Dynamic Wetting in Microfluidic Droplet Formation

The extent to which the carrier fluid wets the walls of a microchannel is crucial in the droplet formation process for segmented flow microfluidic applications and can be influenced by the use of surfactants. Surfactants dynamically modify the microchannel surface leading to stabilization of the two phase interface, affecting the droplet formation process. An experimental study of the influence of hydrophobic surfactant (Span 80) during the formation of water-inoil droplets in a T-shaped microchannel geometry is presented and the wetting properties of the microchannel walls were characterized. The range of data to be analyzed on the microscale is estimated from the macroscopic interfacial tension and contact angle measurements. The critical micelle concentration (CMC) level at the microscale was estimated by observing the trend of droplet length variation with concentration of surfactant in a microchannel. Microchannels used in this work were fabricated using softlithography methods and bonded using a custom-made plasma bonding setup that does not require an ultra high vacuum chamber and hence saves the fabrication cost.