Effect of wettability on static drop formation cycle from a hole in a horizontal flat plate into air was studied experimentally and theoretically. Water, glycerin, kerosene and liquid paraffin were used as the liquid in the experiments, and copper, Teflon, acrylic resin and glass were used as the solid.
The experimental results are classified into the following three cases. 1) Case 1, where the contact line, defined as the boundary among the three phases, is fixed. 2) Case 2, where the contact line is free to move. 3) Case 3, where the liquid wets the solid perfectly.
It is found that the important factor governing the maximum stable drop volume V_max is Bond number for Case 1, and is advancing contact angle for Case 2. A method of predicting V_max in each case is proposed. It is revealed that the drop formation cycle for the three cases can be simulated theoretically by solving the variational problem which is derived from analysis of the potential energy of drops, using the finite element method.