Supra-assembly of siliceous vesicles

We report a new approach to produce macroporous ( approximately 110 nm in diameter) ordered siliceous foams (MOSF) by using block copolymers as templates in the absence of any organic cosolvent. The fine three-dimensional honeycomb structure of MOSF was determined by electron tomography. A formation mechanism of MOSF that spans from the atomic to macroscopic scale is proposed, which involves the cooperative self-assembly of unilamellar vesicles followed by the supra-assembly of vesicles. The fusion of soft vesicles finally leads to MOSF with well-ordered and defined honeycomb structures.     

Evolution of Helical Mesostructures

An intriguing evolution from a simple internal helix to a hierarchical helical (HH) mesostructure with both internal and external helices or a complicated screwlike and concentric circular (CC) mesostructure is successfully observed. The complicated helical structures are determined by TEM studies and 3D electron tomography. We demonstrate a topological helix–coil transition between the internal and external helices to reveal the origin of the HH mesostructure and the relationship between the straight helical and HH rods. Moreover, the boundary condition of the helix–coil transition is clarified to explain in detail the formation of complex helical structures, such as the screwlike mesostructure. It is proposed that the final structural characteristics are determined exactly by the balance between the decrease in the surface free energy and the maintenance of the hexagonal packing in one individual rod, which explains the formation of unusual CC, HH, and screwlike morphologies in one pot. Our success has opened new opportunities in the characterization of complex porous architectures, thus paving a way to remarkable advances in the fields of synthesis, understanding, and application of novel porous materials.     

Energy spectra for decaying 2D turbulence in a bounded domain

We use results derived in the framework of the replica approach to study the liquid-glass thermodynamic transition. The main results are derived without using replicas and applied to the study of the Lennard-Jones binary mixture introduced by Kob and Andersen. We find that there is a phase transition due to the entropy crisis. We compute both analytically and numerically the value of the phase transition point T(K) and the specific heat in the low temperature phase.     

Structural and conductivity studies of Y10−xLaxW2O21

The aim of this work was to determine structural parameters of the Y_10−xLa_xW₂O₂₁ (x=0-10) solid solution series and investigate their electric properties. Crystallographic data shows a gradual increase in symmetry with increasing La content, as the structure evolves from orthorhombic, Y₁₀W₂O₂₁, towards the pseudo-cubic structure of Y₅La₅W₂O₂₁. The solubility limit of La₂O₃ was found to be 50% (x=5). Above this level two phases were observed, La₆W₂O₁₅ and (La,Y)_10+xW_2−xO_21−δ. The conductivity of Y rich samples was very low, with σ of the order 2×10⁻⁵-5×10⁻⁵ S cm⁻¹ at 1000 °C, whilst ionic conductivity was observed for most La rich doped samples. The highest conductivity was observed for La₁₀W₂O₂₁ and its doped analogues, at 1×10⁻³-5×10⁻³ S cm⁻¹ at 1000 °C. Unit cell parameters were determined as a function of temperature from 0 to 1000°C, and thermal expansion of these materials was determined from temperature studies carried out at the Australian Synchrotron facility in Melbourne, Victoria, Australia.     

Electrochemical processes in electrospray ionization mass spectrometry

Editorial Comment Last month we presented, as a Special Feature, a set of five articles that constituted a Commentary on the fundamentals and mechanism of electrospray ionization (ESI). These articles produced some lively discussion among the authors on the role of electrochemistry in ESI. Six authors participated in a detailed exchange of views on this topic, the final results of which constitute this month's Special Feature. We particularly hope that younger scientists will find value in this month's Special Feature, not only for the science that it teaches but also what it reveals about the processes by which scientific conclusions are drawn. To a degree, the contributions part the curtains on these processes and show science in action. We sincerely thank the contributors to this discussion. The give and take of intellectual debate is not always easy, and to a remarkable extent this set of authors has maintained good humor and friendships, even when disagreeing strongly on substance. Graham Cooks and Richard Caprioli Copyright 2000 John Wiley & Sons, Ltd.     

Derivatization for electrospray ionization-mass spectrometry. 4. Alkenes and alkynes

A survey of derivatization strategies and prospective derivatization reactions for conversion of simple alkenes and alkynes to 'electrospray-active' species is presented. General synthetic strategies are discussed and illustrative examples of prospective derivatives prepared from model compounds are presented along with their electrospray ionization (ES) mass spectra. The identified derivatives of these neutral, nonpolar analytes are either ionic or are ionizable in solution through Bronsted acid/base chemistry, by Lewis acid/base chemistry, or by chemical or electrochemical electron-transfer chemistry. Once ionized, the derivatives are expected to be amenable to detection by electrospray ionization-mass spectrometry. Derivatives are identified for positive and negative ion analysis of both alkenes and alkynes. Copyright 2000 John Wiley & Sons, Ltd.     

Superstructure formation and variation in Ni-GDC cermet anodes in SOFC

The microstructures and spatial distributions of constituent elements at the anode in solid oxide fuel cells (SOFCs) have been characterized by analytical transmission electron microscopy (TEM). High resolution TEM observations demonstrate two different types of superstructure formation in grain interiors and at grain boundaries. Energy-filtered TEM elemental imaging qualitatively reveals that mixture zones exist at metal-ceramic grain boundaries, which is also quantitatively verified by STEM energy dispersive X-ray spectroscopy. It was apparent that both metallic Ni and the rare-earth elements Ce/Gd in gadolinium-doped ceria can diffuse into each other with equal diffusion lengths (about 100 nm). This will lead to the existence of mutual diffusion zones at grain boundaries, accompanied by a change in the valence state of the diffusing ions, as identified by electron energy-loss spectroscopy (EELS). Such mutual diffusion is believed to be the dominant factor that gives rise to superstructure formation at grain boundaries, while a different superstructure is formed at grain interiors, as a consequence solely of the reduction of Ce(4+) to Ce(3+) during H(2) treatment. This work will enhance the fundamental understanding of microstructural evolution at the anode, correlating with advancements in sample preparation in order to improve the performance of SOFC anodes.