共查询到20条相似文献,搜索用时 343 毫秒
1.
The Poisson-Boltzmann theory for colloidal electrostatic interactions predicts that charged colloidal spheres dispersed in water should repel each other, even when confined by charged surfaces. Direct measurements on highly charged polystyrene spheres, however, reveal strong, long-ranged confinement-induced attractions that have yet to be explained. We demonstrate that anomalous attractions also characterize the equilibrium pair potential for more weakly charged colloidal silica spheres sedimented into a monolayer above a glass surface. This observation substantially expands the range of conditions for which mean-field theory incorrectly predicts the sign of macroions' interactions, and provides new insights into how confinement induces long-ranged like-charge attractions. 相似文献
2.
3.
Effects of electrostatic interactions and geometrical confinements on depletion interactions in charged colloidal system
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
In a charged colloidal system, the influence on depletion
interaction between two like-charged macro-ions is studied through
Monte Carlo simulation in this paper. The numerical results show
that this depletion force is affected by both the electrostatic
interactions between charged spheres and charged plates and by the
geometrical factor of the two charged plates, and they further
indicate that the influence of geometrical confinement on the
depletion interaction is larger than that of electrostatic
potential. 相似文献
4.
The structure and stability of strongly charged complex fibers, formed by complexation of a single long semi-flexible polyelectrolyte
chain and many oppositely charged spherical macroions, are investigated numerically at the ground-state level using a chain-sphere
cell model. The model takes into account chain elasticity as well as electrostatic interactions between charged spheres and
chain segments. Using a numerical optimization method based on a periodically repeated unit cell, we obtain fiber configurations
that minimize the total energy. The optimal fiber configurations exhibit a variety of helical structures for the arrangement
of macroions including zig-zag, solenoidal and beads-on-a-string patterns. These structures result from the competition between
attraction between spheres and the polyelectrolyte chain (which favors chain wrapping around the spheres), chain bending rigidity
and electrostatic repulsion between chain segments (which favor unwrapping of the chain), and the interactions between neighboring
sphere-chain complexes which can be attractive or repulsive depending on the system parameters such as salt concentration,
macroion charge and chain length per macroion (linker size). At about physiological salt concentration, dense zig-zag patterns
are found to be energetically most stable when parameters appropriate for the DNA-histone system in the chromatin fiber are
adopted. In fact, the predicted fiber diameter in this regime is found to be around 30 nanometers, which roughly agrees with
the thickness observed in in vitro experiments on chromatin. We also find a macroion (histone) density of 5–6 per 11nm which agrees with results from the zig-zag
or cross-linker models of chromatin. Since our study deals primarily with a generic chain-sphere model, these findings suggest
that structures similar to those found for chromatin should also be observable for polyelectrolyte-macroion complexes formed
in solutions of DNA and synthetic nano-colloids of opposite charge. In the ensemble where the mean linear density of spheres
on the chain is fixed, the present model predicts a phase separation at intermediate salt concentrations into a densely packed
complex phase and a dilute phase. 相似文献
5.
Anna Oleksy 《Molecular physics》2013,111(18):2871-2883
As a first step towards a density functional theory (DFT) of wetting by ionic solutions we examine the density profiles of ions and solvent molecules confined near a charged wall, or between two walls, and the corresponding interfacial properties, including adsorption, surface tension, solvation force and electrostatic properties, within the semi-primitive model (SPM) of solutions made up of hard sphere solvent particles and charged hard spheres. Both monovalent and divalent cations with species-dependent diameters are considered. The density functional includes the best available Rosenfeld hard-sphere functional, as well as mean-field and Coulomb correlation contributions. The simpler mean-field functional is found to be adequate, at least for monovalent ions. The size differences lead to an interesting ‘fine structure’ of the density and charge density profiles. Cohesive interactions between all species are shown to lead to significant changes in the density profiles. 相似文献
6.
Riese DO Wegdam GH Vos WL Sprik R Fenistein D Bongaerts JH Grübel G 《Physical review letters》2000,85(25):5460-5463
We investigate the hydrodynamic interaction in suspensions of charged colloidal silica spheres. The volume fraction as well as the range of the electrostatic repulsion between the spheres is varied. Using a combination of dynamic x-ray scattering, cross-correlated dynamic light scattering, and small angle x-ray scattering, the hydrodynamic function H(q) is determined experimentally. The effective hydrodynamic interactions are found to be screened, if the range of the direct interaction is relatively long and the static density correlations are strong. This observation of effective hydrodynamic screening is in marked contrast to hard-sphere-like systems. 相似文献
7.
Hollow silver spheres were successfully prepared by reducing AgNO3 with ascorbic acid and using negatively charged poly-(styrene-methyl acrylic acid) (PSA) spheres as templates in the presence of sodium polyacrylate as a stabilizer. Firstly, silver cations adsorbed on the surface of PSA spheres via electrostatic attraction between the carboxyl groups and silver cations were reduced in situ by ascorbic acid. The silver nanoparticles deposited on the surface of PSA spheres served as seeds for the further growth of silver shells. After that, extra amount of AgNO3 and ascorbic acid solutions were added to form PSA/Ag composites with thick silver shells. In order to obtain compact silver shells, the as-prepared PSA/Ag composites were heated at 150 °C for 3 h. Then hollow silver spheres were prepared by dissolving PSA templates with tetrahydrofuran. 相似文献
8.
