Kenji Saijo

SMALL-ANGLE X-RAY SCATTERING ANALYSIS OF POLYMER-PROTECTED PLATINUM, RHODIUM, AND PLATINUM/RHODIUM COLLOIDAL DISPERSIONS

Formations of poly(N-vinyl-2-pyrrolidone)(PVP)-metal ion (Pt, Rh or Pt/Rh(1/1)) complexes in H2O/C2H5OH (“polymer–metal ion complexes”) before alcohol-reduction and PVP–Pt, Rh, or Pt/Rh(1/1) metal cluster (“polymer–metal cluster”) after alcohol-reduction were studied by small-angle x-ray scattering (SAXS). SAXS intensity of the solution containing polymer–metal ion complexes is higher than that of the reference polymer solution without metal ions, suggesting that concentration fluctuations of polymer segments are enhanced due to the formation of polymer–metal ion complexes. Spatial distributions of metal clusters in colloidal dispersions are different from each other among the cases of Pt, Rh, and Pt/Rh(1/1) colloidal dispersions. The superstructure (greater than 10.0 nm in diameter), whose average sizes highly depend on the metal element employed, are formed. These superstructures are composed of several fundamental clusters with a diameter of ∼2.0–4.0 nm. Colloidal dispersions of Rh form a percolation n...

Photochemical synthesis of silver particles in Tween 20/water/ionic liquid microemulsions

Metal particles of silver (Ag) were synthesized by the photoreduction of silver perchlorate (AgClO(4)) in water-in-ionic liquid (ILs) microemulsions consisting of Tween 20, water and ionic liquids. The ILs were tetrafluoroborate anions associated with the cations 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm][BF(4)]) and 1-octyl-3-methylimidazolium tetrafluoroborate ([OMIm][BF(4)]). The time evolution of Ag particle formation by photoreduction using UV-irradiation was investigated by UV-Vis, cryo-TEM, extended X-ray absorption fine structure (EXAFS) and small angle X-ray scattering (SAXS) measurements. The average diameter of the metallic Ag particles prepared in the water-in-[BMIm][BF(4)] and water-in-[OMIm][BF(4)] microemulsions was estimated from TEM to be 8.9 and 4.9nm, respectively, which was consistent with that obtained from the SAXS analysis. Using Guinier plots in a low q-range (<0.16nm(-1)), we demonstrate that the average diameter of the water droplets that consisted of aggregates of ionic precursors of AgClO(4) before reduction and Ag particles after reduction, in the microemulsions, was estimated to be about 20-40nm. The diameter of the water droplets increased as a function of photoreduction time because of the formation of Ag particles and their aggregates. EXAFS analysis indicated that Ag(+) ions were completely reduced to Ag(0) atoms during the photoreduction, followed by the formation of larger Ag particles.

Characterization of water/AOT/benzene microemulsions during photoreduction to produce silver particles

Colloidal dispersions of silver (Ag) particles were prepared by the photoreduction of silver perchlorate (AgClO(4)) in water/AOT/benzene water-in-oil (w/o) microemulsions consisting of sodium bis(2-ethylhexyl) sulfosuccinate (AOT), water and benzene. Formation mechanisms of Ag particles prepared in the presence of benzoin by photoreduction from Ag(+)-containing w/o microemulsions were investigated by UV-vis, transmission electron microscopy (TEM), extended X-ray absorption fine structure (EXAFS) and small-angle X-ray scattering (SAXS) measurements. By a combination of TEM and EXAFS results, Ag particles show a metallic nature after the photoreduction and the diameter of Ag particles ranges between 5 and 30 nm. In situ time-resolved SAXS measurements show that the integrated rate equation can be applied in the reduction process of Ag(+) ions to Ag(0) atoms, and the autocatalytic Ag particle growth proceeds in the association process of Ag(0) atoms during the photoreduction of Ag(+)-containing w/o microemulsions. The nanometer-sized water droplets microemulsified by AOT in benzene continuous-phase regulated the size of Ag particles, and the size and shape of water droplets were retained during the Ag particle formation.

