ИСТИНА

Control over physical properties of nanoparticle assemblies at a liquid-liquid interface is a key technological advancement to realize a dream about smart electrovariable nanosystems. Electrified interfaces, such as the interface between two immiscible electrolytes solutions (ITIES), are almost an ideal platform to realize this dream. Previously, the research in the field was focused on “vertical” landing of nanoparticles, driven by an external electric field, from the bulk to ITIES to form mirror-type films.[1,2] However, this approach has the major restriction limiting practical applications: slow diffusion of the nanoparticles from the bulk to the interface. In contrast, the interlayer Marangoni effect has been used to power movements of capsules at a liquid-liquid interface (LLI).[3] By definition, the Marangoni effect is the mass transfer along an interface between two fluids – liquid-liquid or liquid-gas – due to changes in interfacial surface tension. In a classical theory developed by V. G. Levich [4] the concept of capillary motion was derived in the presence of a surface tension imbalance on the free surface of a liquid-liquid interface. We used Marangoni effect to induce migration of citrate covered gold nanoparticles located close to the ITIES from the middle region of the cell to its periphery with polarizing of the ITIES.[5] Thus, we called such systems “Marangoni-type shutters”. The necessary difference in surface tension was achieved by using SDS as a surfactant and electric field across the interface. In this work we showed that moving of nanoparticles in-plane of the interface can be performed repeatedly (up to 20 cycles) with significant change of the reflectivity (Fig. 1). This type of electrovariable plasmonics do not have diffusion limitation in comparison with adsorption/desorption of nanoparticles and the entire movement of nanoparticles assemblies happened almost instantly (within a second). This approach opens a fresh view on electrovariable plasmonics and proposes new opportunities to create smart nanosystems at ITIES driven with electric field. Fig. 1. Marangoni-type shutter in action. A part of cyclic voltammogram with corresponding snapshots taken from the recorded video. References: [1] M.E. Flatté, A.A. Kornyshev, M. Urbakh, Understanding voltage-induced localization of nanoparticles at a liquid–liquid interface, J. Phys. Condens. Matter. 20 (2008) 73102. doi:10.1088/0953-8984/20/7/073102. [2] M.E. Flatte, A.A. Kornyshev, M. Urbakh, Electrovariable Nanoplasmonics and Self-Assembling Smart Mirrors, J. Phys. Chem. C. 114 (2010) 1735–1747. doi:10.1021/jp9083234. [3] G. Zhao, M. Pumera, Liquid–Liquid Interface Motion of a Capsule Motor Powered by the Interlayer Marangoni Effect, J. Phys. Chem. B. 116 (2012) 10960–10963. doi:10.1021/jp3057702. [4] V.G. Levich, Physicochemical hydrodynamics, Prentice-Hall, 1962. https://books.google.ch/books?id=DAtRAAAAMAAJ. [5] G.C. Gschwend, E. Smirnov, P. Peljo, H. Girault, Electrovariable Gold Nanoparticle Films at Liquid-Liquid Interfaces: from redox electrocatalysis to Marangoni-shutters, Faraday Discuss. (2016). doi:10.1039/C6FD00238B.