In-situ Characterization of Crystallization and Melting of Soft, Thermoresponsive Microgels by Small-Angle X-ray Scattering

Depending on the volume fraction and interparticle interactions, colloidal suspensions can form different phases, ranging from fluids, crystals, and glasses to gels. For soft microgels that are made from thermoresponsive...

Vesicle shape transformations driven by confined active filaments

In active matter systems, deformable boundaries provide a mechanism to organize internal active stresses. To study a minimal model of such a system, we perform particle-based simulations of an elastic vesicle containing a collection of polar active filaments. The interplay between the active stress organization due to interparticle interactions and that due to the deformability of the confinement leads to a variety of filament spatiotemporal organizations that have not been observed in bulk systems or under rigid confinement, including highly-aligned rings and caps. In turn, these filament assemblies drive dramatic and tunable transformations of the vesicle shape and its dynamics. We present simple scaling models that reveal the mechanisms underlying these emergent behaviors and yield design principles for engineering active materials with targeted shape dynamics.

Magnetic Properties of Bi-Magnetic Core/Shell Nanoparticles: The Case of Thin Shells

Bi-magnetic core/shell nanoparticles were synthesized by a two-step high-temperature decomposition method of metal acetylacetonate salts. Transmission electron microscopy confirmed the formation of an ultrathin shell (~0.6 nm) of NiO and NiFe2O4 around the magnetically hard 8 nm CoFe2O4 core nanoparticle. Magnetization measurements showed an increase in the coercivity of the single-phase CoFe2O4 seed nanoparticles from ~1.2 T to ~1.5 T and to ~2.0 T for CoFe2O4/NiFe2O4 and CoFe2O4/NiO, respectively. The NiFe2O4 shell also increases the magnetic volume of particles and the dipolar interparticle interactions. In contrast, the NiO shell prevents such interactions and keeps the magnetic volume almost unchanged.

Ultrathin Metal Hydroxide/Oxide Nanowires: Crystal Growth, Self-Assembly, and Fabrication for Optoelectronic Applications

The fundamental understanding of transition metal oxides nanowires’ crystal growth to control their anisotropy is critical for their applications in miniature devices. However, such studies are still in the premature stage. From an industrial point of view, the most exciting and challenging area of devices today is having the balance between the performance and the cost. Accordingly, it is essential to pay attention to the controlled cost-effective and greener synthesis of ultrathin TMOS NWs for industrial optoelectronic applications. This chapter provides a comprehensive summary of fundamental principles on the preperation methods to make dimensionality controlled anisotropic nanowires, their crystal growth studies, and optical and electrical properties. The chapter particularly addresses the governing theories of crystal growth processes and kinetics that controls the anisotropy and dimensions of nanowires. Focusing on the oriented attachment (OA) mechanism, the chapter describes the OA mechanism, nanocrystal’s self-assembly, interparticle interactions, and OA-directed crystal growth to improve the state-of-the art kinetic models. Finally, we provide the future perspective of ultrathin TMOS NWs by addressing their current challenges in optoelectronic applications. It is our understanding that the dimension, and single crystallinity of nanowires are the main contributors for building all functional properties, which arise from quasi-1-D confinement of nanowire growth.

Cu1.94S Nanocrystal Superstructure for Photocatalytic Hydrogen Evolution

Ordered nonstoichiometric Cu1.94S nano superstructure are constructed and provide notably improved catalytic H2 evolution reaction performance at 2482.00 µmol g‒1 h‒1. Careful selection of metal organic framework precursors with long range metal ion alignments impact performance, as well-ordered superstructures give rise to uniform electromagnetic fields and organized interparticle interactions that facilitate charge carrier transport. These close packed nanoparticles with negatively charged carboxylate surfaces inhibit large [Ru(bpy)3]Cl2 and triethanolamine transport outwards, but allow smaller H2O particles to enter superstructure interiors. In this case, separation happens not only between electrons and holes but also between reduction and oxidation zones. Abundant dangling bonds also form from the complex nonstoichiometric Cu1.94S structure and bulk aggregation of close packed Cu1.94S, up to hundreds of nanometers, provides abundant catalytic active sites.

Frustrated self-assembly of non-Euclidean crystals of nanoparticles

Self-organized complex structures in nature, e.g., viral capsids, hierarchical biopolymers, and bacterial flagella, offer efficiency, adaptability, robustness, and multi-functionality. Can we program the self-assembly of three-dimensional (3D) complex structures using simple building blocks, and reach similar or higher level of sophistication in engineered materials? Here we present an analytic theory for the self-assembly of polyhedral nanoparticles (NPs) based on their crystal structures in non-Euclidean space. We show that the unavoidable geometrical frustration of these particle shapes, combined with competing attractive and repulsive interparticle interactions, lead to controllable self-assembly of structures of complex order. Applying this theory to tetrahedral NPs, we find high-yield and enantiopure self-assembly of helicoidal ribbons, exhibiting qualitative agreement with experimental observations. We expect that this theory will offer a general framework for the self-assembly of simple polyhedral building blocks into rich complex morphologies with new material capabilities such as tunable optical activity, essential for multiple emerging technologies.