Moisture sorption mechanism of aromatic polyamide fibres: diffusion of moisture into regular Kevlar as observed by time-resolved small-angle X-ray scattering technique

Abstract The general trend of equatorial and meridional small-angle X-ray scattering (SAXS) was investigated for four kinds of Kevlar fibres: regular Kevlar, Kevlar 49, Kevlar 149 and a heat-treated PPTA fibre, over a scattering angle 2θ from 0.3 to 6.0°. Reflecting the fibre structure of highly oriented and extended chain conformation, the equatorial scattering is much more intensive and decreases in intensity more gradually with increasing scattering angle than the meridional scattering: i.e. the electron density fluctuations in the radial direction of the fibre due to interfibrillar and interstitial microvoids were expected to have Bragg spacings in the range from several to a few decades of angstroms, while no particular periodic fluctuation could be found in the fibre axis direction. The effects of total reflection upon the equatorial scattering intensity distribution were also discussed. The moisture sorption rate in a bone-dry regular Kevlar was observed at 25°C at saturated vapour pressure by the time-resolved SAXS technique. The experimental results were analysed assuming the moisture to be sorbed only in the microvoids to form various sizes of water cluster. Normalized moisture sorption rate, {1 − [ J(t) J(0) ] 1 2 } {1 − [ J(∞) J(0) ] 1 2 } , determined from the change in integrated scattering intensity over the angular range 0.3–6.0° with time, J ( t ), was compared with that observed by a gravimetric method, M(t) M(∞) , at a relative vapour pressure of 0.896 at 25°C. Although both rate curves attained equilibrium at almost the same time of about 670 min, the rate curve from the SAXS method showed a sigmoidal shape and the moisture diffusivity was much smaller than that determined from the gravimetric method. The large discrepancy between the two diffusivities was explained using the assumption that the gravimetric method detects the sorbed water in the form of both ‘micro-water clusters’ and ‘macro-water clusters’, but the SAXS method detects only the ‘macro-water clusters’.

Time-resolved detection of x-ray scattering for studies of relaxation phenomena

Abstract An instrument for time-resolved detection of small-angle and wide-angle x-ray scattering is described. The apparatus consists of a 12-kW rotating-anode x-ray generator, a linear position-sensitive detector, a two-parameter multichannel analyzer to record the time-dependence of x-ray scattering patterns, a servo-controlled hydraulic sample deformation device, a temperature-controlled environmental chamber, a programmable function generator, a programmable timer and a microcomputer. The programmable function generator is used to control the mechanical or thermal stimulus on the sample under variable conditions and to synchronize the x-ray data acquisition with the stimulus. The environmental chamber allows temperature control of the sample between −100 and 300°C. Two experimental methods, involving transient and oscillatory experiments, for time-resolved studies with this apparatus are discussed. Experimental studies on kinetics of oriented crystallization of cross-linked polybutadiene and on lamellar deformation of tubular-extruded poly(1-butene) films are presented as typical applications of time-resolved x-ray scattering technique.

Photochemical synthesis of silver particles using water-in-ionic liquid microemulsions in high-pressure CO2.

Silver particles (Ag particles) were synthesized by the photoreduction of silver perchlorate (AgClO(4)) in water-in-ionic liquid (IL) microemulsions consisting of nonionic surfactant Tween 20, water, and ionic liquids, [1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm][BF(4)]) or 1-octyl-3-methylimidazolium tetrafluoroborate ([OMIm][BF(4)])], mixed with a high-pressure (25 MPa) CO(2). The time evolution of the Ag particle formation by photoreduction was investigated by UV-Vis, cryo-TEM, extended X-ray absorption fine structure (EXAFS), and small-angle X-ray scattering (SAXS) measurements. In the particle formation process, aggregation and precipitation of Ag particles were suppressed under high-pressure CO(2). The average diameters of the metallic Ag particles prepared in water-in-[BMIm][BF(4)] and water-in-[OMIm][BF(4)] microemulsions were estimated from TEM to be 3.2 and 3.7 nm, respectively. SAXS analysis shows that the average diameters of the water droplets, which consisted of ionic precursors of AgClO(4) and Ag particles (or Ag aggregates), were estimated to be about 30-40 nm. In the process of Ag particle formation, the water droplet size under high-pressure CO(2) is more effectively regulated than that under ambient air, thereby preventing Ag particles from aggregating and precipitating.

