No abstract

A class of “green” hybrid membranes composed of nanocellulose and an ionic liquid exhibits exceptional separation properties arising from a humidity-responsive size-exclusive “gate” that allows selective CO2 permeation.

Aqueous suspensions of cellulose nanocrystals (CNCs) can spontaneously form a chiral nematic mesophase at a critical concentration (c*). Unfortunately, no current analytical technique permits rapid detection of c*. Herein, we introduce a facile and accurate approach to assess c* rapidly (<2 h) from a small sample volume and compare our results with those obtained by conventional methods. Our strategy employs isothermal titration calorimetry (ITC) to measure the heat associated with interactions in the suspension, which can identify the onset of mesophase formation as the heat signature is sensitive to the suspension viscosity and thus capable of detecting small changes in the suspension environment. We measure c* for CNC samples differing in surface charge and aspect ratio, and find that both lower aspect ratios and higher surface charges increase c*. Our ITC results reveal the role of CNC interactions prior to the visual observation of mesophase formation and elucidate mesomorphic effects related to nanocrystals and their suspensions.

The development of new materials emphasizes greater use of sustainable and eco-friendly resources, including those that take advantage of the unique properties of nanopolysaccharides. Advances in this area, however, necessarily require a thorough understanding of interactions with water. Our contribution to this important topic pertains to the swelling behavior of partially deacetylated nanochitin (NCh), which has been studied here by quartz crystal microgravimetry. Ultrathin films of NCh supported on gold-coated resonators have been equilibrated in aqueous electrolyte solutions (containing NaF, NaCl, NaBr, NaNO 3 , Na 2 SO 4 , Na 2 SO 3 , or Na 3 PO 4 ) at different ionic strengths. As anticipated, NCh displays contrasting swelling/deswelling responses, depending on the ionic affinities and valences of the counterions. The extent of water uptake induced by halide anions, for instance, follows a modified Hofmeister series with F − producing the highest swelling. In marked contrast, Cl − induces film dehydration. We conclude that larger anions promote deswelling such that water losses increase with increasing anion valence. Results such as the ones reported here are critical to ongoing efforts designed to dry chitin nanomaterials and develop bio-based and sustainable materials, including particles, films, coatings, and other nanostructured assemblies, for various devices and applications.