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 CH 3 (CH 2 ) 19 OH and fluorocarbon alkanol CF 3 (CF 2 ) 7 (CH 2 ) 2 OH. 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.

Phase transitions of fluorotelomer alcohols at the water|alkane interface studied via molecular dynamics simulation

“…Unlike 6 : 2 FTOH, LE–C transitions in monolayers of 8 : 2 and 10 : 2 FTOH which have longer fluorinated tails were confirmed by independent experiments: brewster angle microscopy confirmed the existence of two monolayer phases at the water|oil interface, 40 and X-ray reflectivity confirmed that one of these is condensed and solid—confirming the presence of a LE–C transition. 41 Pingali et al 42 studied the competitive adsorption and phase behavior of the long chain alcohol C 20 OH and the fluorotelomer alcohol 8 : 2 FTOH at the water–hexane interface. They found the low-temperature (<24 °C) behavior to be highly sensitive to the molar ratio of the two surfactants in the hexane solution, with each capable of fully displacing the other at the interface.…”