Ultralight Aerogels with Hierarchical Porous Structures Prepared from Cellulose Nanocrystal Stabilized Pickering High Internal Phase Emulsions

Cellulose nanocrystal (CNC)-based aerogels with extremely low density and hierarchical porous structure were constructed via a facile Pickering-emulsion-templated strategy. In this method, aminated CNCs (CNC-NH2) were synthesized to stabilize o/w Pickering high internal phase emulsions (Pickering HIPEs). Amino groups were introduced to CNCs to decrease the net surface charges of CNCs, enhance their aggregation, and therefore achieve Pickering HIPEs stabilized by the particles of ultralow content (∼0.1 wt %). A series of CNC aerogels was then obtained by freeze drying these emulsions. The resulting aerogels were ultralight with a density that reached ca. 0.5 mg/cm3 (an order of magnitude lower than that previously reported for CNC aerogels) and an ultrahigh porosity (up to 99.969%). Contributed to the extremely low density, the thermal conductivity of the aerogels was around 0.021 W/(m·K) which is lower than that of air (0.024 W/(m·K)). This novel strategy could be applied to other materials, such as graphene and carbon nanotubes, to prepare ultralight aerogels with controllable porous structures and unique properties.