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 (N2) to form a low-viscosity CNC suspension. The gelation process and the properties of the hydrogels have been investigated by rheology, ζ 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.