A crafty utilization of intermediate-angle neutron scattering and contrast variation by water-exchange to study the microstructure of microbial cellulose

Incoherent neutron scattering contribution presents a challenge in the structure characterization of many target materials. In this study, we introduce a method of intermediate angle neutron scattering (IANS) to correct the small angle neutron scattering (SANS) data of the water-swollen microbial cellulose (MC) sample, the system of which has significant incoherent contributions from the water solvent, and we describe the effects that the corrections have on the structural analysis. In order to elucidate the structure, the solvent is changed in situ from protonated water to deuterated water to give different scattering contrast, and this water-exchange process has been followed by time-resolved SANS and IANS simultaneously. Our results show that: 1) after incoherent correction, the structure of MC sample is proved to be invariant with solvents; 2) the scattering intensity depends only on the contrast factor, revealing a two-phase system composed of water-resistant crystalline cellulose phase and hydrated phase; 3) The cellulose crystallites have a constant scattering length density of 2.0 × 10¹⁰ cm^-2, determined by the matching point at which the scattering contrast between the two phases is minimum. This value is consistent with that of 1.9 × 10¹⁰ cm^-2 estimated from its chemical structure. (author)