HYDRODYNAMIC EFFECTS IS MEASUREMENTS WITH THE DROP VOLUME TECHNIQUE AT SMALL DROP TIMES .1. SURFACE TENSIONS OF PURE LIQUIDS AND MIXTURES

The drop volume technique represents a standard method in surface science with many advantages: simple handling and temperature control, need for small amounts of solvent and solute, good reproducibility, and applicability to liquid/gas and liquid/liquid interfaces. An automated, commercially available instrument allows not only efficient application but also the systematic study of effects influencing the drop formation process. For example, hydrodynamic effects at small drop times simulate higher surface tensions. These effects depend on the tip radius and can be explained on the basis of a finite drop detachment time. At small drop times these effects are remarkable and must be corrected in order to determine real surface tension values. At drop times down to about Is and for tip radii in the range 0.025-0.2 cm the hydrodynamic effect can be described by a drop detachment time. A circular flow inside the drop as a counter-effect can be neglected under these conditions.