Effect of pH on adsolubilization of toluene and acetophenone into adsorbed surfactant on precipitated silica

The effect of pH on the adsorption of cetyltrimethylammonium bromide on precipitated silica and the adsolubilization of toluene and acetophenone in CTAB admicelles has been examined. Both single and mixed-solute systems were investigated at pH values 5 and 8. Adsorption results show, as expected, that adsorption increased with increasing pH. In the single solute systems, the adsolubilization of both solutes increased with increasing equilibrium concentration of the solute in the aqueous phase. For toluene, pH had little effect on the adsolubilization. In contrast, the pH effect on acetophenone was much more pronounced, with the adsolubilization increasing significantly when the pH was increased from 5 to 8. Thus, the properties of the electrical double layer in the admicelle affect the levels of adsolubilization for polar solutes. In mixed solute systems, the presence of acetophenone had an mildly synergistic effect on toluene adsolubilization whereas the presence of toluene had a strongly synergistic effect on acetophenone adsolubilization. The synergism was approximately the same at both pH values, indicating that the synergism is not a strong function of solution pH.