Modular microfluidics for double emulsion formation.

For many engineering applications such as manipulating two phase flows, generating single and double emulsions, and passively propelling liquids through channels, control over the surface energy of microfluidic channels is essential. In particular, double emulsion formation, which benefits from alternating hydrophobic and hydrophilic sections of channel, represents a challenge in fabricating controlled microfluidic channel surface properties. As double emulsions find further applications in single-cell handling and analysis, straightforward methods for generating them increase in value. Here, we present a method for generating double emulsions in microfluidic channels fabricated from modular fluidic blocks. By using a vapor-phase polymer coating technology-initiated chemical vapor deposition-we are able to fabricate blocks with varying surface properties. Assembling these blocks together then creates step-like changes in surface energy within a microchannel.