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--heptyloxybenzylidene-4--heptylaniline (7O.7) in the crystalline phase. Here, nm high steps are found with a width that varies with temperature between 56 and . 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 . 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 region.
- Received 14 August 2015
- Revised 24 September 2015
DOI:https://doi.org/10.1103/PhysRevE.92.040501
©2015 American Physical Society