A flexible conductive film with high substrate adhesion and its preparation method and application

Abstract

This invention discloses a flexible conductive film with high substrate adhesion, its preparation method, and its applications, belonging to the field of flexible conductive film and its preparation technology. This invention solves the problem of low interfacial stability between the substrate and conductive material in the sensing layer of existing flexible sensors. First, an uncured PDMS film of the same material is spin-coated onto a PDMS substrate. Then, a conductive material is sprayed onto the uncured PDMS film under heating conditions. Utilizing the characteristic that the two materials can fuse together during heating and curing, the mechanical mismatch caused by delamination between the conductive material and the substrate is eliminated, improving interfacial stability. Simultaneously, the interlocking structure between the sprayed conductive material and the uncured PDMS improves the interfacial adhesion between the conductive material and the substrate. The flexible piezoresistive sensor assembled using this flexible conductive film exhibits good cyclic stability and can monitor human activities (such as elbow flexion and gait) in real time.

Description

Technical Field

[0001] This invention relates to a flexible conductive film with high substrate adhesion, its preparation method and application, belonging to the field of flexible conductive film and its preparation technology. Background Technology

[0002] The acquisition of human physiological electrical signals can directly reflect the body's health status. Long-term monitoring of these signals can predict the onset of certain diseases, allowing for timely intervention. Currently, traditional rigid electronic devices are typically made of rigid materials, making it difficult to meet the requirement of conformal adhesion between sensors and human skin, resulting in significant signal errors. Furthermore, traditional medical electronic devices are bulky, require long queues, and cannot meet the needs of long-term monitoring. Therefore, flexible wearable electronic devices have emerged. Unlike traditional rigid electronic devices, they possess advantages such as better flexibility, extensibility, portability, and the ability to bend freely, and are widely used in medical health monitoring, sports and fitness, and other fields. Flexible sensors are a crucial component of flexible wearable electronic devices, serving as a bridge for two-way communication between the human body and external devices. High sensor stability is essential for achieving long-term accurate pressure detection in various practical application scenarios. However, the stability of existing flexible sensors still faces challenges, such as low interface stability between the substrate of the sensing layer and the conductive material, which seriously hinders the practical application of flexible sensors. Summary of the Invention

[0003] This invention addresses the problem of low interface stability between the substrate and conductive material of the sensing layer in existing flexible sensors by providing a flexible conductive film with high substrate adhesion, its preparation method, and its application.

[0004] The technical solution of this invention:

[0005] One objective of this invention is to provide a method for preparing a flexible conductive film with high substrate adhesion, the method comprising the following steps:

[0006] (1) Uncured PDMS solution was spin-coated onto hydrophobic glass, degassed under vacuum, cured by heating, and peeled off to obtain a PDMS film;

[0007] (2) Uncured PDMS solution was spin-coated onto the PDMS film, and carbon nanofiber ethanol solution was sprayed on under heating conditions. After spraying, the film was heated and cured to obtain a flexible conductive film with high substrate adhesion.

[0008] Further specifying, (1) the glass hydrophobication process is as follows: the glass surface is subjected to plasma treatment and fluorination treatment in sequence.

[0009] To further specify, plasma treatment is performed in an oxygen atmosphere at 30–60 W for 3–5 minutes.

[0010] To further specify, the fluorination treatment is as follows: the glass surface that has undergone plasma treatment is treated with 1H,1H,2H,2H-perfluorooctyltrimethoxysilane vapor at 200℃ for 50 to 70 minutes.

[0011] Further specified, (1) the heating curing temperature is 90℃ and the time is 5h.

[0012] Further specified, the uncured PDMS solution in (1) and (2) is made by mixing A glue and B glue in a mass ratio of 10 to 15:1.

[0013] Further specifying, (2) is to spray under conditions of 90 to 150°C.

[0014] Further specifying, the spraying process parameters in (2) are: spraying angle of 80 to 100°, number of spraying times of 15 to 22, and concentration of carbon nanofiber ethanol solution of 1 to 1.5 mg / mL.

[0015] Further specified, (2) the heating curing temperature is 120℃ and the time is 30min.

[0016] The second objective of this invention is to provide a flexible conductive film with high substrate adhesion prepared by the above method.

[0017] The third objective of this invention is to provide an application of the aforementioned flexible conductive film with high substrate adhesion, specifically as a flexible sensing layer in a flexible piezoresistive sensor.

