An experimental procedure to obtain the equilibrium contact angle from theWilhelmy method

The theory of contact angles has been developed using the concept of the Yo ung contact angle, an equilibrium quantity related to perfectly smooth and homogeneous surfaces; on real surfaces it is commonly accepted that one can obtain "metastable" equilibrium states, in l,Inch the shape of the meniscu s along the triple line is not fully equivalent to the "equilibrium" menisc us. In the present paper, a new method is presented to obtain an equilibrium co ntact angle with a simple modification of the Wilhelmy microbalance. The su pply of acoustic energy, to the liquid at a frequency which induces the res onant formation of capillary waves, followed by the reduction of the amplit ude Of the vibration, allows the meniscus to move from the metastable advan cing or receding shape to the stable equilibrium one.