Wei-Tsung Chuang

A small/wide-angle X-ray scattering instrument for structural characterization of air-liquid interfaces, thin films and bulk specimens

At the National Synchrotron Radiation Research Center, a small/wide-angle X-ray scattering (SAXS/WAXS) instrument has been installed at the BL23A beamline with a superconducting wiggler insertion device. This beamline is equipped with double Si(111) crystal and double Mo/B4C multilayer monochromators, and an Si-based plane mirror that can selectively deflect the beam downwards for grazing-incidence SAXS (GISAXS) studies of air–liquid or liquid–liquid interfaces. The SAXS/WAXS instrument, situated in an experimental hutch, comprises collimation, sample and post-sample stages. Pinholes and slits have been incorporated into the beam collimation system spanning a distance of ∼5 m. The sample stage can accommodate various sample geometries for air–liquid interfaces, thin films, and solution and solid samples. The post-sample section consists of a 1 m WAXS section with two linear gas detectors, a vacuum bellows (1–4 m), a two-beamstop system and the SAXS detector system, all situated on a motorized optical bench for motion in six degrees of freedom. In particular, the vacuum bellows of a large inner diameter (260 mm) provides continuous changes of the sample-to-detector distance under vacuum. Synchronized SAXS and WAXS measurements are realized via a data-acquisition protocol that can integrate the two linear gas detectors for WAXS and the area detector for SAXS (gas type or Mar165 CCD); the protocol also incorporates sample changing and temperature control for programmable data collection. The performance of the instrument is illustrated via several different measurements, including (1) simultaneous SAXS/WAXS and differential scanning calorimetry for polymer crystallization, (2) structural evolution with a large ordering spacing of ∼250 nm in a supramolecular complex, (3) SAXS for polymer blends under in situ drawing, (4) SAXS and anomalous SAXS for unilamellar lipid vesicles and metalloprotein solutions, (5) anomalous GISAXS for oriented membranes of Br-labeled lipids embedded with peptides, and (6) GISAXS for silicate films formed in situ at the air–water interface.

Robust non-carbon Ti0.7Ru0.3O2 support with co-catalytic functionality for Pt: enhances catalytic activity and durability for fuel cells

Multifunctional binary metal oxide (Ti0.7Ru0.3O2), a novel functionalised co-catalytic support for Pt, is synthesized in a simple one-step hydrothermal process at low temperature. In practical applications Ti0.7Ru0.3O2 offers both excellent improvements in electrocatalytic activity and durability over commercial carbon supported Pt and PtRu catalysts for direct methanol fuel cell (DMFC), while at the molecular level it provides advantages in terms of its high surface area, and the strong interactions between Pt and the co-catalytic support. The Ti0.7Ru0.3O2 support acts as a co-catalyst supporting Pt activity, due to the high proton conductivity of hydrated Ti0.7Ru0.3O2 which underlies a ‘bifunctional mechanism’ and the synergistic effect between Pt and Ti0.7Ru0.3O2, modifying the electronic nature of the metal particles as well, which additionally enhances CO-tolerance, the catalytic activity and durability for methanol and hydrogen oxidation. Additionally, Ti0.7Ru0.3O2 can be fabricated as a much thinner catalyst layer resulting in improving mass transport kinetics, giving a broad scope for its wider application in other fuel cells, as demonstrated here by its application in a direct methanol fuel cell (DMFC) and polymer electrolyte membrane fuel cell (PEMFC) and can also be extended to other areas such as catalytic biosensor technology.

Effect of rigid amorphous phase on glass transition behavior of poly(trimethylene terephthalate)

Abstract In this work, a three-phase model consisting of crystalline, mobile amorphous and rigid amorphous phases (RAP) was used to describe the structural formation of poly(trimethylene terephthalate) (PTT) at various crystallization conditions. The variation in thickness and fraction of each phase was studied on both crystallization temperature T c and crystallization time t c effects from differential scanning calorimetry and small angle X-ray scattering analyzes. The results showed that the rigid amorphous fraction and thickness of PTT increased with increasing T c . Meanwhile, there is no remarkable change in crystalline fraction and thickness, and long period. A characteristic length ξ a for cooperative motion of polymer chains in amorphous phase was determined from the variation in glass transition interval using dynamic mechanical analysis. The change in this length scale of glass transition was considered to be correlated with the variation in the thickness of rigid and mobile amorphous phases. The T g of PTT increases and the relaxation peak becomes broader at high temperature flank with T c . These facts are considered due to that the RAP formation leads to the suppression of cooperative motion for amorphous chains.

