The interfacial tensions and dihedral angles of hexadecane lenses on aqueous solutions of dodecyltrimethylammonium bromide (DTAB) were measured in air as a function of the molality of DTAB at 298.15 K and atmospheric pressure. The air/water interfacial tension of DTAB solution shows a break point that shifts to a lower concentration in the presence of a hexadecane lens. Ellipsometric measurements showed a continuous variation in ellipticity with concentration for pure DTAB solutions, but a discontinuous change in the ellipticity of the air/water interface in the presence of a hexadecane lens. This behavior can be viewed either as a first-order wetting transition driven by the adsorbed surfactant, or as a gaseous-expanded phase transition in the surfactant adsorbed film induced by the hexadecane. The formation of a microscopic oil film in equilibrium with a lens is rationalized by an attractive long-range potential across the thin film. From the measurement of dihedral angles, it was found that there was a concentration region where a lens exists stably even when complete wetting was expected from measured values of interfacial tensions.
All Science Journal Classification (ASJC) codes
- General Materials Science
- Condensed Matter Physics
- Surfaces and Interfaces