Viscoelastic properties and film morphology of heterogeneous styrene–butadiene latexes

Heterogeneous carboxylated styrene–butadiene (S/Bu) latexes were prepared by a twostage emulsion polymerization process, using three PS seeds with different molecular weights. The second-stage polymer was a copolymer with a fixed S/Bu ratio of 1 : 1 and a methacrylic acid (MAA) content of either 1 or 10 wt %. Morphological studies by transmission electron microscopy (TEM) as well as studies of the viscoelastic properties by mechanical spectroscopy have been performed on films prepared from the latexes. The studies showed that the glass transition temperature, T_g, of the second-stage polymer was considerably affected by copolymerization with MAA. An increase in the MAA content in the second-stage polymer increased the T_g of this phase significantly. Addition of DVB as a crosslinking agent in the preparation of the PS seed phase substantially increased the rubbery moduli of the films, whereas the glass transition temperature of the second-stage polymer was unaffected. On the other hand, the presence of a chain transfer agent reduced the glass transition of the second-stage copolymer containing 1 wt % MAA dramatically, whereas the rubbery modulus was unaffected. When the MAA content was increased to 10 wt % the influence of the MAA monomer had a dominating effect on T_g. Latexes containing 10 wt % MAA had T_g values close to each other, regardless of chain transfer agent present in the second-stage polymerization. It was found that the morphology of the latex particles influenced the rubbery modulus of the films. The presence of irregularly shaped seed particles in samples prepared from a crosslinked PS seed had a considerable reinforcing effect on the films, whereas spherical seed particles originating from core–shell particles had a less reinforcing effect. © 1996 John Wiley & Sons, Inc.     

Water-based radiation-curable latexes

Film-forming polystyrene/poly(n-butyl acrylate-co-glycidyl methacrylate) [PS/P(BA-co-GMA)] core–shell latex particles were prepared via a two-stage emulsion polymerization procedure using a polystyrene latex seed. Delayed addition of GMA was used in order to locate functional epoxy groups close to the particle surfaces. It was found that a temperature of 25°C at the second-stage polymerization, in combination with a redox initiator system, was essential for the formation of a uniform shell of BA–GMA copolymer around the PS core. The latex particle morphology was investigated by transmission electron microscopy (TEM). Reactive double bonds were introduced into the particle shells in order to produce a film-forming latex system that could be cured by ultraviolet (UV)-radiation without any need to use reactive multifunctional monomers or oligomers as crosslinkers. The surface-bound epoxy groups were used as grafting sites for amine or carboxyl functional unsaturated monomers, respectively. The grafting was demonstrated by Fourier transform infrared (FTIR) spectroscopy. Films prepared from modified and unmodified latexes were exposed to UV radiation in the presence of a photoinitiator. Crosslinking was tested by thermal mechanical analysis (TMA) and by determination of swelling and gel content of exposed films. It was demonstrated that films from the modified latexes after irradiation had significantly higher stiffness and gel content and showed lower swelling than unmodified ones. © 1996 John Wiley & Sons, Inc.     

European energy security: An analysis of future Russian natural gas production and exports

The widening gap between EU gas production and consumption may require an 87% increase of import volumes between 2006 and 2030, and there are great uncertainties regarding the amounts of gas that can be expected from new suppliers. The potential of increased production from Norway and Algeria is limited; hence, Russia is likely to play a crucial part of meeting the anticipated growing gas demand of the EU. A field-by-field study of 83 giant gas fields shows that the major producing Russian gas fields are in decline, and by 2013 much larger supplies from the Yamal Peninsula and the Shtokman field will be needed in order to avoid a decline in production. Gas from fields in Eastern Siberia and the Far East will mainly be directed to the Asian and Pacific Rim markets, thereby limiting its relevance to the European and CIS markets. As a result, the maximum export increase to the European and CIS markets amounts only to about 45% for the period 2015–2030. The discourse surrounding the EU’s dependence on Russian gas should thus not only be concerned with geopolitics, but also with the issue of resource limitations.     

Conducting bicomponent fibers obtained by melt spinning of PA6 and polyolefins containing high amounts of carbonaceous fillers

Melt spinning of conductive polymer composites (CPCs) is coupled with some difficulties such as a decrease of conductivity upon drawing and a reduced spinnability with increasing filler concentration. Applying bicomponent technology may provide the possibility to produce fibers from CPCs with a high filler concentration. A pilot‐scale bicomponent melt spinning set‐up was used to produce core/sheath fibers with fiber titers between 13 and 47 dtex. The sheath material was polyamide 6 (PA6) or polypropylene (PP) and the core material was a CPC. Two CPCs were used, polypropylene (PP) with carbon black (CB), denoted by PP/CB, and polyethylene (PE) with multiwalled carbon nanotubes (MWNT), denoted by PE/MWNT. The results showed that both materials could be used with a filler concentration of 10 wt % to obtain melt draw ratios up to 195. The volumetric fraction of core material in the bicomponent structure was 28%. A heat treatment of PP/CB fibers restored the conductivity to the level of the undrawn material, corresponding to an increase in conductivity by a factor 5. The same heat treatment had a positive effect on the conductivity of PE/MWNT fibers although the conductivity was not restored. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis and characterization of surface-active compounds derived from cholesterol derivatives and glucose

The synthesis and characterization of surface-active compounds based on various steroid derivatives and glucose are presented. The hydrophobic and hydrophilic parts of the compounds were linked via glucosidic bonds. All compounds were found to have very low water solubility and only limited solubility in various organic solvents. The compounds were investigated according to their ability to interact with an anionic surfactant, sodium dodecylsulfate (SDS), in order to induce a decrease in the critical micelle concentration (CMC) of the surfactants. This synergistic effect was pronounced for cholestanol-6-on-β-D-glucopyranoside and for cholestan-3,6-diol-β-D-glucopyranoside. These two compounds lowered the CMC from 8 to 6 and 0.6 mM, respectively, for water solutions of SDS/glucoside with a molar ratio of 92∶8. Furthermore, the ability of the compounds to stabilize lipid membranes, in liposomes, at varying concentrations of Ca²⁺, was studied. The compounds were, as expected, found to induced stabilization similar to that of cholesterol.     

