Grafting of montmorillonite nano‐clay with butyl acrylate and methyl methacrylate by atom transfer radical polymerization: Blends with poly(BuA‐co‐MMA)

11‐(2‐Bromo‐2‐methyl)propionyl‐oxy‐undecyl trichlorosilane atom transfer radical polymerization (ATRP) initiator was covalently attached on montmorillonite clay platelets via silylation reactions. The initiator clay was used to polymerize butyl acrylate (BuA) and methyl methacrylate (MMA) on the clay surface. Polymerization was performed in bulk monomer solution or in DMSO. Polymer modified clay was mixed with a poly(BuA‐co‐MMA) matrix. Small angle X‐ray scattering (SAXS) and transmission electron microscopy (TEM) showed that clay modified in DMSO gave exfoliated composites when mixed with the matrix copolymer. Mechanical properties of the composites were studied by dynamic mechanical thermal analysis (DMTA). The results showed that the mechanical properties were improved as a function of clay content, as well with an increasing homogeneity of the nanocomposite. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3086–3097, 2009     

Shear localisation in interfacial particle layers and its influence on Lissajous-plots

Interfacial rheological measurements often show in their nonlinear Lissajous-plots rhombus or saddle-like shapes indicating complex local deformation behaviour. A strong interacting silica particle and an almost not interacting clay particle were studied in respect to their interfacial rheological properties. Large amplitude oscillation shear measurements were performed with a bicone geometry and combined with optical measurements, from which particle tracks were calculated. A correlation was found between the appearance of shear localisation and Lissajous-plot shapes. Silica particles showed shear localisation at the bicone edge and rhombic plateaus in the Lissajous-plot, while the shear localisation for the clay particles was observed at the cup’s wall as saddle-like shaped Lissajous-plots     

Particle release and control of worker exposure during laboratory-scale synthesis,handling and simulated spills of manufactured nanomaterials in fume hoods

Fume hoods are one of the most common types of equipment applied to reduce the potential of particle exposure in laboratory environments. A number of previous studies have shown particle release during work with nanomaterials under fume hoods. Here, we assessed laboratory workers’ inhalation exposure during synthesis and handling of CuO, TiO₂ and ZnO in a fume hood. In addition, we tested the capacity of a fume hood to prevent particle release to laboratory air during simulated spillage of different powders (silica fume, zirconia TZ-3Y and TiO₂). Airborne particle concentrations were measured in near field, far field, and in the breathing zone of the worker. Handling CuO nanoparticles increased the concentration of small particles (<?58 nm) inside the fume hood (up to 1?×?10⁵ cm^?3). Synthesis, handling and packaging of ZnO and TiO₂ nanoparticles did not result in detectable particle release to the laboratory air. Simulated powder spills showed a systematic increase in the particle concentrations inside the fume hood with increasing amount of material and drop height. Despite powder spills were sometimes observed to eject into the laboratory room, the spill events were rarely associated with notable release of particles from the fume hood. Overall, this study shows that a fume hood generally offers sufficient exposure control during synthesis and handling of nanomaterials. An appropriate fume hood with adequate sash height and face velocity prevents 98.3% of particles release into the surrounding environment. Care should still be made to consider spills and high cleanliness to prevent exposure via resuspension and inadvertent exposure by secondary routes.     

Critical networks exhibit maximal information diversity in structure-dynamics relationships

Network structure strongly constrains the range of dynamic behaviors available to a complex system. These system dynamics can be classified based on their response to perturbations over time into two distinct regimes, ordered or chaotic, separated by a critical phase transition. Numerous studies have shown that the most complex dynamics arise near the critical regime. Here we use an information theoretic approach to study structure-dynamics relationships within a unified framework and show that these relationships are most diverse in the critical regime.     

Simulation of quantum wells with ‘spikes’ and ‘dips’

The use of thin high-bandgap ‘spikes’ or thin low-bandgap ‘dips’ inside conventional rectangular quantum wells (QWs) gives supplementary flexibility in engineering intra- and inter-band energy level separation. The paper presents simulation and experimental studies on the effects of ‘spikes’ and ‘dips’ on the fundamental quantum well properties.     

Proximity effects of oxygen atoms on the enthalpies of formation of simple diethers: a computational G3(MP2)//B3 study

The enthalpies of formation of a number of acyclic, straight‐chain ethers and diethers were determined by G3(MP2)//B3 calculations. The principal aim of the work was to study the magnitude of the O…O proximity effect on the enthalpy contents of diethers as a function of the distance (number of bonds) between the O atoms. 1,4‐Diethers and 1,5‐diethers were computed to be destabilized by ca. 4.5 (±0.5) and 3.2 (±0.4) kJ mol^?1, respectively, by the O…O proximity effect. The effect was calculated to be negligible in diethers with the O atoms in positions more remote than 1,5 from each other, whereas 1,3‐diethers (acetals) are stabilized by ca. 22 kJ mol^?1, likely on account of the anomeric effect. Calculations on simple monoethers show that the contributions to of CH₂ groups in the β and γ positions (relative to O) are reduced by ca. 0.8 and 0.3 kJ mol^?1, respectively, relative to those of CH₂ groups more remote from the O atom. The computational enthalpies of formation of the studied monoethers and diethers, both cyclic and acyclic, are generally in good agreement with experimental data, another important result of the present work. Copyright © 2008 John Wiley & Sons, Ltd.     

