CN108294747A - Aligned carbon nanotube adheres to dry electrode and its preparation process certainly - Google Patents

Abstract

The invention discloses an aligned carbon nanotube self-adhesive dry electrode and a preparation process thereof. The dry electrode includes an aligned carbon nanotube self-adhesive layer, a flexible support layer, double-layer flexible conductive films and wires. The present invention uses electrochemical and micromachining methods to prepare dry electrodes. This dry electrode has adhesion and flexibility, and its weight is ultra-light, less than 20g. It can stably contact the skin and reduce motion artifacts, while enhancing The wearable comfort of the user is guaranteed, and it can be removed at any time after use without residue, eliminating the need for cleaning.

Description

Aligned carbon nanotube self-adhesive dry electrode and its preparation process

technical field

The invention relates to the technical field of electrophysiological signal sensing and collection, in particular to an aligned carbon nanotube self-adhesive dry electrode and a preparation process thereof.

Background technique

The monitoring and acquisition of electrophysiological signals is playing an increasingly important role, especially the acquisition sensors surrounding ECG and EEG signals have been vigorously developed in recent years. Under normal circumstances, after the electrodes are worn, in order to form a good and stable electrical contact between the electrodes and the skin, it is necessary to inject conductive paste containing specific ions and conductive properties and having an appropriate viscosity under the electrodes one by one. In order to prevent the conductive paste from overflowing around, the general electrodes are designed into a barrel or bowl shape, and the injected electrode paste is filled between the scalp (skin) and the electrode, which plays a role in moisturizing the skin and eliminating the electrical isolation caused by hair, and provides a protective layer for the brain. Electrical harvesting provides a lower electrode/tissue interface. Until now, this electrode structure and the placement strategy of conductive paste have been an electrophysiological signal acquisition device with the best signal quality.

Although it has an advantage in the quality of electrical signal acquisition, the disadvantages of this electrode mainly exist in three aspects: first, it takes a long time to prepare for use, and conductive paste needs to be injected into the electrodes one by one, and it is difficult for one person to complete the wearing of the electrodes alone; After the tester uses this electrode, there will be serious conductive glue residue on the hair and scalp, which needs to be washed to remove it, causing great inconvenience to the user; third, it is not suitable for long-term chronic electrophysiological signal monitoring. As time goes by, the conductive liquid will gradually volatilize and evaporate, increasing the skin-electrode interface impedance. With the development and deepening of the application of EEG in health monitoring and brain-computer interface, the shortcomings of this electrode + conductive paste method are becoming more and more prominent. In these application scenarios, for the purpose of self-health monitoring or entertainment, it is difficult for users to tolerate the operation mode of using this kind of operation mode that is placed by others and washed after use. For this reason, some institutions have developed dry electrodes that do not require conductive paste. For example, in the article "DryEEG Electrodes" published by M.A. Lopez-Gordo et al. in the SENSORS journal in 2014, the main dry electrode companies and products in recent years were reviewed. And in summary, these dry electrode devices cannot compare with wet electrodes in terms of comfort in use and signal quality. In order to eliminate the barrier of the hair, most of the dry electrode devices adopt a comb-shaped structure, and the comb teeth are used to pass through the hair. In the absence of the conductive paste buffer, the small cross-section of the comb teeth directly contacts the scalp itself, which will cause some discomfort. More stable contact often also requires greater pressure on the comb stem electrodes. In terms of impedance and signal stability, due to the lack of conductive paste buffer, dry electrode devices are often very sensitive to motion interference, which is very unfavorable for systems with wearable requirements. At the same time, it has been found in long-term research that most of the dry electrodes formed by metal electrodes or other polymer materials are too hard and uncomfortable to wear, especially when used in human brain experiments, it brings a certain degree of discomfort to the subjects. feeling of pain. In terms of fixing method, the dry electrode needs a hat or other special devices like the wet electrode, which is very inconvenient to use.

Aiming at the problems of the above-mentioned electrophysiological acquisition sensors and combining the problems of some existing invention patents, a kind of aligned carbon nanotube self-adhesive dry electrode and its preparation process are proposed. This kind of carbon nanotube dry electrode has a villi structure and adhesion Adhesive, which eliminates the process of injecting glue one by one after wearing the electrodes, and realizes immediate wear and use; at the same time, the flexible film support structure makes the device have good flexibility and ductility, and can be closely attached to the skin. The double-layer conductive film can change with the deformation of the flexible support layer, ensuring stable electrical connection and reducing motion artifacts and noise. The silver wire or gold wire is ultra-light in weight, which further reduces the overall quality of the device, realizes the concept of thinness, helps the device to have small inertia in motion, and also reduces noise and artifacts. Due to the thin flexible structure and ultra-light mass, the device greatly improves wearing comfort.

Contents of the invention

(1) Technical problems to be solved

Aiming at the problems of the existing dry and wet electrodes in terms of wearing comfort, long test preparation time, long-term monitoring, and unstable skin electrode interface impedance, the main purpose of the present invention is to provide a self-adhesive dry electrode with aligned carbon nanotubes and Its preparation process. The oriented carbon nanotube self-adhesive dry electrode designed has a double-layer flexible structure, which can be adaptively deformed according to the curvature of the skin, and closely adhered to the skin. At the same time, due to the self-adhesive structure of the aligned carbon nanotubes, it can be adsorbed on the surface of the skin and reduce the contact resistance of the device. Unlike traditional dry electrodes and wet electrodes that need to be fixed with bulky caps and devices, this electrode has a mass of less than 20g and does not require foreign objects to be fixed, which greatly improves the comfort of use.

(2) Technical solutions

In order to achieve the above object, on the one hand, the present invention proposes an aligned carbon nanotube self-adhesive dry electrode, including an aligned carbon nanotube self-adhesive layer, a flexible conductive film, a flexible support layer and a wire, wherein the aligned carbon nanotube The tube self-adhesive layer is fixed on the flexible conductive film, the flexible conductive film is fixed on the flexible support layer, and the wire is connected to the flexible conductive film.

Preferably, the flexible conductive film is a double-layer flexible conductive film, the upper layer is made of conductive polymer material, and the lower layer is made of conductive metal, and the thickness of the flexible conductive film is 50-500 μm.

Preferably, the conductive polymer material is PEDOT or conductive silica gel, and the conductive metal is Ag/AgCl mixture or gold (Au).

Preferably, the material of the flexible support layer is selected from PDMS, PI, EVA or EPDM, and the thickness of the flexible support layer is 20-300 μm.

On the one hand, the present invention also proposes a preparation process for aligned carbon nanotube self-adhesive dry electrodes, including:

forming a flexible support layer on the substrate;

forming a flexible conductive film on the flexible supporting layer;

fixing a plurality of carbon nanotubes on the flexible conductive film;

The base is removed, and wires are connected on the flexible conductive film.

Preferably, before forming the flexible supporting layer, the substrate is first cleaned and dried.

Preferably, the flexible support layer is formed through the following steps: uniformly mixing the conductive polymer material and the curing agent, uniformly coating on the substrate, and then heating and curing, the coating method is preferably spin coating.

Preferably, the flexible supporting layer is surface-treated to make its surface hydrophilic, and the surface treatment is preferably oxygen plasma treatment.

Preferably, the flexible conductive film is formed through the following steps: adding AgCl to the silver paste to obtain an Ag\AgCl mixture, using the Ag\AgCl mixture to form a conductive film, and then coating a conductive polymer material layer on the conductive film.

Preferably, a plurality of carbon nanotubes are fixed on the flexible conductive film by heating and curing.

Preferably, the substrate is selected from copper foil or aluminum foil, and the substrate is removed using an etching solution.

(3) Beneficial effects

It can be seen from the above technical solutions that the present invention uses a flexible material as the main body, combined with carbon nanotube conductors to form a flexible dry electrode that can adapt to the shape of the skin. The formed multilayer flexible carbon nanotube dry electrode has good mechanical properties and comfort, and will not cause pain caused by electrode compression and discomfort caused by a large amount of residual conductive fluid. Along with the adaptive deformation of the flexible support layer to the skin, the stability of the impedance between the skin electrodes is maintained, the quality of the bioelectrophysiological signal is greatly improved, and it is beneficial to monitor the brain signal for a long time. A large number of tests show that the alignment carbon nanotube self-adhesive dry electrode formed by the present invention has a good test effect, can achieve a collection effect similar to that of a commercial electrode, greatly improves comfort, and reduces costs, which proves the present invention feasibility.

