AVS 50th International Symposium
    Electrochemistry and Fluid Solid Interfaces Tuesday Sessions
       Session EC+SS-TuM

Invited Paper EC+SS-TuM7
Molecular Ordering at Liquid-Liquid Interfaces

Tuesday, November 4, 2003, 10:20 am, Room 326

Session: Water at Interfaces I: Structure and Electrochemistry
Presenter: M.L. Schlossman, University of Illinois
Correspondent: Click to Email
Our view of molecular ordering in Langmuir monolayers at the water-vapor interface influences our understanding of molecular ordering at other interfaces, including liquid-liquid interfaces for which structural information is scarce. We present a comparative study of monolayers of long-chain alkanols at the water-vapor and water-hexane interfaces using x-ray reflectivity to highlight significant differences between these two interfaces. The molecules in the Langmuir monolayer form an ordered phase of nearly rigid rods. In contrast, at the water-hexane interface the alkanol molecules form a condensed phase with progressive disordering of the chain from the hydroxy to the methyl group. Surprisingly, at the water-hexane interface the density in the head group region is 10 to 15% greater than either bulk water or the ordered head group region found at the water-vapor interface. It is conjectured that this higher density is a result of water penetration into the head group region of the disordered monolayer. The alkanol monolayers at the water-hexane interface also undergo a solid to gas phase transition as a function of temperature. X-ray off-specular diffuse scattering is used to directly probe the statistical distribution of domains in monolayers of a fluorinated alkanol near the transition temperature. Evidence that the domains are of equilibrium size suggests that the domain line tension can be determined from these measurements.