ISSN:0258-0322    

DOI:10.1002/masy.19930650102

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractWe are proposing a lattice model with chemical input for the computer modelling of the polymer glass transition. The chemical input information is obtained by a coarse graining procedure applied to a microscopic model with full chemical detail. We use this information on Bisphenol‐A‐Polycarbonate to predict it's Vogel‐Fulcher temperature out of a dynamic Monte Carlo Simulation. The microscopic structure of the lattice model is that of a genuine amorphous material, and the structural relaxation obeys the time temperature superpos

ISSN:0258-0322    

DOI:10.1002/masy.19930650103

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractA stress tensor for systems with periodic boundary conditions is presented, which is different from the wellknown Irving‐Kirkwood expression. It is shown that it represents the external stress for particles initially in one of the cells of the periodic system. The statistical properties of the pressure, derived from the stress tensor, are discussed. It is demonstrated that this pressure can be used to simulate a constant pressure ‐ constant enthalpy ensemble. Constant pressure computer simulations on the basis of the proposed stress tensor are free of artificial parameters and the internal pressure is not constrained, in contrast to previously existing constant pressure simulation sche

ISSN:0258-0322    

DOI:10.1002/masy.19930650104

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractUsing the scanning and the hypothetical scanning methods we study a system of many chains with excluded volume contained in a “box” on a square lattice. With these methods the sampling probabilityPof a configuration can be calculated and therefore the entropySis known (S∼ lnP) without the need to resort to thermodynamic integration. Thus, the pressure and the chemical potential can be calculated with high accuracy directly from the entropy using standard thermodynamic relations. The computer simulation results are compared to the approximate theories of Flory, Huggins, Miller and Guggenheim and to the recent improved theories of Freed and co‐

ISSN:0258-0322    

DOI:10.1002/masy.19930650105

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractA new methodology for formulating the averages of elements of generator matrices is presented. Incorporation of this technique to the Rotational Isomeric State (RIS) model allows the efficient generation of the higher and mixed moments of any conformation‐dependent physical property of a polymer chain. The computational technique is based on symbolic manipulation of the generator matrix elements which are treated as character strings. Successful application of the technique is demonstrated by calculating the correlation coefficient between the dipole moment and the end‐to‐end distance of polymer chains with symmetric rotation potentials and in the independent bond rotation approximation. It is shown that the correlation heavily depends on the orientation of the bond dipole moment vector orient

ISSN:0258-0322    

DOI:10.1002/masy.19930650106

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractIn an earlier publication we had presented a Monte Carlo method to calculate the incremental chemical potential between a chain of length v and one of lengthv+1 at any density. (Ref.9) In this paper we begin by formally proving that the chemical potential of a whole chain of length v can be obtained by sequentially summing the incremental chemical potentials of all chains whose lengths are smaller than v under the same conditions. We then compare the numerical value of chain chemical potentials computed in this fashion to those obtained by inserting whole chains into the simulation cell following the configurational bias procedure proposed by Smit and Frenkel. (Ref.5) It is found, for the two cases considered here, that the results obtained from the two different calculations agree within simulation uncertainty, thus verifying the validity of the proposed arguments.

ISSN:0258-0322    

DOI:10.1002/masy.19930650107

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractPolymer RISM (reference interaction site model) theory is a theory of polymer systems in the liquid phase in which account for chemical realism can be made. Results are reported here of phase diagrams (spinodals) for blend systems calculated by means of this theory, using the mean spherical approximation as a closure. The systems investigated are an isotopic blend, a set of homopolymer/copolymer blends, and a model blend containing specific interactions.

ISSN:0258-0322    

DOI:10.1002/masy.19930650108

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractThe critical properties of dense asymmetric binary polymer mixtures are studied by grand canonical simulations within the framework of the 3‐dimensional bond fluctuation lattice model. The monomers interact with each other via a potential ranging over the entire first peak of the pair distribution. An asymmetry is realized by giving the ratio of interactions λ = ∈AA/∈BBbetween monomers of theA‐species and of theB‐species a value different from 1. Using multiple histogram extrapolation techniques for the data analysis, the two phase region, which is a line of first‐order transitions driven by the chemical potential difference, and the critical point are determined for a mixture of chains with 32 monomers each. At a critical potential difference Δμcunmixing occurs below a critical temperatureTc. It is found that Δμcis proportional to the asymmetry (1 ‐ λ) and that the quantity 4kBTc/(3 + λ)∈ is independent of the asymmetry, consistent with the predicti

ISSN:0258-0322    

DOI:10.1002/masy.19930650109

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractWe consider implications of a lattice model which operates with a vacancy fraction h as a measure of structural disorder. Consequences for the configurational thermodynamics of one‐ and multicomponent systems and their phase equilibria are briefly indicated. The principal topic is the glassy state under steady state conditions, as well as the kinetics of relaxational processes toward equilibrium. The central role of the h‐function in its dependence on variables of state is made evident among others by the connection between equation of state and thermo‐elastic properties. Moreover, a dynamics of volume relaxation can be treated by means of a corresponding theory for the h‐function. Applications of this theory to isothermal annealing below the glass temperature Tg, the response to a constant cooling rate of the melt through the transition zone, and the computation of a complex compression modulus are reviewed. The implications of vacancy cluster distributions for the analysis of positron spectroscopy are pointed out. Finally we indicate the basis for the development of correlations between Tgand structural par

ISSN:0258-0322    

DOI:10.1002/masy.19930650110

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractMolecular dynamics simulation has been performed for studying the relation between amorphous structure of polymers and penetrant diffusion. The self‐diffusion coefficients of O2and He in various polymer models, which differ from each other in view of the amorphous structure, were calculated above their glass transition temperatures. The amorphous structure was characterized by considering the percolation of the unoccupied volume. A good correlation was found between the self‐diffusion coefficients and the number of clusters in the unoccupied volume at the critical point of the percolation. Based on the simulated cluster size distribution at the critical point, we defined a parameter into which effects of both the amorphous structure and the penetrant size are well incorporated. It was confirmed that the penetrant diffusion is intimately associated with the amorphous structure of polym

ISSN:0258-0322    

DOI:10.1002/masy.19930650111

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY