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Updated: Aug 17, 2026

Plunge Freezing: A Tool for the Ultrastructural and Immunolocalization Studies of Suspension Cells in Transmission Electron Microscopy
Published on: May 5, 2017
Physical Chemistry of the Freezing Process of Atmospheric Aqueous Drops
Anatoli Bogdan1,2, Mario J Molina3
1Laboratory of Polymer Chemistry, Department of Chemistry, University of Helsinki , P.O. Box 55, FI-00014 Helsinki, Finland.
Abstract:
In supercooled aqueous solutions, ice nucleation is the initial stage of the freezing process. In this paper, we present experimental results that indicate that during the freezing of aqueous solutions, freeze-induced phase separation (FIPS) into pure ice and a freeze-concentrated solution (FCS) takes place. Our observations involve the use of an optical cryo-microscope (OC-M) to record images and movies. The results visually indicate for the first time that there are two freezing processes for (NH4)3H(SO4)2/H2O solutions: (i) contact freezing, as is the case for pure water drops, and (ii) the Wegener-Bergeron-Findeisen process, which is the growth of frozen drops (ice) at the expense of liquid ones. We also present OC-M images of frozen micrometer-scaled H2SO4/H2O drops that support our previous finding that freezing of these solutions generates mixed-phase particles, namely an ice core coated with a FCS. These results are relevant for atmospheric as well as for pharmaceutical sciences.
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