Efeito do pH e força iônica nas interações atrativas montmorilonita-polifosfato

Abstract

The presence of macromolecules or nanoparticles in aqueous solution can significantly alter the interaction profile between two surfaces. Water-soluble polymers with ionizable groups can adsorb particles from colloidal suspensions as well as be free in solution. Regardless of the shape they take, their presence has an important effect on colloidal stability. The polymers can directly affect depletion interactions and bridge-type interactions. Several processes are initiated at the time of adding a polymeric solution to a particle suspension, usually under agitation conditions: polymer mixing throughout the suspension; polymer adsorption for a certain destabilization (or for neutralization of charge or opportunity for "bridge" connection between particles); rearrangement of the adsorbed polymers from an initially extended state to a flatter conformation; collisions between the destabilized particles to generate aggregates and breakage of the aggregates under the influence of applied shear. In this sense, the main objective of this proposal is to evaluate the stabilizing or destabilizing role of the polymer, as well as the effect of pH and ionic strength on aqueous clay-polyphosphate dispersions. Colloidal suspensions involving Green Sodium Bentonite (BSV) and polyphosphate chains were studied. At first, the clay was characterized by Foster's swelling, methylene blue index and zero load point assays. The clay showed a high degree of swelling, as well as a high index of methylene blue. For the colloidal stability analyses, the technique of photosedimentometry was applied with the intention of approaching the sedimentation rate of the particles. The factors that were investigated to verify the influence on sedimentation were: polymer concentration, pH variation and ionic strength. Polyphosphate concentration is an important factor in the colloidal stability of clay dispersions. At lower concentrations, it plays a stabilizing role, while at higher concentrations, it destabilizes dispersions, promoting particle aggregation. The results showed that, regarding the concentration of the polymer, what allowed a more consistent association between the polymeric chains and the clay particles forming strongly bonded aggregates was the system with a concentration of 1.0 mol. L-1. Regarding the effect of pH, it is possible to perceive the strong influence that polyphosphate exerts on the colloidal stability of the systems, considering that the higher the concentration of the polymer, the more instability will be generated between the particles. And finally, a low ionic strength, in the value of 0.001, allowed the minimization of the double electrical layer of the lamellae, making the edges accessible for the adsorption of polymer chains.