430955 Mesostructured Self-Assembly of 12-Hydroxystearate in Organic Solvents

Monday, November 9, 2015
Exhibit Hall 1 (Salt Palace Convention Center)
Ryan Gordon and Cameron F. Abrams, Chemical and Biological Engineering, Drexel University, Philadelphia, PA

Derivatives of R-12-hydroxystearate are currently the main surfactants used in most high-performance grease applications.  While hydroxystearates are known to form organogels, the detailed structure and formation mechanisms of those gels are not understood, leaving a gap in our understanding of the links between molecular structure and grease performance.  This project addresses this gap by using united-atom molecular dynamics simulation to investigate the self-assembly of enantiomerically pure R-12-hydroxystearate in hexane.  In three separate 1-microsecond-long MD simulations beginning from random configurations, we find that self-assembly is driven by two types of hydrogen bonding: the acetic-acid dimer structure between stearate carboxylates and 12-hydroxyl-to-12-hydroxyl H-bonds.  The self-assembly proceeds through formation of mesostructures that are predominantly polarized five- and six-membered rings of molecules that assemble into lamellae that adhere to one another through a registry of acetic-acid ring-to-ring dimerizations.  A simplified kinetic model is fit to the evolution of multimeric species observed directly in the simulations and provides rate constants that should one day prove useful in continuum-level modeling of elastohydrodynamic friction.

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