共查询到20条相似文献,搜索用时 500 毫秒
1.
F. Muller P. Fontaine M. Delsanti L. Belloni J. Yang Y.J. Chen J.W. Mays P. Lesieur M. Tirrell P. Guenoun 《The European physical journal. E, Soft matter》2001,6(2):109-115
The counterion distribution within a spherical polyelectrolyte sparse brush was measured by small-angle X-ray scattering using
contrast variation with different counterions by means of ion dialysis. The brush was made by self-association of charged
diblock copolymers. Thanks to the contrast variation method, we were able to separate the signal due to the monomers and the
signal due to the counterions. At a small length scale, it is demonstrated that the system behaves as independent charged
rods whose counterion distribution follows the Poisson-Boltzmann model.
Received 14 February 2001 and Received in final form 2 May 2001 相似文献
2.
We have performed molecular-dynamics simulations to study the effect of an external electric field on a macroion in the solution
of multivalent Z : 1 salt. To obtain plausible hydrodynamics of the medium, we explicitly make the simulation of many neutral particles along
with ions. In a weak electric field, the macroion drifts together with the strongly adsorbed multivalent counterions along
the electric field, in the direction proving inversion of the charge sign. The reversed mobility of the macroion is insensitive
to the external field, and increases with salt ionic strength. The reversed mobility takes a maximal value at intermediate
counterion valence. The motion of the macroion complex does not induce any flow of the neutral solvent away from the macroion,
which reveals screening of hydrodynamic interactions at short distances in electrolyte solutions. A very large electric field,
comparable to the macroion unscreened field, disrupts charge inversion by stripping the adsorbed counterions off the macroion.
Received 5 December 2001 and Received in final form 10 April 2002 相似文献
3.
Roger M Guenoun P Muller F Belloni L Delsanti M 《The European physical journal. E, Soft matter》2002,9(4):313-326
The concentration profiles of monomers and counterions in star-branched polyelectrolyte micelles are calculated through Monte
Carlo simulations, using the freely jointed chain model. We have investigated the onset of different regimes corresponding
to the spherical and Manning condensation of counterions as a function of the strength of the Coulomb coupling. The Monte
Carlo results are in fair agreement with the predictions of Self-Consistent-Field analytical models. We have simulated a real
system of diblock copolymer micelles of (sodium-polystyrene-sulfonate)(NaPSS)-(polyethylene-propylene)(PEP) with f = 54 hydrophilic branches of N = 251 monomers at room temperature in salt-free solution. The calculated form factor compares nicely with our neutron scattering
data.
Received 18 July 2002 and Received in final form 11 October 2002
RID="a"
ID="a"e-mail: roger@drecam.saclay.cea.fr 相似文献
4.
Ordering of urchin-like charged copolymer micelles: Electrostatic, packing and polyelectrolyte correlations 总被引:1,自引:0,他引:1
F. Muller M. Delsanti L. Auvray J. Yang Y.J. Chen J.W. Mays B. Demé M. Tirrell P. Guenoun 《The European physical journal. E, Soft matter》2000,3(1):45-53
We report the results of small-angle neutron scattering (SANS) studies on aqueous solutions of spherical polyelectrolyte micelles
formed by association of charged-neutral diblock copolymers. The neutral moieties are found to self-assemble into small dense
spheres (cores of the micelles) whose sizes are independent of the polymer concentration c. In the dilute regime, c<c
*, where c* is the overlap concentration of the micelles, the conformation of the charged groups, which form the corona of the micelles,
is found to be extended. A liquid-like order is observed over a wide concentration range spanning from the dilute regime to
the concentrated regime. For c>c
*, polyelectrolyte correlations appear at smaller spatial scales and coexist with the liquid-like order. These results suggest
that for dense brushes, above c*, the rod-like statistics of the charged chains begin to disappear due to contraction of corona arms or by interpenetration
of coronae. For less dense brushes, the charged chains are found to be extended up to concentrations far above c*, before the progressive development of polyelectrolyte correlations.
