Transient behavior and time lags in binary nucleation

Abstract

This chapter examines the transient and time lag behavior of six binary systems representing a wide range of ideal and nonideal solution behavior. It focuses on ethanol–hexanol, a system that forms ideal liquid mixtures even though the equilibrium vapor pressures of the pure components differ by a factor of 226 at the simulation temperature of 260 K. To investigate transient binary nucleation, both qualitatively and quantitatively, it numerically solved the birth–death equations for vapor-to-liquid phase transitions. In its early transient stage, binary nucleation rarely occurs via the saddle point. Instead, most binary systems pass through a temporary stage in which the region of maximum flux extends over a ridge on the free energy surface before reaching the state of saddle point nucleation. Both the number of particles formed and their composition may be affected, and this could be very important for nucleation in glasses and other condensed mixtures for which timescales are very long. To plan experiments, accurate estimates of the time lag are important. The chapter directly calculates the time lag for the saddle point flux using the numerical results presented and compares it with the available analytical predictions. Although the analytical results overestimate the time lag by factors of 2–6, the numerical results followed the predicted analytical trends quite closely under most conditions.