Spreading of oil droplets on silicon oxide surfaces with parallel v-shaped channels

Abstract

The spreading of silicone and paraffin oils has been studied on two energetically and chemically different smooth surfaces (gold and polystyrene). It was found that for these surfaces, neither the surface tension nor the surface free energy influenced the spreading behaviour of the oils. The data for the two different liquids can be transposed onto a master curve when the product of velocity and viscosity is plotted versus the dynamic contact angle. The spreading of paraffin oil droplets was also studied on a set of silicon oxide surfaces containing parallel v-shaped surface channels at various widths and spacings. It was found that the sharp edges of the channel walls strongly affected spreading, and that the droplet shape was distorted from the usual circular shape displayed on a smooth surface. An elongated droplet was formed with the contact line following a channel edge and with the short sides having a semicircular shape. Transverse spreading was very slow and decreased as the spacing was decreased. Increased channel size and decreased spacing produced an increase in the spreading velocity in the direction of the channels.