Benetzungs

Benetzungs (wetting) refers to the interaction that determines whether a liquid will spread on or adhere to a solid surface. It is often quantified by the contact angle theta formed by a liquid on a surface in a surrounding vapor. According to Young's equation, gamma_sv = gamma_sl + gamma_lv cos theta, where gamma_sv is the solid–vapor surface tension, gamma_sl is solid–liquid interfacial tension, and gamma_lv is liquid–vapor surface tension. The contact angle provides the wetting regime: theta near 0 implies complete wetting; 0-90 degrees wetting is typically hydrophilic; 90-180 degrees implies partial or non-wetting; theta above 150 degrees often termed superhydrophobic.

Surface roughness and chemical heterogeneity modify apparent wetting. The Wenzel model accounts for roughness via cos theta* = r cos theta, where r is the roughness factor. The Cassie–Baxter model applies to rough or porous surfaces with multiple constituent wetting states: cos theta* = f1 cos theta1 + f2 cos theta2, with area fractions fi. Dynamic wetting involves advancing and receding contact angles and hysteresis, affected by motion, viscosity, and surface structure. The spreading coefficient S = gamma_sv − gamma_sl − gamma_lv indicates tendency to spread; S>0 favors complete wetting.

Applications span coatings, inkjet printing, microfluidics, and oil recovery. Measurement commonly uses contact-angle goniometry, though roughness, chemical inhomogeneity, and rough textures complicate interpretation and define apparent rather than intrinsic contact angles.

Historically, the concept originated with Thomas Young in 1805; subsequent refinements include Dupré’s work on interfacial tensions and the Wenzel and Cassie–Baxter models for rough surfaces.