Je-Luen Li

Bending Properties of Single Functionalized Graphene Sheets Probed by Atomic Force Microscopy

We probe the bending characteristics of functionalized graphene sheets with the tip of an atomic force microscope. Individual sheets are transformed from a flat into a folded configuration. Sheets can be reversibly folded and unfolded multiple times, and the folding always occurs at the same location. This observation suggests that the folding and bending behavior of the sheets is dominated by pre-existing kink (or even fault) lines consisting of defects and/or functional groups.

Hydrophobic interaction and hydrogen-bond network for a methane pair in liquid water

We employ fully quantum-mechanical molecular dynamics simulations to evaluate the force between two methanes dissolved in water, as a model for hydrophobic association. A stable configuration is found near the methane–methane contact separation, while a shallow second potential minimum occurs for the solvent-separated configuration. The strength and shape of the potential of mean force are in conflict with earlier classical force-field simulations but agree well with a simple hydrophobic burial model which is based on solubility experiments. Examination of solvent dynamics reveals stable water cages at several specific methane–methane separations.

PHONON-INDUCED ANISOTROPIC DISPERSION FORCES ON A METALLIC SUBSTRATE

Surfactant micelles (cetyltrimethylammonium chloride) adsorbed on Au(111) exhibit orientational order dictated by the gold crystal axes. To explain this phenomenon, we take into account the ionic contribution to the dielectric response of the metal. Since the motion of an ion inside the metallic lattice is restricted by its neighbors in an anisotropic way, the total dielectric response of the metal acquires directional dependence. A crystalline substrate is thus able to generate both torque and attraction on geometrically asymmetric objects. Numerical calculations show that the resulting anisotropic van der Waals force is indeed capable of orienting rod-like dielectric micelles on a Au(111) surface.