title: Kinetics of the self-assembly of nanocrystal superlattices measured by real-time in situ X-ray scattering.
abstract: On solvent evaporation, non-interacting monodisperse colloidal particles self-assemble into a close-packed superlattice. Although the initial and final states can be readily characterized, little is known about the dynamic transformation from colloid to superlattice. Here, by using in situ grazing-incidence X-ray scattering, we tracked the self-assembly of lead sulfide nanocrystals in real time. Following the first appearance of an ordered arrangement, the superlattice underwent uniaxial contraction and collective rotation as it approached its final body-centred cubic structure. The nanocrystals became crystallographically aligned early in the overall self-assembly process, showing that nanocrystal ordering occurs on a faster timescale than superlattice densification. Our findings demonstrate that synchrotron X-ray scattering is a viable method for studying self-assembly in its native environment, with ample time resolution to extract kinetic rates and observe intermediate configurations. The method could be used for real-time direction of self-assembly processes and to better understand the forces governing self-organization of soft materials.
authors.affiliation: Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: Mark C
authors.initials: MC
authors.lastname: Weidman
authors.affiliation: Cornell High Energy Synchrotron Source (CHESS), Cornell University, Ithaca, New York 14850, USA.
authors.forename: Detlef-M
authors.initials: DM
authors.lastname: Smilgies
authors.affiliation: Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: William A
authors.identifier: 0000-0002-6615-5342
authors.initials: WA
authors.lastname: Tisdale