Modified interphase theory to determine dielectric constant of particulate composite material at microwave frequency

摘要

The permittivity of composites at 10 GHz is computed using various existing models like mixing law, power law (PL) and interphase power law (IPL). A deviation in permittivity values determined from the existing models with respect to the experimental values is observed, which gets more significant with increase in volume fraction (VF) of the inclusions. Interphase theory, has been modified to predict real part of permittivity of particulate-composite system. A simple linear model is predicted, where the inter phase layer is not considered to have fixed permittivity but varying - from permittivity values of filler (in vicinity to inclusions) to permittivity values of polymer where the interphase layer ends. The model is tested for alumina-polystyrene and titania-polystyrene composite system. XRD, SEM and optical micro graph studies show that the size of filler in the composite is less than that of probing wavelength and distribution of filler is sufficiently uniform in the matrix. The present model termed as, varying inter phase layer permittivity model (VIPLP) gives a very close result to the experimental values. Some inter esting facts that came out of the present model - (a) higher the permittivity difference between the filler and the polymer, the gradient of decrease in permittivity of interphase layer is rapid (b) with the increase in volume fraction of filler, the effective surface area of interaction increases, hence the permittivity of the interphase layer increases.