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Optically active multilayer films based on chitosan and an azopolymer.

The layer-by-layer technique has been widely adopted for the fabrication of nanostructures with tailored properties. In this work, photoactive multilayer films consisting of alternating layers of chitosan and an azopolymer were developed by this method. Taking into account that pH is the factor controlling the charge of weak polyelectrolytes, the influence of this parameter on the structure and properties of the multilayer films was evaluated. Thus, different films were prepared by varying pH conditions as well as bilayer number. The morphology and properties of the films were analyzed by diverse advanced techniques, such as ultraviolet-visible spectroscopy, X-ray diffraction, and atomic force microscopy equipped with PeakForce QNM (Quantitative Nanomechanical Property Mapping). It was found that the thickness, roughness and elastic modulus of the developed multilayer films increased with the decrease of the chitosan solution pH and the increase of the bilayer number. Furthermore, induced birefringence measurements revealed that a higher level of photo-orientation was attained with the decrease of pH and the increase of bilayer number.

Photoresponsive Multilayer Films of Chitosan and an Azopolymer

The main goal of this work was the development of photoactive multilayer films. Taking into account that chitosan is a biodegradable, biocompatible, nontoxic, and antibacterial biopolymer, the fabrication of chitosanbased multilayer films can be an interesting pathway to obtain biopolymer-based films in which properties can be combined with a light-responsive material, such as an azobenzene-containing polymer. In particular, the layer-by-layer technique was used for the fabrication of the optically active films consisting of alternating layers of chitosan and an azopolymer. The influence of the pH and the number of bilayers on the structure and properties of the films was investigated by different experimental techniques and it was found that the roughness and elastic modulus of the multilayer films increased with the decrease in chitosan solution pH. Besides, induced birefringence measurements revealed that a higher level of photoorientation was attained with the decrease in pH and the increase in bilayer number of the developed films.