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 stud ied using a scanning probe technique. After the films were annealed, p hase-separated domains with a lateral dimension of 20-200 nm were obse rved 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 th e difference in the van der Waals interaction of the two branches is n ot 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 ti lt angle.