A flexible pressure sensor and a preparation method and application thereof

Abstract

This invention discloses a flexible pressure sensor, its fabrication method, and its application, belonging to the field of flexible electronics technology. The fabrication method includes: preparing a spin-coating solution of conductive MXene; using polyacrylamide (PAM) as a flexible substrate and preparing a flexible substrate solution; and repeatedly spin-coating the spin-coating solution and the flexible substrate solution alternately through hydrogen bonding formed by the charged groups on the surface of the conductive MXene and the amino and carbon-oxygen double bonds on the surface of the PAM, thereby obtaining a flexible pressure sensor with a void structure. This invention constructs a flexible pressure sensor with an internal void structure by repeatedly spin-coating conductive MXene with a flexible substrate material. The void structure allows the conductive MXene to produce a larger displacement change under pressure, which is beneficial for forming a larger internal resistance change, thereby improving the sensor's sensitivity.

Description

Technical Field

[0001] This invention relates to the field of flexible electronics technology, and in particular to a flexible pressure sensor, its fabrication method, and its application. Background Technology

[0002] Flexible pressure sensors have been widely used in recent years to assist in patient rehabilitation. These sensors detect minute pressure changes generated during human movement and thus accurately reflect human movement information. Based on these signal changes, the information conveyed by the human body can be accurately detected. Aphasic individuals, due to vocal cord damage, are unable to produce correct sounds (Singh A, Khatri G, Handa K K. Unusual cause of dysphagia and dysphonia[J].BMJ Case Reports,2021,14(6):2430-2442.); those with writing difficulties, due to brain damage, are unable to perform correct writing behaviors, typically exhibiting disordered strokes, mirror writing, etc. (Gopee K, Soorya NR, Bellur R. Apraxicagraphia: An insight into the writing disturbances of posterior aphasias[J].Annals of Indian Academy of Neurology,2009,6:120-123.), resulting in impaired written expression and an inability to convey their thoughts through writing. Flexible pressure sensors accurately monitor changes in laryngeal muscle movement and writing pressure during vocalization by detecting minute pressures generated during writing and producing corresponding sensing waveforms. The laryngeal muscle movement is similar when a person is speaking and not speaking; therefore, the sensor signals generated by laryngeal muscle movement can be used to identify vocal content, helping those with aphasia to express themselves normally. Similarly, although the stroke order and position of strokes differ from those of able-bodied individuals, the writing pressure is similar, allowing for accurate identification of written content through the sensor signals generated during writing, thus helping those with writing difficulties to express themselves accurately.

[0003] Currently, the development of flexible pressure sensors is mainly limited by the materials available. Conductive materials cannot undergo significant deformation under pressure, preventing the sensor from generating a large change in resistance. This results in low sensor sensitivity and an inability to accurately monitor small pressures (Li L, Zheng J, Chen J, et al. Flexible pressure sensors for biomedical applications: From ex-vivo to in-vivo[J]. Advanced Materials Interfaces, 2020, 7(17): 667-675.). The pressure generated by the movement of the laryngeal muscles and writing is relatively small, making it difficult for sensors to accurately monitor these physiological activities. Consequently, sensors cannot accurately determine the true semantic meaning of individuals with aphasia or writing difficulties based on sensor signals. Summary of the Invention

[0004] Based on the technical problem raised in the background above—how to design a pressure sensor with ultra-high sensitivity in a small pressure range—this invention provides a flexible pressure sensor, its fabrication method, and its application.

[0005] This invention provides a flexible pressure sensor and its fabrication method, comprising the following steps:

[0006] Preparation of spin-coating solution for conductive material MXene;

[0007] Polyacrylamide (PAM) was used as a flexible matrix and a flexible matrix solution was prepared.

[0008] By forming hydrogen bonds between the charged groups on the surface of the conductive material MXene and the amino and carbon-oxygen double bonds on the surface of polyacrylamide (PAM), the spin coating liquid and the flexible substrate solution are alternately spin-coated multiple times. Different regions of the MXene layer are selected for spin coating when spin coating the flexible substrate layer, resulting in a flexible pressure sensor with a void structure.

[0009] Furthermore, the preparation of the spin-coating solution includes the following steps:

[0010] Titanium aluminum carbide was etched with hydrochloric acid and lithium fluoride, and the excess hydrochloric acid and lithium fluoride were removed by centrifugation and washing. After filtration, the powder was vacuum dried to obtain MXene powder with an accordion-like layer structure.

[0011] MXene powder was uniformly dispersed in a dispersion solvent to form spin-coating solutions of different concentrations.

[0012] Furthermore, the concentration of the hydrochloric acid is 6-10 mol, and the mass ratio of the lithium fluoride to the aluminum titanium carbide is 1:1.

[0013] Furthermore, the concentration of the spin-coating solution is 30–50 mg / mL.

[0014] Furthermore, the dispersing solvent is anhydrous ethanol, dichloromethane, or dimethyl sulfoxide.

