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  • 1
    Digitale Medien
    Digitale Medien
    Intramolecular formation of excimers in model compounds for polymers of 2,6-naphthalene dicarboxylic acid and five glycols in media of different viscosity (1996)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 34 (1996), S. 2623-2633 
    Details
    ISSN: 0887-6266
    Schlagwort(e): excimer ; fluorescence ; naphthalene ; polyester ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Steady-state fluorescence has been used to study the dependence of the intramolecular formation of excimers in media of differing viscosity, η, for model compounds of polyesters containing naphthalene groups. The model compounds are derived from 2-naphthalene carboxylic acid as rigid units and glycols, HO (SINGLEBOND) (CH2)m (SINGLEBOND) OH, m = 2(SINGLEBOND) 6, as flexible spacers. The ratio of the intensity of excimer and monomer emissions, ID/IM, exhibits two regimes: a regime at high η where ID/IM shows an odd(SINGLEBOND) even effect with m, with maxima at odd m, and a regime at low η where the odd-even effect is lost, and the maximum values are obtained for m = 3 and 6. Calculations performed for the equilibrium state using the rotational isomeric state model and Molecular Dynamics (MD) simulations allow the rationalization of the behavior of ID/IM with m in the media of high and low η, respectively. © 1996 John Wiley & Sons, Inc.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    Geometric properties of micelles formed by triblock copolymers and solubilizates in dilute solutions (1997)
    Weinheim : Wiley-Blackwell
    Macromolecular Theory and Simulations 6 (1997), S. 553-563 
    Details
    ISSN: 1022-1344
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: In this work we study the geometric properties of the triblock copolymer micelles with solubilized low-mass molecules in a selective solvent using the Monte Carlo technique on a cubic lattice. The triblock copolymers are of the ABA type, with the two insoluble blocks at the ends. The size of the micelles is characterized by the squared radius of gyration of the micellar core, Rg2, while the shape is treated by the asphericity b and the acylindricity c, which are defined in terms of the principal moments of the radius of gyration tensor. The parameters varied are the amount of solubilizate molecules, the polymer concentration, the interaction parameters between A and B, A and solvent, solute and solvent, solute and B block, and the A and B block length. The micelle size, characterized by Rg2, grows with increasing concentration of the solubilizates and/or the polymer, and stronger interactions between the incompatible species. The A block length is found not to modify Rg2 monotonously, while an increase in B block length results in a decrease in Rg2 at high concentrations. As the size expands, the micellar shape becomes less spherical but retains its cylindricity. In addition to an increase in the averaged Rg2, the distribution of Rg2 becomes broader and the system less homogeneous.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/mats.1997.040060215
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  • 3
    Digitale Medien
    Digitale Medien
    Conformational transitions of end-adsorbed triblock copolymers in a nonselective solvent (1997)
    Weinheim : Wiley-Blackwell
    Macromolecular Theory and Simulations 6 (1997), S. 667-677 
    Details
    ISSN: 1022-1344
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Conformational dynamics of triblock copolymers end-adsorbed onto a surface from a nonselective solvent have been studied by a Monte Carlo lattice simulation technique. The triblock copolymers are ANA BNB ANA with NA = 10 and NB = 5, 10, 20 and 40, at surface interaction parameters ε = -0.5 and -1.0. A is the adsorbing block and B is the nonadsorbing block. The number of chains in the periodic box is varied over the range 100 ≤ n ≤ 500. The triblock copolymer can exist in three states: loop (L), tail (T) and free (F) chain. Fractions of those conformations at different system parameters (n, NB and ε) and the associated lifetimes are calculated from the simulations. A kinetic scheme is constructed and the corresponding transition rate matrix is used in the master formalism equation, the solution of which yields the dynamic modes of the system. A correlation function is defined to produce a single overall view of the rate of transitions between different conformational states. The degree of surface interaction has strong influence on the rate of transitions between the states, in particular, longer average lifetimes and a wider distribution of lifetimes of the loop conformation contribute to the slower decay of the correlation curves. At high surface adsorption, larger NB decrease the rate of all transitions at all values of n. A weak dependence on n is observed for all sizes of NB at both surface energies.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/mats.1997.040060306
