Spreading and breakup of a compound drop on a partially wetting substrate

Abstract

The spreading of a compound drop on a partially wetting solid substrate is numerically simulated using a diffuse-interface method. Compared with a simple drop, the spreading of a compound drop exhibits much more complex behaviour. Depending on the core-shell size ratio and the substrate wettability, various flow regimes are identified in which the interfacial morphology evolves in distinct ways. A phase diagram is constructed in the parameter space of the core-shell size ratio and the wetting angle. For relatively small inner drops, the outer interface does not rupture during the spreading and the inner drop either remains suspended and encapsulated or attaches onto the substrate. Otherwise, the compound drop spontaneously breaks up and releases the inner drop into the ambient fluid. Several breakup scenarios are observed depending on the location of the initial rupture. In some regimes, the wetting of the substrate by one fluid can entrap secondary drops of the other, which can either attach to the substrate or stay suspended. The viscosity ratio mainly affects the spreading rate and plays a minor role in the morphology evolution.

Wicking flow through microchannels

“…If the physical process being studied involves a length scale that shrinks indefinitely, as occurs here in Fig. 5 and during interfacial pinch-off or rupture, 43,44 the finite-effect manifests itself eventually, and is intrinsic to the diffuse-interface formalism. Therefore, the negotiation of the corner in Fig.…”

On the compound sessile drops: configuration boundaries and transitions

“…The two boundaries in (3.7a,b) are plotted in figure 5(d) to define the phase diagram of configuration E with respect to λ versus θ 23 , of which the result is similar to that of a hollow sessile drop (Gao & Feng 2011). Because of cos θ 12 = − √ 3 cos θ 23 in the present study, we can get λ c,1 = λ c,2 = 1 at θ 23 = 90 • , which corresponds to θ 23 = θ 12 .…”

Three dimensional phase-field investigation of droplet formation in microfluidic flow focusing devices with experimental validation

“…Numerical schemes are updated to improve the stability of moving contact line models ( Gao and Wang, 2012;. The phase-field method has been employed to study various multiphase problems, including droplet impact on homogeneous surfaces ( Khatavkar et al,20 07a;20 07b ), droplet spreading on partially wetting substrate ( Gao and Feng, 2011 ), impingement and spreading process of a micro-droplet ( Lim and Lam, 2014 ), electrohydrodynamic multiphase flow ( Lin et al, 2012;Yang et al, 2013a ), as well as droplet formation process in a T-junction configuration ( De Menech, 2006;De Menech et al, 2008 ).…”