Wetting, Young's Equation, Dupre's Equation

In this lecture, we dive into the science of wetting, a phenomenon that significantly influences both our daily activities and various industrial processes. Wetting describes the ability of a liquid to spread across or adhere to a solid surface, a critical factor in activities ranging from painting to the use of detergents. At the heart of understanding wetting lies the interplay between adhesive forces, which attract the liquid to the solid surface, and cohesive forces, which act within the liquid itself.

Central to our exploration are the concepts of surface tension and the contact angle. Surface tension represents the energy required to expand the surface area of a liquid, acting like a resistant "skin." The contact angle, on the other hand, measures the angle where a liquid-vapor interface meets a solid, offering a quantitative measure of wetting.

We categorize wetting into three regimes: complete wetting, partial wetting, and non-wetting, each defined by the contact angle's value. Factors such as surface roughness, chemical composition, and surface charge play crucial roles in influencing wetting behavior.

Furthermore, we delve into the thermodynamic aspects of wetting through the work of adhesion and cohesion, providing insights into the energy dynamics when a liquid contacts a solid surface. This leads us to the Gibbs free energy change associated with wetting, a key indicator of the stability and extent of wetting.

Practical examples and homework problems are provided to enhance understanding and application of the concepts discussed.

For more information and to dive deeper into the fascinating world of wetting, visit
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