Influence of bivalent ions on the low frequency electro-optic response of charged colloids in low electrolyte suspensions

• Published in: Colloids and surfaces. A, Physicochemical and engineering aspects Physicochemical and engineering aspects, 2010-05, Vol.361 (1), p.56-61
• Main Authors: Stoimenova, Maria, Buleva, Maria
• Format: Article
• Language: English
• Subjects: Charging; Chemistry; Colloidal state and disperse state; Colloids; Condensing; Dielectric relaxation of colloids; Electro-optics; Electrolytes; Exact sciences and technology; General and physical chemistry; Interface polarization of colloids; Low frequencies; Low frequency colloidal electro-optics; Oxide colloid particles; Physical and chemical studies. Granulometry. Electrokinetic phenomena; Saturation; Surface chemistry; Surface physical chemistry
• ISSN: 0927-7757; 1873-4359
• DOI: 10.1016/j.colsurfa.2010.03.011

Two low frequency dielectric relaxations are related to the process of surface polarization of charged particles: one, detected in the kHz/MHz frequency domain ( α p) and a second one, detected in the domain of particle rotation ( α n). The paper presents results concerning the second low frequency relaxation. A parameter is defined (the ratio of the two effects α n/ α p), which is representative for the relation of this relaxation to particle surface electric state. The ratio α n/ α p remains constant (or varying in narrow limits) with field intensity. The influence of mono- and bivalent (counter) ions on this parameter is followed as a first step to the analysis of the mechanism of the second relaxation. The results show that the only electro-optic parameter which distinguishes the adsorption of bivalent ions on particle surface is the ratio α n/ α p. The analysis of the second low frequency relaxation is important for elucidating of various problems: the difference in the electro-optic saturation curves taken at ac and dc pulses; the mobility of condensed ions; the significant discrepancy between the variation of particle polarizability and electrophoretic mobility in numerous cases, etc.