Structure analysis of regenerated cellulose hydrogels by small-angle and ultra-small-angle x-ray scattering.

Absolute intensities Deltai(q) of small-angle x-ray scattering (SAXS) and ultra-small-angle x-ray scattering (USAXS) were measured in a wide range of scattering vector q from 2x10(-4) to 0.5 A(-1) for transparent (VI-P) and translucent (VI-L) cellulose hydrogels prepared by coagulation and regeneration of viscose in acid solutions with and without acetone, respectively. We obtained the scattering intensities at very small q conveniently by desmearing the combined data measured by SAXS and USAXS. The plot of Deltai(q)q(2) versus log(10) q showed a peak at -2.5<log(10) q<-1.0. By assuming a two-phase model with the high-density phase (phase 1) composed of only cellulose and with the low-density phase (phase 2) composed of cellulose dispersed in water, volume fractions of phase 1 in VI-P and VI-L were determined to be 0.18 and 0.09, respectively, from the mean-square fluctuation of electron density determined as integral of (Deltai(q)q(2)dq). By fitting the observed scattering profile with the theoretical particle scattering functions of spheres, the average diameter of the high-density region including crystallite was determined to be 120 A for VI-P and 80 A for VI-L. Similar analyses were applied also to freeze-dried VI-P. These results were consistent with those obtained by the wide-angle x-ray-diffraction measurement and also with the observation by scanning probe microscopy.