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1.
G. Strobl 《The European physical journal. E, Soft matter》2000,3(2):165-183
Based on broad and detailed evidence from a large variety of experiments on several polymer systems carried out by other authors
and ourselves, a novel concept for understanding the crystallization of polymers from the melt is developed. The experiments
generally indicate that the formation and growth of the lamellar crystallites is a multi-step process passing over intermediate
states. We suggest a specific route which is compatible with the observations. It is proposed that the initial step is always
the creation of a mesomorphic layer which spontaneously thickens, up to a critical value, where it solidifies through a cooperative
structural transition. The transition produces a granular crystalline layer, which transforms in the last step into homogeneous
lamellar crystallites. The model leads to predictions about the temperature dependencies of the crystal thickness and the
growth rate which are at variance with conventional views but in agreement with findings in recent experiments.
Received 17 February 2000 and Received in final form 30 March 2000 相似文献
2.
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
3.
It has been shown over the last few years that the dynamics close to the glass transition is strongly heterogeneous, both
by measuring the diffusion coefficient of tagged particles or by NMR studies. Recent experiments have also demonstrated that
the glass transition temperature of thin polymer films can be shifted as compared to the same polymer in the bulk. We propose
here first a thermodynamical model for van der Waals liquids, which accounts for experimental results regarding the bulk modulus
of polymer melts and the evolution of the density with temperature. This model allows us to describe the density fluctuations
in such van der Waals liquids. Then, by considering the thermally induced density fluctuations in the bulk, we propose that
the 3D glass transition is controlled by the percolation of small domains of slow dynamics, which allows to explain the heterogeneous
dynamics close to T
g. We show then that these domains percolate at a lower temperature in the quasi-2D case of thin suspended polymer films and
we calculate the corresponding glass transition temperature reduction, in quantitative agreement with experimental results
of Jones and co-workers. In the case of strongly adsorbed films, we show that the strong adsorption amounts to enhance the
slow domains percolation. This effect leads to 1) a broadening of the glass transition and 2) an increase of T
g in quantitative agreement with experimental results. For both strongly and weakly adsorbed films, the shift in T
g is given by a power law, the exponent being the inverse of that of the correlation length of 3D percolation.
Received 21 March 2000 and Received in final form 4 December 2000 相似文献
4.
Recent experiments have demonstrated that the dynamics in liquids close to the glass transition temperature is strongly heterogeneous.
The characteristic size of these heterogeneities has been measured to be a few nanometers at T
g. We extend here a recent model for describing the heterogeneous nature of the dynamics which allows both to derive this length
scale and the right orders of magnitude of the heterogeneities of the dynamics close to the glass transition. Our model allows
then to interpret quantitatively small probes diffusion experiments.
Received 29 March 2002 and Received in final form 11 November 2002
RID="a"
ID="a"e-mail: long@lps.u-psud.fr 相似文献
5.
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
6.
Erichsen J Shiferaw T Zaporojtchenko V Faupel F 《The European physical journal. E, Soft matter》2007,24(3):243-246
Using the cluster-embedding method of V. Zaporojchenko et al. (Macromolecules 34, 1125 (2000)), we measured the glass transition temperature T
g at the polystyrene/vacuum interface of bimodal mixtures of monodisperse polystyrenes of 3.5k and 1000k. Embedding of ≈ 1
nm Au clusters was monitored in situ by X-ray photoelectron spectroscopy (XPS). The clusters were formed by evaporation of Au onto the polymer surface. Only one
glass transition was observed in the mixtures. The surface glass transition temperatures are correlated to but are below the
bulk values of the mixtures and obey the Gordon-Taylor equation. The results suggest that the earlier reported molecular-weight
dependence of the surface glass transition is not due to segregation of short chains to the surface. 相似文献
7.
Roussel F Saidi S Guittard F Geribaldi S 《The European physical journal. E, Soft matter》2002,8(3):283-288
The thermophysical properties of fluorinated acrylate homopolymers are investigated by differential scanning calorimetry (DSC)
and optical microscopy and discussed in terms of relative lengths of the fluorinated chain and the hydrocarbon spacer between
the acrylate moiety and the fluorinated chain. These compounds exhibit an intrinsic microphase-separation (Isotropic+Isotropic
morphology) occurring between the fluorinated chains and the acrylate polymer backbone. It is shown that the enthalpy of mixing
is a function of the length of the lateral fluorocarbon chains. The thermophysical behaviour of these materials may be regarded
as demixed systems exhibiting an Upper Critical Solution Temperature. The photopolymerization process of one of the monomer
is studied by isothermal photocalorimetry. High acrylate double-bond conversion and fast curing rates were obtained thus demonstrating
the promising use of these materials for coating and film processing applications using UV-curing techniques.
Received 30 January 2002 相似文献
8.