Infrared absorption spectrum of matrix-isolated noble-gas hydride molecules: fingerprints of specific interactions and hindered rotation

Noble-gas hydride molecules with the general formula HNgY (Ng denotes noble-gas atom and Y denotes electronegative fragment) are usually prepared in solid noble gases. In many cases, the matrix-isolated HNgY molecules show a characteristic structure of the H-Ng stretching absorption: A close doublet as the main spectral feature and a weaker satellite at higher energy. This characteristic band structure is studied here for matrix-isolated HXeBr and HKrCl molecules. Based on the experimental and theoretical results, we suggest a model explaining the common features of the band structure of the HNgY molecules in noble-gas matrices. In this model, the main doublet bands are attributed to matrix sites where the splitting is caused by specific interactions of the embedded molecule with noble-gas matrix atoms in certain local morphology. The weaker blueshifted band is probably a fingerprint of hindered rotation (libration) of the embedded molecule in the lattice. This librational band has a mirror counterpart at lower energies appearing at higher matrix temperatures. Our present ab initio calculations for the one-to-one Xe...HXeBr complexes and the simulation of hindered rotation in a matrix support this image.     

Extraction, interpretation and validation of information for comparing samples in metabolic LC/MS data sets

LC/MS is an analytical technique that, due to its high sensitivity, has become increasingly popular for the generation of metabolic signatures in biological samples and for the building of metabolic data bases. However, to be able to create robust and interpretable (transparent) multivariate models for the comparison of many samples, the data must fulfil certain specific criteria: (i) that each sample is characterized by the same number of variables, (ii) that each of these variables is represented across all observations, and (iii) that a variable in one sample has the same biological meaning or represents the same metabolite in all other samples. In addition, the obtained models must have the ability to make predictions of, e.g. related and independent samples characterized accordingly to the model samples. This method involves the construction of a representative data set, including automatic peak detection, alignment, setting of retention time windows, summing in the chromatographic dimension and data compression by means of alternating regression, where the relevant metabolic variation is retained for further modelling using multivariate analysis. This approach has the advantage of allowing the comparison of large numbers of samples based on their LC/MS metabolic profiles, but also of creating a means for the interpretation of the investigated biological system. This includes finding relevant systematic patterns among samples, identifying influential variables, verifying the findings in the raw data, and finally using the models for predictions. The presented strategy was here applied to a population study using urine samples from two cohorts, Shanxi (People's Republic of China) and Honolulu (USA). The results showed that the evaluation of the extracted information data using partial least square discriminant analysis (PLS-DA) provided a robust, predictive and transparent model for the metabolic differences between the two populations. The presented findings suggest that this is a general approach for data handling, analysis, and evaluation of large metabolic LC/MS data sets.     

Robust quantification of in vitro angiogenesis through image analysis

An automated image analysis method for quantification of in vitro angiogenesis is presented. The method is designed for in vitro angiogenesis assays that are based on co-culturing endothelial cells with fibroblasts. Such assays are used in many current studies in which anti-angiogenic agents for the treatment of cancer are being sought. This search requires accurate quantification of the stimulatory and inhibitory effects of the different agents. The quantification method gives lengths and sizes of the tubule complexes as well as the numbers of junctions in each of them. The method is tested with a set of test images obtained with a commercially available in vitro angiogenesis assay. The results correctly indicate the inhibitory effect of suramin and the stimulatory effect of vascular endothelial growth factor. Moreover, the image analysis method is shown to be robust against variations in illumination. We have implemented a software package that utilizes the methods. The software as well as a set of test images are available at http://www.cs.tut.fi/sgn/csb/angioquant/.     

Ab initio study on adsorption of hydrated Na+ and Cu+ cations on the Cu(111) surface

The interactions of Na+ and Cu+ cations with a Cu(111) surface in the presence and absence of water molecules were investigated using cluster models and ab initio methods. Adsorption in aqueous solution was modeled with one to five water molecules around the adsorbing cation. The Cu surface was described with Cu10 and Cu18 cluster models and the computational method was MP2/RECP/6-31+G. The effect of the basis set superposition error (BSSE) was taken into account with counterpoise (CP) correction, and the accuracy of HF-level results was examined. The interactions between Na+ and the Cu surface were found to be primarily electrostatic, and the energy differences among the different adsorption sites were small. The largest CP-corrected MP2 adsorption energy for the Cu18 cluster was -188 kJ/mol. When water molecules were added around it, Na+ receded from the Cu surface and finally was surrounded totally by the water molecules. The interactions between Cu+ and the Cu surface were dominated by orbital interactions, and Cu+ preferred to adsorb on sites where it could bind to more than one surface atom. The largest CP-corrected MP2 adsorption energy for the Cu18 cluster was -447 kJ/mol. Adding water molecules around it did not cause Cu+ to draw away from the surface, but instead the water molecules began to form hydrogen bonds with one another. The magnitude of BSSE was substantial in most cases. CP corrections did not, however, have a significant impact on the relative trends among the interaction energies.