Dielectric properties of cleaned and monodisperse polystyrene latexes in microwaves

Abstract

The dielectric behavior (ε′, ε″) of three well-cleaned monodisperse polystyrene latexes having the same particle size and the same number of chemically-bound surface groups has been studied at a fixed microwave frequency (9.4 GHz), as a function of temperature and surface group (SO ⁻₄ , COO⁻, OH).

A large dielectric relaxation was observed in the sulfate-stabilized latex, which has the most polar surface end-group. The anomalous behavior in the thermal dependence of the hydroxyl and carboxyl-stabilized latexes (the OH latex being more pronounced than the COO⁻ latex) may originate from differences in the experimental conditions used for the preparation of such polymer colloids, or due to the presence of ionic species.

On the basis of various dielectric models, the apparent volume fractions of the latexes were calculated. The amount of “bound” water around the latex particle was quantitatively correlated to the polarity of surface end-group (SO ⁻₄ > COO⁻ > OH). The differences between the calculated and actual values were not only a reflection of the thickness of vicinal water, but could also be indicative of the presence of oligomeric species in the suspension's medium (serum) of the latex. The permittivities of hydrated particle and of “bound” water were obtained with a non-linear iterative procedure.