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End-to-end Distance (end-to-end + distance)

Distribution by Scientific Domains

Polymers and Materials Science	83%

Selected Abstracts

Mean-Square End-to-End Distance and Characteristic Ratio of Polyvinylene (Polyacetylene) Chains of Various Configurations

MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 2 2006
í Vohlídal
Abstract Summary: Closed-form analytical expressions are derived for the mean-square end-to-end distance of unperturbed polyvinylene chains of various configurational structure with freely rotating main-chain single bonds. In particular, expressions are derived for (i) stereoregular chains: all- trans, all- cis and cis - trans alternating; (ii) atactic cis - trans chains with a Bernoullian distribution of cis and trans units along the chain and various content of trans units, (iii) regularly segmented cis - trans chains [,cisy,transy,]n and (iv) diblock chains cisx,transy. The conformation factor is determined for several atactic polyvinylenes for which the unperturbed dimensions are available in the literature. [source]

Conformational Behaviour of Comb-Like Poly(4-vinylpyridinium) Salts and their Complexes with Surfactants in Solution and on a Flat Surface

MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 2 2007
Marat O. Gallyamov
Abstract We synthesised P4VP bromides with octyl and dodecyl pendant groups; the bromide anions in these polymer salts were further substituted with dodecylsulfate or bis(2-ethylhexylsuccinate) anions. Direct SFM visualisation of the original P4VP chains, of the macromolecular salts and of their complexes, showed that the attachment of the pendant groups and especially the complexation with the surfactants promotes stretching of the macromolecules while adsorbing on mica substrate. On the other hand, viscosimetry showed that in solution (chloroform) the comb-like chains and their complexes with dodecylsulfate had more compact conformations than those of the original P4VP. The scaling exponents describing the correlation between the contour length and the end-to-end distance of the adsorbed macromolecules were found to be ca. 3/4, which is indicative of 2D self-avoiding walk statistics. [source]

Mean-Square End-to-End Distance and Characteristic Ratio of Polyvinylene (Polyacetylene) Chains of Various Configurations

Polymer Chain Collapse in Supercritical Fluids.

MACROMOLECULAR SYMPOSIA, Issue 1 2009

Abstract A few years ago we reported the first observation, by computer simulations, of polymer chain collapse near the lower critical solution temperature (LCST).1 In the present work, we extended the above study to understand the underlying physics of a single polymer chain collapse near LCST and its relationship to phase boundaries in the T-x plane. Effects of solvent and monomer sizes, and solvent and monomer energetic interactions are studied. Using Monte Carlo simulations, the mean end-to-end distance (R) and gyration radius (Rg) are calculated for a single chain in a supercritical fluid solvent over a broad range of densities, pressures and temperatures. In general, the chain collapses as temperature increases at constant pressure. Upon a further temperature increase, the chain expands again to approach the athermal limit provided that the temperature is sufficiently high. The collapse is related to an LCST phase boundary while the expansion represents the signature of an upper-critical solution temperature (UCST) suggesting the existence of a closed-immiscibility loop. By manipulating the strength of the energetic interactions as well as the solvent-to-monomer size ratio, the size of the size of the immiscibility loop can be fine-tuned. The relationship among size and the segment-solvent energetic interaction are correlated by a conformational parameter (,) for the first time. By monitoring the , behavior, it is possible to predict solution's phase behavior, transition zone from LCST-UCST in a closed-loop miscibility behavior. The above relationship between chain conformation to phase boundaries may be useful in understanding phase stability in compressible polymer-solvent mixtures. [source]

Distribution Function and Thermodynamic Potentials of a Self-Avoiding Chain

MACROMOLECULAR THEORY AND SIMULATIONS, Issue 5 2006
Aleksey D. Drozdov
Abstract Summary: An explicit expression is derived for the distribution function of end-to-end vectors for a flexible self-avoiding chain. Based on this relation, analytical formulas are developed for the free and internal energies of a chain with excluded-volume interactions. Force,stretch relations are obtained at uniaxial tension and compression. The effects of strength of segment interactions on the shapes of the distribution function and the force-displacement diagram, as well as on the mean-square end-to-end distance and stiffness of a chain are studied numerically. The dimensionless distribution function P versus the dimensionless end-to-end vector Q* for self-repellent chains with ,,=,0.0, 0.4, 0.8, 1.2, and 1.6, from top to bottom, respectively. [source]

Molecular dynamics calculations on amylose fragments.

BIOPOLYMERS, Issue 2 2002

Abstract Molecular dynamics simulations (NPT ensembles, 1 atm) using the all atom force field AMB99C (F. A. Momany and J. L. Willett, Carbohydrate Research, Vol. 326, pp 194,209 and 210,226), are applied to a periodic cell containing ten maltodecaose fragments and TIP3P water molecules. Simulations were carried out at 25 K intervals over a range of temperatures above and below the expected glass transition temperature, Tg, for different water concentrations. The amorphous cell was constructed through successive dynamic equilibration steps at temperatures above Tg and the temperature lowered until several points of reduced slope (1/T vs volume) were obtained. This procedure was carried out at each hydration level. Each dynamics simulation was continued until the volume remained constant without up or down drift for at least the last 100 ps. For a given temperature, most simulations required 400,600 ps to reach an equilibrium state, but longer times were necessary as the amount of water in the cell was reduced. A total of more than 30 ns of simulations were required for the complete study. The Tg for each hydrated cell was taken as that point at which a discontinuity in slope of the volume (V), potential energy (PE), or density (,) vs 1/T was observed. The average calculated Tg values were 311, 337, 386, and 477 K for hydration levels of 15.8, 10, 5, and 1%, respectively, in generally good agreement with experimental values. The Tg for anhydrous amylose is above the decomposition temperature for carbohydrates and so cannot be easily measured. However, it has also been difficult to obtain a value of Tg for anhydrous amylose using simulation methods. Other molecular parameters such as end-to-end distances, mean square distributions, and pair distributions are discussed. Published 2002 John Wiley & Sons, Inc. Biopolymers 63: 99,110, 2002 [source]