Non‐invasive depth profiling by space and time‐resolved Raman spectroscopy

Time‐resolved Raman spectroscopy, spatially offset Raman spectroscopy and time‐resolved spatially offset Raman spectroscopy (TR‐SORS) have proven their capability for the non‐invasive profiling of deep layers of a sample. Recent studies have indicated that TR‐SORS exhibits an enhanced selectivity toward the deep layers of a sample. However, the enhanced depth profiling efficiency of TR‐SORS, in comparison with time‐resolved Raman spectroscopy and spatially offset Raman spectroscopy, is yet to be assessed and explained in accordance to the synergistic effects of spatial and temporal resolutions. This study provides a critical investigation of the depth profiling efficiency of the three deep Raman techniques. The study compares the efficiency of the various deep Raman spectroscopy techniques for the stand‐off detection of explosive precursors hidden in highly fluorescing packaging. The study explains for the first time the synergistic effects of spatial and temporal resolutions in the deep Raman techniques and their impact on the acquired spectral data. Copyright © 2013 John Wiley & Sons, Ltd.     

Vibrational spectroscopic studies of laboratory scale polymer melt processing: Application to a thermoplastic polyurethane nanocomposite

A laboratory scale twin screw extruder has been interfaced with a near infrared (NIR) spectrometer via a fibre optic link so that NIR spectra can be collected continuously during the small scale experimental melt state processing of polymeric materials. This system can be used to investigate melt state processes such as reactive extrusion, in real time, in order to explore the kinetics and mechanism of the reaction. A further advantage of the system is that it has the capability to measure apparent viscosity simultaneously which gives important additional information about molecular weight changes and polymer degradation during processing. The system was used to study the melt processing of a nanocomposite consisting of a thermoplastic polyurethane and an organically modified layered silicate.     

温度对氨基苯甲酸在粗糙银表面上行为的影响

本文同时测定了当温度从－１９０℃上升到３０℃和从３０℃下降到－１９０℃对氨基苯甲酸（ｐ－Ａｍｉｎｏｂｅｎｚｏｉｃ Ａｃｉｄ，ＰＡＢＡ）和邻氨基苯甲酸（ｏ－Ａｍｉｎｄｂｅｎｚｏｉｎ Ａｃｉｄ，ＯＡＢＡ）在粗糙的银表面上的表面增强拉曼光谱的变化。结果表明，若吸附质表面拉曼光谱的增强主要表现为化学机理，且整个分子平躺在表面，则分子在表面上的取向不会随温度的变化而改变。而温度的变化会引起基于电磁场增强机理     

Effect of N-substitution on the crystallinity of polylaurolactam

Poly(N-ethyl laurolactam) and poly(N-benzyl laurolactam) were prepared from the corresponding monomers by hydrolyic polymerization. Unlike the partially crystalline poly(N-methyl laurolactam), these two homopolymers were completely amorphous by x-ray diffraction. Diffraction patterns of copolymers of N-ethyl laurolactam or N-benzyl laurolactam with laurolactam were shown to be composition-dependent. For N-ethyl laurolactam copolymers, crystallinity developed with 20% laurolactam as a comonomer and increased steadily with a subsequent change in the x-ray pattern, up to 50% laurolactam. Higher laurolactam percentages resulted in copolymers having a nylon 12 x-ray pattern. N-Benzyl laurolactam copolymers with 30% laurolactam showed only 6% crystallinity. The x-ray patterns of N-benzylated nylon 12 made with more than 50% laurolactam showed patterns similar to that of nylon 12. Differential scanning calorimetry data of all these polymers substantiate the x-ray findings. The effect of type and concentration of the N-substituent on the glass transition, melting, and crystallization temperatures of the polymers is discussed.     

