Line Tension and Entropy for Molecularly Thin Liquid CrystalFilms at Temperatures Corresponding to Less-Ordered BulkPhases

by Joseph Santiago Yarzebinski

Institution: Kent State University
Year: 2016
Keywords: Physics; line tension; line energy; 8CB; monolayer; thin film; Brewster Angle Microscope; BAM
Posted: 02/05/2017
Record ID: 2072840
Full text PDF: http://rave.ohiolink.edu/etdc/view?acc_num=kent1469646126


This thesis considers thin films of 4'-n-octyl-4-cyano-biphenyl (8CB). At room temperature, 8CB forms a monolayer on a water surface in open air, given the right ratio of area to number of molecules. Then, as that ratio is decreased by a small amount, either by decreasing the area of the surface or by adding more 8CB, regions that are three molecules thick appear and coexist with an overall background that is one molecule thick. The separation line between the two distinct fluid phases, monolayer and trilayer, has a line tension, or energy per unit length. As more 8CB is added, trilayer predominates and becomes the background, with monolayer islands, but the behavior of the line separating the two phases remains the same. A Brewster angle microscope images 8CB surface layers on water with good contrast between phases.The objective of this thesis is to measure the line tension associated with this phase boundary as a function of temperature, with particular attention to temperatures at which the bulk liquid crystal would not form layers. A constant non-zero line tension means that domains in a perturbed region of the surface will relax to a circular shape if allowed to reach equilibrium. A hydrodynamic model is employed to correlate the changing shape of a domain during the relaxation process with an associated line tension. Advisors/Committee Members: Mann, Elizabeth (Committee Chair).