[0018] Beneficial effects:

[0019] This invention first spin-coates an uncured PDMS film of the same material onto a PDMS substrate. Then, under heating conditions, a conductive material is sprayed onto the uncured PDMS film. Utilizing the characteristic that the two materials can fuse together during heating and curing, this eliminates the mechanical mismatch caused by delamination between the conductive material and the substrate, improving interfacial stability. Simultaneously, the interlocking structure between the sprayed conductive material and the uncured PDMS improves the interfacial adhesion between the conductive material and the substrate. Furthermore, spraying the conductive material onto the uncured PDMS film under heating conditions improves the dispersion of the conductive material and prevents sedimentation within the uncured PDMS film. Moreover, this method achieves good conductivity even with relatively low carbon nanofiber density compared to blending methods. Attached Figure Description

[0020] Figure 1 A process flow diagram for fabricating the flexible piezoresistive sensor of this invention;

[0021] Figure 2 A cross-sectional scanning electron microscope image of the flexible conductive film prepared in Example 1;

[0022] Figure 3 This is a comparison diagram of the adhesion strength between the conductive layer and the substrate of the flexible conductive film prepared in Example 1 and Comparative Example 1.

[0023] Figure 4 This is a schematic diagram of the sensing mechanism of the flexible piezoresistive sensor prepared in Example 1;

[0024] Figure 5 The image shows a comparison of the sensing signals of the flexible piezoresistive sensor prepared in Example 1 under the same and different applied pressures.

[0025] Figure 6 The real-time response data of the flexible piezoresistive sensor prepared in Example 1 for monitoring elbow flexion;

[0026] Figure 7 The data provided are real-time response data of the flexible piezoresistive sensor prepared in Example 1 for monitoring human standing gait. Detailed Implementation

[0027] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0028] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0029] Secondly, the term "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in various places throughout this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive of other embodiments.

[0030] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0031] Example 1

[0032] (1) Preparation of hydrophobic glass

[0033] To facilitate the peeling of the prepared PDMS film from the glass, the glass needs to be hydrophobically treated. The detailed process is as follows:

[0034] First, the surface of the glass is subjected to plasma treatment, specifically in an oxygen atmosphere at 30W for 3 minutes.

[0035] Then, at 200°C, the glass surface is fluorinated using vapor generated from 1H,1H,2H,2H-perfluorooctyltrimethoxysilane (Aladdin Reagent Co., Ltd.) for 1 hour.

[0036] Finally, let the hydrophobic glass cool before using it.

[0037] (2) Fabrication of flexible sensing layer

[0038] First, an uncured PDMS solution (PDMS, Dow Corning Sylgard 184, precursor to curing agent mass ratio 10:1) was spin-coated onto hydrophobic glass (spin-coating speed 4000 r / min), to a thickness of approximately 70 μm. Second, to prevent interference from air bubbles in the solution, the uncured PDMS solution was degassed under vacuum for approximately 10 minutes. Third, the glass with the spin-coated solution was placed in an oven and cured at 90°C for 5 hours. The resulting PDMS film was then peeled off.

[0039] Then, an uncured PDMS solution (PDMS, Dow Corning, USA, model Sylgard 184, precursor to curing agent mass ratio of 10:1) was spin-coated onto the PDMS film surface. While heating (120°C), a carbon nanofiber ethanol solution with a concentration of 1.5 mg / mL (the carbon nanofibers are approximately 8 μm long and 150 nm in diameter, manufactured by Showa Denko, Japan) was sprayed at a 90° angle, and the number of sprays was 20.

[0040] Finally, the membrane was cured at 120°C for 30 minutes to obtain a flexible conductive membrane, in which the amount of carbon nanofibers was approximately 1.2 mg / cm³. 2 .

[0041] The cross-sectional microstructure of the obtained flexible conductive film was characterized, and the scanning electron microscope images of the cross-section are shown below. Figure 2 As shown in the figure, there is no delamination between the conductive layer and the substrate of the flexible conductive film, and the carbon nanofibers are uniformly dispersed.

[0042] (3) Fabrication of flexible interdigitated electrodes

[0043] First, the pre-treated polyethylene terephthalate (PET, 0.5mm thick) film is cut to the appropriate size and installed on the worktable of the screen printing machine (TP600S, Guangzhou Yude Machinery Co., Ltd.). The PET treatment process involves sonicating it with acetone, ethanol and distilled water for about 15 minutes to remove surface impurities.

[0044] Then, conductive ink (Deyang Xitan Technology Co., Ltd.) is applied to one side of the template for printing.

[0045] Finally, the PET electrode film with the forked electrode morphology was placed in an oven and dried at 70°C for 60 minutes for later use. The flexible forked electrode has 6 pairs of forked fingers, a forked finger width of 1 mm, a finger length of 19 mm, and a line spacing of 1 mm.

[0046] (4) Assembly of flexible piezoresistive sensors

[0047] The two ends of the fabricated interdigital electrodes are connected to copper enameled wires, and then a flexible conductive film is placed on top of the interdigital electrodes and encapsulated to obtain a flexible piezoresistive pressure sensor. The specific fabrication process is as follows: Figure 1 As shown.

