Search results for "Solid"

Chemical speciation of polycyclic aromatic hydrocarbons in sediments: partitioning and extraction of humic substances.

2010

The primary objective of this study was to examine the chemical speciation of polycyclic aromatic hydrocarbons (PAHs) found in sediments endowed with different characteristics. To achieve this purpose and because the nature of the sediments influences the distribution of PAHs, we have analyzed four different types of sediments. To study the role of organic matter in the sequestration of PAHs, we fractionated humic substances into humic acids and humin–mineral fractions. After their separation and purification, the humic components were examined for their sorptive reactivity by extracting them with organic solvents; these extracts were subsequently subjected to GC/MS analysis. Our results sh…

Molecular dynamics of solid polymers as revealed by deuteron NMR

1983

Pulsed deuteron NMR spectroscopy is described, which has recently been developed to become a powerful tool for studying molecular dynamics in solid polymers. It is shown that by analyzing the line shapes of2H absorption spectra and spectra obtained via solid echo and spin alignment, respectively, both type and timescale of rotational motions can be determined over an extraordinary wide range of characteristic frequencies, approximately 10 MHz to 1 Hz. By applying these techniques to selectively deuterated polymers, motional mechanisms involving different segments of the monomer unit can be monitored. In addition, motional heterogeneities in glassy polymers can be detected. The information a…

Homogeneous mixtures of polybetaines with low molecular weight salts

1996

The prepaparation of amorphous, homogeneous blends of zwitterionic polymers with various low molecular weight salts, and in particular with ionic dyes was studied. Homogeneous miscibility was achieved in many cases up to equimolar amounts of salt, even for bulky compounds. Whether miscibility is achieved, or not, depends in a subtle way on the chemical structure of the salt, but no obvious correlation between structure and miscibility could yet be revealed. Spectral shifts of the dye UV/Vis spectra in solution as well as in bulk suggest strong interactions between the polybetaines and the admired salts.

Deuteron n.m.r. in relation to the glass transition in polymers

1985

Abstract 2H n.m.r. is introduced as a tool for investigating slow molecular motion in the glass transition region of amorphous polymers. In particular, we compare 2H spin alignment echo spectra of chain deuterated polystyrene with models for restricted rotational Brownian motion. Molecular motion in the polystyrene-toluene system has been investigated by analysing 2H n.m.r. of partially deuterated polystyrene and toluene, respectively. The diluent mobility in the mixed glass has been decomposed into ‘solid’ and ‘liquid’ components where the respective average correlation times differ by more than 5 decades.

1996

The major new developments in electron crystallography and high resolution imaging of organic molecules are discussed. The aim is to show that the recent rapid advances in computer technology have made it possible to analyze molecules at a level or resolution which was impossible less than a decade ago, thus bringing the concept of molecular design to produce specific physical properties much nearer to realization

PEO/CHCl3. Crystallinity of the Polymer and Vapor Pressure of the Solvent. Equilibrium and Nonequilibrium Phenomena

2003

Vapor pressures were measured for the system CHCl3/PEO 1000 (PEO stands for poly(ethylene oxide) and 1000 for Mw in kg/mol) at 25 °C as a function of the weight fraction w of the polymer by means of a combination of headspace sampling and gas chromatography. The establishment of thermodynamic equilibria was assisted by employing thin polymer films. The degrees of crystallinity α of the pure PEO and of the solid polymer contained in the mixtures were determined via DSC. An analogous degree of polymer insolubility β was calculated from the vapor pressures measured in this composition range. The experiments demonstrate that both quantities and their concentration dependence are markedly affect…

Solid state NMR - A tool for studying molecular motion in polymers

1986

After an introduction describing the development of 1H, 2H, and 13C solid state NMR two sections on 13C and 2H NMR, respectively, outline the physical background as related with molecular motion. Some representative examples demonstrate the potential of recent NMR techniques in polymer dynamics studies.

Monte Carlo simulation studies of the interfaces between polymeric and other solids as models for fiber-matrix interactions in advanced composite mat…

1996

As a coarse-grained model for dense amorphous polymer systems interacting with solid walls (i.e., the fiber surface in a composite), the bond fluctuation model of flexible polymer chains confined between two repulsive surfaces is studied by extensive Monte Carlo simulations. Choosing a potential for the length of an effective bond that favors rather long bonds, the full temperature region from ordinary polymer melts down to the glass transition is accessible. It is shown that in the supercooled state near the glass transition an “interphase” forms near the walls, where the structure of the melt is influenced by the surface. This “interphase” already shows up in static properties, but also h…

Residual order in amorphous dry films of polymer latices: indications of an influence of particle interaction

2002

Abstract We report small angle X-ray scattering and atomic force microscopy measurements on macroscopically thick, dry films of polymer latex particles. While the surface of dried droplets has long range order due to layering effects, the overall bulk structure is amorphous. This holds for both low charge polymethylmetacrylate particles and for highly charged polystyrene particles with additional stabilisation with sodiumdodecylsurfate. In the latter case, however, considerable amounts of residual crystal-like order is observed.

Polymer- and template-related factors influencing the efficiency in molecularly imprinted solid-phase extractions

1999

Abstract This review identifies the factors of importance in the development of molecularly imprinted polymers for use in solid-phase extractions and summarizes the results obtained to date in the area of bioanalysis, pharmaceutical analysis and environmental analysis.