Influence of water on electrical and mechanical properties of PEM films

Self-healing coatings as thin films have been widely exploited in the last decade due to the conformational ability to adhere practically at any surface, bringing multiple regenerations in damaged areas. Poly(ethylene imine) (PEI) and poly(acrylic acid) (PAA) are the most used polyelectrolytes to grow self-healing layer-by-layer films; however, few studies have been dedicated to evaluate the role of water on the electrical and mechanical properties of the films.

Central role of trapped water

During the new study, multilayered (PEI/PAA) structures were easily self-assembled on various substrates, allowing homogeneous and semi-transparent coverages. The researchers associate the exponential and linear growth regimes of (PEI/PAA) with changes in the electrical characteristics acquired after each step of the film formation. They demonstrated the central role of trapped water on the space charge accumulation at polymer/electrode interface, due to the presence of negative differential resistance regions, and the transition of the charge transport to a space charge regime after a critical potential.

The scientists have also investigated changes in the mechanical properties, showing the influence of trapped water in the film elastic modulus, wear resistance, and resistance to plastic deformation.

The study has been published in Progress in Organic Coatings, Volume 150, January 2021.