The role of polymers and surfactants in flocculation and dispersion of aqueous suspensions.

摘要

The dispersion of aqueous suspensions using surfactants and polymers has widespread applications. In addition to the amount adsorbed, the structure of adsorbed surfactant and polymer layers determines the interfacial properties of solid particles and thus suspension stability in these systems. Therefore, an understanding of that structure at the molecular level is very useful. The aim of this work is to study the role of adsorbed layer micro-structural properties, namely micro-polarity, micro-fluidity, and most importantly, molecular conformation and orientation at the solid/liquid interface, in controlling dispersion properties. A multi-pronged approach involving the use of fluorescence, ESR, NMR, computer simulation, along with conventional techniques to measure turbidity and the adsorption isotherm, could be used to explore surfactants/polymers at solid/liquid interfaces.; The adsorption of ionic surfactants (both cationic and anionic surfactants) on alumina in aqueous solution shows regions corresponding to different adsorption mechanisms following a 4-region model. The suspension stability also displays significant changes concomitant with changes in the structure of the adsorbed layer. When polymers are used, their conformation can be manipulated by changing solution conditions such as pH and/or by the addition of a second surfactant or polymer. Such manipulation can be used to obtain a desired level of stabilization or flocculation. In the case of mixed systems involving at least one polymer, the order of addition is found to be an important factor in determining dispersion conditions.; Novel approaches are introduced into the field of flocculation for studying floc structure and flocculation kinetics. Floc structure can be investigated indirectly by examining water signals given by conventional NMR. In addition, a computer program was developed to simulate flocculation kinetics and floc structure for particles with heterogeneous surface properties. It is hoped that the flocculation process can be better understood from further application of these novel approaches.