkPa -1 It shows that the sensitivity value of the pressure sensor according to the present invention is comparable to or even surpasses the sensitivity of a recently developed self-powered sensor. In addition, V OC Wow J SCThe maximum power density of the hydrogel device was determined by multiplying the values ​​of 22 mV and 259 Acm at maximum compression (30%), respectively. -2 Output voltage of 259 μAcm -2 A current density of 5.6 μWcm was generated. -2 This is interpreted as the power output density. These performance indicators were found to surpass those of most state-of-the-art self-powered ionic devices, including ion diodes, electrochemical energy harvesters, and polymer electrolyte hydrogels. The durability of the ion device was examined by performing long-term compression-release cycles at 25% compression, and it was found to exhibit stable performance for 1,000 cycles (Fig. 3j).

[0082]

[0083] For electrical measurements of the fabricated multimode hydrogel-based pressure sensor, schematically illustrated in Fig. 6a, the positive probe of the electrometer was connected to the left electrode, and the negative probe was connected to the right electrode. This electrode configuration, together with the convective ion flow, facilitated local position detection of the applied pressure based on the current signal. As illustrated in the schematic of Fig. 6b, applying pressure to the left side of the upper surface of the laminated hydrogel caused the left lower electrode to have a positive potential. + Convection current is induced and a positive current is generated. Na + Cations can move sideways, but their flow toward the right electrode is impeded by the frictional forces exerted by the solvent and polymer network. Conversely, when pressure is applied to the right side of the laminated hydrogel, Na +A downward convection flow of positive ions is triggered, generating a positive potential and a negative current at the right electrode. The reliability of this process was confirmed by correlating the local locations of applied pressure with the observed current direction (Fig. 6c). Specifically, applying pressure to locations 1 and 2 using a round-tip pen generated synchronized positive currents, whereas applying pressure to locations 3 and 4 generated negative currents. In contrast, applying pressure to location 5, corresponding to the center of the device, induced a current of nearly zero.

[0084] The hydrogel device not only detected the local location of the applied pressure but also identified directional movement. Figure 6d shows that when a horizontal line is drawn from left to right (indicated by a red arrow), the sign of the current synchronized with it changes from positive to negative. This is Na + This is due to the convective motion of ions. Conversely, drawing a horizontal line from right to left (indicated by a blue arrow) changes the current sign in the opposite direction. As shown in Figure 6e, drawing a vertical line from top to bottom (indicated by a red arrow) or bottom to top (indicated by a blue arrow) did not change the current sign. However, the specific position of the vertical line indicates the sign of the output current. An example of current change synchronized with drawing a diagonal line is shown in Figure 7. Furthermore, the hydrogel device according to the present invention integrates the current change information generated while drawing a line to encode any drawn shape into a specific current pattern. For example, drawing a square and a circle in a counterclockwise direction generates a distinct current change sequence corresponding to the combination of component lines (Figure 6f). The hydrogel device also sensed the drawing speed in addition to the drawing direction. Figure 8 shows that drawing quickly results in a rapid change in the current sign, whereas drawing slowly results in a more gradual change.

[0085] As described above, the hydrogel device according to the present invention can not only detect the degree of applied pressure and local location, but also identify the direction and speed of movement through unique current responses, thereby enabling the collective detection of more complex movements. For example, a hydrogel device positioned on a piano keyboard generated synchronized current patterns when playing the notes do, re, and mi, and distinct output currents were also recorded when playing the piano at slow and fast tempos (Fig. 6g). Furthermore, the hydrogel device displayed distinct current patterns encoded when two different individuals wrote the word "hi." Importantly, these patterns were highly reproducible when the same person wrote the same word (Fig. 6h). This consistent reproducibility is attributed to the individual's unique writing characteristics, including stroke order, writing speed, and applied force.

[0086]

[0087] As described above, the present invention proposes an innovative hydrogel-based ion device capable of detecting the magnitude, local position, and directional movement of applied pressure. According to one embodiment of the present invention, the PAAm(S) / PAAc / PAAm(H)-based hydrogel device senses the applied pressure through the cation-selective PAAc hydrogel. + The potential difference and current flow were generated between the NW-Cu electrodes by converting them into ion transport. The NW-Cu electrode formed a higher NW-hydrogel interfacial area than the flat Cu electrode, resulting in a much larger capacitance. Through the demonstration of its performance as a pressure sensor, the pressure-dependent convection Na combined with the electrode configuration of the NW-Cu +It has been demonstrated that various forms of applied pressure can be detected and converted into unique current patterns without complex electrical circuitry through flow. Since more complex movements can be encoded through one-to-one matching of electrical outputs to various pressure-applying movements, the present invention can ultimately be usefully applied to detecting complex human movements.

