C. L. de Vasconcelos

Viscosity-temperature-concentration relationship for starch-DMSO-water solutions

Abstract The rheological behavior of starch–DMSO–water solutions was monitored using a cone-plate rheometer at different temperatures and concentrations. A solvent ratio DMSO/water=80/20 was used and viscosity was correlated with temperature through the Arrhenius equation. The dilute to semidilute flow regime transition concentration, c∗ (which was independent of temperature), was characterized by a change in the value of apparent energy of activation. At c ∗ , it was shown that the pre-exponential term in the Arrhenius equation was a function of concentration. Deviations from the predicted dependence was also used to characterize change in the flow regime. The value of c∗, obtained from the apparent energy of interaction and the pre-exponential term agreed with the one obtained from the usual plot of log ηsp vs. log c.

Polyelectrolytes in solution and the stabilization of colloids

Polyelectrolytes are very versatile macromolecular materials that have found more and more applications in several technologies. In this article applications related to their use as (de)stabilizers for colloids are reviewed. Additionally, some theories that deal with colloid stabilization are described. Finally, the rheology of the disperser phase as well as the relationship between the rheology of the whole colloidal system and polyelectrolyte stabilization are discussed.

Preparation of Acrylic Latexes with Dispersed Magnetite Nanoparticles

Latexes based on ethyl methacrylate and acrylic acid with dispersed magnetite particles were obtained using the technique of miniemulsion polymerization. The polymerizations were carried out (using AIBN as the initiator) after the dispersion of magnetite particles hydrophobized with oleic acid in the acrylic monomers and miniemulsion formation with sodium dodecyl sulfate. Latex nonvolatile content, as well as thermogravimetric behavior of dry solid particles were a function of oleic acid content. Atomic force microscopy analysis of films formed with these latexes revealed the occurrence of ordered patterns on their surfaces.