PARTICLE-SIZE DISTRIBUTION AND DETERMINATION OF CHARACTERISTIC PROPERTIES OF COLLOIDAL BISMUTH-SILICA COMPOUNDS BY SMALL-ANGLE X-RAY-SCATTERING AND INELASTIC LIGHT-SCATTERING

Direct observations by small-angle X-ray scattering techniques (SAXS) and quasi-elastic light scattering (QELS) measurements of Bi3+ charged silica particles have been carried out to study particle size distributions in aqueous solutions where special attention was paid to the scattering profiles from a two-state structure, in which localized ordered, non-space-filling structures coexisted with highly disordered regions. The interference function D0/D(eff), corresponding to the solution structure factor S(Q), has been determined by QELS measurements and compared with the data obtained from SAXS. The interparticle distances (2D(exp)) as determined by SAXS and QELS measurements are in good agreement and insignificantly smaller than those obtained by the assumption of a homogeneous distribution of particles (2D0) in the presence of 0.5 M salt at pH 5.5. Moreover, the structure factor S(Q) determined from SAXS and QELS techniques agreed well in both number and position of the corresponding peaks. Thus the particle size distributions obtained by QELS and SAXS are consistent with the view that the shape of this particular colloidal SiO2 dispersion, upon coating with Bi3+ groups, does not vary significantly with respect to particle size distribution, having the same shape and no severe interparticle interactions due to concentration and charge effects according to the thermodynamic fluctuation theory. The deviation of different radii from QELS measurements of these bismuth-silica particles and, for comparison with a standardized Ludox sample, were estimated to be 15% for R(d), 5% for R(l), 6% for R(f), 14% for R(v) and 11% for R(g) which are the average radii of the intersection length, correlation length, correlation surface, correlation volume and radius of gyration, respectively. The average intersection length [d], the correlation length [l], the correlation surface [f], and the correlation volume [v] were determined from SAXS experiments, providing an overall description of particle size characteristics, i.e. particle size, specific surface area, volume and pore size.