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Mathematical modelling and optical emission spectroscopy are applied to study the effect of the chamber pressure on the structure and properties of supersonic plasma jets formed by a direct current arc. In this installation the plasma is created inside the nozzle where the flow is accelerated. As a result some deviation from thermal and ionization equilibrium can be found, even at the working chamber inlet. In this paper, by means of a two-temperature model, we study the argon jet flow using the data of the emission spectroscopy measurements to make realistic assumptions about the inlet boundary conditions. The results show that, when the chamber pressure is low, a strongly underexpanded jet with a Mach disc is formed. For the higher ambient pressure values, the core region of the jet changes to a mildly underexpanded structure with alternating oblique expansion and compression zones. The predicted shock zone positions are in a very good agreement with measurement. The general analysis shows that the deviation from local thermodynamic equilibrium in the jet is inversely related to the chamber pressure. Along the jet core the deviation from thermal equilibrium is less in the shock regions than in the expansion zones, where the electrons are heated by three-particle recombination. Downstream of the jet core the velocity drops, but the ionization and thermal equilibria are not attained because of the correlation between the characteristic recombination and the hydrodynamic times. Both the modelling and the emission spectroscopy show that the axial electron number density is much closer to its frozen value than to equilibrium value. The results obtained are helpful for different applications such as plasma processing, rocket propulsion systems and the simulation of re-entry conditions.

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Polymerization Compounding (PC) offers the possibility to design composite materials by controlling the architecture of a grafted polymer on the surface of solid substrates to be incorporated in a polymer matrix. The approach consists in involving the surface of a reinforcement in a polymerization process of a polymer to be used either as a matrix in the final composite or else as a special surface treatment to enhance solid/polymer interface properties in the composite. The PC process is illustrated here with fumed silica as a solid substrate and polyurethane as a matrix. The hydroxyl sites on silica particles were reacted consecutively with a toluene diisocyanate (TDI) compound and then with either bis‐phenol‐A (BA) or hydroxy‐terminated polybutadiene (HTPB) in order to obtain the desired coating. Soxhlet extractions were conducted to confirm grafting of the polymer on the solid surface. The amount of grafted polymer was evaluated by thermogravimetric analysis. Modified particles were incorporated into HTPB/TDI compounds at concentrations as high as 25% w/w. Water absorption, thermorheological as well as mechanical properties all show clear contribution of the improved bonding between the solid phase and the binder. POLYM. ENG. SCI. 46:360–371, 2006. © 2006 Society of Plastics Engineers

The aim of this work is to perform the polymerization compounding to improve the properties of Kevlar/PE composites. The approach consists in involving the surface of a reinforcement in a polymerization process of a polymer to be used either as a matrix in the final composite or as a special surface treatment to enhance solid/polymer interface properties in the composite. The polymerization compounding process is illustrated here with the polyaramid fibers as reinforcements and polyethylene as a matrix. The number of active sites on the fiber surface, initially insufficient to anchor the catalyst, were increased by a hydrolysis reaction prior to the polymerization. The anchored catalyst was subsequently used to conduct the Ziegler-Natta polymerization reaction of ethylene. The modified fibers were incorporated into the polyethylene resin to produce composites at fiber concentrations as high as 15 wt%. The morphology of the fibers and the composites was tested using electron microscopy. Finally, the mechanical properties of the composites (in impact and tensile tests) were measured to characterize the properties of model composites. POLYM. COMPOS., 27: 129 -137, 2006.

A smart stretchable material is developed from a composite of carbon nanotube (CNT) and fluoroelastomer (FKM), which is fabricated via an internal melt‐mixer method. A unique, double‐percolated, electrically conductive network is observed with ultralow percolation thresholds of 0.45 phr and 1.40 phr CNT. This provides the CNT/FKM nanocomposites with a wide range of strain sensitivity. Thin‐film nanocomposites at the first plateau of conductivity show an ultrahigh sensitivity with a gauge factor (GF) of 1010 at 23% strain for 0.6 phr and of 6750 at 34% strain for 1 phr. At the second plateau of conductivity, 1.5 phr nanocomposite corresponds to higher levels of strain of 78% strain with ultrahigh GF of more than 4 × 104 and 2 phr nanocomposite to almost 100% strain with GF of 1.3 × 105. The CNT/FKM nanocomposites possess a high elongation at break of 430% and up to 232% strain sensitivity. The unique distribution of CNTs in the polar fluoroelastomer FKM facilitates simultaneous high sensitivity and high stretchability, and improved mechanical strength over reported polymer‐based nanocomposite stretchable sensors. The novel, stretchable CNT‐based FKM conductors have great potential for wearable electronics such as stretchable sensors, stretchable light‐emitting diodes (LEDs), and human motion monitoring.

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IntroductionThe advent of metal flow-diverting stents has provided neurointerventionalists with an option for treating aneurysms without requiring manipulations within the aneurysm sac. The large amount of metal in these stents, however, can lead to early and late thrombotic complications, and thus requires long-term antiplatelet agents. Bioabsorbable stents have been postulated to mitigate the risk of these complications. Here we present early data on the first self-expandable primarily bioabsorbable stent for aneurysms.MethodsBraided stents were developed using poly-L-lactic acid fibers with material surface area similar to metal flow diverters. Crush resistance force, hemolysis, and thrombogenicity were determined and compared with existing commercial devices. Stents were deployed in infra-renal rabbit aortas to determine angiographic side branch patency and to study neointima formation for a 1-month follow-up period.ResultsCrush resistance force was determined to be on the order of existing commercial devices. Hemolytic behavior was similar to existing metal devices, and thrombogenicity was lower than metal flow-diverting stents. A smooth neointimal layer was found over the absorbable stent surface and all covered side branches were patent at follow-up.ConclusionThe design of self-expanding primarily bioabsorbable flow-diverting stents is possible, and preliminary safety data is consistent with a favorable profile in terms of mechanical behavior, hemocompatibility, side branch patency, and histological effects. Additional in vitro and long-term in vivo studies are in progress and will help determine aneurysm occlusion rates and absorption characteristics of the stent.