Self-Assembly of Soft Materials: A Multiscale Computational Approach

1. Self-Assembly of Soft Materials: A Multiscale Computational Approach Richard A. Register, Princeton University, DMR 0213706 Surfactant adsorption at solid-liquid interfaces is important in many industrial processes, including corrosion inhibition, dispersion stabilization, and lubrication. Furthermore, surfactant adsorption may provide novel and exciting means to guide soft materials to self-assemble into a myriad of tailored shapes. Recently, PCCM researchers have made a breakthrough in elucidating the physical mechanisms behind surfactant self-assembly on a graphite surface [1]. Their simulations reveal that graphite-hydrocarbon chain interactions favor specific molecular orientations along the crystallographic directions, leading to the formation of oriented hemimicellar aggregates as observed in previous experiments [2] from PCCM’s IRG2. The results suggest that manipulating the structure of the graphite surface can be employed to tune the orientational order of the hemimicellar aggregates. Top left: snapshot of a C12 aggregate on graphite. Top middle: orientational distribution for varying surface coverage. Top right: schematic of the orientations in the middle panel. Bottom left: snapshot of an SDS aggregate on graphite. Bottom right: orientational distribution for varying surface coverage. Both C12 and SDS molecules display strong orientational bias the single molecule level, while bias disappears at intermediate coverages only to re-emerge at complete filling. References: [1] M. Sammalkorpi, A. Z. Panagiotopoulos, and M. Haataja, “Structure and Dynamics of Surfactant and Hydrocarbon Aggregates on Graphite: A Molecular Dynamics Simulation Study”, J. Phys. Chem. B, submitted (2007). [2] D.A. Saville, J. Chun, J.L. Li, H.C. Schniepp, R. Car, and I.A. Aksay, “Orientational Order of Molecular Assemblies on Inorganic Crystals”, Phys. Rev. Lett., 96, 018301 (2006).