T. Albrecht S. Armbruster S. Keller G. Strobl 《The European physical journal. E, Soft matter》2001,6(3):237-243
Poly(ethylene oxide) (PEO) in the semi-crystalline state shows a reversible surface crystallization and melting; a temperature
decrease leads to a certain crystal thickening, a temperature increase reversely to an expansion of the amorphous intercrystallite
layers. Dynamic calorimetry provides a means to investigate the kinetics of the process. The structural rearrangement in the
region of the crystalline-amorphous interface can only be accomplished if the chains can slide through the crystallites. One
therefore expects the associated time to change with the crystallite thickness. Variations of the crystal thickness of PEO
can be achieved by choosing different crystallization temperatures. We studied the effect of the crystal thickness employing
temperature-modulated differential scanning calorimetry and heat wave spectroscopy, and by carrying out small-angle X-ray
scattering experiments for the structural characterization. The effect of the crystal thickness is clearly observed. Results
indicate that the sliding diffusion through the crystallites takes place by helical jumps of whole stems. Data yield the activation
energy per unit length of the stems.
Received 20 April 2001 and Received in final form 13 August 2001 相似文献
9.
S. Franz T. Garel H. Orland 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(3):463-468
We consider a model of two (fully) compact polymer chains, coupled through an attractive interaction. These compact chains
are represented by Hamiltonian paths (HP), and the coupling favors the existence of common bonds between the chains. We use
a (n=0 component) spin representation for these paths, and we evaluate the resulting partition function within a homogeneous saddle
point approximation. For strong coupling (i.e. at low temperature), one finds a phase transition towards a “frozen” phase where one chain is completely adsorbed onto the
other. By performing a Legendre transform, we obtain the probability distribution of overlaps. The fraction of common bonds
between two HP, i.e. their overlap q, has both lower () and upper () bounds. This means in particular that two HP with overlap greater than coincide. These results may be of interest in (bio)polymers and in optimization problems.
Received 4 December 1998 and Received in final form 10 March 1999 相似文献
10.
E. Orlandini T. Garel 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(1):101-110
We study a single self avoiding hydrophilic hydrophobic polymer chain, through Monte-Carlo lattice simulations. The affinity
of monomer i for water is characterized by a (scalar) charge , and the monomer-water interaction is short-ranged. Assuming incompressibility yields an effective short ranged interaction
between monomer pairs (i,j), proportional to . In this article, we take (resp. ()) for hydrophilic (resp. hydrophobic) monomers and consider a chain with (i) an equal number of hydro-philic and -phobic
monomers (ii) a periodic distribution of the along the chain, with periodicity 2p. The simulations are done for various chain lengths N, in d=2 (square lattice) and d=3 (cubic lattice). There is a critical value p
c
(d,N) of the periodicity, which distinguishes between different low temperature structures. For p >p
c
, the ground state corresponds to a macroscopic phase separation between a dense hydrophobic core and hydrophilic loops. For
p <p
c
(but not too small), one gets a microscopic (finite scale) phase separation, and the ground state corresponds to a chain
or network of hydrophobic droplets, coated by hydrophilic monomers. We restrict our study to two extreme cases, and to illustrate the physics of the various phase transitions. A tentative variational approach is also presented.
Received: 10 March 1998 / Received in final form: 25 June 1998 / Accepted: 1st July 1998 相似文献
11.
Grohens Y Hamon L Reiter G Soldera A Holl Y 《The European physical journal. E, Soft matter》2002,8(2):217-224
We have measured, the thickness dependence of the glass transition temperature T(g)( h), using ellipsometry at variable temperature, for poly(methyl-methacrylate) (PMMA) of various tacticity in confined geometry. We report that several factors significantly affect T(g)( h): i) polymer microstructure (stereoregularity of PMMA) related to local dynamics; ii) interfacial interactions; iii) conformation of the polymer chains. These results raise many fundamental questions on the origin of the thickness-dependent glass transition. Why and how do the interactions with the substrate significantly affect T(g)( h)? Does T(g)( h) depend on the modifications of conformational parameters of the chains (their entropy)? What is the correlation between local dynamics and T(g)( h) in thin films? The aim of this paper is to summarise these open questions, which should stimulate further investigations in the thin polymer film scientific community. 相似文献
12.
