PREPARATION OF ORGANIC THIN-FILMS BY AN ELECTROSPRAY TECHNIQUE .1. CRYSTAL FORMS AND THEIR ORIENTATION IN POLY(VINYLIDENE FLUORIDE) FILMS

The utilization of ions has proved effective for preparing highly oriented films. In this paper, a new electrospray technique (ESP) is discussed. Poly(vinylidene fluoride) (PVDF) solution (0.2 wt.% in dimethylformamide) was passed through a nozzle to which a high voltage (8-15 kV) was applied, and sprayed into dry nitrogen gas. The nitrogen gas was made to flow in order to evaporate the solvent. Charged droplets of the solute were transported to a conductive substrate which was grounded. Then the PVDF film was formed on the substrate. The results of X-ray diffraction and IR measurements indicated that the PVDF films consisted chiefly of form I crystal. From the results of IR dichroic measurements by IR reflection absorption spectroscopy methods with polarized light, it was found that the form I crystal was oriented; molecular chain axes were parallel to the substrate surface, and the CF2 dipole was perpendicular to the surface and parallel to the applied field. Films possessing pyroelectricity could be obtained, and the largest pyroelectric coefficient was 4.0 nC cm-2 K-1 which was larger than that of conventional PVDF pyroelectric films.