Effect of moisture and filler content on the structural,thermal and dielectric properties of polyamide‐6/boehmite alumina nanocomposites

Polyamide‐6 (PA‐6)/boehmite alumina (BA) nanocomposites were prepared via direct melt compounding. Structural, thermal and dielectric properties of ‘as‐received’ (including moisture) and ‘dried’ (thermally treated) specimens were examined. The BA nanofiller was homogeneously dispersed in the PA‐6 matrix. XRD and FTIR revealed that crystallization of PA‐6 in the γ phase was favoured over α phase with increasing BA content. The crystallinity index (CI) and the percentage of α and γ phases were also evaluated. Dried specimens exhibited a lower CI than as‐received specimens while the CI decreased with the addition of filler. Broadband dielectric spectroscopy revealed the presence of γ, β and α relaxations, the Maxwell–Wagner–Sillars effect and the contribution of conductivity relaxation in the as‐received samples. The drying procedure unmasked a double feature of both β and α modes. The results of the complementary techniques were analysed and the effects of moisture and/or the incorporation of BA nanofiller on the microstructure of the PA‐6 matrix are disclosed. © 2019 Society of Chemical Industry     

Optimizing the front end test stand high performance H- ion source at RAL

The aim of the front end test stand project is to demonstrate that chopped low energy H(-) beams of high quality can be produced. The beam line currently consists of the ion source, a 3 solenoid low energy beam transport and a suite of diagnostics. A brief status report of the radio frequency quadrupole is given. This paper details the work to optimize the ion source performance. A new high power pulsed discharge power supply with greater reliability has been developed to allow long term, stable operation at 50 Hz with a 60 A, 2.2 ms discharge pulse and up to 100 A at 1.2 ms. The existing extraction power supply has been modified to operate up to 22 kV. Results from optical spectroscopy measurements and their application to source optimization are summarized. Source emittances and beam currents of 60 mA are reported.     

Three-dimensional distributions of elements in biological samples by energy-filtered electron tomography

By combining electron tomography with energy-filtered electron microscopy, we have shown the feasibility of determining the three-dimensional distributions of phosphorus in biological specimens. Thin sections of the nematode, Caenorhabditis elegans were prepared by high-pressure freezing, freeze-substitution and plastic embedding. Images were recorded at energy losses above and below the phosphorus L2,3 edge using a post-column imaging filter operating at a beam energy of 120 keV. The unstained specimens exhibited minimal contrast in bright-field images. After it was determined that the specimen was sufficiently thin to allow two-window ratio imaging of phosphorus, pairs of pre-edge and post-edge images were acquired in series over a tilt range of +/-55 degrees at 5 degrees increments for two orthogonal tilt axes. The projected phosphorus distributions were aligned using the pre-edge images that contained inelastic contrast from colloidal gold particles deposited on the specimen surface. A reconstruction and surface rendering of the phosphorus distribution clearly revealed features 15-20 nm in diameter, which were identified as ribosomes distributed along the stacked membranes of endoplasmic reticulum and in the cytoplasm. The sensitivity of the technique was estimated at < 35 phosphorus atoms per voxel based on the known total ribosomal phosphorus content of approximately 7000 atoms. Although a high electron dose of approximately 10(7)e/nm2 was required to record two-axis tilt series, specimens were sufficiently stable to allow image alignment and tomographic reconstruction.     

Spectral element method for stability analysis of milling processes with discontinuous time-periodicity

This paper presents an application of the spectral element method for the stability analysis of regenerative machine tool chatter models in milling operations. An extension of the spectral element method is introduced in order to handle the discontinuities in the cutting force in an efficient way. The efficiency of the method is demonstrated on some well-known machine tool chatter models taken from the literature. Efficiency is characterized by the computational time, the convergence of the stability boundaries, and the convergence of critical characteristic multipliers. Results show that compared to the most widespread methods in machining literature, the spectral element method provides significant improvements in computational time while maintaining high accuracy levels.     

Shaping binary metal nanocrystals through epitaxial seeded growth

Morphological control of nanocrystals has become increasingly important, as many of their physical and chemical properties are highly shape dependent. Nanocrystal shape control for both single- and multiple-material systems, however, remains empirical and challenging. New methods need to be explored for the rational synthetic design of heterostructures with controlled morphology. Overgrowth of a different material on well-faceted seeds, for example, allows for the use of the defined seed morphology to control nucleation and growth of the secondary structure. Here, we have used highly faceted cubic Pt seeds to direct the epitaxial overgrowth of a secondary metal. We demonstrate this concept with lattice-matched Pd to produce conformal shape-controlled core-shell particles, and then extend it to lattice-mismatched Au to give anisotropic growth. Seeding with faceted nanocrystals may have significant potential towards the development of shape-controlled heterostructures with defined interfaces.     

