(650e) Role of Collective Degrees of Freedom in Formation and Disintegration of Spherical Micelles

Dynamics of self-assembly and structural transitions in amphiphilic systems play an important role in various processes, ranging from production of nanostructured materials to transport in biological cells. We recently demonstrated [1] that even such simple process as addition of a single surfactant molecule to a micelle involves a complex interplay between micellar microstructure and the monomer configuration. Neglecting cooperative dynamics of these degrees of freedom leads to qualitative discrepancies in predicted surfactant addition rates.

In this talk, we present improvement of our earlier model which enables quantitative predictions of addition/removal rates of surfactants to/from micelles. This is accomplished by a reconstruction of a multi-dimensional free energy landscape parametrized by distance between the micelle and monomer centers of mass, as well as the micellar and monomer configurations. The minimal energy path (MEP) on this landscape is identified. Movement along MEP corresponds to addition and removal of a monomer accompanied by the necessary changes of the micellar and monomer configurations. Analysis of MEP allows us to identify collective degrees of freedom relevant to the monomer addition and removal. However, MEP alone is not sufficient to predict the monomer addition and removal rates since both of these processes involve non-adiabatic stages. Comparable time-scales of several independent degrees of freedom during these non-adiabatic stages imply that the system dynamics cannot be described by a quasi-one-dimensional motion along MEP. Therefore, we obtain solutions of multi-dimensional Langevin equations to correctly describe the non-adiabatic system dynamics.

We conclude this talk by a discussion of extension of the developed methodology to more complex transitions in self-assembled systems.

References

1. G. Mohan and D. I. Kopelevich, ?A multiscale model for kinetics of formation and disintegration of spherical micelles?, J. Chem. Phys.128, 044905 (2008).