Capillarity in microfluidic channels with hydrophilic and hydrophobic walls

The authors investigate the spontaneous filling of microchannels with mixed hydrophilic and hydrophobic walls. We show that in these channels, unlike that case when all the walls are either hydrophilic or hydrophobic, the local distribution of capillary drive can make partial filling of the channel the most favorable filling type. A strategy for finding the most favorable filling type is presented and tested against capillary filling experiments made on oxygen plasma treated SU-8 microchannels. Good agreement is found between the theory and the experiments.

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