Received 8 October 1999 相似文献
5.
Anionic polyacrylate chains (NaPA) form precipitates if alkaline earth cations are added in stoichiometric amounts. Accordingly,
precipitation thresholds were established for three different alkaline earth cations Ca2+, Sr2+ and Ba2+. Close to the precipitation threshold, the NaPA chains significantly decrease in size. This shrinking process was followed
by means of combined static and dynamic light scattering. Intermediates were generated by varying the ratio [MCl2]/[NaPA] with M denoting the respective alkaline earth cation. All experiments were performed at an inert salt level of 0.01M
NaCl. Similar coil-to-sphere transitions could be observed with all three alkaline earth cations Ca2+, Sr2+ and Ba2+. Based on these findings, supplementary conventional and anomalous small-angle X-ray scattering experiments using selected
intermediates close to the precipitation threshold of SrPA were performed. The distribution of Sr counterions around the polyacrylate
chains in aqueous solution provided the desired scattering contrast. Energy-dependent scattering experiments enabled successful
separation of the pure-resonant terms, which solely stem from the counterions. The Sr2+ scattering roughly reflects the monomer distribution of the polyacrylate chains. Different ratios of the concentrations of
[ SrCl2]/[NaPA] revealed dramatic changes in the scattering curves. The scattering curve at the lowest ratio indicated an almost
coil-like behaviour, while at the higher ratios the scattering curves supported the model of highly contracted polymer chains.
Most of X-ray scattering experiments on intermediate states revealed compact structural elements which were significantly
smaller than the respective overall size of the NaPA particles. 相似文献
6.
J.J. Arenzon J.F. Stilck Y. Levin 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(1):79-82
We present a simple model for the possible mechanism of appearance of attraction between like charged polyions inside a polyelectrolyte
solution. The attraction is found to be short ranged, and exists only in the presence of multivalent counterions. It is produced
by the correlations in layers of condensed counterions surrounding each polyion and is only weakly temperature dependent.
We find the attraction to be maximum at zero temperature and dimish as the temperature is raised. The attraction is only possible
if the number of condensed counterions exceeds the threshold, , where is the valence of counterions and Z is the polyion charge.
Received 10 March 1999 and Received in final form 20 April 1999 相似文献
7.
O. Pelletier C. Bourgaux O. Diat P. Davidson J. Livage 《The European physical journal. E, Soft matter》2000,2(2):191-198
We report small-angle X-ray scattering experiments performed in both the isotropic and nematic phases of aqueous V2O5 suspensions. We show that the scattering in the isotropic phase can be well described in the whole accessible q-range by only considering the form factor of non-interacting ribbons. We investigate the influence of concentration and pH on the dimensions of V2O5 ribbons and show that these parameters do not have any significant effect, as long as the system stays well within the chemical
stability domain of the ribbons. We then show that nematic single domains display an anisotropic small-angle scattering pattern,
even at scattering vectors small compared to that at which a characteristic correlation peak is observed. This feature is
expected for a nematic phase, but was rarely observed. We finally try to describe this scattering within the framework of
theories developed for the structure factor of a nematic polymer, and we reach the conclusion that chain ends are certainly
important to understand this pattern.
Received 21 July 1999 and Received in final form 17 December 1999 相似文献
8.
Monolayers of dioctadecyldimethylammonium bromide (DODA) at the air/water interface were used as model for charged surfaces
to study the adsorption of anionic polyelectrolytes. After spreading on a pure water surface the monolayers were compressed
and subsequently transferred onto a polyelectrolyte solution employing the Fromherz technique. The polyelectrolyte adsorption
was monitored by recording the changes in surface pressure at constant area. For poly(styrene sulfonate) and carboxymethylcellulose
the plot of the surface pressure as function of time gave curves which indicate a direct correlation between the adsorbed
amount and surface pressure as well as a solely diffusion controlled process. In the case of rigid rod-like poly(p-phenylene sulfonate)s the situation is more complicated. Plotting the surface pressure as function of time results in a curve
with sigmoidal shape, characterized by an induction period. The induction period can be explained by a domain formation, which
can be treated like a crystallization process. Employing the Avrami expression developed for polymer crystallization, the
change in the surface pressure upon adsorption of rigid rod-like poly(p-phenylene sulfonate)s can be described.
