Self-assembled systems of bile salts and nanocellulose particles

Surfactant self-aggregates can exhibit pronounced viscoelasticity, which can be modulated by adding other molecules and particles, such as nanocellulose. This study investigates the effect of anionic cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs), synthesized via sulfuric acid hydrolysis and TEMPO-mediated oxidation, respectively, on the self-aggregates of the bile salts (BS) sodium deoxycholate (NaDC) and sodium taurodeoxycholate (NaTDC) in aqueous media. Zeta potential measurements indicated colloidal stability, with CNF-containing samples exhibiting more negative values. Small-angle X-ray scattering (SAXS) results revealed anisotropic aggregates, in which the NaDC/nanocellulose systems exhibited a similar characteristic transverse length scale, whereas the NaTDC/nanocellulose systems showed changes in the effective cross-sectional geometry. Rheological analysis of BS-nanocellulose-based systems exhibited non-Newtonian behavior, including shear thinning. Dynamic frequency sweeps showed higher viscoelasticity and gel-like behavior for the systems containing CNF – particularly the NaDC/CNF systems – and the structuring of the systems increased with rising nanofibril concentration. Notably, analogous systems containing 0.050 mol.L -1 BS and 4.8 g.L -1 CNF showed higher elastic modulus (G') values for NaDC (G’ = 184 Pa) than for NaTDC (G’ = 19.5 Pa) systems, approximately ninefold in the first case. Cryo-EM images confirmed cylindrical structures with spherical ones, and greater entanglement was verified for NaDC/CNF systems. These findings support the potential use of these nanocellulose-surfactant systems as rheological modifiers or active-ingredient carrier platforms for food, cosmetic, or pharmaceutical applications.