Piezo - and pyroelectricity in thin films of polyurea synthesized by vapor deposition polymerization

Abstract

Abstract Thin films of polyurea are prepared by evaporating in vacuum a diamine monomer and a diisocyanate monomer and depositing them simultaneously on a substrate. When 4, 4′-diamino diphenylmethane (MDA) and 4, 4′-diphenylmethane diisocyanate (MDI) are used at a stoichiometrically balanced ratio, the as-deposited oligomers consist of approximately 5 monomers. During poling process, polymeri zation of oligomers and field-induced alignment of urea bonds take place at the same time, producing a large residual polarization and piezo- and pyroelectric activities. The piezo- and pyroelectric constants for 500 nm thick aromatic polyurea films are on the same level of PVDF and independent of temperature up to 200°C. The preparation of thin films of aliphatic polyurea from 1, 9-diamine nonane and 1, 9-diisocyanatenonane is succeeded by cooling a sub strate below 0°C.