Received 1st July 2000 and Received in final form 7 December 2000 相似文献
9.
M. Heinrich M. Rawiso J.G. Zilliox P. Lesieur J.P. Simon 《The European physical journal. E, Soft matter》2001,4(2):131-142
The dispersion state of sodium-sulphonated polystyrene ( NaPSS) star-branched polyelectrolytes was investigated in salt-free
aqueous solutions, by use of the small-angle X-ray scattering technique. With respect to polystyrene (PS) star-branched polymers
of identical functionality, the ordering phenomenon occurring in the neighborhood of the overlap concentration c* is reinforced and observed in a larger range of concentrations. Moreover, the degree of order is no longer maximum at c* and is improved as the concentration decreases. The dispersion state is then mainly controlled by the electrostatic interaction.
A crystalline order should therefore be achieved with stars of lower functionality, provided the electrostatic interaction
is added to the osmotic repulsion. On the other hand, unusual scattering patterns are measured for aqueous solutions of NaPSS
star polyelectrolytes. Indeed, a diffuse scattering is revealed at high angles, in addition to the regular diffraction rings
related to preferred interstar distances. It is similar to the broad scattering peak produced by semidilute solutions of NaPSS
linear polyelectrolytes and associated to the electrostatic correlation hole within the isotropic model. In the dilute regime
(c < c
*), it is just an intramolecular characteristic and represents the electrostatic repulsion between arms belonging to the same
star. In the semidilute regime (c > c
*), it also reflects the electrostatic repulsion between arms of distinct stars. So, as the concentration increases, it is
mainly caused by the interpenetration of NaPSS stars. Such an observation is in agreement with the composite structure earlier
proposed by Daoud and Cotton for star semidilute solutions. For c > c
*, NaPSS star aqueous solutions can therefore be pictured as effective stars immersed in a matrix formed by the overlap of
the arm ends. With respect to the dilute regime, the effective stars are smaller; the higher the concentration the smaller
the size.
Received 14 May 1999 and Received in final form 15 March 2000 相似文献
10.
It is known that a large, charged body immersed in a solution of multivalent counterions may undergo charge inversion as the counterions adsorb to its surface. We use the theory of charge inversion to examine the case of a deformable, porous macroion which may adsorb multivalent ions into its bulk to form a three-dimensional strongly-correlated liquid. This adsorption may lead to non-monotonic changes in the size of the macroion as multivalent ions are added to the solution. The macroion first shrinks as its bare charge is screened and then reswells as the adsorbed ions invert the sign of the net charge. We derive a value for the outward pressure experienced by such a macroion as a function of the ion concentration in solution. We find that for small deviations in the concentration of multivalent ions away from the neutral point (where the net charge of the body is zero), the swollen size grows parabolically with the logarithm of the ratio of multivalent ion concentration to the concentration at the neutral point. 相似文献
11.
We report a combined use of small-angle neutron scattering (SANS) and small-angle X-ray scattering (SAXS) to the study of
counterion condensation in ionic micelles. Small-angle neutron and X-ray scattering measurements have been carried out on
two surfactants cetyltrimethylammonium bromide (CTABr) and cetyltrimethylammonium chloride (CTACl), which are similar but
having different counterions. SANS measurements show that CTABr surfactant forms much larger micelles than CTACl. This is
explained in terms of higher condensation of Br− counterions than Cl− counterions. SAXS data on these systems suggest that the Br− counterions are condensed around the micelles over smaller thickness than those of Cl− counterions. 相似文献
12.