Shiqi Zhou 《The European physical journal. E, Soft matter》2000,3(4):343-353
A density functional theory is proposed for nonuniform freely jointed tangential hard sphere polymer melts in which the bonding
interaction is treated on the basis of the properties of the Dirac δ-function, thus avoiding the use of the single chain simulation
in the theory. The excess free energy is treated by making use of the universality of the free energy density functional and
the Verlet-modified (VM) bridge function. To proceed numerically, one of the input parameters, the second-order direct correlation
function of a uniform polymer melt is obtained by solving numerically the Polymer-RISM integral equation with the Percus-Yevick
(PY) closure. The predictions of the present theory for the site density distribution, the partition coefficient and the adsorption
isotherm, near a hard wall or between two hard walls are compared with computer simulation results and with those of previous
theories. Comparison indicates that the present approach is more accurate than the previous integral equation theory and the
most accurate Monte Carlo density functional theories. The predicted oscillations of the medium-induced force between two
hard walls immersed in polymer melts are consistent with the experimental results available in the literature.
Received 18 April 2000 相似文献
13.
Elastic rod model of a supercoiled DNA molecule 总被引:4,自引:0,他引:4
We study the elastic behaviour of a supercoiled DNA molecule. The simplest model is that of a rod-like chain, involving two
elastic constants, the bending and the twist rigidities. Writing this model in terms of Euler angles, we show that the corresponding
Hamiltonian is singular and needs a small distance cut-off, which is a natural length scale giving the limit of validity of
the model, of the order of the double-helix pitch. The rod-like chain in the presence of the cut-off is able to reproduce
quantitatively the experimentally observed effects of supercoiling on the elongation-force characteristics, in the small supercoiling
regime. An exact solution of the model, using both transfer matrix techniques and its mapping to a quantum mechanics problem,
allows to extract, from the experimental data, the value of the twist rigidity. We also analyse the variation of the torque
and the writhe-to-twist ratio versus supercoiling, showing analytically the existence of a rather sharp crossover regime which can be related to the excitation
of plectoneme-like structures. Finally we study the extension fluctuations of a stretched and supercoiled DNA molecule, both
at fixed torque and at fixed supercoiling angle, and we compare the theoretical predictions to some preliminary experimental
data.
Received 1 April 1999 and Received in final form 4 January 2000 相似文献
14.
L.R. Hutchings R.W. Richards R.L. Thompson D.G. Bucknall A.S. Clough 《The European physical journal. E, Soft matter》2001,5(4):451-464
Heterotelechelic deuteropolystyrenes have been synthesised with a tertiary amine functionality at one end and a fluorocarbon
group at the other end of the polymer chain. A layer of this polymer, circa 120 ? thick, has been attached to the surface of a silicon substrate and subsequently covered with a much thicker layer of
hydrogenous polystyrene. The combination has then been annealed at 413 K under vacuum for defined times and the subsequent
distribution of the deutero heterotelechelic polymer determined using nuclear reaction analysis and neutron reflectometry.
The influences of annealing time, molecular weight and thickness of the hydrogenous polymer have been examined. Nuclear reaction
analysis showed that an excess of the heterotelechelic polymer formed at both interfaces with a larger excess remaining at
the substrate-polymer interface. When the molecular weight of the hydrogenous polymer is lower than that of the deuteropolymer,
the deutero layer is initially swollen by the hydrogenous polymer but the thickness then decreases as deutero polymer becomes
detached from the silicon substrate and an additional excess layer is eventually formed at the vacuum-polymer surface. When
the molecular weight of the hydrogenous polymer is higher, there is an initial shrinkage of the deuteropolymer layer, but
the original thickness (∼ radius of gyration of the deuteropolymer) is regained on prolonged annealing. There is no evidence
for bridging between the two interfaces by the heterotelechelic polymer. After five days annealing the volume fraction distribution
of the deuteropolymer at the silicon substrate was well described by a self-consistent field model where the only adjustable
parameter was the sticking energy of the tertiary amine group to the silicon substrate for which a value of 8k
B
T was obtained. Comparison of the dependence of the equilibrium layer thickness of the deuteropolymer on the equilibrium grafting
density at the silicon surface with the predictions of scaling theory for brush-like polymer layers suggested that the grafted
molecules were in the ideal, unperturbed brush region.
Received 12 October 2000 and Received in final form 27 March 2001 相似文献
15.
H.J. Angerman G. ten Brinke J.J.M. Slot 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(3):397-404
In this paper we investigate in a systematic way the influence of polydispersity in the block lengths on the phase behavior
of AB-multiblock copolymer melts. As model system we take a polydisperse multiblock copolymer for which both the A-blocks and the B-blocks satisfy a Schultz-Zimm distribution. In the limit of low polydispersity the expressions for the vertex functions are
clarified by using simple physical arguments. For various values of the polydispersity the phase diagram is presented, which
shows that the region of stability of the bcc phase increases considerably with increasing polydispersity. The strong dependence
of the periodicity of the microstructure on the polydispersity and on the interaction strength is presented.
Received 2 July 1998 相似文献
16.
