Optical Properties of Self-healing Gold Nanoparticles Mirrors and Filters at Liquid–Liquid Interfaces

Abstract

This chapter illustrates a detailed study of optical and morphological properties of lustrous self-healing metal liquid-like nanofilms for different applications (e.g., optical mirrors or filters). Extinction and reflectance of nanofilms were investigated by an integrating sphere in UV, visible and NIR ranges with step-bystep increasing of nanoparticle surface coverage. The interfacial AuNP surface coverage strongly influenced the morphology of the interfacial nanofilms and in turn their maximum reflectance and absorbance. We observed three distinct morphological regimes: (i) smooth 2D monolayers of “floating islands” of AuNPs at low surface coverages, (ii) a mixed 2D/3D regime with the beginnings of 3D nanostructures consisting of small piles of adsorbed AuNPs even at sub-full-monolayer conditions, and, finally, (iii) a 3D regime characterized by the 2D full-monolayer being covered in significant piles of adsorbed AuNPs. Also, comparison of optical properties of nanofilms at different water-organic solvent interfaces is presented. A maximal value of reflectance reached 58% in comparison to a solid gold mirror, when 38 nm mean diameter AuNPs were used at a water–nitrobenzene interface. Meanwhile, interfacial gold nanofilms prepared with 12 nm mean diameter AuNPs exhibited the highest extinction intensities at ca. 690 nm and absorb around 90% of the incident light, making them an attractive candidate for filtering applications. Furthermore, the interparticle spacing, and resulting interparticle plasmon coupling derived optical properties, varied significantly on replacing tetrathiafulvalene with neocuproine as the AuNP capping ligand in the nanofilm.