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

15A/2002G091

Simultaneous 2D SAXS/WAXS study of crystallization of n-Hexadecanein emulsion droplets
Yuya SHINOHARA*1, Satoru UENO2, Yuki BISAIJI1, Eiji TAKEUCHI
Kentaro KAYASHIMA1, Yoshiyuki AMEMIYA1
1
Department of Frontier Sciences, The University of Tokyo, Kashiwano-ha,
Kashiwa, Chiba 277-8561, Japan
2
Graduate School of Biosphere Science, Hiroshima University,Higashi-Hiroshima, Hiroshima 739-8528, Japan
Introduction
Normal alkanes are among the most basic componentsof soft materials such as surfactants, lipids, liquid crystals
and polymers. It is, therefore, important to study thenature of n-alkanes for the further understanding of softmaterials. Precise kinetics of crystallization of n-alkane,
especially n-Hexadecane (C16), has not clarified yet inspite of large number of studies.
In the present study, we have performed simultaneoustime-resolved 2D SAXS/WAXS measurements of C16 inemulsion droplets during crystallization. With thistechnique which provides the information about nanoand subnano-structural change, the transient phase of C16
has been observed at the initial stage of the crystallization.
Experimental
The sample used was of droplets of C16 of an oil-inwater (O/W) emulsion. By using the novel method called
Microchannel method [1], monodisperse and large
droplets were prepared. The average size of droplets was
32.6 ± 3.2 µm.
SAXS/WAXS measurements together with Differential
Scanning Calorimetry (DSC) were performed at BL-15A.
The X-ray wavelength was 1.50 Å and the beam size atsample position was 0.5 mm × 0.5 mm. We performed theexperiments at two different settings to cover wide
scattering-range. At the one setting (setting A), we used
two X-ray CCD detectors coupled with 230 mm diameter
X-ray Image Intensifier (XRII) for SAXS and 150 mm
XRII for WAXS simultaneously (Fig.1). The camera
length was 870 mm for SAXS and 200 mm for WAXS,respectively. At the other setup (setting B), the images ofSAXS and WAXS were recorded with an X-ray CCD
detector coupled with 230 mm diameter XRII. The
distance between the sample and the detector was 239
mm. The sample was sealed in a 1.0 mm thick cell madeof aluminum and cooled from 25 °C to -5 °C with acooling rate of 2K/min. SAXS/WAXS images wererecorded at the intervals of 10 s.
Results and Discussion
Figure 2 shows the time evolution of SAXS intensity
profile from C16 during crystallization which wasobtained at the setting A. It is clearly seen that transient
peaks appear at the initial stage of crystallization.

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Transient peaks have been also observed in WAXS
images which are not shown here. The positions of thesepeaks agree with the rotator phase of C16 which wasobserved by Sirota et al., in bulk sample with onedimensional detector [2], which was detected 9 times outof 85 measurements. In our experiments, the peaks fromthe rotator phase were observed in every measurement.
This result shows that the time-resolved 2D
SAXS/WAXS measurement is a powerful tool for theobservation of peaks which was difficult to be detected.

Figure 1: Schematics of experimental setup

Figure 2: SAXS profiles during crystallization. Transient
peak first appeared first at 14 °C and stable peaks
appeared later.
References[1] T. Kawakatsu et al., J. Am. Oil Chem. Soc. 74, 317(1997).
[2] E. Sirota and A Herhold, Science 239, 529 (1999)* shinohara@x-ray.k.u-tokyo.ac.jp