Search results for "MELT"
showing 10 items of 435 documents
Molecular dynamics simulations of the glass transition in polymer melts
2004
Computer simulations of polymer models have contributed strongly to our understanding of the glass transition in polymer melts. The ability of the simulation to provide information on experimentally not directly accessible quantities like the detailed spatial arrangement of the particles allows for stringent tests of theoretical concepts about the glass transition and provides additional insight for the interpretation of experimental data. Comparing coarse-grained simulations of a bead-spring model and chemically realistic simulations of 1,4-polybutadiene the importance of dihedral barriers for the glass transition phenomenon can be elucidated.
Effect of the elongational flow on morphology and properties of polypropylene/graphene nanoplatelets nanocomposites
2018
Abstract In this work the effect of the presence of graphene nanoplatelets (GnP) on the morphology and mechanical properties of polypropylene/GnP nanocomposites has been investigated when these polymer systems are subjected to non-isothermal elongational flow in a melt spinning operation. The presence of the GnP magnifies the effect of the elongational flow. Indeed, the elastic modulus and the tensile strength of nanocomposites increases with the orientation more than that observed for the pure matrix. Moreover, the elongation at break increases at low values of the draw ratio for the nanocomposites, while, the matrix shows the expected decrease in deformability. These effects have been cor…
Monte-Carlo Simulation of 3-Dimensional Glassy Polymer Melts: Reptation Versus Single Monomer Dynamics
1995
A polymer melt is simulated at finite temperature by the Monte-Carlo method. We use a coarse-grained model for the polymer system, the bond-fluctuation model. Static properties of the melt can be obtained by generating configurations not with single-monomer- dynamics which moves individual monomers locally, but reptation-dynamics which allows collec- tive motion of the chains. This algorithm can produce equilibrated configurations much faster. It is demonstrated that static properties do not differ from those obtained by single-monomer- dynamics. Values of the radius of gyration, the mean square bond length and similar quantities for different temperatures and densities are presented.
Monte Carlo simulations of the polymer glass transition: From the test of theories to material modeling
1997
We present results on the glass transition in polymer melts using Monte Carlo simulations of the bond fluctuation lattice model. There are two questions we address in this work. What is the temperature dependence of the entropy density in such a model polymer melt and how well is it described by theories like the Gibbs-DiMarzio theory of the glass transition? And to what degree is one able to map the Hamiltonian of such an abstract lattice model onto a specific polymer material and use it to model the large scale and long time properties of a realistic polymer melt?
Computer simulations of undercooled fluids and the glass transition
2000
Abstract Two model studies are presented that attempt to describe the static and dynamic properties of glass-forming fluids via molecular dynamics simulations: The first model is an atomistically realistic model of SiO 2 , the second model provides a coarse-grained description of polymer liquids, i.e., typical `fragile' glassformers, while SiO 2 is the prototype of a `strong glassformer'. For both models, attention is given to the questions as to which range of temperatures are properties in equilibrium, and whether such simulations can help to interpret experiments and/or check theoretical predictions. While in the simulation of SiO 2 using the potential of van Beest, Kramer and van Santen…
Thermomechanical Properties of Radiation-Modified Polyethylene/Ethylene-Propylene-Diene Copolymer/Liquid-Crystalline Copolyester Blends
1999
Radiation-modified blends of high-density polyethylene (PE) with ethylene-propylene-diene copolymer (EPDM; 10-65 wt.%) and thermotropic liquid-crystalline polymer (LCP; 10 wt.%) were investigated. The LCP was a liquid-crystalline copolyester of 40% poly(ethylene terephthalate) with 60% 4-hydroxybenzoic acid. The constituents were blended using a circular extruder, the specimens were prepared by compression molding and irradiated by 60Co γ-radiation up to 200 kGy. Mechanical, thermal, and morphological properties in wide temperature range were investigated for the irradiated and non-irradiated specimens. The effects of irradiation on the thermomechanical behaviour of the PE matrix are discus…
1,2,4-Triazoles. Improved synthesis of 5-substituted 4-amino-3-mer-cato-(4H)-1,2,4-triazoles and a facile route to 3,6-disubstituted 1,2,4-triazolo[3…
1997
The reaction of thiocarbohydrazide with carboxylic acids at the melting temperature allows an improved preparation of the S-substituted 4-amino-3-mercapto-1,2,4-triazole heterocycles. The crude 4-amino-5-mercapto-1,2,4-triazoles react easily with carboxylic acids or carboxylic acid chlorides to afford the 1,2,4-triazolo[3,4-fc][1,3,4]thiadiazole ring system.
Studies on electron-beam irradiation and plastic deformation of medical-grade ultra-high molecular weight polyethylene
2011
Abstract Separated and combined electron-beam irradiation and plastic deformation effects on the structures of ultra-high molecular weight polyethylene (UHMWPE) were studied. It was found that the concentration of carbonyl (ketones, esters and peresters), hydroxyl and vinyl groups increases with the growing dose of adsorbed electrons. It also tends to exhibit a slight increase in the melting point and crystallinity of the samples. A mechanical stress in the polymer was found to accelerate radiation-induced degradation. It was concluded that each of the factors studied (i.e. electron beam sterilization and plastic deformation) had a different impact on the polymer structure. The change in th…
Die bestimmung des chemischen potentials und des expansionskoeffizienten in mischungen von polydimethylsiloxanen unterschiedlichen molekulargewichts
1976
Wird ein Polymermolekul in einer Polymerschmelze von gleicher chemischer Art aber anderem Molekulargewicht gelost, so ist das geloste Polymermolekul im allgemeinen relativ zum ungestorten statistischen Knauel expandiert. Der Expansionskoeffizient und der zweite osmotische Virialkoeffizient hangen von den Molekulargewichten der beiden Polymeren ab. Die experimentellen Befunde werden durch die Gittertheorie fur athermische Losungen von Polymeren richtig beschrieben. If a polymer molecule is solved within a polymer melt of the same chemical nature but of different molecular weight, the solved polymer molecule in general is expanded as compared with the unperturbed statistical coil. The expansi…
Guest-Induced Folding and Self-Assembly of Conformationally Adaptive Macrocycles into Nanosheets and Nanotubes
2017
A conformationally adaptive macrocycle is presented, namely zorb[4]arene, which exists in multiple conformations in the uncomplexed state. The binding cavity of zorb[4]arene is concealed, either due to a collapsed conformation or by self-inclusion. The zorb[4]arene with long alkyl chains manifests itself with surprisingly low melting point and thus exist as an oil at room temperature. Binding of a guest molecule induces the folding and conformational rigidity of zorb[4]arene and leads to well-defined three-dimensional structures, which can further self-assemble into nanosheets or nanotubes upon solvent evaporation, depending on guest molecules and the conformations they can induce.