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

Abstract

The present article discusses the electrohydro-dynamics of impacting non-Newtonian dielectricdroplets on superhydrophobic (SH) surfaces. Therole of important parameters like electric Eotvosnumber (Eoe), Weber number (We), dielectric particleconcentration (TiO2 ) and polymer concentration(PEG-400) were elucidated in this experimental study.Due to the interplay of non-Newtonian effects andelectric field, we had observed the suppression of droprebound on SH surfaces at much lower Eoecomparedto its Newtonian counterpart. It has been observedthat with an increase in both polymer concentrationor dielectric particle concentration, the suppression ofdrop rebounds was observed at lower Eoe. In orderto encapsulate the combined effects of electric fieldand non-Newtonian dynamics on drop reboundsuppression, we have introduced the ‘electro-elasticeffect’. Contrary to the common observations of droprebound on SH surfaces, this electro-elastic effectinduces inhibition of drop rebound, thereby resultingin anti-superhydrophobicity. Subsequently, we alsoestablished a scaling relationship to show that therebound suppression is observed as a manifestationof the onset of electro-elastic instability, when aproposed electric Weissenberg number (Wie) exceedsunity. Finally, we demarcated the rebound andrebound suppression regimes of droplet dynamicsthrough a detailed phase map.