Research Of Carbon Nanocomposite-based Flexible Tactile Sensors

Flexible tactile sensors are defined as flexible devices which can transduce physical or environmental stimulus into detectable signals.Since flexible tactile sensors can be used for continuous detection of subtle or large human motions and physiological signals,these sensors have drawn increasing attention in wearable electronic systems in recent years.For practical applications,especially for mechanical sensing such as tensile strain,pressure（compressive strain）and shear force,high sensitivity,wide working range,good flexibility,biocompatibility and good stability are essential to flexible tactile sensors.Therefore,the research of flexible tactile sensors with abovementioned characteristics has become a research hotspot worldwide.However,traditional sensors based on metals and semiconductors usually have high sensitivity with low working range and vice versa.Moreover,the device structure is single,and most of the sensors need external power source.These disadvantages could restrict the sensor’s accuracy and scope of use in practical applications.The carbon nanomaterials and their composite materials possess good electrical conductivity,mechanical properties,biocompatibility,stable physical and chemical properties,and the surface of these materials are easy to be modified.Therefore,they are ideal candidates for fabricating flexible tactile sensors.In order to achieve flexible tactile sensors with different functionalities,such as strain,pressure and shear force sensor,the main content of this dissertation focuses on the fabrication and improvement of carbon-based flexible nanocomposite,and optimization of the sensor structure,leading to high-performance flexible strain,pressure and shear force sensors for tactile sensing.Furthermore,the sensors with self-powered abilities are also achieved.The research results and innovations achieved are as follows:（1）Based on carbon black/silver nanoparticles（CB/Ag NPs）zero-dimensional composite material,a highly sensitive and flexible tensile strain sensor with a wide working range is constructed.A novel zero-dimensional conductive composite of CB/Ag NPs is prepared by surface modification method,and then filled into a thermoplastic polyurethane（TPU）matrix to fabricate the sensor.The introduction of CB/Ag NPs in the TPU matrix can form three different conductive junctions and increase the number of conductive junctions with variable resistance,leading to a good sensitivity of the sensor under high tensile strain（GF of 21.12 at 100%）.The strain sensor also has excellent static stability（50%strain for 600 seconds）and dynamic stability（1000 cycles）.The sensitivity of the strain sensor based on CB/Ag NPs composite at 100%strain is 18 times higher than that of the sensor based on pure CB.（2）An ultrathin stretchable triboelectric sensor（CT-TENG）based on chargeable CB/TPU composite is fabricated.In order to realize the self-powered sensing of the stretchable sensor,and based on the preparation of the conductive composite material in the previous work,the charges capturing ability of CB islands or particles is utilized to increase the surface charge density of CB/TPU by corona charging,thereby significantly improving the performance of the triboelectric sensor.The CB/TPU could act as both electrode layer and friction layer.CT-TENG（C-8）has good stretchability（≈646%）,ultra-thin thickness（≈49.4μm）and light weight（≈62 mg）.After charging,the output performance of C-8 is increased by 8 times,reaching 41 V.（3）A preparation method of conductive porous nanocomposite（PNC）with ultrahigh porosity（86%）is proposed,and a novel pressure sensor（HRPS）with capacitive and resistive hybrid response is achieved based on this material.According to the previous preparation method of carbon-based conductive nanocomposites,coupled with the design of the porous structure,the conductive PNC based on carbon nanotube（CNT）/Ecoflex,the ultrathin insulating layer of polymethylmethacrylate（PMMA）and gold/polyimide（Au/PI）electrodes are stacked layer by layer to construct the sensor,and high sensitivity under a wide working range is achieved,from 3.13 k Pa^-1 under 0-1 k Pa to 0.43 k Pa^-1 under 30-50 k Pa,the sensitivity of HRPS is up to 423%higher than that of the previous reported capacitive pressure sensor in the literature.（4）A self-powered multi-directional pressure sensor with a three-dimensional integrated structure based on carbon black/titanium carbide/polydimethylsiloxane（CB/Ti₃C₂T_x/PDMS）composite material is proposed.By using the cylindrical support structure and the conical sensing structure,MPS can not only realize the detection of normal force,but also can be used for real-time sensing and analysis of tilt force and shear force.The cone sensing structure made of CB/Ti₃C₂T_x/PDMS composite enables MPS to have higher voltage output,good linearity（R²=0.9773）and fast response.In the normal force range of 5.1-76.5 k Pa,the sensitivity(2.97 m V k Pa^-1)is 4.8 times higher than that of the pure PDMS based sensor(0.62 m V k Pa^-1).At the same time,MPS can recognize small shear force as low as 0.05 N（255 Pa）.