[0015] Furthermore, the spin coating speed of the spin coating liquid is 100-300 r / min, and the spin coating speed of the flexible substrate solution is 200-600 r / min; the number of spin coatings for both the spin coating liquid and the flexible substrate solution is 2-4.

[0016] Furthermore, the preparation of the flexible matrix solution includes: uniformly mixing acrylamide and ammonium persulfate, and slowly initiating polymerization to form a flexible matrix solution; wherein the amount of acrylamide used is 2-5g, and the amount of ammonium persulfate used is 30-60mg.

[0017] This invention provides a flexible pressure sensor, comprising: a conductive MXene layer formed by alternating spin coating of multiple layers and a polyacrylamide (PAM) layer with gaps.

[0018] An embodiment of the present invention discloses an application of a flexible pressure sensor, which is used for semantic monitoring of individuals with aphasia and writing difficulties. The monitoring includes:

[0019] The prepared flexible pressure sensor is cut to a size that can fit the human throat or a tabletop, and the flexible pressure sensor is held in place with alligator clips connected to an external digital source meter.

[0020] After attaching and fixing the flexible pressure sensor to the human throat or a tabletop, secure it externally with tape.

[0021] When a flexible pressure sensor is fixed to the human throat, the semantics of the aphasic person can be identified by the sensor signals generated by the movement of the throat muscles of normal people and aphasic people when they say the same words.

[0022] When a flexible pressure sensor is fixed to a desktop, writing in both normal and abnormal states is performed on the sensor. By comparing the writing behavior in the normal and abnormal states, the semantics of people with writing difficulties can be identified.

[0023] Furthermore, the flexible pressure sensor is cut to the following dimensions:

[0024] The flexible pressure sensors used for semantic monitoring of aphasic individuals are 1.5×5cm, 2×6cm, and 2×4cm in size.

[0025] The flexible pressure sensors used for semantic monitoring of people with writing difficulties are 2×8cm, 2×5cm, and 2×6cm in size.

[0026] The flexible pressure sensor, its fabrication method, and its application provided in this invention have the following advantages compared to the prior art:

[0027] This invention addresses the shortcomings of existing flexible pressure sensors, such as low sensitivity and inability to accurately monitor small pressures. It proposes a flexible pressure sensor with an internal void structure and applies it to true semantic monitoring in individuals with aphasia and writing difficulties. The flexible pressure sensor with an internal void structure is constructed by repeatedly spin-coating MXene conductive material with a flexible substrate material in an alternating manner. The void structure allows the conductive MXene material to undergo greater displacement changes under pressure, facilitating a larger internal resistance change and thus improving the sensor's sensitivity.

[0028] Specifically, MXene conductive material was first prepared by etching with hydrochloric acid and lithium fluoride, and then dispersed in different solutions to prepare spin-coating solutions of varying concentrations. A flexible substrate was then prepared as a solution and spin-coated onto a template to form a flexible substrate layer. MXene was then spin-coated onto the flexible substrate layer to form an MXene layer. The flexible substrate was then spin-coated onto different areas of the MXene layer until each area was completely covered by the spin-coated flexible substrate layer, followed by curing. This process was repeated multiple times with spin-coating of MXene and the flexible substrate, followed by drying and curing, to obtain a flexible pressure sensor with an internal porous structure. This sensor can accurately monitor laryngeal muscle movements during speech. By comparing the signals of aphasic individuals with those of normal speech, the semantic meaning of aphasic individuals can be accurately monitored. When used as a writing pad, it can accurately monitor the pressure generated during writing. By comparing the writing pressure signals of normal individuals and those with writing difficulties, the correct text content intended by those with writing difficulties can be identified, which is of great significance for the accurate expression of those with writing difficulties. Attached Figure Description

[0029] Figure 1 This is a physical image of the flexible pressure sensor used in Example 1 of the present invention for monitoring laryngeal muscle movement.

[0030] Figure 2 This is a physical image of the flexible pressure sensor used in Example 2 of the present invention for monitoring writing pressure.

[0031] Figure 3 This is the microstructure of the flexible pressure sensor in Example 1 of the present invention, which contains a void structure and sensitivity.

[0032] Figure 4 Example 3 of this invention refers to the sensor signals generated by the laryngeal muscle movements when a normal person and a person with aphasia speak different words and sentences (the person with aphasia only performs the movements without making a sound when speaking words);

[0033] Figure 5 The flexible pressure sensor prepared in Example 4 of this invention transmits the sensory signals of different words' laryngeal muscle movements.

[0034] Figure 6 The flexible pressure sensor prepared in Example 5 of this invention transmits the sensing signals of different writing conditions of the text.

[0035] Figure 7 This is the monitoring of the gradually decreasing size of the written characters by the flexible pressure sensor prepared in Embodiment 7 of the present invention. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0037] Aphasia is caused by damage to the vocal cords, preventing normal vocalization. Writing difficulties are caused by damage to the brain's central nervous system, hindering normal writing; this typically manifests as mirror writing, incorrect stroke placement, and progressively smaller handwriting. By comparing the laryngeal muscle movement sensor signals of aphasic individuals and the writing pressure sensor signals of writing difficulties with those of normal individuals, the true semantic meaning of aphasic and writing difficulties can be effectively identified. The pressure generated by laryngeal muscle movement and writing pressure is relatively low, making it difficult for conventional sensors to effectively monitor.

[0038] MXene possesses excellent conductivity and can be well dispersed in other materials, providing good conductivity for flexible sensors. The flexible substrate (polyacrylamide, polyimide) exhibits good mechanical properties and can deform under external stimuli, causing movement of the conductive material inside the sensor and generating a significant change in resistance. Therefore, MXene was selected as the conductive material and combined with the flexible substrate via spin coating to fabricate a flexible pressure sensor with an internal void structure. This sensor was then used for real-world semantic recognition in individuals with aphasia and writing difficulties.

[0039] Based on the above problems and technologies, embodiments of the present invention provide a flexible pressure sensor with high sensitivity under low pressure, which is used for laryngeal muscle movement monitoring and writing pressure monitoring to help aphasic individuals and those with writing difficulties to express themselves effectively. The above technical solution includes:

[0040] Step 1) Preparation of MXene spin-coating solution: Titanium aluminum carbide is etched using hydrochloric acid and lithium fluoride. Excess hydrochloric acid and lithium fluoride are removed by centrifugation and washing. After filtration, the solution is vacuum dried to prepare accordion-layered MXene powder. The prepared MXene powder is uniformly dispersed in a solution at a certain ratio to prepare MXene spin-coating solutions of different concentrations.

[0041] Step 2) Construction of the flexible pressure sensor: Acrylamide and ammonium persulfate are uniformly mixed and slowly polymerized to form a low-viscosity solution. This solution is then spin-coated onto a template to form a uniform flexible substrate spin-coating layer. The flexible substrate solution and the obtained MXene spin-coating solution are alternately spin-coated onto a glass plate. Different areas are selected for spin-coating during the flexible substrate layer spin-coating process to allow for the formation of voids within the layer during drying due to volume shrinkage. After spin-coating, the desired flexible pressure sensor is obtained after drying and curing. Specifically, the MXene spin-coating solution prepared in the first step is spin-coated onto the flexible substrate layer to form a uniform MXene layer. Then, the flexible substrate layer is spin-coated onto the MXene layer again, selecting different areas for spin-coating. Once the flexible substrate spin-coating layer in different areas can uniformly cover the MXene layer, it is cured and stabilized at 50°C. The MXene layer is then spin-coated again. This process is repeated multiple times, followed by drying and curing. After curing, a flexible pressure sensor with a void structure is obtained.

[0042] Step 3) Assembly of the flexible pressure sensor: Cut the flexible pressure sensor prepared in step 2) to the required size so that it can fit tightly to the human throat and fix it in the throat to facilitate the monitoring of the throat movement of the aphasic person; cut the prepared sensor into a rectangle and lay white paper on its surface to facilitate the monitoring of the writing status of the person with writing difficulties.

[0043] Step 4) Monitoring the true semantics of aphasic individuals and those with writing difficulties: A flexible pressure sensor is fixed to the throat to monitor the movement of the laryngeal muscles during speech. Laryngeal muscle movement signals are collected from both normal individuals and aphasic individuals. By comparing the sensor signals, the semantics of aphasic individuals are monitored. The flexible pressure sensor is also used as a writing pad to monitor the writer's handwriting. For the same writing content, writing signals are collected from both normal individuals and those with writing difficulties. By comparing the sensor signals, the writing semantics of those with writing difficulties are monitored.

[0044] in:

[0045] Step 1) uses hydrochloric acid with a concentration of 6-12 mol / L and lithium fluoride to aluminum titanium carbide in a mass ratio of 1:1.

[0046] Step 1) The concentration of MXene spin coating solution is 30-60 mg / mL.

[0047] Step 1) The dispersion solution of MXene is dichloromethane, dimethyl sulfoxide, anhydrous ethanol, etc.

[0048] Step 2) The spin coating speed of MXene spin coating liquid is 200-600 r / min, and the spin coating speed of flexible substrate is 100-300 r / min.

[0049] Step 2) The amount of acrylamide used is 2-5g, and the amount of potassium persulfate used is 30-60mg.

[0050] Step 2) The volume ratio of MXene spin coating solution to flexible substrate solution is 1:1.

[0051] Step 2) The spin coating curing time for the flexible substrate layer is 5 to 15 minutes.

[0052] Step 2) The drying and curing time for the sensor is 1 to 5 hours.

[0053] Step 2) The spin coating is repeated 1 to 3 times.

