共查询到20条相似文献,搜索用时 15 毫秒
1.
We discuss the structure and the interaction of telechelic brushes. We show that the association of functionalized chain ends
is capable of giving rise to attractive interactions between telechelic brush-covered surfaces, in contrast to conventional
repulsion. Our predictions for the interaction free energy are in agreement with experimental data.
Received 12 June 2000 and Received in final form 29 January 2001 相似文献
2.
M. Bellour A. Knaebel J.P. Munch S.J. Candau 《The European physical journal. E, Soft matter》2000,3(2):111-121
Static and dynamic light scattering and conductivity experiments were carried out on salt-free aqueous micellar solutions
of cetyltrimethylammonium n-hexane sulfonate (CTAC_6SO_3) and cetyltrimethylammonium n-heptane sulfonate (CTAC_7SO_3) as a function of surfactant concentration. This study confirms the analogy between the behavior
in the semi-dilute regime of elongated micellar systems and “classical” polyelectrolyte solutions. Time-resolved scattering
experiments performed after a variation of concentration from about twice the overlap volume fraction to less than half of it revealed the existence of a structural relaxation with a characteristic time of several hours.
Received 21 December 1999 相似文献
3.
E. Zhulina A.V. Dobrynin M. Rubinstein 《The European physical journal. E, Soft matter》2001,5(1):41-49
We develop a scaling theory for a single polyampholyte chain adsorbed on a charged spherical particle in a theta-solvent.
Adsorption of a polyampholyte molecule is due to its polarization in the electrostatic field of the particle. For large particles
with sizes exceeding the thickness of the adsorbed layer, the conformations of the chain are similar to the one found for
polyampholyte adsorption on charged planar surface. However, an adsorbed polyampholyte chain forms a self-similar flower-like
structure near the particles with sizes smaller than its Gaussian size. These self-similar structures result from the balance
of the polarization energy of loops and the excluded volume interactions between monomers. The structure of an adsorbed polyampholyte
in the flower-like conformation is similar to that of a neutral star polymer.
Received 3 March 2000 and Received in final form 5 July 2000 相似文献
4.
We discuss theoretically the relaxation of charge fluctuations in polyampholyte solutions. It has been shown previously by
some of us (J. Wittmer et al. Europhys. Lett. 24, 263 (1993)) that the charge distribution along the polyampholyte backbone has a dramatic influence on the polarization energy
and hence on the solubility. Here it is demonstrated that a similar effect exists for the charge relaxation. The charge relaxation
mechanism qualitatively depends on the statistics: for alternating polyampholytes the relaxation is mainly due to local dipole
inversion and is not primarily driven by electrostatic interactions, whereas for random polyampholytes it is driven by electrostatic
interactions. Intermediate statistics (with short-ranged (exponential) correlations) appear as a combination of these two
limiting cases: short-wavelength modes are insensitive to the loss of correlations along the backbone, whereas long-wavelength
modes correspond to a random statistics with renormalized charges. The relaxation of the dielectric constant is also calculated.
Received: 20 December 2002 / Accepted: 13 March 2003 / Published online: 24 April 2003
RID="a"
ID="a"e-mail: johner@ics.u-strasbg.fr 相似文献
5.
D. Langevin 《The European physical journal. E, Soft matter》2001,5(1):81-85
Studies of thin liquid films, made from semidilute polyelectrolyte solutions, are presented. The disjoining pressure variation
with film thickness exhibits oscillations, corresponding to film stratification. The oscillations become sharper as the polymer
concentration c increases, and disappear when salt is added. The period of the oscillations scales as c
-1/2. The observed stratification is related to the polymer network and the size of the steps to the mesh size ξ.
Received 25 April 2000 and Received in final form 3 October 2000 相似文献
6.
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
7.
M.M. Britton P.T. Callaghan 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(2):237-249
Using NMR velocimetry and mechanical measurements we study the flow dynamics, within a cone-and-plate rheometer, of the wormlike
micelle system, cetylpyridinium chloride/sodium salicylate (CPyCl/NaSal) at 100 mM/60 mM concentration in distilled water.
