Search

The issue of plastic pollution in the marine environment is of increasing global concern. As plastics typically have an intrinsic durability, water insolubility and slow degradation rates, debris has now become both ubiquitous and persistent in the marine environment. Overtime, plastic ultimately result in the generation of microplastics via photolytic, thermal and biological degradation processes. Although the potential threat of microplastics on marine ecosystems is well recognized, there is no baseline data available for the Arabian Gulf. The Environmental Science Center of Qatar University has now documented the first evidence for the prevalence of microplastics within the Arabian Gulf, specifically in the marine waters of Qatar Exclusive Economic Zone (EEZ). Qatar has an arid climate and is situated midway along the western coast of the semi-enclosed Arabian Gulf. Qatar's coastline is particularly susceptible to marine debris due to the county's rapid urbanization and economic development. Surface seawater samples were collected from 12 stations during May 2015 research cruise of the RV Janan. An optimized and validated protocol was developed for the extraction of microplastics from plankton-rich samples without loss of microplastics present. Plankton present in seawater samples may readily mask the identification of microplastics and lead to an underestimation of the quantity of microplastics present. The protocol involved sample digestion using solutions of 1M NaOH, 10M NaOH, and 16M HNO3 in conjunction at different temperatures. Twenty mL of each solution was spiked with known quantities of reference polymer pellets, of varying diameters (63 μm to 4.70 mm) and used to digest the plankton biomass. The use of 1M NaOH proved to be a more efficient digestion treatment than 10M NaOH and 16M HNO3 solutions. Although 10M NaOH, and 16M HNO3 have been proven effective to mineralize plankton biomass, these solutions also resulted in some structural damage and discoloration of reference polymers with a low pH tolerance: polyvinyl alcohol, polyvinyl chloride, polystyrene, polyethylene, and nylon. After extraction, the microplastics were characterized using Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopy. In total 30 microplastics were isolated from the mineralized samples, with an average concentration of 0.71 particles m− 3 (range 0–3 particles m− 3). Nine out of 30 were identified as polypropylene, with the majority either granular, sizes ranging from 125 μm to 1.82 mm, or fibrous, sizes from 150 μm to 15.98 mm. Microplastics were more prevalent in areas where nearby anthropogenic activities, including oil-rig installations and shipping operations, are present.

Equal channel angular pressing (ECAP) is currently being widely investigated because of its potential to produce ultra-fine grained microstructures in metals and alloys. A sound knowledge of the plastic deformation and strain distribution is necessary for understanding the relationships between strain inhomogeneity and geometry of die. Considerable research has been reported on finite element analysis of this process, assuming 2D plane strain condition. The 2D models are not suitable due to the component geometry, especially for workpiece with cylindrical cross-section. In the present work 3D simulation of ECAP process was carried out, using ABAQUS/Standard software, for different channel angles for a strain hardening aluminium alloy (AA6101). Strain inhomogeneity is presented and discussed for all cases. Pattern of variation of strain along some selected radial lines in steady-state zone is presented. � 2008 Elsevier B.V. All rights reserved.

Design against fatigue requires thorough understanding of the underlying fatigue mechanisms and factors influencing them. The objective of the present work is to study the effect of nanoclay addition on the temperature rise and modulus drop during cyclic loading in polyamide-6 and polyamide-6 base nanocomposite. Isocyclic stress strain curves were used to understand the deformation characteristics of test materials. Polyamide-6 samples exhibited necking and continuous temperature rise until fracture at high stress levels investigated. Addition of nanoclay improved the modulus retention compared to pristine polymers. Nanocomposite samples sustained more than 105 cycles at all stress levels investigated. The performance improvement due to the addition of nanoclay is attributed to decrease in the cyclic strain amplitude at a given stress level which results in reduced hysteresis heating compared to polyamide-6. � 2008 Elsevier Ltd. All rights reserved.

