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1.
The complexation and the distribution of various cations, bound to a poly(styrene sulfonate) brush, have been investigated
using infra-red spectroscopy and neutron reflectivity. Small counterions (like tetremethylammonium) are distributed throughout
the brush in such a way that a local electroneutrality is ensured. They also exchange readily with other bulk small cations.
On the other hand, model polycations are irreversibly trapped to the brush despite a relative small number of ionic bonds
involved in the complexation. These complexed polycations are localized at the outer border of the brush, forming a macromolecular
barrier. However, this spatial segregation does not allow the buildup of polyelectrolyte multilayers. Cationic surfactants
are associated stoichiometrically with the brush sulfonates but unlike small counterions, this complexation is “irreversible”
and induces a restructuring of the polymer interface.
Received 22 August 2000 相似文献
2.
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
3.
Biesheuvel PM 《The European physical journal. E, Soft matter》2005,16(4):353-359
We consider the problem of polyelectrolyte molecules adsorbing on oppositely charged interfaces. For sufficiently long chains, the ground-state dominance approximation can be used which results in a (semi-)analytical solution of the self-consistent field equations (aSCF). Whereas existing aSCF theory assumes a low polyelectrolyte density, here the required electrostatic corrections for a high polymer density are implemented. Adsorbed polymer excludes volume for the solvent and small ions, a volume effect that also leads to a reduced dielectric permittivity and a resulting polarization term in the exchange potential. Calculations show the influence of volume exclusion on the polymer density profile. 相似文献
4.
We have studied the adsorption of neutral polyampholytes on model charged surfaces that have been characterized by contact
angle and streaming current measurements. The loop size distributions of adsorbed polymer chains have been obtained using
atomic-force microscopy (AFM) and compared to recent theoretical predictions. We find a qualitative agreement with theory;
the higher the surface charge, the smaller the number of monomers in the adsorbed layer. We propose an original scenario for
the adsorption of polyampholytes on surfaces covered with both neutral long-chain and charged short-chain thiols.
Received 22 February 2002 and Received in final form 23 April 2002 相似文献
5.
C. Devaux J.P. Chapel E. Beyou Ph. Chaumont 《The European physical journal. E, Soft matter》2002,7(4):345-352
Thin layers of polystyrene were grown from surface-grafted nitroxide initiators via controlled “living” free radical polymerization.
The “reactive” Langmuir-Blodgett deposition method allowed an effective control of the initiator layer density leading to
PS brushes with different and high grafting density and stretching. The influence of the grafting density on the layer structure
was studied. Comparison with theoretical predictions for monodispersed brushes in bad solvent was discussed. The thickness
was found to vary linearly with molecular weight and the density dependence was shown using wetting measurements. Special
features of controlled radical nitroxide polymerization from a surface were discussed. A direct comparison of the molecular
weight and polydispersity between surface and bulk polymers was made by de-grafting the brushes into a toluene/HF solution.
Finally, some evidence of a “surface Fischer” effect was shown from re-initiated layers.
Received 20 December 2001 相似文献
6.
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
7.
Surface quasi-elastic light scattering has been applied to a spread film of a block copolymer of polystyrene and polydimethyl
siloxane. The influence of surface concentration (surface pressure) at a fixed surface wave number has been explored. The
capillary wave frequency and damping showed a similar dependence on the surface concentration as values obtained earlier,
but due to a more appropriate analysis of the correlation functions, surface visco-elastic moduli obtained were distinctly
different. By correlating the values obtained with the variations in solvated polystyrene layer thickness from neutron reflectometry,
the maximum in dilational modulus was shown to occur at the same nominal surface concentration where the layer begins to stretch
and take on brush-like behaviour. This same surface concentration is where the relaxation time of the spread film also has
a maximum value, the relaxation time being calculated using the standard linear model of visco-elasticity, which was found
to fit the frequency dependence of the surface tension and dilational moduli at the resonant nominal surface concentration
of 3.1 mg m-2.
Received 21 August 2001 and Received in final form 11 January 2002 相似文献
8.
