Influence of entanglements on glass transition of atactic polystyrene

Freeze‐dried samples were prepared from dilute solutions of atactic polystyrene (a‐Ps) in benzene in a concentration range of 1 × 10^?1 to 2 × 10^?5 g/mL, and their glass transition temperatures (T_g) were determined by differential scanning calorimetry. It was found that below a critical concentration (C), the T_g of samples decreases linearly with decreasing logarithmic concentration of solutions. The freeze‐dried samples were annealed at a constant temperature for various times or at various temperatures for the same period of time. The T_g of samples prepared from solutions of concentration below C was observed to shift to higher temperature with increasing annealing temperature or annealing time, finally approaching that of the bulk sample. Fourier transform infrared (FTIR) spectra of the freeze‐dried samples were determined and were compared with the bulk sample. Significant changes in line width and absorption intensity were observed in the spectra of the freeze‐dried samples, indicating that the packing of segments is in a more dilatant state. During annealing, the packing of segments in the samples gradually approaches that of the bulk sample, diminishing the differences in FTIR spectra between the freeze‐dried sample and the bulk sample. The experimental observations are discussed, and it is assumed that intrachain and interchain entanglements may play an important role in glass transition. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2243–2251, 2005     

Interaction of Co<Subscript>6</Subscript> cluster with γ-alumina surface: A quantum chemical study

The interaction of Co₆ cluster with partially dehydroxylated γ-alumina surface was studied by the DFT method. Hydrogen atoms of surface hydroxyl groups can be transferred to the metal particle to form partially oxidized cobalt states. The energy characteristics of hydrogen transfer were determined and changes in the electronic structure of supported Co₆ particles were characterized. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2194–2199, October, 2005.     

Method comparison study on soot-selective techniques

In a long-term field study at two locations with different air pollution levels several soot-selective measurement techniques were compared with a thermochemical method which measures non-extractable carbon (NEC) detecting the evolved CO₂ by means of coulometric titration. The attenuation measurement technique (aethalometer) and the aerosol photoemission method showed good correlations to NEC for concentrations ranging from 1.6g/m³ to 40.8g/m³. The specific mass absorption coefficient of black carbon with respect to NEC varied between 8.4m²/g and 13.7m²/g with respect to the measurement sites, but the value was found to remain constant at each site independent of seasonal or meteorological variations. The ratio of photoelectric signal to NEC varied between 16 fA·(g/m³)^–1 and 33 fA·(g/m³)^–1 depending on the age of the aerosol. The diurnal variations of that ratio showed strong similarities to the traffic patterns. Additionally a slight temperature dependence of this ratio was found for the aged aerosol with a proportionality factor of – 0.35 fA·(K·g/m³)^–1. With the reflectance measurement technique (smoke shade method) reliable NEC determination was not possible for NEC concentrations 5 g/m³.     

Effect of the Solvent on the Water Properties of Water/Oil Microemulsions

Porous poly(styrene-divinylbenzene) (PS-DVB) particles were modified by adsorption of hydrophobically-modified dextrans, to provide chromatographic matrices for biomolecule chromatography. The dextran distribution and the pore characteristics of various coated PS-DVB beads were examined using nitrogen adsorption–desorption, mercury intrusion, and size exclusion chromatography. It was found that the adsorption of dextran does not result in homogeneous layers but rather in inhomogeneous ones. At high dextran loading and high content of hydrophobic groups in the adsorbed polymer, most of the pores of the macroporous rigid material are filled with a soft and porous dextran network being stabilized by hydrophobic interactions. According to chromatographic experiments, most of the surface was nevertheless expected to be covered at least by a thin and dense protecting layer since proteins—even those that are small enough to penetrate the dextran network—cannot interact nonspecifically with the internal pore surface. At low content of hydrophobic groups, dextran deposits preferentially as a thicker and more diffuse layer. However, the thickness of the coating is expected to be irregular and probably contributes to an increase in the roughness of the polystyrene surface.     

Solid‐state nuclear magnetic resonance relaxation times in crosslinked macroporous polymer particles of divinylbenzene homopolymers

Monodisperse porous particles of poly(divinylbenzene) prepared by the activated swelling method have been investigated by solid‐state ¹³C crosspolarization magic‐angle spinning (CPMAS) nuclear magnetic resonance (NMR) relaxation measurements. Homopolymeric combinations of two porogens (toluene and 2‐ethylhexanoic acid) and two monomers (meta‐ and para‐divinylbenzene) were studied. Residual vinyl groups were systematically reacted with increasing amounts of bromine, producing 20 different polymers samples for which we measured crosspolarization times, T_CH, proton rotating frame spin‐lattice relaxation, T, ¹³C spin‐lattice relaxation, T, and proton spin‐lattice relaxation, T. These parameters were chosen to reflect expected changes in a wide range of frequencies of motion as a function of structure. Relative differences in the molecular mobility of the major functional groups (aromatic, vinyl and aliphatic) is related to initial reactants used, vinyl concentration, relative reactivity of vinyl groups, distribution of vinyl groups, pore structure, and degree of crosslinking. Variable temperature ¹H combined rotation and multiple pulse NMR (CRAMPS) was used to derive activation energies for selected samples via measurement of the proton spin‐lattice relaxation time, T. Irreversible thermal effects were observed in ambient temperature relaxation after heating to temperatures in the range of 393–418 K. Simple univariate statistical analyses failed to reveal consistent correlations among the known variables. However, the application of more sophisticated multivariate and neural network analyses allowed excellent structure–property predictions to be made from the relaxation time data. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1307–1328, 1999     

