Electrokinetic Properties of Aqueous Suspensions of Rodlike fd Virus Particles in the Gas- and Liquidlike Phase (original) (raw)
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The Journal of Physical Chemistry, 1994
Previous results on the electrophoretic mobility of aqueous suspensions of polystyrene latices at low ionic strengths are controversial. We have reexamined and extended mobility measurements as a function ofpolyion concentration down to salt concentrations smaller than ns = 10-6 M, where the polyions are liquid-like ordered due to screened Coulomb forces. A significant increase in mobility is found below ns 10-4 M. To discuss mobilities as a function of small ion concentration, for the first time electrophoretic mobility and electric conductivity data are combined to estimate salt content. Static light scattering is used to support the latter results and to characterize the structure of the suspensions. The weak polyion concentration dependence and the increase in mobility are discussed in the light of recently published calculations.
Journal of Colloid and Interface Science, 1991
Previous results on the electrophoretic mobility of aqueous suspensions of polystyrene latices at low ionic strengths are controversial. We have reexamined and extended mobility measurements as a function ofpolyion concentration down to salt concentrations smaller than ns = 10-6 M, where the polyions are liquid-like ordered due to screened Coulomb forces. A significant increase in mobility is found below ns 10-4 M. To discuss mobilities as a function of small ion concentration, for the first time electrophoretic mobility and electric conductivity data are combined to estimate salt content. Static light scattering is used to support the latter results and to characterize the structure of the suspensions. The weak polyion concentration dependence and the increase in mobility are discussed in the light of recently published calculations.
Biophysical Journal, 2008
We report a theoretical investigation of the electrohydrodynamic properties of spherical soft particles composed of permeable concentric layers that differ in thickness, soft material density, chemical composition, and flow penetration degree. Starting from a recent numerical scheme developed for the computation of the direct-current electrophoretic mobility (m) of diffuse soft bioparticles, the dependence of m on the electrolyte concentration and solution pH is evaluated taking the known threelayered structure of bacteriophage MS2 as a supporting model system (bulk RNA, RNA-protein bound layer, and coat protein). The electrokinetic results are discussed for various layer thicknesses, hydrodynamic flow penetration degrees, and chemical compositions, and are discussed on the basis of the equilibrium electrostatic potential and hydrodynamic flow field profiles that develop within and around the structured particle. This study allows for identifying the cases where the electrophoretic mobility is a function of the inner structural and chemical specificity of the particle and not only of its outer surface properties. Along these lines, we demonstrate the general inapplicability of the notions of zeta potential (z) and surface charge for quantitatively interpreting electrokinetic data collected for such systems. We further shed some light on the physical meaning of the isoelectric point. In particular, numerical and analytical simulations performed on structured soft layers in indifferent electrolytic solution demonstrate that the isoelectric point is a complex ionic strength-dependent signature of the flow permeation properties and of the chemical and structural details of the particle. Finally, the electrophoretic mobilities of the MS2 virus measured at various ionic strength levels and pH values are interpreted on the basis of the theoretical formalism aforementioned. It is shown that the electrokinetic features of MS2 are to a large extent determined not only by the external proteic capsid but also by the chemical composition and hydrodynamic flow permeation of/within the inner RNA-protein bound layer and bulk RNA part of the bacteriophage. The impact of virus aggregation, as revealed by decreasing diffusion coefficients for decreasing pH values, is also discussed.
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2003
Electrokinetic phenomena are considered in a dilute suspension of spherical colloidal particles in a salt-free medium containing counter-ions only. Simple derivation is given for the electrophoretic mobility of the particles. Expressions for the electrical conductivity and the sedimentation potential are also obtained. An Onsager relation is found to hold between electrophoretic mobility and sedimentation potential. It is shown that if the particle charge Q is lower than a certain critical value, then the electrophoretic mobility and the electrical conductivity due to counter-ions increase linearly with increasing Q . If Q is higher than the critical value, then these quantities become constant independent of Q because of counter-ion condensation effects. The sedimentation potential, however, is not subject to the counter-ion condensation effects, since these effects upon the electrical conductivity and the concentration of the counter-ions cancel out with each other. #
arXiv: Soft Condensed Matter, 2019
We considerably extended the accessible range of concentrations for optical investigations of colloidal electro-kinetics using super-heterodyne Doppler velocimetry with multiple scattering correction. We performed measurements of electro-phoretic mobility and DC conductivity of aqueous charged sphere suspensions under realistically salt free conditions covering more than three orders of magnitude in particle number densities, n, and up to transmissions as low as 40%. At low n, the mobility shows an increase with n, then plateaus at intermediate n, and finally decreases at large n. Our study reconciles previous experimental observations made on restricted concentration ranges, and thus demonstrates the existence of a generic density dependence of the electro-phoretic mobility. Comparison to state of the art electro-kinetic theory suggests its relation to a density dependent particle charge.
