Correlation between the Electrification and Molecular
Mobility of Noble Metal Nanocomposites
Based on Arabinogalactan
M. N. Nikolaeva
, G. P. Aleksandrova
, and A. N. Ionov
Institute of Macromolecular Compounds, Russian Academy of Sciences, St. Petersburg, Russia
Favorskii Irkutsk Institute of Chemistry, Siberian Branch, Russian Academy of Sciences, Irkutsk, Russia
Ioffe Physicotechnical Institute, Russian Academy of Sciences, St. Petersburg, Russia
Received June 3, 2010
Abstract—Spin–spin relaxation of arabinogalactan and its composites with gold and silver nanoparticles in
aqueous solutions was studied from the viewpoint of the possible effect of electrification on the mobility of
AND POLYMERIC MATERIALS
ISSN 1070-4272, Russian Journal of Applied Chemistry, 2011, Vol. 84, No. 3, pp. 450–453. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © M.N. Nikolaeva, G.P. Aleksandrova, A.N. Ionov, 2011, published in Zhurnal Prikladnoi Khimii, 2011, Vol. 84, No. 3, pp. 458–461.
Conducting polymers steadily attract researchers’
attention. However, despite considerable progress in
enhancing the conductivity of conjugated polymers by
doping, there has not yet been success in attainment of
the metallic conductivity in them. At the same time, it
is known that some areas of thin films of dielectric
polymers can occur in the metallic state at E << E
2]. The mechanism by which high conductivity arises
in thin films of dielectric polymers is still understood
incompletely. It was found previously [2–5] that the
factor responsible for formation of highly conducting
channels in a polymer film is its electrification by the
metal of the support, i.e., the charge transfer between
the polymer and metal at their mechanical contact .
Recent studies showed that the conductivity of
polymer films can also be affected by the mobility of
polymer chains [6, 7].
Our goal was to determine whether the excess
charge affects the mobility of macromolecules in
dielectric polymer films. Experiments on studying the
influence exerted on the molecular mobility by the
amount of the metal occurring in contact with the
polymer were performed by NMR relaxation. Using
this method, we revealed the effect of excess charge on
the mobility of polyaniline macromolecules .
Our experiments were performed with arabino-
galactan (AG, Fig. 1) and its nanocomposites with
zero-valent metals. The molecular weight of arabino-
galactan was about 20
000. Nanocomposites of AG
with metals (Au, Ag, Pt) were synthesized by the
method described in . AG–metal nanocomposites
are formed as zero-valent metal particles with a mean
size of 9–17 nm, distributed in a polysaccharide matrix.
The granules of the composites are similar in shape to
globules of AG macromolecules and have a size of
0.17–0.25 μm . The metal nanoparticle size was
determined with a Leo 906E transmission electron
microscope. Aqueous 2.5% solutions of AG com-
posites are stable.
To observe the NMR relaxation, it is necessary to
distort the initial thermodynamic equilibrium of a spin
system placed in a constant magnetic field. The time in
which the system returns to equilibrium after
radiofrequency pulses is the NMR relaxation time .
The relaxation parameters were measured at a proton
resonance frequency of 18 MHz.
We studied 2.5% solutions of AG and its
composites with metals. The metal concentration in the