A sandwich conductive composite film prepared based on ultrasonic welding method and application thereof

Abstract

The application provides a kind of preparation sandwich type conductive composite film based on ultrasonic welding method and application, it is related to advanced material preparation technical field.The application uses conductive filler and polyurethane mixture as conductive coating, uses shape memory polymer polyurethane / polycaprolactone as base film, uses solvent phase separation method to adhere conductive coating on the surface of base film, and prepares a kind of sandwich type conductive composite film by ultrasonic welding method.The application explores shape memory driving program of sandwich type conductive composite film and its application in flexible mechanics sensing field, compared with prior art, can realize high strain fixation rate of composite film by improved shape memory driving program, and adjusts sensing sensitivity, on this basis, realizes response to simultaneous or individual movement of multiple joints of human body, and has certain application prospect in wearable electronics field.

Description

Technical Field

[0001] This invention relates to the field of advanced materials preparation technology, specifically to a method for preparing sandwich conductive composite films based on ultrasonic welding and its applications. Background Technology

[0002] With the development of technology, the application of flexible mechanical sensors has moved beyond simple sensing. Besides pursuing higher sensitivity, tunable-sensitivity flexible sensors have also attracted significant attention from researchers in the field of flexible electronics. Conductive composite thin films, as the sensitive elements of flexible mechanical sensors, require structural optimization to improve sensor performance.

[0003] Chinese patent CN113077942A discloses a method for preparing intelligent flexible conductive films using power ultrasound. This method involves uniformly mixing liquid metal with a polymer substrate to obtain a conductive composite film with shape memory function. It solves the problems of small strain deformation rate range (<300%), low conductive filler filling rate, and narrow sensitivity adjustment range in composite films caused by poor interfacial compatibility between the liquid metal and polymer substrate. However, in the composite system of uniformly mixed liquid metal particles and shape memory polymer, under certain strain conditions, the liquid metal inside the composite film undergoes an irreversible shape change, greatly limiting its sensitivity after multiple shape memory strains. When this intelligent flexible conductive film is applied to mechanical sensors, it suffers from low shape memory effect stability, poor mechanical properties, and a narrow sensitivity variation range under different strain conditions. Summary of the Invention

[0004] The purpose of this invention is to provide a sandwich conductive composite film prepared by ultrasonic welding and its application. The sandwich conductive composite film prepared by this invention has a high shape memory effect shape retention rate and high mechanical properties, and a wide range of sensitivity adjustment under different strain conditions.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for preparing sandwich conductive composite films based on ultrasonic welding, comprising the following steps:

[0007] The conductive filler was mixed with an organic solution of a reactive surfactant and then subjected to ultrasonic modification to obtain a conductive filler dispersion.

[0008] The conductive filler dispersion was dried and then mixed with an organic solution of polyurethane to obtain a conductive slurry.

[0009] A mixed organic solution of polyurethane and polycaprolactone is used to form a film, resulting in a first base film and a second base film.

[0010] The conductive paste is coated on the surface of the first base film, and the conductive filler and polyurethane in the conductive paste are precipitated and adhered to the surface of the first base film by phase separation method to obtain a bilayer composite film; the bilayer composite film includes a first base film and a conductive coating adhered to the surface of the first base film.

[0011] The second base film is placed on the surface of the conductive coating to obtain a three-layer composite film;

[0012] The three-layer composite film is ultrasonically welded to obtain a sandwich conductive composite film.

[0013] Preferably, the reactive surfactant includes dopamine hydrochloride or catechols.

[0014] Preferably, the concentration of the conductive filler in the conductive filler dispersion is 10–90 mg / mL; and the concentration of the reactive surfactant is 0.5–3 mg / mL.

[0015] Preferably, the ultrasonic modification treatment is an insertion ultrasonic treatment; the ultrasonic frequency of the ultrasonic modification treatment is 20-27 kHz; the ultrasonic power is 150-200 W; and the ultrasonic modification treatment time is 9-18 min.

[0016] Preferably, the mass ratio of conductive filler to polyurethane in the conductive slurry is 1 to 20:1.

[0017] Preferably, the mass ratio of polyurethane to polycaprolactone in the polyurethane-polycaprolactone mixed organic solution is 1-9:1-9.

