Photon Factory Activity Report 2004 #22 Part B (2005)
Materials Science

15A/2004G266

In-situ observation of formation of metal nanoparticles and nanocomposites
Ayano CHIBA*1, Hirokazu TANAKA1,2, Hirokazu HASEGAWA1, Takeji HASHIMOTO2
1
Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Katsura,
Kyoto 615-8510, Japan
2
Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195, Japan
Introduction
There has been considerable interest in studies on
preparation of metal nanoparticles in last decade. We
focus our attention on the formation of metalnanoparticles that is stabilized by polymers, because suchpolymer-stabilized metal nanoparticles offers thepossibilities of controlling spatial arrangements of themetal nanoparticles by use of various designs ofpolymers: For example, the morphologies of diblock
copolymers enable us to make highly ordered patterns ofmetal nanoparticles[1]. There are thus many studies on
chemical synthesis of polymer-metal nanocomposites. In
our study, we focus on the formation process of metal
nanoparticles to clarify the particle growth law. In thisreport, we restrict ourselves to present the results ofpalladium nanoparticles stabilized by polystyrene.
ExperimentalTime-resolved SAXS measurements were performed at
the BL-15A, installed at Photon Factory, KEK, Tsukuba,
Japan. The formation of palladium nanopartiles wasinduced by temperature jump from room temperature toaround 180C.
Results
Figure 1 shows typical results of time evolution ofSAXS profiles after a temperature jump. One can see that-1
the maxima and the minima around 2.0nm for (a) and-1
1.0nm for (b) progressively shift toward lower-q region,
showing the growth of the metal particles. Figure 2 shows
a comparison of the scattering profile with a model fitting.
Here, we adopted a spherical form factor with a size
distribution of a Gaussian. The time evolution of theparticle size and its standard deviation were thus
determined from the SAXS profiles. Figure 3 shows atypical electron micrograph of the samples after theSAXS measurements and we confirmed our analysis ofSAXS profiles by these images of the real space.
From the time dependence of the particle size, we
found that the growth of the metal nanoparticles aremainly governed by the diffusion-limited aggregation
process. We also found that the particle size can mainly
controlled by the concentration of stabilizing polymer andthat the size distribution is narrower at lower temperature,i.e., around 150C, than higher temperature, i.e., 180C.
This is attributed to the higher diffusibility of reduced
atoms at higher temperature. That is, the rate-determining
step at 180C would be the reduction process, and, as aresult, the particle size widely distributes from small (i.e.,new) ones to large (old) ones at 180C. Further analysisare currently in progress.
(a)(b)

Fig.1: Time evolution of SAXS profiles after atemperature jump to (a) 180C and (b) 150C.

Fig.2: Comparison of the scattering profile (denoted bycirciles) and model fittings. The dotted line is the curvefor isolated spheres of identical radius, and the solid line
is obtained by the best fit of a model with a Gaussian
distribution for the size of spheres.
(a)

(b)

Fig.3: (a) Transmission electron micrograph of thesample which have been measured by use of SAXS. (b) A
histogram for the sample in (a).
References[1] See, for e.g., T. Hashimoto, Bul. Chem. Soc. Jpn. 78(2005) 1.
* chiba@alloy.polym.kyoto-u.ac.jp

Users' Report185