Controlling the Shape of Nanoparticle Supracrystals with Small Molecules

Self-assembly of nanoscale components is a widely studied bottom-up approach to formation of nano- and microdevices and structured materials. Still, a lot is unknown about what governs the structure of the nanoparticle assemblies, especially without macromolecules and in less polar solvents [1]. Magnetic nanoparticles are especially interesting because of the competition between different types of interactions and possibility of additional control with external magnetic field [2]. Here, we mixed quasi-spherical gold or magnetite nanoparticles (diameters below 10 nm) with small molecules which interact with their surfaces. The mixture crystallized from toluene by gas-phase destabilization method with a more polar non-solvent [3]. Scanning electron microscopy revealed micrometer-sized supracrystals or more disordered assemblies of clearly resolved nanoparticles, with selectivity for one or a few shapes. The supracrystallinity, shape and reversibility of the assemblies are influenced by the non-solvent and by presence of simple, small-molecule, commercially available chemicals. Elongated assemblies (suprawires) of magnetite nanoparticles are obtained in magnetic field.

References:

1. C. Yan, T. Wang, “A new view for nanoparticle assemblies: from crystalline to binary cooperative complementarity”, Chem. Soc. Rev. 2017, 46, 1483-1509.
2. G. Singh, H. Chan, A. Baskin, E. Gelman, N. Repnin, P. Král, R. Klajn, “Self-assembly of magnetite nanocubes into helical superstructures”, Science 2014, 345, 1149-1153.
3. D. Haubold, A. Reichhelm, A. Weiz, L. Borchardt, C. Ziegler, L. Bahrig, S. Kaskel, M. Ruck, A. Eychmüller, “The Formation and Morphology of Nanoparticle Supracrystals”, Adv. Funct. Mater. 2016, 26, 4890-4895.