[0018] Preferably, the conditions for ultrasonic welding include: ultrasonic generator frequency of 20-50kHz; ultrasonic power of 300-540W; ultrasonic welding time of 1-3s; and ultrasonic welding pressure of 0-20N.

[0019] The present invention provides a sandwich conductive composite film prepared by the method described above, comprising a first base film, a conductive coating and a second base film stacked sequentially; the first base film and the second base film comprise polyurethane and polycaprolactone; the conductive coating comprises conductive filler and polyurethane.

[0020] This invention provides the application of the sandwich conductive composite film described above in the field of mechanical sensing.

[0021] Preferably, the application includes: using a shape memory behavior-driven method to fix multiple sandwich conductive composite films under different strains; using multiple sandwich conductive composite films under different strains in parallel to detect motion signals of multiple joints, thereby identifying simultaneous or independent motion signals of multiple joints;

[0022] The shape memory behavior driving method of the sandwich conductive composite film includes the following steps: sequentially stretching the sandwich conductive composite film at room temperature, heating, shaping at room temperature, and restoring it at elevated temperature.

[0023] This invention provides a method for preparing sandwich conductive composite films based on ultrasonic welding. The invention separates the conductive filler from the polymer substrate and uses a layered preparation method to composite the conductive filler as a conductive coating with the polymer substrate to prepare a sandwich conductive composite film. This avoids interface problems between the conductive filler and the polymer, improves the mechanical properties of the composite film, and expands its sensitivity adjustment range. Simultaneously, the substrate film provides shape memory function, avoiding the influence of conductive filler deformation on the shape memory function of the composite film.

[0024] The sandwich conductive composite film prepared by this invention maintains high conductivity over a large strain range, while its mechanical sensing sensitivity can be adjusted through shape memory function, and it can be applied to the field of human joint motion detection. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the process for preparing the sandwich conductive composite film in an embodiment of the present invention;

[0026] Figure 2 The cross-sectional morphology at the interface of the sandwich conductive composite film prepared in Example 1;

[0027] Figure 3 Sensing sensitivity, shape retention and recovery rate of the sandwich conductive composite film prepared in Example 1 under different fixed strains;

[0028] Figure 4 The results of detecting finger and wrist joint movements using sandwich conductive composite films under constant strain of 150% and 250% are presented.

[0029] Figure 5 The results show the detection of the index and middle finger joint movements using a sandwich conductive composite film under constant strain of 150% and 250%. Detailed Implementation

[0030] This invention provides a method for preparing sandwich conductive composite films based on ultrasonic welding, comprising the following steps:

[0031] The conductive filler was mixed with an organic solution of a reactive surfactant and then subjected to ultrasonic modification to obtain a conductive filler dispersion.

[0032] The conductive filler dispersion was dried and then mixed with an organic solution of polyurethane to obtain a conductive slurry.

[0033] A mixed organic solution of polyurethane and polycaprolactone is used to form a film, resulting in a first base film and a second base film.

[0034] The conductive paste is coated on the surface of the first base film, and the conductive filler and polyurethane in the conductive paste are precipitated and adhered to the surface of the first base film by phase separation method to obtain a bilayer composite film; the bilayer composite film includes a first base film and a conductive coating adhered to the surface of the first base film.

[0035] The second base film is placed on the surface of the conductive coating to obtain a three-layer composite film;

[0036] The three-layer composite film is ultrasonically welded to obtain a sandwich conductive composite film.

[0037] This invention involves mixing a conductive filler with an organic solution of a reactive surfactant and then subjecting it to ultrasonic modification to obtain a conductive filler dispersion. In this invention, the conductive filler is preferably liquid metal particles, more preferably a gallium-indium alloy or a gallium-indium-tin alloy. In this invention, the mass ratio of gallium to indium in the gallium-indium alloy is preferably 65–75:35–25; the mass ratio of gallium, indium, and tin in the gallium-indium-tin alloy is preferably 60–70:25–20:15–10, more preferably 66.5:20.5:13.

[0038] In this invention, the reactive surfactant preferably includes dopamine hydrochloride or catechol compounds. This invention uses a reactive surfactant mixed with a conductive filler, which enables the conductive filler to have good dispersibility, thereby obtaining a stable current signal.

[0039] In this invention, the organic solvent in the organic solution of the reactive surfactant preferably includes N,N-dimethylformamide or dimethyl sulfoxide.

