共查询到20条相似文献,搜索用时 15 毫秒
1.
R.R. Netz 《The European physical journal. E, Soft matter》2000,3(2):131-141
The electrostatic interaction of charged particles through or at a low-dielectric slab, such as a lipid bilayer immersed in
water or a self-assembled monolayer (SAM) on a metal substrate, is considered theoretically in the presence of salt within
the Gaussian approximation using a generalized Green's formalism. A number of separate situations are discussed: i) The presence
of a low-dielectric slab leads to pronounced interactions of a single charge with the slab via the formation of polarization
surface charges. For SAMs on metal substrates, there is an intricate crossover from image-charge attraction to the metal substrate
(for large distances) to image-charge repulsion from the SAM (for small distances) with a stable minimum at a distance of
roughly 20 times the thickness of the hydrophobic film. For bilayers in water, the interaction of a single charge is always
repulsive. ii) The surface potential of a SAM is calculated for the case when the hydrophobic layer contains dipole moments,
which might explain the recently observed long-ranged repulsion of hydrophobic scanning tips from PEG-terminated SAMs on gold.
iii) The interaction between charged particles through the bilayer is weakened. Oppositely charged particles still attract
each other through the membrane. The free-energy minimum occurs as a result of the competition between self-repulsion from
the slab and interparticle attraction and is located at a separation from the membrane surface which equals 15 times the membrane
thickness. iv) Surface charges on the two surfaces of a bilayer attract each other through the bilayer unless the surface
charge densities are the same, even if the signs are the same. v) All these effects are strongly influenced by the presence
of salt.
Received 25 January 2000 相似文献
2.
Netz RR 《Physical review letters》2003,91(13):138101
Using dynamic simulations, the electrophoretic mobility of counterions at a substrate with fixed or mobile surface charges under the action of a lateral electric field is studied. The lateral charge inhomogeneity and corrugation of the substrate is taken into account. Because of the pronounced electrofriction between counterions and surface ions, a large fraction of counterions is practically immobilized for highly charged substrates. This explains the experimentally observed saturation of the electrophoretic mobility of charged particles in the limit of high surface charge density. 相似文献
3.
Self-consistent field theory of adsorption of flexible polyelectrolytes onto an oppositely charged sphere
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The adsorption of flexible polyelectrolyte (PE) with the smeared charge distribution onto an oppositely charged sphere immersed in a PE solution is studied numerically with the continuum self-consistent field theory. The power law scaling relationships between the boundary layer thickness and the surface charge density and the charge fraction of PE chains revealed in the study are in good agreement with the existing analytical result. The curvature effect on the degree of charge compensation of the total amount of charges on the adsorbed PE chains over the surface charges is examined, and a clear understanding of it based on the dependences of the degree of charge compensation on the surface charge density and the charge fraction of PE chains is established. 相似文献
4.
Netz RR 《Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics》1999,60(3):3174-3182
The Debye-Hückel theory for bulk electrolyte solutions is generalized to planar interfacial geometries, including screening effects due to mobile salt ions which are confined to the interface and solutions with in general different salt concentrations and dielectric constants on the two sides of the interface. We calculate the general Debye-Hückel interaction between fixed test charges, and analyze a number of relevant special cases as applicable to charged colloids and charged polymers. Salty interfaces, which are experimentally realized by monolayers or bilayers made of cationic and anionic surfactants or lipids, exert a strong attraction on charged particles of either sign at large separations from the interface; at short distances image-charge repulsion sets in. Likewise, the effective interactions between charged particles are strongly modified in the neighborhood of such a salty interface. On the other hand, charged particles which are immersed in a salt solution are repelled from the air (or a substrate) interface, and the interaction between two charges decays algebraically close to such an interface. These general results have experimentally measurable consequences for the adsorption of charged colloids or charged polymers at monolayers, solid substrates, and interfaces. 相似文献
5.
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
6.
Y. S. Jho M. W. Kim S. A. Safran P. A. Pincus 《The European physical journal. E, Soft matter》2010,31(2):207-214
Membranes containing highly charged biomolecules can have a minimal free-energy state at small separations that originates
in the strongly correlated electrostatic interactions mediated by counterions. This phenomenon can lead to a condensed, lamellar
phase of charged membranes that coexists in thermodynamic equilibrium with a very dilute membrane phase. Although the dilute
phase is mostly water, entropy dictates that this phase must contain some membranes and counterions. Thus, electrostatics
alone can give rise to the coexistence of a condensed and an unbound lamellar phase. We use numerical simulations to predict
the nature of this coexistence when the charge density of the membrane is large, for the case of multivalent counterions and
for a membrane charge that is characteristic of biomolecules. We also investigate the effects of counterion size and salt
on the two coexisting phases. With increasing salt concentration, we predict that electrostatic screening by salt can destroy
the phase separation. 相似文献
7.
8.
