共查询到20条相似文献,搜索用时 656 毫秒
1.
M. Geoghegan F. Boué G. Bacri A. Menelle D.G. Bucknall 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(1):83-96
We have used neutron reflectometry to measure interfacial widths between two polystyrene films, where either one or both films
are crosslinked. The observed interfacial width between two networks is larger than the size expected for “dangling ends”,
which suggests motion of heterogeneous regions of the networks. In the case when one of the networks is replaced by a linear
polymer, the interfacial profile can be asymmetric with a diffusion “front” of linear polymer penetrating the network to a
length scale of up to 200 ?. In the case of a more densely crosslinked network and a high molecular weight linear polymer
the interface is symmetric implying negligible penetration.
Received: 4 December 1996 / Revised: 13 October 1997 / Accepted: 23 December 1997 相似文献
2.
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
3.
G. Huber T.A. Vilgis 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(2):217-223
The adsorption of a single ideal polymer chain on energetically heterogeneous and rough surfaces is investigated using a variational
procedure introduced by Garel and Orland (Phys. Rev. B 55, 226 (1997)). The mean polymer size is calculated perpendicular and parallel to the surface and is compared to the Gaussian
conformation and to the results for polymers at flat and energetically homogeneous surfaces. The disorder-induced enhancement
of adsorption is confirmed and is shown to be much more significant for a heterogeneous interaction strength than for spatial
roughness. This difference also applies to the localization transition, where the polymer size becomes independent of the
chain length. The localization criterion can be quantified, depending on an effective interaction strength and the length
of the polymer chain.
Received: 29 October 1997 / Revised: 19 December 1997 / Accepted: 6 March 1998 相似文献
4.
R. Rzehak W. Kromen T. Kawakatsu W. Zimmermann 《The European physical journal. E, Soft matter》2000,2(1):3-30
Static properties of a single polymer fixed at one end and subjected to a uniform flow field are investigated for several
polymer models: the Gaussian chain, the freely jointed chain, and the FENE (Finitely Extensible Nonlinear Elastic) chain.
By taking into account first the excluded-volume interaction and subsequently also the hydrodynamic interaction, the polymer
models are gradually completed and the relevance of each effect for the polymer deformation can be identified. Results from
computer simulations of these bead spring chains are compared with analytical calculations using either the conformational
distribution function or blob models. To this end, in contrast to the blob model with non-draining blobs introduced for a
tethered polymer by Brochard-Wyart, we here develop also a model with free-draining blobs. It turns out that a limited extensibility
of the polymer – described by nonlinear spring forces in the model – leads to a flow velocity dependence of the end-to-end
distance, segment density, etc. which agrees with the power law predictions of the blob model only for very long chains and
in a narrow range of flow velocities. This result is important for comparison with recent experiments on DNA molecules which
turn out to be still rather short in this respect. The relative importance of finite extensibility, the excluded-volume effect,
and hydrodynamic interactions for polymers in flow is not fully understood at present. The simulation of reasonably long chains
becomes possible even when fluctuating hydrodynamic interactions are taken into account without employing averaging procedures
by introducing efficient numerical approximation schemes. At medium velocity of the uniform flow the polymer is partially
uncoiled and simulations show that the effects of excluded-volume and hydrodynamic interactions are position-dependent. Both
are stronger near the free end than near the tethered end of the polymer. A crossover from a nearly non-draining polymer at
small flow velocities to a free-draining almost uncoiled chain at large velocities is found in the simulations. Accordingly,
models assuming the polymer to be composed of either free- or non-draining subunits, like the two blob models, cannot correctly
describe the extension and shape of a tethered polymer in flow, and simple power laws for the polymer extension, etc. cannot
be expected.
Received 21 June 1999 相似文献
5.
Constrained fluctuation theories of rubber elasticity: General results and an exactly solvable model
R. Everaers 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(3):341-350
We present a new model of rubber elasticity where linear forces act to constrain the fluctuations of the eigenmodes of the
phantom model. The model allows us to treat the constrained junction and the tube model within the same, transparent formalism,
does not require any further approximations, and is particularly suited for the analysis of simulation data for (strained)
model polymer networks. As an interesting side result we show that in order for the model to be consistent, the constraints
(but not the mean polymer conformations!) have to deform affinely, a severe restriction that might also apply to other models.