A new dinuclear silver(I)-saccharinato (sac) complex with acetonitrile (MeCN), [Ag-2(sac)(2)(MeCN)(2)](n) has been synthesized and characterized by elemental analysis, IR spectroscopy and single crystal X-ray diffraction. The silver(I) ions are doubly bridged by two sac ligands, leading to a short argentophilic contact of 2.9074(3) angstrom. Each silver(I) ion exhibits a square-planar coordination geometry including the Ag-Ag bonds. The individual dimeric molecules are extended into a two-dimensional layered structure by weak Ag center dot center dot center dot Csac(eta(2)) interactions of ca. 3.2 angstrom. These interactions were discussed and compared with those found in the first silver(I)-sac complex [Ag(sac)](n).

Rotational Isomeric State (RIS) Metropolis Monte Carlo (RMMC) simulations of the conformational properties and chain dimensions of a series of chemically different poly(n-alkyl methacrylates) including poly(methyl methacrylate), poly(n-butyl methacrylate), poly(n-hexyl methacrylate), and poly(phenyl methacrylate), in the state were investigated, and (r2/M)1/2, (s2/M)1/2 and Cn were calculated and compared in order to obtain fundamental understanding of the influence of the chemical structure. Simulations were conducted for different molecular weights. Results obtained from the simulations are compared with experimentally obtained dimensions in the literature using the Mark-Houwink relationship as well as, in some cases, data available from direct determinations in solvents. Good agreement between simulation and experimental data was obtained. The backbone conformation is predominantly trans in these polymers. Increase in bulkiness and rigidity of the substituting acrylate side group results in an increase in trans and a decrease in gauche backbone conformer population. In the case of rotatable bonds in the side-group structure, increase in rigidity of the side group leads to a decrease in the trans population, although this effect is not uniformly observed.

The most significant problem of electron paramagnetic resonance (EPR) fingernail dosimetry is the presence of two signals of non-radiation origin that overlap the radiation-induced signal (RIS), making it almost impossible to perform dose measurements below 5 Gy. Historically, these two non-radiation components were named mechanically induced signal (MIS) and background signal (BKS). In order to investigate them in detail, three different methods of MIS and BKS mutual isolation have been developed and implemented. After applying these methods, it is shown here that fingernail tissue, after cut, can be modeled as a deformed sponge, where the MIS and BKS are associated with the stress from elastic and plastic deformations, respectively. A sponge has a unique mechanism of mechanical stress absorption, which is necessary for fingernails in order to perform its everyday function of protecting the fingertips from hits and trauma. Like a sponge, fingernails are also known to be an effective water absorber. When a sponge is saturated with water, it tends to restore to its original shape, and when it loses water, it becomes deformed again. The same happens to fingernail tissue. It is proposed that the MIS and BKS signals of mechanical origin be named MIS1 and MIS2 for MISs 1 and 2, respectively. Our suggested interpretation of the mechanical deformation in fingernails gives also a way to distinguish between the MIS and RIS. The results obtained show that the MIS in irradiated fingernails can be almost completely eliminated without a significant change to the RIS by soaking the sample for 10 min in water. The proposed method to measure porosity (the fraction of void space in spongy material) of the fingernails gave values of 0.46-0.48 for three of the studied samples. Existing results of fingernail dosimetry have been obtained on mechanically stressed samples and are not related to the "real" in vivo dosimetric properties of fingernails. A preliminary study of these properties of pre-soaked (unstressed) fingernails has demonstrated their significant difference from fingernails stressed by cut. They show a higher stability signal, a less intensive non-radiation component, and a nonlinear dose dependence. The findings in this study set the stage for understanding fingernail EPR dosimetry and doing in vivo measurements in the future. © 2008 Springer-Verlag.

The final publication is available at Springer via http://10.1007/s10853-014-8408-8 Among different strategies to reduce costs in microalgae dewatering process via cross-flow filtration, the one related to membrane material was investigated in order to be decreased. Several materials were tested, starting with the ones commonly used in membrane technology [ceramic, polysulfone (PSf) and polyacrylonitrile (PAN)] to the ones generally employed in packaging industry [acrylonitrile butadiene styrene (ABS), glycol-modified polyethylene terephthalate (PETG) and polylactic acid (PLA)], the latter being considerably cheaper. Experiments carried out showed promising results in terms of permeabilities for PSf-Pluronic® F127 blended membranes and PAN membranes (11 ± 1 L/h/m2/bar and 22 ± 1 L/h/m 2/bar, respectively, instead of 2 ± 2 L/h/m2/bar of PSf membranes), but with high related costs. PLA membranes showed good mechanical properties, biodegradability and price, but low permeability values (5 ± 1 L/h/m2/bar). PETG membranes showed attractive results in terms of costs and permeability, but poor mechanical properties. The polymer that offered the best results was the ABS that reached membrane permeabilities of 19 ± 1 L/h/m2/bar, maintaining good mechanical properties while filtering the microalgae Phaeodactylum tricornutum Bohlin. Thus, a novel functionality was found for these not so common polymers in microalgae dewatering. This indicates that use of these materials could also be considered in other aqueous micro/ultrafiltration applications. In addition, the biodegradable PLA polymer introduces a new concept of cheap and environmental friendly membrane in this application. © 2014 Springer Science+Business Media New York.

