共查询到20条相似文献,搜索用时 31 毫秒
1.
C. Monthus T. Garel H. Orland 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(1):121-130
We consider two different problems involving the localization of a single polymer chain: (i) a periodic AB copolymer at a
selective fluid-fluid interface, with the upper (resp. lower) fluid attracting A (resp. B) monomers (ii) a homopolymer chain
attracted to a hard wall (wetting). Self avoidance is neglected in both models, which enables us to study their localization
transition in a grand canonical approach. We recover the results obtained in previous studies via transfer matrix methods. Moreover, we calculate in this way the loop length distribution functions in the localized phase.
Some finite size effects are also determined and tested numerically.
Received 13 April 2000 相似文献
2.
K. Kunz S.H. Anastasiadis M. Stamm T. Schurrat F. Rauch 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(3):411-419
The effect of the ratio of block lengths on the interfacial partitioning of poly(styrene-block-1,4 isoprene) diblock copolymers
from their mixtures with polystyrene homopolymer melt is investigated utilizing a series of copolymers with almost constant
molecular weight but different compositions. The concentration profile of the copolymer is measured directly using the nuclear reaction analysis technique; a segregation of the diblock is found at both the air/polymer surface, due to the lower
surface energy of polyisoprene, and at the substrate/polymer interface. No significant effect of the block length ratio on
the free-surface excess was observed. The block molecular weights have apparently led to dangling chain conformations in the
non-overlapping mushroom and in the overlapping mushroom regimes whereas the brush regime was not accessible; no indications
of a real border between the two former regimes was found.
Received: 20 July 1998 / Received in final form and Accepted: 11 September 1998 相似文献
3.
M.C. Fauré P. Bassereau M.A. Carignano I. Szleifer Y. Gallot D. Andelman 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(3):365-375
We have studied both experimentally and theoretically the surface pressure isotherms of copolymers of polystyrene-polyethyleneoxide
(PS-PEO) at the air-water interface. The SCMF (single chain mean-field) theory provides a very good agreement with the experiments
for the entire range of surface densities and is consistent with the experiments if an adsorption energy per PEO monomer at
the air-water interface of about one kB T is taken. In addition, the chain density profile has been calculated for a variety of surface densities, from the dilute
to the very dense ones. The SCMF approach has been complemented by a mean-field approach in the low density regime, where
the PEO chains act as a two-dimensional layer. Both theoretical calculations agree with the experiments in this region.
Received: 19 June 1997 / Revised: 2 February 1998 / Accepted: 11 February 1998 相似文献
4.
V.A. Brazhnyi S. Stepanow 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(3):355-362
We consider the adsorption of a random heteropolymer onto an interface within the model of Garel et al. [#!gareletal89!#] by taking into account random self-interactions and ternary repulsive interactions between the monomers.
Within the replica trick and by using a self-consistent preaveraging procedure we map the adsorption problem onto the problem
of binding state of a quantum mechanical Hamiltonian. The analysis of the latter is treated within the variational method
based on the 2nd Legendre transform. Our study reveals a complex behaviour of the localization of the heteropolymer. In particular,
we predict a reentrant localization transition for moderate values of the asymmetry of the distribution function of the monomer
sequences along the heteropolymer.
Received 9 October 2001 and Received in final form 27 February 2002 Published online 6 June 2002 相似文献
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7.
F. Nieto C. Uebing 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(4):523-531
In this work the diffusion of non-interacting adsorbates on a random AB alloy surface is considered. For this purpose a simple
cubic (sc), body-centered cubic (bcc) or face-centered cubic (fcc) auxiliary metal lattice is introduced. The auxiliary lattice
is truncated parallel to its (100) plane in such a way that the fourfold hollow positions of the metal surface form a regular
net of adsorption sites with square symmetry. The adsorption energy of each adsorption site is determined by its own environment,
i.e. by the numbers of direct A or B neighbors. The Monte-Carlo method has been utilized to simulate surface diffusion of adsorbates
on such energetically heterogeneous alloy surfaces and to calculate the tracer, jump and chemical diffusion coefficients.
The chemical diffusion coefficient was calculated via two different approaches: the fluctuation and the Kubo-Green method. The influence of energetical heterogeneities on the
surface diffusion is largely pronounced at low temperatures and low surface coverages, where most of the adatoms are trapped
by deep adsorption sites. It was found that at low temperatures the sequential occupation of the different types of adsorption
sites can be observed.
