SALT EFFECT ON WETTING/NONWETTING BEHAVIORS

We study the phase behavior, the wetting/nonwetting behaviors, and the wetting transition of systems of the type water + n-alkane + diethylene glycol monohexyl ether (C(6)E(2)) + salt. Three systems-water + n-tetradecane + C(6)E(2) + NaCl, water + n-hexadecane + C(6)E(2) + NaCl, and water + n-octadecane + C(6)E(2) + NaCl-are used to demonstrate that the effect of adding a lyotropic salt (NaCl) on phase and interfacial behaviors is equivalent to that of raising the temperature. For all three systems, there exists a middle beta phase wetting transition at the interface separating the upper alpha and lower gamma phases. The wetting transition concentration increases as the chain length of the n-alkane increases. On the other hand, two systems-water + n-tetradecane + C(6)E(2) + NaI and water + n-hexadecane + C(6)E(2) + NaI-are used to demonstrate that the effect of adding a hydrotropic salt (NaI) on phase and interfacial behaviors is equivalent to that of decreasing the temperature. The gamma phase wetting transition at the alpha beta interface is observed in these two systems. The anionic effect on the interfacial wetting transition is also discussed by using three different salts, NaCl, NaBr, and NaI, while salts LiCl, NaCl, and KCl are used for the cationic effect.