Line tension and structure of smectic liquid-crystal multilayers at the air-water interface

At the air-water interface, 4 '-8-alkyl[1,1 '-biphenyl]-4-carbonitrile (8CB) domains with different thicknesses coexist in the same Langmuir film, as multiple bilayers on a monolayer. The edge dislocation at the domain boundary leads to line tension, which determines the domain shape and dynamics. By observing the domain relaxation process starting from small distortions, we find that the line tension lambda is linearly dependent on the thickness difference Delta L between the coexisting phases in the film, lambda=(3.3 +/- 0.2) mN/m Delta L. Comparisons with theoretical treatments in the literature suggest that the edge dislocation at the boundary locates near the center of the film, which means that the 8CB multilayers are almost symmetric with respect to the air-water interface.