Nanoparticle Monolayer Membranes

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NON-TECHNICAL SUMMARY:Nanoparticles offer special opportunities for the design of advanced, next-generation materials. This project investigates the ultimate limit of such nanoparticle-based materials, when their thickness is reduced to that of just one particle. In this limit, single layers (monolayers) of closely packed nanoparticles combine extreme flexibility with remarkable strength. The research exploits these desirable mechanical properties to develop nanoparticle membranes for covering corrugated or porous surfaces and for novel coatings. The availability of highly conforming, ultrathin membranes has the potential to open up a wide range of new applications, including in nanofiltration. The project provides a natural platform for integrating research with training and outreach. It will train one postdoc and one graduate student in vital nanoscience know-how, and during the summer months introduce undergraduates to forefront science. In collaboration with a major science museum, the project will develop and prototype small-scale, hands-on activities for exhibits and demonstrations to the general public.TECHNICAL SUMMARY:This project focuses on a new class of ultra-thin membranes, fabricated from single layers of close-packed metallic nanoparticles, each particle surrounded by a thin coat of short organic molecules (ligands) that act as inter-particle spacers. The membranes are self-assembled in a single processing step from solution onto a solid substrate and can drape themselves over open holes that are hundreds to thousands of nanoparticles wide. The resulting freestanding membranes can be cut and manipulated by ion and electron beams, and they can be rolled up into tubular structures. Monolayer membranes make it possible to investigate the material properties of large assemblies of nanoscale building blocks without interference from a substrate, and at the same time allow for direct experimental access, via a range of probes such as electron or scanning probe microscopies, to the individual building blocks themselves. The research consists of three closely related experimental efforts that investigate different aspects of the mechanical behavior of the membranes. The first investigates the elastic response of hollow tubular structures formed from rolled-up membranes. Its goal is to identify the origin of the large bending stiffness that exceeds predictions based on standard continuum elasticity by up to two orders of magnitude. The second studies the mechanical response in the regime beyond elastic deformation and investigates how details of the local particle-molecule arrangements affect the onset of yielding and fracture in flat membranes as well as tubular structures. The third explores the use of nanoparticle membranes in new applications such as "shrink-wrapping" of surface features for plasmonic amplification and coating of porous substrates for nanofiltration.