  Bringing the interfaces of two miscible fluids into contact naturally
generates strong gradients in surface tension. Here we investigate such a
Marangoni-driven flow by continuously supplying isopropyl alcohol (IPA) on a
film of water, using micron-sized droplets of IPA-water mixtures. These
droplets create a localized depression in surface tension that leads to the
opening of a circular and thin region in the water film. At the edge of the
thin region, there is a rim growing and collecting the water of the film. We
find that the spreading radius scales as $r \sim t^{1/2}$. This result can be
explained from a balance between Marangoni and viscous stresses, assuming that
the gradients in surface tension are smoothened out over the entire size of the
circular opening. We derive a scaling law that accurately predicts the
influence of the IPA flux as well as the thickness of the thin film at the
interior of the spreading front.
