Dielectric behavior of ethylcellulose in concentrated solutions

Abstract

Measurements of dielectric relaxation were made for a series of solutions of ethylcellulose in benzene. The concentrations ranged from 0,s to 20 wt.-% and two polymers of different molecular weight were used. The dielectric dispersion was measured over the frequency range of 30 Hz -3 MHz at 30 -50 "C. The concentration dependence of the critical frequency below and above the critical concentration is interpreted by the free volume effect. It was found that the dielectric relaxation times are constant above the critical concentration and that the activation energy increases with concentration. The observed relaxation time is analyzed by Pri5hlich's theory assuming two limiting relaxation times. The lower limit in the relaxation time, r l , is concentration-independent above the critical concentration, in contrast to the upper relaxation time, r,, which depends on concentration. These relaxation times, r1 and r,, however, are interpreted by the same free volume effect. The unperturbed molecular dimension at the critical concentration is also discussed.