Dynamic Wetting of Ionic Liquid Drops on Hydrophobic Microstructures

Abstract

Ionic liquids (ILs)salts in a liquid stateplay a crucial role in various applications, such as green solvents for chemical synthesis and catalysis, lubricants, especially for micro- and nanoelectromechanical systems, and electrolytes in solar cells. These applications critically rely on unique or tunable bulk properties of ionic liquids, such as viscosity, density, and surface tension. Furthermore, their interactions with different solid surfaces of various roughness and structures may uphold other promising applications, such as combustion, cooling, and coating. However, only a few systematic studies of IL wetting and interactions with solid surfaces exist. Here, we experimentally and theoretically investigate the dynamic wetting and contact angles (CA) of water and three kinds of ionic liquid droplets on hydrophobic microstructures of surface roughness (r = 2.61) and packing fraction (ϕ = 0.47) formed by micropillars arranged in a periodic pattern. The results show that, except for water, higher-viscosity ionic liquids have greater advancing and receding contact angles with increasing contact line velocity. Water drops initially form a gas-trapping, CB wetting state, whereas all three ionic liquid drops are in a Wenzel wetting state, where liquids penetrate and completely wet the microstructures. We find that an existing model comparing the global surface energies between a CB and a Wenzel state agrees well with the observed wetting states. In addition, a molecular dynamic model well predicts the experimental data and is used to explain the observed dynamic wetting for the ILs and superhydrophobic substrate. Our results further show that energy dissipation occurs more significantly in the three-phase contact line region than in the liquid bulk.

Flow and Heat-Transfer Characteristics of Droplet Impingement on Hydrophilic Wires

“…In 2001, Romain et al compiled a summary of six distinct forms of droplet impact on solid surfaces: deposition, prompt splash, corona splash, receding fracture, partial rebound, and complete rebound. In addition, more abundant and complex spreading modes would appear under the condition that droplets impact on structures or inclined walls. , For example, Cassie, Wenzel, or transitional wetting mode will be presented when droplets impact the microstructure wall, while the asymmetry morphology is more common when droplets impact the inclined wall . Recently, Wang et al , comprehensively reviewed the related research progress of droplet impact dynamics.…”