Improving the surface and optical properties of biocompatible chitosan/carboxymethyl cellulose nanofilms by salt annealing

Abstract

Polyelectrolyte multilayers are nanofilms often prepared out of polysaccharides with a wide range of applications as anticorrosion, antireflective or antimicrobial coatings. In this study, we prepared films from two biocompatible polysaccharides, chitosan and carboxymethyl cellulose. Such thin films, when prepared on model surfaces such as silicon or glass, change the optical properties of the surface. For this reason, we modified the films post-adsorption by immersing them in sodium chloride solution, a process known as salt annealing. By varying the salt concentration and duration of annealing, both surface and optical properties of the multilayer were tuned and improved. The untreated films made the substrate reflect light more diffusely, leading to a clouded appearance of the surface. This effect was reduced via salt annealing, resulting in a film which does not affect the optical properties of the surface. In addition to the changes in optical properties, the wetting behaviour of the films was also studied. This study successfully correlates film roughness and the changes in the diffuse reflectance. Furthermore, as a proof of concept for application, the chitosan/carboxymethyl cellulose film was successfully prepared on a cherry tomato where salt annealing successfully diminished the influence of the film on its reflective properties.