Stability of the formation of the chevron structure

A simple model of the formation of the chevron structure and tilted layer structure in the smectic C liquid crystal phase from the bookshelf structure in the smectic A phase is considered. Energetic considerations of this system indicate that in the absence of layer pinning forces at the surface, a transition to the tilted structure is expected. However, combining the model with 'weak' surface positional anchoring effects allows the chevron structure to form.     

On the mechanism of the hofmeister effect

Vibrational sum frequency spectroscopy was used to probe fatty amine monolayers spread on various electrolyte solutions. The spectra revealed ion specific changes in both monolayer ordering and water structure with the former following the Hofmeister series. Separate measurements of the surface potential as a function of ion tracked closely to changes in alkyl chain structure, but less closely to changes in water structure. The disruption of the monolayer ordering could be ascribed to the relative ability of the ions to penetrate past the hydrophilic surface of the monolayer's headgroups and into the more hydrophobic portion of the thin film. The corresponding trends observed in the surface water structure showed significant deviations from the Hofmeister series, leading to the conclusion that the changes in surface water structure, often credited with being the origin of Hofmeister effects, are probably not of primary importance. On the other hand, dispersion forces almost certainly play a large role in the order of the Hofmeister series.     

Molecular dynamics investigation of the intrinsic structure of water-fluid interfaces via the intrinsic sampling method

Capillary wave fluctuations smooth out the structure of fluid interfaces, making difficult the detailed analysis of the interfacial structure. Most computer simulation investigations performed to date have focused on the computation of average density profiles, ignoring the characterization of the intrinsic structure of the interface. Recent theoretical developments have reversed this situation, making possible the detailed investigation of the interfacial intrinsic structure at an unprecedented level of detail. In this article we investigate via molecular dynamics simulations the intrinsic structure of water-alkane (hexane and dodecane) interfaces. The implementation of the recently introduced, intrinsic sampling method to compute the intrinsic surface of water-fluid interfaces is discussed. We provide quantitative molecular information on the structure, corrugation, and stiffness of the liquid surfaces. The intrinsic structure of water at alkane interfaces is shown to be insensitive to the alkane-chain length, and can be very accurately described by the intrinsic structure of the water free surface.     

Silver-cemented frit formation for the stabilization of the packing structure in the microchannel of electrochromatographic microchips

A simple but effective frit formation technique was developed to stabilize the packing structure inside the microchannel of capillary electrochromatographic microchips, utilizing the electroless plating technique. A Ag(NH(3))(2)(+) solution was allowed to diffuse through the colloidal silica packing in the microchannel from the reservoir of the microchip for a limited amount of time, and then it was reduced by an excess amount of formaldehyde solution. A frit structure of ~70 μm in length was formed at the entrance of the microchannel without clogging when treated with 1mM Ag(NH(3))(2)(+) ion and formaldehyde for 30s and 150 s, respectively. The formation of the frit structure was confirmed by a scanning electron microscopy. The stability of the packing structure was tested rigorously and then confirmed by applying alternating electroosmotic flows back and forth with pulsed potential steps on both sides of the frit structure. The effect of the treatment on the electrochromatograms was evaluated after the microchips were repeatedly used and stored for a long period of time. The results indicated that the silver-cemented frit structure extended the lifetime of the fully packed CEC microchips distinctly.     

State of the art in the electrochemical characterization of the surface structure of shape-controlled Pt,Au, and Pd nanoparticles

The application of shape-controlled metal nanoparticles in electrocatalysis has improved significantly the activity, selectivity, and even the stability of many relevant electrocatalytic reactions. It is well accepted that, by controlling the shape of the nanoparticles, it is possible to provide nanoparticles with a preferential surface structure. However, to fully understand the capabilities of these nanomaterials, it is extremely relevant to correlate shape, surface structure, and electrocatalytic reactivity. Particularly, establishing the correlations between surface structure and reactivity is the key point to be studied and understood. Consequently, having tools to characterize the surface structure of these nanoparticles is of critical importance. In this short review, we discuss about the progress in the in situ characterization of the surface structure of shaped Pt, Au, and Pd nanoparticles by electrochemical probes. The results here included clearly demonstrate the potentialities of the electrochemical tools to gain detailed information of the surface structure of these shaped nanomaterials.     

An alternative description of the paulingite structure

The paulingite structure can be described as an invariant transformation of the gismondine structure. Packets of a fourling construction of the gismondine structures, which is closely related to the merlinoite structure, are used to build the structure of paulingite as an interpenetrating sixling.     

Influence of the phase composition of the support on the catalytic activity of bimetallic catalysts

The influence of the nanocrystalline structure of an aluminum-zinc spinel support on the catalytic activity of bimetallic Pt-Sn catalysts in dehydrogenation of 2-methylbutane was studied. The formation of the spinel structure in solid-phase reactions of aluminum and zinc oxides was examined.     

Structure of the xylan from the stems of the cotton plant

Summary 1. The structure of the aldobiuronic acid isolated from the xylan of cotton-plant stems has been established by its reduction and the hydrolysis of the reduced product.2. From a study of the products of the hydrolysis of the methylated xylan from cotton-plant stems the positions of attachment of the side chains in the molecule of the xylan and their structure have been determined, and a most probable structure for the xylan molecule has been put forward.V. I. Lenin Tashkent State University. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 432–435, July–August, 1974.     