Electrophoresis of concentrated suspension of soft particles with volumetrically charged inner core
Colloid and Polymer Science, 2018
The present study deals with the electrophoresis of a concentrated suspension of soft particles. The inner core of the undertaken particles is considered to possess constant volumetric charges and is surrounded by an ion-and fluid-penetrable polyelectrolyte layer (PEL) with uniformly distributed immobile charges. Such types of particles are paradigm of several bio-particles, for example, virus, bacteria, yeasts, and humic substances, to name a few. A unit cell model is employed to take into account the effect of the interaction between neighboring particles. In the present study, we restrict ourselves with the low charge density and weak applied electric field assumptions. The electric potential distribution is obtained from the linearized Poisson-Boltzmann equation. The fluid velocity field inside the PEL and portion of the cell filled with electrolyte solution are determined by solving the Darcy-Brinkman and Stokes equations, respectively. We provide semi-analytical results for the mean electrophoretic mobility of the concentrated suspension of the undertaken soft particles. We have shown extensively that the suspension of the soft particles may switch its propulsion direction depending on the choice of the pertinent parameters. Unlike suspension of bare colloids or full porous particles, the mean electrophoretic mobility of the soft particles may be nonzero even at a net zero charge case. Keywords Electrophoresis • Soft particle • Core charge • Particle volume fraction • Mobility reversal Nomenclature (r, θ, ϕ) Spherical polar coordinate a Inner core radius b Particle radius c Radius of the virtual cell filled with electrolyte solution E Electric field n 0 Bulk electrolyte concentration n i Concentration of i th ionic species z i Valence of the i th ionic species core Permittivity of inner core f Permittivity of electrolyte solution R Permittivity ratio Total electric potential ρ core Volumetric core charge density
Advances in Colloid and Interface Science, 2005
In the last few years, different theoretical models and analytical approximations have been developed addressing the problem of the electrical conductivity of a concentrated colloidal suspension. Most of them are based on the cell model concept, and coincide in using Kuwabara's hydrodynamic boundary conditions, but there are different possible approaches to the electrostatic boundary conditions. We will call them Levine-Neale's (LN, they are Neumann type, that is they specify the gradient of the electrical potential at the boundary), and Shilov-Zharkikh's (SZ, Dirichlet type). The important point in our paper is that we show by direct numerical calculation that both approaches lead to identical evaluations of the conductivity of the suspensions if each of them is associated to its corresponding evaluation of the macroscopic electric field. The same agreement between the two calculations is reached for the case of electrophoretic mobility. Interestingly, there is no way to reach such identity if two possible choices are considered for the boundary conditions imposed to the fieldinduced perturbations in ionic concentrations on the cell boundary (r = b), dn i (r = b). It is demonstrated that the conditions dn i (b) = 0 lead to consistently larger conductivities and mobilities. A qualitative explanation is offered to this fact, based on the plausibility of counter-ion diffusion fluxes favoring both the electrical conduction and the motion of the particles.
Macromolecules, 1990
The effect of adsorbed polyelectrolytes and uncharged polymers on the 'diffusiophoresis" of charged colloids suspended in electrolyte gradients is investigated theoretically. It is known that the diffusiophoretic velocity of colloidal particles has two components: chemiphoretic and electrophoretic. Semianalytic expressions are derived for two parameters A(c) and A(e), which denote the weighting factors by which each of these velocity components is altered due to polymer adsorption. These factors are shown to depend on four dimensionless parameters: a, 8, B, and ((or Z), where a characterizes the distance to which the segments of the adsorbed polymer extend into the solution (and is the same as the "shielding ratio" defied by Varoqui and Dejardin),' 0 characterizes a dimensionless Debye l_ength, B corresponds to the degree of dissociation of the ionizable groups of the adsorbed polyelectrolyte, and { (or 2) is the zeta potential (or surface charge density) of the particle. The alteration in the particle's velocity due to polymer adsorption is estimated for various values of these dimensionless parameters. It is observed that polyelectrolyte adsorption, in certain situations, could lead to (i) particle migration velocities higher than those possible with 'clean" particles under otherwise identical conditions and (ii) a reversal in the direction of migration. The adsorption of uncharged polymers, on the other hand, leads to a reduction in the particle velocity, if the two parameters { and @-a normalized dimensionless mobility difference of the two ions of the electrolyte-have the same sign. However, when and j3 are of opposite signs, a reversal in the direction of particle migration is possible even with uncharged polymers under some conditions. Finally, an offshoot of the present analysis is the additional result that A(s) also represents the factor by which adsorbed polyelectrolytes/uncharged polymers alter the electrophoretic mobilities of colloidal particles subjected to electrophoresis by an externally applied electric field.