The structure and dynamic properties of aqueous mixtures of 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) have been investigated over the whole range of HFIP mole fraction (xHFIP) by large-angle x-ray scattering (LAXS), small-angle reutron scattering (SANS), F19-, C13-, and O-NMR17 chemical shifts, O-NMR17 relaxation, and mass spectrometry. The LAXS data have shown that structural transition of solvent clusters takes place at xHFIP∼0.1 from the tetrahedral-like hydrogen bonded network of water at xHFIP⩽∼0.1 to the structure of neat HFIP gradually formed with increasing HFIP concentration in the range of xHFIP⩾0.15. The Ornstein–Zernike plots of the SANS data have revealed a mesoscopic structural feature that the concentration fluctuations become largest at xHFIP∼0.06 with a correlation length of ∼9 Å, i.e., maximum in clustering and microhetrogeneities. The F19 and C13 chemical shifts of both CF3 and CH groups of HFIP against xHFIP have shown an inflection point at xHFIP∼0.08, implying that the environment of HFIP molecules changes due to the structural transition of HFIP clusters. The O17 relaxation data of water have shown that the rotational motion of water molecules is retarded rapidly upon addition of HFIP into water up to xHFIP∼0.1, moderately in the range of ∼0.1<xHFIP≲0.3, and almost constant at xHFIP≳0.3, reflecting the structural change in the solvent clusters at xHFIP∼0.1. The mass spectra of cluster fragments generated in vacuum from HFIP-water mixtures have shown that the predominant clusters are A1Wn (n<12, A=HFIP, W=water) and water clusters Wn (n=5–8) at xHFIP=0.09 and 0.20 and only HFIP oligomers in a water-rich region of xHFIP=0.005∼0.01. From all the information obtained in the present study, the models are proposed for the aggregation of HFIP and water molecules in HFIP-water mixtures.

Phase separation of acetonitrile-water mixtures by addition of NaCl has been studied on the molecular level by large-angle X-ray scattering (LAXS) and small-angle neutron scattering (SANS) methods. A phase diagram of acetonitrile-water-NaCl mixtures at 298 K has shown that phase separation occurs over a wide range of acetonitrile mole fraction (x AN ) of ∼0.1 < x AN e ∼0.7, where the microheterogeneity of the mixtures occurs. The radial distribution functions obtained by the LAXS measurements have revealed that before phase separation the amounts of preferentially hydrated Na + and Clgradually increase with increasing NaCl concentration and that the number of linear hydrogen bonds among water molecules increases when the concentration of NaCl increases. After phase separation of the acetonitrile-water-NaCl mixtures the structures of the acetonitrile-rich phase are very similar to those of the acetonitrile-water binary mixtures at the corresponding acetonitrile mole fractions. The water-rich phase which contains most of the Na + and Clalso shows structures similar to those of the acetonitrile-water mixtures at the same solvent compositions, except for the hydration structures of Na + and Cl -. The SANS data have shown a change in size of aggregates formed in acetonitrile-D 2 O and acetonitrile-D 2 O-NaCl mixtures before phase separation. The Debye correlation lengths L D determined have demonstrated that aggregation or microheterogeneity in the acetonitrile-D 2 O mixtures is most enhanced with L D ∼ 20 Å between x AN ) 0.3 and 0.4. In the acetonitrile-D 2 O-NaCl mixtures the size of aggregates gradually increases with increasing NaCl concentration and reaches a plateau value L D ∼ 20 Å at x AN ) 0.2 at the salt concentration of ∼80% to a value required for phase separation. A possible mechanism for NaCl-induced phase separation is discussed from the present results.

Low-curvature and large-diameter GaN wafers are in high demand for the development of GaN-based electronic devices. Recently, we have proposed the coalescence growth of GaN by the Na-flux method and demonstrated the possibility of enlarging the diameter of high-quality GaN crystals. In the present study, 2 in. GaN wafers with a radius of curvature larger than 100 m were successfully produced by the Na-flux coalescence growth technique. FWHMs of the 002 and 102 GaN X-ray rocking curves were below 30.6 arcsec, and the dislocation density was less than the order of 102 cm−2 for the entire area of the wafer.