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  • 1
    Electronic Resource
    Electronic Resource
    Nonlinear viscoelasticity of wormlike micelles (and other reversibly breakable polymers) (1990)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 94 (1990), S. 371-375 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100364a063
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  • 2
    Electronic Resource
    Electronic Resource
    Dynamic relaxation of rodlike micelles (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 8529-8536 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We study theoretically the angular relaxation and translational diffusion of stiff rodlike micelles that can undergo reversible scission reactions, in both the dilute and the entangled regime. The very strong dependence of the angular diffusion constant on rod length leads to an anomalous superdiffusive behavior of the typical angular deflection of a subunit at short times. Despite this, angular correlation functions such as 〈u(t)⋅u(0)〉 (also the linear birefringence and entropic stress response) decay exponentially with a relaxation time that is a power law combination of the time scales for reversible scission and for angular rotation of a (hypothetical) unbreakable rod. This relaxation time corresponds to the waiting time for a subunit to find itself on a rod that is short enough to rotate through an angle of order π before recombining with another rod. The translational diffusion of rodlike micelles shows no anomaly in contrast to the angular case. However, the collective diffusion and self-diffusion constants differ by a factor of 2 at all concentration ranges for which rod micelles exist. The diffusion equation for collective motion is nonlinear (even below the overlap threshold) since the mobility of the rods depends on their local concentration. The dynamic structure factor S(q,t) is calculated to order q4, the quartic terms providing, in principle, a probe of the micellar scission time.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460086
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  • 3
    Electronic Resource
    Electronic Resource
    Living networks: The role of cross-links in entangled surfactant solutions (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 1367-1375 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We study theoretically the effects of cross-link formation in the entangled micellar phase of viscoelastic surfactant solutions. We consider equilibrium cross-links, of energy E(very-much-greater-than)kBT, that can arise through local fusion of the micelles. For simplicity, we assume that the end-cap energy is much larger than E, so that the system forms a network in which free ends can be neglected. We consider cases when the material between cross-links is (i) a rigid rod, (ii) a Gaussian chain, and (iii) an excluded-volume chain. In each case, we define a "saturated'' network as one for which L(approximately-equal-to)Lb, where L is the arc length between cross-links and Lb that of a geometrical subunit or "blob'' of the network. (An "unsaturated'' network is, in contrast, one for which L(very-much-greater-than)Lb. ) In the rigid-rod case we predict an unsaturated network at all concentrations. For flexible chains we predict that the network is unsaturated at high concentrations, but as the concentration is decreased, these systems should reach saturation, followed at lower φ by a phase separation between a dilute saturated network and excess solvent. Surprisingly, this phase separation should occur even for the case of a very good solvent: there is an entropy gain associated with creating threefold junction points which increases with dilution, and asymptotically overcomes any finite cross-link energy E. In practice, however, this may often be unobservable due to the very small concentrations required, and/or the effects of free ends. We briefly discuss the possible implications of our results for the viscoelastic properties of surfactant solutions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462172
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  • 4
    Electronic Resource
    Electronic Resource
    Stress relaxation in living polymers: Results from a Poisson renewal model (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 4758-4767 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The problem of stress relaxation in entangled, reversibly breakable polymers (e.g., wormlike micelles) is considered. In the case where the dominant diffusive mode for the polymers is reptation, this problem has been treated in earlier numerical work by coupling the full reaction kinetics of scissions and recombinations to the dynamics of reptation (represented by a one-dimensional stochastic process). Here we study a simplified renewal model, which replaces the exact reaction kinetics by a Poisson jump process that neglects temporal correlations in the chain length experienced by a particular monomer or tube segment. Between jumps in chain length, the stress relaxation is presumed to follow that of an equivalent unbreakable chain. We apply the solution to the case of reptating flexible polymers and compare the resulting complex modulus with the earlier numerical treatments. It is found that agreement is very good. The renewal model is then used to analyze in detail, for the first time, the crossover to a rapid-scission regime in which chain diffusion between scission events is dominated by breathing modes. A third regime, in which the motion between scission events is Rouse-like, remains unsuitable for study with this model, for reasons that we explain. Various implications of the renewal model for the interpretation of experimental results are discussed. We also provide explicit estimates for chain lengths in CTAC/NaSal/NaCl systems using experimental Cole–Cole plots.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462787
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  • 5
    Electronic Resource
    Electronic Resource
    Jamming and static stress transmission in granular materials (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Chaos 9 (1999), S. 511-522 
    Details
    ISSN: 1089-7682
