Solid-solid transformations in a confined soft sphere fluid.

Grand canonical Monte Carlo simulations are used to investigate the structure of frozen phases in a confined soft sphere (Lennard-Jones) fluid for a bulk state point lying close to the liquid-solid freezing line. The study reveals that the pore fluid not only freezes in the pore, but solid-solid transformations occur in the two, and three-layered structures that form as the pore height is varied. Using the in-plane bond angle order parameters and pair-correlation functions, the frozen structures and transformations are related to the variations in solvation force and pore density. Transformations from square to triangular lattices are observed in both the two- and three-layered regimes. In the three-layered regime, transformations occur from the body-centered tetragonal to hcp and fcc lattices as the pore height is increased. During the transition from one to two layers, random buckled structures are observed. The structural transformations from square to triangular lattices in the confined fluid also result in a splitting in the solvation force curve.