Hydrophilic PDMS microchannels for high-throughput formation of oil-in-water microdroplets and water-in-oil-in-water double emulsions.

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Entry by Yuhang Jin, AP225 Fall 2011


Wolfgang-Andreas C. Bauer, Martin Fischlechner, Chris Abell and Wilhelm T. S. Huck, Lab Chip, 2010, 10, 1814.


polyelectrolytes deposition, microdroplets, double emulsions, microfluidics


The paper presents a method of layer-by-layer (LbL) deposition of polyelectrolytes to modify the surface wettability of PDMS-based microfluidic devices. The resulting coatings show stable hydrophylicity and hydrophobicity, and allow for high throughput generation of microdroplets or double emulsions.

This approach has several advantages over previously available ones: long-term stability, simple protocols and negligible distortion of channel dimension.

Results and discussion

Fig.1 (a) Schematic of the LbL surface modification of a PDMS microchannel. (b) Schematic of polyelectrolytes deposited on the channel wall. (c) Fluorescence micrograph of four microchannels modified with different solution sequences.

The LbL method is largely automated by sequentially pumping segments of poly(allylamine hydrochloride) (PAH) solution, poly-(sodium 4-styrenesulfonate) (PSS) and aqueous NaCl washing solution into the plasma-oxidized channel with a syringe, as is shown in Fig. 1. The polyelectrolytes attach to the surface of PDMS via electrostatic interactions. A PAH layer is highly hydrophobic, whereas a PSS layer is hydrophilic. Therefore the wettability of the channel walls rely on the innermost layer of deposition. This modification of surface properties is essentially a permanent effect.

Fig.2 (a) Generation of oil droplets in water using a flow focusing structure. (b) Droplets passing through the device. (c) Close-packed droplets. (d) Distribution of droplet diameter.

Hydrophilic channels enable generation of oil microdroplets in water by a flow focusing geometry, as is seen in Fig. 2. The shear forces arising from the encounter of oil with water around the nozzle break the oil phase into discrete droplets, whose size is rather monodisperse according to subsequent measurements.