Monte Carlo simulation of the shapes of domains in phospholipid monolayers

The dispersed domains which result from phase separation in phospholipid monolayers have long been known to exhibit complex and intriguing geometries. Over the last decade, much work has gone into the theoretical prediction of these shapes using energy minimization calculations. While such studies have provided much insight into the behavior of domain shapes, they ignore the effect of entropy and thus are truly applicable only as the temperature approaches absolute zero. In this paper, we present a Monte Carlo approach for the prediction of domain shapes through simulation, thereby introducing temperature as an explicit parameter. Where applicable, results from this simulation are compared to prior shape calculations and to experimental results. We find that the first order transition predicted between circular and bilobed domains applies only at low temperature. Moreover, we find that bilobed domains should only be found when the domain elongation occurs slowly; rapid elongation produces multiple branched domains. Finally, we find that the width of these branches in elongated domains is independent of both the number of branches and the size of the domain.