PDMS droplet formation and characterization by hydrodynamic flow focusing technique in a PDMS square microchannel

Abstract

This study reports the generation of polydimethylsiloxane (PDMS) droplets by hydrodynamic flow focusing technique in a PDMS square microchannel. The droplet generation was characterized and a flow regime map addressed by the capillary numbers of each phase was assembled. Different flow regimes were found—dripping, jetting, threading and viscous displacement and the respective boundaries were sketched. Droplet size, breakup distance and formation frequency were analysed and quantified for the jetting and dripping regimes. The dripping regime showed better results for droplet formation, leading to the highest throughput of monodisperse droplets: formation frequency of ≈12 Hz and droplets almost uniform in size (2.8% the coefficient of variance). The qualitative analysis and quantitative measurement of the different variables and their correlation within a capillary dependent regime map proved to be an invaluable tool to study droplet formation by hydrodynamic flow focusing technique in a PDMS square microchannel.