Counterion Polarization Research Articles

Radiofrequency dielectric loss relaxation in polyion-induced liposome aggregates

In this note, we present a set of dielectric loss relaxation measurements of aqueous charged liposome suspensions during the whole aggregation process induced by oppositely charged adsorbing polyions. The system experiences two concomitant effects known as “reentrant condensation” and “charge inversion,” resulting in the formation of liposome aggregates whose average size reaches a maximum in the vicinity of the electroneutrality condition, accompanied to a progressive reduction of their overall electrical charge. Far from the neutrality, from both sides, polyion-coated liposomes exist with a charge of opposite sign. The dielectric loss relaxation in these complex aggregating systems has never been measured so far and we report here, for the first time, the dielectric loss behavior of liposomes built up by a cationic lipid and stuck together by poly(acrylate), which is a flexible oppositely charged polyion. The data are analyzed in the framework of standard electrokinetic model theory. The evolution of the aggregation process as a function of the polyion content is mainly characterized by a counterion polarization effect, governed by the surface charge density of the aggregates and hence by the ζ-potential.

Polypeptide multilayer films on colloidal particles: An in situ electro-optical study

The buildup of poly( l-glutamic acid) (PGA) and poly( l-lysine) (PLL) multilayers on β-FeOOH colloidal particles was investigated by means of electro-optics and electrophoresis. The films were built at different (acidic) pH in the absence of salt. We found that the thickness of the film grows linearly when the fully charged PLL (at pH 5.5) is combined with almost fully charged PGA (at pH 6.5), with a thickness of about 2 nm per single layer. When the fully charged PLL is combined with weakly charged PGA (at pH 4.5), the film thickness increases exponentially with the number of deposited layers. The thickness of the exponentially growing film increases to 300 nm after deposition of 16 layers. The exponential film growth is attributed to the ability of the PLL to diffuse “in” and “out” of the film bulk at each deposition step. The variation in the electrical polarizability of the film-coated particles was also monitored as a function of the number of adsorbed layers. The result reveals that the PLL chains, which can diffuse into the film bulk, have no measurable contribution to the electro-optical effect of the films terminated with PLL. It is only due to the polarization of counterions of the PLL adsorbed on the film surface.

Polyion-induced liposomal vesicle aggregation: A radiowave dielectric relaxation study

The radiowave dielectric properties of aqueous heterogeneous systems during the complexation of charged polyions and oppositely charged liposomal particles have been measured in a wide frequency range, between 100 Hz and 2 GHz. The formation of a polyion-liposome complex driven by the correlated polyion adsorption at the particle surface implies two concomitant effects referred to as reentrant condensation and charge inversion. Both of them are governed by electrostatic interactions and there is now strong evidence, based on experiments and simulations, that counterion release is the driving force of the aggregation process. From this point of view, dielectric technique may offer a suitable tool in the investigation of the structural properties of these aggregates. In spite of the fact that interaction of polyions with oppositely charged surfaces was extensively experimentally investigated, there are no papers concerning the dielectric properties during the polyion-induced aggregation. To get an insight into this important topic, the authors present here an extensive set of radiowave dielectric measurements of liposomal vesicle aqueous suspensions where the liposome aggregation was induced by an oppositely charged polyion. The aggregation was followed from the beginning, when most of the isolated liposomes predominate, up to the formation of polyion-coated liposomes of inverted charge, crossing the isoelectric condition, where large, almost neutral, aggregates appear. The authors describe the observed dielectric dispersions as due to counterion polarization in the adjacency of the liposome and liposome aggregate surface, primarily governed by the zeta potential, according to the standard electrokinetic model.

Dielectric Measurement of Individual Microtubules Using the Electroorientation Method

Little is known about the electrostatic/dynamic properties of microtubules, which are considered to underlie their electrostatic interactions with various proteins such as motor proteins, microtubule-associated proteins, and microtubules themselves (lateral association of microtubules). To measure the dielectric properties of microtubules, we developed an experiment system in which the electroorientation of microtubules was observed under a dark-field microscope. Upon application of an alternating electric field (0.5–1.9×105V/m, 10kHz–3MHz), the microtubules were oriented parallel to the field line in a few seconds because of the dipole moment induced along their long axes. The process of this orientation was analyzed based on a dielectric ellipsoid model, and the conductivity and dielectric constant of each microtubule were calculated. The analyses revealed that the microtubules were highly conductive, which is consistent with the counterion polarization model—counterions bound to highly negatively charged microtubules can move along the long axis, and this mobility might be the origin of the high conductivity. Our experiment system provides a useful tool to quantitatively evaluate the polyelectrolyte nature of microtubules, thus paving the way for future studies aiming to understand the physicochemical mechanism underlying the electrostatic interactions of microtubules with various proteins.

Dielectric scaling in polyelectrolyte solutions with different solvent quality in the dilute concentration regime

In this note, we present a set of radiowave dielectric spectroscopy measurements of two dilute, differently-charged polyelectrolyte solutions, under different solvent conditions. We have found that both the dielectric strength, Delta epsilon, and the relaxation time, tau(ion), of the dielectric relaxation process associated with the counterion polarization along a length scale of the order of the correlation length obey the scaling laws with the polyion concentration, according to the Ito model. This is verified with good accuracy independently of the quality of the solvent, which has been varied from poor to good solvent conditions. This finding supports evidence to the fact that, in dilute solutions, the counterion polarization is independent of the polyion concentration, in spite of what occurs at the semi-dilute concentrations.

Dielectric Analysis of a Nanoscale Particle in an Aqueous Solution of Low Electrolyte Concentration

The dielectric spectra of aqueous suspensions of nanoscale silica particles (8 and 24 nm) with low electrolyte concentrations were investigated as a function of the particle concentration. Obvious dispersions observed in the frequency range of 10-10(5) kHz are explained by the multiple effects of the interfacial polarization and the polarization of counterions by using a two-step model and the corresponding dielectric analytical method arising from the combination of Hanai's method and O'Konski's theory. The phase parameters, which reflect the inner properties of constituent phases of the system, are calculated and discussed in detail. The validity of the two-step model was tested in terms of the standard electrokinetic model deduced from pure theories.

Electro-optics of colloids coated with multilayers from strong polyelectrolytes:surface charge relaxation

The electrical properties and structure of polyelectrolyte multilayers prepared by layer-by-layer deposition of poly(sodium 4-styrenesulfonate) (PSS) and poly(diallyldimethylammonium chloride) (PDADMAC) on ellipsoidal β-ferric hydrous oxide particles are examined in situ using the electric light scattering method. In the initial nonlinear growth regime, the electro-optical effect is found to increase almost in the same manner as the thickness of the multilayer film. This reveals an increase in the multilayer surface charge due to the nonlinear increase in polyelectrolyte adsorption. Above five deposition cycles, the electro-optical effect reaches a plateau and the thickness increment per layer becomes constant, indicating regular film growth. Evidence is given that the concentration of small residual ions incorporated into the PSS/PDADMAC film is negligible. Polarization of counterions, bound near to the surface of the last-adsorbed polyion, is assumed to explain the relaxation of the electro-optical effect in the frequency range 10 3–10 5 Hz.

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Broad frequency range dielectric spectroscopy of aqueous suspensions of phospholipid vesicles

The dielectric properties of aqueous suspensions of unilamelar phospholipid vesicles were measured over a broad frequency range extending from 1 kHz to 1 GHz. The low-frequency measurements (1 kHz to 10 MHz) were performed at Tucumán using a HP 4192 A Impedance Analyzer with a variable spacing cell and Short-Open-Load calibration. The high-frequency spectra (1 MHz to 1 GHz) were obtained at Göttingen using a HP 8753 A Network Analyzer with a reflection cut-off measuring cell. The vesicles were prepared using different concentration mixtures of non-ionic and ionic phospholipids: 1,2 Dimyristoyl-sn-Glycero-3 Phosphocholine and L-α-Phosphatidyl-DL-Glycerol-Dimyristoyl (Na-Salt). Their mean diameter had the value of 116 nm, obtained by means of multiple extrusions. They were suspended in either tridistilled water or an aqueous NaCl solution. The dielectric spectra were described and interpreted using existing theoretical models (for the counterion polarization and the membrane charging together with the Maxwell–Wagner dispersion processes) with the ζ potential as the only adjustable parameter.

