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Nonpolar liquids whose dielectric permittivities are close to 2 have very low conductivities, usually below 10 × 10(-10) S/m. Their ionization is suppressed by the lack of solvation resulting from the negligible dipole moment of such liquids' molecules. Ionization could be enhanced by the addition of other substances that could serve as solvating agents, creating inverse micelles around ions and preventing them from reassociating into ion pairs and neutral molecules. Surfactants are normally used for this purpose, but we show here that alcohols could perform a similar function. However, the mechanism of ionization by alcohols turns out to be quite different compared to the mechanism of ionization by surfactant. For instance, the conductivity of poly-α-olefin oil (PAO) depends on the concentration of added octanol (alcohol) as an exponential function above 10% of the octanol content. At concentrations below approximately 10%, octanol does not affect the conductivity at all. This phenomenon has never been observed for surfactant solutions. Apparently, octanol is completely dissolved at concentrations below 10% and forms micelles only above this concentration, which is the cmc for octanol-PAO mixtures. Below the cmc, octanol molecules do not dissociate, despite being able to dissociate in pure octanol, which has a conductivity of about 10 × 10(-7) S/m. This again stresses the importance of the solvating factor in the ionization of liquids. Above 10% concentration, octanol molecules form micelles, which become charged by the disproportionation mechanism when they collide. To explain the exponential dependence of conductivity on octanol content, we assume that charged micelles grow in volume with increasing octanol content faster than neutral ones. Ion-dipole interactions are responsible for the preferential adsorption of octanol molecules onto charged micelles. Additional ionization occurs in such larger micelles, which then break down into smaller ones carrying individual electric charges.

The resolution of water-in-crude oil (W/O) emulsions formed during extraction or desalinaton processes of crude oil is still a problem for the oil industry. Among the main separation processes used today, electrostatic separation induced by the application of DC or AC electric fields is the most interesting because it is ecologically correct. However, the electroseparation efficiency is still limited by the current lack of knowledge concerning the mechanism that is behind this process. Stabilization of the water/crude oil emulsion is guaranteed, mainly, by resins and asphaltenes that are present at the W/O interface, forming a rigid cross-linked film that wraps the droplets. The influence of salts and the salinity of the aqueous phase on the stability of emulsions is poorly known because most researchers use, as the aqueous phase, a complex saline solution composed of a mixture of chlorides and sulfates of mono- and divalent cations to simulate the composition of seawater. Thus, the isolated effect of each type of cation may not be known. In this work, we used the rheology technique to study the effect of cation type and salinity of the aqueous phase on the stability of water/oil emulsions, under application of a DC electric field. It was verified that the stability of the emulsions follow this order: H2O ≪ Na+ ∼ K+ < Ba2+. It was also observed that the presence of salts increases the stability of the emulsions up to a critical value of ionic strength (∼0.1–0.3 mol L–1, depending on the system), above which the stability decreases, tending to that observed for the emulsion produced with water.

We report a systematic experimental investigation on the use of nanofibers to enhance the magnetorheological (MR) effect in conventional (microsphere-based) MR fluids formulated in polyalphaolefin oil/1-octanol. Two kinds of nanofibers are employed that have very similar morphology but very different magnetic properties. On the one hand we use non-magnetic goethite nanofibers. On the other hand we employ magnetic chromium dioxide nanofibers. For appropriate concentrations the on-state relative yield stress increases up to 80% when incorporating the nanofibers in the formulation. A similar yield stress enhancement is found for both nanofibers investigated (magnetic and non-magnetic) suggesting that the main factor behind this MR enhancement is the particle shape anisotropy. The relative yield stresses obtained by partial substitution of carbonyl iron particles with nanofibers are significantly larger than those measured in previous works on MR fluids formulated by partial substitution with non-magnetic micronsized spherical particles. We also demonstrate that these dimorphic MR fluids also exhibit remarkably larger long-term sedimentation stability while keeping the same penetration and redispersibility characteristics.

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as (UFG), Goiânia, Goi as (GO) 74001-970, Brazil

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Two types of carbonyl iron powders, (CIP's, BASF AG), the HS and HS-I (I = insulated, due a coating with phosphate), and two kinds of silica, one hydrophobic (Cab-O-Sil® TS610) and other hydrophilic (Cab-O-Sil® M5), were used to evaluate the influence of the surface treatment of the magnetic particle and the kind of fumed silica on the formulation of some magnetorheological suspensions (MRS). Oscillatory measurements at no field showed an evident difference between the silicas, but not a specific interaction with the phosphate coating on HSI. On the other hand, steady flow experiments also without magnetic field showed that the kind of silica and its specific interactions with the coating on iron powder drove the rheological behavior of the MRS on all region of the shear rate. Under magnetic field, the flow curves differences will be due to the iron particles and its magnetic properties, mainly on the region of higher shear rate. Keywords: Carbonyl iron powder; Magnetorheological suspensions; Phosphate surface coating. 4858 Int. J. Mod. Phys. B 2007.21:4858-4867. Downloaded from www.worldscientific.com by WAKE FOREST UNIVERSITY on 02/02/15. For personal use only.