Boehmite suspension behaviour upon adsorption of methacrylate–phosphonate copolymers

• Novel methacrylate–phosphonate copolymers were synthesised.
• Their dispersant ability was studied on boehmite colloidal particles.
• Polymer adsorption on boehmite is mainly controlled by electrostatic attraction.
• Heterogeneous electrical double layer interactions exist between particles.
• Stability of the particle suspension increases at alkaline pH values.

Two novel methacrylate–phosphonate copolymers were successfully synthesised with varying proportions of methacrylate and phosphonate groups. The dispersant ability of the copolymers was investigated using boehmite colloidal suspensions as a function of pH and polymer concentration. The adsorption and electrochemical behaviour of these methacrylate–phosphonate copolymers onto the boehmite surface was studied as a function of polymer concentration at pH values below and above the IEP of boehmite.It was found that the anionic copolymers adsorbed slightly more on boehmite at pH values below the boehmite IEP (pH 9.4) than above the IEP due to electrostatic attraction with the positively charged aluminate hydroxide groups at the boehmite surface. As a result, boehmite becomes more negatively charged, increasing electrostatic repulsion between boehmite particles and therefore the stability of the boehmite particulate suspension, especially at alkaline pH values around the IEP. It was also found that, for a boehmite surface partially covered by adsorbed copolymer, heterogeneous electrical double layer interaction could occur between a positively charged bare boehmite patch (pH < IEP) and the polymer covered patch, resulting in increased electrical attraction between particles. The increased electrical attraction causes the suspension to be less stable when compared to that either in the absence of polymer or at full polymer surface coverage. Very little differences between the two copolymers were observed in their boehmite adsorption or in their particle dispersion ability which is likely to be due to the low proportion of phosphonate groups that were able to be incorporated in these polymers.

Yield stress of boehmite as a function of pH and copolymer concentration shows that heterogeneous electrostatic interactions between a positive bare boehmite patch (pH < IEP) and a copolymer covered patch on two different particles can occur which results in increased electrical double layer attraction and yield stress compared to that in the absence of polymer or at maximum polymer surface coverage, and therefore in a less stable boehmite suspensions.Figure optionsDownload as PowerPoint slide