Langmuir monolayers as disordered solids: Strain-tilt-backbone coupling and natural order parameters for the swiveling transitions

Tadeusz Luty, David R. Swanson, Craig J. Eckhardt

Research output: Contribution to journalArticle

8 Citations (Scopus)

Abstract

Multistability of Langmuir monolayers, in particular those composed of fatty acids, is reflected by a very rich and complicated phase diagram. We argue that strain-tilt-backbone coupling determines the behavior described by that diagram. Following the solid state approach, we show that a natural order parameter set is defined by thermal averages of spherical harmonics and strain tensor components. In addition, we show that the backbone order parameter can be conveniently represented by an elastic dipole tensor. Treating Langmuir monolayers as disordered solids, we have derived an orientational entropy contribution to the free energy. The swiveling transition between L2(L2h) and L′2(L*2) phases is discussed in detail and is conveniently described in terms of the proposed order parameters. We discuss why the change in the distortion direction of the 2D unit cell tracks the change in tilt direction of the molecules, and also why the cell dimensions involved in the swiveling transition are the same in both phases.

Original languageEnglish (US)
Pages (from-to)2606-2611
Number of pages6
JournalJournal of Chemical Physics
Volume110
Issue number5
DOIs
StatePublished - Feb 1 1999

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monomolecular films
Tensors
Monolayers
tensors
Free energy
Phase diagrams
Entropy
Fatty Acids
fatty acids
spherical harmonics
cells
Molecules
free energy
diagrams
phase diagrams
entropy
dipoles
solid state
Direction compound
molecules

ASJC Scopus subject areas

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry

Cite this

Langmuir monolayers as disordered solids : Strain-tilt-backbone coupling and natural order parameters for the swiveling transitions. / Luty, Tadeusz; Swanson, David R.; Eckhardt, Craig J.

In: Journal of Chemical Physics, Vol. 110, No. 5, 01.02.1999, p. 2606-2611.

Research output: Contribution to journalArticle

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