Received: 24 October 1997 / Accepted: 17 December 1997 相似文献
8.
G.R. Schreiber 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(3):479-490
A generalised integer S Ising spin glass model is analysed using the replica formalism. The bilinear couplings are assumed to have a Gaussian distribution
with ferromagnetic mean . Incorporation of a quadrupolar interaction term and a chemical potential leads to a richer phase diagram with transitions
of first and second order. The first order transition may be interpreted as a phase separation, and contrary to what has been
argued previously, it persists in the presence of disorder. Finally, the stability of the replica symmetric solution with
respect to fluctuations in replica space is analysed, and the transition lines are obtained both analytically and numerically.
Received 13 January 1997 相似文献
9.
Summary Auger measurements of the surface composition have been performed on solid and molten Pb-5at%Sn alloys. They confirm the theoretical
predictions that, in the absence of oxygen, liquid or solid alloys exhibit no significant surface segregation. On the contrary,
surface composition measurements and simultaneous surface tension measurements clearly show that oxygen adsorption strongly
affects the segregation of tin at the liquid-vapour interface. This surface enrichment is driven by the contribution of the
reaction free energy and of the products surface tension. 相似文献
10.
T. Kerle J. Klein K. Binder 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(3):401-410
The capillary broadening of a 2-phase interface is investigated both experimentally and theoretically. When a binary mixture
in a thin film with thickness D segregates into two coexisting phases the interface between the two phases may form parallel to the substrate due to preferential
surface attraction of one of the components. We show that the interfacial profile (of intrinsic width w0) is broadened due to capillary waves, which lead to fluctuations, of correlation length of the local interface positions in the directions parallel to the confining walls. We postulate that acts as an upper cutoff for the spectrum of capillary waves on the interface, so that the effective mean square interfacial
width w varies as . In the limit of large D this yields or respectively for the case of short- or long-range forces between walls and the interface. We used the Nuclear Reaction Analysis
depth profiling technique, to investigate this broadening effect directly in two binary polymer mixtures. Our results reveal
that the interfacial width indeed increases with film thickness D, though the observed interfacial width is lower than the predicted w. This is probably due to surface tension effects imposed by the confining surfaces which are not taken into account in our
model.
Received: 19 February 1998 / Received in final form: 2 September 1998 / Accepted: 8 September 1998 相似文献
11.
H. Schiessel 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(3):373-380
We investigate the bending of flexible charged membranes due to the presence of rigid rodlike macroions in the framework of
the Debye-Hückel approximation. When the macroions are fixed in space at some distance from the bilayer the membrane bends
towards them; we calculate the exact deformation profile. On the other hand a macroion which is adsorbed on the membrane causes
a deflection of the bilayer. Finally, we consider swollen lamellar polyanion/charged-lipid complexes where the macroions are
intercalated between charged lipid bilayers. We predict the occurrence of a double adsorption (pinching effect) of the macroion
for sufficiently flexible membranes.
Received: 9 February 1998 / Revised: 9 June 1998 / Accepted: 2 July 1998 相似文献
12.
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
13.
Kay Jörg Wiese 《Pramana》2005,64(5):817-827
In this paper, we discuss why functional renormalization is an essential tool to treat strongly disordered systems. More specifically,
we treat elastic manifolds in a disordered environment. These are governed by a disorder distribution, which after a finite
renormalization becomes non-analytic, thus overcoming the predictions of the seemingly exact dimensional reduction. We discuss
how a renormalizable field theory can be constructed even beyond 2-loop order. We then consider an elastic manifold embedded
inN dimensions, and give the exact solution forN →ɛ This is compared to predictions of the Gaussian replica variational ansatz, using replica symmetry breaking. Finally, the
effective action at order 1/N is reported. 相似文献
14.
J.L. Goveas G.H. Fredrickson 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(1):79-92
We consider a planar interface between strongly-segregated homopolymers subjected to steady shear in the plane of the interface.
We develop a constitutive equation for stress relaxation in an inhomogeneous system for chains obeying Rouse dynamics. Using
this equation, the interfacial viscosity for a symmetric blend is found to be in agreement with a scaling prediction due to de Gennes, where is the bead friction coefficient, b is the segment length, is the segment volume and is the Flory-Huggins interaction parameter driving the phase separation. We generalize our results to asymmetric blends and
describe a phenomenological extension to entangled melts.
