Asymmetric orientation of toluene molecules at oil-silica interfaces

Nanoscale Faceting and Ligand Shell Structure Dominate the Self-Assembly of Nonpolar Nanoparticles into Superlattices

Self-assembly of nanoscale structures at liquid-solid interfaces occurs in a broad range of industrial processes and is found in various phenomena in nature. Conventional theory assumes spherical particles and homogeneous surfaces, but that model is oversimplified, and nanoscale in situ observations are needed for a more complete understanding. Liquid-phase scanning transmission electron microscopy (LP-STEM) is used to examine the interactions that direct the self-assembly of superlattices formed by gold nanoparticles (AuNPs) in nonpolar liquids. Varying the molecular coating of the substrate modulates short-range attraction and leads to switching between a range of different geometric structures, including hexagonal close-packed (hcp), simple hexagonal (sh), dodecahedral quasi-crystal (dqc), and body-centered cubic (bcc) lattices, as well as random distributions. Langevin dynamics simulations explain the experimental results in terms of the interplay between nanoparticle faceting, ligand shell structure, and substrate-NP interactions.

Investigation of Capillary Filling Dynamics of Multicomponent Fluids in Straight and Periodically Constricted Microchannels

An extensive study of capillary flow of fluids with various viscosities in straight and periodically constricted microchannels with different surface wettability is presented. Capillary filling speed in hydrophilic, less hydrophilic, and hydrophobic microchannels were experimentally monitored and compared with the Washburn theoretical model. For all liquids, a linear relationship was found between the square of propagation distance and time, which is expected for Newtonian fluids. Experimental results indicated slower velocity compared to the theoretical prediction due to simplifications of the Washburn model. Capillary filling speed of fluids into long-fluororinated chain silane modified channels confirmed the expected lyophobic nature of the coating (i.e., not favorable for either hydrophilic or hydrophobic liquids). Presence of the precursor film ahead of the three-phase contact line in the microscopic level was demonstrated. White light and fluorescent images confirmed the presence of precursor film and capillary evaporation at the interface. Evaporation enhanced the deviation between experimental and theoretical results due to continuous wettability alteration of penetrating fluid.