EFFECT OF CATIONIC SURFACTANT ADSORPTION ON SURFACE-CHARGE OF QUARTZ CAPILLARIES

The potential and charge of a quartz surface and its dependence of the concentration C of cetyltrimethylammonium bromide (CTAB) at constant background electrolyte concentration of 5.10(-4) M NaCl have been measured by capillary electro-kinetics. Charge reversal of the quartz surface occurs at C(i) = 10(-4) M CTAB. At C < C(i) adsorption occurs predominantly on charged SiO- centers of the quartz surface; the adsorption potential of CTA+ is close to 15 kT. At C > C(i) the adsorption centers are the hydrophobic sections of the surface. Comparison with data on CTAB adsorption on silica shows that the degree of dissociation of CTAB molecules in the second adsorption layer is 10-12% which is linked to adsorption of the Br- counterions.