Description of drawings

Fig. 1 is a schematic structural view of an aligned carbon nanotube self-adhesive dry electrode according to an embodiment of the present invention;

Fig. 2 is a schematic diagram of the preparation process of the aligned carbon nanotube self-adhesive dry electrode according to the embodiment of the present invention.

Explanation of reference signs:

1-aligned carbon nanotube self-adhesive layer; 2-double-layer flexible conductive film; 3-flexible support layer; 4-wire.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be described in further detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

Fig. 1 is the structural schematic diagram of the self-adhesive dry electrode of aligned carbon nanotubes of the embodiment of the present invention, as can be seen from the figure, the self-adhesive dry electrode of aligned carbon nanotubes comprises the self-adhesive layer of aligned carbon nanotubes 1, double-layer flexible conductive film 2. The flexible supporting layer 3 and the wire 4 .

Oriented carbon nanotube self-adhesive layer 1 is formed by vertical arrangement of multi-walled and metal conductive carbon nanotubes with good electrical conductivity. Neatly arranged between -3 mm (typical height 2 mm) (bulk density 0.7 mg/cm ³ ). The aligned carbon nanotube self-adhesive layer 1 has adsorptive properties and can be pasted on the skin surface, and the growth density and height can be controlled by CVD.

The upper layer of the double-layer flexible conductive film 2 is a conductive polymer material, and the lower layer is a conductive metal. The conductive polymer material can be PEDOT (poly(3,4-ethylenedioxythiophene)), conductive silica gel, etc., and the conductive metal can be Ag/AgCl mixture or gold (Au). In this embodiment, the double-layer flexible conductive film 2 includes a first conductive layer formed by a mixture of Ag\AgCl and a second conductive layer formed by PEDOT. The double-layer flexible conductive film 2 is prepared by MEMS technology and chemical etching process, and has an elongated The thickness of the double-layer flexible conductive film 2 can be 50-500 μm.

The material of the flexible support layer 3 can be selected from polydimethylsiloxane (PDMS), polyimide (PI), ethylene-vinyl acetate copolymer (EVA), ethylene-propylene-diene rubber (EPDM), etc., in In this embodiment, the flexible supporting layer 3 is formed by spin-coating PDMS, and its thickness is controllable, which can be 20-300 μm.

The wire 4 can be a gold wire or a silver wire.

As shown in Figure 2, the preparation process of the aligned carbon nanotube self-adhesive dry electrode of the present invention comprises:

Step 1: First, clean the copper foil in an ethanol solution and put it into an ultrasonic device for 10 minutes to clean off the surface attachments.

Step 2: Put the cleaned copper foil in a vacuum constant temperature drying oven (50°C) and bake for 20-30 minutes until it is completely dry.

Step 3: On a 300um thick glass or silicon wafer, fix the copper foil on the surface of the silicon wafer with high-temperature adhesive tape, and stick it closely to the surface of the silicon wafer.

Step 4: Configure the PDMS solution, mix it with the curing agent at a ratio of 10:1, and fix the silicon wafer with copper foil on the glue spreader, and evenly spin-coat PDMS on the copper foil 6 using the glue spreader to form a thickness of 20- A 600 μm PDMS film serves as a flexible support layer 3 . Then cure for one hour at 100°C on a hot plate. Preferably, vacuumize the mixed solution of PDMS and curing agent to remove air bubbles.

Step 5: Put the cured PDMS film into a plasma etching machine, and perform oxygen plasma etching for 2 minutes to treat the surface of the PDMS film to make it hydrophilic.

Step 6: prepare high-purity silver paste, add a small amount of silver chloride powder according to the ratio of less than 7:3, to form a Ag\AgCl mixture.

Step 7: On the PDMS film, spin-coat the prepared conductive silver paste on the surface of the film evenly along one direction with a scraper to form the first layer of a dense double-layer conductive film 2 .