J. Even M. Bertault L. Toupet A. Girard W.J. Kusto 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(4):479-491
Crystals of p-trimethylammoniumbenzenesulfonate (ZWT) have been obtained from the thermally induced soli d-state reaction of methyl p-dimethylaminobenzenesulfonate (MSE) or by recrystallization in aqueous solution. The characterization of four crystalline
phases has been performed by calorimetric, birefringence, X-ray and Raman scattering studies. An unknown phase transition
at room temperature yielding a new crystallographic phase has been found by calorimetric measurements. ZWT crystalline samples
obtained from the solid state reaction are disordered as compared to ZWT single crystals obtained by growing from aqueous solution. This disorder
is related to different arrangements of the phenyl ring orientations.
Received 21 October 1998 and Received in final form 14 April 1999 相似文献
13.
Screening of a strongly charged macroion by oppositely charged colloidal particles, micelles, or short polyelectrolytes is considered. Because of strong lateral repulsion such multivalent counterions form a strongly correlated liquid at the surface of the macroion. This liquid provides correlation-induced attraction of multivalent counterions to the macroion surface. As a result even a moderate concentration of multivalent counterions in the solution inverts the sign of the net macroion charge. We show that at high concentration of monovalent salt the absolute value of inverted charge can be larger than the bare one. This giant inversion of charge can be observed in electrophoresis. 相似文献
14.
We study the effect of electrostatic interactions on the distribution function of the end-to-end distance of a single polyelectrolyte
chain in the rod-like limit. The extent to which the radial distribution function of a polyelectrolyte is reproduced by that
of a wormlike chain with an adjusted effective persistence length is investigated. Strong evidence is found for a universal
scaling formula connecting the effective persistence length of a polyelectrolyte with the strength of the electrostatic interaction
and the Debye screening length.
Received 4 March 2002 and Received in final form 1 July 2002
RID="a"
ID="a"e-mail: jrudnick@physics.ucla.edu 相似文献
15.
I. Sabbagh M. Delsanti P. Lesieur 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(2):253-260
Anomalous small angle X-ray scattering experiments show that before demixion in sodium polyacrylate/cobalt and sodium polyacrylate/calcium
mixtures all the divalent counterions are in the close vicinity of the polyacrylate chain. The present results are consistent
with previous UV/VIS spectroscopy, which have shown that all cobalt ions are chemically associated with acrylate groups. The
chemical association dehydrates the acrylate monomers. However, the hydrophobicity of the complexed monomers is not strong
enough to induce a collapse of the polymer chain at small spatial scale before the demixion. Indeed, the scattered intensity
(X-ray and neutron scattering) decreases with the scattering vector q as q-x with for q > 0.1 nm
-1 which indicates that the local conformation of the chain is Gaussian.
Received 21 January 1999 相似文献
16.
R. A. Eremin Kh. T. Kholmurodov V. I. Petrenko L. Rosta M. V. Avdeev 《Physics of the Solid State》2014,56(1):81-85
Data of small-angle neutron scattering by a diluted solution of stearic acid in deuterated benzene have been analyzed using the results of molecular dynamics simulation. The molecular dynamics simulation approach has been used to calculate the time-averaged distribution of the neutron scattering length density at the interface between the acid molecule and the solvent. It has been shown that the organization of the solvent at the interface with the acid molecule leads to a modulation of the neutron scattering length density and makes a significant contribution to the scattering. This contribution should be taken into account when interpreting the experimental small-angle neutron scattering curves for both the considered system and its analogues. 相似文献
17.
