(121e) Modeling Colloidal Interactions Mediated by Adsorbing Wormlike Micelles

We have recently explored the formation and rheology of novel ?double network? structures in wormlike micelle (WLM)-nanoparticle mixtures mediated by the formation of micelle-nanoparticle junctions [1]. The formulation of such structures is limited by the colloidal stability of the dispersed nanoparticles, which exhibit strong attractive interactions and thermoreversible phase separation [2]. To describe this new class of colloidal interactions, we have derived an interaction potential mediated by end-adsorbing WLMs based on previously developed theories for telechelic polymers, modified to account for reversible micellar adsorption and chain scission. The model predicts a long-range attraction with a deeper minimum than that predicted for monodisperse polymers due to the equilibrium distribution of chain lengths at sufficiently small separation. Because the model is formulated in terms of measurable structural parameters of the micelles, it allows for a priori predictions of both the microstructure and thermodynamic phase behavior of the dispersed colloids. The model is thus tested against experimental measurements of the static structure factor and colloidal phase diagram, and shows near quantitative agreement in both cases for model WLM-nanoparticle mixtures. These results show that colloidal interactions can be directly controlled by changes in the WLM self-assembly, providing a novel means by which to control the dispersion of colloids in WLMs.

[1] M.E. Helgeson et al., Langmuir 2009, DOI: 10.1021/la100026d.

[2] F. Nettesheim et al., Langmuir 2008, 24(15), 7718-7726.