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have recently developed some simple continuum models of static granular media which display "fragile" behavior: They predict that the medium is unable to support certain types of infinitesimal load (which we call "incompatible" loads) without plastic rearrangement. We argue that a fragile description may be appropriate when the mechanical integrity of the medium arises adaptively, in response to a load, through an internal jamming process. We hypothesize that a network of force chains (or "granular skeleton") evolves until it can just support the applied load, at which point it comes to rest; it then remains intact so long as no incompatible load is applied. Our fragile models exhibits unusual mechanical responses involving hyperbolic equations for stress propagation along fixed characteristics through the material. These characteristics represent force chains; their arrangement expressly depends on the construction history. Thus, for example, we predict a large difference in the stress pattern beneath two conical piles of sand, one poured from a point source and one created by sieving. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.166456
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  • 6
    Electronic Resource
    Electronic Resource
    The role of added polymer in dilute lamellar surfactant phases (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 5467-5480 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We study theoretically the effect of adding polymer to the dilute lamellar phase of surfactant solutions. The polymer, assumed semidilute and in a good solvent, is taken to have a repulsive or attractive interaction with surfactant bilayers, but has no other effect on their properties. Such polymers can mediate an attractive or repulsive interaction between bilayers which we combine with pre-existing interactions (the Helfrich repulsion, van der Waals, and hydration) using a simple additive model. The polymeric contribution to the free energy is estimated using a blob model (for nonadsorbing chains) and the Cahn–de Gennes scaling functional (for adsorbing chains). Phase diagrams for the system are obtained under various conditions. For a lamellar phase which is bound (i.e., which cannot be indefinitely diluted) as a result of van der Waals forces, nonadsorbing polymer is completely expelled as a semidilute solution, leading to a compression of the lamellar stack. Adsorbing polymer can enter the phase, also tending to cause a slight reduction in the maximum layer spacing. For an unbound lamellar phase controlled by Helfrich forces, nonadsorbing polymer is expelled if the bilayers are stiff, but for flexible enough layers, a significant amount of polymer can be solubilized. At too high a volume fraction of polymer, part of the polymer is expelled as a solution, whereas at high surfactant fractions, a phase separation arises between two lamellar phases (one containing polymer, the other not). For the case of adsorbing chains, small amounts of added polymer cause the system to become bound with expulsion of excess solvent. For large amounts of added polymer, the unbound behavior is recovered, whereas for intermediate polymer content, phase equilibria involve either two lamellar phases (each containing polymer), or one such phase coexisting with a polymer solution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465964
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  • 7
    Electronic Resource
    Electronic Resource
    End-evaporation kinetics in living-polymer systems (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 7260-7266 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We study theoretically the process of "end-evaporation'' in living polymer systems, such as wormlike surfactant micelles. End-evaporation occurs when single monomers either break away from, or join onto, a chain end, the rates being described by the (mean-field) rate constants k and k', respectively. Thus the chains can exchange material with one-another via a bath of free monomers. The relaxation of a system of living polymers after a small temperature jump (T-jump) is studied theoretically. The effect of a T-jump is to prepare the system with the wrong mean chain length, which relaxes to its equilibrium value L¯ by end-evaporation. It is found that the number of free monomers in the system relaxes almost completely in a time of order 1/kL¯, while the weight-average chain length, which is the quantity measured in light scattering experiments, relaxes on a time scale τD=4L¯2/k, which is three powers of L¯ longer. We also predict that the stress relaxation after a step strain is dominated by end-evaporation whenever τD(approximately-less-than)τrep, where τrep is the reptation (disengagement) time for a chain of length L¯. In this case the stress relaxation is found to be "stretched exponential'' for times smaller than τD and single exponential for longer times.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465419
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  • 8
    Electronic Resource
    Electronic Resource
    Osmotic pressure of dense emulsion systems: the role of double-layer forces (1993)
    s.l. : American Chemical Society
    Langmuir 9 (1993), S. 2264-2269 
    Details
    ISSN: 1520-5827
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/la00033a004
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  • 9
    Electronic Resource
    Electronic Resource
    Theory of microemulsions: comparison with experimental behavior (1988)
    s.l. : American Chemical Society
    Langmuir 4 (1988), S. 802-806 
    Details
    ISSN: 1520-5827
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/la00082a004
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  • 10
    Electronic Resource
    Electronic Resource
    Rheological properties of semidilute and concentrated aqueous solutions of cetyltrimethylammonium bromide in the presence of potassium bromide (1992)
    s.l. : American Chemical Society
    Langmuir 8 (1992), S. 437-440 
    Details
    ISSN: 1520-5827
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/la00038a020
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