Younjin Min, Chemical Engineering, University of California, Santa Barbara, Engineering II, Santa Barbara, CA 93106, Mustafa Akbulut, Chemical Engineering, Princeton University, Olden st., E-quad A-306, Princeton, NJ 08544, Yuval Golan, Department of Materials Engineering, Ilse Katz Institute of Nanotechnology, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel, Joseph A. Zasadzinski, Department of Chemical Engineering, University of California, Santa Barbara, CA 93106, and Jacob N. Israelachvili, Chemical Engineering, University of California at Santa Barbara, 3357 Engineering II, Santa Barbara, CA 93106-5080.
This presentation describes the study of the fundamental inter-nanoparticle interactions which govern the self- or directed-assembly of functionalized nanoparticles into hierarchical nanostructures, and the exploration of the conditions required for these processes by monitoring the structural evolution of nano-structured films. The effects of shape on nanowire interactions and shear-induced ordering were studied. Both the normal and lateral forces were sensitive to the particles' curvature. (i) No adhesion was observed between the confining surfaces, and the force profiles were short-ranged and mostly reversible for straight wires but longer-ranged and irreversible for curved wires. (ii) Structural phase transitions can occur in confined nanoparticle films. (iii) During shearing, straight wires order or align more easily than curved wires. Also the effects of humidity (water content or activity from 0 to ~0.98) on the frictional properties of surfactant-coated ZnS nanoparticles of various shapes, specifically, nanorods and nanowires were investigated.