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  • American Institute of Physics (AIP)  (10)
  • 1
    Electronic Resource
    Electronic Resource
    Shape asymmetry of star-branched random walks with many arms (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 3720-3726 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Star-branched (off-lattice) random walks with up to F=96 arms and a total chain-length of up to 15 361 segments have been produced by means of Monte Carlo simulation. Several quantities that characterize the shape asymmetry of molecules have been calculated. By suitable regression long-chain limits of these quantities were obtained and analyzed with respect to the number of arms. Shape factors as well as asphericities are described very well by polynomials in F−1 or F−1/2, respectively. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468554
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  • 2
    Electronic Resource
    Electronic Resource
    Shape asymmetry of random walks and nonreversal random walks (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 636-639 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Random walks (RWs) and nonreversal random walks (NRRWs) embedded in various lattices and freely jointed (off-lattice) chains—consisting of up to N≈1000 segments—have been produced and analyzed with respect to their instantaneous shape. While the results of different RWs (as expected) coincide for all chain-lengths examined, the short-chain behavior of NRRWs is strongly dependent on the lattice type. In the limit of infinitely long chains, however, quantities characteristic of the shape converge to common values for all types of RWs and NRRWs examined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466926
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  • 3
    Electronic Resource
    Electronic Resource
    Monte Carlo investigations of dense copolymer systems II, Properties of ABA triblocks (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 428-436 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In the present article we give a detailed analysis of ABA triblock copolymers in a selective solvent that is a good one for the outer blocks and a theta solvent for the inner one. A lattice model is used for the investigations and the concentration ranges from a volume fraction φ=0 up to φ=0.8. The results are compared to the behavior of the constituent homopolymers, i.e., homopolymers in athermal (AAA) and theta solvent (BBB). In the limit φ→0 the concentration dependence of properties of the whole chain as well as properties of individual blocks, may be deduced from pair-data with excellent precision for all systems under consideration. For large concentrations mean square dimensions of ABA markedly exceed that of AAA or BBB, respectively, due to microphase separation which becomes evident for concentrations larger than φ(approximate)0.4 which corresponds to the point where intermolecular and intramolecular interactions are equally important. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480655
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  • 4
    Electronic Resource
    Electronic Resource
    Monte Carlo simulations of asymmetric polymer blends (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 4646-4650 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Quasibinary asymmetric polymer blends (the average chain lengths of one component being 100 while the other is varied between N=1 and N=100) well below the critical temperature were simulated on a five-way cubic lattice using the Monte Carlo method. The bulk density was kept constant by adjusting the energy parameter ε according to a power law ε∼N−0.8. Quantities employed for the characterization of the interface region were its thickness (calculated from the shape of the density profile), the cavity structure (evaluated from the number of heterocontacts) and the roughness of the interface (described by the relative surface enlargement and some sort of fractal dimension). In general, the interface region becomes thinner, the roughness decreases, and the cavity structure becomes less pronounced with decreasing average chain length of one component, due to the reduced degree of entanglement in the interface. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477069
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  • 5
    Electronic Resource
    Electronic Resource
    Shape distribution and correlation between size and shape of tetrahedral lattice chains in athermal and theta systems (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 3691-3698 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Chains embedded in the tetrahedral lattice have been produced by means of Monte Carlo simulation for athermal and for theta conditions. Nonreversal random walks (random walks without backfolding bonds) have been generated as a reference. Probability distributions of an asphericity factor δ*, of a prolatness factor S*, and of shape factors sfi* have been evaluated, the quantities being based on the orthogonal components of the squared radius of gyration taken along the principal axes of inertia. In addition, the correlation between δ* and other shape descriptors as well as between δ* and quantities characteristic of the size of configurations have been evaluated. In accordance with existing literature, the distributions H(δ*) and H(S*) are found to be very broad. The distributions H(sf1*) of the small and H(sf3*) of the large shape factor (sf1*≤sf2*≤sf3*, sf1*+sf2*+sf3*=1) are clearly distinct from each other, while the distribution of sf2* overlaps with that of sf1* and (slightly) with H(sf3*). Distributions of theta chains ("unperturbed" polymer) coincide fairly well with respective distributions of nonreversal random walks (which in turn are nearly identical to those of (off-lattice) random walks. As a matter of course, other shape descriptors are directly correlated with the asphericity factor δ*. Actually, for all systems evaluated, the global size of configurations is strongly correlated with δ* as well: The larger the asymmetry the larger are the dimensions of the configuration under consideration. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476966
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  • 6
    Electronic Resource
    Electronic Resource