Prediction of turbulent gas–solids flow in curved ducts using the Eulerian–Lagrangian method

The flow of particulate two‐phase flow mixtures occur in several components of solid fuel combustion systems, such as the pressurised fluidised bed combustors (PFBC) and suspension‐fired coal boilers. A detailed understanding of the mixture characteristics in the conveying component can aid in refining and optimising its design. In this study, the flow of an isothermal, dilute two‐phase particulate mixture has been examined in a high curvature duct, which can be representative of that transporting the gas–solid mixture from the hot clean‐up section to the gas turbine combustor in a PFBC plant. The numerical study has been approached by utilising the Eulerian–Lagrangian methodology for describing the characteristics of the fluid and particulate phases. By assuming that the mixture is dilute and the particles are spherical, the governing particle momentum equations have been solved with appropriately prescribed boundary conditions. Turbulence effects on the particle dispersion were represented by a statistical model that accounts for both the turbulent eddy lifetime and the particle transit time scales. For the turbulent flow condition examined it was observed that mixtures with small particle diameters had low interphase slip velocities and low impaction probability with the pipe walls. Increasing the particle diameters (>50 μm) resulted in higher interphase slip velocities and, as expected, their impaction probability with the pipe walls was significantly increased. The particle dispersion is significant for the smaller sizes, whereas the larger particles are relatively insensitive to the gas turbulence. The main particle impaction region, and locations most prone to erosion damage, is estimated to be within an outer duct length of two to six times the duct diameter, when the duct radius of curvature to the duct diameter ratio is equal to unity. Copyright © 1999 John Wiley & Sons, Ltd.     

Arsenobetaine-decomposing Ability of Marine Microorganisms Occurring in Particles Collected at Depths of 1100 and 3500 Meters

The arsenobetaine-decomposing ability of microorganisms occurring in sinking particles, which play a main role in the vertical transport of organic substances produced in the photic zone, was investigated. The microorganisms in particles collected in the deep sea, 1100 and 3500 m in depth, clearly showed decomposing ability. With the particles from 1100 m, the degradation products were the same as those produced by microorganisms occurring in sources in the photic zone, i.e. trimethylarsine oxide (TMAO), dimethylarsinic acid (DMA) and inorganic arsenic(V). At 3500 m, the degradation activity was diminished, smalls amount of DMA and TMAO being produced. These results suggest that arsenobetaine contained in the animals starts to degrade immediately after the death of the animals and their transformation to particles. The degradation of arsenobetaine to inorganic arsenic in our tentative arsenic cycle in marine ecosystems (inorganic arsenic to inorganic arsenic via the biosynthesis of arsenobetaine) may apply to the deep sea as well as to the photic zone. © 1997 by John Wiley & Sons, Ltd.     

A Synergistic Effect of Select Organotin Compounds and Ionic Surfactants on Liposome Membranes

Organometallic compounds and surfactants constitute a potential threat to the environment. For that reason we have embarked on a study of their joint action on membranes. Model lecithin liposome membranes were modified with the cationic surfactant trimethyldodecylammonium bromide or the anionic surfactant sodium dodecylsulfonate, and the effect of tripropyltin chloride on the process of calcium (Ca²⁺) and praseodymium (Pr³⁺) desorption from the liposome membrane was studied. Kinetic constants for the process of Ca²⁺ ion desorption from lecithin liposome membranes were determined using the radiotracer method. The percentage of Pr³⁺ ion desorption from liposome membranes was measured by the ¹H NMR method. Trimethyltin, triethyltin and tripropyltin alone caused increased Ca²⁺ and Pr³⁺ desorption from liposome membranes with increasing concentration of the compounds and alkyl chain length. For both the processes studied, a cationic surfactant brought about a lower effectiveness of tripropyltin and an anionic surfactant resulted in a higher effectiveness. The effect observed can be explained by changes in the surface charge of the membrane, induced by the surfactant modifiers and by the concomitant change in the partition coefficient of the organotin. The results obtained indicate a protective or harmful joint action of the surfactants used with tripropyltin on membranes. © 1997 John Wiley & Sons, Ltd.     

Chromatography of functional polymers: A new approach to the characterization of reactive polymers obtained by chemical modification

High-performance liquid chromatography (HPLC) has been used to complement size-exclusion (gel permeation) chromatography (SEC) for the characterization of functional polymers. Whereas SEC is unable to detect compositional changes, HPLC in an appropriate interacting medium can provide detailed information on compositional changes occurring during chemical modification of a polymer. The method has been demonstrated using a normal-phase column consisting of porous monodisperse 10 μm poly(2,3-dihydroxypropyl methacrylate-co-ethylene dimethacrylate) beads that have a homogeneous coverage of aliphatic hydroxyl groups for the analysis of brominated poly(isobutylene-co-4-methylstyrene). Differences of well below 1 mol % of bromomethylstyrene units are easily detected and quantified. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1173–1180, 1997     

Rubber particle agglomeration phenomena in acrylonitrile-butadiene-styrene (ABS) polymers II. Rubber particle agglomeration elucidated by a thermodynamic theory

A thermodynamic theory incorporating Flory-Huggins thermodynamics was developed to elucidate the observed rubber particle agglomeration phenomena in ABS molded under a severe condition. When the particle size of ABS is smaller than a thermodynamically stable domain size (D_s), rubber particle agglomeration can occur. Based on this criterion, rubber particle agglomeration can be explained semiquantitatively, especially for materials which do not have too insufficient graft level and nearly no compositional acrylonitrile mismatch. This finding suggests that the agglomeration results mainly from a driving force produced by thermodynamic incompatibility between components. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys, 35: 553–562, 1997