Spherical polyelectrolyte block copolymer micelles: Structural change in presence of monovalent salt
Muller F Guenoun P Delsanti M Demé B Auvray L Yang J Mays JW 《The European physical journal. E, Soft matter》2004,15(4):465-472
Spherical polyelectrolyte block copolymer micelles were investigated as a function of added NaCl salt concentration using Small-Angle Neutron Scattering (SANS) and Light Scattering (LS). The micelles are formed by the self-association of charged-neutral copolymers made of a long deuterated polyelectrolyte moiety (NaPSSd)251 and a short hydrophobic moiety (PEP)52. In presence of salt, the core shape and the aggregation number of the micelles are not affected. The hydrodynamic radius of the micelle is found to be identical to the radius of the whole micelle deduced from neutron scattering and thus the hydrodynamic radius is a valid measure of the corona thickness. At the lowest salt concentrations investigated the thickness of the corona, Rs, remains essentially constant and a contraction is observed above an added-salt concentration cs of 2×10-2 M where this crossover concentration corresponds to the average ionic strength of the free counterions in the corona. The contraction takes place while maintaining a rod-like behavior of the chains at short scale and obeys to: Rs cs-0.18. The exponent 0.18 suggests an electrostatic persistence length proportional to the Debye screening length. 相似文献
18.
O.V. Borisov E.B. Zhulina 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(2):205-217
We have developed a scaling theory that describes the conformations of weak star-branched polyelectrolytes in dilute solutions.
The dependences of the overall star size on the number of branches and on the ionic strength of the solution (tuned by the
addition of low molecular weight salt) are analyzed. The intrinsic structure of the polyelectrolyte stars in salt-free and
salt-added solutions is discussed in terms of concentration and elastic blobs. In contrast to neutral stars, the swollen corona
of the polyelectrolyte star consists of blobs which are not closely packed. We have shown that the size of star polyelectrolytes
is less sensitive to the variation in the ionic strength than the size of linear polyelectrolytes. The effects of the ionization-recombination
balance in the star polyelectrolyte were taken into account. For polyelectrolytes with small ionization constant, the size
of the star depends nonmonotonically on the number of branches and on the ionic strength of the solution due to recombination
of counterions with charged monomers.
Received: 10 November 1997 / Revised: 16 February 1998 / Accepted: 1st April 1998 相似文献
19.
M. Bellour A. Knaebel J.P. Munch S.J. Candau 《The European physical journal. E, Soft matter》2000,3(2):111-121
Static and dynamic light scattering and conductivity experiments were carried out on salt-free aqueous micellar solutions
of cetyltrimethylammonium n-hexane sulfonate (CTAC_6SO_3) and cetyltrimethylammonium n-heptane sulfonate (CTAC_7SO_3) as a function of surfactant concentration. This study confirms the analogy between the behavior
in the semi-dilute regime of elongated micellar systems and “classical” polyelectrolyte solutions. Time-resolved scattering
experiments performed after a variation of concentration from about twice the overlap volume fraction to less than half of it revealed the existence of a structural relaxation with a characteristic time of several hours.
Received 21 December 1999 相似文献
20.
We investigate the swelling of colloidal spherical polyelectrolyte brushes in the presence of different counterions. The colloidal particles consist of a solid poly(styrene) core of ca. 100 nm diameter onto which linear polyelectrolyte chains are chemically grafted. Two types of polyelectrolyte chains have been used here: The cationic polyelectrolyte poly(2-(acryloyl)ethyltrimethylammonium chloride)) (PATAC) and the anionic poly(styrenesulfonate) (PSS). Both systems are dispersed in water and the degree of swelling of the surface layer is studied by dynamic light scattering. Adding more and more salt leads to a strong shrinking of the surface layer as expected for polyelectrolyte brushes. It is shown that data obtained at low ionic strength can be collapsed on suitable master curves for monovalent and divalent counterions, respectively. For some ions, however, high salt concentrations may lead to a re-swelling of the brush layer in case of the cationic systems. This points to specific interactions of the counterions with the PATAC chains. This strong specific interaction between the counterions and the attached polyelectrolyte may even lead to flocculation of the particles at intermediate salt concentration. Surprisingly, for iodide and magnesium counterions the solubility increases again if the salt concentration is raised to 1 mol/l. Hence, specific interaction leads to salting-out effects as well as to salting-in effects for these colloidal particles. All specific effects seen at high concentrations of added salt can be explained by the increase of the reduced excluded-volume parameter which is due to the adsorption of salt ions. 相似文献