Microstructural characterization of semicrystalline copolymers by Raman spectroscopy

We employ Raman spectroscopy to characterize several microstructural aspects of a family of ethylene-propylene copolymers (EPC). Focus is made on the simultaneous analysis of crystallinity and chemical composition. A curve fitting procedure is used to isolate Raman bands ascribed to polypropylene chains in the crystal lattice from contributions of the amorphous phase. Crystal contents of EPC calculated on this basis are in the range 10–34 wt%, in good agreement with independent wide angle x-ray diffraction and differential scanning calorimetry measurements. Besides, Raman spectroscopy captures in some of the samples a mixed crystalline structure with both, polyethylene and polypropylene crystals, indicating a distinctive molecular architecture. The chemical composition of EPC is obtained from Raman spectra in the melt state to decouple peaks characteristics of the crystal lattice from fundamental vibrational modes of the polymer chain. EPC present ethylene contents in the range 5–26 mol%, in good agreement with parallel results from ¹³C nuclear magnetic resonance analysis. Remarkably, a rather complete characterization of EPC can be achieved on the base of a single experimental technique.     

DNA architectonics: towards the next generation of bio-inspired materials

The use of DNA in nanobiotechnology has advanced to a stage at which almost any two or three dimensional architecture can be designed with high precision. The choice of the DNA sequences is essential for successful self-assembly, and opens new ways of making nanosized monomolecular assemblies with predictable structure and size. The inclusion of designer nucleoside analogues further adds functionality with addressable groups, which have an influence on the function of the DNA nano-objects. This article highlights the recent achievements in this emerging field and gives an outlook on future perspectives and applications.     

Computer generation of nuclear spin species and nuclear spin statistical weights

This article develops computer programs for computer generation of nuclear spin species and nuclear spin statistical weights of rovibronic levels. The programs developed here generate nuclear spin species and statistical weights from the group structures known as generalized character cycle indices (GCCI s) which are computed easily from the character table of the PI group of the molecule under consideration. Procedures are illustrated with examples.     

Microstructural characterization of micro- and nanoparticles formed by polymer-surfactant interactions

We have studied the nano- and microparticles formed by complexation of PDAC [poly(diallyldimethyl-ammoniumchloride)] and SDS (sodium dodecyl sulfate). The complexation phenomenon was characterized by light scattering and zeta-potential measurements. The nature of the complexes was revealed by direct-imaging cryogenic temperature transmission electron microscopy (cryo-TEM), showing nanometric details of the complexes formed around the point of neutralization. The images also reveal how those aggregates are solubilized by excess surfactant, first into faceted particles with threadlike micelles attached to their surfaces, prior to complete solubilization, then into lacelike aggregates, and finally into spheroidal micelles. The nanostructure of the complexes strongly suggests they are made of a hexagonal liquid crystalline phase. This was further supported by small-angle X-ray scattering (SAXS).     

Nanostructured Mn-based oxides as high-performance cathodes for next generation Li-ion batteries

Mn-based oxides have been regarded as a promising family of cathode materials for high-performance lithium-ion batteries,but the practical applications have bee...     

Vacuum-UV influenced design of polymers and dissolution inhibitors for next generation photolithography

An overview of our 157 nm photoresist development activities is presented. Examination of the vacuum ultraviolet (VUV) absorbances of fluorinated monomers and polymers has provided knowledge that influenced copolymer design so that resist transparency in the vacuum-UV can be maximized. Partially fluorinated norbornenes and tricyclononenes (TCNs) have been incorporated into copolymers using metal-catalyzed addition and radical initiators. These materials have orders of magnitude higher transparency at 157 nm compared to their hydrocarbon analogues as measured by variable angle spectroscopic ellipsometry (VASE). We have also synthesized fluorinated dissolution inhibitors for use in a three-component resist system. The results of preliminary lithographic evaluations of resists formulated from these polymers are presented.     

Microstructural and chemical characterization of nanostructured TiAlSiN coatings with nanoscale resolution

Nanoscale resolution electron microscopy analysis combined with ion beam assisted techniques are presented here, to give answers to full characterization of morphology, growth mode, phase formation, and compositional distribution in nanocomposite TiAlSiN coatings deposited under different energetic conditions. Samples were prepared by magnetron sputtering, and the effects of substrate temperature and bias were investigated. The nanocomposite microstructure was demonstrated by the formation of a face-centered cubic (Ti,Al)N phase, obtained by substitution of Al in the cubic titanium nitride (c-TiN) phase, and an amorphous matrix at the column boundary regions mainly composed of Si, N (and O for the samples with higher oxygen contents). Oxygen impurities, predicted as the principal responsible for the degradation of properties, were identified, particularly in nonbiased samples and confirmed to occupy preferentially nitrogen positions at the column boundaries, being mainly associated to silicon forming oxynitride phases. It has been found that the columnar growth mode is not the most adequate to improve mechanical properties. Only the combination of moderate bias and additional substrate heating was able to reduce the oxygen content and eliminate the columnar microstructure leading to the nanocomposite structure with higher hardness (>30 GPa).     

Microstructural and auger microanalytical characterization of Cu-Hf and Cu-Ti catalysts.

