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1.
P. Guenoun M. Delsanti D. Gazeau J.W. Mays D.C. Cook M. Tirrell M. Tirrell L. Auvray 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(1):77-86
Aqueous micellar solutions of ionic/neutral block copolymers have been studied by light scattering, small angle neutron scattering
and small angle X-ray scattering. We made use of a polymer comprised of a short hydrophobic block (polyethylene-propylene)
PEP and of a long polyelectrolytic block (polystyrene-sulfonate) PSSNa which has been shown previously to micellize in water.
The apparent polydispersity of these micelles is studied in detail, showing the existence of a few large aggregates coexisting
with the population of micelles. Solutions of micelles are found to order above some threshold in polymer concentration. The
order is liquid-like, as demonstrated by the evolution with concentration of the peak observed in the structure factor (), and the degree of order is found to be identical over a large range of concentrations (up to 20 wt%). Consistent values
of the aggregation number of the micelles are found by independent methods. The effect of salt addition on the order is found
to be weak.
Received: 19 June 1997 / Received in final form: 4 September 1997 / Accepted: 9 October 1997 相似文献
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The interaction between two parallel plates due to non-adsorbing polymer chains with excluded volume is calculated using the
adsorption method. The adsorption is calculated from the profile of the polymer segment concentration between the plates,
which is obtained from the product function of the concentration profile near a single wall, involving the correlation length.
The renormalization group theory provides expressions for the osmotic pressure and consequently for the osmotic compressibility,
chemical potential and correlation length of a polymer solution. Both the local polymer concentration profiles as well as
the minimum of the interaction potential between the plates agree with recently published self-avoiding random walk computer
simulations.
Received 9 August 2001 相似文献
5.
A.N. Semenov M. Rubinstein 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(1):87-94
The effect of excluded-volume interactions on the reptation dynamics of long polymer chains is considered theoretically. It
is shown that interactions give rise to an exponential increase of the reptation time, , if polymer chains are long enough: , where is the number of monomers per entanglement. We propose a novel dynamical mechanism of activated reptation implying that neighboring
chains exchange conformations of their terminal fragments. It is shown that the exchange mechanism is compatible with the
equilibrium polymer chain statistics and that it provides a bridge between the previous theories.
Received: 25 July 1997 / Accepted: 8 October 1997 相似文献
6.
B. Bassetti C.A. Mantica P. Jona 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(3):359-369
A material surface of pure constituents with a flexible molecular chain (amphiphilics) is considered; thermodynamic behaviour
is studied in the chain length-temperature plane. The Hamiltonian of the system is modelled as the sum of a formation term
which refers to the polymer nature of the chain, and of a fluctuation term with a specific elastic form. For closed systems
the model exhibits phases with uniform curvature and conformational order/disorder or, alternatively, modulated phases; a
critical chain length is found for the existence of modulated phases; the dependence of transition temperature on energy parameters
is determined. A critical region is found for open systems, where conformational disorder drives spontaneous generation of
curvature; this lies above a characteristic chain length and around the shape transition temperature.
Received: 13 November 1996 / Revised: 9 May 1997 / Received in final form: 4
November 1997 / Accepted: 10 November 1997 相似文献
7.
O.V. Borisov E.B. Zhulina 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(2):205-217
We have developed a scaling theory that describes the conformations of weak star-branched polyelectrolytes in dilute solutions.
The dependences of the overall star size on the number of branches and on the ionic strength of the solution (tuned by the
addition of low molecular weight salt) are analyzed. The intrinsic structure of the polyelectrolyte stars in salt-free and
salt-added solutions is discussed in terms of concentration and elastic blobs. In contrast to neutral stars, the swollen corona
of the polyelectrolyte star consists of blobs which are not closely packed. We have shown that the size of star polyelectrolytes
is less sensitive to the variation in the ionic strength than the size of linear polyelectrolytes. The effects of the ionization-recombination
balance in the star polyelectrolyte were taken into account. For polyelectrolytes with small ionization constant, the size
of the star depends nonmonotonically on the number of branches and on the ionic strength of the solution due to recombination
of counterions with charged monomers.
Received: 10 November 1997 / Revised: 16 February 1998 / Accepted: 1st April 1998 相似文献
8.
The intensity of the 18.2 nm Balmer α-transition in C5+ excited in a capillary discharge using alumina and polyacetal tubes was studied. For discharge currents of up to 80 kA in
tubes filled with C2H2, intense radiation from the excitation of C5+ ions and from the recombination of C6+ ions was observed. With increasing length of the discharge, the intensity in the falling edge of the recombination pulse
rises faster than proportional. In contrast to previous investigations, gain by stimulated emission is excluded. The enhancement
is ascribed to an optical guiding of the XUV radiation in the dense plasma created by ablation from the tube walls.
Received: 1 April 1999 / Revised version: 22 July 1999 / Published online: 30 November 1999 相似文献
9.
