X-ray diffraction study of a recently identified phase transition in fatty acid Langmuir monolayers

M. K. Durbin*, A. Malik, R. Ghaskadvi, M. C. Shih, P. Zschack, Pulak Dutta

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

62 Scopus citations

Abstract

Using Brewster angle microscopy to study fatty acid Langmuir monolayers, Overbeck and Mobius (J. Phys. Chem. 1993, 97, 7999) have observed changes of texture indicating a new phase boundary not visible in monolayer isotherms. We have studied Langmuir monolayers of CH3(CH2)17COOH at 30°C using X-ray diffraction. We find that the monolayer undergoes a first-order phase transition from the known L2 phase in which molecules tilt toward a nearest neighbor to a phase with tilt toward a next-nearest neighbor. Both before and after the transition, the structures are hexagonal in the plane perpendicular to the molecules. Neither the intermolecular spacing in this plane (≈ 4.85 A, close to that seen in the Rotator II phase) nor the tilt magnitude has an observable discontinuity at this transition; only the tilt direction changes. As a result, the isotherm area/molecule is also continuous across the transition.

Original languageEnglish (US)
Pages (from-to)1753-1755
Number of pages3
JournalJournal of Physical Chemistry
Volume98
Issue number7
DOIs
StatePublished - Jan 1 1994

ASJC Scopus subject areas

  • Engineering(all)
  • Physical and Theoretical Chemistry

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