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  • 4
    Digitale Medien
    Digitale Medien
    Rationalization of the ratio of excimer-to-monomer fluorescence emission intensity in bichromophoric diesters of 1-pyrenoic acid and mono-, di-, tri-, and tetraethylene glycols (1995)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 33 (1995), S. 1107-1116 
    Details
    ISSN: 0887-6266
    Schlagwort(e): excimer ; fluorescence ; polyester ; pyrene ; rotational isomeric state model ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The ratio of excimer to monomer emission intensities, denoted by ID/IM, was measured for Py-COO(CH2CH2O)mCO — Py, where Py denotes the 1-pyrenyl group and m = 1-4, in solvents of different viscosity, η. Three different systems were used to change the viscosity of the medium: (a) Mixtures of methanol and ethylene glycol at 25°C, (b) linear aliphatic alcohols, H(CH2)nOH, where n =1-6, also at 25°C, and (c) ethylene glycol over the range 6.6-35°C. The ratio ID/IM decreases sharply as η increases, and the rate of the decrease in ID/IM is a function of m. Quantitatively, the dependence of ID/IM on η at high viscosity, i.e., the slope [d(ID/IM)/d(1/η)]∞, is larger in the present work than in another series of 1-pyrenyl diesters in which the flexible spacer is an oligomer of polyethylene, instead of an oligomer of polyoxyethylene. In the limit where η → ∞, the ratio ID/IM assumes its largest value in the bichromophoric compound with m = 2. However, as η decreases the compound with m = 3 becomes the one with the largest ID/IM. A complete rotational isomeric state analysis (for the compounds with m = 1-3) and a Monte Carlo simulation (for the compound m = 4) of the conformations of the diesters can rationalize the behavior of ID/IM in the high viscosity limit. ©1995 John Wiley & Sons, Inc.
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/polb.1995.090330714
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  • 5
    Digitale Medien
    Digitale Medien
    Effect of the directionality of the ester group on the formation of hairpins in polyesters containing naphthalene and a flexible spacer (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 35 (1997), S. 1127-1133 
    Details
    ISSN: 0887-6266
    Schlagwort(e): excimer ; fluorescence ; molecular dynamics ; naphthalene ; polyester ; Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Steady-state fluorescence measurements and molecular dynamics simulations have been used to study the intramolecular formation of excimers in five model compounds for polyesters containing naphthalene groups separated by flexible spacers. The model compounds are derived from 2-hydroxynaphthalene and HOOC—(CH2)n—COOH, n = 2-6. The ratio of the intensity of excimer and monomer emissions, ID/IM, is nearly independent of the viscosity of the medium, η, over the range covered in dilute solution. Although ID/IM is always very small, it shows an odd-even effect for the first four members of the series, with maxima when n is odd. Molecular dynamics simulations provide an explanation for the small values of ID/IM, their weak dependence on η, and the trend of ID/IM with n. The results for the present series of model compounds are compared with previous work, which reported larger values of ID/IM, and a stronger dependence of ID/IM on η, for bichromophoric compounds derived from 2-naphthoic acid and aliphatic glycols, where the direction of the ester groups is reversed. The origin of the difference in the behavior of ID/IM in the two series is identified. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1127-1133, 1997
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    Chain collapse by lattice simulation (1996)
    Weinheim : Wiley-Blackwell
    Macromolecular Theory and Simulations 5 (1996), S. 499-523 
    Details
    ISSN: 1022-1344
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Monte Carlo simulations have been performed on a self-avoiding simple cubic lattice chain with the nearest-neighbor interactions for a range of chain lengths N from 40 to 1000 segments to investigate equilibrium properties of polymer chains from an athermal to a collapsed state. Both the fraction of segments in the clusters and the number of contacts exhibit the three stage process for the chain collapse, consistent with our previous molecular dynamics simulations of a fully atomistic chain. In the collapse region corresponding to the nearest-neighbor interaction parameter larger than 0.5 for a segment-solvent pair, polymer chains are quite spherical and both ends lie nearly randomized within the sphere. The peak height of the specific heat is proportional to N(In N)3/11, as predicted by the renormalization group theory.
