Atmospheric
Optics
Freezing Bubbles
Water caught in the act freezing by Daniela Rapava at Rimavská Sobota Observatory, Slovakia. The air was at about minus 5 Celsius.
Daniela’s bubble mixture was quite concentrated, 1-2 volumes sugar, 2 volumes water and 3 of detergent.
The phase change from water to ice or crystallization needs tiny nuclei, seeds, on which crystals can grow. Otherwise the water stays in a higher Gibbs energy state as a supercooled liquid. Eventually, homogeneous nucleation will occur at temperatures of -40 C or even well below in pure water.
Crystal growth is restricted by the thin film into plate-like habits with strong six-fold hexagonal symmetry. Each crystal grows along three (bi-directional) growth axes. Growth along the fourth (c) axis is restricted. The geometry echoes the underlying structure of ice at the atomic level.
At some stage the sugar could also be crystallizing out. Observe the fascinating growth of the latter on a microscope slide with crossed polarized light.
The colours could be thin film interference and/or birefringence.
Bubble blowing is fun!
All images ©Daniela Rapava
A chemist's ball and stick model of ice showing its hexagonal structure.
The red balls represent large oxygen atoms. Between them along the white sticks but not equidistant are hydrogen atoms.
Each hydrogen is tightly (covalently) bonded to one oxygen and much less so to the other. That the latter weak bonding occurs at all gives ice an open, lower density, structure that allows ice to float and us to exist.
