DYNAMICS OF DOMAIN SHAPE RELAXATION IN LANGMUIR FILMS

The dynamics of domain shape relaxation exhibited by individual domains of finite size have been investigated in a Langmuir film containing the phospholipid dimyristoylphosphatidylcholine (DMPC) and cholesterol. The temporal evolution of shape distortions following a stepped expansion of the film has been monitored by examination of simple geometrical quantities, notably perimeter, enclosed area, and curvature. In addition, spectral shape analysis has been invoked to determine temporal autocorrelation functions for spectral densities representing the primary modes of boundary distortion. This analysis indicates that the mode relaxation is well approximated by an exponential time dependence and that the decay of shape distortions in dipolar fluids of the type represented by Langmuir films is mediated by a monotonic reduction of the domain perimeter, constrained by the condition that the enclosed area remain constant. While these findings would suggest a description of the shape relaxation in terms of an effective line tension, systematic deviations from such an approximation are revealed by quantitative comparison with a pertinent evolution equation describing area-conserving dissipative dynamics of plane curves. These deviations are attributed to the nonlocal action of dipolar forces.