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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 1440-1448 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Microphase separation of symmetric diblock copolymers between two rigid walls is simulated by a coarse-grained model to study the geometry of the microdomains without presupposing their basic shape. The geometry is found to be dependent on the wall separation and the domains can be either aligned horizontally or vertically. The horizontal geometry is induced by wetting at the walls and lamellas parallel to them develop quickly after a quench from the one-phase region. The vertical geometry involves domains oriented perpendicular to the walls and develops much more slowly. For identical walls, some segregation of the wetting phase to the walls is observed for the vertical geometry. This segregation does not significantly change the structure. If the vertical phase develops between walls that attract opposite phases, however, a linear concentration profile develops. In some cases the structure of this vertical phase is found to be quite different from simple, perpendicularly oriented lamellas. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 1579-1588 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present and compare results from Monte Carlo and self-consistent-field studies of a grafted brush of polyelectrolyte chains (of length N), interacting via a screened-Coulombic potential. We examine the brush under a variety of grafting and screening conditions and investigate the various régimes of this system. The agreement between Monte Carlo and self-consistent-field methods is quite good. When the effective interaction strength is reasonably large, and the screening is strong, the polyelectrolyte brush behaves like a neutral brush with an effective excluded volume parameter, in agreement with previous scaling studies. For weaker screenings, we find and describe some region where the behavior of the brush height H resembles the H∼N3 prediction made by Pincus, and more recently by von Goeler and Muthukumar. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 2418-2437 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present results from an extensive lattice Monte Carlo study of the adsorption and desorption of homopolymer chains from semidilute solution onto a solid/liquid interface. We have studied in detail the growth, equilibrium structure and dynamics, and rinsing of layers of homopolymers adsorbed from solution. For solution concentrations at or near the overlap threshold we directly verify the self-similar structure of the adsorbed layer first predicted by de Gennes. This scaling result is confirmed without our having to make any assumptions or inferences as required in experiments. By following the flight of the individual chains, we obtain a detailed description of their structure and dynamics, including direct proof that the adsorbed chains form two broad categories: a tightly bound category with a long characteristic time of exchange with the solution, and a loosely bound category with a very short characteristic time of exchange. We study the differing conformations of these two subpopulations, as well as the kinetics of chain exchange between the adsorbed phases and the bulk solution. Finally, we examine the active displacement of the self-similar adsorbed layer by a solution of different chains. We describe different regimes of desorption, characterized by exponential and faster than exponential decays of the adsorbed layer. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Macromolecules 28 (1995), S. 7817-7821 
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 6897-6905 
    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
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 6006-6013 
    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
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  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 9418-9423 
    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
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  • 8
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 801 (1996), S. 0 
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1432-0878
    Keywords: Key words Tranquilizers ; Cytoskeleton ; Deciliation ; Golgi ; Mitochondria ; Cell motility ; Sea urchin ; Lytechinus pictus (Echinodermata)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract  The mitotic inhibitor, chloral hydrate, induces ciliary loss in the early embryo phase of Lytechinus pictus. It causes a breakdown of cilia at the junction of the cilium and the basal body known as the basal plate. This leaves the plasma membrane temporarily unsealed. The basal apparatus accessory structures, consisting of the basal body, basal foot, basal foot cap, striated side arm, and striated rootlet, are either misaligned or disintegrated by treatment with chloral hydrate. Furthermore, microtubules which are associated with the basal apparatus are disassembled. Mitochondria accumulate at the base of cilia – underneath the plasma membrane – and show alterations in their structural organization. The accumulation of mitochondria is observed in 40% of all electron micrograph sections while 60% show the areas mostly devoid of mitochondria. The microvilli surrounding a cilium and striated rootlet remain intact in the presence of chloral hydrate. These results suggest that deciliation in early sea urchin embryos by chloral hydrate is caused by combined effects on the ciliary membrane and on microtubules in the cilia. Furthermore, it is suggested that chloral hydrate can serve as a tool to explore the cytoskeletal mechanisms that are involved in cilia motility in the developing sea urchin embryo.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1432-0878
    Keywords: Key words Microfilaments ; Cell surface ; Cell division ; Mitochondria ; Organelle transport ; Drosophila melanogaster (Insecta)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract  Insect cell cultures derived from Drosophila melanogaster are increasingly being used as an alternative system to mammalian cell cultures, as they are amenable to genetic manipulation. Although Drosophila cells are an excellent tool for the study of genes and expression of proteins, culture conditions have to be considered in the interpretation of biochemical results. Our studies indicate that significant differences occur in cytoskeletal structure during the long-term culture of the Drosophila-derived cell lines Schneider Line-1 (S1) and Kc23. Scanning, transmission-electron, and immunofluorescence microscopy studies reveal that microfilaments, microtubules, and centrosomes become increasingly different during the culture of these cells from 24 h to 7–14 days. Significant cytoskeletal changes are observed at the cell surface where actin polymerizes into microfilaments, during the elongation of long microvilli. Additionally, long protrusions develop from the cell surface; these protrusions are microtubule-based and establish contact with neighboring cells. In contrast, the microtubule network in the interior of the cells becomes disrupted after four days of culture, resulting in altered transport of mitochondria. Microtubules and centrosomes are also affected in a small percent of cells during cell division, indicating an instability of centrosomes. Thus, the cytoskeletal network of microfilaments, microtubules, and centrosomes is affected in Drosophila cells during long-term culture. This implies that gene regulation and post-translational modifications are probably different under different culture conditions.
    Type of Medium: Electronic Resource
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