Specific features of interaction of polyacrylic and polymethacrylic acids with nanoparticles of amorphous selenium

Article abstract of DOI:10.1023/B:RJAC.0000038819.19783.2a

A study was made of formation of selenium nanoparticles in water from reduction of sodium selenite with ascorbic acid in the presence of polyacrylic and polymethacrylic acids.

Full text of DOI:10.1023/B:RJAC.0000038819.19783.2a

Russian Journal of Applied Chemistry, Vol. 77, No. 5, 2004, pp. 809 812. Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 5,
2004, pp. 814 817.
Original Russian Text Copyright
2004 by Kopeikin, Valueva, Kipper, Filippov, Shishkina, Borovikova, Rumyantseva, Nazarkina, Lavrent’ev.
MACROMOLECULAR CHEMISTRY
AND POLYMERIC MATERIALS
Specific Features of Interaction of Polyacrylic
and Polymethacrylic Acids with Nanoparticles
of Amorphous Selenium
V. V. Kopeikin, S. V. Valueva, A. I. Kipper, A. P. Filippov, G. V. Shishkina,
L. N. Borovikova, N. V. Rumyantseva, Ya. I. Nazarkina, and V. K. Lavrent’ev
Institute of Macromolecular Compounds, Russian Academy of Sciences, St. Petersburg, Russia
Received November 25, 2003; in final form, February 2004
Abstract A study was made of formation of selenium nanoparticles in water from reduction of sodium
selenite with ascorbic acid in the presence of polyacrylic and polymethacrylic acids.
It is well known that nanoparticles of zero-valence
metals and nonmetals, with their specific structural
features and high surface energy, exhibit abnormal
physicochemical properties because of the scale effect
of matter [1]. Of special interest are nanoparticles
of selenium, a chemical element with unique photo-
electric, semiconducting, catalytic, and biological
properties and X-ray sensitivity.
methacrylic acid (PMAA), with molecular weights M
w
6
3
of 27 10 and 25 10 , respectively. This choice
was dictated by close structures and Kuhn segment
sizes of these polymers, of which only PMAA has
side hydrophobic methyl groups [3].
2
The ionic selenium species SeO was reduced
3
at the selenium concentration in solution of 0.01 wt %
and the polymer-to-selenium mass ratio of 9 : 1 (i.e.,
under exhaustive saturation of the adsorption capacity
of nanoparticles, as revealed for other selenium poly-
mer nanostructures [4]).
Ligand-free nanoparticles are metastable and tend
to rapidly aggregate in aqueous solutions. Therefore,
they are usually stabilized by water-soluble polymers
whose interaction with nanoparticles yields nanostruc-
tures of various morphologies [2]. However, the
nature of this interaction in formation of nanoparticles
in aqueous solutions of polymers still remains to be
elucidated.
Using the method of flow birefringence [5], we es-
timated the molecular dispersity of the solutions of
the adsorbates being formed, based on analysis of
the gradient dependence of the birefringence n.
Specifically, we studied the birefringence versus the
gradient of the rotor rotation rate g and the polymer
concentration c at a fixed selenium concentration of
0.01 wt %. We used titanium dynamooptometer with
a 4-cm-high internal rotor and the rotor stator slit
width of 0.03 cm. The solutions for birefringence
measurements were kept at a constant temperature of
21 C to prevent variations of their viscosities and
optical distortions due to the temperature gradient.
The measuring facility was calibrated against 2-phen-
ylethanol having a significant birefringence ( n/g =
This work was aimed at elucidating the nature of
the above-mentioned interactions and their role in
polymer stabilization of selenium nanoparticles (nano-
0
Se ). To this end, we studied for the first time forma-
0
tion of nano-Se particles in the presence of synthetic
polymers differing in the hydrophylic lipophilic
balance. Also, we carried out optical studies of the
morphological characteristics of the nanostructures
being formed.
12
EXPERIMENTAL
17 10 ), as well as against the polystyrene
bromoform system. The intrinsic birefringence [n] =
0
We studied nano-Se nanoparticles prepared by
lim
( n/gc ) (
is the viscosity of the
g
0, c
0
0
0
reducing selenious acid (SA) with ascorbic acid, with
and without polymer additions.
solvent) was measured accurately to within 10%. The
measurements were carried out at g < g , where g is
k
k
0
the rate gradient corresponding to the onset of flow
turbulence.
As polymeric stabilizers of nano-Se served syn-
thetic polymers, polyacrylic acid (PAA) and poly-
1070-4272/04/7705-0809 2004 MAIK Nauka/Interperiodica