Influence of the organization of water-in-ionic liquid microemulsions on the size of silver particles during photoreduction

Metal particles of silver (Ag) have been synthesized by the photoreduction of silver nitrate (AgNO3) in water-in-ionic liquid (IL) microemulsions consisting of nonionic surfactant Tween 20 or Triton X-100, water and ionic liquid, 1-octyl-3-methylimidazolium hexafluorophosphate ([OMIm][PF6]). The formation of microemulsions as well as Ag particles produced by the photoreduction has been investigated by UV-vis, cryo-TEM, small-angle X-ray scattering (SAXS), and extended X-ray absorption fine structure (EXAFS) measurements. At the early stage of Ag particle formation under ambient pressure, the size of Ag particles in water/[OMIm][PF6]/TX-100 microemulsions was slightly larger than that in water/[OMIm][PF6]/Tween20 microemulsions. With an increase in photoirradiation time beyond 30 min, precipitation of larger Ag aggregates occurred. In contrast to the preparation under ambient pressure, the growth of Ag particles and aggregates was suppressed in preparing under high pressure (25 MPa) of CO2, leading to no precipitation of Ag aggregates. The average diameters of the finally-obtained metallic Ag particles prepared under high pressure of CO2 in water/[OMIm][PF6]/Tween20 and water/[OMIm][PF6]/TX-100 microemulsions were estimated from cryo-TEM to be 3.7 nm and 2.8 nm, respectively. By using Guinier plots at q (<0.16 nm(-1)), it was demonstrated that the diameter of the water droplets during Ag particle formation under high pressure of CO2 remained unchanged in the range of 33-37 nm due to their higher stability compared to water droplets, whereas under ambient pressure the diameter drastically increases from 28 nm to 40 nm during the first 60 min of photoirradiation, resulting in the precipitation of larger Ag aggregates, especially in the case of water/[OMIm][PF6]/Tween20 microemulsions.

Self-assembly and morphology of gel networks in l,3:2,4-bis-O-(p-methylbenzylidene)-D-sorbitol/n-dibutylphthalate

We investigated the self-assembling structure of the 1,3:2,4-bis-O-(p-methylbenzylidene)-D-sorbitol (PDTS)/n-dibutylphthalate (DBP) system in the parameter space of temperature T and solute concentration Phi(PDTS). Optical microscopic studies revealed that the phase diagram can be divided into four regions. In region I at high T the system is a homogeneous solution. In region II at lower T and low Phi(PDTS), the system still has fluidity but has microgels having spherulitic texture of PDTS crystallites. Regions III and IV at even lower T but higher Phi(PDTS) are in a gel state. In region III, the PDTS forms volume-filling spherulites due to the solid-liquid phase transition of the saturated PDTS solutions. In region IV at the lowest T, both the liquid-liquid phase-separation process and the solid-liquid transition of the PDTS are involved in the self-assembling processes. In this region a bicontinuous phase-separated structure is first formed by liquid-liquid phase separation via spinodal decomposition (SD). The subsequent solid-liquid transition of the PDTS in the PDTS-rich region forms percolating crystalline fibrils rather than spherulites. The formation of the crystalline fibrils pins further growth of the bicontinuous structure via SD.

Real-time analysis of small-angle X-ray scattering from perfluorocarboxylic ionomer membranes during electrodialysis

Abstract The effects of electrodialysis on the structures of ionic clusters in a perfluorocarboxylic membrane were studied by means of small-angle X-ray scattering (SAXS). Specially made cells for the electrodialysis were used for measuring SAXS profiles in situ and in real time during the electrodialysis. It was found that the electric field did not reshape the structure of ionic clusters during the electrodialysis within our experimental conditions.

Time-resolved small angle X-ray scattering and wide angle X-ray diffraction studies on premelting during annealing of gelation crystallized ultrahigh molecular weight polyethylene films

Abstract The phenomenon of melting-recrystallization during annealing below an equilibrium melting temperature (141.6°C) of gelation crystallized ultrahigh molecular weight polyethylene (UHMWPE) films has been investigated by means of time-resolved small angle X-ray scattering (SAXS) and wide angle X-ray diffraction (WAXD). Isothermal annealing below 130°C shows that the SAXS long period (periodic distance of successive lamellae) increases, then subsequently levels off with increasing annealing time. At 140°C, the long period increases from 118 to 690 A without any sign of levelling off. This type of increase in long period has been customarily attributed to lamellar thickening associated with solid state diffusion of intracrystalline chains. Recent synchrotron radiation studies on annealing of single crystal mats of conventional linear polyethylene demonstrated that melting-recrystallization is responsible for the increase in long period. The present time-dependent WAXD studies show a gradual decrease in crystallinity for some initial periods of annealing at 137°C, which slows down with elapsed time. At 140°C, the terminal melting occurs after 15 min. We propose that the increase in long period during annealing of this gelation crystallized UHMWPE near its melting temperature is due to the melting of successive lamellae rather than lamellar thickening.