Surfaces of freely suspended thick films of 4-n-heptyloxybenzylidene-4-n-heptylaniline (7O.7) in the crystalline-B phase have been imaged using non-contact mode atomic force microscopy. Steps are observed on the surface of the film with a height of 3.0 +/- 0.1 nm corresponding to the upright molecular length of 7O.7. In addition, we find that the step width varies with temperature between 56 and 59 degrees C. The steps are many times wider than the molecular length, suggesting that the steps are not on the surface but instead originate from edge dislocations in the interior. Using a strain model for liquid crystalline layers above an edge dislocation to estimate the depth of the dislocation, we estimate that the number of reconstructed surface layers decreases from 50 to 4 layers as the temperature increases from 56 to 59 degrees C. 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 phase.
Level of Honors
summa cum laude
Jeffrey A. Collett
Martinez Zambrano, Daniel E., "Temperature Dependent Surface Reconstruction of Freely Suspended Films of 4-n-heptyloxybenzylidene-4-n-heptylaniline" (2015). Lawrence University Honors Projects. 81.
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