Electrolyte-Mediated Assembly of Charged Nanoparticles
Abstract
Solutions at high salt concentrations are used to crystallize or segregate charged colloids, including proteins and polyelectrolytes via a complex mechanism referred to as salting-out. Here, we combine small-angle X-ray scattering (SAXS), molecular dynamics (MD) simulations, and liquid state theory to show that salting-out is a long-range interaction, which is controlled by electrolyte concentration and colloid charge density. As a model system, we analyze Au nanoparticles coated with noncomplementary DNA designed to prevent interparticle assembly via WatsonCrick hybridization. SAXS shows that these highly charged nanoparticles undergo gas to face-centered cubic (FCC) to glass-like transitions with increasing NaCl or CaCl2 concentration. MD simulations reveal that the crystallization is concomitant with interparticle interactions changing from purely repulsive to a long range potential well condition. Liquid-state theory explains this attraction as a sum of cohesive and depletion forces that originate from the interelectrolyte ion and electrolyteionnanoparticle positional correlations. Our work provides fundamental insights into the effect of ionic correlations in the salting-out mechanism and suggests new routes for the crystallization of colloids and proteins using concentrated salts.
Document Details
- Document Type
- Technical Report
- Publication Date
- Apr 04, 2016
- Accession Number
- AD1100616
Entities
People
- Chad Mirkin
- Guillermo I. Guerrero-garcía
- Jos W. Zwanikken
- Liane M. Moreau
- Michael Bedzyk
- Monica Olvera de la Cruz
- Sumit Kewalramani
Organizations
- Northwestern University