Phase separation of a self-assembled monolayer made from hydrocarbon-fluorocarbon disulfide

Phase separation of self-assembled monolayers made from an asymmetric disulfide consisting of hydrocarbon and fluorocarbon branches was studied using a scanning probe technique. After the films were annealed, phase-separated domains with a lateral dimension of 20-200 nm were observed and the components of the domains were identified by the friction. The tilt angle of the fluorocarbon chain was found to be larger than that of the hydrocarbon's. A Monte Carlo simulation indicated that the difference in the van der Waals interaction of the two branches is not sufficient to cause the observed phase separation. Other attractive interactions should be introduced, e.g. the dipole-dipole interaction, which changes to being attractive when the molecules have a large tilt angle.