Experimental investigation of the effects of ionic micelles on colloidal stability

The effects of ionic micelles (tetradecyltrimethylammonium bromide (C14TAB) and sodium dodecylsulfate (SDS)) on the stability of a dispersion of highly charged silica particles was investigated both visually and using UV-vis absorption. As the surfactant concentration increased from 0 to 30 cmc, a clear critical flocculation concentration was observed with both surfactants. For SDS, restabilization was observed at 20 cmc. These stability results were compared to energy profiles that were calculated using measured force profiles between a single silica sphere and plate obtained with colloid-probe atomic force microscopy. It was found that flocculation would occur once the energy well formed by depletion attraction exceeded 3 k(B)T, while restabilization occurred once the long range structural energy barrier exceeded 8 k(B)T. These values are consistent with the energy levels needed for flocculation and restabilization predicted by other researchers.