Domain Size Distribution in Phase Separated Cholesterol/Phospholipid Langmuir Monolayers: Line Tension and Transition Kinetics

Abstract

Multicomponent phase separated phospholipid monolayer systems of a canonical cholesterol and DMPC (∼30/70 mole percent) have been used to study several aspects of cholesterol/phospholipid interaction and phase behavior. Despite the successful characterization and theoretical approaches applied to these systems there are still important details of monolayer morphology that are not fully understood. Here, we address the role of transition kinetics on domain size distributions. For our experiments, three different barrier speeds were chosen (4, 40, 400 cm squared per minute) as the monolayer passed through the miscibility phase transition (8.4 mN/m transition pressure). Average domain size was observed to decrease as the barrier speed increased (transition rate). The detailed size distribution measurements also provide the opportunity to measure changes in phase fraction and size distribution with monolayer surface pressures (2, 4, and 6, mN/m). Careful study of factors influencing the size distribution of phase separated domains is particularly relevant to the recently proposed line tension measurement technique (Lee et al., vol. 108 pp. 9425, PNAS 2011). We have implemented this method for the monolayer system studied here. A comparison to previously implemented line tension measurements based on a Fourier analysis of boundary fluctuations approaches will be presented. Finally, a brief comparison on the role of dyes and dye quality will be presented. Comparison among one year old Texas Red and new Texas Red, showed an impact in the sizes of domains.