Spreading of viscoplastic droplets

Abstract

Abstract

Viscoplastic sessile drop coalescence

“…From (1) we see that as Y → 0 the yielded region of the drop vanishes. The shape of the arrested interface h(x, ∞) can then be characterized by the non-linear or- dinary differential equation obtained from (1) in the limit Y → 0,…”

“…They allow us to squeeze toothpaste from tubes, lay mortar for bricks, plaster walls and even paint. Much focus has been spent on yield-stress flows, with a growing interest in capillary flows such as surface spreading for inkjet printing and spray coating [1][2][3][4][5], viscous fingering [6], and the adhesion of pastes [7].…”

“…To minimize deviations from the spherical-cap shape, drops with footprints a < 1 mm were preferred [2]. When yield-stress drops spread on substrates, spreading arrests before drops minimize their surface energy as by the Young-Dupré equation σ cos(α) = σ SV − σ SL [1]. Therefore for our experiments, the smallest obtainable initial coalescence angles α we expect are 6.5 • to 34 • , for τ y = 2 Pa and 50 Pa, respectively [1,2,31].…”

“…When yield-stress drops spread on substrates, spreading arrests before drops minimize their surface energy as by the Young-Dupré equation σ cos(α) = σ SV − σ SL [1]. Therefore for our experiments, the smallest obtainable initial coalescence angles α we expect are 6.5 • to 34 • , for τ y = 2 Pa and 50 Pa, respectively [1,2,31]. Slides were plasma cleaned before each set of experiments to maintain a low substrate surface energy, thereby minimizing α.…”

“…Results -We frame our problem as a 2D viscous flow parallel to the bridge justified by the small relative aspect ratio h 0 /r 0 ≪ 1, and low film Reynolds number [10,13,31]. As the fluid has a yield stress τ y , the system can be described using viscoplastic lubrication theory [1,33],…”