ABS was melt grafted with maleic anhydride at three different levels of 1, 2, and 3 wt %. These three different modified ABSs were melt blended with polycarbonate using a single-screw extruder to choose a suitable maleic anhydride grafting level on ABS for better performance. For the compatibility study, binary blends of polycarbonate with ABS and maleic anhydride-grafted ABS were prepared over the entire range of compositions. Compatibility of these blends was studied using a Dynamic Mechanical Analyzer and by Differential Scanning Calorimetry. Both techniques suggest more partial compatibility for modified blend systems. In addition to this, DSC thermograms show multiple peaks between the transition points of ABS fractions and polycarbonate fractions for the polycarbonate/maleic anhydride-grafted ABS blends. These multiple peaks are characteristic of better partial compatibility with fine microstructure.

This paper describes the design and the manufacturing of a Cubesat platform based on a plastic structure. The Cubesat structure has been realized in plastic material (ABS) using a “rapid prototyping” technique. The “rapid prototyping” technique has several advantages including fast implementation, accuracy in manufacturing small parts and low cost. Moreover, concerning the construction of a small satellite, this technique is very useful thanks to the accuracy achievable in details, which are sometimes difficult and expensive to realize with the use of tools machine. The structure must be able to withstand the launch loads. For this reason, several simulations using an FEM simulation and an intensive vibration test campaign have been performed in the system development and test phase. To demonstrate that this structure is suitable for hosting a complete satellite system, offering innovative integrated solutions, other subsystems have been developed and assembled. Despite its small size, this single unit (1U) Cubesat has a system for active attitude control, a redundant telecommunication system, a payload camera and a photovoltaic system based on high efficiency solar cells. The developed communication subsystem has small dimensions, low power consumption and low cost. An example of the innovations introduced is the antenna system, which has been manufactured inside the ABS structure. The communication protocol which has been implemented, the AX.25 protocol, is mainly used by radio amateurs. The communication system has the capability to transmit both telemetry and data from the payload, in this case a microcamera. The attitude control subsystem is based on an active magnetic system with magnetorquers for detumbling and momentum dumping and three reaction wheels for fine control. It has a total dimension of about 50×50×50 mm. A microcontroller implements the detumbling control law autonomously taking data from integrated magnetometers and executes pointing maneuvers on the basis of commands received in real time from ground. The subsystems developed for this Cubesat have also been designed to be scaled up for larger satellites such as 2U or 3U Cubesats. The additional volume can be used for more complex payloads. Thus the satellite can be used as a low cost platform for companies, institutions or universities to test components in space.

