Marangoni Instability during the Non-Solvent Induced Phase Separation of a Ternary Polymer Solution

Non-solvent induced phase separation (NIPS) processes are widely used by industry and by Nature as a means of controlling the microstructure of polymer materials. While the general principles of the NIPS process have been known for a long time, a detailed quantitative description has proven difficult, in part due to a lack of robust theories and numerical models. We recently addressed this need by developing a multi-fluid model of the NIPS process that combines continuum fluid mechanics with a field-theoretic description of polymer thermodynamics. Using our model, we show that in certain cases non-solvent transport between a polymer-lean and polymer-rich domain can lead to a hydrodynamic instability driven by local surface tension gradients. We will discuss the prerequisites for this instability and its potential impacts on the microstructure of materials made by the NIPS process.