Thin membrane films composed of a single layer of inorganic nanocrystal cores encoded with organic ligands are currently of great interest for a range of applications from nanosieves to electric, magnetic, or photonic devices and sensors. While these membranes have been found experimentally to be flexible yet surprisingly strong under indentation, the underlying microscopic origin of their large tensile strength remains unresolved. Sandia researchers used largescale molecular dynamics simulations to probe the fundamental mechanisms underlying the unique mechanical strength of these twodimensional membranes. Recent multi-million atom simulations of alkanethiol-coated gold nanoparticle membranes were carried out to

simultaneously measure nanoscale interactions while directly comparing membrane properties to experiment. To replicate experimental conditions, researchers first formed the nanoparticle membranes at a water-vapor interface, and

then removed the water to form free-standing membranes. Simulated membranes capture the experimental morphology and structural properties, which provides insight into their underlying mechanisms. Mechanical tests of the resulting membranes

showed that interactions between end-groups on the encoded ligands play a dominant role in determining membrane strength and stiffness. The ligand end-group also affects how these membranes fail under tension as shown in the augmented video accompanying this article. Simulations provide unprecedented molecular detail that cannot be obtained experimentally, and the resulting insights can be used to design nanoparticle membranes with more finely tailored mechanical properties.

Contact: Gary Grest


Free-standing alkanethiol gold nanoparticle membranes with COOH terminal groups viewed from the side (top) and above (bottom). The video shows how different membranes fail under strain.