Depending on precise conditions within the system, two classes of behaviour are observed, one in which the boundary between
different shear rate phases fluctuates rapidly (on the order of tens of milliseconds) and one in which it migrates slowly
with a time constant of many seconds. These modes of behaviour may depend on minor solution impurities, which presumably affect
the detailed constitutive properties, but also on the externally applied shear rate within a given system. We argue that the
slow migrations are governed by stress relaxation effects while the rapid migrations are flow driven and arise from interfacial
instability.
Received: 2 June 1998 / Received in final form and Accepted: 27 July 1998 相似文献
8.
Khokhlov AR Semenov AN Subbotin AV 《The European physical journal. E, Soft matter》2005,17(3):283-306
Shapes of globules formed by amphiphilic multi-block-copolymers in a selective solvent are considered theoretically. We focus on copolymers consisting mostly of insoluble H-units forming large core surrounded by a shell of soluble P-blocks. It is shown that the globule becomes non-spherical when the effective shell tension is low enough. The resultant shape depends on the shell bending energy: it is prolate if this energy is larger than the elastic energy of the core, and oblate in the opposite case. The central result is the prediction of the formation of a surface pattern of fingers accompanying or even preempting the shape transition mentioned above. We elucidate and discuss the following finger morphologies: 1) nearly spherical knob; 2) a necklace of spherical beads extending away from the surface; 3) mostly cylindrical fingers; 4) large thorn-like fingers. The first 3 morphologies develop at equilibrium as the shell area increases (or, equivalently, the shell tension decreases). Considering the relevant kinetical aspects we show that formation of fingers is a nucleation and growth process, and that the energy of their equilibrium nucleation is likely to be high. Therefore, the finger formation may be delayed, and may actually occur in the regime where the plain spherical surface is metastable. It is the last morphology (thorn-like fingers) that characterizes the metastable regimes when the finger formation is controlled by a high activation energy. The universal features of the above predictions inviting experimental tests are discussed. 相似文献
9.
Jarkova E Johner A Maresov EA Semenov AN 《The European physical journal. E, Soft matter》2006,21(4):371-386
A mean-field theory of globules of random amphiphilic copolymers in selective solvents is developed for the case of an annealed
copolymer sequence: each unit can be in one of two states, H (insoluble) or P (soluble or less insoluble). The study is focussed
on the regime when H and P units tend to form long blocks, and when P units dominate in the dilute phase, but are rare in
the globule core. A first-order coil-to-globule transition is predicted at some T = T
cg. The globule core density at the transition point increases as the affinity of P units to the solvent, ˜, is increased. Two
collapse transitions, coil → “loose” globule and “loose” globule → “dense” globule, are predicted if ˜ is high enough and
P units are marginally soluble or weakly insoluble. H and P concentration profiles near the globule surface are obtained and
analyzed in detail. It is shown that the surface excess of P units rises as ˜ is increased. The surface tension decreases
in parallel. Considering the interaction between close enough surfaces of two globules, we show that they always attract each
other at a complete equilibrium. It is pointed out, however, that such equilibrium may be difficult to reach, so that partially equilibrium structures (defined by the condition that a chain forming one globule does not penetrate into the core of the other globule)
are relevant. It is shown that at such partial equilibrium the interaction is repulsive, so the globules may be stabilized
from aggregation. The strongest repulsion is predicted at the coil-to-globule transition point T
cg: the repulsion force decreases with the distance between the surfaces according to a power law. In the general case (apart
from T
cg) the force vs. distance decay becomes exponential; the decay length ξ diverges as T → T
cg. The developed theory explains certain anomalous properties observed for globules of amphiphilic homopolymers. 相似文献
10.
11.