Equilibrium phase coexistence between two chemical species implies the equality of the chemical potentials and of the osmotic
pressures. We study this problem on a deformable membrane when one type of the molecules serves as anchor for polymeric chains
immersed in the surrounding medium (considered as a good solvent). We derive the general conditions for phase coexistence
when both the curvature of the membrane and the density field of the anchor molecule are free to adjust themselves. We show
that curvature favors phase segregation. Our model predicts that membranes decorated with polymeric chains exhibit new shape
bifurcations without equivalent in fixed density systems.
Received: 26 November 2002 / Accepted: 2 April 2003 / Published online: 12 May 2003
RID="a"
ID="a"e-mail: nicolas@drfmc.ceng.cea.fr
RID="b"
ID="b"e-mail: bfourcade@cea.fr 相似文献
9.
10.
We discuss the influence of polymer adsorption on the curvature energy of an interface. Following an article by Clement and
Joanny (J. Phys. II 7, 973 (1997)), a mean-field theory is used to calculate the surface tension, rigidity constants and spontaneous curvature
associated with both reversible and irreversible polymer adsorption. In the case of irreversible polymer adsorption it is
assumed that the amount of adsorbed polymer remains constant upon curving the interface. Unfortunately, constraining the amount
of polymer by adding a Lagrange multiplier affects the thermodynamic state of the (free) polymer far away from the interface.
Clement and Joanny solve this problem by removing the polymers in the bulk. We allow for the presence of free polymers, but
to achieve this we have to apply a local external field to keep the adsorbed amount fixed. The results of the two approaches
are compared and a physical interpretation is given.
Received 25 July 2001 and Received in final form 5 December 2001 相似文献
11.
Molecular-dynamics results on water confined in a silica pore are reviewed and discussed in connection with experiments performed on water in Vycor and with studies of water in contact with proteins. The properties of confined water are studied as a function of both temperature and hydration level. The interaction of water in the film close to the substrate with the silica atoms induces a strong distortion of the hydrogen bond network. At high hydration levels a double dynamical regime is observed. At low hydration an anomalous diffusion is found upon supercooling with a transition from a Brownian to a non-Brownian regime on approaching the substrate in agreement with results found in studies of water in contact with globular proteins.Received: 1 January 2003, Published online: 14 October 2003PACS:
61.20.-p Structure of liquids - 61.20.Ja Computer simulation of liquid structure 相似文献
12.
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
13.
Herminghaus S 《The European physical journal. E, Soft matter》2002,8(2):237-243
It is discussed how the proximity of a free surface or mobile interface may affect the strain relaxation behavior in a viscoelastic
material, such as a polymer melt. The eigenmodes of a viscoelastic film are thus derived, and applied in an attempt to explain
the experimentally observed substantial shift of the glass transition temperature of sufficiently thin polymer films with
respect to the bulk. Based on the idea that the polymer freezes due to memory effects in the material, and exploiting results
from mode-coupling theory, the experimental findings of several independent groups can be accounted for quantitatively, with
the elastic modulus at the glass transition temperature as the only fitting parameter. The model is finally applied discussing
the possibility of polymer surface melting. A surface molten layer is predicted to exist, with a thickness diverging as the
inverse of the reduced temperature. A simple model of thin polymer film freezing emerges which accounts for all features observed
experimentally so far.
Received 8 August 2001 相似文献
14.
15.
Thin poly(methyl methacrylate) (PMMA) films were prepared by a solution casting on different supports (glass and aluminium plates with different gloss). UV-irradiation (λ = 254 nm) was used for polymer modification. Surface properties of PMMA were studied by contact angle measurements, attenuated total reflection infrared spectroscopy and optical microscopy. It was found that support type has no influence on surface properties of virgin PMMA, however, the changes in these properties were observed during UV modification of polymer film. The most efficient photochemical reactions appeared in sample placed on the rough Al, whereas the smallest effect was observed in polymer on the glass. 相似文献
16.
Hu X Jiao X Narayanan S Jiang Z K Sinha S Lurio LB Lal J 《The European physical journal. E, Soft matter》2005,17(3):353-359
We have used measurements of the absolute intensity of diffuse X-ray scattering to extract the interfacial tension of a buried polymer/polymer interface. Diffuse scattering was excited by an X-ray standing wave whose phase was adjusted to have a high intensity at the polymer/polymer interface and simultaneously a node at the polymer/air interface. This method permits the capillary-wave-induced roughness of the interface, and hence the interfacial tension, to be measured independently of the polymer/polymer interdiffusion. 相似文献
17.
