Low frequency dielectric dispersion in ethylcellulose latex. Effect of pH and ionic strength

• Published in: Colloids and surfaces. A, Physicochemical and engineering aspects Vol. 131; no. 1; pp. 95 - 107
• Main Authors: Delgado, A.V., González-caballero, F., Arroyo, F.J., Carrique, F., Dukhin, S.S., Razilov, I.A.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 1998
• Subjects: Ethylcellulose latex; Low frequency dielectric dispersion; Mutual enhancement of adsorption oscillations of ordinary and additional counterions; Ethylcellulose latex; Mutual enhancement of adsorption oscillations of ordinary and additional counterions; Low frequency dielectric dispersion
• ISSN: 0927-7757; 1873-4359
• DOI: 10.1016/S0927-7757(97)00077-0

The study of the conductivity and dielectric response of colloidal suspensions in a.c. electric fields is an excellent probe of the particle double layer characterstics. In fact, the strong dielectric dispersion shown by such systems for frequencies of the field <1 MHz, is intimately related to the polarization mechanisms of both the diffuse and internal parts of the electric double layer. In this work we present experimental determinations of the dielectric constant of latexes of spherical ethylcellulose particles (commercially available as Aquacoat ®). The effect of both the ionic strength (10
−4–10
−3 M KCl) and pH (at constant KCl concentration) is considered. It was found that the dielectric constant of the suspensions decreases with frequency, tending to the pure solution value for frequencies ca 250 kHz. The increase in ionic strength gives rise to higher dielectric constants at any frequency; similar conclusions are valid for increased pH values of 5–8. The absolute value of the contribution of the dispersed phase to the dielectric permittivity was found to be very high. It exceeds several times the values predicted by theories developed for non-conducting particles even if very high surface charge density is assumed. It is proposed in this paper that this fact can be ascribed to the influence of adsorption oscillations of additional hydrogen counterions reversibly adsorbed in the Stern layer.