Adsorption behavior of surfactant-polyacrylamide mixtures with kaolin

The adsorption behavior of three surfactants-hexadecylpyridinium bromide (H PyBr), sodium dodecylbenzene sulfonate (SDBS), and Triton X-100 (TX-100)-on kaolin from aqueous solution is monitored as a function of pH. The nature and shape of the adsorption isotherms are typical and highly dependent on t he surfactant structure. All three surfactants adsorb on kaolin beyond the limits of monolayer coverage. Isotherms for HPyBr fit the Langmuir equation well. SDBS isotherms are typical of a two-stage process, and TX-100 adsorp tion isotherms are S-shaped. The pH-sensitive adsorption of each surfactant and the models used to represent the isotherms are considered together in explaining the mechanism of adsorption in each case. The complex mixture ad sorption behavior from polyacrylamide-surfactant mixtures is also determine d in acidic and basic pH media. Three polyacrylamides, catam1, anam1 and no nam1, are chosen to represent cationic, anionic and nonionic polymers, resp ectively. Both competitive and synergistic effects are noted in the mixture adsorption depending upon the polymer-surfactant pair and the mode of intr oduction of a second component in the presence of another. The results are explained by considering various factors such as changes in the nature of s olvent power of the media, interaction between the polymer and surfactant i n the bulk solution as well as at the kaolin surface, blocking of surface s ites by a preadsorbed component, and the change in the conformation state o f polymer chains.