Received: 18 August 1997 / Received in final form: 1 December 1997 / Accepted: 2 December 1997 相似文献
15.
《Comptes Rendus de l''Academie des Sciences Series IV Physics》2000,1(9):1125-1133
We consider the adsorption of linear polymer and copolymer chains at surfaces and interfaces. We first remind de Gennes' theory for homopolymers, made of a single monomer species. Then we turn to multi block and random copolymers. In the latter case, we consider both cases when the A and B monomer species are distributed along the chain in a noncorrelated and correlated way, respectively. For each case, we discuss single chain adsorption and the saturation of the surface. Various measurable quantities are evaluated. 相似文献
16.
Fernando Pigeard de Almeida Prado Gunter M. Schütz 《Journal of statistical physics》2011,142(5):984-999
We consider a kinetic Ising model which represents a generic agent-based model for various types of socio-economic systems.
We study the case of a finite (and not necessarily large) number of agents N as well as the asymptotic case when the number of agents tends to infinity. The main ingredient are individual decision thresholds
which are either fixed over time (corresponding to quenched disorder in the Ising model, leading to nonlinear deterministic
dynamics which are generically non-ergodic) or which may change randomly over time (corresponding to annealed disorder, leading
to ergodic dynamics). We address the question how increasing the strength of annealed disorder relative to quenched disorder
drives the system from non-ergodic behavior to ergodicity. Mathematically rigorous analysis provides an explicit and detailed
picture for arbitrary realizations of the quenched initial thresholds, revealing an intriguing “jumpy” transition from non-ergodicity
with many absorbing sets to ergodicity. For large N we find a critical strength of annealed randomness, above which the system becomes asymptotically ergodic. Our theoretical
results suggests how to drive a system from an undesired socio-economic equilibrium (e.g. high level of corruption) to a desirable
one (low level of corruption). 相似文献
17.
H. Meyer-Ortmanns T. Reisz 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(4):549-558
Dynamical linked cluster expansions are linked cluster expansions with hopping parameter terms endowed with their own dynamics.
We discuss physical applications to systems with annealed and quenched disorder. Examples are the bond-diluted Ising model
and the Sherrington-Kirkpatrick spin glass. We derive the rules and identify the full set of graphs that contribute to the
series in the quenched case. This way it becomes possible to avoid the vague extrapolation from positive integer n to n = 0, that usually goes along with an application of the replica trick.
Received 13 December 2001
Published online 25 June 2002 相似文献
18.
Pramod Kumar Mishra 《Phase Transitions》2013,86(1):47-54
Lattice model of directed self-avoiding walk has been solved analytically to investigate adsorption–desorption phase transition behaviour of a semiflexible sequential copolymer chain on a two-dimensional impenetrable surface perpendicular to the preferred direction of the walk of the copolymer chain in three dimensions. The stiffness of the chain has been accounted by introducing an energy barrier for each bend in the walk of the copolymer chain. Exact value of adsorption–desorption transition points have been determined using the generating function method for the cases in which one type of monomer is having interaction with the surface, namely (i) no interaction (ii) attractive interaction and (iii) repulsive interaction. Results obtained in each of the case show that for stiffer copolymer chain adsorption transition occurs at a smaller value of monomer surface attraction than a flexible copolymer chain. These features are similar to that of a semiflexible homopolymer chain adsorption. 相似文献
19.
A. Benyoussef D. Dohmi A. El Kenz L. Peliti 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(4):503-510
Using a replica formalism, a generalization of a recent mean field model corresponding to the observed wrinkling transition
in randomly polymerized membranes is presented. In this model we study the effects of global fluctuations of the surface normals
to the flat membrane, which can be introduced by a random local field. In absence of these global fluctuations, we show that,
the model exhibits both continuous and discontinuous transitions between flat and wrinkled phases, contrary to what has been
predicted by Bensimon et al. and Attal et al. Phase diagrams both in replica symmetry and in breaking of replica symmetry in sense of Almeida and Thouless are given. We
have also investigated the effects of global fluctuations on the replica symmetry phase diagram. We show that, the wrinkled
phase is favored and the flat phase is unstable. For large global fluctuations, the transition between wrinkled and flat phases
becomes first order.
Received: 3 December 1997 / Revised: 31 March 1998 / Accepted: 3 August 1998 相似文献