Modulating biopolymer electrical charge to optimize the assembly of edible multilayer nanofilms by the layer-by-layer technique

Abstract

The aim of this work was to study the influence of biopolymer (alginate, ALG; chitosan, CHI) charge on the formation of multilayer nanofilms by the layer-by-layer (LbL) technique. The electrical charge of ALG and CHI (high, medium, or low) was modulated by adjusting the pH of biopolymer solutions. The amount of biopolymer deposited in multilayers depended on the charge of ALG and CHI solutions. The lower the charge the higher the deposition rate due to the higher number of biopolymer molecules needed to neutralize the previous layer. Medium and low charge biopolymers led to a drastic change in the wettability of multilayers, with ALG layers being strongly hydrophilic and CHI layers strongly hydrophobic. The surface ζ-potential alternatively changed from negative to positive using ALG or CHI. This effect was more pronounced using highly charged biopolymers. Results obtained in this study evidenced that the multilayers properties can be tuned by controlling the biopolymer electrical charge.

This research was supported by the Ministerio de Ciencia e Innovacion (Spain) throughout projects ALG2009-11475. A.A.- ́ F. also thanks to the University of Lleida for the predoctoral grant. O.M.-B. acknowledges the Institució Catalana de Recerca i Estudis Avançats (ICREA) for the Academia 2008 Award.