共查询到20条相似文献,搜索用时 562 毫秒
1.
We consider the adsorption of an isolated, Gaussian, random, and quenched copolymer chain at an interface. We first propose
a simple analytical method to obtain the adsorption/depletion transition, by averaging over the disorder the partition function
instead of the free energy. The adsorption thresholds obtained by previous authors at a solid/liquid and at a liquid/liquid
interface for multicopolymer chains can be rederived using this method. We also compare the adsorption thresholds obtained
for bimodal and for Gaussian disorder; they only agree for small disorder. We focus on the specific case of an ideally flat
asymmetric liquid/liquid interface, and consider the situation where the chain is composed of monomers of two different chemical
species A and B. The replica method is developed for this case. We show that the Hartree approximation, coupled to a replica symmetry assumption,
leads to the same adsorption thresholds as obtained from our general method. In order to describe the properties of the adsorbed
(or depleted) chain, we develop a new approximation for long chains, within the framework of the replica theory. In most cases,
the behavior of a random copolymer chain can be mapped onto that of a homopolymer chain at an asymmetric attractive interface.
The values of the effective adsorption energy are different for a random and a periodic copolymer chain. Finally, we consider
the case of uncorrelated annealed disorder. The behavior of an annealed chain can be mapped onto that of a homopolymer chain
at an asymmetric non attractive interface; hence, an annealed chain cannot adsorb at an asymmetric interface.
Received 21 January 1999 相似文献
2.
S. May 《The European physical journal. E, Soft matter》2000,3(1):37-44
The line tension of a symmetric, lipid bilayer in its liquid-crystalline state is calculated on the basis of a molecular lipid
model. The lipid model extends the opposing forces model by an expression for the conformational free energy of the hydrocarbon
chains. We consider a membrane edge that consists of a perturbed bilayer covered by a section of a cylinder-like micelle.
The structural rearrangement of the lipids implies an excess free energy which we minimize with respect to the cross-sectional
shape of the membrane edge, including both the micellar and the bilayer region. The line tension is derived as a function
of molecular lipid properties, like the lipid chain length or the head group interaction strength. We also relate it to the
spontaneous curvature of the lipid layer. We find the line tension to become smaller for lipid layers that tend to curve more
towards the hydrophobic core. Our predictions for the line tension and their relation to experimentally derived values are
discussed.
Received 2 January 2000 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.
A. Lange M. Schröter M.A. Scherer A. Engel I. Rehberg 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(4):475-484
The temporal evolution of a water-sand interface driven by gravity is experimentally investigated. By means of a Fourier analysis
of the evolving interface the growth rates are determined for the different modes appearing in the developing front. To model
the observed behavior we apply the idea of the Rayleigh-Taylor instability for two stratified fluids. Carrying out a linear
stability analysis we calculate the growth rates from the corresponding dispersion relations for finite and infinite cell
sizes. Based on the theoretical results the viscosity of the suspension is estimated to be approximately 100 times higher
than that of pure water, in agreement with other experimental findings.
Received: 12 December 1997 / Revised: 23 March 1998 / Accepted: 28
April 1998 相似文献
5.
L. Szybisz 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(4):733-746
Density functionals proposed in the literature for describing the behaviour of liquid helium at T
=0 K are examined. In so doing, several properties of the ground states of free films of superfluid
4
He are calculated by using zero- and finite-range density functional theories and these results are compared to that computed
with Monte Carlo simulations. We mainly focus the attention on the energy per particle of the slabs, the surface tension and
the width of the liquid-vacuum interfaces, all as a function of the inverse of coverage. The largest differences are found
in the case of the surface widths.
Received 26 July 1999 相似文献
6.
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
7.
C. M. Knobler 《Il Nuovo Cimento D》1994,16(9):1367-1372
Summary Optical studies of Langmuir monolayers of simple amphiphiles such as fatty acids and esters by polarized fluorescence microscopy
and Brewster-angle microscopy reveal a large variety of textures including stripes, stars, and spirals that closely resemble
textures observed in liquid crystals. The textures represent large-scale (>10 μm) spontaneous organization of the molecular
tilt azimuth. Phase transitions within the monolayer can be directly observed by marked changes in texture, revealing a complex
phase diagram. Many of the textures can be explained by a Landau-deGennes theory of tilted hexatic phases that takes into
account the broken-symmetry characteristic of amphiphiles at an interface.
Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994. 相似文献
8.
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
9.
10.
R. Menes N. Grønbech-Jensen P.A. Pincus 《The European physical journal. E, Soft matter》2000,1(4):345-349
Using both theoretical modeling and computer simulations we study a model system for DNA interactions in the vicinity of charged
membranes. We focus on the polarization of the mobile charges in the membranes due to the nearby charged rods (DNA) and the
resulting screening of their fields and inter-rod interactions. We find, both within a Debye-Hückel model and in Brownian
dynamics simulations, that the confinement of the mobile charges to the surface leads to a qualitative reduction in their
ability to screen the charged rods to the degree that the fields and resulting interactions are not finite-ranged as in systems
including a bulk salt concentration, but rather decay algebraically and the screening effect is more like an effective increase
in the multipole moment of the charged rod.
Received 28 September 1999 相似文献
11.
12.
Tilt of hydrocarbon chains of lipid molecules with respect to membrane plane is commonly considered to characterize the internal
structure of a membrane in the crystalline state. However, membranes in the liquid state can also exhibit tilt resulting from
packing constraints imposed on the lipid molecules in diverse biologically relevant structures such as intermediates of membrane
fusion, pores in lipid bilayers and others. We analyze the energetics of tilt in liquid membranes and its coupling with membrane
bending. We consider three contributions to the elastic energy: constant tilt, variation of tilt along the membrane surface
and membrane bending. The major assumption of the model is that the core of a liquid membrane has the common properties of
an elastic continuum. We show that the variation of tilt and membrane bending are additive and that their energy contributions
are determined by the same elastic coefficient: the Helfrich bending modulus, the modulus of Gaussian curvature and the spontaneous
curvature known from previous studies of pure bending. The energy of a combined deformation of bending and varying tilt is
determined by an effective tensor accounting for the two factors. In contrast, the deformation of constant tilt does not couple
with bending and its contribution to the elastic energy is determined by an independent elastic constant. While accurate determination
of this constant requires additional measurements, we estimate its value using a simplified approach. We discuss the relationships
between the obtained elastic Hamiltonian of a membrane and the previous models of membrane elasticity.
Received 10 February 2000 and Received in final form 19 June 2000 相似文献
13.
J. Nissen S. Gritsch G. Wiegand J.O. Rädler 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(2):335-344
We report on the wetting behavior of phospholipid membranes on solid surfaces immersed in aqueous solution. Using fluorescence
microscopy, the spreading velocity of fluid bilayers advancing from a lipid source is investigated. The kinetic spreading
coefficient was measured as a function of temperature for pure DMPC membranes and as a function of charge density and cholesterol
content for binary membranes. A theoretical model for the membrane flow is presented, which takes into account the liquid
crystalline bilayer architecture of the lipid membrane. The spreading power results from the membrane-solid VdW interaction
and is dissipated in hydrodynamic shear flow as well as by inter-monolayer friction within the bilayer. The frictional drag
causes a dynamic tension gradient in the spreading membrane, which is manifested by a single exponential decay of the fluorescence
intensity profile along the spreading direction. Obstacles are shown to act as pinning centers deforming the advancing line
interface. However, no depinning was observed, since the centers are circumflown without abrupt relaxation.
Received 6 November 1998 相似文献
14.
15.
Summary Stiff rod-like chain molecules with harmonic bond length potentials and trigonometric bond angle potentials are used to model
Langmuir monolayers at high densities. One end of the rod-like molecules is strongly bound to a flat two-dimensional substrate
which represents the air-water interface. A ground-state analysis is performed which suggests phase transitions between phases
with and without collective uniform tilt. Large-scale off-lattice Monte Carlo simulations over a wide temperature range show
in addition to the tilting transition the presence of a strongly constrained melting transition at high temperatures. The
latter transition appears to be related to two-dimensional melting of the head group lattice. These findings show that the
model contains both, two- and three-dimensional ergodicity breaking solidification transitions. We discuss our findings with
respect to experiment.
Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994. 相似文献
16.