[0088]

[0089] The present invention is not limited to the above-described embodiments, but can be manufactured in a variety of different forms. Those skilled in the art will appreciate that the present invention can be implemented in other specific forms without altering the technical spirit or essential characteristics of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

[0090] The hydrogel-based self-powering smart pressure sensor according to the present invention is an innovative hydrogel-based ion-conductive pressure sensor that generates an electric signal proportional to the magnitude of external pressure applied to an ion-conductive hydrogel without an external power supply and an additional electric circuit, can distinguish the position where the external pressure is applied through the sign of the output electric signal, and can detect changes in the external pressure and the rate of change through changes in the electric signal.

Claims

1. In a pressure sensor including a first electrode, a pressure sensing unit, and a second electrode, The above pressure sensing unit includes a polymer hydrogel laminate, The above polymer hydrogel laminate is, A rigid polymer hydrogel layer; A polymer hydrogel layer having ion selectivity, which is laminated on the above rigid polymer hydrogel layer; and A pressure sensor comprising a soft polymer hydrogel layer laminated on a polymer hydrogel layer having the above ion selectivity.

2. In paragraph 1, The first electrode is formed on the lower part of the rigid polymer hydrogel layer of the polymer hydrogel laminate, A pressure sensor characterized in that the second electrode is formed on the upper part of the soft polymer hydrogel layer of the polymer hydrogel laminate.

3. In paragraph 2, The first electrode includes a metal plate and a metal nanowire layer, A pressure sensor characterized in that the metal nanowire layer is formed between the metal plate and the hard polymer hydrogel layer.

4. In paragraph 2, The second electrode comprises a metal plate and a metal nanowire layer, A pressure sensor characterized in that the metal nanowire layer is formed between the metal plate and the soft polymer hydrogel layer.

5. In paragraph 1, The first electrode and the second electrode are, A pressure sensor characterized in that the rigid polymer hydrogel layer of the polymer hydrogel laminate is formed at a predetermined interval from each other on the lower side.

6. In paragraph 5, The first electrode and the second electrode are, A pressure sensor characterized in that it is formed on both ends of the lower portion of the rigid polymer hydrogel layer of the polymer hydrogel laminate.

7. In paragraph 5, The first electrode and the second electrode include a metal plate and a metal nanowire layer, A pressure sensor characterized in that the metal nanowire layer is formed between the metal plate and the hard polymer hydrogel layer.

8. In paragraph 1, The first electrode and the second electrode are, A pressure sensor characterized in that the soft polymer hydrogel layer of the polymer hydrogel laminate is formed on top of the polymer hydrogel layer and spaced apart from each other at a predetermined interval.

9. In paragraph 8, The first electrode and the second electrode are, A pressure sensor characterized in that it is formed on both ends of the upper portion of the soft polymer hydrogel layer of the polymer hydrogel laminate.

10. In paragraph 8, The first electrode and the second electrode include a metal plate and a metal nanowire layer, A pressure sensor characterized in that the metal nanowire layer is formed between the metal plate and the soft polymer hydrogel layer.

11. In any one of paragraphs 3, 4, 7 and 10, The above metal nanowires are, a core made of silver (Ag) nanowires; and A pressure sensor characterized by a core-shell structured gold-silver nanowire (Ag-Au nanowire) including a shell layer made of gold (Au) covering the outer surface of the silver nanowire.

12. In paragraph 1, A pressure sensor characterized in that the polymer hydrogel layer having the above ion selectivity enables selective movement of cations.

13. In paragraph 1, The above rigid polymer hydrogel layer comprises a cross-linked rigid polyacrylamide (PAAm) hydrogel and an electrolyte dispersed within the hydrogel, The polymer hydrogel layer having the above ion selectivity comprises a cross-linked polyacrylic acid (PAAc) hydrogel, A pressure sensor characterized in that the soft polymer hydrogel layer comprises a cross-linked soft polyacrylamide (PAAm) hydrogel and an electrolyte dispersed within the hydrogel.

14. In paragraph 13, A pressure sensor characterized in that the electrolyte is one or a combination of two or more selected from the group consisting of NaCl, KCl, Na2HPO4, KH2PO4, Na2SO4, Li2SO4, MgSO4, PBS buffer, and Tris-HCl buffer.

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