[0040] In this invention, the concentration of the conductive filler in the conductive filler dispersion is preferably 10-90 mg / mL; the concentration of the reactive surfactant is preferably 0.5-3 mg / mL, more preferably 1.5-3 mg / mL.

[0041] In this invention, the ultrasonic modification treatment is preferably performed using immersion ultrasound, more preferably with the ultrasonic probe submerged less than half of the liquid surface. In this invention, the ultrasonic frequency of the ultrasonic modification treatment is preferably 20–27 kHz; the ultrasonic power is preferably 150–200 W; and the ultrasonic modification treatment time is preferably 9–18 min. In this invention, the ultrasonic modification treatment is preferably performed in an ice-water bath. During the ultrasonic modification treatment process, dopamine hydrochloride polymerizes to form PDA, which coats the surface of the dispersed conductive filler.

[0042] After obtaining the conductive filler dispersion, the present invention dries the conductive filler dispersion and mixes it with an organic solution of polyurethane to obtain a conductive slurry. In the present invention, the drying preferably includes: allowing the conductive filler dispersion to stand for 1-2 hours, removing the supernatant, and then drying it in a 70°C oven for 5-6 hours to obtain a slurry-like slurry.

[0043] In this invention, the polyurethane is preferably a polyester-type polyurethane or a polyether-type polyurethane. In this invention, the mass ratio of conductive filler to polyurethane in the conductive slurry is preferably 1–20:1, more preferably 10–15:1. In this invention, the organic solvent in the organic solution of the polyurethane preferably includes N,N-dimethylformamide (DMF) or dimethyl sulfoxide. In this invention, the concentration of the organic solution of the polyurethane is preferably 150–300 mg / mL, more preferably 225 mg / mL.

[0044] This invention involves forming a film from a mixed organic solution of polyurethane and polycaprolactone to obtain a first base film and a second base film. In this invention, the polyurethane in the mixed organic solution of polyurethane and polycaprolactone is preferably a polyether-type polyurethane or a polyester-type polyurethane; the number-average molecular weight of the polycaprolactone is preferably 30,000 to 150,000. In this invention, the organic solvent in the mixed organic solution of polyurethane and polycaprolactone preferably includes N,N-dimethylformamide or dimethyl sulfoxide. In this invention, the total concentration of polyurethane and polycaprolactone in the mixed organic solution of polyurethane and polycaprolactone is preferably 150 to 300 mg / mL; the mass ratio of polyurethane to polycaprolactone in the mixed organic solution of polyurethane and polycaprolactone is preferably 1 to 9:1 to 9, more preferably 1.5:1.

[0045] In this invention, the preferred method for film formation is casting film formation. Preferably, the film formation process includes: degassing the polyurethane-polycaprolactone mixed organic solution in a mold using a casting film formation method, followed by drying at 60°C for 6 hours to obtain a first base film and a second base film.

[0046] In this invention, the thickness of the first basement membrane and the second basement membrane is preferably 50-200 μm, more preferably 150 μm.

[0047] After obtaining the conductive paste and the first substrate film, the present invention coats the conductive paste onto the surface of the first substrate film, and uses a phase separation method to precipitate and adhere the conductive filler and polyurethane in the conductive paste to the surface of the first substrate film, thereby obtaining a bilayer composite film. In the present invention, the size of the first substrate film is preferably 5mm × 25mm; the coating volume of the conductive paste is preferably 50-200μL, more preferably 100μL.

[0048] In this invention, the phase separation method preferably includes: coating the conductive paste onto the surface of the first substrate film, immersing it in a solvent, removing it, and then drying it. In this invention, the solvent is preferably water or ethanol, more preferably ultrapure water. In this invention, the immersion time in the solvent is preferably 5–60 s, more preferably 15–30 s; the drying temperature is preferably 50–70 °C; and the drying time is preferably 5–10 min. This invention preferably repeats the above steps of immersion in the solvent and drying 1–10 times, more preferably 5 times.

[0049] This invention uses a phase separation method to adhere a conductive coating to the surface of a first base film. On the one hand, the solvent (DMF) in the conductive coating can cause the base film to swell slightly. During the phase separation process, the solvent (DMF) is replaced and removed, resulting in better adhesion between the conductive coating and the base film. On the other hand, the conductive coating and the base film contain the same component, polyurethane, which further enhances their adhesion.

