Solvation effects and contact angle saturation in electrowetting

TL;DR

This paper investigates how solvation effects influence contact angle saturation in electrowetting, revealing that manipulating solvation energy differences can control droplet deformation and prevent saturation, with implications for microfluidic applications.

Contribution

It introduces a method to control contact angle saturation by varying solvation energy differences, supported by a derived electrokinetic model.

Findings

Saturation can be suppressed by increasing solvation energy difference.

Ion transfer from the drop causes contact angle saturation.

Derived an expression linking contact angle to ion concentration and solvation strength.

Abstract

Electrowetting of nanodrops is studied for aqueous electrolyte mixtures. We report a new method for controlling the degree of deformation and minimum attainable contact angle by varying the difference of solvation strengths between the two solvents, which determines the ratio of ion concentrations. This implies that the commonly observed saturation of the contact angle with the applied electric field can be suppressed by increasing the solvation energy difference, a finding of practical significance for micro and nanofluidics. Saturation is traced to be caused by the transfer of ions from the drop to the surrounding medium. Furthermore, we derive an expression, based on the electrokinetic equations, for the dependency of the drop's contact angle on the ion concentration and the strength of the solvation potential in the absence of external electric fields.