摘要:

Sound velocity and density measurements were performed in polymeric aqueous solutions of poly(ethylene glycol) (PEG 600) and poly(ethylene glycol methyl ether) (PEGME 550) as a function of concentration and temperature. The experimental data unambiguously show that the presence of the polymer changes the water structure near the solute, building up a more compact arrangement in which up to two water molecules for each monomeric unity are allowed. Moreover we tested, at low concentration, a model to study the change induced in the polymer hydration by the addition of salt. No direct evidence of interaction between the hydration water of the polymer and salt is brought to light by the obtained results.

ISSN:0026-8976    

DOI:10.1080/00268979300100311

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Despite the fact that the surface tension for a Lennard-Jones fluid has been simulated many times in the past, there is some considerable disagreement between the results. This paper calculates the surface tension and density profiles for the liquid-vapour interface of a Lennard-Jones fluid using molecular dynamics (MD) simulation techniques for a variety of system sizes, film thicknesses, interfacial areas, interatomic potential cut-offs, and temperatures. The results are compared with previous work in order to resolve some of the discrepancies of the past work. Combining this work with some reliable results from the past, the minimum system size, film thickness, and equilibration time necessary for the accurate description of the surface tension was determined. Using simulation results calculated for computationally-economic values of the potential cut-off, the surface tension was extrapolated to the full potential value using a tail correction and the results compared to simulations performed with longer cut-offs. The results indicated the possibility of obtaining estimates of the surface tension for models employing a large cut-off from those with a more moderate cut-off value. The criteria established for obtaining accurate results for the pure components was applied to binary mixtures of Lennard-Jones particles approximating mixtures of argon and krypton. The preferential adsorption at the interface was examined, the tail correction was applied to the mixtures, and the ‘corrected’ surface tensions compared to experimental results.

ISSN:0026-8976    

DOI:10.1080/00268979300100321

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

An approach is suggested for the investigation by computer simulation of systems which contain free electrons. Summation over the occupied free electron states makes it possible to exclude quantum particles from explicit consideration. This procedure leads to renormalized effective interatomic potentials which are generally weaker than the initial direct ones and allows us to apply computer simulation methods developed for classical systems to the study of systems with free electrons. The approach suggested is illustrated by molecular dynamics studies of concentrated lithium-ammonia solutions.

ISSN:0026-8976    

DOI:10.1080/00268979300100331

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The classical centrifugal-sudden approximation (cCSA) in molecular collision dynamics is studied. Following the traditional quantal approach, the problem is first formulated in the body-fixed (BF) coordinate system exactly. Attempts to deduce the cCSA from the BF Hamiltonian, however, fail to provide proper directional information for the relative motion. Instead, the cCSA can be derived from the uncoupled angular momentum representation in the space-fixed coordinate system, and directional information can then be obtained. The cCSA is applied to the study of transport and relaxation cross-sections of the He-N2and Ar-N2systems. For both systems the dynamical error is investigated by comparing the cCSA results with exact classical trajectory results, while for the He-N2system the quantization error is obtained by comparing the cCSA and quantal centrifugal-sudden approximation results. The cCSA is found to be accurate for the viscosity and diffusion cross-sections. Encouraging results were found for the relaxation cross-sections for depolarized Rayleigh light scattering, the viscomagnetic effect and the field effect on the thermal conductivity. When comparisons are possible, the quantization error is usually found to be larger than the dynamical error.

ISSN:0026-8976    

DOI:10.1080/00268979300100341

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

ISSN:0026-8976    

DOI:10.1080/00268979300100351

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor