Preparation And Dielectric Sensing Property Of Modified Graphene/Thermalplastic Polyurethane

Nowadays,polymer based composites had played a wide range of roles in dielectric sensing fields.Normally,materials with high dielectric constants were expected to show superior sensing properties,while researches on this topic only attracted few concerns.Hence,more relative attentions should be paid to this field to further increase the dielectric constant of the material.According to previous researches,graphene is one of the most promising candidate fillers,which could greatly improve the dielectric properties of composites.However,it has poor dispersion when it was blended with polymer matrix,and this shortcoming seriously hampered the performance of the obtained sensors.Based on this background,this work used two different methods to modify graphene layers and then dispersed them into the thermoplastic polyurethane matrix.The obtained composites were fabricated as different kinds of capacitive sensors,and the relationship among processing,structure and properties was investigated.Specially,they were described as follows:In the first part,we explored the improvement of dispersity when different molecules were used to modify graphene layers.And we had developed a graphene-based elastomer with tunable dielectric properties,which was further employed to construct a flexible capacitive sensor with highly anisotropic responses to the out-of-plane bending and in-plane stretching.The results shows:the uniform dispersion enables to elevate dielectric performance in composites leading to a high relative permittivity value of 97.3.In addition,adjacent graphene flakes are parallel to the hot plates due to the thermo-compression-induced alignment,thus behaving as microcapacitors to contribute to the sensitivity enhancement in the resulting sensors.Particularly,such sensors exhibit a sensitive response to the out-of-plane bending(30~180~o),but are insensitive to the in-plane stretching(0~40 N).We further demonstrate that this sensor has a potential application in the field of virtual typing output.In the second part of this study,Chitosan was used to wrap the graphene layers,and then the wrapped graphene was reduced by ascorbic acid.The results indicates that chitosan could greatly increase the dispersity of modified graphene and dramatically enhanced the interfacial polarization.We further dispersed modified graphene into polymer matrix and prepared a composites with high dielectric constant and low threshold.The obtained composites was used to fabricate two kinds of capacitive sensors:continuous dielectric units sensor and independent dielectric units sensor array.Those sensors showed high sensitivity and good stability,which would have important applications in capacitive sensing.In addition,we also explored the organic sensing transistors and had successfully fabricated sensor arrays by printing methods.