Drying Blends of Polymer Colloids: How to Harness Physics to Control Film Formation

Colloidal self-assembly methods, using particles suspended in a solvent as the building blocks, have been recently proposed as a single-step alternative for obtaining surfaces “on demand”.¹ We recently proved experimentally how in blends of polymer colloids of two different sizes, small particles can segregate during drying into a layer on top of the larger particles.² The moving interface causes a density, and hence a pressure, gradient in the drying film, which pushes larger particles away from the moving interface faster than it pushes smaller particles. By using stimuli-responsive particles, which swell with increasing pH, it is possible to switch stratification on and off by just changing the pH of the initial dispersion.³ For a certain size, stratification is supressed because of the increased solids content, which reduces particle mobility and reduces the osmotic pressure gradient. This type of self-assembly allows the independent control of the properties of the top and the bottom of the final film, dictated by the functionality of the large and small particles. Modelling shows it is a really strong and reliable effect, taking place for a wide range of particle size ratios and evaporation rates. However, agreement with experiments is limited, because of coffee-ring effects and Marangoni flows that are not usually present in models. In this talk, I will discuss the progress we made in this field and how we can harness the Physics of polymer colloid systems to control the final film structure towards a certain application.

References
¹Schulz, M.; Keddie, J. L. Soft Matter. 2018, 14, 6181–6197.
²Fortini, A.; Martín-Fabiani, I.; De La Haye, J. L.; Dugas, P. Y.; Lansalot, M.; D’Agosto, F.; Bourgeat-Lami, E.; Keddie, J. L.; Sear, R. P. Phys. Rev. Lett. 2016, 116, 1–5.
³Martin-Fabiani, I.; Fortini, A.; Lesage de la Haye, J.; Koh, M. L.; Taylor, S. E.; Bourgeat-lami, E.; Lansalot, M.; Agosto, F. D.; Sear, R. P.; Keddie, J. L. 2016.