Magnetophoresis of poly (SODIUM 4-STYRENESULFONATE)Fe3O4 clusters the influence of colloidal stability
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Date
2016-06-01
Authors
Yeap Swee Pin
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Abstract
The present work is dedicated to reveal the influence of colloidal stability
towards magnetophoresis of Fe3O4 particles. First of all, colloidal stability of bare
Fe3O4 was successfully enhanced after surface coating with a strong anionic polymer,
poly(sodium 4-styrenesulfonate) of molecular weight 70K Da (PSS 70K), through
electrostatic-induced post-coating technique conducted at pH ~3.50. Enhanced
colloidal stability attained by the resultant PSS 70K/Fe3O4 clusters is mainly
contributed from the electrostatic and the steric repulsion, which overwhelm the
magnetic dipole-dipole attraction, when the interparticle distance is < 97 nm and < 50
nm, respectively. However, magnetic separation study showed that the more
colloidally stable the Fe3O4 is, the harder it is to be magnetically separated. By
carefully tracking on the magnetophoresis profiles under magnetic field gradient of
average magnitude 40.55 T/m, it was found that bare Fe3O4 attained ~ 100 %
separation within 8 minutes; while there was no complete separation for PSS
70K/Fe3O4 clusters even the magnetic separation time was extended to 1 hour. In
another words, the polymer coating that was initially employed to electrosterically
stabilize the Fe3O4 in turn compromises their magnetic responsiveness. Unlike the bare
Fe3O4 which undergo a typical cooperative magnetophoresis, it was found that the PSS
70K/Fe3O4 clusters experienced a size-fractionation based magnetophoresis in which
the magnetic separation was controlled by the presence of distribution of
hydrodynamic sizes in the suspension. Besides that, microscopic study further
revealed the differences between both entities in which PSS 70K/Fe3O4 clusters tend
to self-oriented into thread-like structures; while bare Fe3O4 tend to self-aggregate into
fractal structures of various dimensions. A simple electrostatic-mediated assembly
approach was proposed in this study to produce PSS 70K/Fe3O4 clusters of various
sizes (~200 nm up to ~ 700 nm). Here, it was found that PSS 70K/Fe3O4 clusters of
average cluster size 459 nm not only possess good colloidal stability, but also offer
high magnetic separability (> 98 % separation efficiency was attained when exposed
to the same magnetic field gradient for just 5 minutes). This finding indicates that
manipulating the cluster sizes of the PSS 70K/Fe3O4 clusters can be used as the
solution for the trade-off concern between enhanced colloidal stability and magnetic
separability. In the last part of this study, it was revealed that the colloidal stability of
PSS 70K/Fe3O4 clusters being deteriorated after addition of metal ions (e.g., Ag+, Cu2+,
Cr3+, Ca2+, Mg2+). Results showed that it is the concentration of the metal cation,
instead of the conventionally believed ionic strength, plays a more decisive role in
enhancing the aggregation process. In addition, with the presence of Cu2+ ion, dissolve
organic matters such as humic acid and sodium alginate was found to form complexes
with the PSS 70K/Fe3O4 clusters. This formation of complexes can later on influence
the colloidal stability and thus magnetophoresis behavior of the PSS 70K/Fe3O4
clusters.