810
KOPEIKIN et al.
essed by the Zimm method, by double extrapolation
The experimentally determined intrinsic birefring-
ence [n] in a general case (dn/dc 0, where dn/dc is
the increment of the refractive index of the solution,
estimated for PAA Se H O and PMAA Se H O
systems at 0.245 and 0.165, respectively) has three
components: [n] = [n] + [n] + [n] , where [n] is
the intrinsic anisotropy; [n] , microform effect; and
2
(c
0,
0) of the plots of Kc/R vs. sin ( /2) +
kc (K is the calibration constant, and k, numerical
constant).
0
0
2
2
We determined the average hydrodynamic particle
e
fs
f
e
sizes R by quasielastic (dynamic) light scattering
H
fs
method [7]. Based on the experimental R -to-R ratio
g
H
[n] , macroform effect [5]. The full segment anisot-
f
for the nanostructures, we estimated the parameter *
characterizing the conformation of the nanostructure
[8 11].
ropy [n] + [n] is determined by the equilibrium
fs
e
rigidity A of the polymer chain and by the structure of
the polymer unit, and [n] is related to the shape
asymmetry parameter p of the macromolecule (par-
ticle) as
f
The optical component of the facility for measuring
the dynamic light scattering comprised an ALV-SP
(Germany) goniometer (a Spectra-Physics He Ne laser
with a wavelength = 632.8 nm, power ca. 20 mV, as
light source). The correlation function of the scattered
light intensity was obtained on a 288-channel Photo
Cor-FC correlator (Anteks Closed Joint-Stock Com-
pany, Russia). Data processing was carried out by
standard methods of cumulants and Tikhonov regulari-
zation, using appropriate software.
[n]f = [(n2s + 2)/3]2[Mw (dn/dc)2 f (p)]/(30 RTns )
= constMw (dn/dc)2f (p),
(1)
where M is the molecular weight of the adsorbate
macromolecule; n , refractive index of the solvent;
T, absolute temperature; R, universal gas constant; and
f(p), tabulated function of the ratio of the axes of a
rigid (impermeable by the solvent) ellipsoid approxi-
mating the particle [5].
w
s
According to the static light scattering data, the
7
parameter M remains unchanged (M = 27 10 ) in
w
w
0
going from the PAA H O to PAA Se H O system,
i.e., in the presence of PAA, no nanostructure is
formed. For the PMAA Se H O system, M was
estimated at 1.5 10 , i.e., it increased by a factor of
4300 relative to free PMAA macromolecules. This
unambiguously suggests the deciding importance of
hydrophobic interactions between macromolecules
2
2
Relationship (1) is valid both for isolated macro-
molecule and nanostructure; all what is needed of a
particle is to be impermeable by the solvent. Thus, for
high-molecular-weight flexible-chain and moderately
rigid-chain polymers (A < 5 nm), having minor optical
anisotropy and low-molecular-weight units, the intrin-
sic birefringence can be fitted by the approximation
[n] [n] , which allows the parameter p to be esti-
mated directly from the experimentally measured
birefringence [5].
0
2
w
8
0
and nano-Se in formation of nanostructures.
f
The second virial coefficient A for the PMAA
2
0
Se H O system is equal to zero, which suggests an
2
ideal thermodynamic quality of the solution. For the
PAA Se H O system, A is negative, namely, 0.8
Using the elastic (static) light scattering method
[6], we estimated M and the root-mean-square inertia
radii R of the polymers and nanostructures, as well as
their affinity for solvent, water (from the second virial
0
2
2
w
4
3
2
10
cm mol g , which suggests a bad thermo-
g
dynamic quality of the solution. Thus, adsorption of
0
macroions on nano-Se improves the thermodynamic
coefficient A ). Based on the ratio of the parameters
2
quality of the solution.
M
for poly acids and nanostructures they form, we
w
0
The parameter R for nano-Se particles obtained
determined the number of the macromolecules ad-
H
0
without polymeric stabilizer was estimated at 170 nm.
The particle size of the PMAA Se adsorbate, es-
sorbed on the nano-Se surface. The reduced intensity
of light scattering by solutions R was measured on
a Fica photogoniodiffusometer. The wavelength of the
incident, vertically polarized, light was 546.1 nm.
The measurements were carried out at light scattering
angles within 30 150 .The solutions and solvents
0
0
timated by dynamic and static light scattering meth-
ods, is much smaller (root-mean-square inertia radius
R = 90 nm and mean hydrodynamic radius R
=
g
H
