  The submicron- and micron-scale structures of composite hydrogels based on
bacterial cellulose (BC) and polyacrylamide were studied by spin-echo
small-angle neutron scattering (SESANS). These hydrogels were synthesized via
free-radical polymerization of acrylamide carried out in pellicle of BC swollen
in the reaction solution. No neutron scattering was observed for the samples
swollen in heavy water to the equilibrium state, but a SESANS signal appeared
when TbCl$_{3}$ salt was added to the solvent. The SESANS dependences obtained
for these samples revealed the anisotropy of mesostructure for the hydrogels
under investigation. Density inhomogeneities on the characteristic scale of
11.5 $\pm$ 0.5 $\mu$m were detected in one specific orientation of the sample,
i.e. with growth plane of BC parallel to plane formed by neutron beam and
spin-echo length. The uniaxial anisotropy revealed agrees with the proposed
model, which attributes this behavior to the existence of the tunnel-like
oriented structures inside BC.
