A pellicle, a gel film of microbial cellulose, is a supermolecular system containing 99% of water by
weight, which is closely related to an amorphous structure in it. Using ultra-small–angle neutron scattering,
in order to cover over a wide range of length scales from nm to 10 μm, we examined the hierarchical
amorphous structure in the microbial cellulose, which is synthesized by a bacterium (Acetobacter xylinum).
The microbial cellulose swollen by water shows small-angle scattering that obeys a power law q-behavior
according to q
− as a function of the magnitude of the scattering vector q. The power law, determined by
scattering, is attributed to a mass fractal due to the distribution of the center of mass for the crystallite
(microfibril) in amorphous cellulose swollen by water. As q increases, takes the values of 2.5, 1, and 2.35,
corresponding, respectively, to a gel network composed of bundles, a bundle composed of cellulose ribbons,
and concentration fluctuations in a bundle. From the mass fractal q-behavior and its length scale limits,
we evaluated a volume fraction of crystallite in microbial cellulose. It was found that 90% of the cellulose
bundle is occupied by amorphous cellulose containing water.