Observation of Coalescence of Two Polyisobutylene Droplets in Polydimethylsiloxane under Large Step Shear Strain.

Abstract

We observed collision and coalescence after application of large step shear strains for two polyisobutylene (PIB) droplets in polydimethylsiloxane (PDMS) matrix using a stereo microscope. When coalescence occurred, interface vanished in an overlapped area of deformed droplets. Then a single droplet recovered to spherical shape. Time necessary for recovery to spherical shape with coalescence was longer than that without coalescence. Coalescence was easy to occur for larger strain and smaller d 0 /r 0 , where d 0 and r 0 represent initial distance between centers of droplets and initial droplet radius, respectively. In the case of shape recovery without coalescence, the distance between the centers after shape recovery was smaller than d 0 . Time dependence of shape of droplets was similar in both cases with coalescence and without coalescence. Ratio of length of overlap, l ov ', to length of semi major axis, a', in view perpendicular to shear plane determines occurrence of coalescence.

Hydrodynamic Interaction Model for Two Droplets under Large Step Shear Strains

“…Our experimental results indicate that the stress is affected by droplet size distribution and/or interaction between adjacent droplets. 20,23) Concerning the interaction between adjacent droplets, our recent observation 24,25) revealed that attractive interaction acts on two polyisobutylene (PIB) droplets in polydimethylsiloxane (PDMS) matrix on the same shear plane during the shape recovery of the droplets after application of large step shear strains: The droplets approach by each strain. We have shown that the origin of the interaction is hydrodynamic interaction between the droplets based on a simple model using the hydrodynamic interaction tensor.…”