Bimodal drop size distributions during the early stages of shear induced coalescence

TL;DR

This study investigates early-stage shear-induced coalescence in specific polymer systems, revealing bimodal drop size distributions that evolve into unimodal distributions, with analysis based on collision dynamics.

Contribution

It provides new insights into the bimodal nature of drop size distributions during initial coalescence under shear in polymer blends.

Findings

Bimodal distributions occur in early coalescence stages.

Drop size distributions become unimodal after prolonged shearing.

Gaussian shape of distribution peaks is consistent across cases.

Abstract

Drop sizes and drop size distributions were determined by means of an optical shear cell in combination with an optical microscope for the systems polyisobutylene/poly(dimethylsiloxane) (I) and poly(dimethyl-co-methylphenylsiloxane)/poly(dimethylsiloxane) (II) at low concentrations of the suspended phases and at different constant shear rates ranging from 10 to 0.5 s-1 . After pre-shearing the two-phase mixtures (I: 50 s-1; II: 100 s-1) for the purpose of producing small drop radii, the shear rate was abruptly reduced to the preselected value and coalescence was studied as a function of time. In all cases one approaches dead end drop radii, i.e. breakup is absent. The drop size distributions are for sufficiently long shearing always unimodal, but within the early stages of coalescence they are in some cases bimodal; the shape of the different peaks is invariably Gaussian. The results are discussed by means of Elmendorp diagrams and interpreted in terms of collision frequencies and collision efficiencies.