Liquid-to-Solid Phase Transition of a 1,3-Dimethylimidazolium Chloride Ionic Liquid Monolayer Confined between Graphite Walls

Molecular dynamics simulations were performed to study the phase behavior of a monolayer of room temperature ionic liquid 1,3-dimethylimidazolium chloride ([Dmim][Cl]) confined between two graphite walls at 425 K. These simulations predict a first-order freezing transition from a liquid monolayer to a solid monolayer induced by varying the distance between the parallel graphite walls (H = similar to 0.65-0.95 nm). The resulting monolayer solid consisting of a hydrogen-bonded network structure is very different from bulk crystalline [Dmim][Cl]. The phase transition can be induced only at a molecular surface density of rho = 1.9/nM(2).