Photocatalytic hydrogen production on nickel-loaded LaxNa1−xTaO3 prepared by hydrogen peroxide-water based process

A green production process for producing nickel-loaded LaxNa1−xTaO3, using a hydrogen peroxide-water based solvent system (HW-derived), is reported. The H2 evolution of the HW-derived sample is about 1.8 times higher than samples made using ethanol as a solvent. The activity of the sample can be further increased 9.3 times by depositing nanosized nickel as a co-catalyst on the surface of the La0.02Na0.98TaO3. Possible mechanisms of H2 evolution from pure water and from aqueous methanol solutions using nickel in three states (i.e.Ni metal, NiO oxide, and Ni/NiO core/shell)-La0.02Na00.98TaO3, are discussed systematically for the first time. It is clearly shown that the activity of hydrogen generation from pure water is in sequence: Ni/NiO > NiO > Ni, whereas the activity sequence with respect to aqueous methanol is: Ni > Ni/NiO > NiO. Metallic Ni presents the most active sites and favors the formation of hydrogen from aqueous methanol. The Ni in Ni/NiO core/shell induce the migration of photogenerated electrons from the bulk to catalyst surface, while NiO act as H2 evolution site and prevent water formation from H2 and O2. The recombination is interrupted by the effective capture of the holes by methanol acting as a sacrificial reagent, thereby leading to higher hydrogen evolution. In contrast, the competition between the recombination and the charge-transfer reaction occurs in pure water leading to a possible back reaction between H2 and O2 on the photocatalysts surface. The photocatalyst synthesis avoids the use of organic solvents and thereby contributes to the environmentally friendly production of hydrogen.

Competition between Phase Separation and Crystallization in a PCL/PEG Polymer Blend Captured by Synchronized SAXS, WAXS, and DSC

We conducted simultaneous, small-angle, X-ray scattering/differential scanning calorimetry (SAXS/ DSC) and simultaneous, wide-angle, X-ray scattering (WAXS)/DSC measurements for a polymer blend of poly(ε-caprolactone)/poly(ethylene glycol) (PCL/PEG). The time-dependent SAXS/DSC and WAXS/DSC results, measured while the system was quenched below the melting temperature of PCL from a melting state, revealed the competitive behavior between liquid-liquid phase separation and crystallization in the polymer blend. The time-dependent structural evolution extracted from the SAXS/WAXS/DSC results can be characterized by the following four stages in the PCL crystallization process: the induction (I), nucleation (II), growth (III), and late (IV) stages. The influence of the liquid-liquid phase separation on the crystallization of PCL was also observed by phase-contrast microscope and polarized microscope with 1/4λ compensator.

New SmCG phases in a hydrogen-bonded bent-core liquid crystal featuring a branched siloxane terminal group.

In this study, we synthesized three analogous bent-core molecules, a hydrogen-bonded complex and a covalent-bonded compound with branched siloxane units (H-SiO and C-SiO, respectively) and a hydrogen-bonded complex with an alkyl unit (H-Alk), and investigated the effects of the hydrogen bonding and branched siloxane terminal units on their mesomorphic properties. The covalent-bonded compound C-SiO and the hydrogen-bonded complex H-Alk exhibited typical SmCP phases; in contrast, the hydrogen-bonded complex H-SiO exhibited a series of general tilt smectic (SmCG) phases with highly ordered layer structures (i.e., SmC̃G(2)P(F)-USmCG(2)P(A)-SmCG(2)P(F)-SmCGP(F) upon cooling). During the SmCG-type phase transition process, a 2D-modulated ribbon structure transferred into highly ordered layers via undulated layers, as the hydrogen-bonding strength increased with reduced temperatures. As the SmCG domains were aligned under dc electric fields, a gradual decrease in the leaning angle from ca. 60° to 50° (while the tilt angle kept at ca. 31°) could be determined by in situ wide-angle X-ray scattering (WAXS). Combined with Fourier transform infrared and Raman spectroscopic data, our results suggest that the change in the leaning angle was governed by the competition of the hydrogen bonds and microsegregation of siloxane units within the bilayer structure of the hydrogen-bonded complex H-SiO. In addition, the ferroelectric-(antiferroelectric)-ferroelectric transitions proven by the switching current responses in the SmCG-type phases of H-SiO reveal that the polar switching occurred through collective rotations around the long axis of H-SiO. Therefore, novel SmCG phases with a series of highly ordered 2D-structures were induced by the effects of the hydrogen bonding and branched terminal siloxane unit in the bent-core hydrogen-bonded LC complex H-SiO.