Manning GS 《The European physical journal. E, Soft matter》2011,34(4):39-7
We calculate the relaxation, rise, and frequency dependence of the parallel polarization of counterions condensed on rodlike
polyelectrolytes and charged colloids. Emphasis is placed on an effective counterion mobility along the rod as strongly influenced
by electrostatic interactions. 相似文献
9.
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
10.
O.V. Borisov F. Hakem T.A. Vilgis J.-F. Joanny A. Johner 《The European physical journal. E, Soft matter》2001,6(1):37-47
We present a scaling theory for the adsorption of a weakly charged polyelectrolyte chain in a poor solvent onto an oppositely
charged surface. Depending on the fraction of charged monomers and on the solvent quality for uncharged monomers, the globule
in the bulk of the solution has either a spherical conformation or a necklace structure. At sufficiently high surface charge
density, a chain in the globular conformation adsorbs in a flat pancake conformation due to the Coulombic attraction to the
oppositely charged surface. Different adsorption regimes are predicted depending on two screening lengths (the Debye screening
length monitored by the salt concentration and the Gouy-Chapman length monitored by the surface charge density), on the degree
of ionization of the polymer and on the solvent strength. At low bulk ionic strength, an increase in the surface charge density
may induce a transition from an adsorbed necklace structure to a uniform pancake due to the enhanced screening of the intra-chain
Coulombic repulsion by the counterions localized near the surface.
Received 12 April 2001 相似文献
11.
R. M. Thaokar 《The European physical journal. E, Soft matter》2010,31(3):315-325
The effect of counterions on the instability of a charged cylinder is investigated. Both axisymmetric and asymmetric perturbations
are considered. The analysis shows that the Rayleigh-Plateau instability is modified for a charged cylinder in the presence
of counterions. For the axisymmetric instability, the counterions have a stabilizing effect at low values of k \kappa , the inverse Debye layer thickness. However, the effect is destabilizing at higher values of k \kappa . The asymmetric modes which are stable for an uncharged cylinder are rendered unstable at high values of k \kappa . The analysis should be important in pearling instability of charged cylindrical vesicles. The expression for the correlation
time of thermally induced shape fluctuations of charged cylindrical vesicles is also derived. 相似文献
12.
L. Belloni M. Olvera de la Cruz M. Delsanti J. P. Dalbiez O. Spalla M. Drifford 《Il Nuovo Cimento D》1994,16(7):727-736
Summary A queous solutions of highly charged flexible polyelectrolytes phase separate in the presence of multivalent counterions.
We present a theoretical model which explains this behavior in terms of electrostatic bridging between monomers via the condensed
counterions. The ?Polymer Reference Interaction Site Model? with the Debye-Hückel closure (equivalent to the ?Random Phase
Approximation?) is sufficient to understand the crucial role of the valency of the counterions, to predict a demixion above
a given valency and a redissolution of the precipitate in excess of added salt. The model successfully reproduces the different
experimental phase diagrams of polystyrene sulfonate suspensions with different added electrolytes.
Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994. 相似文献
13.
Grand canonical Monte Carlo (GCMC) simulations have been performed to investigate the components of the force between parallel charged surfaces in an electrolyte. The solvent primitive model (SPM) was used to investigate the effect of neutral hard sphere solvent particles on the force between the surfaces. The effects of particle size, wall charge density, charge valency of the electrolyte, and the exclusion of neutral hard sphere are discussed. When solvent particles are considered, the total force between the charged surfaces is always repulsive, even for divalent counterions. This is different from the earlier conclusion reached with a restricted primitive model electrolyte. The repulsive force decreases in going from monovalent counterions to divalent counterions. 相似文献
14.
Stanisław Lamperski Douglas Henderson Lutful Bari Bhuiyan 《Molecular physics》2019,117(23-24):3527-3537
ABSTRACTGrand canonical Monte Carlo simulation results are reported for the structure and capacitance of a planar electric double layer containing off-centre charged rigid sphere cations and centrally charged rigid sphere anions. The ion species are assigned asymmetric valencies, +2:?1 and +1:?2, respectively, and set in a continuum dielectric medium (solvent) characterised by a single relative permittivity. An off-centre charged ion is obtained by displacing the ionic charge from the centre of the sphere towards its surface, and the physical double layer model is completed by placing the ionic system next to a uniformly charged, non-penetrable, non-polarizable planar electrode. Structural results such as electrode-ion singlet distribution functions, ionic charge density and orientation profiles are complemented by differential capacitance results at electrolyte concentrations of 0.2?mol/dm3 and 1?mol/dm3, respectively, and for various displacements of the cationic charge centre. The effect of asymmetry due to off-centre cations and valency asymmetry on the double layer properties is maximum for divalent counterions and when the cation charge is closest to the hard sphere surface. 相似文献
15.
