Line tension and entropy in a liquid crystal Langmuir film*

Often two or more phases coexist within a monolayer or bilayer; the connection between these and possible dynamic or static microdomains within cell membranes is still debated. The line tension associated with the boundary between two phases within a monolayer or bilayer controls the size distribution, shape, and dynamics of domains. Theoretical models for this energy remain relatively untested. This work considers a model fluid system, trilayer/monolayer coexistence within a Langmuir film. The line tension associated with the boundary between these phases is measured as a function of temperature over a large range (12-37$^{\circ}$C). Compact, isolated trilayer domains are stretched from their equilibrium circular shape, and the free relaxation is analyzed with a hydrodynamic model previously tested by Wintersmith et al. [1] Line tension decreased with rising temperature. A careful treatment of the thermodynamics of the line boundary allow us to estimate the line entropy associated with the trilayer, and to test possible models for the boundary.\\[4pt] [1] Wintersmith, Jacob R.; Zou, Lu; Bernoff, Andrew J.; Mann, J. Adin Jr; Kooijman, Edgar E.; and Mann, Elizabeth K.. ``Determination of Interphase Line Tension in Langmuir Films.'' Physical Review E 75 (2007).