[0050] In this invention, the bilayer composite film comprises a first base film and a conductive coating adhered to the surface of the first base film. In this invention, the thickness of the conductive coating is preferably 30–150 μm, more preferably 80 μm.

[0051] After obtaining the bilayer composite film, the present invention places the second base film on the surface of the conductive coating to obtain a trilayer composite film. In this invention, the area of ​​the second base film is preferably the same as the area of ​​the first base film. In this invention, the composition of the second base film is preferably the same as the composition of the first base film.

[0052] Before placing the second base film on the surface of the conductive coating, the present invention preferably further includes: sintering both ends of the conductive coating and embedding copper wires or copper foil in the sintering area. In the present invention, the sintering is preferably mechanical sintering; the width of the sintering is preferably 1-2 mm; and the distance of the sintering area from both ends is preferably 1 mm.

[0053] After obtaining the three-layer composite film, the present invention performs ultrasonic welding on the three-layer composite film to obtain a sandwich conductive composite film. In the present invention, the ultrasonic welding preferably includes: applying pressure and ultrasonic vibration to the three-layer composite film using an ultrasonic probe.

[0054] In this invention, the conditions for ultrasonic welding include: the frequency of the ultrasonic generator is preferably 20–50 kHz, more preferably 20–40 kHz; the ultrasonic power is preferably 300–540 W, more preferably 360 W; the ultrasonic welding time is preferably 1–3 s, more preferably 2 s; and the ultrasonic welding pressure is preferably 0–20 N, more preferably 10 N. In this invention, the shape of the ultrasonic probe used for ultrasonic welding is preferably circular or rectangular; and the shape of the ultrasonic probe is preferably the same as the shape of the three-layer composite film.

[0055] In the ultrasonic welding process for preparing sandwich conductive composite films, the large acoustic impedance at the interface allows the polymer at the interface to rapidly heat to a viscous flow state without damaging the base film. The three-layer composite film is welded under pressure, and the welded interface maintains excellent interfacial bonding after stretching and shape memory cycling. Using polyurethane-polycaprolactone as a substrate can endow the sandwich conductive composite film with shape memory function. The composite film has different sensing sensitivities under different fixed strains, which has great application prospects in the sensitivity adjustment of flexible mechanical sensors.

[0056] This invention provides a sandwich conductive composite film prepared by the method described above, comprising a first base film, a conductive coating, and a second base film stacked sequentially; the first and second base films comprise polyurethane and polycaprolactone; the conductive coating comprises conductive filler and polyurethane. In this invention, the total thickness of the sandwich conductive composite film is preferably 300–600 μm, more preferably 350–400 μm.

[0057] This invention provides the application of the sandwich conductive composite film described above in the field of mechanical sensing, preferably in the field of wearable sensors, and specifically in the detection of joint motion signals. In this invention, the application preferably includes: using a shape memory behavior-driven method to fix multiple sandwich conductive composite films under different strains; using multiple sandwich conductive composite films under different strains in parallel to detect motion signals of multiple joints, thereby identifying simultaneous or independent motion signals of multiple joints.

[0058] In this invention, the shape memory behavior driving method for the sandwich conductive composite film includes the following steps: sequentially subjecting the sandwich conductive composite film described in the above technical solution to room temperature stretching, heating, room temperature shaping, and temperature recovery. In this invention, the strain during room temperature stretching is preferably 0-400%, more preferably 150-350%, and even more preferably 250%. After room temperature stretching, the shape of the sandwich conductive composite film is fixed by external force. In this invention, the heating temperature is preferably 60-70°C; the holding time is preferably 15-30 minutes. In this invention, the room temperature shaping is preferably achieved by air cooling for 15 minutes at room temperature. After room temperature shaping, the external force is removed to achieve the shaping of the sandwich conductive composite film. In this invention, the temperature for temperature recovery is preferably 60-80°C, more preferably 70-80°C; the holding time is preferably 10-15 minutes. This invention achieves shape recovery of the sandwich conductive composite film through temperature recovery.

[0059] The shape memory behavior driving method provided by this invention can significantly improve the shape memory behavior retention rate of sandwich conductive composite films. This invention can enable sandwich conductive composite films to have a high strain fixation rate and adjust their sensing sensitivity through the shape memory driving method, thereby achieving a response to the simultaneous or individual movement of multiple joints in the human body, which has certain application prospects in the field of wearable electronics.