Structure of poly(N-methyl laurolactam)

The structure of poly(N-methyl laurolactam) has been studied in the solid state and in solution. In oriented, annealed monofilaments, the chain exhibits a distorted extended planar zigzag conformation. Upon orientation, an increase in crystallinity and a slight shift of the large d spacing in the diffraction pattern to a higher value is observed. In the crystalline regions of the polymer, the amide groups are proposed to have the anti conformation, whereas the amorphous regions may consist of both the syn and anti forms. Differential scanning calorimetry and thermal mechanical analysis showed multiple melting endotherms which probably result from partial melting and reorganization of small, imperfect crystallites. In solution, nuclear magnetic resonance spectroscopy showed the presence of a conformational equilibrium of the syn and anti amide groups in the polymer chains. The effect of thermal and mechanical treatments on certain infrared group frequencies of the amide moieties was studied and correlated with other pertinent analytical data.     

Thermal expansion op NbSe2 and TaS2

The lattice parameters a₀ and c₀ of the hexagonal 2H polytype of NbSe₂; have been measured over the temperature range 156–478 K for a₀, and 138–482 K for c₀. The lattice parameter c₀ of the hexagonal 2H polytype of TaS₂ has been measured between 151 and 472 K. The lattice parameters a₀ and c₀ for the octahedral 1T polytype of TaS₂ been measured between 165 and 488 K. Over these temperature ranges, the following average coefficients of thermal expansion have been measured; 2H-NbSe₂, 6.6 × 10^?6K^?1 along the a-axis, 19.9 × 10^?6 K^?1 along the c-axis; 2H-TaS₂, 15.6 × 10^?6 K^?1 along the c-axis; IT-TaS₂, 12.7 × 10^?6 K^?1 along the c-axis. The parameter c₀ of 1T-TaS₂ undergoes two transitions which may be explained in terms of charge density waves.     

Self-assembly and encoding of polymer-stabilized gold nanoparticles with surface-enhanced Raman reporter molecules

Polymer-stabilized gold nanoparticles (AuNPs) were prepared and encoded with a range of surface-enhanced Raman reporter molecules. A range of as-synthesized polymers produced by reversible addition fragmentation chain transfer (RAFT) polymerization were demonstrated to self-assemble at the surface of AuNPs dispersed in water. The method involved the coprecipitation of polymer-gold conjugates by the addition of polymer dissolved in a water-miscible solvent to gold AuNPs dispersed in water. This method represents a simplification of the preparation of polymer-stabilized AuNPs compared with other published methods, in that the AuNPs do not need to be first transferred to an organic solvent. The process enabled the polymer stabilized AuNPs to be easily recovered by filtration or by phase transfer of the AuNPs to an organic solvent in which the RAFT polymer was soluble. The polymer-stabilized AuNPs were characterized by a range of methods including UV-visible spectrophotometry, transmission electron microscopy, thermogravimetric analysis, dynamic light scattering, and attenuated total reflection Fourier transform infrared spectroscopy. Furthermore, 1H pulsed field gradient spin echo NMR was utilized to characterize the self-diffusion of the polymer-stabilized AuNPs. Finally, we then demonstrated that these polymer-stabilized AuNPs maintained their ability to be encoded with surface-enhanced Raman spectroscopy reporter molecules.     

Polymer brushes on multiwalled carbon nanotubes by activators regenerated by electron transfer for atom transfer radical polymerization

The synthesis and characterization of multiwalled carbon nanotube (MWCNT) polymer brushes produced by activators regenerated by electron transfer (ARGET) in atom‐transfer radical polymerization (ATRP) was discussed. The polymer brushes were synthesized by esterification of the MWCNT carboxylic acid groups with hydroxyethyl‐2‐bromoisobutyrate and subsequently used in ARGET ATRP. This created a well defined living polymer brush carbon nanotube of comparatively low polydispersity and a polymer layer 10 nm thick. As, ARGET ATRP uses only minute concentrations of copper (II) catalyst, and is less sensitive to air compared to other living polymerization techniques, this process is a more industry‐compatible route for the commercialization of such materials. The structural and chemical properties were explored by a range of techniques including high resolution transmission electron microscopy, gel permeation chromatography, elemental analysis, Fourier transform infrared spectroscopy, thermogravimetric analysis, and differential scanning calorimetry. In addition, the polymer brush nanotubes were explored for their potential use in films and as fillers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011