Phenomenological contact line friction coefficient

An important feature of contact line motion, as an irreversible process, is its dissipative nature, which can dominate the dynamics during the early stages of droplet spreading. A phenomenological contact line friction coefficient , obtained through direct matching of phase‐field simulations and experimental observations, emerges as an effective parameter for quantifying this dissipation. This paper provides a comprehensive overview of , its experimental determination, and its relevance across a variety of surfaces and conditions. We discuss when and why becomes the dominant source of dissipation, and examine how it is modulated by factors such as liquid viscosity, surface chemistry, substrate topography, and external stimuli including electric potential. This review highlights the importance of in bridging molecular‐scale processes and macroscopic wetting dynamics, reflecting the intrinsic material response of the three‐phase system.