[0060] In this invention, the sandwich-type conductive composite film is preferably bonded to the joint surface; the sandwich-type conductive composite film is preferably connected to an electrochemical workstation via alligator clips for motion signal detection. In this invention, the voltage for motion signal detection is preferably 0.01–1V; the detection time is preferably 1000s.

[0061] In a specific embodiment of the present invention, the preferred method of application includes: fixing the strain of the two sandwich conductive composite films at 150% and 250% respectively; attaching the two sandwich conductive composite films to two different joints and connecting them to an electrochemical workstation; and using the electrochemical workstation to record the current changes during the movement of the two joints in real time.

[0062] This invention can distinguish between the simultaneous or individual movements of multiple joints by signal differences. Unlike traditional multi-joint motion detection which requires multiple signal transmission channels, this application can provide real-time feedback on the motion signals of multiple joints simply by connecting multiple sandwich conductive composite films with different sensitivities in parallel.

[0063] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0064] Example 1

[0065] like Figure 1 As shown, 15 mg of dopamine hydrochloride and 10 mL of N,N-dimethylformamide were added to a beaker. After dissolution, 900 mg of liquid metal particles (Ga 66.5 wt%, In 20.5 wt%, Sn 13 wt%) were added. The mixture was sonicated in an ice-water bath for 9 min at an ultrasonic amplitude of 20 kHz and an ultrasonic power of 200 W, with the ultrasonic probe submerged less than half of the liquid surface, to obtain a liquid metal particle dispersion. After the liquid metal particle dispersion was allowed to stand for 1 h, the supernatant was removed, and the mixture was dried in an oven at 70 °C for 5 h to obtain a slurry-like liquid metal particle slurry. 400 μL of a 225 mg / mL TPU DMF solution was added to the slurry, and the mixture was stirred for 1 h to ensure uniform mixing, thus obtaining a conductive slurry (LMs slurry).

[0066] 1.2 g of polyurethane (TPU) and 0.8 g of polycaprolactone (PCL) were dissolved in the organic solvent DMF to obtain a TPU-PCL mixed organic solution with a concentration of 150 mg / mL. The TPU-PCL mixed organic solution was used to prepare a base film (TP base film) with a thickness of 150 μm by casting film formation method, and the film was cut into rectangular strips of 5 mm × 25 mm.

[0067] 100 μL of the conductive paste was uniformly coated on the surface of the substrate film and quickly immersed in ultrapure water for 15 seconds. Liquid metal particles and TPU were precipitated and adhered to the surface of the substrate film by phase separation. After drying at 70°C for 5 minutes to remove moisture and solvent, the above coating steps were repeated 5 times to obtain a double-layer composite film with a conductive coating (LMs conductive layer) thickness of 80 μm. Mechanical sintering was performed at both ends of the conductive coating. After embedding copper wires, a substrate film of the same area was covered on the surface to obtain a three-layer composite film.

[0068] A pressure of 10N was applied to the three-layer composite film using an ultrasonic probe. The ultrasonic frequency was 20kHz, the ultrasonic power was 360W, and the welding time was 2s to obtain a sandwich conductive composite film (TP-LMs-TP composite film).

[0069] The total thickness of the sandwich conductive composite film prepared in this embodiment is 350 μm.

[0070] Figure 2 The cross-sectional morphology at the interface of the sandwich conductive composite film is given by... Figure 2 It can be seen that after ultrasonic welding, the interface between the base film and the conductive coating is well bonded, and no interface debonding occurs after stretching. Statistical analysis of the particle size difference of the liquid metal in the conductive coating indicates that the particle size and distribution of the liquid metal particles were not changed under these welding conditions.

[0071] The sandwich conductive composite film prepared in this embodiment has an elongation at break of 800%, which is significantly better than the 400% elongation at break of the conductive film in CN113077942A.

