Effect of Volume Fraction on Droplet Breakup in a Concentrated Emulsion*

In droplet microfluidics, micro-droplets are used as biochemical reactors. In contrast to solid wells, drops are metastable and prone to break-up, which compromises the accuracy and throughput of the assay. Unlike single drops, the break-up process in a concentrated emulsion is stochastic. We examine the stability of a concentrated emulsion during its flow in a tapered microchannel consisting of a narrow constriction, a geometry commonly used for the interrogation of droplet content. Analysis of the behavior of a large number of drops (N~ 5000) shows that the probability of break-up increases with increasing drop packing (i.e. volume fraction). There also exists a critical volume fraction below which drop break-up probability reduces to zero. This work represents an important step towards understanding the interactions among the drops governing instability in concentrated emulsions.