Metastability Limit for the Nucleation of NaCl Crystals in Confinement.
We study the spontaneous nucleation and growth of sodium chloride crystals induced by controlled evaporation in confined geometries (microcapillaries) spanning several orders of magnitude in volume. In all experiments, the nucleation happens reproducibly at a very high supersaturation S ∼ 1.6 and is independent of the size, shape, and surface properties of the microcapillary. We show from classical nucleation theory that this is expected: S ∼ 1.6 corresponds to the point where nucleation first becomes observable on experimental time scales. A consequence of the high supersaturations reached at the onset of nucleation is the very rapid growth of a single skeletal (Hopper) crystal. Experiments on porous media also reveal the formation of Hopper crystals in the entrapped liquid pockets in the porous network and consequently underline the fact that sodium chloride can easily reach high supersaturations, in spite of what is commonly assumed for this salt.
†Van der Waals-Zeeman Institute, Institute of Physics, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands.
Julie
J
Desarnaud
‡ETH, Institut für Technologie in der Architektur, HIL E 46.3, Wolfgang-Pauli-Strasse 15, 8093 Zürich Hönggerberg, Switzerland.
Hannelore
H
Derluyn
‡ETH, Institut für Technologie in der Architektur, HIL E 46.3, Wolfgang-Pauli-Strasse 15, 8093 Zürich Hönggerberg, Switzerland.
Jan
J
Carmeliet
†Van der Waals-Zeeman Institute, Institute of Physics, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands.
Daniel
D
Bonn
†Van der Waals-Zeeman Institute, Institute of Physics, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands.
Noushine
N
Shahidzadeh
Hopper crystal; confinement; crystallization; metastability limit; porous media; supersaturation