Characteristics of dynamic contact-angle in presence of surface-charge

TL;DR

This paper derives analytical expressions linking dynamic contact angles to surface charges, capillary number, and interfacial forces, bridging micro- and macro-scale physics and explaining experimental anomalies in ionic liquids.

Contribution

It introduces a hydrodynamic model incorporating surface charge effects into dynamic contact angle analysis, providing a unified framework for various observed behaviors.

Findings

Connection between micro- and macro-scale physics at contact line

Transition from strong to weak surface charge influence with speed

Explanation of anomalous length scales in ionic liquids

Abstract

We account for the presence of surface charges towards describing variations in the dynamic contact angle of an advancing liquid-gas meniscus. Starting from the thin-film based formalism, we present closed-form analytical expressions relating the dynamic contact-angle with the capillary number (essentially normalized contact-line speed) and other interfacial parameters. Specifically, our analysis presents, within the realm of hydrodynamic paradigm, a connection between the micro- and macro-scale physics at the vicinity of the contact-line region, taking the combined confluence of viscous and capillary forces along with van der Waals and electrostatic interactions. This connection rationalizes the hitherto reported anomalous window of the magnitude of the microscopic length scales required to corroborate experimental data for ionic liquids. Moreover, our analysis shows the possibility of a transition from strong to weak influence of surface charge in a dynamic fashion with contact-line speed along with other electrochemical parameters, leading towards substantiating the reported multiple asymptotic behavior of dynamic contact-angle over a wide range of capillary numbers.