Search results for "Exponent"
showing 10 items of 896 documents
Tracer diffusion properties of core-shell latex films studied by photoinduced grating relaxation
2007
This article reports the application of the Photo-Induced Grating Relaxation technique (also known as Forced Rayleigh Scattering) to investigate the dynamics of films prepared from structured core–shell latex particles via the transport property of the photochromic tracer molecule Aberchrome 540®. The core–shell particles were prepared with a fluoropolymer core (immiscible and impenetrable to the tracer) and a poly(butyl methacrylate) shell. The incompletely dried films (with residual water) manifest their spatial heterogeneity via non-Fickian behavior (spatial scale- dependent apparent diffusion coefficient). The diffusion data was interpreted using the two-state diffusion model, previousl…
Correlations of the nonexponentiality and state dependence of mechanical relaxations with bond connectivity in Ge-As-Se supercooled liquids
1992
We have studied the mechanical responses of supercooled Ge-As-Se liquids to flexural strains and temperature steps. The departures from exponential relaxation correlate well with the variations in connectivity. The structural state dependence of the mechanical relaxation, detected in pure and weakly cross-linked Se, is suppressed completely at the rigidity percolation threshold {l angle}{ital r}{sub {ital c}}{r angle}, where the liquid fragility is a minimum. The shapes of the decay functions of samples with the same {l angle}{ital r}{sub {ital c}}{r angle} but different compositions are not universal at {ital T}{sub {ital g}} probably because of chemical effects near the binary edges of th…
Unusual crystallization kinetics in a hard sphere colloid-polymer mixture.
2008
We investigated the crystallization kinetics of a hard sphere colloid-polymer mixture at conditions where about 95% of solid coexists with about 5% of fluid. From time resolved Bragg and small angle light scattering, we find that the crystallite size increases with a power law of exponent alpha approximately 1/3 during both the conversion and the coarsening stage. This observation points to a single conserved order parameter for both stages and cannot be explained if the mixture is regarded as an effective one-component system. We alternatively suggest that--based on local geometric demixing--the polymer density takes the role of the conserved order parameter.
Glassy dynamics of simulated polymer melts: Coherent scattering and van Hove correlation functions
2001
Whereas the first part of this paper dealt with the relaxation in the β-regime, this part investigates the final relaxation (α-relaxation) of a simulated polymer melt consisting of short non-entangled chains in the supercooled state above the critical temperature of ideal mode-coupling theory (MCT). The temperature range covers the onset of a two-step relaxation behaviour down to a temperature merely 2% above . We monitor the incoherent intermediate scattering function as well as the coherent intermediate scattering function of both a single chain and the melt over a wide range of wave numbers q. Upon approaching the coherent α-relaxation time of the melt increases strongly close to the max…
Dynamical Scaling in Polymer Solutions Investigated by the Neutron Spin-Echo Technique
1979
Chain dynamics in polymer solutions was investigated by means of the recently developed neutron spin echo spectroscopy. — By this technique, it was possible for the first time to verify unambiguously the scaling predictions of the Zimm model in the case of single chain behaviour and to observe the cross over to many chain behaviour. The segmental diffusion of single chains exhibits deviations from a simple exponential law, indicating the importance of memory effects. Mit Hilfe der erst kurzlich entwickelten Neutronen-Spin-Echo-Spektroskopie wurde die Kettendynamik von Polymermolekulen im gelosten Zustand untersucht. - Die Methode eroffnete die Moglichkeit, zum ersten Mal fur das Einzelkette…
Long Range Bond-Bond Correlations in Dense Polymer Solutions
2004
The scaling of the bond-bond correlation function $C(s)$ along linear polymer chains is investigated with respect to the curvilinear distance, $s$, along the flexible chain and the monomer density, $\rho$, via Monte Carlo and molecular dynamics simulations. % Surprisingly, the correlations in dense three dimensional solutions are found to decay with a power law $C(s) \sim s^{-\omega}$ with $\omega=3/2$ and the exponential behavior commonly assumed is clearly ruled out for long chains. % In semidilute solutions, the density dependent scaling of $C(s) \approx g^{-\omega_0} (s/g)^{-\omega}$ with $\omega_0=2-2\nu=0.824$ ($\nu=0.588$ being Flory's exponent) is set by the number of monomers $g(\r…
Scaling behavior of topologically constrained polymer rings in a melt
2014
Large scale molecular dynamics simulations on graphic processing units (GPUs) are employed to study the scaling behavior of ring polymers with various topological constraints in melts. Typical sizes of rings containing $3_1$, $5_1$ knots and catenanes made up of two unknotted rings scale like $N^{1/3}$ in the limit of large ring sizes $N$. This is consistent with the crumpled globule model and similar findings for unknotted rings. For small ring lengths knots occupy a significant fraction of the ring. The scaling of typical ring sizes for small $N$ thus depends on the particular knot type and the exponent is generally larger than 0.4.
Adsorption Transition of a Polymer Chain at a Weakly Attractive Surface: Monte Carlo Simulation of Off-Lattice Models
2002
A bead-spring model of a polymer chain with one end attached to a wall is studied by Monte Carlo simulations for chain lengths 16 ≤ N ≤ 256. Two types of adsorption potentials, 9-3 and 10-4 Lennard-Jones (LJ) potentials, between the effective monomers and the wall are assumed. For both cases the adsorption transition where the chain changes its asymptotic statistical properties from a three-dimensional to a two-dimensional configuration is located using a scaling analysis. It is shown that the crossover exponent φ = 0.50 ± 0.02 is the same for both LJ potentials. This value is compatible with recent theoretical predictions and simulation results for lattice models with short-range wall pote…
Osmotic pressure of catenanes in solution
1989
We propose a nonuniversal scaling for the osmotic pressure in the case of concatenating ring polymers. The size exponent depends on the molecular weight of the catenans. The effect is more significant the shorter and the stiffer the molecules are.
Selfdiffusion of polymer chains in solutions and melts
2005
Anomalous diffusion of monomers of polymer chains, as well as motion of these chains as a whole, is discussed with an emphasis on Monte Carlo simulations and simple scaling concepts. While the behavior of isolated chains in good solvents or Theta-solvents without excluded volume interactions is fully accounted for by the Rouse model, the behavior is less clear both for isolated chains in bad solvents and for chains in dense melts. Collapsed chains are shown to diffuse as g3(t) = <([rCM (t) -rCM(0)]2〉 ∝ tξ3 where the (effective?) exponent ξ3 simply seems to be linearly temperature-dependent for temperatures T lower than the Σ-temperature, ξ3 T/Θ. A relaxation time τ oc N3 is found, and scali…