Submitted by Vitor Silverio Rodrigues (vitorsrodrigues@reitoria.unesp.br) on 2014-05-27T11:23:35Z No. of bitstreams: 0Bitstream added on 2014-05-27T14:46:13Z : No. of bitstreams: 1 2-s2.0-54549121437.pdf: 885557 bytes, checksum: 38cf2d9fe5a3b52d357d251a082df3a4 (MD5) Made available in DSpace on 2014-05-27T11:23:35Z (GMT). No. of bitstreams: 0 Previous issue date: 2008-07-01 Item merged in doublecheck by Felipe Arakaki (fe.arakaki@gmail.com) on 2015-11-11T12:00:30Z Item was identical to item(s): 69942, 9193 at handle(s): http://hdl.handle.net/11449/70460, http://hdl.handle.net/11449/9444 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Fiber-metal laminates (FML) composed of alternating layers of unidirectional fibers-reinforced plastic (FRP) laminae and aluminum-alloy sheets offer some superior mechanical properties, compared with either conventional laminates consisting of only, FRP laminae or high-strength monolithic aluminum alloys. The environmental factors can limit the applications of composites by deteriorating the mechanical properties during service. Usually, polymeric matrix absorbs moisture when exposed to humid environments and metals are prone to surface corrosion. on the other hand, FML laminates presents more resistance of moisture when compared with their constituents. Evaluation of shear properties is particularly important in the design of mechanically, fastened parts and components, which are subject to parallel and opposing loads. In this work, the shear behavior was studied for Glare laminates and its constituents in dry and wet conditions. UNESP Dept. of Materials and Technology, Guaratinguetá, SP CTA-IAE Materials Division, Säo José dos Campos, SP UNESP Dept. of Materials and Technology, Guaratinguetá, SP FAPESP: 05/54358-7 FAPESP: 03/04240-4 CNPq: 306053/2006-3

Different polymeric materials have been prepared from the organogels formed by a polymerizable methacrylic mixture (methyl methacrylate/ethylene glycol dimethacrylate, 1:1, w/w) and the macrocyclic pseudopeptide 1. The use of (2,4,6-trimethylbenzoyl)diphenylphosphine oxide as a very efficient radical initiator allows polymeric materials in which the structure of the fibrils formed by self-assembly of the organogelator 1 is truly preserved to be obtained. Removal of the pseudopeptidic molecule provides materials with a porous structure reflecting that of the original self-assembled fibrils. The use of fluorescent probes such as rhodamine B and pyrene greatly facilitate the study of the porous structures formed and, accordingly, that of the morphology of the original fibrils. Those studies reveal the presence of a permanent porosity and the organization of the substructures as a porous network. This confirms the existence of a nucleation and growth mechanism for the generation of the fibrils, giving rise to the formation of spherulitic structures. Those spherulites are additionally linked by connections of variable size. A series of diffusion experiments allowed establishment of a direct dependence of the inner porosity of the materials on the amount of self-organizing template used for their preparation.

The nature of the charge carriers in conducting organic polymers (COPs) is a long standing problem. Polythiophene is one of the prototypes of COPs and intensively studied. Because doping leads to changes in UV/vis spectra that are characteristic of the absorbing species, UV/vis spectra of charged thiophene oligomers with up to 25 rings were calculated with time-dependent density functional theory. The credibility of the method was established by comparing the results with a variety of theoretical levels and with experiment. Effects due to counterions (Cl3-) and solvent (CH 2Cl2) were examined. It was found that TDDFT employing hybrid functionals is accurate enough to distinguish the absorbing species. The findings offer an explanation for the experimentally observed difference in UV-spectra of medium-sized and long oligomers upon doping. As chain lengths of the oligomers increase and energy levels get closer, configuration interaction leads to additional absorption peaks in the high energy sub-band region (at around 1.5-2.5 eV). Thus, long oligomers do not behave differently from medium-sized ones upon doping, only their spectra are different. At low doping levels radical cations (polarons) are produced. At higher doping levels, dications that harbor weakly interacting polaron pairs are formed. Bipolarons are predicted only on very short chains or at high doping levels. There is no bipolaron binding energy and disproportionation of monocations into dications and neutral species is energetically unfavorable. © 2008 American Chemical Society.

Small molecule sorption and desorption in and out of polyacrylamide (PAAm) gels were studied at various temperatures. Pyranine (P(y)) dissolved in water used as a probe. Fluorescence emission intensity, I(p) from P(y) was monitored for studying sorption and desorption processes. Scattered light intensities, I(SC) from PAAm gel was also monitored to observed structural variations during sorption and desorption process. Li-Tanaka model was applied to produce the swelling time constants, tau(C) and sorption coefficients, D(C) for the swelling processes. on the other hand, sorption and desorption processes were studied and coefficients were produced by using Fickian model. Related activation energies were also calculated from the corresponding physical processes. Publisher's Version Q3 WOS:000256716900012

