X-ray scattering as a liquid and solid phase probe of ordering within sub-monolayers of iron oxide nanoparticles fabricated by electrophoretic deposition

Quantitatively controlled electrophoretic deposition of nanocrystal films from non-aqueous suspensions

This study presents a novel method to correlate the mass and charge transfer kinetics during the electrophoretic deposition of nanocrystal films by using a purpose-built double quartz crystal microbalance combined with simultaneous current-measurement. Our data support a multistep process for film formation: generation of charged nanocrystal flux, charge transfer at the electrode, and polarization of neutral nanocrystals near the electrode surface. The polarized particles are then subject to dielectrophoretic forces that reduce diffusion away from the interface, generating a sufficiently high neutral particle concentration at the interface to form a film. The correlation of mass and charge transfer enables quantification of the nanocrystal charge, the fraction of charged nanocrystals, and the initial sticking coefficient of the particles. These quantities permit calculation of the film thickness, providing a theoretical basis for using concentration and voltage as process parameters to grow films of targeted thicknesses.

Colloidal Materials for 3D Printing

In recent years, 3D printing has led to a disruptive manufacturing revolution that allows complex architected materials and structures to be created by directly joining sequential layers into designed 3D components. However, customized feedstocks for specific 3D printing techniques and applications are limited or nonexistent, which greatly impedes the production of desired structural or functional materials. Colloids, with their stable biphasic nature, have tremendous potential to satisfy the requirements of various 3D printing methods owing to their tunable electrical, optical, mechanical, and rheological properties. This enables materials delivery and assembly across the multiple length scales required for multifunctionality. Here, a state-of-the-art review on advanced colloidal processing strategies for 3D printing of organic, ceramic, metallic, and carbonaceous materials is provided. It is believed that the concomitant innovations in colloid design and 3D printing will provide numerous possibilities for the fabrication of new constructs unobtainable using traditional methods, which will significantly broaden their applications.

Space- and time-resolved small angle X-ray scattering to probe assembly of silver nanocrystal superlattices

The structure of nanocrystal superlattices has been extensively studied and well documented, however, their assembly process is poorly understood. In this work, we demonstrate an in situ space- and time-resolved small angle X-ray scattering measurement that we use to probe the assembly of silver nanocrystal superlattices driven by electric fields. The electric field creates a nanocrystal flux to the surface, providing a systematic means to vary the nanocrystal concentration near the electrode and thereby to initiate nucleation and growth of superlattices in several minutes. Using this approach, we measure the space- and time-resolved concentration and polydispersity gradients during deposition and show how they affect the superlattice constant and degree of order. We find that the field induces a size-selection effect that can reduce the polydispersity near the substrate by 21% leading to better quality crystals and resulting in field strength-dependent superlattice lattice constants.

Reversible, Tunable, Electric-Field Driven Assembly of Silver Nanocrystal Superlattices

Nanocrystal superlattices are typically fabricated by either solvent evaporation or destabilization methods that require long time periods to generate highly ordered structures. In this paper, we report for the first time the use of electric fields to reversibly drive nanocrystal assembly into superlattices without changing solvent volume or composition, and show that this method only takes 20 min to produce polyhedral colloidal crystals, which would otherwise need days or weeks. This method offers a way to control the lattice constants and degree of preferential orientation for superlattices and can suppress the uniaxial superlattice contraction associated with solvent evaporation. In situ small-angle X-ray scattering experiments indicated that nanocrystal superlattices were formed while solvated, not during drying.

Insight into Nanoparticle Charging Mechanism in Nonpolar Solvents To Control the Formation of Pt Nanoparticle Monolayers by Electrophoretic Deposition

We report on the formation of Pt nanoparticle monolayers by electrophoretic deposition from nonpolar solvents. First, the growth kinetics of Pt nanoparticles prepared by the reverse micelle technique are described in detail. Second, a model of nanoparticle charging in nonpolar media is discussed and methods to control the nanoparticle charging are proposed. Finally, essential parameters of the electrophoretic deposition process to control the deposition of nanoparticle monolayers are discussed and mechanisms of their formation are analyzed.