A Research Paper Published in Applied Surface Science

The study examined the possibility of tuning the surface and optical properties of a biocompatible nanofilm (a polyelectrolyte multilayer) composed of chitosan/carboxymethyl cellulose using a sodium chloride solution after preparation, a process called salt annealing. In the first part of the study, these nanomaterials were prepared on a silicon wafer. The influence of salt concentration and the annealing duration on the film’s surface properties (morphology, roughness, and wettability) was analyzed. Afterwards, the thin films were prepared on a glass substrate, and the impact of salt annealing duration on the surface and optical properties was investigated. The study successfully established a correlation between the surface roughness of the film and its optical properties. Additionally, it was demonstrated that a one-second treatment with the salt solution is sufficient to eliminate the nanofilm's impact on the optical properties of the substrate. Moreover, the films were found to be stable even after prolonged exposure (8 days) to the salt solution. Finally, to explore the potential application of salt annealing, the film was applied to a cherry tomato. The reflectance of the tomato was measured before and after film deposition, as well as after exposure of the film to the salt solution. It was found that the film’s effect on the tomato’s appearance could be completely removed with a one-second sodium chloride solution treatment. This confirmed the potential application of salt solution treatment on various substrates as a highly effective method for mitigating the influence of thin films on the optical properties of the substrate.

The results of this research build upon studies initiated by Antun Habajec during the courses Advanced Physical Chemistry Laboratory 1 and Advanced Physical Chemistry Laboratory 2, which were further expanded into a research project that received the Rector’s Award from the University of Zagreb. The paper represents a significant advancement in the application of salt annealing for tuning the properties of biocompatible thin films as bio-optical materials.