Zhang F Skoda MW Jacobs RM Zorn S Martin RA Martin CM Clark GF Weggler S Hildebrandt A Kohlbacher O Schreiber F 《Physical review letters》2008,101(14):148101
Negatively charged globular proteins in solution undergo a condensation upon adding trivalent counterions between two critical concentrations C and C, C 相似文献
9.
A systematic study of zeta potential for a spherical double layer (SDL) around a colloidal particle in electrolyte solutions, is performed using density functional theory and Monte Carlo simulation. The usual recipe under the solvent primitive model is employed to model the system, where macroion, counterions, and coions are represented by charged hard spheres of uniform charge density and the presence of solvent is taken into account by modelling it as neutral hard spheres. All the components of the system are embedded in a dielectric continuum in order to consider the electrostatic effect of the solvent. The density functional theory employs a suitable weighted density approximation to calculate the hard-sphere contribution, whereas the residual electrostatic interactions are calculated as a small perturbation around the uniform fluid. The zeta potential profiles of a SDL in the presence of a number of electrolytes have been calculated and are found to be considerably influenced in the presence of solvent with an increase in the concentration of the electrolyte. The theory successfully predicts the maxima and sign reversal of the zeta potential profiles at high macroion surface charge density and in the presence of multivalent counterions, as obtained from the Monte Carlo simulation. 相似文献
10.
11.
Closed-form solution of mid-potential between two parallel charged plates with more extensive application
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
《中国物理 B》2015,(10)
Efficient calculation of the electrostatic interactions including repulsive force between charged molecules in a biomolecule system or charged particles in a colloidal system is necessary for the molecular scale or particle scale mechanical analyses of these systems. The electrostatic repulsive force depends on the mid-plane potential between two charged particles. Previous analytical solutions of the mid-plane potential, including those based on simplified assumptions and modern mathematic methods, are reviewed. It is shown that none of these solutions applies to wide ranges of interparticle distance from 0 to 10 and surface potential from 1 to 10. Three previous analytical solutions are chosen to develop a semi-analytical solution which is proven to have more extensive applications. Furthermore, an empirical closed-form expression of mid-plane potential is proposed based on plenty of numerical solutions. This empirical solution has extensive applications, as well as high computational efficiency. 相似文献
12.
The adsorption of model charged proteins on charged surfaces with and without grafted polymers is studied using a molecular approach. The ability of the polymer layer to reduce the amount of proteins adsorbed on top of the surface (primary adsorption) and at the same time to increase the adsorption of the proteins on top of the polymer layer (secondary adsorption) is presented. It is found that charging the free ends of the chains can result in an efficient way to enhance adsorption at the tip of the brush. Increasing the surface coverage of the polymers with charged free ends enhances the amount of proteins adsorbed at the tip of the polymer layer, while at the same time strongly reduces the number of proteins adsorbed directly onto the surface. The interplay between the attractive van der Waals protein-surface interactions, the steric polymer-protein interactions and the effect of the electrostatic interactions in determining the final adsorption is discussed. The manipulation of solution conditions to tune the amount of secondary adsorption is presented. 相似文献
13.
We study the effective dielectric constant of dilute suspensions of metallic spheres in a transparent background, e.g. glass or water. In the low density limit the effective dielectric constant as a function of frequency exhibits a strong absorption peak corresponding to the dipolar surface plasmon of isolated spheres. We investigate how the absorption peak is modified at higher density due to electrostatic interactions between spheres. We find appreciable deviations from the Clausius-Mossotti formula which may be seen most clearly in a Cole-Cole plot of the effective dielectric constant. 相似文献
14.
Kiril Kolikov Dragia Ivanov Georgi Krastev Yordan Epitropov Stefan Bozhkov 《Journal of Electrostatics》2012,70(1):91-96
In the paper we consider the problem of the electrostatic interaction between two charged conducting spheres with arbitrary electrical charges and radiuses. Using the image charges method we determine exact analytical formulas for the force F and for the potential energy W of the interaction between these two spheres as well as for the potential V of the electromagnetic field in an arbitrary point created by them. Our formulas lead to Coulomb’s law for point charges.We theoretically prove the experimentally shown fact that two spheres with the same type (positive or negative) of charges can also attract each other. 相似文献
15.
A.S. Foster L.N. Kantorovich A.L. Shluger 《Applied Physics A: Materials Science & Processing》2001,72(7):S59-S62
Macroscopic "background" interactions, such as van der Waals and electrostatic forces, determine the frequency change in non-contact atomic force microscopy (NC-AFM). We demonstrate that by analysing the distance dependence of these interactions one can extract more information about the tip radius, charge and chemical composition, as well as about the surface charging and conductivity. For this purpose we calculate the interaction of different NC-AFM tips with a charged and neutral CaF2 (111) surface and with an ideal metal surface. Force versus distance curves demonstrate a remarkably different behaviour, especially at long distances, dependent on whether the tip is conductive, oxidised or charged. Comparison with experimental curves proves that this analysis can predict tip properties. 相似文献
16.
