Chitosan Nanocoatings N-acylated with Decanoic Anhydride: Hydrophobic, Hygroscopic and Structural Properties

Márton, Péter and Rácz, Adél and Szolnoki, Beáta and Madarász, János and Nagy, Norbert and Fodor, Bálint and Basa, Péter and Rohonczy, János and Hórvölgyi, Zoltán (2024) Chitosan Nanocoatings N-acylated with Decanoic Anhydride: Hydrophobic, Hygroscopic and Structural Properties. CARBOHYDRATE POLYMERS : A JOURNAL DEVOTED TO SCIENTIFIC AND TECHNOLOGICAL ASPECTS OF INDUSTRIALLY RELEVANT POLYSACCHARIDES, 343. No.-122480. ISSN 0144-8617 (print); 1879-1344 (online)

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Abstract

Thin (ca. 340 nm) chitosan coatings were deposited onto glass substrates via dip-coating, then modified with the methanol solution of decanoic anhydride (0.17–56 mM). NMR, FTIR and XPS measurements confirmed that the acylation degree increased from 18 % to 45 %, and at the highest degree, the whole layer was acylated homogeneously by the reagent molecules. The coating thickness increased (up to 60%), and the refractive index decreased (from 1.541 to 1.532) due to the acylation, that was determined by UV–visible spectroscopy. The AFM did not reveal morphological changes, but wetting tests showed that the acylation rendered the coating hydrophobic (water contact angle increased from ca. 75◦ to 100◦). The contact angle, however, decreased to 85◦ due to the development of a second molecular layer of the decanoic acid by-product at the highest (over 25 mM) reagent concentrations. XRD studies showed a self-assembling structuring of the alkyl-chains in the bulk phase, which occurred in the case of the highest degree of acylation. This also manifested itself in a significant decrease of the layer hygroscopicity: the swelling degree decreased from 40% to 8% in a saturated water atmosphere monitored by spectroscopic ellipsometry.

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