On the effect of concentration and wettability on polymer drops impact, dynamics and energy dissipation

Abstract

The present study aims to understand the influence of small quantities of poly-ethylene oxide (PEO) diluted in pure distilled water with concentrations of 50, 100 and 200 parts per million (ppm) in the impact phenomenon of drops onto substrates of Parafilm M, aluminium and glass. Both the static aspects (i.e., maximum spreading area) and the dynamic aspect (i.e., recoiling velocities), and different parameters of contact angle oscillations of the droplet are analysed. Results show that the maximum spreading diameter, dissipation mechanisms, and oscillations period all increase with the release height. Unlike contact angles oscillations envelope which gets thinner, oscillations length decreases with the increase of release height. Polymer concentration influences the maximum spreading base diameter of drops on non-hydrophobic substrates, i.e., higher concentration slows down recoiling velocities, reduces oscillations length, enhances dissipation mechanisms, and influences oscillations period as well. In addition, the wettability of substrates influences the spreading phase, drop rebound, and can damp recoiling of the polymer drops. A hydrophilic substrate reduces the oscillations length, increases their period and lessens their amplitude decay. The dependence of oscillations on the concentration illustrates a clear different behaviour on Aluminium surfaces (hydrophilic) and on Parafilm M surfaces (hydrophobic). The initial amplitude and the damping rate were analysed and related to the concentration.