Experiments and computer simulations provide a new perspective that strong correlations of counterions with charged nanoparticles can influence the localization of nanoparticles at liquid−liquid interfaces and support the formation of voltage-tunable nanoparticle arrays. We show that ion condensation onto charged nanoparticles facilitates their transport from the aqueous-side of an interface between two immiscible electrolyte solutions to the organic-side, but contiguous to the interface. Counterion condensation onto the highly charged nanoparticles overcomes the electrostatic barrier presented by the low permittivity organic material, thus providing a mechanism to transport charged nanoparticles into organic phases with implications for the distribution of nanoparticles throughout the environment and within living organisms. After transport, the nanoparticles assemble into a two-dimensional (2D) nearly close-packed array on the organic side of the interface. Voltage-tunable counterion-mediated interactions between the nanoparticles are used to control the lattice spacing of the 2D array. Tunable nanoparticle arrays self-assembled at liquid interfaces are applicable to the development of electro-variable optical devices and active elements that control the physical and chemical properties of liquid interfaces on the nanoscale.

See:  Mrinal K. Bera , Henry Chan , Daniel F. Moyano §, Hao Yu , Sabina Tatur , Daniel Amoanu , Wei Bu , Vincent M. Rotello §, Mati Meron , Petr Král *†‡, Binhua Lin *, and Mark L. Schlossman * , “Interfacial Localization and Voltage-Tunable Arrays of Charged Nanoparticles”, Nano Lett., 14 (12), 6816 (2014).

Author affiliations  Department of Physics, University of Illinois at Chicago; Department of Chemistry, University of Illinois at Chicago; § Department of Chemistry, University of Massachusetts;  Department of Chemical Engineering, University of Illinois at Chicago;  Center for Advanced Radiation Sources, University of Chicago.