Henk F. Arnoldus 《Surface science》2007,601(2):450-459
An oscillating magnetic dipole located near a perfect conductor induces a current density on the surface of the metal. We have derived an expression for this current density, and studied its field line patterns for various orientations of the dipole moment. When the dipole moment is perpendicular to the surface, the field lines are circles which run clockwise and counterclockwise. For a linear dipole oriented parallel to the surface, the field line pattern is much more complex, and it contains singular points. When the dipole moment rotates in a plane parallel to the surface, the field lines are spirals. A field line spirals inward from infinity to some given point, after which it spirals outward back to infinity. We have also considered the Poynting vector of the electromagnetic field near the surface, and we found that its field lines can have singular points or exhibit a vortex. 相似文献
17.
M. Hamm M.M. Kozlov 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(4):519-528
We present an alternative model of structure and energetics of the inverted amphiphilic mesophases. The previous studies of
the inverted hexagonal, HII, and inverted micellar cubic, QII, phases considered the amphiphilic monolayers to be homogeneously bent. In contrast, we assume a unit cell of an inverted
mesophase to consist of flat fragments of monolayer. Hence, the unit cells of the HII and QII phases are represented by a hexagonal rod and a polyhedron, respectively. Our model is motivated by Turner and Gruner's X-ray
diffraction reconstruction of structure of the HII phase. The only deformation of the amphiphilic monolayers we consider is tilt of the hydrocarbon chains with respect to the
monolayer surface, determined by the packing constraints imposed in the mesophases. Applying our recent model for the elastic
energy of tilt in liquid membranes [#!ref23!#], we show that: i) tilt accounts in a natural way for the frustration energy
of mesophases resulting from filling by the hydrocarbon chains the corners of the unit cells, ii) the energy of tilt variation
along the membrane surface is analogous to the bending energy. We compute the energetics of the HII, QIIsc and QIIfcc phases and obtain a hypothetical phase diagram in terms of the elastic constants of monolayers. Moreover, we calculate the
structural dimensions of the mesophases. We verify the model showing that the obtained phase diagram describes the recent
data for the glycolipids/water systems; the predicted dimensions of the QII phase are in accord with the measured values; the model treats quantitatively the structural features observed for the HII phase.
Received: 9 February 1998 / Revised: 4 June 1998 / Accepted: 3 July 1998 相似文献
18.
V. Yu. Aristov O. V. Molodtsova V. M. Zhilin Yu. A. Ossipyan D. V. Vyalikh B. P. Doyle S. Nannarone M. Knupfer 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,57(4):379-384
A detailed investigation of the chemistry and electronic structure during the formation of the interfaces between thin films
of the archetypal organic molecular semiconductor copper phthalocyanine (CuPc) and Ag or Sn deposited on it was performed
using photoemission and near-edge X-ray absorption
spectroscopies with synchrotron light. Our study demonstrates the formation
of sharp, abrupt interfaces, a behavior which is of particular importance
for applications in organic devices. Moreover, for Ag on CuPc we demonstrate
that this interface is free from any reaction, whereas there is slight
interface reaction for Sn/CuPc. 相似文献
19.
In an earlier report we explored structural correlations at a liquid-solid interface with molecular dynamics simulations of a model aluminium system using the Ercolessi-Adams potential and up to 4320 atoms. Substrate atoms were pinned to their equilibrium fcc crystalline positions while liquid atoms were free to move. A direct correlation between the amount of ordering in the liquid phase and the underlying substrate orientation was found. In the present paper we extend this study to the case of a fixed bcc substrate in contact with liquid aluminium. We find surprisingly similar results for the density profiles of both (100) and (110) substrates. However, there is a far greater in-plane ordering in the (100) than for the (110) system. For the (100) substrates we observe adsorption of liquid atoms into the terminating plane of the bcc (100) substrate, effectively transforming the bcc (100) plane into an fcc (100) plane. 相似文献
20.
S. Residori E. Pampaloni P.K. Buah-Bassuah F.T. Arecchi 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(2):331-334
As a drop of fluid is deposited on the surface of a miscible fluid (that we call the solvent), it undergoes a strong pulling
due to its surface rupture and it acquires a kinetic energy independently of gravity. For the drop and the solvent being of
the same fluid we observe a drop injection at an initial velocity which scales as the square root of the surface tension of
the drop against air. Once injected, the drop develops a transverse instability giving rise to an expanding ring. Viscosity
terminates the process and stops the ring. We show that the final ring height follows a scaling law whereas two asymptotical
scaling regimes can be identified for the ring radius.
Received 31 August 1999 相似文献