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arXiv · 2605.27251

Resolving Capillary Mode Transitions in Microparticles at Fluid Interfaces

Sungwan Park·Justin Jeongwoo Choi·Albert Tianxiang Liu
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Abstract

Capillarity-driven self-assembly at fluidic interfaces offers a scalable route to large, reconfigurable materials. Microscale particles with high horizontal-to-vertical aspect ratios become attractive building blocks for shape-directed organization, but the capillary rules governing their assembly remain incompletely understood. Here, we combine experiments and theory to explain the transition between two capillary regimes: monopolar interactions arising from millimeter-scale curved interfaces, and quadrupolar interactions arising from local contact-line distortions. We show that the conventional Bond number is insufficient to predict this transition because it omits key material and surface-topography effects. Instead, we identify a new dimensionless parameter that captures the coupled roles of particle size, density, surface roughness, contact angle, and quadrupolar strength. This criterion correctly predicts when gravitationally induced monopolar attraction or surface-pinning-induced quadrupolar attraction dominates, providing a general design rule for interfacial particle assembly. The resulting model explains how particles self-organize across length scales and offers guiding principles for engineering next-generation interfacial materials from miniaturized particulate building blocks.

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Sungwan Park, Justin Jeongwoo Choi, Albert Tianxiang Liu. 2026-05-26. Resolving Capillary Mode Transitions in Microparticles at Fluid Interfaces. https://arxiv.org/abs/2605.27251

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