CO2-Switchable Cellulose Nanocrystal Hydrogels

A carbon-dioxide-switchable (CO2-switchable) hydrogel was prepared by adding imidazole to a suspension of cellulose nanocrystals (CNCs). Sparging of CO2 through the imidazole-containing CNC suspension led to gelation of the CNCs, which was reversible by subsequent sparging with nitrogen (N-2) to form a low -viscosity CNC suspension. The gelation process and the properties of the hydrogels have been investigated by rheology, potential, pH, and conductivity measurements, and the gels were found to have interesting and reversible tunable mechanical properties. The present work describes a straightforward way to obtain switchable CNC hydrogels without the need to functionalize CNCs or add strong acids or bases. These CO2-responsive CNC hydrogels have potential for application in stimuli-responsive adsorbents, filters, and flocculants.