A smectic liquid crystal Langmuir film at the air/water interface: boundaries, thermodynamics and dynamics

Molecularly-thin smectic liquid crystal films at the air/water interface phase separate into regions with different numbers of layers, in analogy with free-standing smectic liquid crystalline films. We explore the boundary between two such regions, using a variety of experimental and numerical methods. We measure the line tension by stretching domains from their equilibrium circular shape and analyzing the free relaxation with a hydrodynamic model. We connect the line tension associated with the boundary to boundary structure and use the association to suggest effective line-active agents, to control the line tension and thus the domain size distribution, shape and dynamics. Such line-active agents, which are not well-understood and have proved difficult to design, are empirically important to dynamic functional domains within cell-membranes.