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  • 1
    Electronic Resource
    Electronic Resource
    Entanglement between a polymeric ring and a rod (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 7136-7143 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ring polymers are represented on a computer with the bead–stick model. If an infinitely thin spike is inserted at some (minimum) distance r from the center of mass of a Gaussian ring of contour length N, the probability P(r,N,w) of the ring winding a nonzero number of times w about the spike is nearly given by A exp[−(r/Rg)2/2σ2], where A and σ depend on N and w, and Rg is the radius of gyration of the polymer. We also find that the asymptotic results of related theoretical calculations cannot be realized in systems of practical size. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470342
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  • 2
    Electronic Resource
    Electronic Resource
    Pattern recognition by polyelectrolytes (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 4723-4731 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The statistical mechanical problem of recognition of different patterns imprinted on a surface by polyelectrolyte chains is studied. The necessary condition for the binding of a polyelectrolyte in a salt solution to an oppositely charged pattern is derived in terms of the charge densities of the polymer and the pattern, Debye length, characteristic size of the pattern, and the molecular weight of the polymer. The key features of the criterion for the binding are supported by Monte Carlo simulations. We find the kinetics of the recognition process to take place in two distinct stages: a fast complexation without registry and a very slow occurrence of registry. We show that the distance between different trajectories in the second stage diverges with time due to the untimely minimization of temporal free energy. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470691
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  • 3
    Electronic Resource
    Electronic Resource
    The influence of shear on the ordering temperature of a triblock copolymer melt (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 1589-1599 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The effect of shear on the ordering temperature of a triblock copolymer melt of polystyrene-polybutadiene-polystyrene (SBS) is examined by in situ small angle neutron scattering (SANS). Results obtained by SANS are compared to the rheologically determined order–disorder transition temperature, TRODT=115±5 °C. The SANS measurements from a Couette geometry shear cell are then used to construct a "dynamical phase diagram'' based on characteristic changes in the scattering with temperature and shear rate, γ(overdot). A shear rate dependent ordering temperature, Tord(γ(overdot)), is identified as the system is sheared isothermally from the disordered state. The scattering behavior is shown to be highly strain dependent. We compare our findings on the shear rate dependence of the ordering transition in triblock materials with previous observations on diblock copolymer materials and theoretical expectations for the shear rate dependence of the order–disorder transition temperature. A simple scaling argument leads to a good description of the shear rate dependence of Tord(γ(overdot)) in both diblock and triblock copolymer measurements over the range of shear rates examined. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470747
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  • 4
    Electronic Resource
    Electronic Resource
    Localized structures of polymers with long-range interactions (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 691-700 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The configurational properties of a heteropolymer with prescribed sequences of known concentrations of dipolar segments are investigated. The theoretical analysis of a model chain capable of aggregation into domains shows that entropic frustrations lead to localized structures. In these structures, polymer size is determined dominantly by the formation of aggregates and not by the chain length. This localization effect occurs in addition to the familiar aspects of helix-coil and coil-globule transitions. The formation of localized structures as predicted by the theory is verified by Monte Carlo simulations of heteropolymers bearing segments with dipolar interactions. The transition of a rodlike configuration into a coil can be induced in a sharp manner also by dilution of the chain backbone. The simulations show that disordered homopolymers bearing segments with dipolar or other long-ranged inverse power law interactions do not undergo any phase transition to an ordered state at nonzero temperatures. The ability of a heteropolymer with dipolar and neutral segments to form localized structures is found to be nontrivially controlled by the specificity of the sequences. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470866
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  • 5
    Electronic Resource
    Electronic Resource
