Air entrainment dynamics of aqueous polymeric droplets from dilute to semidilute unentangled regimes.

Recent studies have revealed the air-cushioning effect of droplet impact upon various surfaces and although pure water droplets have extensively been studied, the air entrainment dynamics for aqueous polymeric droplets was the focus of this study. Herein, droplets of low to moderate Weber numbers, We ∼ O (1 − 10) , displayed air film thickness gradients which was strongly influenced by the viscoelastic properties of the aqueous polymeric droplets in the dilute to the semidilute unentangled regimes. Aqueous polyethylene oxide droplets impacting a smooth thin oil film surface formed a submicrometer air layer, moments prior to impact, which was tracked by a high-speed total internal reflection microscopy technique. The radial changes in the air film thickness were related to the polymer concentration, thus providing an alternative tool for comparing the rheometer-derived overlap concentrations with a contactless optical technique. [ABSTRACT FROM AUTHOR]