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

15A/2003G232

Structural Change of Emulsions in Forming of Metal Colloids
in Water-in-scCO2 Microemulsions
Masafumi HARADA*1, Kenji SAIJO2, Yoshifumi KIMURA3, and Takeji HASHIMOTO2
1
Department of Textile and Apparel Science, Faculty of Human Life and Environment,
Nara Women’s University, Nara 630-8506, Japan2
Department of Polymer Chemistry, Graduate School of Engineering,
Kyoto University, Kyoto 606-8501, Japan
3
International Innovation Center, Kyoto University, Kyoto 606-8501, Japan

Results and Discussion
Figure 1 shows SAXS profiles (log I(q) vs. q) of waterin-scCO2 microemulsions (water content in the system is0.285 wt%) prepared from FAR-2 with (a) w=317 and (b)w=3.17 before and after photo-reduction, respectively.
Here q is the magnitude of the scattering vector, definedas q = (4π/λ) sin(θ/2) where θ is the scattering angle andλ is the wavelength of X-ray. The intensity at a small q

124

Users' Report

CF342

Intensity / a.u.

Experimental
Ag nanoparticles were synthesized in a high-pressure
SUS 316 cell (inner volume of 13.5 mL) equipped withfour optical windows: two of them were diamondwindows for in-situ SAXS measurements and the othertwo were quartz windows for the irradiation of UV lightfrom a 500W high-pressure Hg lamp. Water-in-scCO2
microemulsions containing AgClO4 were prepared byadding sc-CO2 into the cell which contained a mixture ofa fluorinated surfactant FAR-2 ethanol solution (kindly-4
provided by NEOS Co. Ltd.) and AgClO4 (4.3 × 10 mol)aqueous solution. The water-to-surfactant molar ratios(w) were w=317 and 3.17 in the case of FAR-2. The cellwas then kept at 35 °C and 25MPa for 60 min with
continuousstirringtoform
asingle-phasemicroemulsions. After stirring, the microemulsions wereirradiated with UV light at designated time to perform thereduction of Ag ions to form Ag(0) particles in themicroemulsions.
The in-situ measurements wereperformed at BL-15A. The scattering data was collectedby the position sensitive proportional counter (PSPC).

-1range (q < 0.5 nm ) CF 3 C F CF3
depends
ontheC C
surfactant
employed, CF C F O
CH2CH2OH
3and tends to slightlyCF3increase
withtheFAR-2 M.W. = 568
reduction
timeincreasing.
However, a decrease in intensity wasobserved after more than 1 hour reduction, as not shownin this report, which suggests that the formation ofaggregates (or precipitates) of Ag particles might occur.
Moreover, the larger ratio w does not remarkably give riseto the increase of scattering intensity in the small q range.
Thus
itis100
suggested that(a)AgClO /H O + FAR-2/EtOH
the size of water
10Reduction Timepool in water0 min
5 min
1in-scCO215 min
60 minmicroemulsions
0.1
would dependon the sort of0.01
w = 317
surfactant used,
0.001
and does not so
0.0
0.5
1.0
1.5
2.0
2.5
much change inq / nm100
the formation(b)
process of Ag
AgClO /H O + FAR-2/EtOH
10Reduction Timeparticles during
0 min
5 min
thephoto15 min
160 min
reduction. The
detailed analysis
0.1
is in progress.
-1

42

Intensity / a.u.

Introduction
The use of compressed carbon dioxide as a reaction
medium, either as a liquid or a supercritical fluid (sc-CO2),
offers the opportunity not only to replace conventional
hazardous organic solvents but also to optimize andcontrol the effect of solvent on chemical synthesis [1]. In
this work, we have synthesized silver nanoparticles (Agnanoparticles) by the photo-reduction of AgClO4 in thepresence of fluorinated surfactants in water-in-scCO2
microemulsions [2, 3], and have investigated the average
size of the Ag nanoparticles and their aggregates in the
microemulsions during the photo-reduction by means ofsmall angle X-ray scattering (SAXS) measurements.

0.01

w = 3.17
Fig. 1. SAXS0.001
0.0
0.5
1.0
1.5
2.0
profiles obtained
q / nm-1
from water/scCO2/FAR-2 emulsions, (a) w=317 and (b) w=3.17.

2.5

References[1] J. M. DeSimone and W. Tumas, Green Chemistry
using liquid and supercritical carbon dioxide, Oxford
University Press, New York, 2003.
[2] M. Ji et al., J. Am. Chem. Soc. 121, 2631 (1999).
[3] N. Kometani et al., Chem. Lett. 682 (2000).
* harada@cc.nara-wu.ac.jp