Pearling process of a fluid strip on a partially wetting surface

J. DIEZ; A. G. GONZÁLEZ; R. GRATTON; J. M. GOMBA

Guanajuato (México)

Simposio; IUTAM Symposium Interactions for Dispersed Systems in Newtonian and Viscoelastic Fluids; 2006

International Union of Theoretical and Applied Mechanics

   We study the evolution of a long strip of viscous fluid sitting on a horizontal glass substrate under partial wetting conditions (contact angle ≈ 50 − 60◦ ). We observe that for long times this initial condition develops into an array of quasi-equidistant droplets. The special feature of this dewetting scenario is that the pearling process, consisting of succesive stages of bulge growth and pinch off, does not occur simultaneously all along the strip but propagates from the ends towards the strip center. By means of simple optical techniques we investigate the shape of the resulting drops, andmeasure the nonuniform contact angle along their periphery. We find that the contact surface of the droplets is non-circular, but has an almost elliptical shape. A remarkable feature of the pinchingprocess is the formation of a chain of satellite drops of decreasing size. We find that the primary large drops, as well as the secondary and tertiary drops, share the same angular pattern and the aspect ratio of the elliptical contact surfaces. A model based on the energy balance of the initial and final states shows that the number of drops can be predicted by assuming that the energy dissipatedis proportional to the area covered by the droplets.