Solvent-Mediated Control of Bacterial Cellulose Nanofiber Conformations: From Colloidal Dynamics to Solid-Film Properties

We present a systematic investigation of bacterial cellulose nanofibers (CNFs) by examining their behavior from colloidal dispersions to bulk materials. By varying Hansen solubility parameters and thus the polymer-solvent interaction parameter (χ) across different solvents, we probe the fundamental relationships between thermodynamic interactions and CNF morphology.

Rheological characterization reveals solvent-dependent critical overlap concentrations (c*), reflecting variations in excluded volume effects. Small-angle X-ray scattering (SAXS) measurements quantify conformational changes through shifts in radius of gyration. At the same time, zeta potential analysis elucidates the role of electrostatic stabilization in colloidal dispersions with concentrations beyond the gel crowding factor and the subsequent deviations from the general trend. CNF dispersions in the dilute regime exhibit expanded conformations with enhanced excluded volume effects in thermodynamically favorable solvents, resulting in increased intrinsic viscosities. Notably, the transition from dispersion to solid state reveals that electrostatic repulsion dominates the state transformation: films cast from electrostatically stabilized dispersions (with concentrations beyond the gel crowding factor) demonstrate superior mechanical properties despite suboptimal thermodynamic interactions.

This work establishes a qualitative framework for understanding the interplay between solvent thermodynamics and electrostatic forces in CNF assembly from colloidal dispersions to solid films, providing crucial insights for processing optimization in sustainable materials development.