Smart Cellulose Nanofluids Produced\nby Tunable Hydrophobic Association of Polymer-Grafted Cellulose Nanocrystals

Abstract

Cellulose\nfibrils, unique plant-derived semicrystalline nanomaterials with exceptional\nmechanical properties, have significant potential for rheology modification\nof complex fluids due to their ability to form a physically associated\nsemiflexible fibrillary network. Here, we report new associative cellulose\nnanocrystals (ACNCs) with stress-responsive rheological behaviors\nin an aqueous solution. The surface-mediated living radical polymerization\nwas employed to graft poly­(stearyl methacrylate-<i>co</i>-2-methacryloxyethyl phosphorylcholine) brushes onto the nanofibrils,\nand then 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated\noxidation was conducted to produce nanoscale ACNCs in the aqueous\nsolution. The ACNCs displayed interfibril association driven by the\nhydrophobic interaction that resulted in the formation of a nanofibrillar\ncrystalline gel phase. We observed that the viscosity of the ACNC\nfluid showed reversible shear thinning and temperature-induced thickening\nin response to applied shear stress and thermal shock. Moreover, thanks\nto generation of a mechanically robust nanofibrillar crystalline gel\nnetwork, the ACNC suspension showed extraordinary stability to changes\nin salinity and pH. These results highlighted that the interfibril\nhydrophobic association of ACNCs was vital and played an essential\nrole in regulation of stimuli-responsive sol–gel transitions.