[Truncated abstract] Surface forces are driving most physical and chemical processes at colloidal and molecular levels. The present study aims to develop an in-depth understanding on surface forces in dispersions, in particular (a) how molecular attributes of adsorbed additive affect the nature of surface forces, and (b) to bring new insight in the characterizing technique of flocculated-dispersed state transition for dilute colloidal dispersions. Firstly, a conformational structure-surface force correlation was developed by evaluating the effects of pure enantiomeric and racemate malic acids on the yield stress of α-Al2O3 (alumina) suspensions to determine the nature of inter- or intra-molecular forces responsible for the type of surface forces operating in the suspension. The effect of pH on the yield stress and zeta potential behaviours of alumina dispersions with the addition of D-, L- and racemate (DL) malic acids were evaluated. Conformational structures and intra-molecular hydrogen bonding of the adsorbed malic acids obtained via molecular modeling were used to explain the surface forces operating in the dispersions. It was found that the yield stress-pH behaviour is almost identical for D-, L- and DL- malic acids. At low surface coverage of adsorbed malic acid, the maximum yield stress was reduced by as much as 55%. At complete surface coverage the reduction decreased to ~40%. Molecular modelling showed the presence of intra-molecular hydrogen between the hydroxyl and the (free) charged carboxylate group within the malic acid molecule. Intra-molecular hydrogen bonding and the high number of strongly bound water molecules (hydration number of malic di-ionic species) were likely responsible for the di-ionic malic acid species acting as a very effective steric agent.
|Qualification||Doctor of Philosophy|
|Publication status||Unpublished - 2013|