    Zusätzliches Material: 22 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/mats.1996.040050308
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  • 7
    Digitale Medien
    Digitale Medien
    Intramolecular excimer formation in naphthalene-containing polyesters. Bichromophoric model compounds derived from phthalic, succinic or malonic acid and 2-hydroxynaphthalene or 2-hydroxymethylnaphthalene (1995)
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 196 (1995), S. 1779-1790 
    Details
    ISSN: 1022-1352
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Steady state fluorescence measurements in dilute solutions are performed for bis(2-naphthyl) phthalate, bis(2-naphthylmethyl) phthalate, bis(2-naphthyl) succinate, bis(2-naphthylmethyl) succinate, bis(2-naphthyl) malonate and bis(2-naphthylmethyl) malonate, as models for polyesters containing naphthalene in their rigid units and flexible spacers that impose differences in the types of interactions between successive naphthalene units. The amount of intramolecular excimer in dilute solution depends on the type of flexible spacer, and also whether the compound is derived from 2-naphthol or 2-hydroxymethylnaphthalene. No excimer is detected from the compounds derived from 2-naphthol, but all compounds derived from 2-hydroxymethylnaphthalene showed excimer formation. These results are rationalized with a theoretical analysis of the conformations of the flexible spacers.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/macp.1995.021960532
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  • 8
    Digitale Medien
    Digitale Medien
    Simulations of rotational isomeric state models for poly(propylene) melts on a high coordination lattice (1998)
    Weinheim : Wiley-Blackwell
    Macromolecular Theory and Simulations 7 (1998), S. 613-617 
    Details
    ISSN: 1022-1344
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: In the last two years, a method was developed for the Monte Carlo simulation of coarse-grained representations of the chains in polyethylene (PE) melts, under conditions where individual snapshots can be“reverse-mapped” back to continuous space, with all atoms present. In its original form, the symmetry of the torsion potential energy function, E(φ) = E(-φ), was exploited in the mapping of a coarse-grained version of the rotational isomeric state (RIS) model of PE onto a high coordination lattice. Recently the symmetry restriction was relaxed, so that the simulation could treat isolated RIS poly(propylene) (PP) chains of any stereochemical sequence. Here that simulation of isolated PP chains is extended to PP melts, by introducing the intermolecular interactions required for maintenance of cohesion with the proper cohesive energy. The method is applied to melts of isotactic PP and syndiotactic PP, and satisfactory cohesion is achieved. Satisfactory equilibration of the PP melts requires utilization of a reptation move, in addition to the single bead moves employed previously in simulations of PE melts.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    The Förster radius for energy transfer from naphthalene to anthracene in polyesters with oxyethylene spacers (1996)
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 197 (1996), S. 1349-1360 
    Details
    ISSN: 1022-1352
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Model compounds for a series of polyesters in which 3,6,9, and 12-rotatable CH2—O and CH2—CH2 bonds separate rigid units have been studied using the efficiency of nonradiative singlet energy transfer from naphthalene to anthracene. The model compounds have the structure naph-CO—(OCH2CH2)m—OOC-anth with m of 1-4, where naph and anth denote 2-naphthyl and 9-anthranyl groups, respectively. This series of compounds covers a larger range of potential separation of the two chromophores than was possible in an earlier study, in which the flexible spacers consisted of 2-6 methylene units. The nonradiative singlet energy transfer has an efficiency that depends on the solvent viscosity and on m. The theoretical analysis employs a rotational isomeric state model for the conformations of these molecules. The Förster radius for transfer from naphthalene to anthracene in this system is 16 ± 2 Å, and is nearly independent of whether the spacers are constructed from oxyethylene or methylene units.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/macp.1996.021970414
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  • 10
    Digitale Medien
    Digitale Medien
    Molecular dynamics study of the persistence lengths of a new class of polyimide fibers (1996)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 34 (1996), S. 565-573 
    Details
    ISSN: 0887-6266
    Schlagwort(e): Fiber ; persistence length ; polyimide ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The transformation matrix method and the concept of virtual bonds has been applied to the study of the persistence lengths of two recently developed polyimide fibers, PMDA-PFMB, synthesized from pyromellitic dianhydride (PMDA) and 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (PFMB), and BPDA-PFMB, synthesized from 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) and PFMB. The elements of the averaged transformation matrices are obtained from a molecular dynamics trajectory of 1 ns and from a consideration of the symmetry of the torsion potential energy function for selected bonds. The persistence length is found to be ∼ 496 AÅ for PMDA-PFMB and ∼ 66 AÅ for BPDA-PFMB. The large persistence length of PMDA-PFMB, comparable to that of the rodlike polymer poly(benzobisoxazole) (PBO), is caused by the colinearity of the virtual bonds in the chain and the stiffness of the bond angles. The inclusion of the electrostatic interactions does not seem to affect the result significantly, although a very slight decrease (∼ 5%) of the persistence length was detected. The effect of substitution of methyl groups for the trifluoromethyl groups in these polyimide fibers is also studied, with an increase of ∼ 14% in the persistence length of PMDA-PFMB and ∼ 1.4% in the persistence length of BPDA-PFMB. Since a good solvent that would be appropriate for use in a light scattering measurement has not been found for either of these polyimide fibers, the theoretical estimates of the persistence length cannot be compared with experiment. © 1996 John Wiley & Sons, Inc.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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