Dielectric analysis of chitosan microsphere suspensions: study on its ion adsorption

Abstract.

The dielectric properties of chitosan microsphere beds in aqueous electrolyte solutions were investigated in a frequency range of 1–500 MHz. Distinct dielectric relaxation was observed around 10 MHz in weakly acidic solutions (pH 4–6), and the relaxation intensity depended on electrolyte concentration. The dielectric relaxation was analyzed on the basis of interface polarization, and the relative permittivity and conductivity of the microsphere interior were estimated from the relaxation parameters using Hanai's mixture equation. The internal conductivity of the microspheres was much higher than the conductivity of the external medium, and was attributed to counterions accumulated around fixed charges of chitosan and unknown ion conduction mechanisms, for example, protonic transport through the ionized sites. The adsorption abilities of the microspheres were also examined for Ca²⁺, Mg²⁺, Cu²⁺, and La³⁺ ions, which showed that Cu²⁺ ions are more tightly bind to chitosan than the other ions.