Complementary, we prove in analogy to the derivation of the virial theorem that introducing constraints into the phantom network
Hamiltonian leads to extra terms in addition to the usual Doi-Edwards formulas for the polymer contribution to the stress
tensor which vanish only for affinely deforming constraints.
Received: 28 November 1997 / Received in final form and accepted: 31 March 1998 相似文献
6.
7.
S. Müller L. Schäfer 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(3):351-369
We give a detailed analysis of the intersection properties of polymers. Using the renormalization group we provide a full
crossover function for the dependence of the number of intersections in a single polymer on chain length and excluded volume
strength. We compare our results with Monte-Carlo data and with exact calculations for a random walk, finding good agreement
in all respects. Restricting to the vicinity of the eight ternary fixed points we also calculate the number of intersections
between two chains placed at a fixed distance, including the two halves of a block-copolymer. The analysis of these systems
confirms the interpretation of the different contributions to the number of intersections in a single chain. Due to the highly
nontrivial character of the correlations in a polymer chain the correction exponents in both cases however are different.
None of the results can be extracted from any Flory-type estimate.
Received: 1 April 1997 / Revised: 24 October 1997 /
Accepted: 29 January 1998 相似文献
8.
The simulation of a two-dimensional, broadly polydisperse, living polymers system at high concentration reveals an unusual
conformational behaviour for the longer chains. Unlike in three dimensions, the longer chains are not swollen but are squeezed
by the smaller chains. This observation is discussed in terms of a two dimensional solvent- polymer mixture whose solvent
particules are larger than the polymer monomers.
Received: 13 December 1996 / Revised: 16 March 1998 / Accepted: 27 March 1998 相似文献
9.
10.
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
11.
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
12.
V. Fourmaux-Demange A. Brûlet F. Boué P. Davidson P. Keller J.P. Cotton 《The European physical journal. E, Soft matter》2000,1(4):301-317
We have studied the rheology and the conformation of stretched comb-like liquid-crystalline polymers. Both the influence of
the comb-like structure and the specific effect of the nematic interaction on the dynamics are investigated. For this purpose,
two isomers of a comb-like polymetacrylate polymer, of well-defined molecular weights, were synthesized: one displays a nematic
phase over a wide range of temperature, the other one has only an isotropic phase. Even with high degrees of polymerization
N, between 40 and 1000, the polymer chains studied were not entangled. The stress-strain curves during the stretching and relaxation
processes show differences between the isotropic and nematic comb-like polymers. They suggest that, in the nematic phase,
the chain dynamics is more cooperative than for a usual linear polymer. Small-angle neutron scattering has been used in order
to determine the evolution of the chain conformation after stretching, as a function of the duration of relaxation t
r. The conformation can be described with two parameters only: , the global deformation of the polymer chain, and p, the number of statistical units of locally relaxed sub-chains. For the comb-like polymer, the chain deformation is pseudo-affine:
is always smaller than (the deformation ratio of the whole sample). In the isotropic phase, has a constant value, while pincreases as tr. This latter behavior is not that expected for non-entangled chains, in which p varies as t
r
1/2 (Rouse model). In the nematic phase, decreases as a stretched exponential function of t
r, while p remains constant. The dynamics of the comb-like polymers is discussed in terms of living clusters from which junctions are
produced by interactions between side chains. The nematic interaction increases the lifetime of these junctions and, strikingly,
the relaxation is the same at all scales of the whole polymer chain.
Received 5 May 1999 and Received in final form 18 October 1999 相似文献
13.
14.
M.T. Batchelor D. Bennett-Wood A.L. Owczarek 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(1):139-142
We provide general formulae for the configurational exponents of an arbitrary polymer network connected to the surface of
an arbitrary wedge of the two-dimensional plane, where the surface is allowed to assume a general mixture of boundary conditions
on either side of the wedge. We report on a comprehensive study of a linear chain by exact enumeration, with various attachments
of the walk's ends to the surface, in wedges of angles and , with general mixed boundary conditions.
Received: 20 October 1997 / Accepted: 13 May 1998 相似文献
15.