Polyethylene glycol) (PEG)-containing quasi-model amphiphilic polymer conetworks (APCNs) were prepared by reversible addition fragmentation chain transfer (RAFT) polymerization using α,ω-bis(2-cyanoprop-2-yl dithiobenzoate)-PEG as a bifunctional RAFT macrochain transfer agent (macro-CTA) and stepwise additions of a hydrophobic monomer and a crosslinker (crosslinker: macro-CTA = 10:1, reaction time 24 h). Three different types of monomers, methyl methacrylate (MMA), n-butyl acrylate and styrene, were employed as the hydrophobic monomers, whereas ethylene glycol dimethacrylate, ethylene glycol diacrylate and 1,4-divinylbenzene served as the respective crosslinkers. PEG homopolymer hydrophilic quasi-model networks were also prepared by RAFT-polymerizing the three crosslinkers directly onto the two active ends of the PEG-based macro-CTA. From the three ABA triblock copolymers prepared, the MMA-containing one was obtained at the highest polymerization yields. The crosslinking yields of the three ABA triblock copolymers with the corresponding crosslinkers were higher than those of the PEG-based macro-CTA with the same crosslinkers. The degrees of swelling (DSs) of all conetworks were measured in water and in tetrahydrofuran (THF). The DSs of the APCNs in THF were higher than those in water, whereas the reverse was true for the DSs of the hydrophilic homopolymer networks. Finally, the aqueous DSs of the APCNs were lower than those of the corresponding hydrophilic homopolymer networks. © 2008 Wiley Periodicals, Inc. 46 22 7556 7565

The product quality of energetic materials is predominantly determined by the crystallization process applied to produce these materials. It has been demonstrated in the past that the higher the product quality of the solid energetic ingredients, the less sensitive a plastic bonded explosive containing these energetic materials becomes. The application of submicron or nanometric energetic materials is generally considered to further decrease the sensitiveness of explosives. In order to assess the product quality of energetic materials, a range of analytical techniques is available. Recent attempts within the Reduced-sensitivity RDX Round Robin (R4) have provided the EM community a better insight into these analytical techniques and in some cases a correlation between product quality and shock initiation of plastic bonded explosives containing (RS-)RDX was identified, which would provide a possibility to discriminate between conventional and reduced sensitivity grades. In this paper experimental results of two relatively new crystallization techniques are shown. Submicron and nanometric RDX particles have been produced and characterized. Also results on the characterization of different commercial RDX grades will be shown, including data related to a part of the samples received within the R4 programme. Finally, experimental data will be presented and discussed on insensitive plastic bonded explosives (PBXs). © 2008 WILEY-VCH Verlag GmbH & Co. KGaA.

The swelling and diffusion characteristics of a polar polymer [ethylene vinyl acetate (EVA)] and a nonpolar polymer [low-density polyethylene (LDPE)] were studied with swelling experiments of the polymers in asphalt at different temperatures. The study showed that the diffusion mechanisms for LDPE and EVA were different and temperature-dependent. In the case of LDPE, the observed diffusion was anomalous at both swelling temperatures (70 and 90°C). LDPE at 90°C showed sigmoidal solvent-uptake behavior during the initial period of swelling and a sorption overshoot in a later period. EVA showed Fickian transport at 60°C and anomalous diffusion at a higher swelling temperature (70°C) with sigmoidal uptake behavior. An analysis of the diffusion coefficients and the Fourier transform infrared results showed that the diffusing molecules were different in the case of LDPE and EVA, and there were possible polymer–asphalt interactions. Differential scanning calorimetry and swelling studies showed that penetrant-induced crystallization affected the diffusion process in the case of LDPE. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

A study was conducted to determine the core functionality of well-defined covalent polymer networks with precisely located cleavable sites. Covalent polymer networks consists of chemically interconnected polymer chains that are insoluble in all solvents. The core functionality of these networks includes, the elastic chain length and the composition. The study used a cleavable bifunctional initiator for network synthesis and the incorporation of initiator in the middle of the polymer chain. The study found that the cleavage of the initiator in the network can convert them to carboxylic acid end-functional star polymers. The degradable linear polymers of methyl methacrylate (MMA) were synthesized by ground transfer polymerization (GTP) to test the tetraacetal initiator for polymerization and hydrolysis. 41 16 5957 5959

