An Attenuated Total Reflection FT‐IR Spectroscopic Study of Polyamide 6/Clay Nanocomposite Fibers

Summary: An attenuated total reflection FT‐IR spectroscopic study of the hydrogen bonding, molecular orientation, and crystalline phase transitions in polyamide 6 (PA6)/clay nanocomposite (PA6CN) fibers is proposed. The nanoscale dispersed clay layers lowered the degree of order of hydrogen bonding, affected little the hydrogen bonding strength, and increased the degree of orientation of both γ crystalline and overall domains. A partial γ to α phase transition appeared with time.

Schematic representation of the attenuated total reflection FT‐IR dichroism measurements.     

Rubbing‐induced molecular alignment and its relaxation in polystyrene thin films

Rubbing‐induced molecular alignment and its relaxation in polystyrene (PS) thin films are studied with optical birefringence. A novel relaxation of the alignment is observed that is distinctly different from the known relaxation processes of PS. First, it is not the Kohlrausch–Williams–Watts type but instead is characterized by two single exponentials plus a temperature‐dependent constant. At temperatures several degrees or more below the glass‐transition temperature (T_g), the relaxation time falls between that of the α and β relaxations. Second, the decay time constants are the same within 40% for PS with weight‐average molecular weights (M_w's) of 13,700–550,000 Da at temperatures well below the sample T_g's, indicating that the molecular relaxations involved are mostly local within the entanglement distance. Nonetheless, the temperature at which the rubbing‐induced molecular alignment disappears (T₀) exhibits a strong M_w dependence and closely approximates the T_g of the sample. Furthermore, T₀ depends notably on the thickness of the polymer in much the same way as previously found for the T_g of supported PS films. This suggests that the α process becomes dominant near T_g. Preliminary spectroscopic studies in the mid‐infrared range show a significant degree of bending of the phenyl ring toward the sample surface, with the C? C bond connecting the phenyl ring and the main chain tends to lie along the rubbing direction, which indicates that the relaxation is connected with the reorientation of this C? C bond. We exclude the observed relaxation, as predominantly a near‐surface one, because detailed studies on the effects of rubbing conditions on the degree of molecular alignment indicate that the alignment is not local to the polymer–air surface. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2906–2914, 2001     

Synthesis of Copper-Substituted CoS2@CuxS Double-Shelled Nanoboxes by Sequential Ion Exchange for Efficient Sodium Storage

The construction of hybrid architectures for electrode materials has been demonstrated as an efficient strategy to boost sodium-storage properties because of the synergetic effect of each component. However, the fabrication of hybrid nanostructures with a rational structure and desired composition for effective sodium storage is still challenging. In this study, an integrated nanostructure composed of copper-substituted CoS₂@Cu_xS double-shelled nanoboxes (denoted as Cu-CoS₂@Cu_xS DSNBs) was synthesized through a rational metal–organic framework (MOF)-based templating strategy. The unique shell configuration and complex composition endow the Cu-CoS₂@Cu_xS DSNBs with enhanced electrochemical performance in terms of superior rate capability and stable cyclability.     

NiMn-Based Bimetal–Organic Framework Nanosheets Supported on Multi-Channel Carbon Fibers for Efficient Oxygen Electrocatalysis

Developing noble-metal-free bifunctional oxygen electrocatalysts is of great significance for energy conversion and storage systems. Herein, we have developed a transformation method for growing NiMn-based bimetal–organic framework (NiMn-MOF) nanosheets on multi-channel carbon fibers (MCCF) as a bifunctional oxygen electrocatalyst. Owing to the desired components and architecture, the MCCF/NiMn-MOFs manifest comparable electrocatalytic performance towards oxygen reduction reaction (ORR) with the commercial Pt/C electrocatalyst and superior performance towards oxygen evolution reaction (OER) to the benchmark RuO₂ electrocatalyst. X-ray absorption fine structure (XAFS) spectroscopy and density functional theory (DFT) calculations reveal that the strong synergetic effect of adjacent Ni and Mn nodes within MCCF/NiMn-MOFs effectively promotes the thermodynamic formation of key *O and *OOH intermediates over active NiO₆ centers towards fast ORR and OER kinetics.     