The effect of stiffness in a 2D living polymer system is investigated by Monte-Carlo simulation in a canonical ensemble. As
the flexibility decreases, the mean chain contour length decreases and goes through a local maximum. The mean end to end square distance shows a non-monotonic behaviour due to the
coil-to-rod transition and the decrease in chain contour length. Near the maximum of chain ordering in the bulk, the chain
length distribution adapts itself to increase the configurational entropy. With the parameters used in this simulation, it
seems that the effect of the stiffness for high stiffness is to decrease as in the isotropic case, since the ordering decreases again.
Received: 16 September 1997 / Revised: 27 June 1998 / Accepted: 29 June 1998 相似文献
10.
R.R. Netz H. Orland 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(1):81-98
Variational methods are applied to a single polyelectrolyte chain. The polymer is modeled as a Gaussian chain with screened
electrostatic repulsion between all monomers. As a variational Hamiltonian, the most general Gaussian kernel, including the
possibility of a classical or mean polymer path, is employed. The resulting self-consistent equations are systematically solved
both for large and small monomer-monomer separations along the chain. In the absence of screening, the polymer is stretched
on average. It is described by a straight classical path with Gaussian fluctuations around it. If the electrostatic repulsion
is screened, the polymer is isotropically swollen for large separations, and for small separations the polymer correlation
function is calculated as an analytic expansion in terms of the monomer-monomer separation along the chain. The electrostatic
persistence length and the electrostatic blobsize are inferred from the crossover between distinct scaling ranges. We perform
a global analysis of the scaling behavior as a function of the screening length and electrostatic interaction strength , where is the Bjerrum length and A is the distance of charges along the polymer chain. We find three different scaling regimes. i) A Gaussian-persistent regime with Gaussian behavior at small, persistent behavior at intermediate, and isotropically swollen behavior at large length
scales. This regime occurs for weakly charged polymers and only for intermediate values of the screening length. The electrostatic
persistence length is defined as the crossover length between the persistent and the asymptotically swollen behavior and is given by and thus disagrees with previous (restricted) variational treatments which predict a linear dependence on the screening length
.ii) A Gaussian regime with Gaussian behavior at small and isotropically swollen behavior at large length scales. This regime occurs for weakly
charged polymers and/or strong screening, and the electrostatic repulsion between monomers only leads to subfluent corrections
to Gaussian scaling at small separations. The concept of a persistence length is without meaning in this regime. iii) A persistent regime , where the chain resembles a stretched rod on intermediate and small scales. Here the persistence length is given by the
original Odijk prediction, , if the overstretching of the chain is avoided. We also investigate the effects of a finite polymer length and of an additional
excluded-volume interaction, which modify the resultant scaling behavior. Applications to experiments and computer simulations
are discussed.
Received 24 December 1997 相似文献
11.
Y.O. Popov A.N. Semenov 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(2):245-256
Nematic ordering in anisotropic non-Gaussian elastomers is considered theoretically using mean field approximation. We focus on the effect of anisotropy during network
cross-linking on the system elasticity and, in particular, on the so-called soft deformation mode. As the main result, we
calculate the dependence of the elastomer free energy on the angle between the axis of “frozen” anisotropy and the nematic
director. The dependence of the isotropic-nematic transition point on the orientational field acting on the monomers during
the cross-linking process is also calculated.
Received: 5 November 1997 / Revised and Accepted: 29 June 1998 相似文献
12.
A. Albersdörfer E. Sackmann 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(4):663-672
In this paper we study the effect of monovalent and divalent ions on the swelling behavior and viscoelastic parameters of ultrathin layers of the natural polyelectrolyte hyaluronic acid
covalently coupled to glass substrates. A colloidal probe technique is applied for this purpose based on latex beads, hovering over the polymer cushion. By analyzing the vertical Brownian motion of these beads with reflection
interference contrast microscopy (RICM) we determined the equilibrium layer thickness (with 3 nm vertical resolution), the
interfacial interaction potential, and the characteristic mesh size limiting the hydrodynamic flow within the polyelectrolyte
film as a function of the ionic strength. The experimental results are interpreted in terms of three different theoretical
models: the polyelectrolyte brush approximation of Pincus [#!ref1!#], a modified polyelectrolyte brush approximation in the
high salt concentration limit of Ross and Pincus [#!ref2!#] and the simple scaling approximation for neutral adsorbed polymers
of de Gennes [#!ref3!#]. Within experimental error all of these different models fit our experimental data and yield comparable
results for the equilibrium layer thickness. Moreover we determine a thickness dependent, effective surface coverage from
both brush models. The hydrodynamic properties of the films are interpreted in terms of the Brinkmann model of elastic porous
media by assuming an effective mesh size, which depends linearly on the Debye screening length. The salt induced condensation
of the polyelectrolyte films can be described microscopically in terms of a progressive contraction of the mesh size with
increasing salt concentration.
Received 10 September 1998 and Received in final form 30 November 1998 相似文献
13.
Y. Rouault 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(3):321-324
A living polymer system is used to study the effect of concentration on a broad, polydisperse two-dimensional polymer system.
It is found that the mean squared end-to-end radius of a chain of L monomers does not decrease by following a simple power law of the concentration but by a function of the form . An origin for such a behaviour is proposed.