This work describes the fabrication, characterization, and biological evaluation of a thin protein-resistant poly(ethylene glycol) (PEG)-based hydrogel coating for antifouling applications. The coating was fabricated by free-radical polymerization on silanized glass and silicon and on polystyrene-covered silicon and gold. The physicochemical properties of the coating were characterized by infrared spectroscopy, ellipsometry, and contact angle measurements. In particular, the chemical stability of the coating in artificial seawater was evaluated over a six-month period. These measurements indicated that the degradation process was slow under the test conditions chosen, with the coating thickness and composition changing only marginally over the period. The settlement behavior of a broad and diverse group of marine and freshwater fouling organisms was evaluated. The tested organisms were barnacle larvae (Balanus amphitrite), algal zoospores (Ulva linza), diatoms (Navicula perminuta), and three bacteria species (Cobetia marina, Marinobacter hydrocarbonoclasticus, and Pseudomonas fluorescens). The biological results showed that the hydrogel coating exhibited excellent antifouling properties with respect to settlement and removal. © 2008 American Chemical Society.

Interfacial polycondensation (IP) is an important technique used in the encapsulation of a variety of active ingredients and synthesis of thin film composite membranes. The present work seeks to advance our understanding of the mechanisms underlying the reaction, phase separation and film formation in this process, and hence, of how the film properties are influenced by preparation conditions. The model presented here incorporates all the essential physicochemical processes at a fundamental level through simple phenomenologies: ionic equilibria in the aqueous phase, resistances due to external mass transfer, diffusion through polymer film, interfacial reaction, thermodynamics of phase separation, and formation of a coherent film. The model has been tested against the data previously communicated [S.J. Wagh, Studies in interfacial polycondensation. Ph.D. Thesis. IIT Bombay, 2004; S.J. Wagh, S.S. Dhumal, A.K. Suresh, An experimental study of polyurea membrane formation by interfacial polycondensation, Journal of Membrane Science, submitted for publication] on polyurea microcapsules. The influence of the model parameters and preparation conditions, on the properties of the polymer and film and their development during reaction, have been studied. The study provides important insights into the process and should help in designing synthesis methodologies to suit the application., © Elsevier

The objective was to provide an answer to "how to grow/survive in aggregative physiology" through evaluating the relation between physical stress and observed biomass characteristics. For that, a lab-scale sequencing batch reactor was operated at an anaerobic-aerobic mode and under altered hydraulic selection pressures of settling time (10-1 min) and hydrodynamic shear rates due to mechanical mixing (15.5-12.0cm/s) and/or aeration (1.76-0.24cm/s). Main physical stress experienced by the biomass was mechanical mixing, which resulted in extreme shearing conditions at the first operational stage (days 1-86), during which first granules formed but settling properties deteriorated and biomass was almost totally washed out. After relaxing the overall shear stress at the second stage, biomass formation accelerated, settling properties enhanced and granulation proceeded (days 86-136), until disturbance of the process at the last month of operation (days 136-163). Aggregative physiology-related parameters, being cell surface hydrophobicity and extracellular polymeric substances (EPS), followed increasing trends parallel to the progress of granulation, and then decreased upon disturbance of the process. There was an increase in the EPS production also during the first stage under extreme shear, while a substantial amount of biomass was present in the system. A direct correlation was also found between %hydrophobicity and EPS-composition expressed as ExoPN/ExoPS. © IWA Publishing 2008.

We describe the one-pot synthesis of a large panel of nucleic bases and related compounds from formamide in the presence of iron sulfur and iron-copper sulfur minerals as catalysts. The major products observed are purine, 1H-pyrimidinone, isocytosine, adenine, 2-aminopurine, carbodiimide, urea, and oxalic acid. Isocytosine and 2-aminopurine may recognize natural nucleobases by Watson-Crick and reverse Watson-Crick interactions, thus suggesting novel scenarios for the origin of primordial nucleic acids. Since the major problem in the origin of informational polymers is the instability of their precursors, we also investigate the effects of iron sulfur and iron-copper sulfur minerals on the stability of ribooligonucleotides in formamide and in water. All of the iron sulfur and iron-copper sulfur minerals stimulated degradation of RNA. The relevance of these findings with respect to the origin of informational polymers is discussed.

