Nucleation of liquid bridges and bubbles in nanoscale capillaries

Nucleation of liquid bridges and bubbles during condensation and evaporation of Lennard-Jones fluid in cylindrical pores is explored by Monte Carlo simulation. The isotherm of constrained critical nuclei is constructed using the gauge cell method. We confirm the Everett–Haynes scenario of bridging through the formation of a bump/undulation on the adsorption film. The molecular structure of growing bridges and cavitating bubbles is revealed. A new simulation approach is introduced to calculate the nucleation energy barriers. The method is based on the introduction and subsequent removal of a virtual “ghost” potential field with a tunable magnitude. Two computation schemes for determining the free energy of nuclei are elaborated based on the thermodynamic integration along a trajectory of states generated in the tunable ghost field and on the umbrella sampling. The methods developed are applicable to study various nucleation phenomena.