Order-Disorder Phase Transitions in Quasicrystals

Yusuke Imai,^†Hiroshi Abe,^*,^† Takefumi Goto,^‡ YukihiroYoshimura^‡_,Shogo Kushiyama,^† and Hitoshi Matsumoto^†

By in-situ observations using simultaneous X-ray diffraction and DSC (Differential Scanning Calorimetry) method, effect of water, methanol, ethanol and benzene on the crystallization has been observed in ionic liquid (IL)-rich phase. The IL is hydrophilic ionic liquid, N, N-diethyl-N-methyl-N-2-methoxyethyl ammonium tetrafluoroborate, [DEME][BF₄]. At a small amount of the above additional molecules in the IL, conventional preferred orientation on the Debye rings was seen by the X-ray diffraction. At 0.9 mol% H₂O, twin like crystal domains develop extraordinary on the microdomains. By the “crystal-growth enhancement effect” at a slight amount of water, composite domain structure, which consists of the large domain and the weakly orientated microdomains, is formed without internal strains. Above 2.9 mol% H₂O, the domain structure, however, disappears completely. It is remarkable that, in a thermal cycling experiment using pure [DEME][BF₄], the similar composite domain structure appeared. This is also caused by an uptake of a slight amount of water.

	Figure 1. Simultaneous X-ray diffraction and DSC measurements at the first thermal cycle using pure [DEME][BF₄]; (a) Thermographs on cooling and heating by DSC, X-ray diffraction patterns along the radial direction on (b) cooling and (c) heating. Close squares and open circles correspond to calculated 2q values of orthorhombic and monoclinic, respectively (See ref. [7]). Cooling rate was 8.5 ^oC/min and heating one was 3 ^oC/min. T_c, T_m1 and T_m2 reveal crystallization temperature, the first melting point and second one, respectively.
	Figure 2. (a) Enlarged X-ray diffraction pattern along the radial direction of Figure 1c. (b) Temperature dependence of the peak position of Bragg reflections. Peak separations of Bragg refection are observed both on cooling and heating.
	Figure 3. The q dependence of full width at half maximum (FWHM) of Bragg reflection along the radial direction at the first and fifth thermal cycles using pure [DEME][BF₄]. As a resolution function in the beam optics, Bragg reflections of standard Si polycrystal are measured.
	Figure 4. Rocking curves (transverse direction) at the third, fourth and fifth thermal cycles at -70 ^oC using pure [DEME][BF₄]. At the fifth thermal cycle, preferred orientation of crystal domains is remarkably observed.
	Figure 5. Rocking curves as a function of temperature at (a) the third and (b) the fifth thermal cycles (pure [DEME][BF₄]). Heating rate was 3 ^oC/min. The rocking curves at T_m1 and T_m2 are shown as thick curves.
	Figure 6. Concentration dependence of water for the rocking curve at ?70 ^oC. Extensive preferred orientation occurs at a specific region of water concentration in [DEME][BF₄]-water mixtures.
	Figure 7. Rocking curves of [DEME][BF₄]-methanol, [DEME][BF₄]-ethanol and [DEME][BF₄]-benzene mixtures.

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