Experimental study of interfacial phase transitions in three-component surfactant systems

Abstract

In a three-phase equilibrium system, the middle phase either wets or does not wet the interface between the upper and lower phases. In this work, we perform a systematic experimental search for wetting transitions between wetting and nonwetting regimes in three-component water--n-alkane--${\mathrm{C}}_{\mathit{i}}$${\mathrm{E}}_{\mathit{j}}$ systems, where ${\mathrm{C}}_{\mathit{i}}$${\mathrm{E}}_{\mathit{j}}$ denotes the surfactant polyoxyethylene alcohol ${\mathrm{C}}_{\mathit{i}}$${\mathrm{H}}_{2\mathit{i}+1}$(${\mathrm{OC}}_{2}$${\mathrm{H}}_{4}$${)}_{\mathit{j}}$OH. It is found that the water--n-hexadecane--${\mathrm{C}}_{6}$${\mathrm{E}}_{2}$ and water--n-octadecane--${\mathrm{C}}_{6}$${\mathrm{E}}_{2}$ systems exhibit a wetting transition lying at least 10\ifmmode^\circ\else\textdegree\fi{} C below the upper critical temperature, and one system, water--n-tetradecane--${\mathrm{C}}_{6}$${\mathrm{E}}_{2}$, exhibits a wetting transition lying 4.3\ifmmode^\circ\else\textdegree\fi{} C below the upper critical temperature. Measurements of the contact angles as a function of temperature indicate that the wetting transition is of first order.