In situ atomic force microscopy of modified dextrin adsorption on hydrophobic and hydrophilic layered silicate minerals.

We have used in situ atomic force microscopy (AFM), captive bubble contact angle measurements, and colloid-probe AFM to investigate the adsorption of two modified dextrins (a phenyl succinate substituted dextrin, PS Dextrin, and a styrene oxide substituted dextrin, SO Dextrin) on the basal plane surfaces of talc and clinochlore. The experiments have probed the effect that the polymers have on the mineral hydrophobicity and on the expected particle-particle interactions in single mineral aggregation. Distinct correlations were seen between the adsorbed polymer layer morphology (coverage, thickness) and the ability of the polymers to reduce the contact angle of the talc basal plane surfaces (SO Dextrin>PS Dextrin). Both polymers were seen to lower the contact angle of clinochlore to an apparent limiting value of approximately 25 degrees. The effect of the polymers on the forces between hydrophobic surfaces (talc basal plane and a hydrophobised titania sphere) and between hydrophilic surfaces (clinochlore cleaved surface and a silica sphere) was seen to be a complicated relationship between the adsorbed layer morphology and bulk polymer properties, with polymers exhibiting a clear tendency to bridge between hydrophobic surfaces. Neither of the dextrins was found to encourage attraction between hydrophilic surfaces, in spite of adsorbing to a significant extent on the clinochlore cleaved surface.