The Influence of Hydrophobic Surfaces on the Freezing Point of Water Studied by XRD

Introduction

Approximately 70% of the earth’s surface is covered by water. In addition, a significant amount of water exists as vapor in the atmosphere. Since the solubility of water in air depends on the temperature, liquid water commonly forms on cold surfaces in humid environments (condensation).

Water is the only non-metallic substances that expands as it freezes. The formation of ice crystals, and the volume increase associated with it, can damage materials or surfaces and can lead to bursting of containers or pipes. Ice is also a poor thermal and electrical conductor compared to liquid water. This can lead to damage in electronic and mechanical equipment.

In addition, the reduced friction of frozen roads leads to a significant number of accidents every year. For these reasons, methods to protect surfaces and mechanical parts from freezing are of great interest for industry and academia. Different approaches to prevent freezing can be used, e.g. heating or thermal insulation of critical parts, or dehumidification of the surrounding atmosphere. These approaches all come with their own drawbacks, and are usually only applicable under certain conditions. An alternative, more general solution, is surface treatment or coating. Modifying certain physical properties of surfaces can reduce the thermal contact with water droplets on the surface, and therefore lower the temperature at which freezing occurs.

Four samples with different hydrophobic surface coatings were investigated by X‑ray diffraction (XRD) in this report. XRD is a useful method for such investigations, as it can clearly identify the transition from the amorphous (liquid water) to crystalline (frozen water) state.