Seminars Archive

Nanoscale Self-assembly via Electrostatic Interactions

Abstract
One of the primary goals of nanoscience is the bottom-up synthesis of new materials and functional devices from nanoscopic components. In this approach, one determines the resulting structure by carefully controlling how components interact with one another and with their environment. To this end, electrostatic interactions provide a promising – and, to date, an under appreciated – candidate for controlling nanoscale assemblies just as Nature uses them to build ionic/molecular crystals as well as supramolecular structures like proteins and DNA. In this talk, I describe how electrostatic interactions – either charge-charge or light-induced dipole-dipole – can be used to mediate the assembly of metal nanoparticles (NPs) into both static and \"dynamic\" structures. In the first approach, gold NPs are functionalized with positive and negatively charged ligands to give \"nanoions,\" which can be assembled into the nanoscale equivalent of ionic crystals. Due to their size, however, charged NPs behave unlike smaller molecular ions or larger colloidal particles with interesting consequences for their use as self-assembling components. In the second approach, light-induced self-assembly (LISA) is mediated by divalent, photoisomerizable ligands tethered onto the NPs. These ligands give rise to light-induced dipole-dipole forces between the NPs and, at the same time, can be used to crosslink the assemblies to give \"dynamic\" (i.e., light-reversible) crystalline assemblies or \"plastic\" spherical aggregates. The latter can be used in a hierarchical (multiscale) assembly process, which yields structured, macroscopic materials from nanoscale building blocks.