A.I. Gómez-Merino

The primary electroviscous effect of polystyrene latexes

Abstract An investigation on the primary electroviscous effect of polystyrene latexes has been made. Capillary viscometers of Ubbelohde type have been used. The comparison of the results obtained with the theories allow us to conclude that the effect is underestimated for low electrolyte concentrations. We suggest that this underestimation is due to an additional surface conductance into the electric double layer. This interpretation is consistent with previous studies on electrophoretic mobility of the same system.

An experimental study on the influence of a dynamic Stern-layer on the primary electroviscous effect

Abstract The most recent theory by Watterson and White for the primary electroviscous effect of a suspension of charged spherical particles has been extended by considering the influence of a dynamic Stern-layer. In this work we have tested the theoretical results by measuring the viscosity of polystyrene suspensions in different electrolyte concentrations. Zeta potential values have been obtained by electrophoresis and conductivity experiments using the theoretical approachs by Mangelsdorf and White that include the Stern-layer conductance. In order to obtain the same potential values calculated from these two independent methods, we have fitted the Stern-layer parameters of our systems. These parameters and zeta values have been used to calculate the theoretical viscosity. The theoretical results have been compared with the experimental viscosity data obtained with a semiauthomatic Ubbelohde capillary viscometer. We can conclude that the dynamic Stern-layer model used in this work has only a slight influence on the correction of the primary electroviscous effect theory due to Watterson and White. We suggest to study the correction supplied by another dynamic Stern-layer model due to Dukhin and Semenikhin, considering its success when is applied to electrophoresis.

The additional surface conductance: its role in the primary electroviscous effect

The influence of the additional surface conductance on the primary electroviscous effect has been checked by means of an experimental study. Polystyrene latexes and alumina suspensions have been used as the colloidal systems. Combined electrokinetic techniques have been used to determine -potential and Stern parameters of the systems. The results suggest that this conductance mechanism, that takes place into the Stern layer, has a great influence on the primary electroviscous effect.

Estimation of Ion Diffusion Coefficients at the Stagnant Layer Using TiO2 Aqueous Suspension Zeta Potential Data

The solid-liquid interface of anatase-water nanofluids has been characterized. Combined data of electrophoretic mobility and conductivity of the colloidal suspensions have been used to evaluate zeta-potentials. Plots of the suspension conductivity as a function of the bulk conductivity are essentially linear, allowing for the establishment of the entire surface conductivity. The main contribution to the surface conductivity stemmed from the counter charge behind the slip plane. Whereas the diffuse layer surface conductivity is generic, the stagnant layer conductivity is system-specific; therefore, evaluation of the later requires insight into such properties as the distribution of charges and lateral mobilities. Based on a simple analytical theory we can also estimate the diffusion coefficient of counterions in the stagnant layer. The results lead to a good agreement between theory and experiment.

On the steady shear behavior of hydrophobic fumed silica suspensions in PPG and PEG of low molecular weight

ABSTRACT Fumed silica with n-hexadecane molecules anchored onto its surface (Aerosil®R816) was dispersed in polypropylene glycol of low molecular weight (PPG400). This system showed a complex steady shear behavior: shear-thickening between two shear-thinning regions. Only shear-thinning behavior was observed when R816 was dispersed in polyethylene glycol of low molecular weight (PEG200). To conciliate both experimental results, Raman spectra of linear hexadecane, n-hexadecane/PPG400, and n-hexadecane/PEG200 mixtures were obtained. Results pointed out a distinct population of conformers could exist in each n-hexadecane-polymer mixture. More specifically, alkyl chains acquired straighter conformation in the PPG400 solvent, while the same alkyl chains showed globular conformations in PEG200.

THE INFLUENCE OF HIGH-CONCENTRATION Na HEXAMETAPHOSPHATE DISPERSANT ON THE RHEOLOGICAL BEHAVIOR OF AQUEOUS KAOLIN DISPERSIONS

Previous studies of dispersant—aqueous kaolin dispersions have indicated clearly that the concentration of the dispersant determines the type of rheological behavior. Those studies focused on the use of dispersant concentrations below the limit of saturation, ignoring what might have happened at concentrations above that limit, and the practical uses to which such information might be put. The present study examined the influence of sodium hexametaphosphate dispersant on the viscous and viscoelastic properties of aqueous kaolin dispersions when its concentration was greater than the saturation limit. A concentric-cylinders geometry sensor system (with a narrow gap between the cylinders) was used to test the rheological behavior of Na hexametaphosphate-aqueous kaolin dispersions. Aqueous kaolin dispersions were viscoplastic, thixotropic, and viscoelastic fluids. The analysis of frequency sweep tests in the linear viscoelastic limit and steady-flow curves led to the conclusion that an increase in the dispersant concentration above the limit of saturation gave way to ‘solid-like’ dispersions.

Rheological Properties of Binary Suspensions TiO2/Al2O3. Effect of Ionic Strength

The aim of the present work is to compare the influence of ionic strength on rheological properties of TiO2/Al2O3 suspensions at different volume fractions, and solid particle composition (1:1, 2:1, 1:2). The relative ratio of titania to alumina particles is important in determining the dispersion of the binary suspension with salt addition. In the case of systems containing the same number fraction of dissimilar oxides, the colloidal stability is mainly governed by the aggregation, as can be seen from the higher values of the stress in the flow curves and the yield stress values compared with those obtained in 2:1 and 1:2 situations. An attempt to provide a clearer picture concerning the stability determined by delicate balance between the van der Waals, and electrostatic, as well as the possible mechanisms of this balance tuned by environmental conditions has also been made.