Received: 21 November 1997 / Received in final form: 21 April 1998 / Accepted: 24 April 1998 相似文献
14.
T.A. Vilgis M. Stapper 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(1):69-74
The behavior of microgels near surfaces and their adsorption is studied by simple scaling theory. Two different types of microgels
can be studied, i.e., fractal type microgels and randomly crosslinked polymer chains. In the first case the gel can be described mainly by introducing
a spectral dimension. The second type requires more attention and uses the number of crosslinks as parameter. The main result
is that soft gels with weakly coupled crosslinks and a low number of crosslinks adsorb much better than hard gels, with many
crosslinks. Similar results for fractal gels and branched polymer are presented. Fractal gels with low connectivity adsorb
easier than gels with a large connectivity dimension. We discuss also consequences on surface protection by microgels.
Received: 11 August 1997 / Received in final form: 20 November 1997 / Accepted 22 January 1998 相似文献
15.
M.C.P. van Eijk M.A. Cohen Stuart S. Rovillard J. De Coninck 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(2):233-244
Nonequilibrium processes play a key role in the adsorption kinetics of macromolecules. It is expected that the competition
between transport of polymer towards an interface and its subsequent spreading has a significant influence on the adsorbed
amount. An increase of the transport rate can lead to an increase of the adsorbed amount, especially when the polymer has
too little time to spread at the interface. In this study we present both molecular dynamics simulations and analytical calculations
to describe some aspects of the adsorption kinetics. From MD simulations on a poly(ethylene oxide) chain in vacuum near a
graphite surface, we conclude that the spreading process can, in first approximation, be described by either a simple exponential
function or by first-order reaction kinetics. Combining these spreading models with the transport equations for two different
geometries (stagnation-point flow and overflowing cylinder) we are able to derive analytical equations for the adsorption
kinetics of polymers at solid-liquid and at liquid-fluid interfaces.
Received: 18 July 1997 / Received in final form: 27 October 1997 / Accepted: 6 November 1997 相似文献
16.
H.-B. Jiang A. Grossmann Th.W. Hänsch 《Applied Physics A: Materials Science & Processing》1998,66(1):119-122
Received: 17 November 1997/Accepted: 18 November 1997 相似文献
17.
Reflection properties of metallic photonic crystals 总被引:1,自引:0,他引:1
B. Temelkuran E. Ozbay M. Sigalas G. Tuttle C.M. Soukoulis K.M. Ho 《Applied Physics A: Materials Science & Processing》1998,66(3):363-365
Received: 10 November 1997/Accepted: 16 November 1997 相似文献
18.
J.J. Arenzon J.F. Stilck Y. Levin 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(1):79-82
We present a simple model for the possible mechanism of appearance of attraction between like charged polyions inside a polyelectrolyte
solution. The attraction is found to be short ranged, and exists only in the presence of multivalent counterions. It is produced
by the correlations in layers of condensed counterions surrounding each polyion and is only weakly temperature dependent.
We find the attraction to be maximum at zero temperature and dimish as the temperature is raised. The attraction is only possible
if the number of condensed counterions exceeds the threshold, , where is the valence of counterions and Z is the polyion charge.
Received 10 March 1999 and Received in final form 20 April 1999 相似文献
19.
J. Biegel C. Hundegger B. Nadig R. Weber 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(3):525-536
This paper resumes light scattering investigations of saltfree aqueous solutions of two component mixtures of charged spheres
by extending those measurements to systems in which one component is replaced by essentially stiff rodlike particles. In a
second step of investigations these were replaced by linear flexible particles. Fd-virus particles (length l=883 nm) or macromolecules of NaPSS of four different contour lengths have been used as representatives. Mostly the concentration
of latex spheres was fixed at 0.02 Vol%. The concentration of the other component was varied over a wide range. Concerning
the scattering intensity, the contribution of the latex spheres dominates, in particular in the systems containing NaPSS particles.
This simplifies the interpretation of data considerably. A rearrangement of the spheres is observed, depending on the shape
of the other sort of particles. These conclusions can be drawn from the shift of measured static structure factor with concentration c. A power law is found for the q-value of the maximum. The exponent depends on the properties of the second component. For the lower molecular weight (MW)
samples of NaPSS below a critical concentration, the exponent is smaller than 1/3, decreasing the more the smaller the MW
of the samples is. A tentative explanation in terms of charge number of NaPSS particles is given. The short time dynamics
has been explored too. From the data a “dynamically determined structure factor” can be derived, that can be compared with
the measured static structure factor. Good (fd) and fair (NaPSS) agreement is obtained respectively. Only at small wavenumbers
below the maximum of deviations occur which increase with concentration; they are consistent with hydrodynamic interaction.
Received 30 July 1998 and Received in final form 14 December 1998 相似文献
20.
Y.-Z. Wan D.W. Zhang Z.-J. Liu J.-T. Wang 《Applied Physics A: Materials Science & Processing》1998,67(2):225-231
Received: 28 August 1997/Accepted: 18 November 1997 相似文献