An instrument for time-resolved and anomalous simultaneous small- and wide-angle X-ray scattering (SWAXS) at NSRRC

A SWAXS (small- and wide-angle X-ray scattering) instrument was recently installed at the wiggler beamline BL17B3 of the National Synchrotron Radiation Research Center (NSRRC), Taiwan. The instrument, which is designed for studies of static and dynamic nanostructures and correlations between the nano (or meso) structure (SAXS) and crystalline structure (WAXS), provides a flux of 1010–1011 photon s−1 at the sample at energies between 5 and 14 keV. With a SAXS area detector and a WAXS linear detector connected to two data acquisition systems operated in master–slave mode, the instrument allows one to perform time-resolved as well as anomalous scattering measurements. Data reduction algorithms have been developed for rapid processing of the large SWAXS data sets collected during time-resolved measurements. The performance of the instrument is illustrated by examples taken from different classes of ongoing projects: (i) time-resolved SAXS/WAXS/differential scanning calorimetry (DSC) with a time resolution of 10 s on a semicrystalline poly(hexamethylene terephthalate) sample, (ii) anomalous SAXS/WAXS measurements on a nanoparticulate PtRu catalyst, and (iii) grazing-incidence SAXS of a monolayer of oriented semiconductor quantum wires, and humidity-controlled ordering of Alamethicin peptides embedded in an oriented lipid membrane.

Anomalous small- and wide-angle X-ray scattering and X-ray absorption spectroscopy for Pt and Pt-Ru nanoparticles

We have characterized the structures of two kinds of catalytic nanoparticles of Pt and Pt–Ru, using anomalous small-angle X-ray scattering (ASAXS), anomalous wide-angle X-ray scattering (AWAXS) and extended X-ray absorption fine structure (EXAFS) spectroscopy. With several X-ray energies near the Pt LIII edge, the AWAXS data reveal a face-centered cubic (f.c.c.) crystalline structure for Pt nanoparticles supported on carbon black, whereas the ASAXS data characterize the monometallic nanoparticles as polydisperse spheres with a mean size of 23 A and a size distribution of 20%. With similar X-ray energies, ASAXS and AWAXS data for the Pt–Ru nanoparticles indicate that they have a mean size of ~29 A and a slightly Pt-rich core that can be characterized by an f.c.c. crystalline structure similar to that of the pure Pt nanoparticles. The coordination numbers of the bimetallic nanoparticles extracted from the EXAFS data, collected at the Pt LIII edge and Ru K edge, also reveal a consistent structure of largely, but not completely, intermixed Pt and Ru atoms in the nanoparticles.

Controlled Handedness of Twisted Lamellae in Banded Spherulites of Isotactic Poly(2-vinylpyridine) as Induced by Chiral Dopants.

Herein, we suggest a unique approach to control the handedness of twisted lamellae in banded spherulites of a stereoregular polymer, isotactic poly(2-vinylpyridine) (iP2VP). When (R)- or (S)-hexahydromandelic acid (HMA), which can associate with iP2VP, was introduced as a chiral dopant, mirror-image CD spectra in the complex systems showed induced circular dichroism (ICD) of the iP2VP by chiral HMA. Banded spherulites resulting from lamellar twisting due to the imbalanced stresses at the opposite folding surfaces could be formed by crystallization of the iP2VP/HMA complexes, which had a crystalline structure similar to that of neat iP2VP. A preferential sense of the twisted crystalline lamellae was found in the iP2VP/HMA complex, thus suggesting homochiral evolution from conformational to hierarchical chirality.

Birefringence Control of Semicrystalline Block Copolymers by Crystallization under Confinement

A series of semicrystalline block copolymers (BCPs), poly(4-vinylpyridine)-block-poly(ε-caprolactone) (P4VP-PCL), with lamellar phases have been synthesized. P4VP-PCL BCP thin films with large-scale, oriented lamellar microdomains were obtained by rimming coating process followed by oscillated shearing using a homemade shear device. Owing to the vitrified P4VP microdomains and strongly segregated microphase separation, specific PCL crystalline chain orientation can be formed from the growth of anisotropic PCL crystallites under confinement so as to uniformly increase the birefringence of the BCP thin films. The enhanced birefringence corresponds well with the increase of PCL crystallinity. Consequently, the birefringence of the P4VP-PCL thin-films can be fine-tuned by PCL crystallization. The variation on the birefringence of the BCP thin films attributed to crystallization and melting is a reversible process with respect to temperature. The BCP thin films can thus be used as temperature-stimulated materials with controllable birefringence via crystallization kinetics.