We use a highly localized resistive heating technique to grow vertically aligned multiwalled nanotube films and aligned single-walled nanotubes on substrates with an average temperature of less than 100 degrees C. The temperature at the catalyst can easily be as high as 1000 degrees C but an extremely high temperature gradient ensures that the surrounding chip is held at much lower temperatures, even as close as 1 mu m away from the local heater. We demonstrate the influence of temperature on the height of multiwalled nanotube films, illustrate the feasibility of sequential growth of single-walled nanotubes by switching between local heaters and also show that nanotubes can be grown over temperature-sensitive materials such as resist polymer. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.2981398]

cited By 9; International audience; Thermoplastic elastomers (TPEs) are block copolymers made up of "hard" (glassy or crystalline) and "soft" (rubbery) blocks that self-organize into "domain" structures at a length scale of a few tens of nanometers. Under typical processing conditions, TPEs also develop a "polydomain" structure at the micron level that is similar to that of metal polycrystals. Therefore, from a continuum point of view, TPEs may be regarded as materials with heterogeneities at two different length scales. In this work, we propose a constitutive model for highly oriented, near-single-crystal TPEs with lamellar domain morphology. Based on small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) observations, we consider such materials to have a granular microstructure where the grains are made up of the same, perfect, lamellar structure (single crystal) with slightly different lamination directions (crystal orientations). Having identified the underlying morphology, the overall finite-deformation response of these materials is determined by means of a two-scale homogenization procedure. Interestingly, the model predictions indicate that the evolution of microstructure-especially the rotation of the layers-has a very significant, but subtle effect on the overall properties of near-single-crystal TPEs. In particular, for certain loading conditions-namely, for those with sufficiently large compressive deformations applied in the direction of the lamellae within the individual grains-the model becomes macroscopically unstable (i.e., it loses strong ellipticity). By keeping track of the evolution of the underlying microstructure, we find that such instabilities can be related to the development of "chevron" patterns. © 2008 Elsevier Ltd. All rights reserved.

WOS: 000260243100001, A new monomer, 4-(thiophen-3-yl methyleneamino)benzene sulfonate) (ThSA), was synthesized and characterized. Electrochemical polymerization of ThSA yields a water-soluble and self-doped polymer (PThSA). This polymer was characterized by FT-IR, NMR, DSC, XRD and conductivity measurements. (C) Koninklijke Brill NV, Leiden, 2008, TUBITAK [104M406], Authors gratefully thank TUBITAK for grant No. 104M406, DOSAP program METU and S. Seyyidoglu for running the XRD Studies.

The product quality of energetic materials is predominantly determined by the crystallization process applied to produce these materials. It has been demonstrated in the past that the higher the product quality of the solid energetic ingredients, the less sensitive a plastic bonded explosive containing these energetic materials becomes. The application of submicron or nanometric energetic materials is generally considered to further decrease the sensitiveness of explosives. In order to assess the product quality of energetic materials, a range of analytical techniques is available. Recent attempts within the Reduced-sensitivity RDX Round Robin (R4) have provided the EM community a better insight into these analytical techniques and in some cases a correlation between product quality and shock initiation of plastic bonded explosives containing (RS-)RDX was identified, which would provide a possibility to discriminate between conventional and reduced sensitivity grades. In this paper experimental results of two relatively new crystallization techniques are shown. Submicron and nanometric RDX particles have been produced and characterized. Also results on the characterization of different commercial RDX grades will be shown, including data related to a part of the samples received within the R4 programme. Finally, experimental data will be presented and discussed on insensitive plastic bonded explosives (PBXs). © 2008 WILEY-VCH Verlag GmbH & Co. KGaA.

A hydrolyzable model network comprising interconnected star polymers was prepared by the sequential group transfer polymerization of methyl methacrylate and the acid-labile diacetalbased dimethacrylate crosslinker bis[(2-methacryloyloxy)ethoxymethyl] ether. In contrast to other polymer networks previously synthesized by our group, all the branching points of this polymer network were found to hydrolyze under mildly acidic conditions, giving a linear copolymer with the theoretically expected molecular weight and composition. The ease of hydrolysis of this polymer network renders it a good candidate for use in the biomedical field. The characterization of the synthesized network, its linear and star polymer precursors and the hydrolysis products of the network and its precursors, by a variety of techniques, established the successful synthesis and hydrolysis of this well-defined polymer nanostructure. 209 10 1021 1028 Cited By :15

