Effects of Pseudoplasticity on Spread and Recoil Dynamics of Aqueous Polymeric Solution Droplets on Solid Surfaces

Abstract

The postimpact spreading and recoil behavior of millimeter-size liquid droplets of pure water, water-glycerol solution, and non-Newtonian aqueous solutions of medium-grade hydroxyl ethyl cellulose (HEC 250 MR) on dry horizontal hydrophobic (Teflon) and hydrophilic (glass) substrates is presented. The drop spread-recoil dynamics are captured using a high-speed high-resolution digital video recording and image processing. The non-Newtonian effects of aqueous polymeric solutions on postimpact spreading are contrasted with those for a water-glycerol solution with identical surface tension and zero-shear rate viscosity. For a broad range of drop Weber numbers (20 ≤ We ≤ 200), dynamic visualized records of impact, spreading, and recoil are presented along with their measured temporal variations in dropdiameter-scaled spread and film height. The shear-rate-dependent viscosity of the polymer solution is found to give rise to highly complex spread-recoil dynamics compared to Newtonian liquids. During initial spread, because the shear rate tends to be high, shear-thinning or pseudoplasticity effects manifest in polymer solution drops to alter their spread dynamics. Contrarily, during recoil their higher low-shear apparent viscosity tends to retard recoil and dampen shape oscillations. Shear-rate-dependent non-Newtonian behavior is further seen at low We (low shear rate during spreading), where the maximum spread of HEC solution droplets is comparable to that of high-viscosity water-glycerol solution, whereas at high We (high shear rate during spreading), their maximum spreads are closer to those of low-viscosity water droplets.

Drop impact on solids: contact-angle hysteresis filters impact energy into modal vibrations

“…2011; Manglik et al. 2013; Ravi, Jog & Manglik 2013; Snoeijer & Andreotti 2013). Notable work in the inertial spreading regime includes that of Cox (1998), who used a matched asymptotic analysis to relate the macroscopic contact angle to the CL velocity for small capillary number and moderate Reynolds number , a result which was later confirmed experimentally by Stoev, Ramé & Garoff (1999).…”

Surface roughness effect on droplet impact characterization: Experimental and theoretical study

“…As a matter of fact, the spread factor on Smooth and Medium surfaces do not undergo oscillations; deformation in these cases reveal a gradual flattening of the droplet. The viscous dissipation resulting from spread-recoil oscillation can significantly reduce the kinetic energy of the droplet and dampen the magnitude of spread-recoil oscillations [36]. These oscillations have more tendency to damp out quickly at Smooth and Medium surfaces.…”

Study of spreading, vibration, and fracture behavior of double droplets after positive collision

“…Shi et al 14 experimentally found that single droplet colliding a hydrophilic wall would have a longer motion wave resulting in more energy dissipation during the oscillation process. Manglik et al 15 and Ravi et al 16 equated the vibration of a single droplet to a springdamped system, used a triangular fitting function to describe the droplet height change, gave a damped oscillation equation, and verified Fedorchenkod's droplet oscillation cycle theory. Yang et al 17 derived the period of single droplet height oscillation on a hydrophobic surface through a single-degree-of-freedom vibration model.…”