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11.
We investigate polyelectrolyte brushes in the osmotic regime using both theoretical analysis and molecular dynamics simulation techniques. In the simulations at moderate Bjerrum length, we observe that the brush height varies weakly with grafting density, in contrast to the accepted scaling law, which predicts a brush thickness independent of the grafting density. We show that such behavior can be explained by considering lateral electrostatic effects (within the non-linear Poisson-Boltzmann theory) combined with the coupling between lateral and longitudinal degrees of freedom due to the conserved polymer volume (which are neglected in scaling arguments). We also take the non-linear elasticity of polyelectrolyte chains into consideration, which makes significant effects as chains are almost fully stretched in the osmotic regime. It is shown that all these factors lead to a non-monotonic behavior for the brush height as a function of the grafting density. At large grafting densities, the brush height increases with increasing the grafting density due to the volume constraint. At small grafting densities, we obtain a re-stretching of the chains for decreasing grafting density, which is caused by lateral electrostatic contributions and is controlled by the counterion-condensation process around polyelectrolyte chains. These results are obtained assuming all counterions to be trapped within the brush, which is valid for sufficiently long chains of large charge fraction.Received: 14 May 2003, Published online: 11 November 2003PACS:
61.25.Hq Macromolecular and polymer solutions; polymer melts; swelling - 36.20.-r Macromolecules and polymer molecules - 61.20.Qg Structure of associated liquids: electrolytes, molten salts, etc. 相似文献
12.
Similarly and highly charged plates in the presence of multivalent counterions attract each other and form electrostatically bound states. Using Monte-Carlo simulations, we obtain the interplate pressure in the global parameter space. The equilibrium plate separation, where the pressure changes from attractive to repulsive, exhibits a novel unbinding transition. A systematic and asymptotically exact strong-coupling field theory yields the bound state from a competition between counterion entropy and electrostatic attraction, in agreement with simple scaling arguments and simulations. 相似文献
13.
Gordeev SN Zhukov AA de Groot PA Jansen AG Gagnon R Taillefer L 《Physical review letters》2000,85(21):4594-4597
We report on transport measurements of YBa 2Cu 3O (7-delta) single crystals with different oxygen contents in the geometry B, J ||ab (J perpendicularB). Our data show that the vortices become confined between the Cu-O planes below a well-defined temperature at which the effective size 2xi of the vortex core is approximately equal to the period of the Cu-O layers. This confinement strongly increases the vortex liquid freezing temperature. A new melting line is found separating a vortex liquid and a smectic phase, which shows an oscillatory field dependence reflecting differences between commensurate and incommensurate smectic states. 相似文献
14.
The European Physical Journal E - The Poisson-Boltzmann (PB) approach gives asymptotically exact counter-ion density profiles around macroscopic charged objects and forces between macroscopic... 相似文献
15.
16.
Ming Xia LI Yan Ming WANG Ru Ru CHEN* Research Institute of Elemento-Organic Chemistry Nankai University Tianjin Pittsburgh University Medical Center Pittsburgh PA U. S. A 《中国化学快报》2001,(6)
The chiral diols ((,(,((,((-Tetraaryl-1,3-dioxolane-4,5-dimethanols) have been used for the formation of cyclic titanates and similar derivatives of Mg, Al and Zr. These complexes of oxophilic metal centers were employed in catalytic and stiochiometric enantioselective reactions such as enantioselective addition reactions of carbon-centered nucleophiles to aldehydes1, [2+2] cycloadditions2, and Diels-Alder reactions3. So far, the two hydrogen atoms of all this type of diols are in trans form… 相似文献
17.
We consider diffraction by a semi-infinite crack located alonga fusion interface between two differing elastic media. Twotypes of crack, namely open and partially closed cracks, areinvestigated. An open crack is modelled by a stress-free contactboundary condition and a partially closed crack is modelledby a spring contact boundary condition. For the latter, thejump in the stress across the crack is assumed to be proportionalto the jump in the displacement across the crack. This situationarises in, for example, a K-weld where the fine grain of theparent material (for example, ferritic or forged austeniticsteel) is in stark contrast with the coarse-grained weld metal(for example, austenitic weld metal). In the metal weld thedirection of the grain axis varies through the metal. However,diffraction is a local phenomenon and so the austenitic steelis assumed to have a zonal axis so that it may be modelled bya transversely isotropic composite. The ferritic or forged austeniticsteel will be modelled as an isotropic material. 相似文献
18.
The quadrupole moment of the 535 keV state of 133La has been derived from a time-differential perturbed angular correlation measurement in an environment of La metal. The effective electric gradient is known from a nuclear quadrupole resonance measurement with the ground state of 139La. The result Q = 0.35 ± 0.03 b does not confirm a proposed shape isomerism. 相似文献
19.
E. Gerdau J. Birke H. Winkler J. Braunsfurth M. Forker G. Netz 《Zeitschrift für Physik A Hadrons and Nuclei》1973,263(1):5-14
Spinrotation spectra of polycrystalline (NH4)3HfF7 in which radioactive181Hf was incorporated have been measured in the temperature range from ?196 °C to + 70 °C. The spectra were interpretated on the base of the stochastic model of M. Blume. It was assumed that reorientations of the [HfF7]3? polyhedra take place at random. The resulting fluctuation rates can be understood as to be caused by an activation process. The activation energy was determined to 0.324(12) eV in agreement with NMR measurements on19F in this compound. 相似文献
20.
We consider the linearized time-dependent Navier-Stokes equation including finite compressibility and viscosity. We first
constitute the Green's function, from which we derive the flow profiles and response functions for a plane, a sphere and a
cylinder for arbitrary surface slip length. For high driving frequency the flow pattern is dominated by the diffusion of vorticity
and compression, for low frequency compression propagates in the form of sound waves which are exponentially damped at a screening
length larger than the sound wave length. The crossover between the diffusive and propagative compression regimes occurs at
the fluid's intrinsic frequency w \omega ∼ c
2
r0 \rho_{0}^{}/h \eta , with c the speed of sound, r0 \rho_{0}^{} the fluid density and h \eta the viscosity. In the propagative regime the hydrodynamic response function of spheres and cylinders exhibits a high-frequency
resonance when the particle size is of the order of the sound wave length. A distinct low-frequency resonance occurs at the
boundary between the propagative and diffusive regimes. Those resonant features should be detectable experimentally by tracking
the diffusion of particles, as well as by measuring the fluctuation spectrum or the response spectrum of trapped particles.
Since the response function depends sensitively on the slip length, in principle the slip length can be deduced from an experimentally
measured response function. 相似文献