Portal de Periódicos da CAPES

Positional order in Langmuir monolayers: An x-ray diffraction study

1999; American Physical Society; Volume: 59; Issue: 2 Linguagem: Inglês

10.1103/physreve.59.2141

1538-4519

Vladimir M. Kaganer, Gerald Brezesinski, Helmuth Möhwald, Paul B. Howes, K. Kjær,

Material Dynamics and Properties

The structural phase transition from the hexagonal to a distorted-hexagonal (centered rectangular) phase (the $\mathrm{LS}\ensuremath{-}S$ transition) in Langmuir monolayers of octadecanol is studied in a grazing incidence x-ray diffraction experiment. We find algebraic decay of positional correlations, which suggests solid-like order in both phases at the distances accessible in the present x-ray diffraction experiment. The transition is accompanied by strong positional disorder, which is evident from the drastic increase of the exponent $\ensuremath{\eta}$ to values $\ensuremath{\eta}>2$ close to the transition. Remarkably, on approaching the transition, the continuous increase of $\ensuremath{\eta}$ is apparent already at $20\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ above it. The positional disorder is attributed to elastic distortions around pretransitional fluctuations.