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Total-reflection X-ray absorption fine structure (TR-XAFS) technique was applied for the first time to an interface between two immiscible electrolyte solutions under potentiostatic control. The hydration structure of bromide ions was investigated at polarized 2-octanone/water interfaces. TR-XAFS spectra at Br K-edge measured in the presence of hexyltrimethylammonium bromide (C6TAB) were slightly modified depending on the Galvani potential difference (Δowϕ). The extended X-ray absorption fine structure analysis exposed hydration structure changes of bromide ions at the polarized interface. The coordination structure of bromide ions at the interface could be analyzed as compared with bromide ions dissolved in aqueous solution and Br−-exchanged resin having quaternary ammonium groups. The results indicated that bromide ions were associated with C6TA+ at the polarized interface. The relative contribution of ion association form of bromide ions with quaternary ammonium groups was enhanced at a potential close to the ion transfer of C6TA+, where the interfacial concentration of C6TA+ is increased as a function of Δowϕ. [ABSTRACT FROM AUTHOR]

The effect of the temperature on the surface layering of ionic liquids has been studied for two ionic liquids, trioctylmethylammonium bis(nonafluorobutanesulfonyl)amide([TOMA+][C4C4N–]) and trihexyltetradecylphosphonium bis(nonafluorobutanesulfonyl)amide ([THTDP+][C4C4N–]), using X-ray reflectivity measurements at 285, 300, and 315 K. Both [TOMA+][C4C4N–] and [THTDP+][C4C4N–] develop multilayers at the surface. The structure of the multilayers at the [TOMA+][C4C4N–] surface shows little temperature-dependent change, whereas that at the [THTDP+][C4C4N–] surface clearly becomes diffused with increasing temperature. The different temperature dependence seems to be related to the difference in the recently reported ultraslow dynamics of the interfacial structure of [TOMA+][C4C4N–] and [THTDP+][C4C4N–] at the ionic liquid|water interface. [ABSTRACT FROM AUTHOR]

Time-resolved X-ray reflectivity measurements for lysozyme (LSZ) adsorbed at an air/water interface were performed to study the mechanism of adsorption-induced protein unfolding. The time dependence of the density profile at the air/water interface revealed that the molecular conformation changed significantly during adsorption. Taking into account previous work using Fourier transform infrared (FTIR) spectroscopy, we propose that the LSZ molecules initially adsorbed on the air/water interface have a flat unfolded structure, forming antiparallel β-sheets as a result of hydrophobic interactions with the gas phase. In contrast, as adsorption continues, a second layer forms in which the molecules have a very loose structure having random coils as a result of hydrophilic interactions with the hydrophilic groups that protrude from the first layer. [ABSTRACT FROM AUTHOR]

Thephase transition and domain formation of the adsorbed filmof two kinds of hybrid alcohols (CF3(CF2)m-1(CH2)nOH, FmHnOH), 2-perfluorooctylethanol (F8H2OH) and 2-perfluorohexylhexanol (F6H6OH), asa mixture at the hexane/water interface was investigated by interfacialtensiometry and X-ray reflection. The interfacial tension γversus total molality mcurve of pure F8H2OH has a break point at high concentration, and thus,the mean area per molecule Achanges discontinuouslyat high interfacial pressure π, corresponding to the phase transitionbetween expanded and condensed films. The Fresnel divided reflectivity R/RFversus Qzplots in the expanded state was well-fittedby the domain model for incoherent interference to determine the interfacialcoverage, which is the fraction of the interface covered by the condensedphase. This indicates that the expanded film is heterogeneous andconsists of a condensed F8H2OH domain, the sizeof which is larger than the X-ray coherence length (∼5 μm).In the mixed system, the discontinuous change in Aat the phase transition point becomes small with increasing thebulk composition of F6H6OH X2in the mixture, and eventually the Avalue changes continuously; i.e, the phase transition becomes obscurein X2≥ 0.6. This behavior waslinked to an increase in interfacial coverage with X2. Furthermore, the R/RFversus Qzplot was fitted by the domain model for coherent interference, suggestingthat the size of the domain is smaller than 5 μm. These resultsare probably due to the reduction of domain line tension by preferentialadsorption of F6H6OH at the F8H2OH domain boundary. [ABSTRACT FROM AUTHOR]

A novel spectro-electochemical cell for X-ray absorption spectroscopy in the tender X-ray region (TX-XAS) was designed and fabricated to investigate the electrochemical behavior of common battery materials with liquid electrolytes under in situ/operando conditions. The cell has several unique features, such as high X-ray transmittance, high signal to noise ratio, and high vacuum tightness. These features enable us quick and reliable XAS measurements. Operando P K-edge XAS measurements of an olivine-type LiFePO4 composite positive electrode were carried out to clarify its phosphorus environment during the electrochemical charging process. Results of spectral analysis show that there is no significant change in the oxidation state of phosphorus and in the coordination of the phosphate anions in the charging process, but a closer look of the consecutive XAS spectra suggests the shrinkage of the PO4 cage during the charging process, and the structural changes in a biphasic manner. These results demonstrate the usefulness of the cell for in situ/operando TX-XAS observations of light elements in practical batteries. [ABSTRACT FROM AUTHOR]

The total-reflection XAFS measurement possessing bromide ion selectivity at the interfacial region was applied to the adsorbed film of hexadecyltrimethylammonium chloride (HTAC) and dodecyltrimethylammonium bromide (DTAB) mixture. The surface compositions XjHof individual ions j( j= HTA +, Cl −, DTA +, and Br −) were evaluated by combining the surface excess concentration of Br −estimated from the XAFS with the surface composition of the respective surfactants from the surface tension results. It is clearly shown that HTA +and Br −are preferentially adsorbed to DTA +and Cl −at the air/water interface. The preferential adsorption was estimated numerically in terms of activity coefficient fi± H,pof component iand excess Gibbs energy of adsorption ĝprH,E. Then, the magnitude of ĝprH,Ewas compared with that of ĝinH,Eattributable to intrinsic interaction between ions. [ABSTRACT FROM AUTHOR]

Abstract  Small-pixel TES is promising for imaging-spectroscopy applications. Researchers demand a high-spatial-resolution energy-resolving detector for many kinds of applications. However the spatial resolution and the energy resolution are quite restricted in the present semiconductor detector, so we are developing a new pixellated array based on the transition edge sensor (TES) technology. In this measurement, we developed an Ir-TES array which consists of 9 small TESs and are voltage biased in parallel. We performed measurements at SPring-8 with 6 keV X-rays and scanned the TES using a collimator by the two-dimensional scanning method. Position dependency on pulse height and risetime has been analyzed in detail. [ABSTRACT FROM AUTHOR]