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Capillary Filling of Ferrofluid in Homogeneous Hydrophilic PDMS Microchannels

The capillary filling speed of ferrofluid in hydrophilic polydimethylsiloxane (PDMS) microfluidic channels is investigated under various temperature and magnetic field conditions. Microchannels with a depth of 100 μm and widths ranging from 100 to 400 μm are fabricated using conventional photolithography techniques and an oxygen plasma bonding process. The capillary filling speed of the ferrofluid is measured experimentally and compared with that of DI water. It is found that the filling speed of the ferrofluid is significantly lower than that of DI water. Moreover, the filling speed reduces with a reducing channel width, an increasing ferrofluid concentration, a lower operating temperature, and an increased filling length. By contrast, the filling speed increases under the effects of an external magnetic field.