nonwetting

Nonwetting describes the property of a solid surface or interface that resists wetting by a liquid. A nonwetting surface is one for which a liquid forms a high contact angle with the solid, typically greater than 90 degrees; a truly nonwetting or superhydrophobic surface may exhibit contact angles above 150 degrees with low contact angle hysteresis, causing droplets to bead up and roll off easily.

The degree of wetting is described by Young's equation relating the interfacial tensions of the solid–vapor, solid–liquid, and liquid–vapor interfaces. On rough or structured surfaces, the apparent contact angle is governed by models such as Wenzel or Cassie-Baxter; roughness can amplify nonwetting by trapping air beneath the droplet in a Cassie-Baxter state, leading to very high apparent contact angles.

Common materials with nonwetting properties include fluorinated polymers, silicones, and engineered micro- or nano-structured surfaces designed to create low solid–liquid contact. Water is the most common probe liquid, but wetting behavior depends on surface energy and the liquid’s properties, including polarity and surface tension. Nonwetting has wide-ranging applications, including self-cleaning coatings, anti-icing and anti-fogging surfaces, corrosion resistance, drag reduction, and microfluidics.

Measurement of nonwetting is typically performed with contact angle goniometry, using methods such as sessile drops, tilting plate, or captive bubble techniques. Advancing and receding contact angles provide information about surface heterogeneity and roughness.

Limitations include environmental sensitivity to temperature and humidity, susceptibility to contamination, and the durability of engineered surface textures. Nonwetting concepts intersect with hydrophobic and oleophobic behavior and with phenomena such as wetting transitions and immersion in liquids.