Microfluidic Mass Transfer Process Intensification for Micron Droplet Generation with Dilute Surfactant Concentration

Microfluidic emulsification always involves fresh interface formation during droplet generation, which induces surfactant mass transfer and thus dynamic interfacial tensions (IFTs). As surfactant transfer onto freshly created interface often limits decrease of IFTs and droplet sizes, excessive amounts of surfactant would usually be added to speed up surfactant transfer and eliminate dynamic effects. Here we have systematically investigated the dynamic effects of surfactants in our newly designed capillary embedded T-junction microfluidic device. Within the asymmetric devices, hydrodynamic forces would intensify surfactant molecules concentrating to the point of droplet break-up, leading to extremely low dynamic IFTs temporarily (~0mN/m). Micron droplets could thus be generated with dilute surfactant concentrations (dynamic effects would be eliminated with surfactant concentrations of SDS 0.05wt% 1/6 CMC, Tween20 0.20wt% 4/7 CMC, F68 0.20wt% 2/3 CMC). The presented results provide us with more in-depth understanding of dynamic effects of surfactants as well as a novel method for surfactant mass transfer intensification and thus micron droplet generation with dilute surfactant concentrations.