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  • 1
    Electronic Resource
    Electronic Resource
    On the partitioning of cosurfactant in mixed micelles: size enhancement and nematic stability (1985)
    s.l. : American Chemical Society
    Langmuir 1 (1985), S. 101-103 
    Details
    ISSN: 1520-5827
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/la00061a016
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  • 2
    Electronic Resource
    Electronic Resource
    A van der Waals picture of the isotropic-nematic liquid crystal phase transition (1980)
    s.l. : American Chemical Society
    Accounts of chemical research 13 (1980), S. 290-296 
    Details
    ISSN: 1520-4898
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ar50152a007
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  • 3
    Electronic Resource
    Electronic Resource
    Photodissociation of the formaldehyde molecule: does it or doesn't it? (1980)
    s.l. : American Chemical Society
    Chemical reviews 80 (1980), S. 403-416 
    Details
    ISSN: 1520-6890
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/cr60327a002
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  • 4
    Electronic Resource
    Electronic Resource
    Nonradiative electronic relaxation under collision-free conditions (1977)
    s.l. : American Chemical Society
    Chemical reviews 77 (1977), S. 793-833 
    Details
    ISSN: 1520-6890
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/cr60310a002
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  • 5
    Electronic Resource
    Electronic Resource
    Identification of two Drosophila TGF-β family members in the grasshopper Schistocerca americana (1995)
    Springer
    Journal of molecular evolution 41 (1995), S. 155-160 
    Details
    ISSN: 1432-1432
    Keywords: TGF-β superfamily ; decapentaplegic gene ; Drosophila melanogaster ; Schistocerca americana ; Gene comparison
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Intercellular signaling molecules of the transforming growth factor-β (TGF-β) superfamily are required for pattern formation in many multicellular organisms. The decapentaplegic (dpp) gene of Drosophila melanogaster has several developmental roles. To improve our understanding of the evolutionary diversification of this large family we identified dpp in the grasshopper Schistocerca americana. S. americana diverged from D. melanogaster approximately 350 million years ago, utilizes a distinct developmental program, and has a 60-fold-larger genome than D. melanogaster. Our analyses indicate a single dpp locus in D. melanogaster and S. americana, suggesting that dpp copy number does not correlate with increasing genome size. Another TGF-β superfamily member, the D. melanogaster gene 60A, is also present in only one copy in each species. Comparison of homologous sequences from D. melanogaster, S. americana, and H. sapiens, representing roughly 900 million years of evolutionary distance, reveals significant constraint on sequence divergence for both dpp and 60A. In the signaling portion of the dpp protein, the amino acid identity between these species exceeds 74%. Our results for the TGF-β superfamily are consistent with current hypotheses describing gene duplication and diversification as a frequent response to high levels of selective pressure on individual family members.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00170667
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  • 6
    Electronic Resource
    Electronic Resource
    Flow-induced gelation of living (micellar) polymers (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 7710-7727 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We consider the effect of shear velocity gradients on the size (L) of rodlike micelles in dilute and semidilute solution. A kinetic equation is introduced for the time-dependent concentration of aggregates of length L, consisting of "bimolecular'' combination processes L+L' →(L+L') and "unimolecular'' fragmentations L→L'+(L−L'). The former are described by a generalization (from spheres to rods) of the Smoluchowski mechanism for shear-induced coalesence of emulsions, and the latter by incorporating the tension-deformation effects due to flow. Steady-state solutions to the kinetic equation are obtained, with the corresponding mean micellar size (L¯) evaluated as a function of the Peclet number P, i.e., the dimensionless ratio of flow rate γ(overdot) and rotational diffusion coefficient Dr. For sufficiently dilute solutions, we find only a weak dependence of L¯ on P. In the semidilute regime, however, an apparent divergence in L¯ at P(approximately-equal-to)1 suggests a flow-induced first-order gelation phenomenon.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462371
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  • 7
    Electronic Resource
    Electronic Resource
