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

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.

Phase separation of an ionic liquid mixture assisted by a temperature gradient

“…The present paper paves a way in binary mixture recycling. The impact of UCST behavior and spatial patterning in the cavity will be the object of future works [55][56][57][58]. The thickness variation of the wetting film is difficult to quantify with confocal experiments, but interferometric methods allow us to obtain at least one relative variation in height between two points [59].…”

Blood Plasma Self-Separation Technologies during the Self-Driven Flow in Microfluidic Platforms

“…Dean vortex effect methods could only process the diluted blood samples due to the limitation of viscosity and velocity of the fluid in the spiral microchannel, although they have good efficiencies and short separation times [115][116][117][118][119][120][121][122]. In wettability control technologies, pure plasma could be extracted from whole blood successfully, but separation time is comparably long, and surface modification is a complex process in microchannel fabrication [123][124][125][126][127]. Dean vortex effect 20-25% Hct blood 85 Yang et al [91] Bifurcation effect Sheep whole blood 100 Shatova et al [105] Bifurcation effect whole blood 100 Maria et al [95] Wettability control whole blood N/A Lee et al [57] Wettability control whole blood N/A…”

Surface Wettability Tuning of Acrylic Resin Photoresist and Its Aging Performance

“…When used in microfluidics or other fields, the stability of the hydrophilic polymer surfaces obtained by plasma or UV/ozone treatments should be paid attention to, because of the hydrophobic recovery with time [ 39 , 40 , 41 ]. As reported, low storage temperature and low humidity is beneficial for the hydrophilic stability [ 19 ].…”