Ligand structure and mechanical properties of single-nanoparticle thick membranes

Journal Article · Tue Jun 16 00:00:00 EDT 2015 · Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics

DOI:https://doi.org/10.1103/PhysRevE.91.062403· OSTI ID:1235281

Salerno, Kenneth Michael ^[1]; Bolintineanu, Dan S. ^[1]; Lane, J. Matthew D. ^[1]; Grest, Gary S. ^[1]

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1. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

We believe that the high mechanical stiffness of single-nanoparticle-thick membranes is the result of the local structure of ligand coatings that mediate interactions between nanoparticles. These ligand structures are not directly observable experimentally. We use molecular dynamics simulations to observe variations in ligand structure and simultaneously measure variations in membrane mechanical properties. We have shown previously that ligand end group has a large impact on ligand structure and membrane mechanical properties. Here we introduce and apply quantitative molecular structure measures to these membranes and extend analysis to multiple nanoparticle core sizes and ligand lengths. Simulations of nanoparticle membranes with a nanoparticle core diameter of 4 or 6 nm, a ligand length of 11 or 17 methylenes, and either carboxyl (COOH) or methyl (CH₃) ligand end groups are presented. In carboxyl-terminated ligand systems, structure and interactions are dominated by an end-to-end orientation of ligands. In methyl-terminated ligand systems large ordered ligand structures form, but nanoparticle interactions are dominated by disordered, partially interdigitated ligands. Core size and ligand length also affect both ligand arrangement within the membrane and the membrane's macroscopic mechanical response, but are secondary to the role of the ligand end group. Additionally, the particular end group (COOH or CH₃) alters the nature of how ligand length, in turn, affects the membrane properties. The effect of core size does not depend on the ligand end group, with larger cores always leading to stiffer membranes. Asymmetry in the stress and ligand density is observed in membranes during preparation at a water-vapor interface, with the stress asymmetry persisting in all membranes after drying.

• Research Organization: Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA)
• Grant/Contract Number: AC04-94AL85000
• OSTI ID: 1235281
• Alternate ID(s): OSTI ID: 1184884
• Report Number(s): SAND--2015-1157J; 567065
• Journal Information: Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics, Journal Name: Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics Journal Issue: 06 Vol. 91; ISSN 1539-3755
• Publisher: American Physical Society (APS)
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE