Membranes formed from self-assembled nanoparticle monolayers have mechanical properties that may make them suitable for use in micro-scale devices.  Experimental tests of membranes with different cores and ligands indicate that ligand length as well as core-ligand and ligand-ligand interactions influence mechanical response of the membrane.  Using explicit-atom molecular dynamics simulations, we examine the properties of two-dimensional hexagonal arrays of alkanethiol-coated Au nanoparticles. Results are presented for nanoparticle core diameters from 4-6nm, ligand lengths of 10-18 units, and carboxyl or methyl end groups, all of which influence the mechanical properties of the membranes.  Nanoparticle lattice spacing is comparable to those measured experimentally.  Simulations indicate that hydrogen bonding can play a significant role in systems with carboxyl-terminated ligands, increasing the equilibrium nanoparticle spacing and significantly increasing the membrane strength in tension, consistent with experimental findings.  Membranes formed from carboxyl-terminated ligands can sustain large tensile deformations, while membranes with methyl-terminated ligands fail at smaller strains.  Simulations also indicate that interdigitation of ligands from neighboring nanoparticles varies with ligand length and terminal group.  Interdigitation is enhanced for longer ligands and for methyl-terminated ligands.  This interdigitation can result in an increase in measured elastic moduli.  As in experiment, simulations indicate that the response of the deformed membrane is purely elastic with no observed viscous effects.   Elastic moduli are measured to be up to 1 GPa for the strongest membranes.  These findings represent a systematic approach to evaluating the role of ligand length and composition on membrane mechanical properties.  Knowledge of how microstructure and composition influence membrane properties could lead to more efficient membrane manufacture and improved mechanical properties. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Mechanical properties of 2D alkanethiol gold nanoparticle membranes

248th National Meeting (2014)

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