Thinning and breakup of freestanding polymer films

Freestanding liquid films present an interesting environment for polymer chains in solution, as the chains are confined while being subjected to capillary and hydrodynamic stresses, with relevance for foaming processes. In the present work we first discuss how polymer solution films provide ideal model system to study the hydrodynamic breakup regime of thin liquid films and how the critical thickness is controlled by both material properties and hydrodynamic conditions. Second, we provide evidence that such thin films of polymer solutions can be stabilized through lateral, osmotic-based transport of polymer chains to produce several of the phenomena that are associated with interfacial, Marangoni-based stresses. Phenomena such as cyclic dimple formation, vortices, and dimple recoil were observed. The factors which lead to enhanced lifetime of the films as a consequence of these flow instabilities can be used to either stabilise foams or, conversely, prevent foam formation.