International audience; Poly[3-(4-octylphenyl) thiophene] (PORT) and poly[3-(4-octylphenoxy) thiophene] (POPOT) with high head-to-tall regioregularitlis have been synthesised and photovoltaic properties have been investigated. POPT-blend-PCBM exhibits an interesting behaviour in bulk heterojunction whereas POPOT presents poor photovoltaic performances. UV-visible absorption and AFM images of the blends are presented to explain these results. Copyright © 2008 WILEY-VCH Verlag GmbH & Co. KGaA.

A novel technique based on in situ steady state fluorescence (SSF) measurements is introduced for studying drying and swelling Of kappa(-) carrageenan (kappa carrageenan) gels at various temperatures. kappa(-) carrageenan gels were completely dried and then swelled in water vapor. Pyranine was embedded in kappa(-) carrageenan and used as a fluorescence probe. Scattered light intensities, I-SC and fluorescence intensities, I were monitored during the drying and swelling Of kappa(-) carrageenan gels. it was observed that the fluorescence intensity decreased linearly as drying time was increased. A simple model consisting of Case II diffusion was used to quantify the drying processes of the kappa(-) carrageenan gels. This moving boundary model provided packing constant, kappa(o). During swelling, fluorescence intensity increased exponentially as time is increased. The increase in I, was modeled using Li-Tanaka equation from which swelling time constants, tau(c) and cooperative diffusion coefficients, D-c were determined. It was observed that swelling time constants, tau(c) decreased and diffusion coefficients, D-c increased as the swelling temperature was increased. Activation energies for drying and swelling were also obtained and found to be 53.9 and 47.2 kJ mol(-1), respectively. Publisher's Version Q3 WOS:000256716900006

Energy level alignment in polyfluorene-based polymer light-emitting diodes (PLEDs) is studied with electroabsorption spectroscopy and cyclic voltammetry (CV). Using an active layer containing a blend of three polyfluorenes, it is found that the built-in potential values are determined by the interplay of the contacts work function and the lowest and highest lying energy levels of the blend components.

Polymer-encapsulated silver nanoparticles were synthesized and sterically stabilized by a new core-shell type system consisting of poly(S-alt-MA)-graft- PMMA copolymer that acts as a scaffold for the synthesis of size confined nanoparticles. The graft copolymer is synthesized via ambient temperature ATRP using the CuBr/PMDETA catalytic system at ambient temperature. The graft copolymer is hypothesized to function as a scaffold with the anhydride part interacting strongly with the silver ions, while the PMMA graft functions as a polymer brush that stabilizes the dispersion and prevents the particle aggregation due to a 'polymer brush effect'. UV absorption and TEM studies confirm that the synthesized silver composite particles have a core-shell structure. � 2008 WILEY-VCH Verlag GmbH & Co. KGaA.

The possibility of reducing the impurity content at the crystallite boundaries of high-temperature nickel alloys is considered. The research data permit the development of a smelting technology for high-performance Kh20N80 alloy. © 2008 Allerton Press, Inc.

This work describes the fabrication, characterization, and biological evaluation of a thin protein-resistant poly(ethylene glycol) (PEG)-based hydrogel coating for antifouling applications. The coating was fabricated by free-radical polymerization on silanized glass and silicon and on polystyrene-covered silicon and gold. The physicochemical properties of the coating were characterized by infrared spectroscopy, ellipsometry, and contact angle measurements. In particular, the chemical stability of the coating in artificial seawater was evaluated over a six-month period. These measurements indicated that the degradation process was slow under the test conditions chosen, with the coating thickness and composition changing only marginally over the period. The settlement behavior of a broad and diverse group of marine and freshwater fouling organisms was evaluated. The tested organisms were barnacle larvae (Balanus amphitrite), algal zoospores (Ulva linza), diatoms (Navicula perminuta), and three bacteria species (Cobetia marina, Marinobacter hydrocarbonoclasticus, and Pseudomonas fluorescens). The biological results showed that the hydrogel coating exhibited excellent antifouling properties with respect to settlement and removal. © 2008 American Chemical Society.