Dilute Bulk Research Articles

An improved potential for krypton

An improved potential for krypton is presented. It has the simple but realistic form used by Aziz and Chen for argon based on the HFD potential suggested by Ahlrichs et al. The potential, with known long-range behaviour, was fitted to second virial, viscosity and thermal conductivity data. The potential appears to have the best overall predictive ability for dilute gas, bulk and micro-scopic data.

Intermolecular forces in mixtures of helium with the heavier noble gases

Crossed beams differential scattering cross sections have been measured for HeAr, HeKr, and HeXe with a new beam modulation technique at two energies. Interatomic potential functions have been found which describe both scattering and dilute gas bulk properties for these systems. Potential functions independently determined from gas phase bulk properties are shown to give a very good account of the scattering data. The potential well depth is found to be about equal for the three systems, in agreement with Chen et al. [J. Chem. Phys. 59, 601 (1973)], although our values are in average 17% larger than those found in the cited work. Also, the deviations of the three potentials from a common shape are smaller than those found by Chen et al. The ability of combining rules to predict the mixed interaction from a knowledge of the pure gas interactions is tested. In contrast to some of the previous work in the field, we conclude that simple combining rules can be found that give useful predictions.

A new realistic potential for neon based on dilute gas bulk properties

A potential based on the simple Maitland-Smith generalized n-6 form and fit solely to three dilute gas bulk properties is proposed. The potential predicts not only dilute gas bulk properties but also spectroscopic and molecular beam data as favorably as much more complex realistic potentials.

Dilute gas properties of neon

The intermolecular potentials which were recently proposed for neon are examined as to their ability to predict dilute gas bulk properties. The ESMSV III potential due to Farrar et al. is found to characterize dilute gas behaviour best.

Comparison of predictions of dilute gas bulk properties on the basis of some new krypton potentials

The krypton potentials of Barker et al., Buck et al., Gough et al. (Maitland and Smith (n-6)) and Thakkar and Smith (MIST 2C and 6B) are compared as to their ability to predict dilute gas properties (second virial, viscosity, self-diffusion and thermal conductivity coefficients and thermal diffusion factors). The potentials of Barker et al. and Buck et al. and Gough et al. (MS) accurately predict these properties almost equally. The MIST potentials do not fare quite so well. The isotopic thermal diffusion factor, the dilute gas property most sensitive to the shape of the potential, is best described by the Buck et al. and MS potentials. An analysis of this property suggests the correctness of the slope of the repulsive wall of these potentials.

Irreversible statistical mechanics of polymer chains. III. A dynamic model of vinyl polymers

Computational works are made of the dynamic rotational isomer model of vinyl polymers, of which theoretical foundation has been given in the first paper of this series. First, a concept of ``simple elementary mode'' is newly introduced, based on the assumption of short-range order of vinyl polymers, and 2317 simple elementary modes for ν ≤ 14 (where ν is the length of local chains) are found with the aid of a computer. Langevin equations for local chains rotating in a viscous medium are introduced to derive transition probabilities for these modes. They are given as functions of the monomer size (Rm), the free volume (νf) of the system, and a hydrodynamic parameter (ε). Two kinds of systems, dilute polymer solutions and bulk polymers (including concentrated polymer solutions), are discussed separately. Two dimensionless quantities, [Da] (intrinsic diffusion coefficient) and [Ta] (intrinsic relaxation time) for normal coordinates Qa, are newly defined and they are computed numerically for various ε, Rm, νf, and gauche state energy (Eg). The following are found in the present work. (1) [Dα] strongly depends on νf both in the range 0≤α̃≤ 0.3 and 0.8≤α̃≤ 1, but not on 0.4 ≤α̃≤ 0.75, where α̃=α/N. (2) [Dα] is almost independent of Rm and Eg in the whole range 0≤α̃≤ 1. (3) In dilute solutions (i.e., νf=∞) all the (2317) elementary modes participate in the Brownian motion of the polymer chains, but with the increase in polymer concentration (i.e., with the decrease in νf the larger elementary modes begin to freeze up and, near the glass-transition temperature, the only two smallest modes, (4,1)S and (6,2)S remain unfrozen. (4) Even in dilute solutions, the Brownian motion of the normal coordinate with a large α̃(0.3≤α̃≤ 1) is determined by several small elementary modes alone. (5) [τα̃] takes its minima [τα]min in the range 0.4≤ α ≤ 0.75. (6) [τα] strongly depends on both νf and Eg, but [τα]min depends only on Eg. The following subjects are also discussed: The superposition of time and temperature changes, behaviors of long elementary modes, and the glass-transition phenomena.