Polyacrylic acid adsorption and conformation in concentrated alumina suspensions

Particulate suspensions used in many industrial processes are typically hig hly concentrated and it is often difficult to keep them well dispersed or f locculated. Polymer adsorption is usually employed to achieve desired collo idal and rheological properties of such suspensions. In this work, adsorpti on of polyacrylic acid (PAA) in concentrated alumina dispersions has been m onitored to determine the effect of solids loading on both the adsorption a s well as the conformation of the adsorbed species. Fluorescence and electr on spin resonance (ESR) spectroscopy were used to determine the conformatio n of labeled PAA adsorbed on alumina particles. Solids loading was found to have interesting effects on PAA adsorption and conformation at the alumina -water interface. As the solids loading is increased, the adsorption densit y of PAA was found to decrease under conditions of a fixed high initial pol ymer concentration. However, in the case of adsorption using reduced initia l polymer concentration, this solids loading dependence was removed. Confor mational studies (conducted at a constant adsorption density) showed the po lymer molecules to become more stretched with increasing solids loading. Th e relationship between the polymer conformation and the particle dispersion was also investigated. Stretching of the adsorbed polymer was found in thi s case to produce an increase in the settling rate obtained, suggesting bri dging effects. (C) 2001 Elsevier Science B.V. All rights reserved.