90 nm). The parameter * = R /R is equal to unity,
g
H
3
were purified by centrifugation at 15 10 rpm for
which suggests virtually ideal spherical shape of the
particles of the adsorbate being formed [8 11].
1 1.5 h. The refractive index increment dn/dc was
determined from the refractive indices measured on an
IRF-23 instrument.
To determine the radius of the selenium particles
occurring in the core of the nanostructure, we lyo-
0
The experimental light scattering data were proc-
philically dried an aqueous solution of PMAA Se ,
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SPECIFIC FEATURES OF INTERACTION OF POLYACRYLIC AND POLYMETHACRYLIC ACIDS
811
and the resulting dry pelletized product was examined
by small-angle X-ray scattering. We estimated the
radius of the spherical Se particles at 15 nm, which is
( n/d 0c)g
108
0
0
by an order of magnitude smaller than that of seleni-
um particles obtained without polymeric stabilizer.
0
Thus, the nano-Se particles in aqueous solutions have
a ca. 75-nm-thick polymer shell.
c, wt %
c dependence for the PMAA Se
H O system. ( n) Dimensionless birefringence of the
polymer; (g) flow rate gradient, s ; ( ) viscosity of the
0
Fig. 1. ( n/g c)
Optical studies of the PAA and PMAA macro-
molecules showed that, in the nonionized state, these
are Gaussian globules with the asymmetry parameter
0
g
0
2
1
0
1
solvent, cm s g ; and (c) concentration of the polymer.
p
2 [12].
Calculation of the parameter p in the [n] [n] ap-
f
0
0
proximation for the PAA Se H O and PMAA Se
H O systems yielded, respectively, p 1 (spherical
2
2
conformation) and p 2 (which is inconsistent with
the value of the parameter p*, corresponding to the
spherical conformation of the nanostructure) [5]. Also,
the fact that the reduced optical anisotropy for the
0
PMAA Se H O system is independent of the con-
2
centration (Fig. 1) suggests that the parameter p tends
to unity, i.e., that the nanostructure is spherical [5].
The fact that hybrid nanostructures formed by macro-
molecules and nanoparticles have a spherical shape,
even in the case of such a rigid macromolecule as
3
1
g
10 , s
Fig. 2. Variation of the birefringence n with the flow rate
gradient g for the PMAA Se H O system. c
(1) 0.1, (2) 0.071, (3) 0.049, (4) 0.0195, and (5) 0.0048.
DNA [13], suggests that the [n] [n] approximation
f
0
, wt %:
PMAA
0
2
is invalid for the PMAA Se H O system. Evidently,
2
in this case a significant contribution to the optical
anisotropy comes from an effect similar to the micro-
shape effect for an isolated macromolecule (Lyubina
[12] showed that the intrinsic optical anisotropy even
for PMAA with its high degree of ionization is
negligible). This is supported by the fact that the
CONCLUSIONS
(1) Reduction of sodium selenite with ascorbic
acid in an aqueous solution of polymethacrylic acid
0
yielded spherical nano-Se particles with a size of
0
n = f(g) curves (Fig. 2) for the PMAA Se H O
ca. 15 nm.
2
system reach saturation. This suggests an increase in
the rigidity of the PMAA macromolecules owing to
hydrophobic interactions. Thus, hydrophobic interac-
tions of nonpolar fragments of the macromolecules
with one another and with nano-Se constitute the
major driving force of adsorption.
(2) Molecular-optical studies showed that the poly-
methacrylic acid macromolecules adsorbed on nano-
0
Se form an ultra-high-molecular-weight (MW =
6
150 10 ) spherical nanostructure with a size of ca.
0
90 nm, comprising over 4000 densely packed macro-
molecules.
In the case of PAA, no nanostructure is formed,
and the conformation of the macroions changes, in
contrast to nonionic hydrophilic polymers such as
polyacrylamide [4]. This is presumably due to dipole
dipole interactions of PAA with selenium nano-
particles.
0
(3) The PMAA Se H O system exhibits an in-
2
duced conformational transition of polyacrylic acid
from a Gaussian globule to a sphere.
(4) The hydrophobic interactions of the macro-
molecules with nano-Se play the deciding role in
their adsorption on nanoparticles.
0
We showed that selenium nanoparticles are adsorp-
tion matrices suitable for accommodating in high local
concentrations anionic polyelectrolytes containing
hydrophobic methyl groups in the side chains. Our
results can be applied to molecular designing of new
materials with desired properties.
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