Thermodynamics and Modeling of Collective Effects in the Organic Ligand Shell of Colloidal Quantum Dots.

ConspectusColloidal nanocrystals are an interesting platform for studying the surface chemistry of materials due to their high surface area/volume ratios, which results in a large fraction of surface atoms. As synthesized, the surfaces of many colloidal nanocrystals are capped by organic ligands that help control their size and shape. While these organic ligands are necessary in synthesis, it is often desirable to replace them with other molecules to enhance their properties or to integrate them into devices.

Thermodynamics of Polyethylene Glycol Intrusion in Microporous Water.

Polymers can be used to augment the properties of microporous materials, affording enhanced processability, stability, and compatibility. Manipulating polymers to target specific properties, however, requires detailed knowledge of how different polymers and microporous materials interact. Here, we report a study of the thermodynamics of polyethylene glycol (PEG) intrusion into a representative hydrophobic zeolite (silicalite-1) and metal-organic framework [ZIF-67; Co(2-methylimidazolate)] in water, both of which can be formed into colloidally stable aqueous dispersions─termed "microporous water"─with dry, guest-accessible pore networks.

Evidence and Structural Insights into a Ligand-Mediated Phase Transition in the Solvated Ligand Shell of Quantum Dots.

As synthesized, nanocrystal surfaces are typically covered in coordinating organic ligands, and the degree of packing and order of these ligands are ongoing questions in the field of colloidal nanocrystals, particularly in the solution state. Recently, isothermal titration calorimetry coupled with H NMR has been used to probe ligand exchanges on colloidal quantum dots, revealing the importance of the composition of the ligand shell on exchange thermodynamics. Previous work has shown that the geometry and length of a ligand's aliphatic chain can influence the thermodynamics of exchange.

Precursor Chemistry of Lead Bromide Perovskite Nanocrystals.

We investigate the early stages of cesium lead bromide perovskite formation through absorption spectroscopy of stopped-flow reactions, high-throughput mapping, and direct synthesis and titration of potential precursor species. Calorimetric and spectroscopic measurements of lead bromide complex titrations combined with theoretical calculations suggest that bromide complexes with higher coordination numbers than previously considered for nonpolar systems can better explain observed behaviors. Synthesis mapping of binary lead halides reveals multiple lead bromide species with absorption peaks higher than 300 nm, including a previously observed species with a peak at 313 nm and two species with peaks at 345 and 370 nm that also appear as reaction intermediates during the formation of lead bromide perovskites.

A Global Perspective on Socioeconomic Determinants of Cardiovascular Health.

Cardiovascular disease (CVD) is the leading cause of mortality in the world. From 2005 to 2008, the World Health Organization (WHO) planned an initiative to reduce the mortality rate of CVD by 2030 by addressing health, finance, transport, education, and agriculture in these communities. Plans were underway by many countries to meet the goals of the WHO initiative.