Exploring Three-Phase Contact Line Dynamics in Wetting and Non-Wetting Configurations: Role of Roughness

Wettability plays a significant role in numerous industries, and it is designated from studying the dynamics of the three-phase contact line, where the liquid interacts with the solid surface. Wettability can be quantified by the interfacial energies and contact angle (CA) of a droplet on the surface. Knowledge of the interfacial properties is significant for achieving precise control over fluid transport phenomena, which directly impact the operation/quality of various commercial devices/products. Therefore, this thesis begins by introducing a novel experimental approach to determine the interfacial energy between a wettable solid and a liquid using the CAs of the droplet and the roughness of the underlying surface. Furthermore, the methodology is employed for single- and multi-layer graphene samples. The obtained results are then compared with molecular dynamics simulations to explore the utility of the methodology at the molecular level. The present methodology also explores the frictional resistance forces that impede fluid motion as the contact line advances/recedes on a solid substrate. Adam and Jessop as well as Good proposed that these frictional forces are equal. However, recent research has indicated that this assumption may not hold true for real-world (rough) surfaces. This led to exploring the relationship between frictional resistance forces in this work, which may be beneficial for engineering surfaces for various industrial applications where contact angle hysteresis plays a crucial role. The CAs were measured using the sessile droplet (SD) method for a set of liquids and solids. For cases of highly wettable solids, the captive bubble (CB) method is used as an alternative because the SD method fails to provide a receding contact angle. But the CB method gives the air front CAs. Marmur et al. proposed a supplementary relationship between the dynamic CAs measured by the SD and CB methods for atomically smooth surfaces. However, for real (rough) surfaces, this supplementary relationship does not hold true. This thesis provides a modified mathematical relationship between the dynamic CAs obtained by the SD and CB methods for rough wettable surfaces. The thesis underscores the fundamentals of contact-line dynamics for various applications and emphasizes the hurdles that need to be overcome to achieve further progress in this field.