    Molecular theory of curvature elasticity in surfactant films (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 6800-6817 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We develop a microscopic-level formulation for the curvature elasticity of monolayer and bilayer systems of typical surfactant molecules. It is argued that both the bending and saddle-splay force constants k and k¯ are determined primarily by the conformational entropy of the flexible hydrocarbon chain rather than by the electrostatic interactions associated with hydrophilic head groups. A priori estimates of the chain contributions are made for the first time, without the use of any adjustable parameters. Both k and k¯ are shown to be calculable wholly from the conformational statistics describing the planar film. In particular, these constants are expressed in terms of the derivatives and moments of the lateral pressure profile characterizing chain packing in the unbent layers. By considering the dependence of the curvature elasticity on chain length, area per molecule, and composition in mixed films, we are able to account for the order-of-magnitude variations in k observed in a variety of different surfactant systems. The replacement of long chain molecules by short ones is shown to be especially efficient in lowering the bending energy from 10's of kBT to kBT. The effect of "free'' vs "blocked'' exchange are also presented and contrasted with the case of fixed area-per-molecule bending deformation. Finally, monolayer vs bilayer results are compared and the calculated signs and magnitudes of k and k¯ are discussed in the context of planar bilayer stability.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458267
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  • 8
    Electronic Resource
    Electronic Resource
    Effect of elongational flow on the orientational order phase transitions and viscosity of hard rod fluids (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 597-598 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We consider the generalized Smoluchowski equation for the orientational distribution of interacting hard rod-like particles. Using the Onsager theory of excluded volume in these systems, we solve for steady-state solutions to this equation in the special case of elongational flow. Accordingly, we obtain explicit predictions concerning the effect of such flow on the suppression of orientional ordering phase transitions and on the nonlinear behavior (dependence on velocity gradient) of the viscosity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456459
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  • 9
    Electronic Resource
    Electronic Resource
    Curvature defects in lamellar phases of amphiphile–water systems (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 3030-3041 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Within the framework of two complementary models, we show that the densities and patterns of defects in amphiphile–water systems with lamellar organization are coupled to the strength of the bilayer–bilayer interactions and hence to the overall surfactant concentration. We consider defects which introduce curvature (i.e., larger head-group area per molecule) while preserving the integrity of stacked bilayers at surfactant volume fractions of several tenths. These features are favored if the molecules comprising the lamellae are preferentially packed with a nonplanar aggregate–water interface: curvature defects lower the local free energy in systems constrained by aggregate–aggregate interactions to lamellar geometry. As the amphiphile volume fraction is increased—and the bilayer–bilayer spacing thereby decreased—we predict phase transitions between lamellar phases of different defect patterns on the bilayer surface, with concurrent decrease in the defect area fraction per bilayer. Specifically, there is a progression from a stripe-like pattern of parallel channels to a random network of line defects to a pore phase, with the latter appearing at the highest amphiphile concentrations but characterized by the lowest density of defects. Connection is made with experimental work which has recently suggested various departures from classical lamellar structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459826
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  • 10
    Electronic Resource
    Electronic Resource
    Isotropic–nematic transition in micellized solutionsa) (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 5616-5623 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We treat the isotropic-to-nematic transition in polydisperse suspensions of micellar rods. By generalizing an early theory of Onsager, we obtain a first-order transition in which the ordered rods are significantly longer than those in the (coexisting) isotropic phase. We show that this "growth'' is driven by the free energy term arising from loss of orientational entropy upon alignment. For large aggregates the product ρ¯L¯2D (where L¯ is a number-averaged length, D the diameter of the rods, and ρ¯ the number density of aggregates) is roughly constant for each phase at coexistence. The transition value of the (nematic) order parameter ((approximately-equal-to)〈P2(cos θ)〉) first increases linearly with aggregation number s (for small rods) and approaches unity asymptotically (for large s). We compare our results to those of an earlier, monodisperse treatment of this system and interpret the nematic-induced growth in terms of coupling between rod size and alignment in micellar solutions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.448597
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