Confined tubes : Periodic mesoporous organosilica (PMO) mesophases were synthesized within the confined tubular environment of anodic alumina membrane (AAM) channels, resulting in the formation of either the hexagonal circular or the cubic mesophase.
The spherical gold nanoparticle reference materials RM 8011, RM 8012, and RM 8013, with a nominal radius of 5, 15, and 30 nm,
respectively, have been available since 2008 from NIST. These materials are recommended as standards for nanoparticle size
measurements and for the study of the biological effects of nanoparticles, e.g., in pre-clinical biomedical research. We report
on determination of the size distributions of these gold nanoparticles using different small-angle X-ray scattering (SAXS)
instruments. Measurements with a classical Kratky type SAXS instrument are compared with a synchrotron SAXS technique. Samples
were investigated in situ, positioned in capillaries and in levitated droplets. The number-weighted size distributions were
determined applying model scattering functions based on (a) Gaussian, (b) log-normal, and (c) Schulz distributions. The mean
radii are 4.36 ± 0.04 nm (RM 8011), 12.20 ± 0.03 nm (RM 8012), and 25.74 ± 0.27 nm (RM 8013). Low polydispersities, defined
as relative width of the distributions, were detected with values of 0.067 ± 0.006 (RM 8011), 0.103 ± 0.003, (RM 8012), and
0.10 ± 0.01 (RM 8013). The results are in agreement with integral values determined from classical evaluation procedures,
such as the radius of gyration (Guinier) and particle volume (Kratky). No indications of particle aggregation and particle
interactions—repulsive or attractive—were found. We recommend SAXS as a standard method for a fast and precise determination
of size distributions of nanoparticles.
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