Time-scales of solutal Marangoni flow

Depositing a microliter isopropanol (IPA) drop on a deep water layer results in a complex mixing process of these fully soluble liquids. Due to the difference in surface tension, the IPA spreads in radial direction after forming a lens in the region of drop deposition. This film spreading reaches a finite radius until it eventually retracts, which is yet not entirely understood. Conducting the drop deposition experiments with IPA drops ranging from 7 to 80 µl, we can provide quantitative results regarding the spreading as well as the retraction time scales. Using particle imaging, we were able to derive the film radius over time and the flow field in the water layer. An analysis of this data enables the derivation of the physical laws involved in the spreading and retraction. Moreover, an estimation of the energy that is converted from the difference in surface tension into the kinetic energy of the bulk may help to estimate the amount of IPA that is actually spreading from the center of deposition compared to the amount of IPA that directly mixes with the water at the center of the IPA deposition.