Search results for "dynamics"

Segmental dynamics in polymer electrolytes

2002

Polymer dynamics in poly(ethylene oxide) (PEO)–salt mixtures is investigated by means of quasi-elastic neutron scattering (QENS). In a previous study, we reported QENS data from the NEAT spectrometer (BENSC) that evidenced, for the first time, a dynamic heterogeneity in PEO–salt mixtures induced by salt addition. This finding is supported by molecular dynamics (MD) simulations carried out by Borodin et al. In agreement with MD simulations, our QENS data revealed two distinct processes: a fast motion corresponding to the bulk polymer and a slower relaxation, which we attribute to formation of PEO–cation complexes. In this paper we present new QENS data from the high-resolution spectrometer I…

Microphase separation in linear multiblock copolymers under poor solvent conditions

2010

Molecular dynamics simulations are used to study the phase behavior of linear multiblock copolymers with two types of monomers, A and B, where the length of the polymer blocks $N_{A}$ and $N_{B}$ ($N_{A}=N_{B}=N$), the number of the blocks $n_{A}$ and $n_{B}$ ($n_{A}=n_{B}=n$), and the solvent quality varies. The fraction $f$ of A-type monomers is kept constant and equal to 0.5. Whereas at high enough temperatures these macromolecules form coil structures, where each block A or B forms rather individual clusters, at low enough temperatures A and B monomers from different blocks can join together forming clusters of A or B monomers. The dependence of the formation of these clusters on the va…

Polymer Dynamics in a Polymer-Solid Interphase: Molecular Dynamics Simulations of 1,4-Polybutadiene At a Graphite Surface

2014

A chemically realistic model of 1,4-polybutadiene confined by graphite walls in a thin film geometry was studied by molecular dynamics simulations. The chemically realistic approach allows for a quantitative determination of a variety of experimentally accessible relaxation functions (e.g., dielectric, NMR, or neutron scattering responses). The simulations yield these experimental observables. Additionally, the simulations can be resolved as a function of distance to the solid interface on a much finer scale than experimentally possible, providing a detailed mechanistic picture of the segmental and large scale motions of polymers in the interfacial region between bulk polymer melts and soli…

Critical adsorption of a single macromolecule in polymer brushes.

2014

The adsorption of long flexible macromolecules by polymer brush-coated surfaces is studied by molecular dynamics simulations and by calculations using density functional and self-consistent field theories. The case of repulsive interactions between the substrate surface and the monomers of both the brush polymers and the extra chains that can get absorbed into the brush is considered. Under good solvent conditions, critical absorption can occur, if the interaction between the monomers of the brush polymers and the extra chain is (weakly) attractive. It is shown that it is possible to map out the details of the critical absorption transition, if the chain length and/or the grafting density o…

Structure of Polymer-Grafted Nanoparticle Melts.

2020

The structure of neat melts of polymer-grafted nanoparticles (GNPs) is studied via coarse-grained molecular dynamics simulations. We systematically vary the degree of polymerization and grafting density at fixed nanoparticle (NP) radius and study in detail the shape and size of the GNP coronas. For sufficiently high grafting density, chain sections close to the NP core are extended and form a dry layer. Further away from the NP, there is an interpenetration layer, where the polymer coronas of neighboring GNPs overlap and the chain sections have almost unperturbed conformations. To better understand this partitioning, we develop a two-layer model, representing the grafted polymer around an N…

Role of the Intercrystalline Tie Chains Network in the Mechanical Response of Semicrystalline Polymers

2017

We examine the microscopic origin of the tensile response in semicrystalline polymers by performing large-scale molecular dynamics simulations of various chain lengths. We investigate the microscopic rearrangements of the polymers during tensile deformation and show that the intercrystalline chain connections known as tie chains contribute significantly to the elastic and plastic response. These results suggest that the mechanical behavior of semicrystalline polymers is controlled by two interpenetrated networks of entanglements and tie chains.

Statistical properties of linear-hyperbranched graft copolymers prepared via "hypergrafting" of AB(m) monomers from linear B-functional core chains: …

2015

The reaction of ABm monomers (m = 2, 3) with a multifunctional Bf-type polymer chain ("hypergrafting") is studied by coarse-grained molecular dynamics simulations. The ABm monomers are hypergrafted using the slow monomer addition strategy. Fully dendronized, i.e., perfectly branched polymers are also simulated for comparison. The degree of branching of the molecules obtained with the "hypergrafting" process critically depends on the rate with which monomers attach to inner monomers compared to terminal monomers. This ratio is more favorable if the ABm monomers have lower reactivity, since the free monomers then have time to diffuse inside the chain. Configurational chain properties are also…

1993

4-(4-Carboxyphenyl)-3,5-dioxo-1,2,4-triazolidin-1-yl moieties resulting from 4-(3,5-dioxo-1,2,4-triazolin-4-yl)benzoic acid (U4A) randomly attached to 1,4-polybutadiene form supramolecular aggregates which act as effective junction zones in new thermoplastic elastomers. Deuteron nuclear magnetic resonance (2H NMR) spectroscopy was used to investigate the molecular dynamics of the polymer backbone and the junction zones in selectively labelled samples. The spectra show motional heterogeneity along the polymer chain as well as in the supramolecular domains. Polybutadiene segments which are adjacent to these polar clusters are restricted in their mobility, even at temperatures 100 K above the …

Effects of pressure and of thermal history on the structural phase transition of KCN

1992

The cubic-noncubic structural phase transition of a KCN single crystal is studied as a function of thermal history and of hydrostatic pressure up to 2 kbar. The standard sequence of phases is cubic-monoclinic-orthorhombic on cooling and orthorhombic-cubic on heating. The monoclinic phase is also absent in first cooling runs at low pressures (p≦250 bar). The width of the monoclinic field inp, T phase diagram is increased in second cooling runs. The effects are discussed in terms of a martensitic transformation behavior and random strain fields.

Crystallization Behaviour at High Cooling Rates of Two Polypropylenes

1993

Phase distribution of quenched samples of two isotactic polypropylenes, having different molecular weight distributions, was evaluated by a deconvolution procedure of WAXD spectra. The dependence on cooling rate of the two resins shows the low molecular weights rich polymer is characterized by a faster kinetics with an α-monoclinic to mesomorphic transition taking place at higher cooling rates.