Water-in-air droplet formation in plasma bonded microchannels fabricated by Shrinky-Dink® lithography

Abstract

This thesis presents the first work on water-in-air droplet microfluidics. Polymeric microchannels were prototyped to illustrate water droplet formation in air by the T-junction meditated design. The first part of the thesis is on the proof of using unfiltered air as the process gas for plasma-assisted bonding of polydimethylsiloxane (PDMS) microchannels. A series of bilayered PDMS prototypes were plasma bonded under various plasma treatment parameters to determine the optimal settings for high-strength bonding. Pressure rupture tests were conducted to measure the bonding interface strength, which were shown to be as high as 135 psi. The second part of the thesis illustrates the formation and dispersion of water droplets in a continuous air flow in microchannels, and discusses the mechanisms of how droplets are formed. The Shrinky Dinks lithography and plasma-assisted bonding were used to prototype leakage-free microcbannels for testing droplet production. Droplets are formed under the competition between the fluid viscosity and surface tension forces. The channel dimensions and the fluid flow rates dictate the mechanism of droplet formation. The major finding is that the droplet length increases and droplet velocity decreases with increasing water flow rates, but some droplets were not formed at the T-Junction. These findings are discussed.