The Preparation And Structure-Properties Study Of Polyurethane/Nano Silver Composite Films

Conductive polyurethane / graphite-silver nanoparticles (PU/C-Ag) composite films have been successfully prepared. The silver nanoparticles were introduced via in-situ reduction of the incorporated silver salts. PU/Ag composite films have also been fabricated by employing two different silver complexes. TEM and SEM were used to observe the micro structure of the composite films. XRD measurement was preformed to trace the silver reduction and aggregation process. The influences of heat treatment temperature and time on the reduction of silver have been studied. Also, the growth and conglomeration of the silver nanoparticles and their effects on the conductivity of the PU/C composite films have been investigated.Surface resistance measurements indicated that the conductivity of PU/C-Ag was obviously higher than PU/C. It is suggested that the silver particles, which were introduced by thermal reduction of the incorporated silver complexes and uniformly distributed in the polymer matrix, act as conductive path in the composite system by contacting the graphite particles in the system and therefore give a better conductivity.In order to study the influence of flexibility of polymer chain on the silver's migration, PU/Ag and polyimide (PI)/Ag composite films were prepared in our work. The morphology and surface topography of the films were observed by TEM and SEM. And it is found that the silver particles had not migrated to the films surface as it happened in PI/Ag system. This is because the PU has a lower Tg and therefore more flexible chains as compared with the PI's, which would result in a more compacted polymer chains and restricted the migration of silver particles. In contrast, the PI chains are rigid and difficult to be packed very closely. Therefore there is a larger free volume which could facile the silver migration at high temperature to the surface of the composite films.Silver acetate (AgAc) and silver nitrate (AgNO₃) were used as silver precursors in our research to prepare PU/Ag composite films. The shapes of the formed silver particles are rather different. For the silver acetate system, the silver is present as spherical particles. While for the silver nitrate system, irregular particles were observed.PU/Ag composite films with modest reflectivity( 35-50% on the upside, 40-60% on the underside) were prepared when AgAc were used as silver origins.