Wettability patterning in microfluidic devices using thermally-enhanced hydrophobic recovery of PDMS

TL;DR

This paper introduces a novel method for creating spatial wettability patterns in PDMS microfluidic devices by locally heating plasma-treated surfaces to accelerate hydrophobic recovery, enabling in situ patterning without additional chemistry.

Contribution

The study demonstrates a simple, in situ thermo-patterning technique that leverages temperature-induced hydrophobic recovery to control surface wettability in PDMS microfluidics.

Findings

Localized heating speeds up hydrophobic recovery in PDMS.

Wettability patterns are quantifiable using fluorescent probes.

The method allows patterning without additional surface chemistry.

Abstract

Spatial control of wettability is key to many applications of microfluidic devices, ranging from double emulsion generation to localized cell adhesion. A number of techniques, often based on masking, have been developed to produce spatially-resolved wettability patterns at the surface of poly(dimethylsiloxane) (PDMS) elastomers. A major impediment they face is the natural hydrophobic recovery of PDMS: hydrophilized PDMS surfaces tend to return to hydrophobicity with time, mainly because of diffusion of low molecular weight silicone species to the surface. Instead of trying to avoid this phenomenon, we propose in this work to take advantage of hydrophobic recovery to modulate spatially the surface wettability of PDMS. Because temperature speeds up the rate of hydrophobic recovery, we show that space-resolved hydrophobic patterns can be produced by locally heating a plasma-hydrophilized PDMS surface with microresistors. Importantly, local wettability is quantified in microchannels using a fluorescent probe. This "thermo-patterning" technique provides a simple route to in situ wettability patterning in closed PDMS chips, without requiring further surface chemistry.