Studies of TGS/P(VDF-TrFE) and MMT/P(VDF-TrFE) 0-3 composites

Abstract

Ferroelectric ceramic/polymer composites have been widely studied in recent years due to the combination of good mechanical performance and high electroactive capabilities. In this project, triglycine sulfate (TGS)/poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE), 70/30 mol%) 0-3 composites with various volume percents of TGS were fabricated by compression moulding. Three series of composites were prepared: (I) unpoled composites, (II) composites with only the TGS phase poled and (III) composites with both phases poled. The structure, phase transitions and dielectric, piezoelectric and pyroelectric properties of the composites were investigated. Scanning electron microscope (SEM) studies of the composites showed that the TGS particles were uniformly dispersed in the copolymer matrix. The reflection peaks of both the TGS and P(VDF-TrFE) phase appeared in the X-ray diffraction (XRD) patterns of the composites and the phase transitions of the two phases were observed in the differential scanning calorimetry (DSC) thermograms of the composites. The relative permittivity and pyroelectric coefficient of the composites were found to increase with increasing TGS content. The relative permittivity and pyroelectric coefficient were compared with the theoretical predictions of the Bruggeman model and the effective medium model, respectively, and good agreement was obtained. It was also found that if the two phases were poled in the same direction, the pyroelectric contributions from TGS and P(VDF-TrFE) reinforced while piezoelectric contributions partially canceled. Thus the composite with 43 vol% of TGS exhibited a high pyroelectric coefficient and high pyroelectric figures of merit together with a low piezoelectric coefficient. The low piezoelectric activity is a significant advantage in pyroelectric sensor application since it will give rise to a low vibration induced noise. Montmorillonite (MMT)/P(VDF-TrFE) (80/20 mol%) 0-3 nanocomposites with 1 wt% and 4 wt% of MMT were also fabricated. Na+-MMT was first modified with cetyltrimethylammonium bromide (CTAB) before being incorporated into the copolymer matrix. The nanocomposites were characterized by means of XRD and DSC. The dielectric permittivity, polarization hysteresis, piezoelectric coefficient and pyroelectric coefficient were also measured. The XRD patterns showed that P(VDF-TrFE) copolymer chains had been intercalated into the layered nanostructures of the CTAB treated MMT. The DSC thermograms indicated that the Curie temperature of the nanocomposites were higher than that of the pure copolymer. The relative permittivity and remnant polarization of the nanocomposites were found to increase with MMT content. The piezoelectric coefficient and pyroelectric coefficient were also enhanced in the MMT/P(VDF-TrFE) nanocomposites.