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Using dislocations to probe surface reconstruction in thick freely suspended liquid crystalline films

J. A. Collett and Daniel Martinez Zambrano
Phys. Rev. E 92, 040501(R) – Published 8 October 2015

Abstract

Surface interactions can cause freely suspended thin liquid crystalline films to form phases different from the bulk material, but it is not known what happens at the surface of thick films. Edge dislocations can be used as a marker for the boundary between the bulk center and the reconstructed surface. We use noncontact mode atomic force microscopy to determine the depth of edge dislocations below the surface of freely suspended thick films of 4-n-heptyloxybenzylidene-4-n-heptylaniline (7O.7) in the crystalline B phase. Here, 3.0±0.1 nm high steps are found with a width that varies with temperature between 56 and 59C. Using a strain model for the profile of liquid crystalline layers above an edge dislocation to estimate the depth of the dislocation, we find that the number of reconstructed surface layers increases from 4 to 50 layers as the temperature decreases from 59 to 56C. This trend tracks the behavior of the phase boundary in the thickness dependent phase diagram of freely suspended films of 7O.7, suggesting that the surface may be reconstructed into a smectic F region.

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  • Received 14 August 2015
  • Revised 24 September 2015

DOI:https://doi.org/10.1103/PhysRevE.92.040501

©2015 American Physical Society

Authors & Affiliations

J. A. Collett* and Daniel Martinez Zambrano

  • Department of Physics, Lawrence University, 711 East Boldt Way, Appleton, Wisconsin 54911, USA

  • *jeffrey.a.collett@lawrence.edu

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Issue

Vol. 92, Iss. 4 — October 2015

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