Effect of electric double layer on electro-spreading dynamics of electrolyte drops

•Electric double layer (EDL) effects in drop spreading dynamics have been studied.•EDL-induced hydrophilization leads to augmented drop spreading.•EDL effects also impact the different scaling regimes for drop spreading.•Similarity with electrowetting-driven spreading is witnessed.

A theoretical model is proposed to study the spreading of electrolyte drops on charged surfaces. A nanoscopic-thick electric double layer (or EDL) is triggered when an electrolyte drop comes in contact with a charged solid - therefore, the focus of the present study is to theoretically probe a multiscale problem where a nanoscopic EDL affects the spreading of a macroscopic electrolytic drop. The genesis of this multiscale effect is the fact that this EDL induces an electrostatic wetting tension, WEDL which lowers the drop equilibrium contact angle analogous to the “electrowetting” effect. This lowering significantly affects the electro-spreading dynamics by enhancing the rate of change of the contact radius (R) and the dynamic contact angle during drop spreading. We further show that the prefactors and timescales dictating the scaling relationships between R and spreading time (t) for the initial and the final regimes are affected directly by WEDL, while the timescales for the attainment and termination of the regimes where R ∼ tα (α < 1) are also influenced by WEDL. Finally, we explain that this multiscale EDL-mediated electrospreading is analogous to the applied electric driven induced electrowetting-driven spreading of drops with the role of the applied electric field being played by the EDL-induced electric field. While the EDL-mediated statics of drop wetting has been known for a while, this is for the first time we unravel the EDL effects on this dynamics of drop wetting providing a novel mechanism of controlling dynamics by merely controlling the charge of the substrate and the salt content of the drop.

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