Rough capillary rise

Abstract

Capillary rise within rough structures is a wetting phenomenon that is fundamental to survival in biological organisms, deterioration of our built environment, and performance of numerous innovations, from 3D microfluidics to carbon capture. Here, to accurately predict rough capillary rise, we must couple two wetting phenomena: capillary rise and hemiwicking. Experiments, simulations, and theory demonstrate how this coupling challenges our conventional understanding and intuitions of wetting and roughness. Firstly, the critical contact angle for hemiwicking becomes separation-dependent so that hemiwicking can vanish for even highly wetting liquids. Secondly, the rise heights for perfectly wetting liquids can differ between smooth and rough systems, even with the same 0^∘ contact angle. Finally, the raised liquid volumes are substantially increased in rough compared to smooth systems. To explain and predict all rise heights and volumes with quantitative accuracy, we present the Dual-Rise model that is valid for general roughness, liquids, and surface wettabilities.

Capillary rise is a process whereby a liquid spontaneously rises against gravity within a narrow space due to capillary forces; but even though it is a well-understood phenomenon in smooth channels, predictive models to account for surface roughness are lacking. Here, the authors develop a theory of capillary rise in textured channels, supported by simulations and experiments, demonstrating the complex interplay between channel width, texture and wettability.