Polyelectrolyte complexes as sustainable, functional coatings

Polyelectrolytes coatings have recently gained wide attention as environmentally benign alternatives to commonly used coatings. Polyelectrolytes are molecules (often, polymers) containing multiple charges, which can be used as strong interacting moieties. In coatings, they are traditionally applied in a layer-by-layer fashion. While this method has proven useful, it is highly laborious and does not allow for easy application at large scales. Therefore, recently, application of polyelectrolyte complexes has come into attention. Polyelectrolyte complexes form when two oppositely charged polyelectrolytes start interacting electrostatically, with the opposite charges forming effective ‘crosslinks’ within the material. These crosslinks result in the formation of a strong network, which often makes these complexes solid and tough.

As such, the potential of these polyelectrolyte complexes as coatings has been increasingly uncovered, as well as methods of application. In this project, we use the dependence of charge on the pH of the solution, to selectively start complexation when the coating is applied. The coating mixture is primarily made in water, which makes then inherently more sustainable than conventional solvent-based coatings. To change the pH after application, we add a small amount of ammonia, which evaporates during drying, causing the pH to drop and complexation to occur. (1)

This method works very well for creating dense, homogeneous layers which serve as barriers to oxygen as well. However, to truly reach novel coatings of interest, in this project we aim to add additional functionalities. As a thesis project or internship, this means that you will add a functionality by changing parts of the coating, and afterwards quantify the functional effect, homogeneity and mechanical properties. Relevant methods consist of (advanced) microscopy, rheology, DMA/TGA and surface analysis techniques (AFM, contact angle).

Li J, Van Ewijk G, Van Dijken DJ, Van Der Gucht J, De Vos WM. Single-Step Application of Polyelectrolyte Complex Films as Oxygen Barrier Coatings. ACS Appl Mater Interfaces. 2021 May 12;13(18):21844–53.