ALTA: An automated lag-time apparatus for studying the nucleation of supercooled liquids

Abstract

An automated apparatus for studying repeatedly the nucleation of a sample of supercooled liquid is designed and constructed. Many of the ideas are developed from an apparatus of M. Baldwin and B. Vonnegut [Rev. Sci. Instrum. 53, 1911 (1982)]. After preparation of a nonequilibrium state, ALTA measures repeatedly the ‘‘lag time’’ or ‘‘induction’’ time before nucleation and growth of the equilibrium state. A single sample is used in all experiments. The operation of the apparatus is demonstrated by generating a time series of lag times for the nucleation of supercooled water on (insoluble) AgI crystals at the temperature 269.2 K. The same sample is repeatedly frozen and thawed over 350 times. An average lag time τ can be measured precisely and reproducibly. However, nucleation of this sample is shown to be a stochastic process obeying ‘‘first-order’’ kinetics. Improved methods for analyzing time series of nucleation data are presented and tested.