Effect of Volume Fraction and Temperature on Dielectric Relaxation Spectroscopy of Suspensions of PS/PANI Composite Microspheres

Abstract

In this work, we aim to contribute new data on the dielectric relaxation behavior of suspensions of nonconducting/conducting composite microspheres (polystyrene/ polyaniline, PS/PANI). Then, the dielectric investigation over the frequency range of 40 Hz to 110 MHz has been carried out to display the characteristic of dielectric relaxation spectroscopy of suspensions with PS/PANI composite microspheres from two contributions which are the dependences of dielectric relaxation spectroscopy of suspensions on the volume fraction of particles (ϕ) and temperature (T), individually. Two relaxations can be identified in dielectric spectroscopy of suspensions: the so-called α- relaxation (typically at kHz) due to the polarization of counter-ions, and the Maxwell−Wagner−O’Konski (M−W−O) relaxation (typically at MHz) ascribed to a consequence of an accumulation of polarized charges on the boundary surfaces of the dispersed particles. The dependences of dielectric parameters by fitting data with Cole−Cole equations on ϕ and T have been discussed in detail, respectively. According to the dielectric analysis, several interesting phenomena arise in the range of investigation: First, special dielectric increments, where ∂εl = (εl − εm)/ϕ and ∂εh = (εm − εh)/ϕ denoting the low- and high-frequency relaxation amplitude of suspensions of PS/PANI particles per unit volume, respectively, are increasing with the enhancement of volume fraction ϕ. Second, all high-frequency permittivities (εh) are higher or much higher than the permittivity of aqueous solution (80.05 at 18 ± 1 °C). On the basis of the comparisons between PS/PANI and PS, PS/PPY, PS/ZnO particles, we extract some proposals to responsible for such interesting phenomena, namely, except for the two distinct relaxations, α-relaxation and M−W−O relaxation, suspension exhibits an additional dielectric relaxation over the megahertz frequency range, due to the polarization of internal double layer of the thin layer of conducting polymer PANI when an external field is employed. Meanwhile, the different dependences of εh on ϕ for suspensions of PS/PANI (PS/PPY) and PS/ZnO particles are ascribed to the different conducting mechanism and surface morphology of conducting polymer PANI (PPY) and ZnO shells. Finally, after the detailed analysis we obtained the activation energy Ea of the low- and high-frequency relaxations of suspensions of PS/PANI microspheres which is experimentally determined by the dielectric data, individually.