We introduce the behavior of a droplet spreading on a smooth substrate with obstacle(s). As experimental works have indicated, the macroscopic contact line, or three-phase boundary line, of a droplet exhibits a significant deformation resulting in a local acceleration by interaction with a tiny obstacle after the meniscus formation (Mu et al., 2017; Mu et al., 2018), and that successive interactions with an array of tiny obstacles settled on the substrate enhance the local acceleration (Mu et al., Langmuir 35, 2019). We focus on the menisci formation and resultant pressure and velocity fields inside a liquid film in a single and two- spherical-particle systems to realize an optimal design of the effective liquid transport phenomenon (Nakamura et al., 2020a; Nakamura et al., 2020b). Asymmetric meniscus around the particle foot produces a net pressure force driving liquid and accelerating the liquid-film front. In the case of multiple obstacles, it is found the meniscus around the first particle plays an additional role as the reservoir of the liquid supplied toward the second particle, which enhances the total pumping effect.
References:
Mu, L., et al., Sharp acceleration of a macroscopic contact line induced by a particle, J. Fluid Mech. 830, R1, 2017.
Mu, L., et al., Control of local wetting by microscopic particles, Colloids and Surfaces A 555, 615-620, 2018.
Mu, L., et al., Quick liquid propagation on a linear array of micropillars, Langmuir 35, 9139-9145, 2019.
Nakamura et al., Pumping effect of heterogeneous meniscus formed around spherical particle, Journal of Colloid and Interface Science 562, 133-141, 2020a.
Nakamura et al., Enhancement of meniscus pump by multiple particles, Langmuir 36, 4447-4453, 2020b.