ISSN 1070-4272, Russian Journal of Applied Chemistry, 2007, Vol. 80, No. 9, pp. 1558!1561. + Pleiades Publishing, Ltd., 2007.
Original Russian Text + Yu.A. Mirgorod, N.A. Efimova, 2007, published in Zhurnal Prikladnoi Khimii, 2007, Vol. 80, No. 9, pp. 1525!1528.
Relationship between Size of Cadmium Sulfide Nanoparticles
and Water Pool Diameter in Reverse Micelles
Yu. A. Mirgorod and N. A. Efimova
Kursk State University, Kursk, Russia
Received December 25, 2006; in final form, April 2007
Abstract-Preparation of CdS nanoparticles in water3sodium bis(2-ethylhexyl) sulfosuccinate3isooctane
reverse micelles with various water contents is studied. A direct correlation between the water pool diameter
in the reverse micelles and the mean size of CdS nanoparticles is found.
Recently a great interest has been attracted to prep-
aration and characterization of nanomaterials .
Reverse micelles in hydrocarbon solvents proved to be
appropriate systems for nucleation and growth of
nanoparticles. Water droplets (pools) in surfactant-
based micelles act not only as microreactors, but also
as steric inhibitors of aggregation of atoms and mole-
cules. Micellar synthesis was used to prepare various
nanomaterials, among them CdS (see review ).
Cadmium sulfide is a semiconductor used as a work-
ing medium in lasers and also as a material for fab-
rication of photoresistors, photodiodes, and solar bat-
teries. The advantages of the synthesis of nanopar-
ticles in reverse micelles are, first, in mild conditions
of the process (no high temperature and pressure is
required) and, second, in that the size and shape of
nanoparticles can be controlled by the micelle struc-
ture and dynamics.
Presently, in this research field, the major focus is
on preparation and characterization of nanoparticles,
but not on properties of the dispersions. Particularly,
it remains to be understood whether the properties of
the micelles and microemulsions are different in
the course of synthesis of nanoparticles.
Subdivision into micelles and microemulsions can
be made by the microphase sizes in the system water3
sodium bis(2-ethylhexyl) sulfosuccinate (AOT)3isooc-
tane, as dependent on the temperature at various
O]/[AOT] ratios w . At 503 60oC, these depen-
dences are different: at w = 15 there is a descending
curve, and at w = 18, an ascending one, suggesting
formation of micelles and microemulsions at w <15
and w > 18, respectively. According to [2, 3], over the
range 0 < w <15318, water occurs in the bound state,
and with further increasing w, the structure of water is
the same as in straight water. This hypothesis is sup-
ported by the trends in various physicochemical prop-
erties of water. For example, in the former case, the
activity of emulsified water increases with increasing
w, reaching saturation at w = 15. Similar trend is
observed for the chemical shifts of protons of water,
and the lifetime of hydrated electrons produced by
radiolysis decreases, flattening out at w = 15 .
Here we report on synthesis of CdS nanoparticles
in micelles and microemulsions at w =5318. Particu-
larly, we analyzed the interrelation between the water
pool diameter and nanoparticle size.
In synthesis we used CdCl
(AOT), and isooctane from Sigma3Aldrich. Water was
distilled from potassium permanganate. The projected
area of the AOT molecule was measured in a mono-
molecular layer. The surface tension of the aqueous
AOT solution was determined by the plate method.
The area of the AOT molecule in the adsorption layer
was estimated from the surface tension isotherm ob-
tained at 298 K (Fig. 1) at the water/air interface, as-
suming that the resulting area does not differ from
that at the water/hydrocarbon interface. There are
two features in the isotherm: one corresponding to
the critical micelle concentration, and the second one,
to the concentration at which the maximal adsorption
is attained. The quantity G
was estimated by
the Gibbs equation :
= 3ÄÄÄ ÄÄÄÄÄ, (1)
RT § log c
where s is the surface tension of the solution