Degradation processes occurring at the surface and in the bulk of Cu-based amorphous alloys during cathodic hydrogen charging were used for promoting the catalytic activity of such alloys. These processes modifying the structure, composition, and morphology of the substrate proved to be useful methods for transforming Cu-Hf and inactive Cu-Ti amorphous alloy precursors into active and durable catalysts. Indeed, their catalytic activity for dehydrogenation of 2-propanol increased up to a conversion level of approximately 60% at selectivities to acetone of about 99% for Cu-Ti and to conversion of approximately 90% at selectivities of approximately 95% for Cu-Hf. Previous attempts carried out by aging in air or hydrogen charging from the gas phase resulted in a maximum conversion level up to 15% for Cu-Hf and up to 3% for Cu-Ti. High resolution Auger spectroscopy allowed changes occurring during the activation process to be identified, namely, the formation of small Cu particles on the HfO2 surface and the formation of highly porous particles containing mostly Cu and some Ti and O (Cu-Ti-O) on a Cu-Ti substrate. Differences in the chemistry and structure of both catalysts are discussed, and the implications for catalytic function are considered. A probable configuration of active sites on the Cu-Ti-O/Ti-O-Cu catalyst for dehydrogenation of 2-propanol is proposed.     

Self-transforming stainless-steel into the next generation anode material for lithium ion batteries

Here,an extremely cost-effective and simple method is proposed in order to morphologically selftransform stain less steel from a completely inactive material to a fully operati onal,nanowire-structured,3D anode material for lithium ion batteries.The reagentless process of a single heating step of the plain stainless steel in a partially reduci ng atmosphere,converts the stain less steel into an active anode via metal-selective oxidation,creating vast spinel-structured nanowires directly from the electrochemically in active surface.The simple process allows the complete utilizati on of the 3D mesh structure as the electrochemically-active spinel nanowires greatly enhance the active surface area.The novel material and architecture exhibits high capacities(-1000 mAh/g after-400 cycles),long cycle life(>1100 cycles)and fast rate performance(>2C).Simple modulation of the substrate can result in very high areal and volumetric capacities.Thus,areal capacities greater than 10 mAh/cm² and volumetric capacities greater than 1400 mAh/cm³ can be achieved.Using the proposed method,the potential reduction in cost from the use of battery-grade graphite is at least an order of magnitude,with considerable better results achieved in terms of capacity and intrinsic structural benefits of the substrate,which include direct contact of the active material with the current collector,lack of delamination and binder-free performance.This work provides a new paradigm and a key step in the long route to replace the commercial graphite anode as the next-geneation anode material.     

Flexible and stretchable electrodes for next generation polymer electronics: a review

Transparent conductive electrodes play a significant role in the fabrication and development of optoelectronic devices. As next generation optoelectronic devices tend towards mobile and wearable devices, the added attribute of flexibility or stretchability for these electrodes becomes increasingly important. However, mechanical requirements aside, transparent conductive electrodes must still retain high transparency and conductivity, with the metrics for these parameters being compared to the standard, indium tin oxide. In the search to replace indium tin oxide, two materials that have risen to the forefront are carbon nanotubes and silver nanowires due to their high transparency, conductivity, mechanical compliance, and ease of fabrication. This review highlights recent innovations made by our group in electrodes utilizing carbon nanotubes and silver nanowires, in addition to the use of these electrodes in discrete devices and integrated systems.     

An algorithm for the generation of nuclear spin species and nuclear spin statistical weights

This article develops a set of algorithms for the computer generation of nuclear spin species and nuclear spin statistical weights potentially useful in molecular spectroscopy. These algorithms generate the nuclear spin species from group structures known as generalized character cycle indices (GCCI s). Thus the required input for these algorithms is just the set of all GCCI s for the symmetry group of the molecule which can be computed easily from the character table. The algorithms are executed and illustrated with examples.     

Microstructural characterization of SLS-PA12 specimens under dynamic tension/compression excitation

This paper describes the effect of dynamic tension/compression loading on selective laser sintered components in polyamide. To gain more insight in the fatigue phenomena, both thermal and microstructural studies were performed on the fracture surfaces of the test specimens. The presented micrographs, DSC curves, hysteresis loops and S/N-line facilitate an improved understanding of the fatigue properties of selective laser sintered materials, polyamide in particular. The results show that crack initiation starts from inclusions in the material caused by unfused powder particles. The inclusions give rise to the formation of semi-spherical depressions with raised edges. Ductile fatigue striations were noted on the sides of these depressions indicating the irreversible plastic deformation dominated by shear stress, which is typical for fatigue failure. Consequently, microstructural analysis indicates that the material density is a crucial factor influencing the fatigue life of SLS-PA12 components. The lower the density, the more unfused powder particles and the higher the chance of crack initiation.     

Zinalco and Zircaloy-4 nuclear characterization

Zinalco and Zircaloy-4 samples were used in order to measure the gamma-ray attenuation coefficients for three different gamma-ray energies. Using the neutron activation analysis technique, the elemental composition of Zinalco and Zircaloy-4 was measured.     

2,5,8,11-Tetraboronic ester perylenediimides: a next generation building block for dye-stuff synthesis

Via an unprecedentedly reported ruthenium catalyzed reaction, an efficient and straightforward method was developed for the synthesis of 2,5,8,11-tetraboronate perylenediimide derivatives. A possible reaction mechanism is proposed. The synthesis of 2,5,8,11-tetra-iodo and tetra-amino perylenediimides derivatives is also reported.     

Synthesis and characterization of lower generation broom molecules

Dendritic molecules with dodecyl groups as the hyperbranchs were synthesized in methanol by Michael addition with dodecylamine and methyl acrylate as raw materials. This new-type dendritic molecules were called vividly ＂broom molecules＂ in this report. The surface tension of the aqueous solution of broom molecule terminated amino group was measured by using the dropvolume method. The demulsification performance of the broom molecules for the oil/water （O/W） simulated crude oil emulsion was examined. The experimental results revealed that, as a new-type of surfactants, the broom molecules terminated amino groups showed demulsification for the O/W simulated crude oil emulsion. 2007 Jun Wang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All fights reserved.