Effects of feeding chenodeoxycholic acid on metabolism of cholesterol and bile acids in germ-free rats

The aim of this investigation was to study the influence of chenodeoxycholic acid administration on cholesterol and bile acid synthesis in germ-free rats. Seven rats were fed a basal diet and 2 groups of 4 rats received the same diet supplemented with 0.4 and 1% chenodeoxycholic acid, respectively. After 6 weeks, feces were collected in one 3- and one 4-day pool for analysis of cholesterol and bile acids. When the sampling period was finished, the rats were killed and the liver microsomal fractions isolated. The activities of HMG CoA reductase and cholesterol 7α-hydroxylase were determined, the 7α-hydroxylase by a mass fragmentographic method. The 2 dominating bile acids in the untreated rats were cholic acid and β-muricholic acid. During treatment with chenodeoxycholic acid, 60–70% of this bile acid was converted into α- and β-muricholic acid, indicating a high activity of the 6β-hydroxylase. The excretion of cholic acid was almost completely inhibited and the 7α-hydroxylase activity was decreased ca 75% in the rats fed 1% chenodeoxycholic acid. The activity of the hepatic HMG CoA reductase was unchanged. The fecal excretion of cholesterol increased 2–3 times. An accumulation of cholesterol was seen in the rats treated with 1% chenodeoxycholic acid, which was probably a result of the decreased catabolism of cholesterol to bile acids.     

Melt spinning of conductive textile fibers with hybridized graphite nanoplatelets and carbon black filler

In this study, two different carbon fillers: carbon black (CB) and graphite nanoplatelets (GNP) are studied as conductive fillers for the preparation of conductive polypropylene (PP) nanocomposites. In order to obtain a homogenous dispersion of GNP, GNP/PP composites were prepared by two different methods: solid state mixing (SSM) and traditional melt mixing (MM). The result shows that MM is more efficient in the dispersion of GNP particles compared to SSM method. PP nanocomposites containing only one conductive filler and two fillers were prepared at different filler concentrations. Based on the analysis of electrical and rheological properties of the prepared nanocomposites, it shows that a hybridized composite with equal amounts of GNP and CB has favorable processing properties. Conductive fibers with a core/sheath structure were produced on a bicomponent melt spinning line. The core materials of these fibers are the hybridized GNP/CB/PP nanocomposite and the sheath is pure polyamide. It was found that GNPs were separated during melt and cold drawing which results in the decrease of conductivity. However, the conductivity could partly be restored by the heat treatment. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2579–2587, 2013     

Proving refinement using transduction

Summary. When designing distributed systems, one is faced with the problem of verifying a refinement between two specifications, given at different levels of abstraction. Suggested verification techniques in the literature include refinement mappings and various forms of simulation. We present a verification method, in which refinement between two systems is proven by constructing a transducer that inputs a computation of a concrete system and outputs a matching computation of the abstract system. The transducer uses a FIFO queue that holds segments of the concrete computation that have not been matched yet. This allows a finite delay between the occurrence of a concrete event and the determination of the corresponding abstract event. This delay often makes the use of prophecy variables or backward simulation unnecessary. An important generalization of the method is to prove refinement modulo some transformation on the observed sequences of events. The method is adapted by replacing the FIFO queue by a component that allows the appropriate transformation on sequences of events. A particular case is partial-order refinement, i.e., refinement that preserves only a subset of the orderings between events of a system. Examples are sequential consistency and serializability. The case of sequential consistency is illustrated on a proof of sequential consistency of a cache protocol.     

An Experimental Toolbox for Structure-Based Hit Discovery for P. aeruginosa FabF,a Promising Target for Antibiotics

FabF (3-oxoacyl-[acyl-carrier-protein] synthase 2), which catalyses the rate limiting condensation reaction in the fatty acid synthesis II pathway, is an attractive target for new antibiotics. Here, we focus on FabF from P. aeruginosa (PaFabF) as antibiotics against this pathogen are urgently needed. To facilitate exploration of this target we have set up an experimental toolbox consisting of binding assays using bio-layer interferometry (BLI) as well as saturation transfer difference (STD) and WaterLOGSY NMR in addition to robust conditions for structure determination. The suitability of the toolbox to support structure-based design of FabF inhibitors was demonstrated through the validation of hits obtained from virtual screening. Screening a library of almost 5 million compounds resulted in 6 compounds for which binding into the malonyl-binding site of FabF was shown. For one of the hits, the crystal structure in complex with PaFabF was determined. Based on the obtained binding mode, analogues were designed and synthesised, but affinity could not be improved. This work has laid the foundation for structure-based exploration of PaFabF.     

Toward a global understanding of the effects of the IDEA model for designing instructional risk and crisis messages: A food contamination experiment in Sweden

Communicating to publics at risk can be challenging for spokespersons during crises. Knowing what content to include in such messages can be instrumental in achieving effective behavioural results among disparate publics and may differ across cultures. Whereas the IDEA model has demonstrated itself to be an effective framework for designing instructional risk and crisis messages in the United States, this study builds on the conclusions drawn previously by examining the model's utility in Sweden. Results of the experiment confirm that messages constructed according to the IDEA model are effective in Sweden's state‐oriented risk culture, as well. Future research should focus on the model's utility for various risk and crisis types among both Swedish populations and populations in additional countries.