271167 Experimental and Theoretical Investigation of the Depletion Force Generated by CTAB Micelles

Monday, October 29, 2012
Hall B (Convention Center )
Greg K. James, Chemical Engineering, Virginia Tech, Blacksburg, VA and John Y. Walz, Chemial Engineering, Virginia Tech, Blacksburg, VA

The technique of colloidal probe atomic force microscopy was used to measure the equilibrium depletion force between a relatively large (30 μm diameter) spherical silica particle and a flat silica plate in solutions of cetyltrimethylammonium bromide (CTAB) surfactant. Previous work has indicated that the observed depletion force from CTAB micelles is smaller than that predicted by hard-sphere models. The objective of this work was to establish if CTAB micelles could be modeled using the well established equations for charged, hard-sphere depletants, or if corrections to these approaches are needed to account for the unique physical properties of micelles. Experiments were performed in solutions of CTAB below and sufficiently above the critical micelle concentration that not only equilibrium depletion forces but also long-range structural forces could be discerned. The force profiles were then compared to models that have been found to work well in systems using charged nanospheres as the depletants.

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