  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 is linearly dependent on the thickness difference
between the coexisting phases in the film. 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.