    Monte Carlo simulations of symmetric polymer blends. I. Characterization of the interface (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 8214-8225 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A new method is presented for the simulation of the interface between nearly immiscible amorphous polymer phases. Strictly speaking, two independent interfaces are developed whose positions remain fairly in place during the whole simulation process. The interface is characterized by its thickness, by the excess number of contacts between segments of different type in the interface region (a quantity being characteristic of cavities that contain the other type of polymer) as well as by the fractal dimension and the relative surface enlargement (compared to a totally flat interface) similar to the methods introduced earlier for polymer surfaces. Further quantities that are used for a proper description of the interface are density profiles of polymer segments as well as of end segments and centers of mass. A variation of the repulsive energy between the two types of polymers on the one hand and a variation of the (average) chain length on the other hand reveals that the roughness of the interface decreases with increasing immiscibility (increasing energy parameter) and decreasing chain length (when the product of energy parameter and chain length is kept constant). © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476177
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  • 7
    Electronic Resource
    Electronic Resource
    Shape distribution and correlation between size and shape of star-branched tetrahedral lattice chains in athermal and theta systems (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 4668-4677 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: By means of Monte Carlo simulation, linear (F=2) and star-branched tetrahedral lattice chains with F=3–12 arms of length n=480 connected to a hard core consisting of MIN(5,F+1) segments (the total number of segments thus ranging from 963 to 5765) were produced for athermal and theta conditions. Nonreversal random walks (random walks without backfolding bonds) were generated as a reference. Several quantities (asphericity factor δ*, prolateness factor S*, and shape factors sfi*) characteristic of the instantaneous shape of molecules—being based on the orthogonal components of the squared radius of gyration taken along the principal axes of inertia—were computed. The probability distributions of these quantities were calculated and their interdependence as well as their correlation with quantities characteristic of the size of configurations was analyzed. Shape and size of star-branched chains for athermal as well as for theta conditions are highly correlated as earlier found for linear chains and random walk stars. The broadness of distribution functions decreases with increasing number of arms, but remains appreciably for F=12, the system with the largest functionality evaluated. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478350
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  • 8
    Electronic Resource
    Electronic Resource
    Monte Carlo simulations of symmetric polymer blends. II. Chain properties in interface regions (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 8226-8234 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Making use of a previously introduced lattice model for binary polymer blends of limited miscibility Monte Carlo simulations have been performed in order to investigate the influence of different thermodynamic conditions on mass segregation and global structure as well as on microstructure of homopolymers when passing from one bulk phase through the interface to the other. The calculations show an enrichment of shorter chains at the interface as well as a decreasing miscibility with decreasing average chain length (at constant bulk density) of the polymer matrix on the one hand and relate the compression of the coils at the interface to the observed orientation and deformation effects on the other. Surprisingly, an additional expansion of the polymer coils (belonging to the minority component) can be found at some distance from the actual interface due to attractive interactions between pairs of chains in rather "diluted" layers. Furthermore, all phenomena are discussed from two different viewpoints: (i) The average chain length is kept constant while the energy parameter is varied, and (ii) the chain length is varied and the bulk densities are held constant by use of identical relative energy parameters. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476178
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  • 9
    Electronic Resource
    Electronic Resource
    Concentration dependence of static chain properties 2, off-lattice Monte Carlo simulations (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 10214-10224 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Monte Carlo simulations of polymer chains in off-lattice systems under theta and athermal conditions have been performed in order to support results obtained for cubic lattice chains in assemblies of varying concentration. Global as well as local quantities are investigated in detail in order to point out the differences as well as the similarities of the results and the reliability of the two models, especially with respect to local packing effects. Furthermore, the results are discussed with reference to theoretical predictions of the scaling theory. Probably the most important finding is the fact that an isolated θ chain and a chain in bulk exhibit totally different microscopic structures (which is in full concordance with our previous lattice simulations), although the global dimensions of bulk polymers tend to converge to the values of an isolated θ chain. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474162
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  • 10
    Electronic Resource
    Electronic Resource
    Monte Carlo simulation studies of the correlation between global size and helical structures in biopolymers (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 6236-6242 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: There are several secondary structures in biological macromolecules such as beta sheets, loops, and helices. The subject of the present paper is to adopt different methods of inducing certain quotas of helical regions in macromolecules and to examine how the quota of helices influences global properties such as the radius of gyration. Two different methods were used to produce the chains on a tetrahedral lattice; a static step-by-step method with deliberately chosen probabilities of bond vectors in order to favor helices, and a dynamic method with intrachain potentials which induced the formation of helices, the latter approach being a simple model of self organization. Comparison of the results of the different methods revealed correspondence in many points but—not unexpectedly—also some differences, because of the use of different effective potentials in the polymer formation processes. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1398589
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