[0054] Step 3) The sensor sizes used for semantic monitoring of aphasic individuals are 1.5×5cm, 2×6cm, and 2×4cm.

[0055] Step 3) The sensor sizes used for semantic monitoring of people with writing difficulties are 2×8cm, 2×5cm, and 2×6cm.

[0056] In step 4), the voltage used for testing is 1 to 4.5V. The aphasic person's vocalization action is to only simulate the vocalization of words without making a sound (only opening the mouth without making a sound). The writing state of the person with writing difficulties is mirror writing, writing with disordered stroke positions, and writing with the font getting smaller and smaller.

[0057] Step 4) A flexible pressure sensor is fixed to the Adam's apple in the human throat. It monitors the content of speech by the movement of the laryngeal muscles when the throat makes a sound. The voltage is 1 to 4.5V.

[0058] Step 4) Fix the flexible pressure sensor to the desktop as a writing board, ensuring it fits snugly against the desktop without any gaps. Place white paper on the sensor and write on it. Monitor the writing content by measuring the pressure generated during writing. The voltage is 1–4.5V.

[0059] Several specific embodiments of the above technical solution are as follows:

[0060] Example 1

[0061] 1) Preparation of MXene spin-coating solution: 4g of lithium fluoride and 9mol / L hydrochloric acid (40mL) were uniformly mixed in a polytetrafluoroethylene container. Under ice bath conditions, 4g of titanium aluminum carbide was slowly added. After stirring for 24h, the solution was centrifuged and washed multiple times until the pH was greater than 6, and then filtered to obtain MXene powder. The MXene powder was dispersed in 10mL of anhydrous ethanol to a concentration of 40mg / mL.

[0062] 2) Construction of the flexible pressure sensor: Dissolve 2g of acrylamide and 50mg of potassium persulfate in 10mL of water, place in ice water and stir evenly to allow the acrylamide to slowly polymerize and form a low-viscosity solution. Spin-coat 1mL of the solution evenly onto a glass plate at 200r / min to form a uniform thin film. Spin-coat MXene spin-coating solution (300r / min) with a volume of 1mL onto the polyacrylamide film. After the MXene layer dries, spin-coat multiple areas of the MXene layer with polyacrylamide solution (total volume 4mL). After the polyacrylamide completely covers the MXene layer in different areas, dry at 40℃ for 10min to cure. Repeat the spin-coating of MXene and polyacrylamide three times, each time with a volume of 3mL. Dry in an oven at 60℃ for 5h to obtain the flexible pressure sensor. See [link to documentation] Figure 1 and Figure 3 .

[0063] 3) Assembly of the flexible pressure sensor: Cut the sensor prepared in step 2) into a 1.5×5cm piece and connect it to the digital source meter using alligator clips. Fix the 1.5×5cm sensor to the throat area and secure it with tape.

[0064] 4) Monitoring the true semantics of aphasic individuals: Select words and short sentences, and collect sensor signals when normal people are speaking normally and sensor signals (voltage 3V) when aphasic individuals are not speaking (only opening their mouths, without making a sound). Compare the two types of sensor signals to effectively identify the vocal content of aphasic individuals.

[0065] Example 2

[0066] 1) Preparation of MXene spin-coating solution: 3g of lithium fluoride and 6mol / L hydrochloric acid (30mL) were uniformly mixed in a polytetrafluoroethylene container. Under ice bath conditions, 3g of titanium aluminum carbide was slowly added. After stirring for 24h, the solution was centrifuged and washed multiple times until the pH was greater than 6, and then filtered to obtain MXene powder. The MXene powder was dispersed in 10mL of dichloromethane to a concentration of 30mg / mL.

[0067] 2) Construction of the flexible pressure sensor: Dissolve 3g of acrylamide and 40mg of potassium persulfate in 10mL of water, place in ice water and stir evenly to allow the acrylamide to slowly polymerize and form a low-viscosity solution. Spin-coat 4mL of the solution evenly onto a glass plate at 300r / min and dry at 50℃ for 15min to form a uniform film. Spin-coat MXene spin coating solution (100r / min) with a volume of 4mL onto the polyacrylamide film. After the MXene layer dries, spin-coat multiple areas of the MXene layer with polyacrylamide solution (total volume 4mL). After the polyacrylamide completely covers the MXene layer in different areas, dry at 40℃ for 10min to cure. Repeat the spin-coating of MXene and polyacrylamide three times, each time with a coating volume of 2mL, and dry in an oven at 60℃ for 3h. During the drying process, the polyacrylamide layer gradually shrinks, creating voids. After drying, the flexible pressure sensor is obtained. See [link to documentation]. Figure 2 .

[0068] 3) Assembly of the flexible pressure sensor: Cut the sensor prepared in step 2) into 2×4cm pieces and connect it to the digital source meter using alligator clips. Fix the 2×4cm sensor to the throat area and secure it with tape.

[0069] 4) Monitoring the true semantics of aphasic individuals: Select words and short sentences, and collect sensor signals when normal people are speaking normally and sensor signals (voltage 2V) when aphasic individuals are not speaking (only opening their mouths, without making a sound). Compare the two types of sensor signals to effectively identify the content of the aphasic individuals' speech.

[0070] Example 3

[0071] 1) Preparation of MXene spin-coating solution: 5g of lithium fluoride and 12mol / L hydrochloric acid (50mL) were uniformly mixed in a polytetrafluoroethylene container. Under ice bath conditions, 5g of titanium aluminum carbide was slowly added. After stirring for 24h, the solution was centrifuged and washed multiple times until the pH was greater than 6, and then filtered to obtain MXene powder. The MXene powder was dispersed in 10mL of anhydrous ethanol to a concentration of 50mg / mL.

[0072] 2) Construction of the flexible pressure sensor: Dissolve 5g of acrylamide and 50mg of potassium persulfate in 10mL of water, place in ice water and stir evenly to allow the acrylamide to slowly polymerize and form a low-viscosity solution. Spin-coat 2mL of the solution evenly onto a glass plate at 500r / min and dry at 50℃ for 5min to form a uniform film. Spin-coat MXene spin coating solution (200r / min) with a volume of 2mL onto the polyacrylamide film. After the MXene layer dries, spin-coat multiple areas of the MXene layer with polyacrylamide solution (total volume 2mL). After the polyacrylamide completely covers the MXene layer in different areas, dry at 40℃ for 10min to cure. Repeat the spin-coating of MXene and polyacrylamide four times, each time with a volume of 2mL, and dry in an oven at 60℃ for 5h. During the drying process, the polyacrylamide layer gradually shrinks, creating voids. After drying, the flexible pressure sensor is obtained.

[0073] 3) Assembly of the flexible pressure sensor: Cut the sensor prepared in step 2) into 2×6cm pieces and connect it to the digital source meter using alligator clips. Fix the 2×6cm sensor to the throat area and secure it with tape.

[0074] 4) Monitoring the true semantic meaning of aphasic individuals: Select words and short phrases, and collect sensor signals when normal individuals are speaking normally and when aphasic individuals are not speaking (only opening their mouths, without emitting sound) (voltage 4.5V). Compare the two types of sensor signals to effectively identify the content of the aphasic individual's speech. See also Figure 4 (a) Sensory signals of different words (Normal represents normal people, Voiceless represents aphasic people); (b) Sensory signals of different sentences (Normal represents normal people, Voiceless represents aphasic people); The results show that normal people and aphasic people have the same sensory signals for the same words or short sentences. By comparing the sensory signals of the two, the expression content of aphasic people can be identified, which can help them express themselves normally.

[0075] Example 4

[0076] 1) Preparation of MXene spin-coating solution: 2g of lithium fluoride and 12mol / L hydrochloric acid (20mL) were uniformly mixed in a polytetrafluoroethylene container. Under ice bath conditions, 2g of titanium aluminum carbide was slowly added. After stirring for 24h, the solution was centrifuged and washed multiple times until the pH was greater than 6, and then filtered to obtain MXene powder. The MXene powder was dispersed in 10mL of dimethyl sulfoxide to a concentration of 30mg / mL.

[0077] 2) Construction of the flexible pressure sensor: Dissolve 2g of acrylamide and 30mg of potassium persulfate in 10mL of water, place in ice water and stir evenly to allow the acrylamide to slowly polymerize and form a low-viscosity solution. Spin-coat 4mL of the solution evenly onto a glass plate at 400r / min and dry at 50℃ for 15min to form a uniform film. Spin-coat MXene spin coating solution (200r / min) with a volume of 4mL onto the polyacrylamide film. After the MXene layer dries, spin-coat multiple areas of the MXene layer with polyacrylamide solution (total volume 2mL). After the polyacrylamide completely covers the MXene layer in different areas, dry at 40℃ for 10min to cure. Repeat the spin-coating of MXene and polyacrylamide twice, each time with a volume of 3mL. Dry in an oven at 60℃ for 5h. During the drying process, the polyacrylamide layer gradually shrinks, creating voids. After drying, the flexible pressure sensor is obtained.

[0078] 3) Assembly of the flexible pressure sensor: Cut the sensor prepared in step 2) into 2×6cm pieces and connect it to the digital source meter using alligator clips. Fix the 2×6cm sensor to the throat area and secure it with tape.

[0079] 4) Monitoring the true semantic meaning of aphasic individuals: Select words and short phrases, and collect sensor signals when normal individuals are speaking normally and when aphasic individuals are not speaking (only opening their mouths, without emitting sound) (voltage 3.5V). Compare the two types of sensor signals to effectively identify the content of the aphasic individual's speech. See also Figure 5 (a) Sensor signals for “East, West, South, North”; (b) Sensor signals for “Front, Back, Left, Right”; (c) Sensor signals for “East, West, South, North”; (d) Sensor signals for “Front, Back, Left, Right”. The results show that the sensor generates different sensor signals for different words, proving that the sensor can accurately distinguish different words.

[0080] Example 5

[0081] 1) Preparation of MXene spin-coating solution: 4g of lithium fluoride and 10mol / L hydrochloric acid (40mL) were uniformly mixed in a polytetrafluoroethylene container. Under ice bath conditions, 4g of titanium aluminum carbide was slowly added. After stirring for 24h, the solution was centrifuged and washed multiple times until the pH was greater than 6, and then filtered to obtain MXene powder. The MXene powder was dispersed in 10mL of anhydrous ethanol to a concentration of 40mg / mL.

[0082] 2) Fabrication of the flexible pressure sensor: Dissolve 4 g of acrylamide and 40 mg of potassium persulfate in 10 mL of water, place it in ice water and stir evenly to slowly polymerize acrylamide to form a solution with a relatively low viscosity. Spin-coat 4 mL of the solution evenly on a glass plate at a rotation speed of 400 r / min and dry it at 50 °C for 15 min to form a uniform film. Spin-coat the MXene spin-coating solution (100 r / min) on the polyacrylamide film, with a dosage of 4 mL. After the MXene layer is dried, spin-coat the polyacrylamide solution (with a total dosage of 3 mL) on multiple areas of the MXene layer. After the polyacrylamide in different areas completely covers the MXene layer, dry it at 40 °C for 10 min to make it dry and solidify. Spin-coat MXene and polyacrylamide three times, with a spin-coating amount of 2 mL each time, and place it in an oven to dry at 60 °C for 3 h. During the drying process, the polyacrylamide layer gradually shrinks to generate voids, and the flexible pressure sensor can be obtained after the drying is completed.

[0083] 3) Assembly of the flexible pressure sensor: Cut the sensor prepared in step 2) into 2×5 cm and connect it to a digital source meter through alligator clips. Fix the 2×5 cm sensor on the desktop and fix it with tape, and lay white paper on it for easy writing.

[0084] 4) Recognition of the writing semantics of people with writing difficulties: Apply a voltage of 4.5 V to both ends of the sensor through a digital source meter and write on the sensor, and collect the writing signals of normal people and the sensing signals generated in the writing states of mirror writing, stroke disorder writing, and gradually shrinking font respectively. After comparing the abnormal writing signals with the normal writing signals, the semantics of people with writing difficulties can be recognized. See Figure 6 , (a) The writing sensing signal of "行" (normal represents normal people, image represents mirror writing, confusion represents writing with stroke position disorder); (b) The writing sensing signal of "好" (normal represents normal people, image represents mirror writing, confusion represents writing with stroke position disorder); The results show that the sensor can accurately monitor the writing signals under normal writing, mirror writing, and stroke position disorder conditions. After comparing the sensing signals of mirror writing and stroke position disorder writing with the normal writing signals, the correct text content can be recognized.

[0085] Example 6

[0086] 1) Preparation of MXene spin-coating solution: 3g of lithium fluoride and 9mol / L hydrochloric acid (30mL) were uniformly mixed in a polytetrafluoroethylene container. Under ice bath conditions, 3g of titanium aluminum carbide was slowly added. After stirring for 24h, the solution was centrifuged and washed multiple times until the pH was greater than 6, and then filtered to obtain MXene powder. The MXene powder was dispersed in 10mL of anhydrous ethanol to a concentration of 50mg / mL.

[0087] 2) Construction of the flexible pressure sensor: Dissolve 3g of acrylamide and 50mg of potassium persulfate in 10mL of water, place in ice water and stir evenly to allow the acrylamide to slowly polymerize and form a low-viscosity solution. Spin-coat 4mL of the solution evenly onto a glass plate at 600r / min and dry at 50℃ for 15min to form a uniform film. Spin-coat MXene spin coating solution (300r / min) with a volume of 4mL onto the polyacrylamide film. After the MXene layer dries, spin-coat multiple areas of the MXene layer with polyacrylamide solution (total volume 3mL). After the polyacrylamide completely covers the MXene layer in different areas, dry at 40℃ for 10min to cure. Repeat the spin-coating of MXene and polyacrylamide three times, each time with a coating volume of 2mL. Place in an oven and dry at 60℃ for 3h. During the drying process, the polyacrylamide layer gradually shrinks, creating voids. After drying, the flexible pressure sensor is obtained.

[0088] 3) Assembly of the flexible pressure sensor: Cut the sensor prepared in step 2) into 2×8cm pieces and connect it to the digital source meter using alligator clips. Fix the 2×8cm sensor on the table and secure it with tape. Place white paper on the sensor for writing.