[0072] Example 2

[0073] like Figure 1 As shown, 15 mg of dopamine hydrochloride and 10 mL of N,N-dimethylformamide were added to a beaker. After dissolution, 900 mg of liquid metal particles (Ga 66.5 wt%, In 20.5 wt%, Sn 13 wt%) were added. The mixture was ultrasonicated in an ice-water bath for 18 min at an ultrasonic amplitude of 20 kHz and an ultrasonic power of 200 W, with the ultrasonic probe submerged less than half of the liquid surface, to obtain a liquid metal particle dispersion. After the liquid metal particle dispersion was allowed to stand for 1 h, the supernatant was removed, and the mixture was dried in an oven at 70 °C for 5 h to obtain a slurry-like liquid metal particle slurry. 400 μL of a 225 mg / mL TPU DMF solution was added to the slurry, and the mixture was stirred for 1 h to ensure uniform mixing, thus obtaining a conductive slurry.

[0074] 1.2 g of polyurethane (TPU) and 0.8 g of polycaprolactone (PCL) were dissolved in the organic solvent DMF to obtain a TPU-PCL mixed organic solution with a concentration of 150 mg / mL. The TPU-PCL mixed organic solution was used to prepare a base film with a thickness of 150 μm by casting film formation method, and the film was cut into rectangular strips of 5 mm × 25 mm.

[0075] 100 μL of the conductive paste was uniformly coated on the surface of the substrate film and quickly immersed in ultrapure water for 30 seconds. Liquid metal particles and TPU were precipitated and adhered to the surface of the substrate film by phase separation. After drying at 70°C for 5 minutes to remove moisture and solvent, the above coating steps were repeated 10 times to obtain a double-layer composite film with a conductive coating thickness of 150 μm. Mechanical sintering was performed at both ends of the conductive coating. After embedding copper wires, a substrate film of the same area was covered on the surface to obtain a three-layer composite film.

[0076] A pressure of 20N was applied to the three-layer composite film using an ultrasonic probe. The ultrasonic frequency was 20kHz, the ultrasonic power was 540W, and the welding time was 1s, resulting in a sandwich conductive composite film.

[0077] The total thickness of the sandwich conductive composite film prepared in this embodiment is 400 μm.

[0078] Comparative Example 1

[0079] 15 mg of dopamine hydrochloride and 10 mL of N,N-dimethylformamide were added to a beaker. After dissolution, 900 mg of liquid metal particles (Ga 66.5 wt%, In 20.5 wt%, Sn 13 wt%) were added. The mixture was sonicated in an ice-water bath for 18 min at an ultrasonic amplitude of 20 kHz and an ultrasonic power of 200 W, with the ultrasonic probe submerged less than half of the liquid surface, to obtain a liquid metal particle dispersion. After the liquid metal particle dispersion was allowed to stand for 1 h, the supernatant was removed, and the mixture was dried in an oven at 70 °C for 5 h to obtain a slurry-like liquid metal particle slurry. 400 μL of a 150 mg / mL TPU DMF solution was added to the slurry, and the mixture was stirred for 1 h to ensure uniform mixing, thus obtaining a conductive slurry.

[0080] 1.2 g of polyurethane (TPU) and 0.8 g of polycaprolactone (PCL) were dissolved in the organic solvent DMF to obtain a TPU-PCL mixed organic solution with a concentration of 150 mg / mL. The TPU-PCL mixed organic solution was used to prepare a base film with a thickness of 150 μm by casting film formation method, and the film was cut into rectangular strips of 5 mm × 25 mm.

[0081] 100 μL of the conductive paste was uniformly coated on the surface of the substrate film and quickly immersed in ultrapure water for 30 seconds. Liquid metal particles and TPU were precipitated and adhered to the surface of the substrate film by phase separation. After drying at 70°C for 5 minutes to remove moisture and solvent, the above coating steps were repeated once to obtain a double-layer composite film with a conductive coating thickness of 30 μm. Mechanical sintering was performed at both ends of the conductive coating. After embedding copper wires, a substrate film of the same area was covered on the surface to obtain a three-layer composite film.

[0082] The three-layer composite film was subjected to a pressure of 20N using an ultrasonic probe. The ultrasonic frequency was 20kHz, the ultrasonic power was 200W, and the welding time was 5s. Due to the low welding power, a multilayer conductive composite film could not be obtained.

