The effect of polymer chain architecture on the adsorption properties of derivatised polyisobutylenes at the carbon/n-heptane interface

Adsorption isotherms for derivatised polyisobutylene (PIB) molecules from n-heptane onto activated carbon have been determined. Nine polyisobutylene samples were studied: three different molecular weight groups (1000, 2000 and 3000), with each molecular weight group having three different chain architectures, i.e. having one, two or three derivatised (azacarboxylate) terminal head groups. The adsorbed amounts of the various PIBs were found to be dependent not only on their structure, but also on their solubility in n-heptane. The difunctional PIB was found to adsorb the most strongly. The areas per molecule, particularly for the higher molecular weight samples, suggest that the PIBs adsorb at the surface in an aggregated form, resulting in multilayers at higher coverages. Furthermore, all the PIBs are highly solvated at the solid/solution interface. These two factors enable the polymer to confer good steric stabilisation effects on the carbon dispersions. Compared with previous studies of the adsorption of succinimide derivatives of PIBs onto carbon, the PIBs used in this work adsorb to a lesser extent, suggesting that the azo head group does not provide as effective an anchor to the particle surface as the corresponding succinimide.