Multiscale Investigation of Liquid Imbibition on an Electrodeposited Rough Surface.

Abstract

Hydrophilic and superhydrophilic surfaces are often used in various applications, such as biomedical surface modification, heat pipe design, lab-on-chip devices, microelectronic structure design, etc. Deposition of molecules on surfaces and chemical modification of the surface are two of the frequently adopted techniques to fabricate hydrophilic surfaces. However, achieving controlled and precise surface roughness is an expensive process, and the multiscale nature of liquid imbibition on rough surfaces complicates the system's physics. To address this challenge, we propose an alternative approach for creating controlled rough surfaces by electrodeposition of copper ions on copper electrodes, explore the influence of various length scales encountered in roughened surfaces, ranging from micrometers to angstroms, and examine the associated physics. The microscale roughnesses are controlled by adjusting the deposition time. A molecular level investigation is employed to probe the intriguing physics of liquid imbibition on the created rough surface. The molecular analysis of droplet contact line dynamics, including the contact angle and footprint radius, shows qualitative alignment with the real systems. Additionally, this study provides new insights into the flow velocities during imbibition within surface asperities at the molecular level. Directional velocities, such as axially downward and horizontally outward flows, which are otherwise challenging to measure experimentally, are also evaluated on a molecular scale. These findings provide a fundamental understanding of the intricate phenomena of liquid spreading and imbibition on metallic surfaces with randomly distributed rough textures, deepened by molecular-scale insights. The agreement, on a qualitative scale, between the experiments and simulations is successfully established, providing a fundamental understanding of the complex phenomena of water droplet imbibition dynamics on an electrodeposited surface.