We investigate the phenomenon of multilayer formation via
layer-by-layer deposition of alternating charged polyelectrolytes.
Using mean-field theory, we find that a strong short-range
attraction between the two types of polymer chains is essential for
the formation of multilayers. For strong enough short-range
attraction, the adsorbed amount per layer increases (after an
initial decrease), and finally it stabilizes in the form of a
polyelectrolyte multilayer that can be repeated hundreds of times.
For weak short-range attraction between any two adjacent layers, the
adsorbed amount (per added layer) decays as the distance from the
surface increases, until the chains stop adsorbing altogether. The
dependence of the threshold value of the short-range attraction as
function of the polymer charge fraction and salt concentration is
calculated. 相似文献
18.
Kraikivski P Lipowsky R Kierfeld J 《The European physical journal. E, Soft matter》2005,16(3):319-340
We study the thermally activated motion of semiflexible polymers in double-well potentials using field-theoretic methods. Shape, energy, and effective diffusion constant of kink excitations are calculated, and their dependence on the bending rigidity of the semiflexible polymer is determined. For symmetric potentials, the kink motion is purely diffusive whereas kink motion becomes directed in the presence of a driving force. We determine the average velocity of the semiflexible polymer based on the kink dynamics. The Kramers escape over the potential barriers proceeds by nucleation and diffusive motion of kink-antikink pairs, the relaxation to the straight configuration by annihilation of kink-antikink pairs. We consider both uniform and point-like driving forces. For the case of point-like forces the polymer crosses the potential barrier only if the force exceeds a critical value. Our results apply to the activated motion of biopolymers such as DNA and actin filaments or of synthetic polyelectrolytes on structured substrates. 相似文献
19.
In this paper, polymer brushes are studied via molecular-dynamics simulations at very high grafting densities, where the crossover
between the brush regime and the polymer-crystal regime is taking place. This crossover is directly observed with the structure
factor and pair-correlation function. With increasing grafting density, this crystallization is progressing from the core
layer of the brush towards the surface layer. The same process is analyzed using the lateral fluctuations of the monomers
as a signature of their diminishing mobility. Additionally, bond forces and the chain excess free energy indicate a transition
from the brush regime to the overstretched regime, which is in agreement with predictions of a modified self-consistent field
theory. 相似文献
20.
Berret JF Cristobal G Hervé P Oberdisse J Grillo I 《The European physical journal. E, Soft matter》2002,9(4):301-311
We report on the phase behavior and scattering properties of colloidal complexes made from block copolymers and surfactants. The copolymer is poly(sodium acrylate)-b-poly(acrylamide), hereafter abbreviated as PANa-PAM, with molecular weight 5000 g/mol for the first block and 30000 g/mol for the second. In aqueous solutions and neutral pH, poly(sodium acrylate) is a weak polyelectrolyte, whereas poly(acrylamide) is neutral and in good-solvent conditions. The surfactant is dodecyltrimethylammonium bromide (DTAB) and is of opposite charge with respect to the polyelectrolyte block. Combining dynamical light scattering and small-angle neutron scattering, we show that in aqueous solutions PANa-PAM diblocks and DTAB associate into colloidal complexes. For surfactant-to-polymer charge ratios Z lower than a threshold (Z(C) approximately 0.3), the complexes are single surfactant micelles decorated by few copolymers. Above the threshold, the colloidal complexes reveal an original core-shell microstructure. We have found that the core of typical radius 100-200 A is constituted from densely packed surfactant micelles connected by the polyelectrolyte blocks. The outer part of the colloidal complex is a corona and is made from the neutral poly(acrylamide) chains. Typical hydrodynamic sizes for the whole aggregate are around 1000 A. The aggregation numbers expressed in terms of numbers of micelles and copolymers per complex are determined and found to be comprised between 100-400, depending on the charge ratio Z and on the total concentration. We have also shown that the sizes of the complexes depend on the exact procedure of the sample preparation. We propose that the driving mechanism for the complex formation is similar to that involved in the phase separation of homopolyelectrolyte/surfactant systems. With copolymers, the presence of the neutral blocks prevents the macroscopic phase separation from occurring. 相似文献