Carbon Nanotube Composite Films Liquid Droplet/Gas Sensors

Flexible wearable electronic devices have attracted more attention with the development of science and technology and the improvement of living standards.As one of the important components of flexible wearable electronic devices,flexible sensors have been widely used owing to their simple structure and convenient operation.Many kinds of flexible sensors are widely used in a wide range of fields,such as human behavior and health monitoring,testing the composition and content of substances（solid,liquid,gas）in the environment and reaction to light and temperature.With the abundant research,flexible sensors have made a lot of results in medical health,flexible electronic skin,environmental monitoring and other fields.Carbon Nanotubes（CNTs）are one-dimensional nanomaterials with excellent mechanical properties,electrical conductivity and flexibility.Self-supporting single-walled CNT films with controllable thickness（from nanometer to micron）are prepared by chemical vapor deposition（CVD）.The CNT films have a porous network structure,large specific surface area and much adsorption sites.CNT films have been widely used in the synthesis of flexible sensors because of their excellent properties.Here,we prepare single-wall CNT films by chemical vapor deposition.CNT/PVA composite films are fabricated by in-situ cyclic deposition based on single-wall CNT films and polyvinyl alcohol（PVA）with high toughness and stretchability.CNT/PVA composite films have uniform structure,and CNT is continuously distributed in the PVA matrix.A constructed uniformly distributed stress network makes CNT/PVA composite films have high stretchability and uniform deformation characteristics.CNT/PVA composite films can be stretched up to 4 times their original length and the local strain is only 10%of the total strain at a large strain（300-358%）.Based on the swelling property of PVA to water and the shrinkage property of CNT to organic solvents,CNT/PVA composite film can realize the reversible response to droplet and the recognition of various liquids（water,Na Cl solution and various organic solvents）.The response of CNT/PVA composite film to 3μL water is up to 35%.And the CNT/PVA composite film still has good droplet sensing performance after stretching.In addition,CNT/anatase Ti O₂（a-Ti O₂）composite films are prepared by in-situ hydrolysis and calcination basis on ultra-thin CNT films.CNT/a-Ti O₂ composite films have a coaxial structure with CNT as the axis and porous a-Ti O₂ nanoparticles as the shell.Such structure makes the CNT/a-Ti O₂ composite films have a large specific surface area.CNT/a-Ti O2 gas sensors have high sensitivity to NO,selectivity and stability.The sensitivity（△R/R₀）of CNT/a-Ti O₂ gas sensor is 41%to 50 ppm NO.First-principles calculation shows that the response to NO is related to the energy level distribution of a-Ti O₂.In addition,the unique alternate structure of rigid part（CNT@a-Ti O2）and flexible part（CNT）makes CNT/a-Ti O₂ have excellent flexibility,which has good gas sensing property under extreme deformation.