THE MECHANISM OF ADSORPTION OF NONIONIC S URFACTANTS ON CAB-O-SIL ANDTHE EFFECTS OF SURFACE MICELLIZATION ON THE STABILITY OF SILICA SUSPENSION

The adsorption isotherms of Triton X-100(TX 100) on a flame-hydrolyzed silica (CAB-O-SIL) from aqueous solutions and from sodium chloride (1 .0 mol/L) at 290.7 K and 304.2 K have been determined. The results sho w that the adsorption increases with increasing temperature and salini ty. Based on the theory of surfactant adsorption we proposed previousl y, the equilibrium constant of surface micellixation (K), surface mice lle aggregation number (n(sm)), surface micelle concentration (smc) an d the standard thermodynamics functions (Delta G(sm)(0), Delta S-sm(0) , Delta H-sm(0)) of surface micellization are calculated, The results show the value of n(am) increases with increasing temperature. Tn addi tion, similar to the micellization in bulk solution, the surface micel lization is also an entropy-driven process. The effects of TX-100 (wit h or without 1.0 mol/L sodium chloride) on the aggregative stability o f silica suspension have also been investigated. In the low concentrat ion range of TX 200, the stability of suspension increases with increa sing concentration of TX 100. Above the surface micelle concentration (smc) of TX 100, the stability of suspension decreases with increasing concentration of TX 100, However if the concentration approaching to the cme of TX 100, the stability of suspension increases again, The ad dition of sodium chloride enhances the surface micelle formation and r esults in a depression of stability of suspension, Based on the adsorp tion isotherms of TX 100, a model concerning surface micellization is proposed to explain the above experimental results reasonably.