lyophobic

Lyophobic is an adjective used in chemistry and materials science to describe substances that show little affinity for a given liquid and do not wet well with it. In colloid chemistry, a lyophobic substance (or lyophobic sol) has a dispersed phase that is not readily wetted by the dispersion medium. Such sols are typically unstable and require protective colloids or electrolytes to prevent coagulation; examples include many metal sols in water, such as gold or silver sols, which coagulate when diluted or when electrolytes are added.

The term also describes the interaction between a liquid and a solid surface. A lyophobic surface is poorly wetted by the liquid, causing droplets to bead up and form a relatively high contact angle. This behavior is solvent-specific; a surface can be lyophobic to water while being more easily wetted by another liquid. Conversely, a lyophilic surface readily wets a liquid and spreads, often forming a thin film.

Etymology traces to Greek roots associated with liquid and fear or aversion, reflecting the idea of a liquid-repelling tendency. In modern use, the concept is closely related to wettability and wetting properties, though the term is most often encountered in colloid and surface science. It is important to note that lyophobicity is not a universal property across all liquids for a given material; a surface or material can be lyophobic with respect to one liquid and lyophilic with respect to another.