The modified dipolar Poisson-Boltzmann(MDPB) equation,where the electrostatics of the dipolar interactions of solvent molecules and also the finite size effects of ions and dipolar solvent molecules are explicitly taken into account on a mean-field level,is studied numerically for a two-plate system with oppositely charged surfaces.The MDPB equation is solved numerically,using the nonlinear Multigrid method,for one-dimensional finite volume meshes.For a high enough surface charge density,numerical results of the MDPB equation reveal that the effective dielectric constant decreases with the increase of the surface charge density.Furthermore,increasing the salt concentration leads to the decrease of the effective dielectric constant close to the charged surfaces.This decrease of the effective dielectric constant with the surface charge density is opposite to the trend from the dipolar Poisson-Boltzmann(DPB) equation.This seemingly inconsistent result is due to the fact that the mean-field approach breaks down in such highly charged systems where the counterions and dipoles are strongly attracted to the charged surfaces and form a quasi two-dimensional layer.In the weak-coupling regime with the electrostatic coupling parameter(the ratio of Bjerrum length to Gouy-Chapman length) Ξ 1,where the MDPB equation works,the effective dielectric constant is independent of the distance from the charged surfaces and there is no accumulation of dipoles near the charged surfaces.Therefore,there are no physical and computational advantages for the MDPB equation over the modified Poisson-Boltzmann(MPB) equation where the effect of dipolar interactions of solvent dipoles is implicitly taken into account in the renormalised dielectric constant. 相似文献
16.
Mei Y Lauterbach K Hoffmann M Borisov OV Ballauff M Jusufi A 《Physical review letters》2006,97(15):158301
We consider the interaction of multivalent counterions with spherical polyelectrolyte brushes (SPB). The SPB result if linear polyelectrolyte (PE) chains (contour length: 60 nm) are densely grafted to colloidal spheres of 116 nm in diameter. Dispersed in water, the surface layer consisting of chains of the strong PE poly(styrene sulfonic acid) (PSS) will swell. We demonstrate that successive addition of trivalent ions (La3+) leads to a collapse in which the surface layer is shrinking drastically. All findings are discussed on the base of a theoretical mean-field approach using the Donnan equilibrium. The ion exchange and a strong binding of trivalent ions by PE chains is followed up by a drop in the osmotic pressure inside the brush. This reduction is the driving force for the collapse. The strong ion-chain correlation is discussed with results obtained from molecular dynamics simulations. 相似文献
17.
M. Deserno 《The European physical journal. E, Soft matter》2001,6(2):163-168
The classical instability of a charged spherical droplet is reconsidered in the presence of counterions. An ensemble of such
droplets is studied within a simplified cell model. Screening of the electric field by the counterions is found to increase
the equilibrium droplet size. Furthermore, if the ions can enter the droplet, a first-order phase transition occurs upon increasing
Bjerrum length, surface tension or droplet density, leading to a phase separation. Simple scaling properties of the free energy
give the shape of the phase boundary and show the system to be scale-invariant there. Pearl-necklace structures of hydrophobic
polyelectrolytes are discussed as an application.
Received 30 August 2001 相似文献
18.
G. S. Manning 《The European physical journal. E, Soft matter》2009,30(4):411-415
The low-field transverse polarizability of the counterions condensed on an isolated charged rod is small. We show that it
can be much larger if the rod is a member of an assembly of aligned rods. The polarization free energy of the assembly of
rods in a transverse field is then similar to its polarization free energy in a field parallel to the rods. The polarization
free energy of the assembly in a transverse field becomes lower than in a parallel field if the extent of the assembly (as
measured, for example, by the diameter of a cylindrical assembly) is larger than the length of the individual rods. We suggest
that this model may provide a reasonable explanation for the occurrence of “anomalous” birefringence in systems of interacting
charged rodlike particles. 相似文献
19.
摘要:应用聚合电介质吸附的定标理论,根据介质和表面电介质常数的比率,考虑多化合价吸附电介质之间强相关性作用,我们提出一种表面排斥电荷的近似定标理论方法,根据这种方法把电介质表面吸附层的相图分为本质上不同的两大类。从相图可知:当表面电荷密度低(或体带相反电荷离子密度高),这时表面和体带相反电荷离子密度几乎相同;一旦表面电荷密度足够高,就使带相反电荷的离子在表面上浓缩。据此,可确定在这个区域内,低化合价聚合电介质形成一个相关的多链状态,当化合价足够高时,由于近邻链之间的更强排斥增强,使状态转变成单链。 相似文献
20.
应用聚合电介质吸附的定标理论,根据介质和表面电介质常数的比率,考虑多化合价吸附电介质之间强相关性作用,我们提出一种表面排斥电荷的近似定标理论方法,根据这种方法把电介质表面吸附层的相图分为本质上不同的两大类。从相图可知:当表面电荷密度低(或体带相反电荷离子密度高),这时表面和体带相反电荷离子密度几乎相同;一旦表面电荷密度足够高,就使带相反电荷的离子在表面上浓缩。据此,可确定在这个区域内,低化合价聚合电介质形成一个相关的多链状态,当化合价足够高时,由于近邻链之间的更强排斥增强,使状态转变成单链。 相似文献