Figure 3: Collapse of the dynamics according to a simple model of viscoelastic dissipation.
From: A moving contact line as a rheometer for nanometric interfacial layers
The microscopic contact angles have been obtained for three different lengths of PDMS (N=79, 126, 232 in yellow squares, red circles and blue triangles). By examining the microscopic angle, the bulk hydrodynamic contribution to the dynamics has been removed and what remains is attributable to the viscoelastic response of the pseudo-brush layer under the contact line. In all cases, the hysteresis is small and an equilibrium angle can be identified with little ambiguity as the mid-point between the advancing and receding angles at the lowest velocities; θeq=(θA−θR)/2. Since the equilibrium angle varies slightly with the PDMS length (see Table 1), for comparison between surfaces, deviations from equilibrium are shown. The velocity has been scaled by the thickness of the PDMS layer and the Rouse relaxation time τ. The data for different N collapse onto a master curve with a best fit (solid line) of slope 0.81.
