Triggering of electro-elastic anti-superhydrophobicity during non-Newtonian droplet collision

Abstract

The present article discusses the electrohydro-dynamics of impacting non-Newtonian dielectric droplets on superhydrophobic (SH) surfaces. The role of important parameters like electric Eotvos number ( Eo e ), Weber number ( We ), dielectric particle concentration ( TiO 2 ) and polymer concentration ( PEG-400 ) were elucidated in this experimental study. Due to the interplay of non-Newtonian effects and electric field, we had observed the suppression of drop rebound on SH surfaces at much lower Eo e compared to its Newtonian counterpart. It has been observed that with an increase in both polymer concentration or dielectric particle concentration, the suppression of drop rebounds was observed at lower Eo e. In order to encapsulate the combined effects of electric field and non-Newtonian dynamics on drop rebound suppression, we have introduced the ‘electro-elastic effect’. Contrary to the common observations of drop rebound on SH surfaces, this electro-elastic effect induces inhibition of drop rebound, thereby resulting in anti-superhydrophobicity. Subsequently, we also established a scaling relationship to show that the rebound suppression is observed as a manifestation of the onset of electro-elastic instability, when a proposed electric Weissenberg number ( Wi e ) exceeds unity. Finally, we demarcated the rebound and rebound suppression regimes of droplet dynamics through a detailed phase map.