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271.
M. Castelnovo P. Sens J.-F. Joanny 《The European physical journal. E, Soft matter》2000,1(2-3):115-125
We investigate the equilibrium charge distribution along a single annealed polyelectrolyte chain under different conditions.
The coupling between the conformation of the chain and the local charge distribution is described for various solvent qualities
and salt concentration. In salt free solution, we find a slight charge depletion in the central part of the chain: the charges
accumulate at the ends. The effect is less important if salt is added to the solution since the charge inhomogeneity is localized
close to the chain ends over a distance of order of the Debye length. In the case of poor solvent conditions we find a different
charge per monomer in the beads and in the strings in the framework of the necklace model. This inhomogeneity leads to a charge
instability and a first order transition between spherical globules and elongated chains.
Received 19 March 1999 and Received in final form 2 August 1999 相似文献
272.
Chi-Xing Zhou Department of Polymeric Materials Science Engineering Shanghai Jiao Tong University Shanghai China 《高分子科学》1999,(2):151-158
Conceptually, an imagined conformation ellipsoid is supposed to represent the shape of a polymerchain for polymer melts in flow fields and to be equivalent to the volume element in a mathematical sense incontinuum mechanics. A power law dependence of shear modulus of polymer melts on detC, referred to asenvelope volume, is proposed. Based on those assumptions and the non-linear relation of shear modulus, aphenomenological viscoelastic model is derived. The model is tested in simple shear flow, simpleelongational flow, oscillatory shear flow, and relaxation process after flow suddenly stopped. The resultsshow that the model works well to predict the change of internal structure and viscoelastic performance ofpolymer melts in flow fields. 相似文献
273.
M.‐H. Kim J. D. Londono A. Habenschuss 《Journal of Polymer Science.Polymer Physics》2000,38(18):2480-2485
The melt structures of linear polyethylene and the isotactic vinyl polymers polypropylene, poly(1‐butene), and poly(4‐methyl‐1‐pentene), along with the corresponding methyl, ethyl, and isobutyl side chains, were studied with wide‐angle X‐ray diffraction. As the size of the side branch increases from zero (polyethylene) to methyl, ethyl, and isobutyl, a prepeak appears below the main diffraction peak in the total structure factor. The prepeaks become stronger and shift to lower scattering vectors with increasing bulkiness of the side chain. There is a strong correlation between the position of the prepeaks in the melt and the average nearest‐neighbor helix–helix packing distance in the crystals, implying similar helical conformations in the melts. © 2000 John Wiley & Sons, Inc.* J Polym Sci B: Polym Phys 38: 2480–2485, 2000 相似文献
274.
275.
Michael Wendlandt Tobias Kerle Marcus Heuberger Jacob Klein 《Journal of Polymer Science.Polymer Physics》2000,38(6):831-837
Using nuclear reaction analysis composition‐depth profiling, we investigate the influence of symmetric/asymmetric confining walls on the equilibrium configuration of thin films of phase‐separated polymer blends. Depth profiles of samples annealed under symmetric boundary conditions show a laterally averaged concentration, while samples confined by nonsymmetric walls show (as in earlier studies) clear separation into two thin layers of coexisting phases. This suggests that for phase separation under symmetric boundary conditions the interface between the two phases is orthogonal to the sample plane, in line with recent theoretical discussion. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 831–837, 2000 相似文献
276.
Venkat Padmanabhan Amalie L. Frischknecht Michael E. Mackay 《Macromolecular theory and simulations》2012,21(2):98-105
Nanoparticles in a flexible polymer melt film often segregate to the substrate due to attractive depletion interactions between the nanoparticles and the substrate. Here, molecular dynamics simulations are performed to study the effect of chain stiffness on this segregation. The nanoparticles are modeled as spheres and the polymers as semi‐flexible bead‐spring chains. Both purely repulsive and attractive forces are considered, while assuming non‐selective interactions among all species. The nanoparticles are found to be well‐dispersed in the system having repulsive forces only and aggregate into clusters in the completely attractive system. For the repulsive system, adding chain stiffness substantially decreases the nanoparticles' segregation, and hence their concentration, at the substrate.
277.
Tadeusz Pakula 《Macromolecular Symposia》2004,214(1):307-316
Various non-linear highly branched polymers such as multiarm stars, block copolymer micelles and bottlebrush-like polymers have been studied in order to analyze their intramolecular structure and effects of spatial ordering resulting from their specific macromolecular architecture. These polymers constitute a class of compact macromolecules which, due to the high intramolecular density, interact strongly, excluding each other in space. Investigations of the structure and dynamics in such systems, using various experimental methods as well as computer simulations, have been performed. Small angle X-ray scattering is used to characterize the structure and mechanical spectroscopy is used for the detection of the dynamic behavior of the systems. Simulations have been performed using the cooperative motion algorithm with lattice polymers equivalent to the considered macromolecules. Results of both experiments and the simulation seem to support the concept of slow structural cooperative rearrangements controlling the flow in such systems. The effects are analogous to those related to flow in low molecular liquids but take place on another size scale. The new slow relaxation processes creates new super soft-states which are characterized by shear modulus plateau lower than 104 Pa. 相似文献
278.
Pierre-Gilles de Gennes 《Macromolecular Symposia》2003,191(1):7-10
We present a qualitative argument suggesting that a statistical (AB) copolymer should display a certain form of weak segregation, with A rich and B rich regions of size comparable to the coil radius. This should occur if the Flory parameter χ is larger than unity (much larger than for the phase separation of A and B of homopolymers) in agreement with detailed calculations by Frederikson, Milner and Leibler. We achieve a certain qualitative insight for the resulting microphase. 相似文献