  Physical properties of composite materials can be pre-engineered by
controlling their structure and composition at the mesoscale. Yet, approaches
for achieving this are limited and rarely scalable. We introduce a new breed of
self-assembled nematogels formed by an orientationally ordered network of thin
cellulose nanofibers infiltrated with a thermotropic nematic fluid. The
interplay of orientational ordering within the nematic network and that of the
small-molecule liquid crystal around it yields a composite with highly tunable
optical properties. By means of combining experimental characterization and
modeling, we demonstrate sub-millisecond electric switching of transparency and
facile responses of the composite to temperature changes. Finally, we discuss a
host of potential technological uses of these self-assembled nematogel
composites, ranging from smart and privacy windows to novel flexible displays.