[0089] 4) Recognition of writing semantics in individuals with writing difficulties: A 1V voltage is applied across the sensor using a digital source meter, and writing is performed on the sensor. The sensor signals generated by normal writing, mirror writing, writing with disordered strokes, and writing with gradually shrinking characters are collected. By comparing the abnormal writing signals with the normal writing signals, the semantics of individuals with writing difficulties can be identified.

[0090] Example 7

[0091] 1) Preparation of MXene spin-coating solution: 5g of lithium fluoride and 12mol / L hydrochloric acid (50mL) were uniformly mixed in a polytetrafluoroethylene container. Under ice bath conditions, 5g of titanium aluminum carbide was slowly added. After stirring for 24h, the solution was centrifuged and washed multiple times until the pH was greater than 6, and then filtered to obtain MXene powder. The MXene powder was dispersed in 10mL of dichloromethane to a concentration of 50mg / mL.

[0092] 2) Fabrication of the flexible pressure sensor: Dissolve 5 g of acrylamide and 60 mg of potassium persulfate in 10 mL of water, place it in an ice bath and stir evenly to slowly polymerize acrylamide to form a solution with a low viscosity. Spin-coat 2 mL of the solution evenly on a glass plate at a rotation speed of 600 r / min and dry it at 50 °C for 15 min to form a uniform film. Spin-coat the MXene spin-coating solution (300 r / min) on the polyacrylamide film, with a dosage of 2 mL. After the MXene layer is dried, spin-coat the polyacrylamide solution (with a total dosage of 3 mL) on multiple areas of the MXene layer. After the polyacrylamide in different areas completely covers the MXene layer, dry and cure it at 40 °C for 10 min. Spin-coat MXene and polyacrylamide four times repeatedly, with a spin-coating amount of 2 mL each time, and place it in an oven to dry at 60 °C for 2 h. During the drying process, the polyacrylamide layer gradually shrinks to generate voids, and the flexible pressure sensor can be obtained after drying.

[0093] 3) Assembly of the flexible pressure sensor: Cut the sensor prepared in step 2) into 2×6 cm and connect it to a digital source meter through alligator clips. Fix the 2×6 cm sensor on the desktop and fix it with tape, and lay white paper on the sensor for easy writing.

[0094] 4) Recognition of the writing semantics of people with writing difficulties: Apply a voltage of 1 V to both ends of the sensor through a digital source meter and write on the sensor to collect the writing signals of normal people and the sensing signals generated in the writing states of mirror writing, stroke disorder writing, and gradually shrinking font writing respectively. After comparing the abnormal writing signals with the normal writing signals, the semantics of people with writing difficulties can be recognized. See Figure 7 , (a) The Chinese character "大" gets smaller and smaller; (b) The Chinese character "小" gets smaller and smaller; The results show that for the gradually shrinking writing font, the sensor can also accurately recognize its text content.

[0095] Example 8

[0096] 1) Preparation of the MXene spin-coating solution: Uniformly mix 2 g of lithium fluoride and 9 mol / L hydrochloric acid (40 mL) in a polytetrafluoroethylene container. Slowly add 2 g of aluminum titanium carbide under ice bath conditions. After stirring for 24 h, centrifuge and wash the solution. After washing multiple times to make its pH greater than 6, then perform suction filtration to obtain MXene powder. Disperse the MXene powder in 10 mL of dimethyl sulfoxide at a concentration of 30 mg / mL.

[0097] 2) Construction of the flexible pressure sensor: Dissolve 2g of acrylamide and 30mg of potassium persulfate in 10mL of water, place in ice water and stir evenly to allow the acrylamide to slowly polymerize and form a low-viscosity solution. Spin-coat 4mL of the solution evenly onto a glass plate at 300r / min and dry at 50℃ for 15min to form a uniform film. Spin-coat MXene spin coating solution (200r / min) with a volume of 4mL onto the polyacrylamide film. After the MXene layer dries, spin-coat multiple areas of the MXene layer with polyacrylamide solution (total volume 3mL). After the polyacrylamide completely covers the MXene layer in different areas, dry at 40℃ for 10min to cure. Repeat the spin-coating of MXene and polyacrylamide twice, each time with a volume of 3mL, and dry in an oven at 60℃ for 1.5h. During the drying process, the polyacrylamide layer gradually shrinks, creating voids. After drying, the flexible pressure sensor is obtained.

[0098] 3) Assembly of the flexible pressure sensor: Cut the sensor prepared in step 2) into 2×8cm pieces and connect it to the digital source meter using alligator clips. Fix the 2×8cm sensor on the table and secure it with tape. Place white paper on the sensor for writing.

[0099] 4) Recognition of writing semantics in individuals with writing difficulties: A 3V voltage is applied across the sensor using a digital source meter, and writing is performed on the sensor. The sensor signals generated by normal writing, mirror writing, writing with disordered strokes, and writing with gradually shrinking characters are collected. By comparing the abnormal writing signals with the normal writing signals, the semantics of individuals with writing difficulties can be identified.

