The universal electro-optic response of charged colloids in low electrolyte suspensions

Stoimenova, Maria

doi:10.1016/j.jcis.2008.04.004

Cited by 8 publications

(5 citation statements)

References 36 publications

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“…What is clear at this stage is the strong sensitivity of this effect to surface adsorption of different species . The hypothesis, based on previous investigations, , is that it originates in electro-osmotic flows along the polarized particle, which create a negative torque on the particle and its reorientation. If this hypothesis is accepted, the jump in the value of R in the interval 10 −2 to 10 −1 M NaCl might be due to the swelling of the adsorbed layer and realization of such processes in the limits of the polymer coils.…”

Section: Resultsmentioning

confidence: 98%

“…As generally accepted, the first effect is provoked by a dipole moment due to field-induced polarization of the surface electrical double layers, favoring the orientation of particle long axes along the field direction. , The second effect is negative, i.e., it is provoked by a negative torque on the particles. Electro-osmotic flows provoked by the field-induced deformation of the Debye ionic atmosphere are suggested to be the cause for this effect. , …”

Section: Methodsmentioning

confidence: 99%

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Electrical Properties of Polyelectrolyte Layers Adsorbed on Colloidal Particles at Different Ionic Strength

et al. 2010

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The investigation presents results on the low-frequency electrical polarization of β-FeOOH particles with adsorbed layers from sodium salts of poly(4-styrene sulfonate), poly(acrylic acid), and carboxymethyl cellulose, obtained by electric light scattering. The adsorption is realized in aqueous NaCl solutions of different concentration, and the suspensions of the coated particles are then rinsed to low conductivity. Several electro-optical parameters are sensitive to the conformation of the adsorbed polyelectrolyte layer. The particle electrical polarizability increases drastically with the concentration of NaCl (correlating with significant increase of the adsorbed amount of polyelectrolyte), while their electrophoretic mobility remains practically unchanged. Two time scales are involved in the stepwise relaxation of the electrical polarizability. The faster process is attributed to movement of ions in the polymer layer, restricted by the coiled conformation to smaller distances. The contribution of the Debye atmosphere outside the polymer layer remains almost unchanged, which correlates with the low sensitivity of the electrophoretic mobility to the increasing amount of adsorbed polyelectrolyte. Abrupt increase in a narrow interval of salt concentrations is observed both for the low-frequency component of the particle polarization and for the hydrodynamic layer thickness, indicating changes in the surface electric state, most probably due to swelling of the adsorbed polymer layer.

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Section: Resultsmentioning

confidence: 98%

Section: Methodsmentioning

confidence: 99%

Electrical Properties of Polyelectrolyte Layers Adsorbed on Colloidal Particles at Different Ionic Strength

et al. 2010

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“…Polarization of charged particles in the low-frequency region is detected by two relaxations of the electro-optical effect: one in the kilohertz/megahertz frequency region and the second one in the domain of particle rotation (hertz region). It is generally accepted that the first effect is provoked by a dipole moment due to field-induced polarization of the surface electrical double layers, favoring the orientation of particle long axes along the field direction. , The second effect is negative, and it seems to be provoked by electro-osmotic flows due to the field-induced deformation of the particle’s electrical double layers …”

Section: Methodsmentioning

confidence: 99%

“…36,37 The second effect is negative, and it seems to be provoked by electro-osmotic flows due to the field-induced deformation of the particle's electrical double layers. 38 The steady-state electro-optical effect is defined as where I E and I 0 are the intensity of scattered light when an electric field of strength E is applied and at zero field. 36 The transient process of Brownian particle disorientation after switching the applied field off…”

Section: ■ Materials and Methodsmentioning

confidence: 99%

Complexation of Ferric Oxide Particles with Pectins of Ordered and Random Distribution of Charged Units

et al. 2011

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Complexation between ferric oxide particles and pectins with degree of methylation 50% but having ordered or random arrangement of free carboxyl groups is investigated by electric light scattering and electrophoresis. The influence of charge distribution in pectin chain on the electrical properties of oppositely charged oxide particles and stability of their suspensions is examined as a function of pectin concentration. Although the difference in charge density of pectin samples is ~5%, we found small but measurable difference in the behavior of both oxide/pectin complexes. This is attributed to condensation of counterions near the chains of pectin with ordered distribution of charges, leading to a decrease in the effective charge density and to a corresponding decrease in the contour length of the adsorbing pectin chains. Two parameters are sensitive to the conformation of the adsorbed chains in suspensions, stabilized by pectin adsorption (at particle charge reversal). The electro-optical effect is higher for the complex with less charged pectin, which is explained with larger amount of chains, adsorbed in more coiled conformation than the chains of pectin with random distribution of free carboxyl groups. The addition of small amounts of CaCl(2) has no significant influence on the thickness of the layer from the less charged pectin, in agreement with a more compact conformation of the chains in this adsorbed layer. In contrast, the thickness of the layer from pectin with random distribution of charged groups decreases with increasing concentration of CaCl(2), indicating a more loose structure of this layer.

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“…Two effects are generally observed in colloidal suspensions when a sinusoidal electric field is applied [17]. The first one appears in the range of particle rotation (Hz region) and its origin is still under investigation [17,19]. The second electrooptical effect (in the kilohertz range) is related to polarization of the particle electrical double layers [17,18,20].…”

Section: Electric Light Scatteringmentioning

confidence: 99%

The effect of ionic strength on electrical properties of polyelectrolyte multilayers on colloidal particles

Milkova¹,

Radeva²

2010

J. Phys.: Condens. Matter

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The effect of ionic strength on the electrical properties of poly(styrene sulfonate)/poly(allylamine) (PSS/PAH) multilayer film was investigated using electric light scattering and electrophoresis. A multilayer film was created by sequential adsorption of fully charged polymers from solutions containing 10 (- 1) M NaCl and its properties were compared to those of a PSS/PAH film prepared in the absence of salt. All measurements were carried out after rinsing the films with an aqueous solution of HCl to adjust the pH to 4.6. We found that the electrical polarizability of the film coated particles and its frequency of relaxation increase when the film was constructed in the presence of salt. The increase in the electrical polarizability value is due to the screening-enhanced adsorption. We hypothesize that the increase in the relaxation frequency of the electrical polarizability is a consequence of the adsorption of the polymer chains in more coiled conformations. This restricts the movement of small ions to shorter distances than in the film prepared without salt. In both cases, the small ions are located near the film surface, which indicates the key role of the last deposited polymer for the behavior of the entire PSS/PAH film.

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The universal electro-optic response of charged colloids in low electrolyte suspensions

Cited by 8 publications

References 36 publications

Electrical Properties of Polyelectrolyte Layers Adsorbed on Colloidal Particles at Different Ionic Strength

Electrical Properties of Polyelectrolyte Layers Adsorbed on Colloidal Particles at Different Ionic Strength

Complexation of Ferric Oxide Particles with Pectins of Ordered and Random Distribution of Charged Units

The effect of ionic strength on electrical properties of polyelectrolyte multilayers on colloidal particles

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