The Microstructure of Cellulose Nanocrystal Aerogels as Revealed by Transmission Electron Microscope Tomography

The
microstructure of highly porous cellulose nanocrystal (CNC)
aerogels is investigated via transmission electron microscope (TEM)
tomography. The aerogels were fabricated by first supercritically
drying a carboxylated CNC organogel and then coating via atomic layer
deposition with a thin conformal layer of Al2O3 to protect the CNCs against prolonged electron beam exposure. A
series of images was then acquired, reconstructed, and segmented in
order to generate a three-dimensional (3D) model of the aerogel. The
model agrees well with theory and macroscopic measurements, indicating
that a thin conformal inorganic coating enables TEM tomography as
an analysis tool for microstructure characterization of CNC aerogels.
The 3D model also reveals that the aerogels consist of randomly orientated
CNCs that attach to one another primarily in three ways: end to end
contact, “T″ contact, and “X″ contact.