Towards polyelectrolyte complex films by means of plasticisation

Researchers have successfully applied polyelectrolyte complex coatings in one step. To form a homogenous solution, the properties of the plasticisers and the polyelectrolytes should match.

A laboratory.
Both polyols and amphiphilic ionic liquids showed a sufficient plasticising effect.  Image source: FreeProd - Fotolia (symbol image).

Polyelectrolyte complexes (PECs) show great promise as functional coatings, including as oxygen barrier coatings for food packaging, but the brittleness of dry PECs limits their application. In a new work, the possibility of plasticising polyethylenimine/poly(4-styrenesulfonic acid) (PEI/PSS) films was investigated. Three different classes of plasticisers were chosen: salt, polyols, and ionic liquids (ILs). They were successfully incorporated in the evaporation-based single-step method. Potassium bromide or sorbitol plasticised films all showed crystallisation upon evaporation, while films plasticised by glycerol, polyethylene glycol, and imidazole-based ILs all showed a clear brittle-to-ductile transition in their mechanical properties.

Controlled mechanical properties

The hydrophilicity of polyols and the amphiphilicity of these ILs allowed them to form homogenous casting solutions, but also increased their water sensitivity. The ionic nature of ILs make them more efficient as plasticisers since they can replace part of the PE-PE ionic-crosslinks, resulting in a more flexible network. According to the researchers, their work demonstrates that ductile PEC films can be formed in a single step with controlled mechanical properties through plasticisation.

The study has been published in Progress in Organic Coatings, Volume 177, April 2023.

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