Influência de nanopartículas de celulose na autoagregação de sais de bile

Abstract

Surfactant self-aggregates can exhibit pronounced viscoelasticity, which can be modulated according to the addition of different molecules to the medium in which they are inserted. In this work, the effect of adding cellulose nanocrystals (CNCs) or cellulose nanofibrils (CNFs), synthesized by acid hydrolysis with sulfuric acid and TEMPO-mediated oxidation, respectively, was studied on self-aggregates of sodium deoxycholate (NaDC) and/or or sodium taurodeoxycholate (NaTDC) in aqueous medium, in different proportions of surfactant/nanocellulose. The size of NaTDC/nanocellulose aggregates increased with nanocellulose addition and were larger than NaDC/nanocellulose and NaDC/NaTDC/nanocellulose samples, respectively. Zeta potential (ZP) data indicated the colloidal stability increased with nanocellulose concentration increasing. Samples containing CNFs were more stable and binary equimolar (50 mM) bile salt systems with CNCs or CNFs was more stable than the ones containing a unique bile salt. The non-Newtonian behavior of fluids was observed since systems presented shear thinning and/or shear thickening phenomena. The dynamic frequency assay demonstrated more viscoelastic systems and a gel-like behavior for the ones containing CNFs. Aggregates of the equimolar NaDC/NaTDC sample with 4.80 g/L CNF have more entanglements, since they have a higher elastic modulus value on the plateau, G0, (2011 Pas) being around 10 (210.1 Pas) and 90 (22.58 Pas) times higher than G0 of the analogous systems of NaDC/CNF and NaTDC/CNF, respectively. Small-angle X-ray scattering (SAXS) curves showed the formation of more elongated cylinders for aggregates containing CNFs and shorter ones for those containing CNCs. NaTDC/CNF aggregates are the shortest and the NaDC/NaTDC/CNF aggregates are the longest. More elongated cylindrical aggregates favor entanglements between aggregates and the formation of stronger gels, and intermolecular interactions played an important role in this. Therefore, these new materials are part of a current context for the development of systems aimed at application as rheological modifiers for use in paints and encapsulation/controlled release of interesting molecules, important for the cosmetics and pharmaceutical industries.