Dilute polymer solution drops impacting on heated surfaces: New impact morphologies and impact regime maps

Abstract

[EN] The impact morphology of dilute polymer solution drops on a heated surface is studied experimentally by means of high-speed imaging, with respect to the following parameters: surface temperature; impact Weber number; polymer concentration; polymer molecular weight. In addition to impact morphologies observed in Newtonian drops (deposition, rebound, secondary atomisation and breakup/splashing), three new impact regimes have been identified: (i) a single satellite droplet ejected in the direction of bouncing but tethered to the main drop by a thin liquid filament; (ii) a splashing-like behaviour (semi-splashing), where the rim instability generates satellite droplets tethered to the lamella by thin liquid filaments; (iii) a spray-like behaviour (semi-spray), where a fine secondary atomisation generated upon impact is quickly absorbed back into the drop globule. Experiments were carried out using drops of aqueous polyethylene oxide (PEO) solutions, with mass concentrations of 100 ppm, 200 ppm and 400 ppm, and PEO molecular weights of 2 MDa, 4MDa, and 8MDa. The impact morphology on a polished aluminium surface with temperatures ranging between 160°C and 400°C was investigated for impact Weber numbers between 20 and 170, taking side view images of impacting drops at a rate of 1,000 frames per second.