[0048] Comparative Example 1

[0049] The difference between this comparative example and Example 1 is that in step (2) during the preparation of the flexible sensing layer, an uncured PDMS solution (PDMS, Dow Corning, USA, model Sylgard 184, with a precursor-to-curing agent mass ratio of 10:1) is spin-coated onto the surface of the PDMS film. The film is cured at 120°C for 30 minutes. Then, a carbon nanofiber ethanol solution with a concentration of 1.5 mg / mL (the carbon nanofibers are approximately 8 μm long and 150 nm in diameter, manufactured by Showa Denko, Japan) is sprayed at a spray angle of 90° and 20 times to obtain a flexible conductive film. The remaining process steps and parameter settings are the same as in the example.

[0050] The adhesion strength between the conductive layer and the substrate of the flexible conductive films prepared in Example 1 and Comparative Example 1 was tested. Specifically, the conductive flexible film was first glued to glass, and then a rigid wooden rod was glued to the upper surface of the conductive flexible film. Finally, the adhesion strength between the conductive material and the flexible film was tested using a universal testing machine (manufacturer: Shenzhen Sansi Zongheng Technology Co., Ltd., model UTM2501). The irregular area caused by glue adhesion was calculated using ImageJ software. The results are as follows: Figure 3As shown in the figure, compared with Comparative Example 1, which directly sprays conductive carbon nanofiber material onto the surface of cured PDMS, the preparation method of Example 1, which sprays conductive carbon nanofiber material onto the surface of uncured PDMS and then heats and cures PDMS simultaneously, can effectively improve the adhesion strength between the conductive layer and the substrate.

[0051] The current response of the flexible piezoresistive sensor prepared in Example 1 under different pressures was tested, and the results are as follows: Figure 5 As shown in the figure, (a) represents different applied pressures, and (b) represents the same applied pressure. The figure shows that the sensing signal is consistent under both the same and different applied pressures, indicating that the sensor has good stability. Furthermore, the current response increases with increasing applied pressure. This is because as the applied pressure increases, the contact area between the sensing layer and the interdigitated electrodes gradually increases, causing a decrease in contact resistance. Simultaneously, as... Figure 4 As shown, applying pressure causes deformation of the sensing layer, reducing the distance between conductive fillers within the flexible conductive film to the quantum size (tunneling effect) or contact (percolation effect). This leads to tunneling and percolation effects within the flexible conductive film, further increasing its resistance change. Therefore, under the synergistic effect of the contact area change rate, tunneling effect, and percolation effect, the current response increases with increasing applied pressure, effectively improving the sensitivity and detection range of the flexible piezoresistive sensor.

[0052] Furthermore, the flexible piezoresistive sensor prepared in Example 1 was used for monitoring elbow and standing gait. Specifically, the sensor was attached to different parts of the body to measure corresponding resistance changes. Different movement states of the body (such as elbow and standing gait monitoring) were identified by observing the signals monitored by the sensor during movement. The results are as follows... Figure 6 and Figure 7 As shown in the figure, the sensor exhibits good stability whether used for elbow or standing gait monitoring, which is of great significance for human health monitoring.

[0053] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. A method for preparing a flexible conductive film with high substrate adhesion, characterized in that, include: (1) Uncured PDMS solution was spin-coated onto hydrophobic glass, degassed under vacuum, cured by heating, and peeled off to obtain PDMS film; (2) Uncured PDMS solution was spin-coated onto the PDMS film, and carbon nanofiber ethanol solution was sprayed on under heating conditions. After spraying, the film was heated and cured to obtain a flexible conductive film with high substrate adhesion. (2) Spraying is carried out at 90~150°C; (2) The spraying process parameters are: spraying angle is 80~100°, spraying times are 15~22 times, and carbon nanofiber ethanol solution concentration is 1~1.5mg / mL.

2. The preparation method according to claim 1, characterized in that, (1) The process of hydrophobic treatment of glass is as follows: plasma treatment and fluorination treatment are performed on the glass surface in sequence.

3. The preparation method according to claim 2, characterized in that, Plasma treatment is performed at 30-60W for 3-5 minutes in an oxygen atmosphere; fluorination treatment is performed by treating the plasma-treated glass surface with 1H, 1H, 2H, 2H-perfluorooctyltrimethoxysilane vapor at 200℃ for 50-70 minutes.

4. The preparation method according to claim 1, characterized in that, (1) The curing temperature is 90°C and the curing time is 5h.

5. The preparation method according to claim 1, characterized in that, In (1) and (2), the uncured PDMS solution is made by mixing A glue and B glue in a mass ratio of 10~15:

1.

6. The preparation method according to claim 1, characterized in that, (2) The curing temperature is 120°C and the time is 30 min.

7. A flexible conductive film with high substrate adhesion prepared by the method shown in any one of claims 1 to 6.

8. An application of the flexible conductive film with high substrate adhesion as described in claim 7, characterized in that, Used as a flexible sensing layer in flexible piezoresistive sensors.

Images