An extended Maxwell–Wagner theory for the electric birefringence of charged colloids

Saville, D. A.; Bellini, Tommaso; Degiorgio, Vittorio; Mantegazza, Francesco

doi:10.1063/1.1311593

Cited by 63 publications

(87 citation statements)

References 15 publications

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“…O'Konski 18 found that the presence of a conducting shell (like the double layer surrounding a nonconducting particle) can be taken into account by assigning a certain bulk conductivity to the particle's material. Because this is often the case, 7,19 the relaxation is usually called Maxwell-Wagner-O'Konski (MWO) relaxation. It has been shown that in colloids the electrokinetic features of the polarizability can be included using an asymptotic theory that employs an appropiate surface conductivity.…”

Section: Theoretical Reviewmentioning

confidence: 99%

“…It has been shown that in colloids the electrokinetic features of the polarizability can be included using an asymptotic theory that employs an appropiate surface conductivity. Thus, at high ionic strengths, high potentials, and high frequencies, 19 the conduction processes on the particle surface can be considered by means of an equivalent particle surface conductivity, K σ , that can be expressed in terms of the -potential, . Hence, the application of Maxwell-Wagner-O'Konski formula to colloids is usually called extended Maxwell Wagner model.…”

Section: Theoretical Reviewmentioning

confidence: 99%

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Broadband Dielectric Spectra of Spheroidal Hematite Particles

et al. 2003

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In this paper, we contribute new data on the dielectric dispersion of suspensions of two kinds of spheroidal hematite particles (R-Fe 2 O 3 ). One of the samples consisted of nearly spherical particles, and the other included almost spindle-like particles. We intended to demonstrate the unique potential applications of dielectric dispersion measurements on the characterization of the electrical double layer of nonspherical particles. Thus, we show that while the electrophoretic velocity is practically the same for both systems, the dielectric spectra differ very significantly from each other. In addition to analyzing the role of axial ratios on the electrokinetic behavior, we have also focused on the effect of pH and of the frequency range in which experiments are performed. Thus, two relaxations can be identified in the suspensions: the so-called R-relaxation (typically in the kilohertz region), related to the polarization of the electrical double layer, and the Maxwell-Wagner-O'Konski relaxation (of the order of megahertz), a consequence of conductivity and permittivity mismatch between the particle and the supporting solution. We show that the dielectric increment in the R-relaxation is larger when particles have larger aspect ratio and that there is a secondary relaxation process at both low and high frequencies, a manifestation of the anisotropy of the particles. To obtain more information about this secondary relaxation, a logarithmic derivative method is used to approximate the imaginary part of the dielectric constant. The results are interpreted in the light of existing models. A qualitative agreement is found between the main features of the models and the results, although dielectric data appear to require higher -potentials to be explained than electrophoresis does. We suggest that, while at low frequencies this could be a result of electrode polarization effects, data at high frequencies, less prone to be affected by such effects, confirm the existence of stagnant-layer conductivity in hematite particles.

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Section: Theoretical Reviewmentioning

confidence: 99%

Section: Theoretical Reviewmentioning

confidence: 99%

Broadband Dielectric Spectra of Spheroidal Hematite Particles

et al. 2003

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“…[27][28][29] If these are not spherical, their electric polarizability is anisotropic, 5,11,13,30 and for axially symmetric particles, this anisotropy can be expressed by the scalar quantity ∆α e = α e b −α e a , being α e b (α e a ) the electric polarizability along their major(minor) axis, b and a, respectively. In general, this quantity is different from zero, and hence, the total dipole moment induced by an applied field is not parallel to the latter.…”

Section: Electro-orientation Of Non-spherical Particlesmentioning

confidence: 99%

“…Electric Birefringence Spectroscopy (EBS), the analysis of the behaviour of the birefringence as a function of the frequency of the applied field, albeit yet incomplete, can provide exhaustive information about the different polarization mechanisms of the nanoparticles and their electric double layers (EDLs). 2,5,6,[10][11][12][13] However, although the foundations of the electric birefringence have been long-established, the process is hitherto not understood on the whole and cannot yet be considered as a widespread characterization technique. 12,[14][15][16] Thus, microscopic models relating the nanoparticle properties to their macroscopic birefringent response are to date not completely satisfactory.…”

