Voltage-Tunable 2D and 3D Structures of Gold Nanoparticles at a Water/1,2-Dichloroethane Interface

It has been established that local electromagnetic field enhancements due to optical excitation at the plasmon resonance increases when the electromagnetic field of individual metals or nanoparticles couple through nanoscale inter-particle spacing. Discrete clusters made from closely spaced gold nanoparticles have enhanced electromagnetic fields with useful applications in plasmonics, medical diagnosis, emulsion stabilization, catalysis, optical sensing, electro-voltaic devices and catalysis leading to a worldwide interest in the development of these next-generation materials. Liquid interfaces play a key role in the development of these novel devices since nanoparticles are often stabilized in colloidal forms. The fluidity of a liquid interface presents a novel environment for assembling nanoparticles in different configurations. In spite of the growth, interest and potential in assembling nanoparticles at a liquid interface, nanoparticle adsorption at a liquid interface is poorly understood. It is evident in theory, simulation and experiment that the simple electrostatic and van der Waals forces that DLVO theory considers for nanoparticles in bulk solutions is not enough to explain the adsorption and stability of nanoparticles at liquid interfaces. Instead, the interactions of the nanoparticles at liquid interface are governed by interfacial tension stabilization, hydration forces, capillary forces, electrostatic correlations and long range-dipole due to asymmetry of ion clouds. In this study, we use an electrochemical-based technique to remotely tune the interfacial interactions between nanoparticles at a liquid-liquid interface of water/1, 2-dichloroethane system. We demonstrate the formation of 2D and 3D structures of nanoparticles using X-ray measurements to probe the structures. The X-ray measurements techniques are X-ray reflectivity and grazing incidence small angle X-ray scattering.