Step 8: Bake on a hot plate at 80°C for 1 hour to form an Ag\AgCl mixture film, and spin-coat PEDOT (poly(3,4-ethylenedioxythiophene)) on a coater to form a double-layer conductive film 2 Second Floor.

Step 9: Divide the carbon nanotubes 1 grown by CVD on SiO ₂ along the size of the scribing before growth, and each piece has a length and width of 2*2 mm, and clamp it with tweezers and place it vertically on the PEDOT conductive film.

Step 10: Place the electrode sheet after transferring the carbon nanotubes in a constant temperature drying oven, place a steel block vertically above the carbon nanotubes and press it, and keep it at 50°C for 30 minutes to cure the second layer (PEDOT) of the conductive film 2 and carbonize it. Nanotube 1 is immobilized.

Step 11: Etching the copper foil to release the thin film carbon nanotube electrodes. Release the copper foil from the silicon wafer, put the copper foil into the etching solution using a horizontal porous platform, and let it float on the surface of the etching solution. The etching solution cannot overflow the copper foil, so as to avoid affecting the conductive film 2 and carbon nano Tube 1.

Step 12: Take out the thin film device after corrosion, put it in an oven for 20 minutes, and wait for packaging after taking it out.

Step 13: Packaging and testing, using gold wire or silver wire 4 to pressure-bond the package on a bonding station, so that the device can be used and tested.

The specific embodiments described above have further described the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above descriptions are only specific embodiments of the present invention, and are not intended to limit the present invention. Within the spirit and principles of the present invention, any modifications, equivalent replacements, improvements, etc., shall be included in the protection scope of the present invention.

Claims (10)

1. An aligned carbon nanotube self-adhesive dry electrode, comprising an aligned carbon nanotube self-adhesive layer, a flexible conductive film, a flexible support layer and a wire, wherein the aligned carbon nanotube self-adhesive layer is fixed on the flexible On the conductive film, the flexible conductive film is fixed on the flexible support layer, and the wire is connected to the flexible conductive film. 2. orientation carbon nanotube self-adhesive dry electrode as claimed in claim 1, is characterized in that, described flexible conductive film is double-layer flexible conductive film, and upper strata is conductive polymer material, and lower floor is conductive metal, and described flexible conductive film The thickness of the conductive film is 50-500 μm. Preferably, the conductive polymer material is PEDOT or conductive silica gel, and the conductive metal is Ag/AgCl mixture or gold (Au). 3. orientation carbon nanotube self-adhesive dry electrode as claimed in claim 1, is characterized in that, the material of described flexible supporting layer is selected from PDMS, PI, EVA or EPDM, and the thickness of described flexible supporting layer is 20- 300 μm. 4. A preparation process for aligned carbon nanotube self-adhesive dry electrodes according to any one of claims 1-3, comprising: forming a flexible support layer on the substrate; forming a flexible conductive film on the flexible supporting layer; fixing a plurality of carbon nanotubes on the flexible conductive film; The base is removed, and wires are connected on the flexible conductive film. 5 . The preparation process according to claim 4 , wherein, before forming the flexible support layer, the substrate is first cleaned and dried. 6 . 6. The preparation process according to claim 4, wherein the flexible support layer is formed through the following steps: uniformly mixing the conductive polymer material and the curing agent, uniformly coating it on the substrate, and then heating and curing, The coating method is preferably spin coating. 7. The preparation process according to claim 4, characterized in that, the flexible supporting layer is surface-treated to make its surface hydrophilic, and the surface treatment is preferably oxygen plasma treatment. 8. The preparation process as claimed in claim 4, wherein the flexible conductive film is formed by the following steps: adding AgCl to the silver paste to obtain a Ag\AgCl mixture, utilizing the Ag\AgCl mixture to form a conductive film, and then conducting A conductive polymer material layer is coated on the film. 9. The preparation process according to claim 4, wherein a plurality of carbon nanotubes are fixed on the flexible conductive film by heating and curing. 10 . The preparation process according to claim 4 , wherein the substrate is selected from copper foil or aluminum foil, and the substrate is removed by an etching solution. 11 .