期刊
ACS NANO
卷 13, 期 5, 页码 5760-5770出版社
AMER CHEMICAL SOC
DOI: 10.1021/acsnano.9b01292
关键词
solvent restructuring; colloidal nanocrystals; molten salts; ionic liquids; small-angle X-ray scattering; X-ray pair distribution function; molecular dynamics simulations
类别
资金
- National Science Foundation [DMR-1611371]
- Office of Basic Energy Sciences, the US Department of Energy [DE-SC0019375]
- Department of Defense (DOD) Air Force Office of Scientific Research [FA9S50-15-1-0099]
- University of Chicago Materials Research Science and Engineering Center - NSF [DMR-1420709]
- DOE Office of Science [DE-AC02-06CH11337]
- University of Chicago Research Computing Center
- U.S. Department of Energy (DOE) [DE-SC0019375] Funding Source: U.S. Department of Energy (DOE)
The nature of the interface between the solute and the solvent in a colloidal solution has attracted attention for a long time. For example, the surface of colloidal nanocrystals (NCs) is specially designed to impart colloidal stability in a variety of polar and nonpolar solvents. This work focuses on a special type of colloids where the solvent is a molten inorganic salt or organic ionic liquid. The stability of such colloids is hard to rationalize because solvents with high density of mobile charges efficiently screen the electrostatic double-layer repulsion, and purely ionic molten salts represent an extreme case where the Debye length is only similar to 1 angstrom. We present a detailed investigation of NC dispersions in molten salts and ionic liquids using small-angle X-ray scattering (SAXS), atomic pair distribution function (PDF) analysis and molecular dynamics (MD) simulations. Our SAXS analysis confirms that a wide variety of NCs (Pt, CdSe/CdS, InP, InAs, ZrO2) can be uniformly dispersed in molten salts like AlCl3/NaCl/KCl (AlCl3/AlCl4-) and NaSCN/KSCN and in ionic liquids like 1-butyl-3-methylimidazolium halides (BMIM+X-, where X = Cl, Br, I). By using a combination of PDF analysis and molecular modeling, we demonstrate that the NC surface induces a solvent restructuring with electrostatic correlations extending an order of magnitude beyond the Debye screening length. These strong oscillatory ion-ion correlations, which are not accounted by the traditional mechanisms of steric and electrostatic stabilization of colloids, offer additional insight into solvent-solute interactions and enable apparently impossible colloidal stabilization in highly ionized media.
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