Fluid fronts in hydrophilic and hydrophobic microchannels

Abstract

An experimental setup is designed and experimental studies are done in order to investigate the behavior of fluid fronts in different microchannels. Different levels of hydrophobicity and pressure are explored, getting very different results for hydrophobic and hydrophilic microchannels. For hydrophilic microchannels and any driving pressure difference the distribution of velocities corresponds to a Gaussian distribution and the front advances with h ~ tv with the classical Washburn exponent v = 0.5 for hydrophilic microchannels. The same results are obtained for hydrophobic microchannels at large driving pressure differences. For hydrophobic microchannels and when the pressure di¿erence is decreased, the distribution of velocities corresponds to a Gumbel distribution that correctly characterizes rare events like avalanches and the front advances with an exponent v as small as 0.38.