Dielectric spectroscopy of sedimentary rocks

A physiochemical model for the complex dielectric response of sedimentary rocks is used to invert broadband dielectric spectra for effective grain size distributions. The complex dielectric response of each grain within the “water‐wet” granular matrix is obtained by superimposing the polarization of the electrochemical double layer, which is assumed to surround each grain, with the complex dielectric response of the dry mineral grain. The effective complex dielectric response of the water‐wet matrix (grains and surface phase) is obtained by volume averaging over the entire distribution of particle sizes. The complex dielectric response of the total mixture (water‐wet matrix and bulk pore solution) is obtained using the Bruggeman‐Hanai‐Sen effective medium theory. Studies of Berea sandstone show that the grain size distribution, obtained by inverting the real part of the complex dielectric spectra, is similar to the grain size distribution obtained from optical images of the sample in thin section. The current model, however, does not account for surface roughness effects or the polarization of counterions over multiple grain lengths; therefore the grain size distribution obtained by dielectric spectroscopy is broader than the image‐derived distribution. The dielectric‐derived grain size distribution can be fit with two separate power laws that crossover at R ≅ 1 μm, which corresponds to a relaxation frequency of 2 kHz. The low‐frequency dielectric response (f < 2 kHz) is primarily controlled by the macroscopic grain fraction (mainly quartz grains), which has a fractal dimension of d = 1.84±0.05. The high‐frequency dielectric response (f > 2 kHz) is primarily controlled by the clay size grains and surface roughness, which has a fractal dimension of d = 2.48±0.07. At very low frequencies (f < 0.1 Hz) the dielectric response appears to be controlled by the electrochemical polarization of counterions over multiple grain lengths. A more general model should account for the effects of surface roughness and grain interactions on the dielectric response. It would also be useful to develop a simplified version of this model, perhaps similar in form to the empirically derived Cole‐Cole response, which could be more easily used to model and interpret electrical geophysical field surveys (e.g., induced‐polarization, ground‐penetrating radar, and time domain reflectometery measurements).

Electric Properties of Adsorbed Polystyrenesulfonate: I: Dependence on the Polyelectrolyte Molecular Weight

The influence of molecular weight on the counterion polarization of sodium polystyrenesulfonate (NaPSS) is investigated by electric light scattering. The polyelectrolyte is adsorbed in excess on β-ferric hydrous oxide particles (β-FeOOH), which are shown to assume the charge characteristics of the polymer. Two dispersion regions of the electro-optical effect (below and above 10 kHz) are found to exist due to the polarization of counterions. The high-frequency (HF) effect is attributed to polarization of free counterions along the polymer-coated particle axis and does not depend on the molecular weight of the adsorbed polymer. The amplitude and critical frequency of relaxation of the low-frequency (LF) effect, which is attributed to polarization of bound counterions along the polymer axis, depend on the polyelectrolyte molecular weight. The polarization of bound counterions seems to be responsible for the permanent-like dipole moment behavior of NaPSS at low frequencies of the applied electric field.

Electric Properties of Adsorbed Polystyrenesulfonate: II: The Effect of Low Molecular Salts

Counterion polarization of sodium and magnesium polystyrenesulfonate (NaPSS and MgPSS), adsorbed in an excess onto ellipsoidal β-ferric hydrous oxide particles (β-FeOOH), is studied in both the absence and the presence of added simple electrolytes, NaCl and MgCl2. The amplitude of the low-frequency (102–104 Hz) and the high–frequency (104–106 Hz) electro-optical effects of NaPSS is found to decrease with increasing NaCl concentration, while the critical frequency of relaxation of both effects remains unchanged. Addition of MgCl2 to the suspension containing MgPSS also reduces the amplitude of the low-frequency electro-optical effect, but the amplitude of the high-frequency effect increases. The increased number of mobile (not bound) divalent ions, which produce larger charge fluctuation, could explain the high-frequency effect increase in the presence of a small excess of MgCl2. Substitution of Na+ counterions of PSS by Mg2+ is found to increase the critical frequency of relaxation and to reduce the amplitude of the low-frequency effect, probably due to the strong repulsion between bound divalent counterions. The polyion length remains nearly unchanged during this substitution, as evidenced by the constant relaxation time of the polyelectrolyte-coated particles. The increase of counterion valence is not found to affect the amplitude of the high-frequency electro-optical effect in the absence of added salt.

