Retraction Phenomena of Surfactant Solution Drops upon Impact on a Solid Substrate of Low Surface Energy

The impact of surfactant solutions drop on a low-surface-energy solid substrate is investigated using a high-speed photographic technique (one picture every 100 μs) which allows simultaneous top and side views. The influence of physicochemical properties is analyzed by varying the adsorption kinetics of the surfactants and the initial diameter and velocity of the drop before impact. Generally, the drop spreads and retracts under the action of inertia and capillarity, respectively. During spreading, the drop shape changes from a “truncated sphere” to a “flat pancake” and the drop surface is increased such that it is no longer at thermodynamic equilibrium. The relevant surface property is therefore the dynamic surface tension which is evaluated at the maximum diameter γdmax, using the maximum bubble pressure apparatus. The dynamic surface tension has a critical influence on the drop behavior at the maximum diameter dmax and during the subsequent retraction. A simple relation combining γdmax and the dynamic ...