Small – angle X-ray scattering study on PVA/Fe3O4 magnetic hydrogels
A synchrotron small-angle X-ray scattering (SAXS) study on PVA/Fe3O4 magnetic hydrogels has been performed to investigate the effect of clustering on their magnetic properties. The hydrogels were prepared through freezing -thawing (F-T) processes. The structure, morphology and magnetic properties of magnetite (Fe3O4) nanoparticles were investigated using Xray diffractometry (XRD), transmission electron microscopy (TEM) and a superconducting quantum interference device (SQUID) magnetometer, respectively. In this study, SAXS data were used to reveal the structural dimensions of the magnetite and its distribution in the polymer-rich PVA and magnetic hydrogels. As calculated using the Beaucage and Teubner-Strey models, the average of the structural dimensions of the PVA hydrogels was 3.9 nm (crystallites), while the average distance between crystallites was approximately 18 nm. Further analysis by applying a two-lognormal distribution showed that the magnetite nanoparticles comprised secondary particles with a diameter of 9.6 nm that were structured by primary particles (~3.2 nm). A two-lognormal distribution function has also been used in describing the size distributions of magnetite nanoparticles in magnetic hydrogels. The clusters of magnetite nanoparticles in the magnetic hydrogels are significantly reduced from 30.4 to 12.8 nm with decreasing concentration of the nanoparticles magnetite from 15 to 1 wt%. The saturation magnetization values of the magnetite nanoparticles, the 15% and 1% magnetic hydrogels were 34.67, 6.52, and 0.37 emu/g, respectively
SAXS pattern of magnetite nanoparticles (NP) and magnetic hydrogel with a filler of magnetite content of: 1 wt%, 2.5 wt%, 5 wt%, 7.5 wt%, 10 wt%, 12.5 wt%, and 15 wt%.
Parameters of the size distribution of magnetite nanoparticles in magnetic hydrogels resulting from applying the global fitting procedure to the synchrotron SAXS data. The r1 is the radius of the primary particle, r2 is the radius of the secondary particles and ϛ is the average diameter of the clusters.
SQUID patterns of magnetite nanoparticles, magnetic hydrogel (15 wt%), and (1 wt%). The insert picture is the SQUID pattern for the magnetite.