High-frequency dielectric and conductometric properties of poly-l-lysine aqueous solutions at the crossover between semidilute and entangled regime

The dielectric and conductometric properties of poly-l-lysine aqueous solutions have been investigated in the frequency range from 1 MHz to 1.8 GHz, where micro-Brownian dynamics and internal motion of side-chain polar groups result in a well-defined relaxation process, intermediate between that caused by counterion polarization (characteristic of the polyelectrolyte nature of the polyion investigated) and that associated with the orientational polarization of the aqueous phase. The polymer concentration has been varied in a wide interval in order to investigate the influence of different chain conformations on the dielectric parameters as a consequence of the different concentration regimes occurring in these systems. With the help of polymer scaling theories, scaling relations for the dielectric strength and the relaxation time are presented, predicting, as the polymer concentration is increased, a transition from semidilute-unentangled to semidilute-entangled regimes. We compare these predictions with the experimental findings over the whole concentration range investigated, with a qualitative agreement. Deviations from the scaling behavior related to a crossover regime between unentangled and entangled regions are briefly discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3123–3130, 1999

High‐frequency dielectric and conductometric properties of poly‐l‐lysine aqueous solutions at the crossover between semidilute and entangled regime

The dielectric and conductometric properties of poly-l-lysine aqueous solutions have been investigated in the frequency range from 1 MHz to 1.8 GHz, where micro-Brownian dynamics and internal motion of side-chain polar groups result in a well-defined relaxation process, intermediate between that caused by counterion polarization (characteristic of the polyelectrolyte nature of the polyion investigated) and that associated with the orientational polarization of the aqueous phase. The polymer concentration has been varied in a wide interval in order to investigate the influence of different chain conformations on the dielectric parameters as a consequence of the different concentration regimes occurring in these systems. With the help of polymer scaling theories, scaling relations for the dielectric strength and the relaxation time are presented, predicting, as the polymer concentration is increased, a transition from semidilute-unentangled to semidilute-entangled regimes. We compare these predictions with the experimental findings over the whole concentration range investigated, with a qualitative agreement. Deviations from the scaling behavior related to a crossover regime between unentangled and entangled regions are briefly discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3123–3130, 1999

Effects of pH on Dielectric Relaxation of Montmorillonite, Allophane, and Imogolite Suspensions

Dielectric measurements were performed on montmorillonite, allophane, and imogolite suspensions under various pH conditions, using time domain reflectometry over the frequency range 10 kHz–20 GHz. A dielectric relaxation peak due to bound water could be observed for all the clays. Allophane has two peaks, indicating that its peaks are very similar to those of silica–alumina gels. Although imogolite has a similar chemical composition, only one peak was found. The relaxation strength of montmorillonite is greater than that of the other two clays. For all the clays, the relaxation strength depended on the pH. A change in the relaxation strength according to a change in pH is explained in terms of the different network structures of the clay particles. It is suggested that bound water influences the network structure formation. In montmorillonite, a great relaxation process detected at low frequency is caused by surface polarization of counterions. The change in measure of the structural unit with the pH, identified from Schwartz's theory, has a tendency similar to that postulated by other experimental techniques, and surface charge densities identified are close to those estimated from CEC.

Polarization of counterions in polyelectrolytes.

A theory of the polarization of counterions bound to a polyion, such as a DNA, in low and high electric field strengths is developed using statistical mechanics of inhomogeneous systems. For low fields, one finds that the polarizability p is (Zq)2rho0betaL3/(12[l + Lrho0sigma(L, b, xi, Z, I, rho0)]), where sigma = integral1 0(lambda' - lambda0) ¿dc(lambda - lambda')/dlambda¿lambda = lambda0 dlambda']), Z and L are the valence and the length of the polyion, respectively, q is the proton charge, beta = 1/kBT, T is the temperature, kB is the Boltzmann constant, I is the ionic strength, lambda = x/L and lambda0 = x0/L are scaled distances, x0 is a reference point such that the inhomogeneous counterion density at x0 is equal to rho0--the uniform density in the absence of an electric field E--and c(x) is the direct correlation function of the homogeneous counterion-polyion phase, which includes attractive and repulsive interactions. If Lsigma(L, ...) is much less than one, then the polarizability is proportional to L3. If the term Lsigma(L, ...) is much larger than one, the polarizability scales as L2. The induced dipole moment saturates and its value is the same as that of Mandel-Manning theories. The onset of the saturation, however, depends critically on the direct correlation function and hence polyelectrolyte effects. In the formalism, the polarization of the counterions is the equilibrium response to an electric field provided E is less than Esaturated. A dynamical scheme that incorporates the fact that in high fields the bound counterions conduct is discussed.

