X‐Ray Studies of Surfactant Ordering and Interfacial Phases at the Water‐Oil Interface

Abstract

X‐ray reflectivity studies of surfactants at the water‐oil interface yield structural information with sub‐nanometer resolution. In this presentation, we reviewed recent X‐ray reflectivity measurements of the interface between water and a hexane solution of the hydrocarbon alkanol CH₃(CH₂)₁₉OH and fluorocarbon alkanol CF₃(CF₂)₇(CH₂)₂OH. The mixed system exhibits three monolayer phases, two of which are similar to single surfactant phases. A transition from a liquid monolayer to a solid monolayer occurs with increasing temperature. This unusual phase transition and the qualitative features of the phase diagram are predicted by an appropriate superposition of the behavior of the two single surfactant systems.

Keywords:

• X‐ray reflectivity
• surfactants
• water‐oil interface

Acknowledgments

We acknowledge conversations with Professor Dirk Morr (UIC Physics). This work was supported by the donors of The Petroleum Research Fund administered by the ACS, the UIC Campus Research Board, and the NSF Division of Materials Research. Brookhaven National Laboratory is supported by the U.S. Department of Energy.