[0083] Test Example 1

[0084] The sandwich conductive composite film prepared in Example 1 was stretched to strains of 150%, 250%, and 350% using a stretching machine. Its shape was then constrained by clamps and placed in an oven at 70°C for 15 minutes. After removal and cooling at room temperature for 15 minutes, the clamps were removed to fix its shape, and its shape retention rate was tested. Under these conditions, its sensing sensitivity within a 20% strain range was tested, yielding sensing sensitivities of -3.150, -0.486, and 2.322 at strains of 150%, 250%, and 350%, respectively. The composite film was then placed in an oven at 70°C for 15 minutes to allow its shape to recover, and its recovery rate was tested. The shape retention rates of the sandwich conductive composite film at strains of 150%, 250%, and 350% were 94.2%, 96.2%, and 97.5%, respectively, with recovery rates of 68.9%, 59.2%, and 47.6%, respectively.

[0085] Figure 3 The sensor sensitivity, shape retention rate, and recovery rate of the sandwich conductive composite film prepared in Example 1 under different fixed strains are shown. The sensitivity adjustment range of the sandwich conductive composite film prepared in this invention is -3.150 to 2.322, which is a wide adjustment range.

[0086] Comparative Test Example 1

[0087] The sandwich conductive composite film prepared in Example 1 was heated in an oven at 70°C for 15 minutes and then stretched to strains of 150%, 250%, and 350%. Its shape was then constrained with clamps, removed, and cooled at room temperature for 15 minutes. The clamps were removed to fix its shape, and its shape retention rate was tested. Under these conditions, its conductivity was 0 in all cases. The composite film was then placed in an oven at 70°C for 15 minutes to allow its shape to recover, and its recovery rate was tested. The shape retention rates of the sandwich conductive composite film at strains of 150%, 250%, and 350% were 83.2%, 88.2%, and 93.5%, respectively, and the recovery rates were 38.9%, 49.2%, and 57.6%, respectively.

[0088] Based on the results of Test Example 1 and Comparative Test Example 1, it can be seen that in Comparative Test Example 1, the shape memory program for the composite film involves heating the film, stretching it to induce strain, and then cooling it to set the shape. The film's conductivity was found to be 0, making it unsuitable as a strain sensor. However, in Test Example 1, the composite film was first stretched and strained before being heated and cooled to set the shape; in this case, the film was conductive. This demonstrates that only when the present invention employs a shape memory behavior program involving stretching, heating, room temperature setting, and temperature recovery can it be used as a strain sensor.

[0089] Application Example 1

[0090] The sandwich conductive composite film with a strain of 150% from Test Example 1 was attached to the index finger joint, and the sandwich conductive composite film with a strain of 250% was attached to the wrist joint. The two sandwich conductive composite films were connected in parallel to the electrochemical workstation. The voltage was set to 0.01V and the test time was 1000s. The real-time current during the joint movement was recorded and converted into a curve of normalized resistance changing with time.

[0091] Figure 4 The results of detecting finger and wrist joint movements using a sandwich conductive composite film under constant strain of 150% and 250% are shown. When the index finger joint moves alone, the peak value of the normalized resistance change is 4%. When the wrist joint moves alone, the peak value of the normalized resistance change is 1.5%. When both joints move simultaneously, the peak value of the normalized resistance change is 5.5%. When the two joints move step by step in the sequence of index finger bending - wrist and index finger bending simultaneously - wrist returning - index finger returning, the normalized resistance changes accordingly. It first reaches 4% and obtains a peak. Then the normalized resistance signal increases to 5.5%, then decreases to 4%, and finally returns to the initial state.

[0092] Because the sandwich conductive composite film at 150% strain has higher sensitivity, it exhibits a larger signal change, while the sandwich conductive composite film at 250% strain has lower sensitivity and exhibits a smaller signal change. When the composite films at different constant strains are connected in series to detect the fingers and wrists, different joint movements can be detected based on the magnitude of their output signals. For example, a larger output signal can be identified as index finger movement, while a smaller output signal can be identified as wrist movement. Furthermore, each joint also has a different signal output when moving step by step.

[0093] Application Example 2

[0094] The sandwich conductive composite film with a strain of 150% from Test Example 1 was attached to the middle finger joint, and the sandwich conductive composite film with a strain of 250% was attached to the index finger joint. The two sandwich conductive composite films were connected in parallel to the electrochemical workstation. The voltage was set to 0.01V and the test time was 1000s. The real-time current during the joint movement was recorded and converted into a curve of normalized resistance changing with time.

