The Preparation, Modification And Investigation Of Strucuture And Performances Of Polyvinylidene Fluoride/carbon Blacks Composite Thin Films

More recently, the electro-conductive composite sensing materials prepared by filling some conductive stuffing such as carbon black, metal powder, carbon fiber, graphite and carbon nanotubes etc. into polymer matrices were regarded as an interesting subject. At present we probe into the gas sensing conductive performance based on the swell model and crystal theory, however, the discussion on the microstructure was less reported. The material developements would be accelerated if the relation between response performances and the microstructure would be discussed clearly.A novel polyvinylidene fluoride/carbon blacks (PVDF/CB) polymeric conductive sensitive composite film was prepared by filling different kinds of carbon blacks into polyvinylidene fluoride matrix. The percolation behavior and PVC (Positive vapor coefficient, PVC) peculiarity were investigated. The relationship between structure and vapor response behavior of the conductive composite films was elucidated by investigating into the modification of PVDF/CB conductive composite films via plasma glow discharge technology and KOH/ethanol or KOH/KMnO₄ solution and heat treatment.The vapor sensitivity of the conductive thin films to acetone vapor could be intensified, the response speed could be enhanced and the response reproducibility could also be improved by O2 plasma treatment, especially in the presence of the cross-linker triallyl Isocyanurate (TAIC), the response intensity of the thin films treated with 60 W O2 plasma to acetone vapor reached 6400 times and the response time was shortened. From FT-IR we think that the hydrogen bond between the polar oxygenous group on the thin film surface treated with plasma and acetone molecules would enlarge the distance between the carbon black particles, resulting in the addition of the electrical resistance, then the response behavior of the thin film to acetone was improved greatly. Whereas the surface shell of the thin films surface-modified by plasma technique was destroyed or etched, especially in the presence of TAIC, the highcross-linked reticulate structure was formed, which was proved by ESEM. Therefore, there was excess porosity on the film surface which was favorable for solvent vapor molecules to absorption, pervasion and infiltration into the PVDF matrix.Some functional groups such as double bond, hydroxyl and aether bond were introduced into the molecule structure of PVDF after treated with alkali solution demonstrated by FT-IR. When the PVDF matrix was mixed with carbon blacks and radiated with ultrasonic, a grafted PVDF/CB conductive composite material could be acquired. By analysing WAXD and DSC spectras we think that the reaction occurred in the non-crystal region, and had no effect on the crystal region and the structure of main chain. However, the aggregate structure change in the non-crystal regions altered the interaction between polymer and solvent, resulting in the change of polymeric swell effect and the response performance of the thin films.The effect of different ways of thermal treatments on the PVC peculiarity was different. Annealing treatment could improve the behavior of crystallization and response performance of the PVDF/CB sensing films. The results showed that the initial resistance values of the thin films undergoing different heat-treatments all declined compared with those of the untreated films. The responsive patterns and responsibility of the composite materials under thermal treatment to acetone and THF vapors obviously improved. Especially, the resistance reproducibility of the thin films annealed at 80 °C for 2 h to acetone and THF vapors was optimal.