Self-Assembly of Soft Materials: A Multiscale Computational Approach. Richard A. Register, Princeton University, DMR 0213706.
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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 . 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  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:  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).
 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).