Post polymerisation hypercrosslinking of styrene/divinylbenzene poly(HIPE)s: Creating micropores within macroporous polymer

Porous copolymers of styrene and divinylbenzene (DVB) were prepared by emulsion templating using high internal phase emulsions (HIPEs) as precursors for monoliths. The ratio of monomers was varied in order to obtain samples with different degrees of crosslinking and different amounts of unreacted vinyl groups originating from DVB. PolyHIPE monoliths were subjected to reswelling and treatment with a radical initiator. Significant enlargement of the amount of meso- and micropores in the material was found resulting in a substantial increase of BET surface area, up to 7.2 times compared to untreated polyHIPEs. The treated PolyHIPE monoliths retained the open macroporous morphology typical of polyHIPE materials. Solid state ¹³C NMR experiments were used to determine the amount of unreacted vinyl groups in polyHIPE samples, both before and after the hypercrosslinking treatment.     

Microcalorimetric and FTIR Study of the Adsorption of Carbon Dioxide on Alkali-Metal Exchanged FER Zeolites

Adsorption of CO₂ on alkali-metal exchanged (Li⁺, Na⁺, K⁺) FER zeolites was investigated by means of microcalorimetry and FTIR spectroscopy. The adsorption enthalpies strongly depend on coverage for all investigated materials and they are also influenced by concentration of Al in the framework. Especially, samples of Na- and K-FER with lower Si/Al ratio (8.6) exhibited substantially larger initial interaction energy than samples with Si/Al 27.5. Differences in zero-coverage adsorption energy of zeolites with different cation concentration (Si/Al ratio) are 9 and 7.2 kJ/mol for Na- and K-FER zeolites respectively. This phenomenon is attributed to formation of bridged CO₂ adsorption complexes formed between two cations, which are characterized by IR absorption band of ν₃ stretching vibration mode at 2370 and 2357 cm^?1 for Na- and K-FER respectively.     

Heterogeneous ion-selective membranes: the influence of the inert matrix polymer on the membrane properties

Heterogeneous ion-exchange membranes were prepared by mixing small particles of sulfonated poly(1,4-phenylene sulfide) or sulfonated styrene–divinylbenzene copolymer with a matrix polymer. Four kinds of polymers were tested as a matrix: highly flexible linear polyethylene, medium-flexible fluoroelastomer, rigid polystyrene (all highly hydrophobic) and hydrophilic cellulose prepared by hydrolysis of cellulose acetate butyrate. Membrane morphologies were studied by scanning electron microscopy, IR spectroscopy and density measurements. Subsequently, the membranes were characterised with respect to their swelling in water, electrochemical characteristics and transport properties. Ion-exchange capacity and proton conductivity together with the permeability to hydrogen and methanol were investigated. The important impact of the ion-exchange particles as well as of the polymer matrix used was observed. The increasing rigidity of the polymer matrix resulted in a decrease in membrane permeability, but at the same time in deterioration of its ion-exchange capacity and subsequently of the proton conductivity, too. This was explained in terms of the limited elasticity of the polymer matrix, in each sample under study, which does not allow the ion-exchange particles to swell to an identical degree.     

Analogue filter group delay optimization using a stochastic approach

An analogue filter group delay response is optimized using an all‐pass network connected in the cascade of the filter. This contribution introduces an original method of all‐pass network correction designing of using a random‐based approach. The main objective of the method is the calculation of an optimal all‐pass network order and optimal coefficients of its transfer function. To realize this objective it is necessary to find minima of so‐called optimization spaces. The spaces definition provides an important generalization of the optimization task. The original stochastic approach is used to find the mentioned minima of the spaces. The minima can be detected using several probability densities. The method combines advantages of a numerical approach with rigorous analytical pre‐processing. Compared to current optimization methods, the described approach provides very good convergence, velocity and especially independence from the initial estimation of the all‐pass network transfer function coefficients. The original objective function ensures absolutely stable convergence in the multidimensional optimization spaces. This objective function was developed with regard to properties of the analogue filters. The designed method is illustrated by a few practical optimizations. A well‐known circuit simulator, Micro‐Cap, is used as a comparative system because of its relatively good optimization algorithm. All the presented original algorithms and functions are debugged in the MATLAB^® environment. Copyright © 2009 John Wiley & Sons, Ltd.     

Stability of fat‐soluble vitamins and PUFA in simulated shallow‐frying

Fat‐soluble vitamins and essential polyunsaturated fatty acids (PUFA) are nutrients that are sensitive to heat treatment and oxidation and therefore can be partly lost during cooking. It is well‐documented that a long‐term deep‐frying process leads to a substantial degradation of PUFA and vitamins in a frying medium. In this study, the stability of vitamins and fatty acids was investigated in a series of liquid margarines (82% fat) varying in fat blend and the content of minor components. The tested samples were subjected to the standardised treatment that has been developed to mimic shallow‐frying of food at 180°C and the recovery of individual nutrients is reported. The results show that fat‐soluble vitamins possessed reasonable stability under the condition of the shallow‐frying test. Essential PUFA of the frying medium were hardly affected by the treatment. Overall evaluation of the results suggests that oil‐based cooking media rich in vitamins and PUFA have a positive impact on nutritional value of food prepared by appropriate means of cooking.     

