Capillary flow in microchannels

Abstract

The surface of microchannels, especially polymer channels, often needs to be treated to acquire specific properties. This study investigated the capillary flow and the interface behavior in several glass capillaries and fabricated microchannels using a photographic technique and image analysis. The effect of air plasma treatment on the characteristics of capillary flow in three types of microfluidic chips, and the longevity of the acquired surface properties were also studied. It was observed that the dynamic contact angles in microchannels were significantly larger than those measured from a flat substrate and the angle varied with channel size. This suggests that dynamic contact angle measured in situ must be used in the theoretical calculation of capillary flow speed, especially for microfabricated microchannels since the surface properties are likely to be different from the native material. This study also revealed that plasma treatment could induce different interface patterns in the PDMS channels from those in the glass and PC channels. The PDMS channel walls could acquire different level of hydrophilicity during the plasma treatment, and the recovery to hydrophobicity is also non-homogeneous.