[0095] Figure 5 The results of the sandwich conductive composite film on the movement of the index and middle finger joints under constant strain of 150% and 250% are as follows: when the index finger joint moves alone, the peak value of the normalized resistance change is 5%; when the middle finger joint moves alone, the peak value of the normalized resistance change is 18%; and when both joints move simultaneously, the peak value of the normalized resistance change is 23%.

[0096] Because the composite film at 150% strain has higher sensitivity, it exhibits a larger signal change, while the composite film at 250% strain has lower sensitivity and exhibits a smaller signal change. When the composite films at different constant strains are connected in parallel to detect the movement of two fingers, different finger movements can be detected based on the magnitude of their output signals. For example, a larger output signal can be identified as the movement of the middle finger, a smaller output signal can be identified as the movement of the index finger, and the largest output signal indicates that both fingers are moving simultaneously.

[0097] This invention uses a mixture of conductive filler and polyurethane as a conductive coating, and a shape memory polymer polyurethane / polycaprolactone as a base film. The conductive coating is adhered to the surface of the base film using a solvent phase separation method, and a sandwich-type conductive composite film is prepared by ultrasonic welding. This invention explores the shape memory actuator of the sandwich-type conductive composite film and its application in the field of flexible mechanical sensing. Compared with existing technologies, the improved shape memory actuator can achieve a high strain fixation rate for the composite film and adjust its sensing sensitivity. Based on this, it can respond to the simultaneous or individual movements of multiple joints in the human body, showing promising application prospects in the field of wearable electronics. As can be seen from the application examples, the sandwich-type conductive composite film prepared by this invention can be applied to the field of intelligent human motion monitoring.

[0098] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing sandwich conductive composite films based on ultrasonic welding, comprising the following steps: A conductive filler is mixed with an organic solution of a reactive surfactant and then subjected to ultrasonic modification to obtain a conductive filler dispersion; the conductive filler is a liquid metal particle. The conductive filler dispersion was dried and then mixed with an organic solution of polyurethane to obtain a conductive slurry. A mixed organic solution of polyurethane and polycaprolactone is used to form a film, resulting in a first base film and a second base film. The conductive paste is coated on the surface of the first base film, and the conductive filler and polyurethane in the conductive paste are precipitated and adhered to the surface of the first base film by phase separation method to obtain a bilayer composite film; the bilayer composite film includes a first base film and a conductive coating adhered to the surface of the first base film. The second base film is placed on the surface of the conductive coating to obtain a three-layer composite film; The three-layer composite film is ultrasonically welded to obtain a sandwich conductive composite film. The reactive surfactant includes dopamine hydrochloride or catechols; The mass ratio of conductive filler to polyurethane in the conductive slurry is 1~20:1; The conditions for ultrasonic welding include: ultrasonic generator frequency of 20~50kHz; ultrasonic power of 300~540W; ultrasonic welding time of 1~3s; and ultrasonic welding pressure of 0~20N.

2. The method according to claim 1, characterized in that, The concentration of the conductive filler in the conductive filler dispersion is 10~90 mg / mL; the concentration of the reactive surfactant is 0.5~3 mg / mL.

3. The method according to claim 1, characterized in that, The ultrasonic modification treatment is an insertion ultrasonic treatment; the ultrasonic frequency of the ultrasonic modification treatment is 20~27kHz; the ultrasonic power is 150~200W; and the ultrasonic modification treatment time is 9~18min.

4. The method according to claim 1, characterized in that, The mass ratio of polyurethane to polycaprolactone in the polyurethane-polycaprolactone mixed organic solution is 1~9:1~9.

5. A sandwich conductive composite film prepared by the method according to any one of claims 1 to 4, comprising a first base film, a conductive coating, and a second base film stacked sequentially; the first base film and the second base film comprising polyurethane and polycaprolactone; the conductive coating comprising conductive filler and polyurethane.

6. The application of the sandwich conductive composite film according to claim 5 in the field of mechanical sensing.

7. The application according to claim 6, characterized in that, include: Using a shape memory behavior-driven method, multiple sandwich conductive composite films are fixed under different strains; multiple sandwich conductive composite films under different strains are connected in parallel to detect motion signals of multiple joints, thereby identifying the simultaneous or independent motion signals of multiple joints. The shape memory behavior driving method of the sandwich conductive composite film includes the following steps: sequentially stretching the sandwich conductive composite film at room temperature, heating, shaping at room temperature, and restoring it at elevated temperature.

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