title: Real Space Imaging of Nanoparticle Assembly at Liquid-Liquid Interfaces with Nanoscale Resolution.
abstract: Bottom up self-assembly of functional materials at liquid-liquid interfaces has recently emerged as method to design and produce novel two-dimensional (2D) nanostructured membranes and devices with tailored properties. Liquid-liquid interfaces can be seen as a "factory floor" for nanoparticle (NP) self-assembly, because NPs are driven there by a reduction of interfacial energy. Such 2D assembly can be characterized by reciprocal space techniques, namely X-ray and neutron scattering or reflectivity. These techniques have drawbacks, however, as the structural information is averaged over the finite size of the radiation beam and nonperiodic isolated assemblies in 3D or defects may not be easily detected. Real-space in situ imaging methods are more appropriate in this context, but they often suffer from limited resolution and underperform or fail when applied to challenging liquid-liquid interfaces. Here, we study the surfactant-induced assembly of SiO2 nanoparticle monolayers at a water-oil interface using in situ atomic force microscopy (AFM) achieving nanoscale resolved imaging capabilities. Hitherto, AFM imaging has been restricted to solid-liquid interfaces because applications to liquid interfaces have been hindered by their softness and intrinsic dynamics, requiring accurate sample preparation methods and nonconventional AFM operational schemes. Comparing both AFM and grazing incidence X-ray small angle scattering data, we unambiguously demonstrate correlation between real and reciprocal space structure determination showing that the average interfacial NP density is found to vary with surfactant concentration. Additionally, the interaction between the tip and the interface can be exploited to locally determine the acting interfacial interactions. This work opens up the way to studying complex nanostructure formation and phase behavior in a range of liquid-liquid and complex liquid interfaces.
authors: ESRF-The European Synchrotron 71 , Avenue des Martyrs. 38100 Grenoble, France.
authors: Luca
authors: L
authors: Costa
authors: ESRF-The European Synchrotron 71 , Avenue des Martyrs. 38100 Grenoble, France.
authors: Giovanni
authors: G
authors: Li-Destri
authors: Department of Oral Biology, School of Dentistry and Molecular and Nanoscale Physics Group, School of Physics and Astronomy, University of Leeds , LS2 9JT Leeds, United Kingdom.
authors: Neil H
authors: NH
authors: Thomson
authors: ESRF-The European Synchrotron 71 , Avenue des Martyrs. 38100 Grenoble, France.
authors: Oleg
authors: O
authors: Konovalov
authors: ESRF-The European Synchrotron 71 , Avenue des Martyrs. 38100 Grenoble, France.
authors: Diego
authors: D
authors: Pontoni
keywords: Nanomaterials; force spectroscopy; interparticle distance; surface coverage; tapping mode AFM; thin films