Search results for "Dynamic"

Molecular Simulation of Polymer Melts and Blends: Methods, Phase Behavior, Interfaces, and Surfaces

2016

Penetrant diffusion in frozen polymer matrices: A finite-size scaling study of free volume percolation

1996

The diffusion of penetrant particles in frozen polymer matrices is investigated by means of Monte Carlo simulations of the bond fluctuation model. By applying finite-size scaling to data obtained from very large systems it is demonstrated that the diffusion process takes place on a percolating free volume cluster describable by a correlated site percolation model which falls into the same universality class as random percolation. The diverging correlation length entails a pronounced dependence of the diffusion constant on the size of the simulated system. It is shown that this dependence is appreciable for a wide range of parameters around the transition. \textcopyright{} 1996 The American …

Photon correlation spectroscopy to study the dynamics of α- and β-relaxation in amorphous poly(Alkylmethacrylates) above Tg

2008

A short survey of the underlying principles of isotropic light scattering from amorphous bulk polymers is given. The interrelation between the time dependent longitudinal compliance and the autocorrelation function of density fluctuations is briefly reviewed and a comparison with poly(vinylacetate) PVAc is presented. For four poly-(alkylmethacrylates) - poly(methylmethacrylate) PMMA, poly(ethylmethacrylate) PEMA, poly(n-butylmethacrylate) PBMA and poly(n-hexylmethacrylate) PHMA - the results of photon spectroscopic studies are given and discussed in terms of the occurrence of primary and secondary relaxation processes within the accessible time range of the experiment.

Effect of physical aging on the low-frequency vibrational density of states of a glassy polymer

2003

The effects of the physical aging on the vibrational density of states (VDOS) of a polymeric glass is studied. The VDOS of a poly(methyl methacrylate) glass at low-energy (<15 meV), was determined from inelastic neutron scattering at low-temperature for two different physical thermodynamical states. One sample was annealed during a long time at temperature lower than Tg, and another was quenched from a temperature higher than Tg. It was found that the VDOS around the boson peak, relatively to the one at higher energy, decreases with the annealing at lower temperature than Tg, i.e., with the physical aging.

Effects of inhomogeneities of cross-links on a microphase separation of polymer mixtures

1994

We generalize de Gennes' theory of the microphase separation of cross-linked polymer mixtures to take into account the spatial fluctuations of the elasticity constant c, preventing the mixture from complete segregation. Within a mean-field analysis we found that the spatial fluctuations of c(r), which are assumed to obey the Poisson distribution, enlarge the size of the domains. The latter is obtained to be temperature dependent.


Nanoscale hybrid silica/polymer Janus particles with a double-responsive hemicorona

2015

Abstract We report a versatile large-scale synthesis strategy for hybrid Janus nanoparticles with a silica core and a unilaterally attached polymer corona in a size range below 100 nm. The stimuli-responsive behavior of these nanoparticles with a poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) hemicorona is investigated. The synthesis is based on a modified version of the Pickering emulsion polymerization technique in combination with surface-initiated atom transfer radical polymerization (ATRP) in a “grafting from” approach. In a first step, poly(vinyl acetate) (PVAc) latex particles are prepared via Pickering emulsion polymerization. Colloidal stability is provided by 30 nm silica nan…

Processing and properties of blends with liquid crystal polymers

1990

Experimental data on the processing behavior and on the rheological and mechanical properties of blends with a liquid crystal polymer as one component are presented. The blends with low amounts of LCP show easier processability and lower viscosity than the thermoplastic matrix. The elastic modulus is also improved. The reduction of viscosity has been attributed to the lower pressure entry, due to the formation of fibrils and to the immiscibility of the two phases.

Cellulose-click-ferrocenes as docking spots for cyclodextrin

2012

A novel synthesis of ferrocene-modified cellulose, prepared from 6-azido-6-deoxy-cellulose and ethynylferrocene, is presented. The two components were coupled via copper-catalyzed click-type cycloaddition under microwave-assisted conditions. The surface structure of the cellulose derivative was investigated in comparison with that of pure, microcrystalline cellulose using electron microscopy (scanning, transmission and scanning transmission), showing iron atoms of ferrocene as homogeneously distributed particles. They are detectable as clear signals in the energy-dispersive X-ray profile. In addition, Rame-β-cyclodextrin was supramolecularly attached to cellulose and the complex formed was …

Diffusion of spherical micronetworks in polymer diluent systems and melts studied by dynamic light scattering techniques

1994

Spherical polystyrene (PS) micronetworks can be prepared in microemulsion with bulk radii of 5–60 nm and different cross-linking densities. The diffusion of these PS spheres has been studied in polymer diluent systems ranging from dilute solutions to plasticized melts by using forced Rayleigh scattering and photon correlation spectroscopy. On increasing the PS concentration, a colloid glass transition is observed at a volume fraction ΦC ≈ 0.64 of the swollen spheres. At higher concentration inside the “colloid glass” state the sphere diffusion is slowed down and becomes very complex but can be observed up to the limit of a melt of collapsed spheres.

Connectivity defects enhance chain dynamics in supramolecular polymer model-network gels

2016

Supramolecular polymer networks exhibit twofold dynamics: that of their polymer chains and that of the transient bonds between them, which is further complexed when irregular network structures lead to local variation of both. A typical irregularity is imperfect network-chain connectivity. To assess the impact of that, we study the diffusion of three different types of tracer polymers in supramolecular model networks of four-arm star-shaped poly(ethylene glycol). First, we focus on tracers that carry three stickers and one fluorescent label at their four arms, thereby creating an inherent network connectivity defect in their vicinity. Second, we embed tracers that carry four stickers and fo…