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  • 1
    Electronic Resource
    Electronic Resource
    Effects of a fumed silica network on kinetics of phase separation in polymer blends (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 9418-9423 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have carried out a systematic investigation of the kinetics of domain growth of a model binary mixture in contact with a fractal network similar to the fumed silica network used in recent experiments with polymer blends. This network has selective affinity for one component of the blend. We study the morphology of the growing domains and the wetting layer, the growth exponent, and dynamical scaling behavior for a critical composition of the mixture. We find that the characteristic size of domains grows as t1/3 for deep quenches, as long as the average domain size is small compared to the average "pore" radius of the unoccupied region. This suggests that the kinetics of domain growth at intermediate times is not appreciably perturbed by the presence of the network. For off-critical compositions, we study domain growth in two different situations where either the majority or the minority component of the blend wets the network. When the majority component wets the network, a network-induced nucleation is possible for sufficiently off-critical mixtures due to the reduction or elimination of the local nucleation barrier for the minority phase near the network. For this reason, minority droplets nucleate predominantly near the network before they appear in the bulk. When the minority phase wets the network, a slowdown in wetting layer growth is found to occur at late times due to a depletion of the system of its minority component. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479854
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  • 2
    Electronic Resource
    Electronic Resource
    Hydrodynamic effects on domain growth in off-critical polymer blends (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 6006-6013 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Starting from a coarse-grained model, which includes hydrodynamic interactions, we numerically study kinetics of phase separation in a two-dimensional model of a polymer blend. In the absence of hydrodynamics, domains grow according to the Lifshitz–Slyozov power law without any evidence of pinning, regardless of the relative concentration of the blend components. In the presence of hydrodynamics, our results suggest that critical and off-critical mixtures are characterized by different growth laws. For the critical composition of the blend, hydrodynamic effects are found to be important during the entire growth process and this leads to a larger growth exponent. On the other hand, for off-critical blends, hydrodynamic effects are important only for blends with volume fraction not far away from the critical value. Even in these cases, domains show a faster growth only at intermediate times under the influence of hydrodynamics; subsequently the growth exponent crosses over to a Lifshitz–Slyozov value at late times. This gives strong support to the argument that the apparent pinning of domain growth observed in experiments on off-critical polymer blends may be due to this crossover phenomenon. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476013
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  • 3
    Electronic Resource
    Electronic Resource
    Shear effects on phase separating polymer solutions: A molecular dynamics study (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 10582-10587 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We study phase separation of quenched polymer solutions under an external shear flow by using a stochastic molecular dynamics method. We observe the formation of a stringlike pattern of polymer domains normal to the direction of the shear flow. The characteristic size of the layered domains has a power law relation with the shear rate. Shear-induced rheological behavior of the mixture is also examined in terms of the excess viscosity. We find that the maximum excess viscosity scales as the shear rate, and that the numerical value of the power-law exponent agrees well with theoretical scaling predictions. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481692
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  • 4
    Electronic Resource
    Electronic Resource
    Morphology of thin block copolymer films on chemically patterned substrates (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 6897-6905 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present results from a numerical study of a coarse-grained model of di-block copolymer (BCP) thin films confined between two hard walls. One of these walls is neutral to the components of the BCP melt and the other one contains chemical inhomogeneities with a repeat spacing length scale comparable to the linear size of the BCP molecules. We find that the morphology of the BCP thin film is strongly influenced by the commensurability between the bulk unconstrained lamellar size λ*, and the linear size of the surface inhomogeneities w. When w(approximate)λ*/2, the ordered morphology of the diblock copolymers has a strong overlap with the pre-assigned substrate chemical pattern throughout the film. However, for w(approximate)λ*, the overlap strongly depends on the distance from the substrate surface. Close to the substrate surface, the overlap of the morphology with the pre-assigned chemical pattern is large but the pattern becomes out-of-phase at a distance of approximately λ*/2 from the substrate. For w(approximate)3λ*/4, the morphology of the diblock copolymers is either similar to that for w(approximate)λ*/2 or for w(approximate)λ*, depending on the film thickness. For some film thickness, the morphology shows a mixed characteristics of the morphologies for w(approximate)λ*/2 and w(approximate)λ*.© 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476118
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  • 5
    Electronic Resource
    Electronic Resource