Cyclohexene dehydrogenation and hydrogenation on Pt(111) monitored by SFG surface vibrational spectroscopy: different reaction mechanisms at high pressures and in vacuum

The hydrogenation and dehydrogenation reactions of cyclohexene on Pt(111) crystal surfaces were investigated by surface vibrational spectroscopy via sum frequency generation (SFG) both under vacuum and high pressure conditions with 10 Torr cyclohexene and various hydrogen pressures from 30 up to ~600 Torr. At high pressures, the gas composition and turnover rate (TOR) were measured by gas chromatography. In vacuum, cyclohexene on Pt(111) undergoes a change from π/σ‐bonded, σ‐bonded cyclohexene and c‐C₆H₉ surface species to adsorbed benzene when the surface was heated from 130 to 330 K. A site‐blocking effect was observed at saturation coverage of cyclohexene that caused dehydrogenation to shift to somewhat higher surface temperature. At high pressures, however, none of the species observed in vacuum conditions were detectable. 1,4‐cyclohexadiene (1,4‐CHD) was found to be the major species on the surface at 295 K, even with the presence of nearly 600 Torr of hydrogen. Hydrogenation was the only detectable reaction at the temperature range between 300 and 400 K with 1,3‐cyclohexadiene (1,3‐CHD) on the surface, as revealed by SFG. Further increasing the surface temperature results in a decrease in hydrogenation reaction rate and an increase in dehydrogenation reaction rate and both 1,3‐CHD and 1,4‐CHD were present on the surface simultaneously. The simultaneous observation of the reaction kinetic data and the chemical nature of surface species allows us to postulate a reaction mechanism at high pressures: cyclohexene hydrogenates to cyclohexane via a 1,3‐CHD intermediate and dehydrogenates to benzene through both 1,4‐CHD and 1,3‐CHD intermediates. Isomerisation of the 1,4‐CHD and 1,3‐CHD surface species is negligible. This revised version was published online in July 2006 with corrections to the Cover Date.     

Fracture toughness assessment of poly(ethylene terephthalate) blends with glycidyl methacrylate modified polyolefin elastomer using essential work of fracture method

The static fracture toughness of poly(ethylene terephthalate) (PET) melt blended with a modifier containing glycidyl methacrylate (GMA)‐grafted ethylene‐propylene rubber and homopolymerized GMA was studied on injection molded specimens by adopting the essential work of fracture (EWF) method. It was found that the essential and nonessential or plastic work both decrease with an increasing amount of modifier (up to 20 wt %) if the PET matrix is amorphous and nonaged. The scatter in the EWF data for the blend with 10 wt % modifier was found by presuming concurrent mechanisms between microcrystallization and morphology‐dependent cavitation and fibrillation processes. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 842–852, 2001     

Macromolecular Engineering via Carbocationic Polymerization: Branched Structures,Block Copolymers and Nanostructures

This article features macromolecular engineering via carbocationic polymerization, the focus of research of the recently established Macromolecular Engineering Research Centre (MERC) at the University of Western Ontario. The fundamental philosophy of MERC is interdisciplinary research with a strong industrial orientation, while emphasizing the quest for fundamental understanding of polymerization processes and polymer structure‐property relationships. First, a brief overview of living polymerizations in general, and living carbocationic polymerizations in particular will be given. This latter technique is of interest because some monomers (e. g., isobutylene) can be polymerized by cationic techniques only, to yield polymers with unique properties (e. g., polyisobutylene with superior chemical and oxidative stability, low permeability and high damping). This will be followed by an overview of our research strategy and a summary of our latest results. These include the development of a fiber‐optic mid‐FTIR method for the real‐time monitoring of low temperature polymerization processes, the discovery that selected epoxides initiate effectively the living carbocationic polymerization of isobutylene, fundamental studies into the mechanism and kinetics of living carbocationic polymerization, and the design and synthesis of various polymer architectures (e. g., branched homo‐ and block copolymers) with improved properties and nanostructured phase morphologies.     

Hygrothermal aging and fracture behavior of styrene‐acrylonitrile/acrylate based core–shell rubber toughened poly(butylene terephthalate)

A study of hygrothermal aging in terms of the kinetics of moisture absorption by poly(butylene terephthalate) (PBT) and styrene‐acrylonitrile/acrylate based core–shell rubber (CSR) toughened PBT (PBT‐CSR) was undertaken. The diffusion of water into the PBT compounds with various CSR contents was investigated by immersion of specimens in water at temperatures between 30 and 90°C. It was observed that the equilibrium moisture content and the diffusion coefficient of the PBT both increased with increasing CSR content. The fracture behaviors of the PBT and PBT‐CSR were investigated. The focus of investigation was on the effect of an internal parameter (rubber content) and external parameters (testing temperature, deformation rates, and hygrothermal aging) on the fracture behavior of these materials. The fracture response of the various materials was evaluated by the fracture toughness and energy measured on static‐loaded compact tension specimens. The tensile and fracture behavior of PBT and PBT‐CSR was affected by both the internal and external parameters. On its own the CSR impact modifier failed to improve the toughness of PBT at either high testing speed or subambient temperature (−40°C). Based on the dynamic mechanical analysis study, the CSR is believed to behave as a rigid particulate filler in the PBT that consequently reduces the ductility of the PBT. All the materials tested showed poor retention of the tensile and fracture properties upon exposure to hygrothermal aging at 90°C, and these properties could not be restored by subsequent drying. This was attributed to severe hydrolytic degradation of the PBT that caused permanent damage to the materials. The failure modes of PBT and PBT‐CSR were assessed by fractographic studies in a scanning electron microscope. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2470–2481, 1999     

Relationship between the properties of polyisobutenyl succinic anhydrides and their additive derivatives

Engine oils today include detergency dispersancy additives to keep the engine clean, hold insolubles in dispersion, and neutralise acidic compounds. This paper describes the synthesis of a type of detergent-dispersant based on polyisobutenyl succinimides. The type and route of synthesis influence the molecular structure, performance, and applicability of the synthesised compounds. In particular, the average molecular weight of the polyolefin chain of the intermediates used has a decisive effect. A newly developed intermediate allows the preparation of polysuccinimides with a polymeric structure.