Recent Developments in Micro/Nanochannel Emulsification for Controlled Production of Monodisperse Emulsions

Microfluidic techniques for producing emulsions have been proposed over the last decade. Major advantages of microfluidic techniques include the production of monodisperse emulsions with a coefficient of variation (CV) of typically <5%, superior controllability of droplet size and monodispersity, and in situ microscopic monitoring. Microchannel (MC) emulsification, proposed by our research group, is a unique and robust technique to produce monodisperse emulsions with controlled droplet sizes of >1 μm. In MC emulsification, droplet generation via MC arrays does not require any external shear/elongational stress; i.e., the dispersed phase that passed through MCs is transformed spontaneously into uniform droplets due to hydrodynamic instability of the oil-water interface. Here we present some of the recent findings obtained from MC emulsification studies and the controlled production of monodisperse submicron emulsions by novel nanochannel (NC) emulsification. The first topic on MC emulsification is the influence of operating temperature (10 to 70 °C) on production of oil-in-water (O/W) emulsions using a surface-oxidized silicon MC array plate with an MC depth of 8 μm. The droplet generation results were correlated well with the contact angle of the dispersed phase to the MC walls that was measured using a novel method using parallel long MCs. Another topic on MC emulsification is the development of stainless-steel MC emulsification devices. Stainless-steel MC array plates with an MC depth of 100 or 150 μm were mechanically fabricated using an end mill. The use of the stainless-steel MC array plates enabled stably producing monodisperse O/W emulsions with an average droplet diameter of up to 550 μm. We also recently developed silicon NC array plates with the smallest NC depth of 50 nm. NC emulsification experiments demonstrated successful production of monodisperse submicron O/W emulsions with the smallest average droplet diameter of 480 nm. The diameter of the droplets generated by NC emulsification was measured by a novel technique that exploits nanospace.