Controlled Sol-Gel Transitions of Metal-Organic Membrane-Enveloped Cellulose Nanofibrils via Metal Coordination in Aqueous Media.

We report a metal coordination-driven sol-gel transition system where cellulose nanofibrils are enveloped by a rationally designed metal-organic membrane (MOM) in an aqueous medium. Specifically, 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized bacterial cellulose (TOBC) is encapsulated within an MOM comprising Zn and the chelator phytic acid (PA), denoted TOBC. Using the DLVO theory, we elucidate how tuning the metal ion valence in TOBC modulates the sol-gel transition by controlling interfibrillar attractive forces. Notably, TOBC fluids exhibit relaxation times consistent with the Kohlrausch-Williams-Watts (KWW) function. Significantly, we demonstrate reversible, sustainable sol-gel transitions in TOBC under stepwise mechanical strain. This facile approach enables rheological tailoring of aqueous media, promising for the development of advanced stimuli-responsive smart fluids for applications in cosmetics, food science, and pharmaceutical formulations.