Oelschlaeger C Buhler E Waton G Candau SJ 《The European physical journal. E, Soft matter》2003,11(1):7-20
The mixed micellization between the cationic gemini surfactant [ C12H25( CH3)2N+( C2H4) N+( CH3)2 C12H25•2Br-] and the cationic cetyltrimethylammonium bromide (CTAB) in 150 mM KBr solutions has been investigated. The variation of the
cmc of the mixtures, measured by surface tension experiments, with composition revealed synergism in micelle formation. T-Jump
and light scattering experiments performed in the vicinity of the crossover volume fraction showed the existence of two micellar
populations, possibly linear and toroidal micelles. Rheological and dynamic light scattering experiments allowed to fully
characterize the linear viscoelasticity of the mixtures. These measurements revealed synergistic gains in viscoelastic properties
with a maximum of the stress-relaxation time around the equimolar composition. These effects are ascribed to a progressive
intermicellar crosslinking resulting from a continuous increase of the end-cap energy with the 12-2-12 content in the mixture.
Received: 18 November 2002 / Accepted: 8 April 2003 / Published online: 27 May 2003
RID="a"
ID="a"e-mail: candau@fresnel.u-strasbg.fr 相似文献
12.
Dielectric measurement in the range 0.1 Hz to 1 MHz were used to study the motions of polymers and ions in an ion-conducting
polymer, polypropylene oxide containing small quantities (on the order of 1%) of lithium ions (LiClO4), confined as a sandwich of uniform thickness between parallel insulating mica surfaces. In the dielectric loss spectrum,
we observed three peaks; they originated from the normal mode of the polymer, segmental mode of the polymer, and ion motions.
With decreasing film thickness, the peak frequencies corresponding to the normal mode and ion motion shifted to lower frequencies,
indicating retardation due to confinement above 30 nm. This was accompanied by diminished intensity of the dielectric normal-mode
relaxation, suggesting that confinement diminished the fluctuations of the end-to-end vector of the chain dipole in the direction
between the confining surfaces. On the contrary, the segmental mode was not affected at that thickness. Finally, significant
retardation of the segmental mode was observed only for the thinnest film (14 nm). The different dynamical modes of the polymer
(segmental and slowest normal modes) respond with different thickness and temperature dependence to confinement.
Received 31 August 2001 and Received in final form 30 October 2001 相似文献
13.
Higgins AM Sferrazza M Jones RA Jukes PC Sharp JS Dryden LE Webster J 《The European physical journal. E, Soft matter》2002,8(2):137-143
We investigate the dynamics of spinodal dewetting in liquid-liquid polymer systems. Dewetting of poly(methyl-methacrylate)
(PMMA) thin films on polystyrene (PS) “substrates” is followed in situ using neutron reflectivity. By following the development of roughness at the PS/PMMA interface and the PMMA surface we extract
characteristic growth times for the dewetting process. These characteristic growth times are measured as a function of the
molecular weight of the two polymers. By also carrying out experiments in the regime where the dynamics are independent of
the PS molecular weight, we are able to use dewetting to probe the scaling of the PMMA thin film viscosity with temperature
and molecular weight. We find that this scaling reflects bulk behaviour. However, absolute values are low compared to bulk
viscosities, which we suggest may be due in part to slippage at the polymer/polymer interface.
Received 25 June 2001 and Received in final form 5 December 2001 相似文献
14.
In a SANS experiment, we have directly determined for the first time the conformation of hyaluronan, a model semirigid polyelectrolyte. At high ionic strength, this is completely possible, where the scattered intensity crosses over (when decreasing q) from a q(-1) rod variation to a q(-2) and, where fitting to the "wormlike" chain model gives the backbone, intrinsic, persistence length: L0 = 86.5 A. At low ionic strength, we can safely check that the measured persistence length appears increased by at least the amount predicted by Odijk for the electrostatic contribution, L(e) (approximately kappa(-2), square of the Debye screening length). However, the intensity at the lowest q is not only due to the single chain, since it crosses over from a q(-1) to a q(-4) variation, characteristic of polymer associations. 相似文献
15.
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
16.
Binder K 《The European physical journal. E, Soft matter》2002,9(3):293-298
After a brief review of the scaling concepts for static and dynamic properties of polymer brushes in good solvents and Theta
solvents, the Monte Carlo evidence is discussed. It is shown that under typical conditions the diameter of the last blob is
of the order of 10-20% of the brush height, and therefore pronounced deviations from the self-consistent field predictions
occur. In bad solvents, lateral microphase separation occurs leading to an irregular pattern of “dimples”. Particularly interesting
is the response of brushes to shear deformation, and the interaction between two interpenetrating brushes. Recent attempts
to understand the resulting shear forces via molecular-dynamics simulations are briefly described, and an outlook on related experiments is given.
