Photon Factory Activity Report 2004 #22 Part B (2005)
Instrumentation and Technique

4A, 15A/2002G091

Development of laser-trap technique for microbeam SAXS study ofcrystallization in droplet floating in solution
Naohiko KAWASKI1, Satoru UENO2, Atsuo IIDA3, and Yoshiyuki AMEMIYA*1
1
Department of Frontier Sciences, The University of Tokyo, Kashiwa, 277-8651, Japan
2
Faculty of Applied Biological Science, Hiroshima Univ, 3Photon factory, Institute of Materials
Structure Science, Tsukuba
Introduction
Microbeam X-ray scattering is a useful method to get
information about inhomogeneity of nano- andsubnano-scale structure in materials. Conventionally, asample is scanned by a microbeam X-ray by moving thesample itself. But, when a sample of interest is floatingor sinking in solution, it is impossible to hold and/or
move the sample at an X-ray beam position, because it ismoving involuntarily in the sample cell. So, it is required
to develop a technique to hold a sample in solution, suchas an emulsion, so that the microbeam X-ray scattering
method can be applied. If this technique is realized,
microbeam X-ray scattering method will be used morewidely.
Experimental[1]
We have adopted a “laser trap” technique ; a focusedlaser beam produces optical forces enough to hold asmall particle. This is widely used as noninvasive
micro-manipulators for biological objects.
We have built a laser optical system, and combined itwith microbeam X-ray optical system at BL-4A. (Fig.1)
The laser beam was incident diagonally to a sample
holder so as not to obstruct an X-ray beam. The scanningof the laser beam was performed by moving the entire
laser system. The beam from a fiber laser (wavelength:1064nm, power: 1.0w) was focused by objective lens
(×10, NA=0.28).

C C D cam era

TV m onitor

objective len s(for m icroscopy)

vacuum tub epinhole

sam ple holder

x-ray
m irrorK -B m irror

lightsource
ob jective lenslaser-irradiating systemlaser light source

C C D-based X -rayd etector

Fig.1: Optical system including a laser beam and an
microbeam X-ray.
As a sample, we used oil-in-water (O/W) emulsion,
which consisted of distilled water as continuous phase,n-hexadecane (oil) as disperse phase and Tween20 assurface-active agent. The size of oil droplets was 30µm

in diameter. We tried to examine the structure of oil
crystal in a single oil droplet.
X-ray beam size at the sample position was 5µm and
X-ray wavelength was 1.5A.
Results and discussion
We have successfully picked up a single oil droplet in
the sample cell, and moved it at will to the X-ray beam
position by moving the laser beam. Then, the droplet wascrystallized upon cooling. Small-angle X-ray scattering(SAXS) pattern was obtained from the single droplet asshown in Fig.2.

Fig.2: SAXS pattern from n-hexadecane lamellae in asingle oil droplet.
In Fig.2, X-ray scattering from n-hexadecane lamellae
appears as a spot-like pattern rather than a ring pattern. Inaddition, the spot-like pattern seems to be rather oriented
but not at random. This means that the size ofn-hexadecane crystal in a single droplet is comparable tothat of the X-ray beam, and that the crystal grains have acertain preferred orientation in a single droplet.
This SAXS pattern was obtained from a droplet inwhich the oil was crystallized. However, we couldn’t
examine the crystallization process, because the droplet
moved when it crystallized, in spite of being trapped bylaser. The reason may be that the refractive index of oilchanged when it crystallized and that optical force given
to the droplet was changed. We need to build an
improved system, in which a droplet doesn’t move evenduring the crystallization by using two laser beams.
References[1] A.Ashikin IEEE J. Sel. Top. Quantum Electronics 6841-856 (2000).
* amemiya@k.u-tokyo.ac.jp

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