Usual and unusual crystallization from solution

Nucleation is a stochastic phenomenon and the probability of observing the critical nuclei formation is very low. Our aim is to enhance nucleation in the metastable zone enabling us to locate and control it. The first step is to determine the nucleation rate, and thus the nucleation behavior of the molecule studied. The two usual methods for determining nucleation rate are measuring induction time by direct counting/observation and direct determination of the steady-state rate of homogeneous nucleation. The second step consists in acting on nucleation, to control, locate and observe it. We develop unusual approaches, adding an external field to the crystallization conditions or using confinement. Ultrasounds reduce induction time and increase the number of crystals. The light irradiation induces nucleation by forming radicals. The electric field tends to localize the nucleation near one electrode depending on the polarity of the molecule studied in acting locally on the density of the solution. Lastly confinement was tested, and results indicate that this approach is very promising for controlling nucleation spatially and generate one single crystal per droplet. (C) 2010 Elsevier B.V. All rights reserved.