Liquid Jet Instability and Dynamic Surface Tension Effect on Breakup

We studied the instability of a liquid jet by confocal microscopy, a non-invasive three-dimensional imaging technique. The amplitude of jet oscillation can be measured from its early stage to the vicinity of the jet breakup with a radial resolution of 80 nm. A continuous jet with a diameter of 100 mu m and mean velocity of 5.6 ms(-1) was perturbed at a frequency of 11.8 kHz. The growth rate of the sinusoidal instability was used to determine the dynamic surface tension of water and of surfactant solutions at a surface age of <= 1 ms, using an established linear, axisymmetric, constant property model. A commercial aqueous non-ionic Gemini surfactant Surfynol 465 reduced the dynamic surface tension more efficiently than an anionic surfactant sodium dodecyl sulphate (SDS). The effect of surfactant on the jet breakup length has also been studied. We applied the confocal imaging system to study the temporal evolution of a ligament which starts from a concave neck and eventually develops into a satellite drop. The pinch-off process has been studied in detail. It is found that the final stages of ligament rupture are the same for water and surfactant solutions. The time taken for the satellite drop to be engulfed by the following drop depends on the surfactant concentration.