B. Lotz 《The European physical journal. E, Soft matter》2000,3(2):185-194
Contrary to most or all other materials, crystallization of chiral but racemic polymers such as isotactic polypropylene is
accompanied by a conformational rearrangement which leads to helical geometries: the building units of the crystal are helical
stems, -20nm long, which can be either right-handed or left-handed. Helical hand cannot be reversed within the crystal structure: it is therefore a permanent marker and an indicator of molecular processes (in particular segregation/selection of helical hands) which take place during crystal
growth, and more precisely during the crucial step of “efficient” helical stem deposition. The issue of proper helical hand
selection during polymer crystal growth is mainly illustrated with isotactic polypropylene. Its various crystalline polymorphs
(, , and smectic) display virtually all possible combinations of helical hands, azimuthal settings and even non-parallel orientation
of helix axes in space. Furthermore, a specific homoepitaxy which generates a lamellar branching in the phase “quadrites” and composite structures makes it possible a) to determine the helical hand and associated azimuthal setting of every stem in
the crystalline entities and b) to determine the impact on the crystal structure and morphology of “mistakes” in helical hand
of the depositing stem. Analysis of these morphologies demonstrates that the crystallization of isotactic polypropylene (and
by implication of other achiral, helical polymers) is a highly sequential and “substrate-determined” process, i.e. that the depositing stem probes the topography of the growth face prior to attachment. These observations appear difficult to reconcile with crystallization schemes in which molecules (helical segments) are
prearranged in a kind of pseudo-crystalline bundle (and as such, are not subjected to the high constraints of crystal symmetry)
before deposition as a preassembled entity on the substrate.
Received: 5 May 2000 相似文献
17.
N. Clarke 《The European physical journal. E, Soft matter》2001,4(3):327-336
We study the early stages of phase separation in a mixture of a polydisperse and a monodisperse polymer within the Cahn-Hilliard
framework. We model the polydisperse component using a finite, but arbitrarily large, number of components, and show that
the number of components required for convergent behaviour to be achieved is computationally undemanding. We study the growth
rate of fluctuations following a quench into the two-phase region of the phase diagram. The q-dependence of the growth rate is shown to be commensurate with the behaviour of a monodisperse-monodisperse mixture, with
the major difference being an effective mobility that is dependent on the quench depth. We also study the deviation of the
time dependence of the scattering function from single exponential behaviour.
Received 29 June 2000 and Received in final form 20 November 2000 相似文献
18.
M. Deserno C. Holm J. Blaul M. Ballauff M. Rehahn 《The European physical journal. E, Soft matter》2001,5(1):97-103
The osmotic coefficient of solutions of rod-like polyelectrolytes is considered by comparing current theoretical treatments
and simulations to recent experimental data. The discussion is restricted to the case of monovalent counterions and dilute,
salt-free solutions. The classical Poisson-Boltzmann solution of the cell model correctly predicts a strong decrease in the
osmotic coefficient, but upon closer look systematically overestimates its value. The contribution of ion-ion-correlations
are quantitatively studied by MD simulations and the recently proposed DHHC theory. However, our comparison with experimental
data obtained on synthetic, stiff-chain polyelectrolytes shows that correlation effects can only partly explain the discrepancy.
A quantitative understanding thus requires theoretical efforts beyond the restricted primitive model of electrolytes.
Received 25 July 2000 and Received in final form 4 December 2000 相似文献
19.
Serghei A Mikhailova Y Huth H Schick C Eichhorn KJ Voit B Kremer F 《The European physical journal. E, Soft matter》2005,17(2):199-202
Broadband Dielectric Spectroscopy is employed to investigate the molecular dynamics in thin films of hyperbranched polyesters (type AB1B2, with -OH and -OCOCH3 as terminal groups). Three relaxation processes are detected: alpha, beta and gamma. While the latter two are not influenced by the confinement, a pronounced effect is observed on the alpha relaxation: with decreasing film thickness the slower relaxation modes of the dynamic glass transition are gradually suppressed, resulting in an increase of the average relaxation rate and in a linear decrease of the dielectric strength. This is attributed to an immobilization in confinement of the polymeric segments located at the periphery of the hyperbranched macromolecular structures. 相似文献
20.
J. van Mourik 《The European physical journal. E, Soft matter》2000,2(1):75-89
We introduce -dimensional lattice gas versions of three common models of random hetero-polymers, in which both the polymer density and
the density of the polymer-solvent mixture are finite. These solvable models give valuable insight into the problems related
to the (quenched) average over the randomness in statistical mechanical models of proteins, without having to deal with the
hard geometrical constraints occurring in finite-dimensional models. Our exact solution, which is specific to the -dimensional case, is compared to the results obtained by a saddle-point analysis and by the grand ensemble approach, both
of which can also be applied to models of finite dimension. We find, somewhat surprisingly, that the saddle-point analysis
can lead to qualitatively incorrect results.
Received 15 June 1999 and Received in final form 14 October 1999 相似文献