Electrokinetics in extremely bimodal suspensions

Jiménez, María Luisa Gómez; Arroyo, Francisco J.; Delgado, A.V.; Mantegazza, Francesco; Bellini, Tommaso; Rica, Raúl A.

doi:10.1016/j.jcis.2007.01.067

Cited by 8 publications

(4 citation statements)

References 34 publications

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“…This investigation was originally suggested by previous results obtained by this and other groups, , where it was demonstrated that the addition of even small amounts of tiny particles to a suspension of larger colloids could greatly affect the polarization of the solid/liquid interface and hence the response of the suspension to externally applied electric fields. Whereas the phenomenon has been widely described in polar liquids and low fields, the investigation in nonpolar media has focused on the effect of magnetic fields on the rheology of bimodal magnetic colloid suspensions. , As mentioned above, much less is known regarding the behavior of mixed colloids widely different in size when subjected to high-strength electric fields in nonaqueous media.…”

Section: Resultsmentioning

confidence: 80%

Negative Electrorheological Behavior in Suspensions of Inorganic Particles

2010

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An investigation is described on the electric-field-induced structures in colloidal dispersions. Both rheological determinations and direct microscopic observations are used with that aim. The starting point of this study is the so-called electrorheological (ER) effect, consisting of the mechanical reinforcing of a fluid or suspension due to formation of chains of molecules or particles after being polarized by the action of the field. One macroscopic manifestation of this phenomenon is the transformation of the fluid from a typically Newtonian behavior to a viscoelastic material, with finite yield stress and high elastic modulus. The systems investigated were suspensions of elongated goethite (β-FeOOH) particles in silicone oils with varying amounts of silica nanoparticles. The results showed the rather unusual behavior known as "negative ER effect", which can be best described by saying that the application of an electric field reduces the yield stress and the elastic modulus, that is, produces destruction of structures rather than their build up. The negative behavior is also found for suspensions of other inorganic powders, including hematite and quartz. On the contrary, the usual positive ER response is found for suspensions of cellulose and montmorillonite clay. The same happens if goethite suspensions are prepared in high volume fractions, high-viscosity fluids, or both. All of the results found are compatible with the so-called interfacial model of electrorheology: the reduction of the yield stress of goethite suspensions when the applied field is high enough is the consequence of particle migration toward the electrodes because of charge injection and subsequent electrophoresis. The migration leaves the gap between the electrodes devoid of particles and explains the decrease in yield stress. The addition of silica nanoparticles contributes to reduce the strength of this effect by hindering the charging and making it necessary to increase the field strength to observe the negative effect. The model appears to also be applicable to cellulose, although the positive response found for such particles is explained by their large size: larger diameters bring about larger attraction forces between particles, leading to a tendency to produce strong aggregates. This is likely to occur in suspensions of colloids which, because of their relatively high electrical conductivity, tend to acquire charge even in such nonpolar liquids as silicone oils.

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Section: Resultsmentioning

confidence: 80%

Negative Electrorheological Behavior in Suspensions of Inorganic Particles

2010

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“…It is probably not an exaggeration to claim that few physical quantities are so informative about the electrical state of the solid/liquid interface, and its non-equilibrium properties as the permittivity ε ⁎ of colloidal suspensions [1]. If one has the possibility to determine it over a wide enough frequency range (actually not very demanding: a few kHz to a few MHz is sufficient), then one has at hand a very versatile technique, that can be equally well applied to dilute and concentrated suspensions, to aqueous and non-aqueous systems, or to particles of different shapes, to mention some examples [1,2].…”

Section: Introductionmentioning

confidence: 99%

Dielectric dispersion in aqueous colloidal systems

Grosse

Delgado

2010

Current Opinion in Colloid & Interface Science

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114

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“…In fact, as the structure of the flocs is likely to change throughout the experiment, the relationship between τ and size will change accordingly. Furthermore, Jiménez et al [55] found that bimodal suspensions had an effect on the relaxation process. The presence of nanoparticles was found to change the characteristic relaxation time of a larger particle.…”

Section: Interpreting Modeled Values Of τmentioning

confidence: 99%