Experimental and theoretical investigation on the relative stability of the PdS2- and pyrite-type structures of PdSe2

Under ambient condition PdSe2 has the PdS2-type structure. The crystal structure of PdSe2 under pressure (up to 30 GPa) was investigated at room temperature by X-ray diffraction in an energy-dispersive configuration using a diamond anvil cell with a mixture of water/ethanol/methanol as a pressure transmitting medium. A reversible structural transition from the PdS2-type to the pyrite-type structure occurs around 10 GPa, and the applied pressure reduces the spacing between adjacent 2/proportional to [PdSe2] layers of the PdS2-type structure to form the three-dimensional lattice of the pyrite-type structure. First principles and extended Hückel electronic band structure calculations were carried out to confirm the observed pressure-induced structural changes. We also examined why the isoelectronic analogues NiSe2 and PtSe2 adopt structures different from the PdS2-type structure on the basis of qualitative electronic structure considerations.     

Features of the real structure of pseudoboehmites: Violations of the structure and layer packing caused by crystallization water

Rietveld structure refinement and simulation of the diffraction patterns of partially disordered materials are used to study the real structure of nanoscale pseudoboehmite samples obtained by different technologies. The effect of various violations in the structure of these nanomaterials on diffraction patterns is analyzed. The introduction of corrections for the Lorentz and polarization factors in the determination of the cell parameter b by the position of the 020 diffraction peak in the pattern is shown to be important. A model for the atomic structure of pseudoboehmite is proposed. The model involves additional water molecules as compared to the structure of boehmite. The water molecules in the interlayer space of the layered boehmite structure are found to violate its regularity, which results in a decrease in the size of crystallites.     

Effect of γ-irradiation on the molecular-topological structure of the polyethylene matrix of glass-reinforced plastic

The molecular-topological structure of polyethylene (PE) and a PE matrix in a glass-reinforced plastic (GRP) after γ-irradiation of the plastic was studied by means of thermomechanical spectroscopy. The four-block topological structure of unirradiated PE (one amorphous block and three crystalline phases with different initial melting temperatures) is transformed into a three-block structure in the GRP already at a minimal radiation dose of 25 kGy. The intermediate crystalline phase disappears under these conditions, the molecular relaxation characteristics in all topological blocks alter, and chemical branching points appear in the pseudonetwork structure of the amorphous matrix block.     

Characterization of the benzene-insoluble fraction of the hydrolyzate of phenyltrimethoxysilanes in the presence of benzyltrimethylammonium hydroxide

The insoluble fraction obtained from the hydrolysis and condensation of (4-dimethylamino-, 2-methyl-, and nonsubstituted)phenyltrimethoxysilanes in the presence of benzyltrimethylammonium hydroxide in benzene was characterized. IR, ¹H NMR, and ²⁹Si NMR suggested that the insoluble fraction was composed of RSi(O )₃, that is, a T³ structure. X-ray diffraction indicated the presence of a long-range ordered structure composed of a mixture of crystals. Raman spectroscopy strongly suggested a cage structure by the presence of a ring-opening vibration assignable to a cubic structure at 475–482 cm⁻¹. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4587–4597, 2004     

Preparation of echinus-like SiO2@Ag structures with the aid of the HCP phase

A novel echinus-like hybrid structure composed of a SiO(2)@Ag core-shell and many silver nanorods was synthesized. These silver rods have a rare HCP structure, while the initial silver nuclei have a FCC structure. The rapid and free growth of silver nuclei resulted in the appearance of the HCP phase.     

What is the structure of the patellamides?

The compound with the structure (2) elucidated for patellamide B was synthesized and found to be not identical with that cyclopeptide. A new proposition for the structure of patellamide B is given.     

A study of the globulins of cotton seeds XX. Stability of the quaternary structure of the 11S-globulin

The 11S-globulin has a complex stable quaternary structure in the formation of which three types of subunits participate. The aim of the work was to determine what forces form and stabilize the quaternary structure of this protein. The products of the maleylation and acetylation of the 11S-globulin and also the stability of the native 11S-globulin in the presence of ionic and nonionic detergents were investigated by disk electrophoresis. It was shown that hydrophobic interactions play a deciding role in the formation and stabilization of the quaternary structure of the 11S-globulin.     

苯氧基蒽醌的合成及光致变色机理探讨

介绍了3-甲基-1-苯氧基-9,10-蒽醌的光致变色机理,用紫外-可见光谱探讨了目标化合物在240—300 nm及300—550 nm两个波段范围内其由“trans”醌式转变为“ana”醌式的光致变色行为,并用紫外-可见光谱数据证实了苯氧基蒽醌光致变色行为中醌结构的变化.     

Dependence of the conformational parameters of polyimides on the chemical structure of the chain

The flexibility of some polyimide chains has been studied theoretically as a function of the chemical structure of the repeat unit. It has been shown that the thermodynamic flexibility can be varied over a wide range by the choice of the unit structure. For three polyimides, as an example, the flexibility of cyclochain structures approximates that for free rotation.     

Effect of polymorphism on the C?H stretching region of the infrared spectrum of polyethylene

A complex fine structure in the C? H stretching region of the infrared spectrum of deformed polyethylene single crystals is reported. The deformed crystals are shown to be transformed from the orthorhombic crystal form to a monoclinic structure. The previously deduced C_2/m monoclinic structure does not account for the appearance of the new bands. An alternative but similar monoclinic structure is proposed. The symmetry of this structure is consistent with the Fermi resonance interactions required for the observation of these bands.     

对功能高分子课程教学的思考

功能高分子的设计思想是功能高分子课程的灵魂 ,它以高分子物理学所研究的结构与性能之间关系为基础。结构与性能之间的关系是贯穿功能高分子课程始末的主线。功能高分子材料有三种设计途径 ,即化学结构设计、聚集态结构设计和复合结构设计