Flow-induced Coalescence of Two Deformable Drops

Yosang Yoon
Department of Chemical Engineering
UCSB Doctoral Candidate

Date: Thursday March 23 , 2006
Time: 4:00 p.m.
Place: Engineering II, Room 3361

ABSTRACT

The coalescence of liquid drops plays an important role in many applications, such as in the formation and stability of emulsions and polymer blends. Surfactant or copolymers (often called compatibilizers) are commonly used to stabilize drops and inhibit the coalescence. In the present study, the flow-induced coalescence of two deformable drops was investigated experimentally and numerically. In contrast to the conventional blending studies, we experimentally studied the coalescence process at the level of individual drops, using a four-roll mill. The goal of the experimental studies is to understand how the coalescence between two polymeric drops is affected by a copolymer. A small amount of copolymer at the interface was sufficient to greatly suppress coalescence. The required minimum concentration was quantified, and the mechanism by which the compatibilizer influences the coalescence was discussed.

We also investigated the axisymmetric interaction of two equal-sized deformable drops, using a boundary-integral method. An adaptive mesh refinement method was used to resolve the local small-scale dynamics in the gap and to retain a reasonable speed of computation. The results were compared with the experimental results, as well as the scaling theories for thin film drainage. In the present numerical study, our goal is to investigate the thin film dynamics, which are crucial to understanding the complex and unexpected experimental results. A secondary objective is to assess the relevance of this classical continuum theory in describing the coalescence process, which typically occurs when the film thickness is minuscule.