Section: Introductionmentioning

confidence: 99%

Electric birefringence spectroscopy of montmorillonite particles

et al. 2016

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Electric birefringence (EB) of suspensions of anisotropic particles can be considered an electrokinetic phenomenon in a wide sense, as both liquid motions and polarization of the electrical double layer (EDL) of the particles participate in the process of particle orientation under the applied field. The EB spectrum can be exploited for obtaining information on the dimensions, average value and anisotropy of the surface conductivity of the particles, and concentration and Maxwell-Wagner polarization of the EDLs. It is thus a highly informative technique, applicable to non-spherical particles. In this paper, we investigate the birefringent response of plate-like montmorillonite particles as a function of the frequency and amplitude of the applied AC electric field, for different compositions (pH, ionic strength, particle concentration) of the suspensions. The transient electric birefringence (i.e., the decay of the refractive index anisotropy with time when the field is switched off) is used for estimating the average dimensions of the particle axes, by modeling it as an oblate spheroid. The obtained values are very similar to those deduced from electron microscopy determinations. The frequency spectra show a very distinct behaviour at low (on the order of a few Hz) and high (up to several MHz) frequencies: the α and Maxwell-Wagner-O'Konski relaxations, characteristic of EDLs, are detected at frequencies above 10 kHz, and they can be well explained using electrokinetic models for the polarization of EDLs. At low frequencies, in contrast, the birefringence changes to negative, an anomalous response meaning that the particles tend to orient with their symmetry axis parallel to the field. This anomaly is weaker at basic pHs, high ionic strengths and low concentrations. The results can be explained by considering the polydispersity of real samples: the fastest particles redistribute around the slowest ones, inducing a hydrodynamic torque opposite to that of the field, in close similarity with results previously described for mixtures of anisometric particles with small amounts of spherical nanoparticles.

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“…O'Konski proposed a surface conductance term to account for the effect of electric double layer [87], and the same mechanism was also extended to the study of ellipsoidal colloids [88]. The Maxwell-Wagner-O'Konski theory has a simple analytic formulation which gives qualitatively correct predictions, but it suffers from one main drawback: Since the theory is entirely formulated in terms of macroscopic properties, such as the conductivities and permittivities, the polarization charges are taken to be localized at the particle/medium interface, and their spatial distribution is entirely neglected.…”

Section: Maxwell-wagner Theory and Electrokinetic Theorymentioning

confidence: 99%

Computer simulations of single particles in external electric fields

Zhou

Schmid

2015

Soft Matter

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Applying electric fields is an attractive way to control and manipulate single particles or molecules, e.g., in lab-on-a-chip devices. However, the response of nanosize objects in electrolyte solution to external fields is far from trivial. It is the result of a variety of dynamical processes taking place in the ion cloud surrounding charged particles and in the bulk electrolyte, and it is governed by an intricate interplay of electrostatic and hydrodynamic interactions. Already systems composed of one single particle in electrolyte solution exhibit a complex dynamical behaviour. In this review, we discuss recent coarse-grained simulations that have been performed to obtain a molecular-level understanding of the dynamic and dielectric response of single particles and single macromolecules to external electric fields. We address both the response of charged particles to constant fields (DC fields), which can be characterized by an electrophoretic mobility, and the dielectric response of both uncharged and charged particles to alternating fields (AC fields), which is described by a complex polarizability. Furthermore, we give a brief survey of simulation algorithms and highlight some recent developments.

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An extended Maxwell–Wagner theory for the electric birefringence of charged colloids

Cited by 63 publications

References 15 publications

Broadband Dielectric Spectra of Spheroidal Hematite Particles

Broadband Dielectric Spectra of Spheroidal Hematite Particles

Electric birefringence spectroscopy of montmorillonite particles

Computer simulations of single particles in external electric fields

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