TY - JOUR
T1 - Diffuse-interface simulations of drop coalescence and retraction in viscoelastic fluids
AU - Yue, Pengtao
AU - Feng, James J.
AU - Liu, Chun
AU - Shen, Jie
N1 - Funding Information:
Acknowledgment is made to the Donors of The Petroleum Research Fund, administered by the American Chemical Society, for partial support of this research. J.J.F. was also supported by the NSF (CTS-0229298, CTS-9984402), the NSERC and the Canada Research Chairs program, and the NNSF of China (No. 20174024 and No. 20490220). J.S. was supported by the NSF (DMS-0074283, DMS-0311915). C.L. was supported by the NSF (DMS-0405850). We acknowledge discussions with Professor M. M. Denn, Professor W. Yu and Professor C. Zhou.
PY - 2005/9/20
Y1 - 2005/9/20
N2 - 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.
AB - 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.
UR - http://www.scopus.com/inward/record.url?scp=26844565496&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=26844565496&partnerID=8YFLogxK
U2 - 10.1016/j.jnnfm.2005.07.002
DO - 10.1016/j.jnnfm.2005.07.002
M3 - Article
AN - SCOPUS:26844565496
SN - 0377-0257
VL - 129
SP - 163
EP - 176
JO - Journal of Non-Newtonian Fluid Mechanics
JF - Journal of Non-Newtonian Fluid Mechanics
IS - 3
ER -