Search results for "Molecule"
showing 10 items of 5162 documents
Atomistic Molecular Dynamics Simulations of the Static and Dynamic Properties of a Polyethylene Melt
1999
I will discuss in this work the atomistic modelling of polymer melts using Molecular Dynamics (MD) simulations. After a general introduction into the problems one faces in the computer simulation of polymers in general and the atomistic simulations in particular, I will present some recent work on the atomistic modelling of an — C 100 H 202 melt,i.e. short chain polyethylene (PE). The aim of this work is to establish a quantitatively validated atomistic model which then can be used in two directions. One direction is the generation of input for the calibration of parameters in coarse-grained models, which in turn can be used to simulate the polymer under investigation over a much broader te…
Entropy theory and glass transition: A test by Monte Carlo simulation
1997
This article reviews the results of a test of the Gibbs-DiMarzio theory by Monte Carlo Simulation. The simulation employed the bond-fluctuation model on a simple cubic lattice. This model incorporates two kinds of interactions: the excluded volume interaction among all monomers of the melt and an internal energy of the chains, which favors large bonds and makes the chains stiffen with decreasing temperature. The stiffening of the chains leads to an increase of their volume requirements, which competes with the packing constraints at low temperatures. This competition strongly slows down the structural relaxation of the melt and induces the glassy behavior. The model therefore takes into acc…
Allylammonium hydrogen oxalate hemihydrate
2014
In the title hydrated molecular salt, C3H8N+·C2HO4−·0.5H2O, the water O atom lies on a crystallographic twofold axis. The C=C—C—N torsion angle in the cation is 2.8 (3)° and the dihedral angle between the CO2and CO2H planes in the anion is 1.0 (4)°. In the crystal, the hydrogen oxalate ions are linked by O—H...O hydrogen bonds, generating [010] chains. The allylammonium cations bond to the chains through N—H...O and N—H...(O,O) hydrogen bonds. The water molecule accepts two N—H...O hydrogen bonds and makes two O—H...O hydrogen bonds. Together, the hydrogen bonds generate (100) sheets.
Temperature effects on counterion binding to spherical polyelectrolytes: the charge-discharge transition of lignosulfonate
1995
Abstract The effect of temperature on the effective charge numbers and diffusion coefficients of polyelectrolytes has not nobee dealth with in many studies. The present study concerns the temperature behavior of lignosulfonate. Lignosulfonate is a polydisperse polyelectrolyte whose molecules are compact spheres in aqueous solutions. One of its most remarkable properties is that is loses its charge in 0.1 M NaCl aqueous solution at about 40°C. In order to explain this charge-discharge transition, a theory for ion binding to spherical polyelectrolytes based on the relative population of two hydration states of the charged groups is presented. The water molecules adjacent to the charged groups…
Physical and structural characterization of blends made with polyamide 6 and gamma-irradiated polyethylenes
1996
Abstract Morphological, calorimetric and rheological results of blends made with polyamide 6 and polyethylene gamma irradiated in air are presented. The polar oxidized groups grafted in the poliolefin chains through gamma-radiation induce “compatibilization” effects in the blends with a more uniform and finer distribution of the polyethylene “phase” in the polyamide matrix, with respect to blends made with the unirradiated polymer. This effect, observed with polyethylenes of different molecular structure, i.e. low density, linear low density and high density, was attributed to the presence of interactions among the functional oxidized groups of the polyethylene chains and the polyamide. Tes…
Structural induced modifications in blends of polyamide with gamma irradiated low density polyethylene
1992
Abstract Blends of gamma irradiated and unirradiated low density polyethylene and polyamide 6 were made in order to study possible modifications induced by this irradiation. Results indicate that blends with gamma irradiated polyethylene have structure and properties significantly different with respect to blends made with the unirradiated one. This difference has been ascribed to the formation of functionalized groups in the polyethylene chains, which interact with polyamide.
Radiolabeling of DOTATOC with the long-lived positron emitter 44Sc.
2010
Abstract The positron-emitting radionuclide 44 Sc with a half-life of 3.97 h and a β + branching of 94.3% is of potential interest for clinical PET. As so far it is available from a 44 Ti/ 44 Sc generator in Mainz, where long-lived 44 Ti decays to no-carrier-added (nca) 44 Sc. The 44 Sc is a trivalent metal cation and should be suitable for complexation with many well established bifunctional chelators conjugated to peptides or other molecular targeting vectors. Thus, the aim of this work was to investigate the potential of 44 Sc for labeling of DOTA-conjugated peptides. DOTA-D-Phe 1 -Tyr 3 -octreotide (DOTATOC) was used as a model molecule to study and optimize labeling procedure. Reaction…
Investigation of the glass transition and melting of polymers by nuclear magnetic resonance
2007
Investigations of the glass transition and melting of partially crystalline polymers by nuclear magnetic resonance provide valuable information on the nature of noncrystalline regions. The broad line NMR signal was separated into a narrow component and a broad component by using a new method which does not imply the ambiguity usually present. From the intensity of the narrow component the mobile fraction was determined. This fraction was extrapolated to “infinite” temperature. By subtracting the mobile fraction from the noncrystalline fraction, the noncrystalline rigid fraction was obtained. Comparison of the measured second moments of the two components of the NMR line with calculated seco…
Can one detach a fully adsorbed flexible polymer chain by an ultra-small external force?
2013
Full adsorption of flexible chains onto typical solid substrates occurs at a surface interaction energy of (5–10) kBT. The corresponding detachment force is in the range 10–50 pN. In contrast to “bare” solid substrates common to non-living materials, surfaces coated with brush-like polymer layers are very common in biological soft matter. We employ a simple mean-field approach to describe the effects of weak attraction between a floating long macromolecule and the brush. We show that even for a moderately thick brush a very small effective attraction is enough to produce complete binding of the long chain. The detachment force scales as , where W is the brush thickness. Hence the force coul…
Conformational studies of bottle-brush polymers absorbed on a flat solid surface.
2010
The adsorption of a bottle-brush polymer end-grafted with one chain end of its backbone to a flat substrate surface is studied by Monte Carlo simulation of a coarse-grained model, that previously has been characterized in the bulk, assuming a dilute solution under good solvent conditions. Applying the bond fluctuation model on the simple cubic lattice, we vary the backbone chain length $N_b$ from $N_b=67$ to $N_b = 259$ effective monomeric units, the side chain length $N$ from N=6 to N=48, and the grafting density $\sigma=1$, i.e., parameters that correspond well to the experimentally accessible range. When the adsorption energy strength $\epsilon$ is varied, we find that the adsorption tra…