Ionic Polarization of Carrageenans with Different Charge Densities As Studied by Electric Birefringence Measurements

Ionic polarizability of the κ-, ι-, and λ-carrageenans have been investigated by the electric birefringence method. These carrageenan samples were selected because they have different numbers of sulfuric acid residues on their linear polysaccharide chains; that is, their charge densities are different from each other. The analysis of both the polymer concentration dependence and the added salt concentration dependence showed that these three carrageenans have almost the same ionic polarizability irrespective of their different charge densities when they were compared in the same conditions. The results were analyzed by using two groups of theories. That is, one is based on the “loosely bound” counterion polarization, and the other is based on the “condensed” counterion polarization. The ionic strength dependence of the experimentally obtained polarizability could be fitted by Manning's and Rau and Charney's “loosely bound” counterion polarization theories.

Studies of dielectric properties of mammalian tissues after gamma-irradiation

In vitro dielectric measurements (relative permeability and conductivity) of excised liver, kidney, cardiac muscle, spleen and eye of rabbits, were carried out at frequencies of 1–250 kHz and at room temperature. These were done before, immediately and 7 days after gamma irradiation at doses 1–5 Gy. The obtained results indicated significant increase in both relative permitivity and conductivity of tissues at higher doses immediately after irradiation. After 7 days, the changes showed some recovery, more obvious at lower doses. These changes in dielectric properties, after irradiation, may reflect the particular biological organization of each tissue and some mechanisms of radiation damage to these tissues particular to cell membrane, counter-ion polarization associated with intrinsic membrane charges and conductive transport in extracellular medium. This may help to elucidate the mechanisms of variation of dielectric properties of different tissues under the effect of radiation.

Electro-Optical and Hydrodynamic Properties of Synthetic Polyribonucleotides in Solutions as Studied by Electric Birefringence

Abstract The electro-optical and hydrodynamic properties of four synthetic polyribonucleic acids were clarified by electric birefringence methods which take the molecular-weight distribution into consideration. Parallel double-stranded helices, poly(adenylic acid)·poly(protonated adenylic acid), I, and poly(cytidylic acid)·poly(protonated cytidylic acid), II, are known to possess an electric permanent dipole moment, because the reversing-pulse electric birefringence (RPEB) signals of these duplexes exhibit dips upon pulse reversal. The RPEB signals of antiparallel double-stranded poly(adenylic acid)·poly(uridylic acid), III, and poly(guanylic acid)·poly(cytidylic acid), IV, show no dip; therefore, these polynucleotides have no permanent dipole moment. By analyzing the relaxation time of the birefringence decay signals, the axial translations of the polynucleotides per base-pair were determined to be 4.0 Å for I, 2.7 Å for III, and 2.4 Å for IV, respectively. By analyzing the dependence of the steady-state birefringence values on the electric-field strength, the magnitudes of the permanent dipole moments per unit length of I and II projected onto the helix axes were found to be ca. 0.4 debye Å−1. The electric properties unraveled by electric birefringence experiments were compared with calculations based on a recent Manning theory. An unsaturable induced dipole moment may result from the polarization of the Debye–Hückel ion-atmosphere, while a saturable induced dipole moment is probably caused by the polarization of counter ions that are condensed on the charged sites of a polyion. The experimental values deviate from calculated values at ionic strengths lower than 0.0001; hence, the Manning theory is not applicable in this region.

Brownian dynamics simulations of DNA electric dichroism at high electric field strengths

Brownian dynamics simulations have been used to investisate the orientation dynamics when applying an electric field pulse to a DNA solution. Including only counter ion polarization effects, both the orientation and the off-field relaxation are monotonous processes. If, instead, the hydrodynamic coupling between different parts of the molecule is the dominating mechanism, one observes a small maximum in orientation before reaching a steady-state and a pronounced undershoot during the relaxation back to equilibrium. Such an amplitude inversion, with the DNA molecules transiently perpendicularly oriented relative to the electric field, has also been observed in electric dichroism experiments at high electric fields.