Pengtao Yue, James J. Feng, Chun Liu & Jie Shen
Journal of Non-Newtonian Fluid Mech. 129, 163-176 (2005)
Abstract - Drop dynamics plays a central role
in defining the interfacial morphology in two-phase complex fluids such
as emulsions and polymer blends. In such materials, the components are
often microstructured complex fluids themselves. To model and simulate
drop behavior in such systems, one has to deal with the dual complexity
of non-Newtonian rheology and evolving interfaces. Recently, we
developed a diffuse-interface formulation which incorporates complex
rheology and interfacial dynamics in a unified framework. This paper
uses a two-dimensional implementation of the method to simulate drop
coalescence after head-on collision and drop retraction from an
elongated initial shape in a quiescent matrix. One of the two phases is
a viscoelastic fluid modeled by an Oldroyd-B equation and the other is
Newtonian. For the parameter values examined here, numerical results
show that after drop collision, film drainage is enhanced when either
phase is viscoelastic and drop coalescence happens more readily than in
a comparable Newtonian system. The last stage of coalescence is
dominated by a short-range molecular force in the model that is
comparable to van der Waals force. The retraction of drops from an
initial state of zero-velocity and zero-stress is hastened at first,
but later resisted by viscoelasticity in either component. When
retracting from an initial state with pre-existing stress, produced by
cessation of steady shearing, viscoelasticity in the matrix hinders
retraction from the beginning while that in the drop initially enhances
retraction but later resists it. These results and the physical
mechanisms that they reveal are consistent with prior experimental
observations.