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.