title: Synchrotron X-ray studies of rapidly evolving morphology of self-assembled nanoparticle films under lateral compression.
abstract: Interfacial nanostructures represent a class of systems that are highly relevant to studies of quasi-2D phases, chemical self-assembly, surfactant behavior, and biologically relevant membranes. Previous studies have shown that under lateral compression a Langmuir film of gold (Au) nanoparticles assembled at the liquid-air interface exhibits rich mechanical behavior: it undergoes a rapid structural and morphological evolution from a monolayer to a trilayer via an intermediate hash-like phase. We report the results of studying this structural evolution using grazing incidence X-ray off-specular scattering (GIXOS). We utilize GIXOS to obtain a quantitative mapping of electron density profile normal to the liquid surface with a subnanometer resolution and follow the structural evolution of the Au nanoparticle film under lateral compression with a subminute temporal resolution. As the surface pressure is increased, the self-assembled nanoparticle monolayer first crinkles into a double-layer phase before forming a trilayer. This study reveals the existence of a transient bilayer phase and provides a microscopic picture of the particle-level crinkling phenomena of ultrathin films. These studies were previously impossible due to the relatively short time scales involved in crinkling formation of these transient phases and their intrinsically inhomogeneous nature.
authors.affiliation: Department of Physics, University of California, San Diego , La Jolla, California 92093, United States.
authors.forename: Yeling
authors.initials: Y
authors.lastname: Dai
authors.forename: Binhua
authors.initials: B
authors.lastname: Lin
authors.forename: Mati
authors.initials: M
authors.lastname: Meron
authors.forename: Kyungil
authors.initials: K
authors.lastname: Kim
authors.forename: Brian
authors.initials: B
authors.lastname: Leahy
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Witten
authors.forename: Oleg G
authors.initials: OG
authors.lastname: Shpyrko
mesh_terms: D006046:Gold / Q000737:chemistry*; D055595:Mechanical Phenomena; D053768:Metal Nanoparticles / Q000737:chemistry*; D017356:Synchrotrons; D013997:Time Factors; D014961:X-Ray Diffraction / Q000295:instrumentation*
chemical_list: D006046:Gold