Preliminary comparison of ballistic electron emission spectroscopy measurements on InAs quantum dots in a GaAs/AlGaAs heterostructure grown by MBE and MOVPE

Self-assembled InAs quantum dots (SAQDs) in GaAs/GaAlAs structures grown by molecular beam epitaxy (MBE) and metal-organic vapour phase epitaxy (MOVPE) of similar size was examined by ballistic electron emission spectroscopy. Ballistic current-voltage characteristics through the QD in the voltage range from 0.55 to 0.9 V (range where the presence of resonance states of QD is expected) with its derivative (the derivation of the spectroscopic characteristics represents quantum levels in the QD) are given. Differences in the intensities and sharpnesses of the QD levels for MBE and MOVPE grown QDs are observed.     

Non-conductive TiO2 as the anode catalyst support for PEM water electrolysis

The applicability of a non-conductive TiO₂ as the support of the anodic catalyst for PEM water electrolysis was tested. Three TiO₂ samples with different specific surface areas were modified by IrO₂ using a modified version of the Adams fusion method. A constant weight ratio of IrO₂/TiO₂ of 0.6 was maintained in all cases. The size, specific surface area and morphology of IrO₂ electrocatalyst crystallites were investigated by X-ray diffraction, nitrogen adsorption (BET) and scanning electron microscopy, respectively. The electron conductivity of compressed catalyst powders was evaluated. Their electrochemical properties were studied on a rotating disk electrode (RDE) and finally in a laboratory electrolyser. Utilization of the TiO₂ support resulted in a reduction in the size of the IrO₂ crystallites. It was found that the lower the specific surface area of the supports, the higher was the electrochemical activity of the catalyst. This is most likely due to the formation of a conductive IrO₂ film on the surface of non-conductive supports. For the supports with a higher surface area, the amount of IrO₂ used was not sufficient to form an adequately compact film. This resulted in high electron resistance of such a catalyst. The RDE results were confirmed by a laboratory electrolysis test. Taken together with the excellent stability of TiO₂ in an anodic environment, these results suggest that these materials are promising supports if the appropriate amount of iridium is deposited.     

Hydroxy-PCBs, PBDEs, and HBCDDs in serum from an elderly population of Swedish fishermen's wives and associations with bone density

Lack of human exposure data is frequently reported as a critical gap in risk assessments of environmental pollutants, especially regarding "new" pollutants. The objectives of this study were to assess serum levels of the persistent 2,2',4,4',5,5'-hexachlorobiphenyl (CB-153), hydroxylated polychlorinated biphenyl metabolites (OH-PCBs), polybrominated diphenyl ethers (PBDEs), and hexabromocyclodode-canes (HBCDDs) in a group of Swedish middle-aged and elderly women expected to be relatively highly exposed, and to evaluate the impact of potential determinants (e.g., fish intake, age) for the inter-individual variation, as well as to investigate the association between these pollutants and bone density. No associations were found between bone mineral density or biochemical markers of bone metabolism and the analyzed environmental pollutants. Relatively high levels of CB-153 (median 260 ng/g fat) and sigma 3-OH-PCBs (median 1.7 ng/mL serum), and low concentrations of sigma6PBDEs (median 3.6 ng/g fat) were determined. Total level of HBCDDs in serum was quantified by gas chromatography with mass spectrometric detection (median 0.5 ng/g fat). HBCDD diastereomeric and enantiomeric patterns were determined by liquid chromatography with mass spectrometric detection. The dominating stereoisomer was (-)alpha-HBCDD, but 1-3% of gamma-HBCDD was also detected in the serum samples.     

Rheological properties of homogeneous and heterogeneous poly(2‐hydroxyethyl methacrylate) hydrogels

The swelling and rheological behaviour of hydrogels of morphology varying from non‐porous to highly porous was investigated. The hydrogels were prepared by redox free radical copolymerization of 2‐hydroxyethyl methacrylate with 0.1 to 5 mol% of di(ethylene glycol) dimethacrylate in the presence of water varying from 40 to 80 wt%. Various compositions led to clear, turbid or macroporous gels. The morphology of the gels was characterized using optical microscopy and cryoscan electron microscopy. The oscillatory shear and creep of swollen gels revealed that there was a pronounced difference between homogeneous or microheterogeneous and macroporous gels with communicating pores. The achievement of optimum conditions for the correct determination of shear modulus was also analysed. Copyright © 2011 Society of Chemical Industry