No abstract

Contact angle is an essential physical quantity that characterizes the wettability of a substrate. Although it is widely used in the studies of surface wetting, capillary phenomena, and moving contact lines, the contact angle measurements in simulations and experiments are still complicated and time-consuming. In this paper, we present an efficient scheme for the measurement of contact angle on curved wetting surfaces in lattice Boltzmann simulations. The measuring results are in excellent agreement with the theoretical predictions without considering the gravity effect. A series of simulations with various drop sizes and surface curvatures confirm that the present scheme is gridindependent. Then, the scheme is verified in gravitational environments by simulating the deformations of sessile and pendent droplets on the curved wetting surface. The numerical results are highly consistent with experimental observations and support the theoretical analysis that the microscopic contact angle is independent of gravity. Furthermore, the method utilizes only the microscopic geometry of the contact angle and does not depend on the droplet profile; therefore, it can be applied to nonaxisymmetric shapes or moving contact lines. The scheme is applied to capture the dynamic contact angle hysteresis on homogeneous or chemically heterogeneous curved surfaces. Importantly, the accurate contact angle measurement enables the dynamic mechanical analysis of moving contact lines. The present measurement is simple and efficient and can be extended to implementations in various multiphase lattice Boltzmann models.

Contact angle is an essential parameter to indicate substrate wettability. The measurement of contact angle in experiments and simulations is a complex and time-consuming work. In this paper, we propose an improved measuring method of contact angle in multiphase lattice Boltzmann simulations, which can accurately obtain the real-time contact angle at low temperatures and larger density ratios. The three-phase contact point is determined by an extrapolation, and its position is not affected by the local deformation of flow field at the three-phase contact region. A series of simulations confirm that the present method has high accuracy and gird-independence. The contact angle keeps an excellent linear relationship with the chemical potential of the surface, so that it is very convenient to specify the wettability of a surface. The real-time contact angle measurement enables us to obtain the dynamic contact angle hysteresis on chemically heterogeneous surfaces, while the mechanical analyses can be effectively implemented at the moving contact line.