Dynamic contact angle of a droplet spreading on heterogeneous surfaces

Spreading of viscous droplets on model surfaces obtained by microcontact printing is studied. Here, the special case where surface heterogeneities are in the form of micro-chemical stripes is considered. It is shown that an elongated flow occurs, which develops through the relaxation of the longitudinal curvature of the liquid-air interface. Finally, we find that the dynamic contact angle of a droplet spreading along the chemical stripes shows similar variation with spreading velocity as that for a droplet spreading on a homogeneous surface.