Liquid-to-crystal nucleation: Automated lag-time apparatus to study supercooled liquids

The statistics of liquid-to-crystal nucleation are studied using an automat ed lag-time apparatus. A single 500 muL sample of distilled water is repeat edly supercooled to a fixed temperature below its equilibrium freezing temp erature, held until freezing occurred, and then thawed. Our raw data is the n a set of approximately 300 lag-times for each of three set supercooling t emperatures. In each case, a small insoluble AgI crystal was added to ensur e heterogeneous nucleation and average nucleation temperatures around Delta T=8 K. The distribution of lag-times is analyzed, and shown to be well appr oximated by a single exponential decay, with average lag-times in the range of 1000-3000 seconds. This average lag-time decreases markedly at deeper l evels of supercooling, and for the present data, this decrease is fit equal ly well by exponential, power law decay, and classical nucleation functiona l forms. (C) 2001 American Institute of Physics.