Photon Factory Activity Report 2005 #23 Part B (2006)
Materials Science

15A/2004G075

Effect of surfactants on crystallization of n-Hexadecane in emulsion droplet
Tadashi TAKAMIZAWA1, Yuya SHINOHARA*1, Satoru UENO2, and Yoshiyuki AMEMIYA1
1
The University of Tokyo, Kashiwa, Chiba 277-8561, Japan
2
Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8528, Japan
Introduction
Crystallization inside a droplet such as an oil-in-water(O/W) emulsion now attracts large attention due to its
possibility to control the polymorph inside a droplet. It issuggested that interfacial heterogeneous nucleation haslarge effects on the process of crystallization in emulsion
droplets [1]. Recent study shows that a transient phase ofn-Hexadecane (C16), so-called rotator phase [2], plays avital role of crystallization of C16 inside the emulsion
droplets and that it has a relationship with the surfactant
at the oil-water interface [3,4]. The effect of the interface
on the crystallization inside the droplet, however, has notbeen clarified. In the present study, we performed timeresolved two-dimensional SAXS-WAXS together withDifferential Scanning Calorimetry (DSC) during thecrystallization of C16 and investigated the effect of
surfactant at the oil-water interface on the crystallization
inside the droplet.

strongly influences the crystallization behavior insideemulsion droplets. Further study will reveal the effect of
surfactants on crystallization in a single emulsion droplet.

Experimental
The sample used was n-Hexadecane (C16) droplets in
an O/W emulsion. Samples of C16 with > 99% purity
were purchased from Sigma Chemicals and no further
purification steps were taken. Surfactants were Tween 40(polyoxyethelene sorbitan monolpalmitate: C62H122O26),Tween 80 (polyoxyethelene sorbitan monooleate:C64H124O26). The O/W emulsion droplets were made bymicrochannel emulsification technique [5], by which we
obtained large droplets with nearly monodisperse size
distribution. The average diameter of sample was around32.5 µm.
Time-resolved 2D SAXS-WAXS-DSC experiments
were performed at BL-15A. The X-ray wavelength was1.50 Å. An X-ray CCD detector coupled with a large
aperture X-ray Image Intensifier (270 mmφ) [6] was used
as a detector. The sample-to-detector distance was around
160 mm. Sample were heated to ~25 °C above themelting temperature and then were cooled to -8 ˚C with acooling rate of 2 °C/min.

Fig. 1: DSC (line) and time evolution of scattering
intensity from the SAXS 2nd peak of the stable phase(shown as triangle), and the SAXS 2nd peak of the rotatorphase (shown as circle) during cooling of C16 emulsion
droplets. Red and blue lines show the results with Tween
40 and Tween 80, respectively.

Results & Discussion
Figure 1 show the result of DSC and time evolution ofSAXS intensity from the C16 emulsion during
crystallization. The SAXS data are obtained byazimuthally averaging x-ray intensity of SAXS 2nd peakof rotator phase and stable phase. Both the SAXS andDSC data show that the C16 in emulsion droplet withTween 40 rapidly crystallized into the stable phase via therotator phase at around 13 ˚C, while C16 with Tween 80
slowly crystallized into the stable phase. These results
suggest that the surfactant at the oil-water interface

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References[1] S. Ueno et al., Cryst Growth Des. 3, 6 (2003).
[2] E. Sirota and A. Herhold, Science, 283, 529 (1999).
[3] Y. Shinohara et al., Phys. Rev. Lett., 94, 097801(2005).
[4] Y. Shinohara et al., PF Act. Rep. 2004 Part A, 9,(2005).
[5] T. Kawakatsu et al., J. Am. Oil Chem. Soc. 74, 317(1997).
[6] Y. Amemiya et al., Rev. Sci. Instrum. 66, 2290 (1995).
*shinohara@x-ray.k.u-tokyo.ac.jp