Synthesis of Hydroxyapatite Nanorods under Mild Conditions and Their Drug Release Properties

Hydroxyapatite (HAp) nanorods possess vast potential applications in various fields, and here HAp nanorods with high aspect ratio were synthesized via a convenient two‐stage precipitation‐hydrolysis process at 60°C under atmospheric pressure. The precursor of CaHPO₄ at precipitation stage is well crystallized as nubby morphology with CTAB as surfactant, while CaHPO₄ was dissolved and CTA⁺ stabilized the HAp nuclei during the hydrolysis stage. OH^? ions were absorbed onto the active crystal surface, where Ca²⁺ and PO₄³⁺ reacted with OH^? to make the nuclei grow into larger crystals, and highly crystalline HAp nanorods were obtained by Ostwald ripening. The loaded drug of IBU on the HAp crystals can be 100% released in 24 h. PVP modified HAp nanorods can increase the drug‐loading capacity and release drug faster than pure HAp nanorods. The results indicate that HAp nanorods modified with suitable surfactants are of great use in drug delivery system.     

Transforming Large Collections of Scientific Publications to XML

We describe an experiment transforming large collections of L ^a T_EX documents to more machine-understandable representations. Concretely, we are translating the collection of scientific publications of the Cornell e-Print Archive (arχiv) using LaTeXML, a L ^a T_EX to XML converter currently under development. While the long-term goal is a large body of scientific documents available for semantic analysis, search indexing and other experimentation, the immediate goals are tools for creating such corpora. The first task of our arXMLiv project is to develop LaTeXML bindings for the (thousands of) L ^a T_EX classes and packages used in the arχiv collection, as well as methods for coping with the eccentricities that T_EX encourages. We have created a distributed build system that runs LaTeXML over the collection, in part or entirely, while collecting statistics about missing bindings and other errors. This guides debugging and development efforts, leading to iterative improvements in both the tools and the quality of the converted corpus. The build system thus serves as both a production conversion engine and software test harness. We have now processed the complete arχiv collection through 2006 consisting of more than 400,000 documents (a complete run is a processor-year-size undertaking), continuously improving our success rate. We are now able to convert more than 90% of these documents to XHTML+MathML. We consider over 60% to be successes, converted with no or minor warnings. While the remaining 30% can also be converted, their quality is doubtful, due to unsupported macros or conversion errors.     

Wide angle X‐ray diffraction and Fourier transform infrared dichroism studies of stretched‐recovery‐restretched process of polyurethane/clay nanocomposite

An intercalated polyurethane (PU) /clay nanocomposite was prepared by in situ intercalative polymerization. The PU/clay nanocomposite pellet or film samples were stretched‐recovery‐restretched, using selfmade microstretching tools. The changes of the basal spacings of clay and the orientation of polymer chain segments during the stretched‐recovery‐restretched process were studied by wide angle X‐ray diffraction (WAXD) and Fourier transform infrared (FTIR) dichoism techniques. The WAXD results show that the basal spacing of clay did not change obviously, indicating that no macromolecular chains entered or moved out of the interlayer space, and the orientations of both hard and soft segments inside the interlayer space did not change obviously, either. The FTIR dichroism tests suggest that outside the interlayer space, the orientation of the hard chain segment increased, decreased, and then increased again during the stretched‐recovery‐restretched process. However, no obvious changes of the degree of orientation of the soft segment were observed during the processes, the slightly orientation might be released during the relaxation process before the measurements. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 654–660, 2007     

Mechanical Properties and Orientation of Atactic Poly(methyl methacrylate): Sub‐Tg Annealing and Stereocomplex Formation

The mechanical properties and orientation behavior of atactic poly(methyl methacrylate) films cast from acetone (A‐aPMMA films) and chloroform (C‐aPMMA films), with subsequent sub‐T_g annealing, have been studied. The formation of a stereocomplex in sub‐T_g‐annealed A‐aPMMA films and C‐aPMMA films was demonstrated by means of differential scanning calorimetry. Stereocomplex in A‐aPMMA films is more pronounced than in C‐aPMMA films at each annealing temperature. It is proposed that stereocomplex formation can process at temperatures below T_g, leading to enhanced yield stress and higher orientation.     

升温在位红外研究物理老化对间规聚苯乙烯结晶行为的影响

通过在位红外光谱测量研究了物理老化对非晶和δ晶型的间规聚苯乙烯（ＳＰＳ）升温结晶过程的影响。发现对于晶样品来说,在物理老化前后,其结晶（即非晶→α晶型）的温度区间变化不大;但对于δ晶型的样品而言其物理老化后的晶型转变（即δ晶型→γ晶型）温度区间是１０４～１２７℃,与未物理老化的晶型转变温度区间９０～１１２℃相比,转变温度升高了约１４℃,这充分说明了物理老化使溶致型的δ晶型更加稳定,其溶剂与晶体的结