Dedicated to Prof. H.E. Stanley on the occasion of his 60th birthday
Received 11 March 2002 and Received in final form 3 June 2002 相似文献
17.
Mattioni L Wittmer JP Baschnagel J Barrat JL Luijten E 《The European physical journal. E, Soft matter》2003,10(4):369-385
Correlations in the motion of reptating polymers in a melt are investigated by means of Monte Carlo simulations of the three-dimensional
slithering-snake version of the bond-fluctuation model. Surprisingly, the slithering-snake dynamics becomes inconsistent with
classical reptation predictions at high chain overlap (created either by chain length N or by the volume fraction φ of occupied lattice sites), where the relaxation times increase much faster than expected. This
is due to the anomalous curvilinear diffusion in a finite time window whose upper bound (N) is set by the density of chain ends φ/N. Density fluctuations created by passing chain ends allow a reference polymer to break out of the local cage of immobile
obstacles created by neighboring chains. The dynamics of dense solutions of “snakes” at t ≪ is identical to that of a benchmark system where all chains but one are frozen. We demonstrate that the subdiffusive dynamical
regime is caused by the slow creeping of a chain out of its correlation hole. Our results are in good qualitative agreement
with the activated-reptation scheme proposed recently by Semenov and Rubinstein (Eur. Phys. J. B, 1 (1998) 87). Additionally, we briefly comment on the relevance of local relaxation pathways within a slithering-snake scheme.
Our preliminary results suggest that a judicious choice of the ratio of local to slithering-snake moves is crucial to equilibrate
a melt of long chains efficiently.
Received: 18 December 2002 / Accepted: 3 April 2003 / Published online: 12 May 2003
RID="a"
ID="a"e-mail: jwittmer@dpm.univ-lyon1.fr
RID="b"
ID="b"Current address: University of Illinois at Urbana-Champaign. 相似文献
18.
We present an experimental study of the adsorption of hydrophobic highly charged polyelectrolytes on a neutral and hydrophobic
surface, the air/water interface. The polymer was a randomly sulphonated polystyrene with charge fractions between 0.3 and
0.9 and the adsorbed layers were characterised by Langmuir through measurements, ellipsometry and X-ray reflectivity. The
adsorption rate is always very slow and the resulting layers are very thin (< 3 nm). A maximum of adsorption with the charge
fraction is observed which we relate to the conformation of the chains in solution. We show that adsorption is partially irreversible,
strongly hysteretic and that the state of an adsorbed layer depends on its history.
Received 16 June 2000 相似文献
19.
G. Migliorini V.G. Rostiashvili T.A. Vilgis 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(1):61-73
The Langevin dynamics of a self-interacting chain embedded in a quenched random medium is investigated by making use of the
generating functional method and one-loop (Hartree) approximation. We have shown how this intrinsic disorder causes different
dynamical regimes. Namely, within the Rouse characteristic time interval the anomalous diffusion shows up. The corresponding
subdiffusional dynamical exponents have been explicitly calculated and thoroughly discussed. For the larger time interval
the disorder drives the center of mass of the chain to a trap or frozen state provided that the Harris parameter, (Δ/b
d)N
2 - νd≥1, where Δ is a disorder strength, b is a Kuhnian segment length, N is a chain length and ν is the Flory exponent. We have derived the general equation for the non-ergodicity function f (p) which characterizes the amplitude of frozen Rouse modes with an index p = 2πj/N. The numerical solution of this equation has been implemented and shown that the different Rouse modes freeze up at the same
critical disorder strength Δ
c ∼ N
- γ where the exponent γ ≈ 0.25 and does not depend from the solvent quality.
Received 17 December 2002 Published online 23 May 2003
RID="a"
ID="a"e-mail: vilgis@mpip-mainz.mpg.de 相似文献
20.
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