    Stretch-collapse transition of polyelectrolyte brushes in a poor solvent (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 11335-11346 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: This paper describes the behavior of charged, polymer brushes in electrolyte solutions of varying solvent quality. The brush height, d, dependence on the chain length, L (=Nl, where l is the Kuhn length), the grafting density σ, and solvent conditions is determined. We consider a monomer–monomer potential consisting of three components: (1) a long-ranged, screened Coulombic component of strength v¯/l (l is the Kuhn length) and range κ−1; (2) a short-ranged, two-body component of strength w¯l; and (3) a short-ranged, three-body component of strength u¯l3. In particular, we examine the transition from a stretched state to a collapsed state in a poor solvent (w¯〈0) as the solvent quality is decreased. Using dimensional analysis, Monte Carlo methods, and a variational technique, a first order transition is observed as predicted by the scaling arguments of Ross et al. and Borisov et al. for high charge/grafting densities. Using a variational procedure, we derive an analytical expression for the brush size and determine, quantitatively, the critical conditions for a first order transition in terms of key dimensionless variables, vN5/2, κlN1/2, wN3/2, and uN2 (where v=2πσl2v¯, w=σl2w¯, and u=σ2l4u¯). © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472984
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  • 6
    Electronic Resource
    Electronic Resource
    Dynamics of a suspension of spheres and rigid polymers: Effect of geometrical mismatch (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 4846-4870 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An effective medium approach together with a multiple scattering formalism is considered to study the steady-state dynamics of suspensions of spheres and polymer chains without excluded volume interactions. The polymer chains are assumed to obey rigid-body dynamics (without rotation) and are taken to be so long that Gaussian statistics is applicable. We have considered the dynamics of probe objects (either a sphere or a polymer) in a solution containing spheres and polymers. The significance of the dimensionless variables appearing when solving the effective medium equations and, in particular, the role of the geometrical parameter t=Rg/a (a is the radius of any sphere and Rg the radius of gyration of a polymer chain) are discussed. The translational diffusion coefficients of the moving probe sphere DS and of the center-of-mass of the probe polymer chain DP, and the shear viscosity of the suspensions have been derived. Both the friction coefficient of the probe sphere or that of the probe polymer chain and the shear viscosity diverge as ΦPOL→0.31 in the presence of polymers in the solution. Also, when polymers are diffusing in a suspension of fixed spheres an optimum range of ΦSP that maximizes the difference in the diffusion coefficients of polymer chains characterized by distinct t values has been noticed. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472322
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  • 7
    Electronic Resource
    Electronic Resource
    Polyelectrolyte Brush Density Profiles (1995)
    s.l. : American Chemical Society
    Macromolecules 28 (1995), S. 6608-6617 
    Details
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ma00123a031
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  • 8
    Electronic Resource
    Electronic Resource
    Theory of Concentration Dependence of Polymer Relaxation Times in Dilute Solutions (1978)
    s.l. : American Chemical Society
    Macromolecules 11 (1978), S. 843-852 
    Details
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ma60065a001
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  • 9
    Electronic Resource
    Electronic Resource
    Huggins Coefficient for Polymer Solutions with Excluded Volume (1977)
    s.l. : American Chemical Society
    Macromolecules 10 (1977), S. 899-906 
    Details
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ma60059a005
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  • 10
    Electronic Resource
    Electronic Resource
    Double screening in polyelectrolyte solutions: Limiting laws and crossover formulas (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 5183-5199 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have derived general expressions for the Helmholtz free energy of a polyelectrolyte solution and the average size of a labeled chain as functions of polyelectrolyte concentration, salt concentration, and the strengths of excluded volume and electrostatic interaction all varying from very low to very high. We have shown that the bare excluded volume interaction and the electrostatically screened Coulomb interaction between any two segments are both screened by the presence of polyelectrolyte chains at nonzero concentrations. The screening length associated with this excluded volume screening is a function of Debye length and the entropy of the connected polymer and consequently depends on the polyelectrolyte concentration differently at different salt concentrations. By treating the correlation of the monomer density fluctuations, we have derived integral equations coupling the effective interaction between any two segments and the effective step length of a labeled chain. In the limit of the excluded volume screening length and the effective step length being independent of wave vectors, they are related by algebraic equations. These equations reduce to scaling laws with numerical prefactors for semidilute and concentrated polyelectrolyte solutions. Our development provides limiting laws and analytical interpolation formulas for the excluded volume screening length, effective step length, free energy of the polyelectrolyte solution, and the average size of a chain for various polyelectrolyte concentrations in an isotropic solution and for arbitrary strengths of excluded volume and electrostatic interactions. The excluded volume screening leads to an attractive component in the effective potential interaction at intermediate distances between two segmental charges of the same sign. The strength and range of the attractive potential are determined by the concentrations of the polyelectrolyte and the various ions. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472362
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