This lecture covers the Gibbs model of an interface, focusing on the thermodynamics of adsorption at gas/liquid interfaces. It explains the concept of interfacial excess and the formation of micelles in surfactant solutions. The instructor discusses the factors driving micellization and the measurement of surface pressure in monolayers. Additionally, the lecture explores the different phases of monolayers and the structures of colloidal aggregates. Practical examples and calculations related to surface tension and micelle formation are presented to illustrate the theoretical concepts.