[0100] In summary, the advantages of the technical solution of the present invention are as follows:

[0101] (1) The conductive material MXene obtained by etching with hydrochloric acid and lithium fluoride has a large number of end-capping groups (-O, -F-, -OH) on its surface, and the flexible matrix (polyacrylamide) has a large number of electronegative groups on its surface. The groups on the flexible matrix and the MXene surface will interact to form a large number of hydrogen bonds, so that the two can be effectively combined.

[0102] (2) The flexible pressure sensor prepared by this invention has ultra-high sensitivity (0-1 kPa, GF = 45.95 kPa-1) in a small pressure range, and can accurately monitor small pressure stimuli. It has good monitoring effect on the muscle movement of the throat when speaking and the small pressure generated by writing. Because of its high sensitivity in a small pressure range, it can also be flexibly applied to pressure monitoring in a small pressure range.

[0103] (3) The present invention constructs a flexible pressure sensor by repeatedly spin coating. The sensor has a void structure inside, which allows the internal conductive network to generate greater deformation under pressure, which is beneficial to the improvement of sensor sensitivity. It can provide a reference for the preparation of high-sensitivity flexible pressure sensors.

[0104] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for preparing a flexible pressure sensor, characterized by, Includes the following steps: Preparation of spin-coating solution for conductive material MXene; Polyacrylamide (PAM) was used as a flexible matrix and a flexible matrix solution was prepared. By forming hydrogen bonds between the charged groups on the surface of the conductive material MXene and the amino and carbon-oxygen double bonds on the surface of polyacrylamide (PAM), the spin coating liquid and the flexible substrate solution are alternately spin-coated multiple times. Different regions of the MXene layer are selected for spin coating when spin coating the flexible substrate layer, resulting in a flexible pressure sensor with a void structure.

2. The method for fabricating the flexible pressure sensor as described in claim 1, characterized in that, The preparation of the spin-coating solution includes the following steps: Titanium aluminum carbide was etched with hydrochloric acid and lithium fluoride, and the excess hydrochloric acid and lithium fluoride were removed by centrifugation and washing. After filtration, the powder was vacuum dried to obtain MXene powder with an accordion-like layer structure. MXene powder was uniformly dispersed in a dispersion solvent to form spin-coating solutions of different concentrations.

3. The method for fabricating the flexible pressure sensor as described in claim 2, characterized in that, The concentration of hydrochloric acid is 6-10 mol, and the mass ratio of lithium fluoride to aluminum titanium carbide is 1:

1.

4. The method for fabricating the flexible pressure sensor as described in claim 2, characterized in that, The concentration of the spin coating solution is 30~50 mg / mL.

5. The method for fabricating a flexible pressure sensor as described in claim 2, characterized in that, The dispersing solvent is anhydrous ethanol, dichloromethane, or dimethyl sulfoxide.

6. The method for fabricating the flexible pressure sensor as described in claim 1, characterized in that, The spin coating speed of the spin coating liquid is 100~300 r / min, and the spin coating speed of the flexible substrate solution is 200~600 r / min; the number of spin coatings for both the spin coating liquid and the flexible substrate solution is 2~4.

7. The method for fabricating the flexible pressure sensor as described in claim 1, characterized in that, The preparation of the flexible matrix solution includes: uniformly mixing acrylamide and ammonium persulfate, and slowly initiating polymerization to form a flexible matrix solution; wherein the amount of acrylamide used is 2~5g, and the amount of ammonium persulfate used is 30~60mg.

8. A flexible pressure sensor prepared according to the method of any one of claims 1 to 7, characterized in that, include: A conductive MXene layer and a gapped PAM layer are formed by alternating spin coating of multiple layers.

9. An application based on the flexible pressure sensor of claim 8, characterized in that, The flexible pressure sensor is used for semantic monitoring of individuals with aphasia and writing difficulties, and the monitoring includes: The prepared flexible pressure sensor is cut to a size that can fit the human throat or a tabletop, and the flexible pressure sensor is held in place with alligator clips connected to an external digital source meter. After attaching and fixing the flexible pressure sensor to the human throat or a tabletop, secure it externally with tape. When a flexible pressure sensor is fixed to the human throat, the semantics of the aphasic person can be identified by the sensor signals generated by the movement of the throat muscles of normal people and aphasic people when they say the same words. When a flexible pressure sensor is fixed to a desktop, writing in both normal and abnormal states is performed on the sensor. By comparing the writing behavior in the normal and abnormal states, the semantics of people with writing difficulties can be identified.

10. The application of the flexible pressure sensor as described in claim 9, characterized in that, The flexible pressure sensor is cut to the following sizes: The flexible pressure sensors used for semantic monitoring of aphasic individuals are 1.5×5cm, 2×6cm, and 2×4cm in size. The flexible pressure sensors used for semantic monitoring of people with writing difficulties are 2×8cm, 2×5cm, and 2×6cm in size.

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