CHITOSAN FILMS AS FLEXIBLE SUBSTRATE TO FABRICATE ELECTRONIC SENSING DEVICES

At present, the electronic information industry is still dominated by rigid devices, which have matured processing technologies and industrial chains while also having certain limitations. Compared with rigid devices, flexible electronic devices can withstand various deformations, such as stretching, squeezing and bending, and are suitable for complex working surfaces. It can be widely used in many fields such as signal sensing, biomedical, solar cells, wearable electronics, etc. Flexible electronics provide a new idea for the development of modern electronics. The preparation of flexible electronic sensing devices begins with the selection of suitable flexible materials to make substrates. Flexible materials can reduce the pollution of electronic waste with natural degradable properties such as cellulose, chitosan and other polysaccharide substances. It also reduces the risk of implantable electronic medical devices. With unique antibacterial properties, biocompatibility and degradability, chitosan is considered as a flexible material with great potential for development. However, its application is greatly limited by the fact that natural chitosan is almost insoluble in water and has weak mechanical property after film formation.

In the thesis, chitosan was selected as an analysis object, and its mechanical and other properties were modified with quaternization and plasticization. Upon modification the solubility and mechanical property of chitosan could be enhanced. By adding glycidyl trimethyl ammonium chloride (GTMAC) into the raw material, the quaternization modification of chitosan improved the water solubility of chitosan and broadened the applicable range of chitosan. Based on the modification of chitosan by quaternization, the experiments improved the elongation at break and the surface adhesion of chitosan films by introducing glycerol as a plasticizer and tannic acid as a cross-linking agent to plasticize quaternized chitosan. PEDOT:PSS, the polymer which has high transparency and good electrical conductivity, was selected as the conductive ink and printed on the surface of the flexible films by screen printing to form the film devices. The optical properties of the printed chitosan film were characterized by UV/Vis spectrophotometer, and it was found that the printed chitosan film still has good transparency. Meanwhile, the electrical properties of the film surface were characterized, and it showed that the transparent electrode on the surface of the film after double-layer PEDOT:PSS printing has excellent electrical property.

The chitosan film samples were tested and found to have good self-healing ability under the weak cutting effect, which can restore the surface morphology in a short period of time; the self-healing performance of the film can be enhanced if a certain amount of moisture is supplied or the air humidity is kept high. A simple flexible capacitive sensor was formed by coating a designed functionalized pattern on the surface of the flexible film, and signal sensing was achieved, confirming the feasibility of chitosan film being used as a substrate for electronic sensing devices.

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