    Surface-induced ordering in block copolymer melts (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 3310-3317 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Surface-induced ordering in block copolymer melts is studied numerically. For symmetric copolymers, the thickness of the surface-enrichment layer is found to scale as Req∼Nθ with θ≈0.6, suggesting the system is undergoing a surface-induced strong segregation. The density profile perpendicular to the interacting surface is described quite well by the form predicted by Fredrickson in a mean-field analysis. In asymmetric copolymers, the surface is found to have a profound effect on domain formation. For some off-critical compositions, domains were found to form near the surface with a geometry different from that in the bulk; while for stronger asymmetry in composition, minority domains were nucleated near the wall only, long before any formed in the bulk. These interesting pattern formation processes should be observable in experiments using a depth profiling technique.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467578
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  • 6
    Electronic Resource
    Electronic Resource
    Phase separation dynamics in off-critical polymer blends (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 2451-2458 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A numeric integration of the spinodal decomposition process in an off-critical mixture of binary polymer blends is carried out to late times. The thermal fluctuation term in the evolution equation is found to be essential to avoid "freezing'' of domain growth for such systems, an effect not present in small molecule systems. For deep quenches, late time domain growth follows the Lifshitz–Slyozov law and the scaling hypothesis is found to hold, although the scale invariant function differs in shape from the one obtained for a critical quench to the same temperature. For shallow quenches, although no freezing is observed, domain growth is found to be progressively slower as the spinodal curve is approached. For the model considered here, we do not find any evidence of the sharp transition in behavior that would be associated with a "transnodal''.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464172
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  • 7
    Electronic Resource
    Electronic Resource
    Structure formation in self-associating polymer and surfactant systems (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 3251-3254 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We use Monte Carlo simulation techniques to investigate the important factors controlling the aggregation of self-associating polymers and surfactants in solution. We consider both irreversible and reversible aggregation among the association sites on the polymers. For different monomer concentrations and chain lengths we compute the number of intrachain and interchain associations. It is found that the monomer concentration separating regimes of primarily intra- and interchain associations depends upon the location of association sites on the polymers. This suggests that the distribution of stickers along the chains can be an important factor in controlling macroscopic properties of these systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461969
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  • 8
    Electronic Resource
    Electronic Resource
    Dynamics of phase separation in a binary polymer blend of critical composition (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 6899-6909 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report results of a detailed numerical study of the phase separation process in a three dimensional model of polymer blends. The model system considered by us is described by Flory–Huggins–de Gennes free-energy functional. For a critical quench, we numerically integrate the corresponding time evolution equation for the conserved order parameter based on the above free-energy functional. We study the time dependence of the characteristic domain size as well as the pair correlation function and the structure factor for several quench temperatures. The results indicate that the growth law for the characteristic domain size is given by a modified Lifshitz–Slyozov law and the growth law exponent is independent of the quench temperature. We also find that both the pair correlation function and the structure factors show dynamical scaling at late times.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458277
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  • 9
    Electronic Resource
    Electronic Resource
    Computer simulation of the aggregation process in self-associating polymer and surfactant systems (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 5687-5693 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present results of numerical simulations of a new model for the clustering process in self-associating polymer systems. We focus on two experimentally interesting systems; telechelic ionomers and reverse micelles. The clustering dynamics introduced by us is an extension of the Eden method, previously used in the context of single particle aggregation. The structure of the aggregates seen in the simulations is qualitatively similar to that observed in experimental systems. The quantitative predictions of the model are found to be similar to those found in simulations of a model based on a diffusion-limited-aggregation-type process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457522
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  • 10
    Electronic Resource
    Electronic Resource
    Spin-glass transition in the random anisotropy axis model (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 3735-3737 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The critical behavior of the Random Anisotropy Axis model (RAM) is studied by the Monte Carlo simulation method in the limit of infinite anisotropy. Finite size scaling analysis of the data for equilibrium averages strongly suggests a zero temperature critical point in two dimensions and a finite temperature phase transition in three dimensions. The values of the critical exponents in both two and three dimensions indicate that RAM belongs to the same universality class as that of short-range Ising spin-glass models.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.341163
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