RecedingWinkel

RecedingWinkel is a term used in surface science to denote the receding contact angle—the angle formed at the three-phase contact line when a liquid droplet on a solid surface retracts, or de-wets, from the surface. It is one component of contact angle hysteresis, the difference between the advancing angle (measured as the liquid spreads or is driven onto the surface) and the receding angle. The receding angle reflects the balance of interfacial tensions among solid, liquid, and vapor, and it depends on surface chemistry, roughness, and the properties of the liquid. In many systems the receding angle is smaller than the advancing angle, and the exact value can be influenced by the speed of withdrawal and contact-line pinning.

Measurement and observation: The receding angle can be determined with methods such as tilting plate, pendant-drop, or sessile-drop experiments, typically by recording the angle as the droplet recedes. Dynamic receding angles may differ from static ones due to hysteresis and viscous dissipation at the moving contact line. Roughness or chemical heterogeneity on the surface can pin the contact line, yielding higher receding angles or irregular dewetting.

Applications and significance: Receding angles are used to characterize wetting properties of coatings, inks, and microfluidic devices, and to design surfaces with controlled liquid spreading or dewetting. Surfaces with low receding angles tend to dewet easily, whereas high receding angles indicate stronger liquid retention. Related concepts include advancing angle and contact-angle hysteresis.