Contact Angle Measurement on Curved Wetting Surfaces in Multiphase Lattice Boltzmann Method

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.

Pinning–depinning transition of droplets on inclined substrates with a three-dimensional topographical defect

“…20,21 Prior experimental and theoretical works have shown that chemical patterning can also induce stick-slip motion of droplets on inclined substrates. [22][23][24][25] All the works mentioned above that investigate substrates with topography involve multiple topographical defects. But it is also important to consider the case of a single defect on a substrate to gain fundamental understanding of how the different geometric features of a defect influence droplet motion.…”

Dispersion Behavior of a Droplet Impacting a Single Fiber

“…These patterns not only provide visual information about the behavior of droplet impacts but also lay the foundation for further in-depth study and theoretical analysis. By adjusting various parameters, such as geometrical parameters, , fiber surface wettability, − impact conditions, , fiber inclination, and fiber shape, researchers have been able to record a series of typical images depicting droplet impact on a single fiber. In this regard, Hung et al .…”

“…For instance, when a droplet impacts a hydrophilic fiber, three flow patterns can occur: double membrane fall, single membrane fall, and single droplet fall. Conversely, when a droplet impacts a superhydrophobic fiber, only the double membrane fall phenomenon is observed. − Moreover, in the case of droplets impacting superhydrophobic fibers, researchers have also observed the formation of unstable “wing-shaped” liquid columns at the end of the retraction process, known as convergent fragmentation . The eccentric impact of the droplet also significantly affects its morphology.…”