本文采用一种简易制备静电场样品的方法,基于以下物理事实:一个置于薄导电碳膜上的非导电粒子,例如直径为0.31μm聚乙烯乳剂小球,在电镜中观察时,由于静电积累效应,它将成为一个荷电体,很显然,这个荷电体带有正电量Q,并能用一个点电荷场来模拟这个合成电场.采用这个模型,能用电子全息法观测由该点电荷所形成的静电场分布及荷电量的大小. 相似文献
17.
José Rafael Bordin Rudolf Podgornik Christian Holm 《The European physical journal. Special topics》2016,225(8-9):1693-1705
Coarse-grained implicit solvent Molecular Dynamics (MD) simulations have been used to investigate the structure of the vicinal layer of polarizable counterions close to a charged interface. The classical Drude oscillator model was implemented to describe the static excess polarizability of the ions. The electrostatic layer correction with image charges (ELCIC) method was used to include the effects of the dielectric discontinuity between the aqueous solution and the bounding interfaces for the calculation of the electrostatic interactions. Cases with one or two charged bounding interfaces were investigated. The counterion density profile in the vicinity of the interfaces with different surface charge values was found to depend on the ionic polarizability. Ionic polarization effects are found to be relevant for ions with high excess polarizability near surfaces with high surface charge. 相似文献
18.
We investigate the repulsive electrostatic interactions between a DNA polyelectrolyte and the charged walls of a fluidic nanoslit. The scaling of the DNA coil size with the physical slit height revealed electrostatic depletion regions that reduced the effective slit height. These regions exceeded the Debye screening length of the buffer, λ(D)(buffer), and saturated at ≈ 50 nm when λ(D)(buffer) reached 10 nm. We explain these results by modeling a semiflexible charged rod near a charged wall and the electrostatic screening by the polyelectrolyte. These results demonstrate the surprisingly long range over which a nanofluidic device can exert field-effect control over confined molecules. 相似文献
19.
F. Cousin J. Jestin G. Chaboussant S. Gautrot A. Menelle F. Ott 《The European physical journal. Special topics》2009,167(1):177-183
We demonstrate in this paper the possibilities offered by
Grazing Incidence Small Angle Neutron Scattering (GISANS) for the study of
solid/liquid interfaces. We present experimental results obtained by
Specular Neutron Reflectivity (SNR) and GISANS on a model system made of
silica nanospheres adsorbed on a silicon wafer by electrostatic interactions
both at solid/air interface and solid/liquid interfaces. At the solid/liquid
interface, we demonstrate that grazing incidence scattering enables to
discriminate the surface and the bulk scattering. The surface structure
factor derived from GISANS shows that the nanospheres are organized as a
repulsive liquid system, with a surface fraction occupation consistent with
values obtained by SNR. This original setup highlights a direct correlation
between the structure of the silica nanospheres in solution and their
organization on the surface: due to the strong electrostatic repulsions
between spheres, their organization at the surface is close to the
projection in 2D of the 3D organization of the nanospheres in solution. 相似文献
20.
A. V. Filippov 《Journal of Experimental and Theoretical Physics》2009,109(3):516-529
The electrostatic interaction of two spherical macroparticles in a plasma has been considered. Primary attention has been
focused on investigating the electrostatic interaction at short distances where polarization effects of the surface charge
of finite-size macroparticles begin to play a dominant role. The first part of this study is devoted to the interaction of
a point charge with a charged conducting sphere in an equilibrium plasma. It has been shown that the presence of a plasma
in the system leads to a decrease in the potential barrier when two like-charged macroparticles approach each other and that
this decrease proves to be the most significant in the case where the macroparticle radius is comparable to the Debye screening
length. The second part of this study is concerned with the interaction of two conducting spheres in the bispherical system
of the coordinates under the assumption that the charges of the conducting spheres are constant and under the assumption that
the surface potentials of the spheres are constant. The latter case is closer to the physics of electrostatic interaction
of two macroparticles in a plasma medium where the electrostatic potential of their surface is determined by the floating
potential of the plasma. It has been demonstrated that the interaction potentials in these two cases are substantially different
from each other and that, at constant macroparticle charges, the energy of the electrostatic field is an interaction potential,
but, in the case of macroparticles with constant surface potentials, which are independent of the interparticle distance,
the energy of the electrostatic field is not an interaction potential. In the latter case, account must be taken of the work
done by external sources on the macroparticle potentials to maintain them constant. The form of the interaction potential
has been established in this case from the analysis of the interaction force in terms of the Maxwell tension tensor. In the
third part of this study, the interaction of two macroparticles has been considered in the spherical system of coordinates
and analytical expressions for the interaction potentials have been derived for both the case of constant macroparticle charges
and the case of constant surface potentials of the macroparticles. 相似文献