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  • American Institute of Physics (AIP)  (8)
  • 1995-1999  (5)
  • 1985-1989  (3)
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  • 1
    Electronic Resource
    Electronic Resource
    Phase diagram and dynamics of Yukawa systems (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 3286-3312 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The phase diagram and dynamical properties of systems of particles interacting through a repulsive screened Coulomb (Yukawa) potential have been calculated using molecular and lattice dynamics techniques. The phase diagram contains both a melting transition and a transition from fcc to bcc crystalline phases. These phase transitions have been studied as a function of potential shape (screening length) and compared to phenomenological criteria for transition temperatures such as those of Lindemann and of Hansen and Verlet. The transition from fcc to bcc with increasing temperature is shown to result from a higher entropy in the bcc phase because of its softer shear modes. Even when the stable solid phase below the melting temperature is fcc, bcc-like local order is found in the liquid phase. This may substantially slow crystallization. The calculated phase diagram and shear modulus are in good agreement with experiments on colloidal suspensions of polystyrene spheres. The single particle dynamics of Yukawa systems show several unusual features. There is a pronounced subdiffusive regime in liquids near and below the melting temperature. This regime reflects the existence of two time scales: a typical phonon period, and the time for a particle to feel a new environment. The second time scale becomes longer as the temperature is lowered or the range of interaction (screening length) increases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453924
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  • 2
    Electronic Resource
    Electronic Resource
    A comparison between integral equation theory and molecular dynamics simulations of dense, flexible polymer liquids (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 1357-1364 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Recently we (J.G.C. and K.S.S.) formulated a tractable "reference interaction site model'' (RISM) integral equation theory of flexible polymer liquids. The purpose of this paper is to compare the results of the theory with recent molecular dynamics simulations (G.S.G. and K.K.) on dense chain liquids of degree of polymerization N=50 and 200. Specific comparisons were made between theory and simulation for the intramolecular structure factor ωˆ(k) and the intermolecular radial distribution function g(r) in the liquid. In particular it was possible to independently test the assumptions inherent in the RISM theory and the additional ideality approximation that was made in the initial application of the theory. This comparison was accomplished by calculating the intermolecular g(r) using the simulated intramolecular structure factor, as well as, ωˆ(k) derived from a freely jointed chain model.The RISM theory results, using the simulated ωˆ(k), were found to be in excellent agreement, over all length scales, with the g(r) from molecular dynamics simulations. The theoretical predictions using the "ideal'' intramolecular structure factor tended to underestimate g(r) near contact, indicating local intramolecular expansion of the chains. This local expansion can be incorporated into the theory self consistently by including the effects of the "medium induced'' potential on the intramolecular structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457159
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  • 3
    Electronic Resource
    Electronic Resource
    The nature of flexible linear polyelectrolytes in salt free solution: A molecular dynamics study (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 1669-1690 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present results of molecular dynamics simulations of linear polyelectrolytes in solution. The fundamental model for polyelectrolytes in solution is studied. Specifically, simulations are performed for multichain systems of a flexible chain model of charged polymers. The full Coulomb interactions of the monomers and counterions are treated explicitly. Experimental measurements of the osmotic pressure and the structure factor are reproduced. The simulations reveal a new picture of the chain structure based on calculations of the structure factor, persistence length, end-to-end distance, etc. We present a detailed discussion of the chain structure and a comparison with present theories. In contrast to the predicted dilute limit of rodlike chains, we find that the chains have significant bending at very low densities. Furthermore, the chains contract significantly before they overlap. We also show that counterion condensation dramatically alters the chain structure. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470698
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  • 4
    Electronic Resource
    Electronic Resource
    Efficient continuum model for simulating polymer blends and copolymers (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 10583-10594 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An efficient continuum model for simulating polymer blends and copolymers is presented. In this model, the interactions are short-range and purely repulsive, thus allowing for excellent computational performances. The driving force for phase separation is a difference in the repulsive interaction strength between like and unlike mers. The model consists essentially of a molecular-dynamics algorithm, supplemented by an appropriate Monte Carlo exchange process. To demonstrate the effectiveness of the model we study two systems, a symmetric binary blend of polymers and a symmetric diblock copolymer system. For the binary blend, we determine the phase diagram and find, as predicted by theory, that the critical interaction parameter scales with the inverse of the chain length of the polymers. For the diblock copolymer system, we study both the one-phase region and the microphase separated lamellar region. For the latter, we show that constant-pressure algorithms are more appropriate since, contrary to recent lattice simulations, the lamellar spacing can self-adjust in such an ensemble. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472978
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  • 5
    Electronic Resource
    Electronic Resource
    From many monomers to many polymers: Soft ellipsoid model for polymer melts and mixtures (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 4340-4348 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present an extremely efficient and rather general model in which whole polymer chains are represented as soft particles. The particles are characterized by their overall sizes and shapes, as given by the conformations of the underlying chains. The probability of occurrence of a particle with a given size determines its internal free energy. The density of monomers within each particle is calculated from all conformations that have the same size. The interaction between two particles is taken to be proportional to the spatial overlap of their monomer density distributions. When a large number of such particles are brought into contact, as is the case for a polymer melt, the interactions between the particles force them to shrink and modify the equilibrium size distribution. We show by simulations that this model leads to a Gaussian statistics of the chains in melt. Since the internal degrees of freedom of a chain are integrated out, a large number (of order 104) of long (e.g., N=100) chains can be simulated within reasonable computer time on a single work-station processor. A straightforward extension of this model is used to study symmetric polymer blends. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475835
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  • 6
    Electronic Resource
    Electronic Resource
    A new mechanism for penetrant diffusion in amorphous polymers: Molecular dynamics simulations of phenol diffusion in bisphenol-A-polycarbonate (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 6061-6068 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Atomistic molecular dynamics simulations are performed to analyze the diffusion of phenol molecules in a bisphenol-A-polycarbonate melt in the zero concentration limit for the temperature range from 500 K to 640 K. The transition from a hopping diffusion to a continuous diffusion is observed. Visualization of the diffusion process reveals a strong coupling between the polymer dynamics, i.e., size and shape fluctuations of the pore space and the hopping of the penetrant. Proper equilibration of the melt has been ensured by application of a novel multiscale simulation approach. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479904
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  • 7
    Electronic Resource
    Electronic Resource
    Time–temperature and time–density superposition in the simulation of rheological properties of polymers (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3288-3293 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Applying a periodical elongational strain in a computer simulation of polymer melts and networks, we are able for the first time to employ a time–temperature and time–density superposition in a numerical experiment for the study of the dynamic moduli. The simulation results can be analyzed and understood within the semiempirical free volume concept. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479608
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  • 8
    Electronic Resource
    Electronic Resource
    Critical exponents and scaling functions of a self-avoiding walk interacting with a defect plane (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 5882-5887 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We analyze the behavior of a single self-avoiding walk (single polymer in good solvent) in the presence of a penetrable (d−1) dimensional defect layer by the use of Monte Carlo simulations. The layer can be either neutral to the bonds or can be attractive or repulsive. We analyze the data by means of a scaling picture and show that there is an excellent agreement with the deGennes, Bray, and Moore conjecture cursive-phi=1−ν for the crossover exponent. This corrects a recent estimate of cursive-phi made by a series analysis of enumeration data of short chains.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449618
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