Abstract
Penetration of liquid with distinct volumes into a funnel-like pore structure is widely observed in nature and technical applications. However, when the droplet size is comparable with the pore size, the penetration criterion, i.e., under which condition the droplet can penetrate into the pore, remains an open question. In this work, we present theoretical models to address the penetration criteria in terms of the droplet size, the intrinsic wettability, and the opening angle of the funnel-shaped structure. The proposed theoretical models are well corroborated by phase-field simulations. Our findings demonstrate a critical contact angle below which a finite-volume droplet can penetrate into a hydrophobic pore. This critical contact angle is intimately related to the opening angle and the droplet size, which provides a complement to previous literature. Note that for a certain-sized droplet, the critical contact angle becomes invariant when the opening angle is greater than a certain threshold. Moreover, we find that for a constant opening angle, the critical contact angle decreases with the increase of the droplet size. As the droplet volume tends to be infinite, the opening angle has almost no influence on the penetration, and the critical contact angle asymptotically approaches , being consistent with previous works. Our observations illuminate a special mechanism for a precise maneuver of droplets in pore structures with potential applications in filter systems and microfluidic platforms.
1 More- Received 5 October 2021
- Accepted 3 May 2022
- Corrected 15 June 2022
DOI:https://doi.org/10.1103/PhysRevFluids.7.054004
©2022 American Physical Society
Physics Subject Headings (PhySH)
Corrections
15 June 2022
Correction: The previously published Figure 6 contained errors in the images in panels (c) and (d) and has been replaced.