J. Jimenez R. Rajagopalan 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(2):237-243
We introduce a new simulation method, which we call the contact-distribution method, for the determination of the Helmholtz potential for polymer/colloid systems from lattice Monte-Carlo simulations. This
method allows one to obtain forces between finite or semi-infinite objects of any arbitrary shape and dimensions in the presence
of polymer chains in solution or physisorbed or chemisorbed at interfaces. We illustrate the application of the method using
two examples: (i) the interaction between the tip of an atomic force microscope (AFM) and a single, end-grafted polymer chain
and (ii) the interaction between an AFM tip and a polymer brush. Numerical results for the first two cases illustrate how
the method can be used to confirm and extend scaling laws for forces and Helmholtz potentials, to examine the effects of the
shapes and sizes of the objects and to examine conformational transitions in the polymer chains.
Received: 15 May 1998 / Revised: 11 June 1998 / Accepted: 12 June 1998 相似文献
16.
C.M. Granzow A. Liebman G. Mahler 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(1):131-142
Continuous measurement models are conveniently based on master equations specified by the respective Hamiltonian and appropriate
environment operators. As demonstrated by stochastic unraveling, the latter specify the dynamical process rather than static
detection modes. We show that certain environment operators acting on a simple system may, in fact, require extended networks
for implementation: Their Hamilton parameters re-appear in the effective environment operators of the reduced model. The resulting
quantum trajectories typically involve competing paths, which may give rise to different fluctuation and noise properties
even when the corresponding ensemble behavior is practically the same.
Received: 21 July 1997 / Received in final form: 10 November 1997 / Accepted: 27 October 1997 相似文献
17.
D.J. Read 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(3):431-449
There are many experimental situations in which polymer chains are constrained or localised into a small region of space (e.g. melt chains confined to a “tube”, network chains pinned by crosslinks). We show that detailed consideration of the quenched
variables is vital in these experiments. This paper provides a crucial link between microscopic models with localising constraints
and scattering patterns by a generalisation of the Random Phase Approximation (RPA) which allows for quenched translational
variables. A method is developed which deals with correlations between the quenched variables brought about by incompressiblity
(for example, in a polymer melt there are correlations between tubes because of the interaction between chains). As an example,
the generalised RPA is applied to models based on the Warner-Edwards picture of the tube. Theoretical results for a melt of
H-shaped copolymers are compared with experimental scattering. Early results suggest that to fit the scattering we may be
forced to relax one of the central assumptions of the tube model; that the tube deforms affinely, that all chains retract
by the same amount or that the tube diameter does not couple to the strain.
Received 26 October 1998 and Received in final form 19 March 1999 相似文献
18.
Y.I. Latyshev B. Pannetier P. Monceau 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(4):421-426
We demonstrate for the first time that a periodic array of submicrometer holes (antidots) can be patterned into thin single
NbSe3 crystals. We report on the study of Charge Density Wave (CDW) transport of the network of mesoscopic units between antidots.
Size of the elementary unit can be as small as 0.5 μm along the chain axis and in cross-section. We observe size effects for Ohmic residual resistance and in CDW transport current-voltage characteristics
in submicronic networks.
Received: 25 November 1997 / Received in final form: 30 March 1998 / Accepted: 6 April 1998 相似文献
19.
A phenomenological model is presented to describe weakly charged polymer gels based on the classical elasticity theory. The
structure factor of the gel is calculated considering both thermal and frozen concentration fluctuations as well as the screened
Coulomb interaction. In agreement with the recent experimental finding the result shows anomalous crosslink-density dependence
of the scattering profiles.
Received: 28 March 1997 / Revised: 4 September 1997 / Accepted: 23 October 1997 相似文献
20.
P.I.C. Teixeira E.M. Terentjev 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(2):237-245
We propose a microscopic model of a chiral polymer chain with permanent transverse dipoles interacting with an external electric
field. Its behaviour has been investigated by computer simulation in the limit of weak chirality. Large-scale (tertiary) helical
winding induced along the field direction has been found above a threshold field Ec, and the helix parameters have been calculated as functions of the field strength. Below Ec there is no coherent helical structure of the chain conformation. We find a characteristic scaling of the threshold and the
winding radius a with the chain bending modulus , and .
Received: 15 November 1997 / Accepted: 16 February 1998 相似文献