The macroscopic motion of liquids on a flat solid surface was manipulated reversibly by photoirradiation of a photoisomerizable monolayer covering the surface. When a liquid droplet several millimeters in diameter was placed on a substrate surface modified with a calix[4]resorcinarene derivative having photochromic azobenzene units, asymmetrical photoirradiation caused a gradient in surface free energy due to the photoisomerization of surface azobenzenes, leading to the directional motion of the droplet. The direction and velocity of the motion were tunable by varying the direction and steepness of the gradient in light intensity. The light-driven motion of a fluid substance in a surface-modified glass tube suggests potential applicability to microscale chemical process systems.

The synthesis, characterization, and catalytic properties of 1-3 nm-diameter bimetallic PdAu dendrimer-encapsulated catalysts are reported. Both alloy and core/shell PdAu nanoparticles were prepared. The catalytic hydrogenation of allyl alcohol was significantly enhanced in the presence of the alloy and core/shell PdAu nanoparticles as compared to mixtures of single-metal nanoparticles.

Bifunctionalized poly(amidoamine) dendrimers having both quaternary ammonium groups and primary amines on their periphery were prepared. Pd and Pt nanoparticles were encapsulated within these dendrimers by extraction of the metal ions into their interior, followed by chemical reduction. The high positive charge on the surface of these dendrimers reduces the likelihood of agglomeration, and the unquaternized amine groups provide a reactive handle for immobilizing the dendrimer-encapsulated nanoparticles (DENs) onto surfaces. High-resolution transmission electron microscopy images reveal that both encapsulated Pd and Pt nanoparticles are nearly monodisperse with an average diameter of 1.7 ( 0.3 nm. Pd and Pt DENs were immobilized onto Au surfaces using an intermediary self-assembled monolayer as an adhesion layer. Only a small fraction of the resulting nanoparticle monolayer is lost when sonicated in an acidic aqueous solution or subjected to electrochemical cycling.

This paper describes the correlation between the ability to control nematic liquid crystal (LC) alignment and wetting properties of mixed monolayers formed by coadsorption of two O-octacarboxymethylated calix[4]resorcinarenes (CRA-CMs) with either perfluorooctyl-or octylazobenzene units. Photoirradiation of CRA-CM monolayers induces reversible photoisomerization reaction of the surface azobenzenes, which causes changes in LC alignment and wettability of the monolayers. The photogenerated LC alignments are considerably influenced by the surface compositions of the mixed monolayers. When LC cells fabricated with substrate plates modified with single-component monolayers of CRA-CM with p-octylazobenzenes are subjected to oblique irradiation with non-polarized UV light, the orientation of LC molecules is changed from homeotropic to homogeneous alignments tilting toward the direction of light propagation. In contrast, singlecomponent and mixed monolayers of CRA-CM with p-perfluorooctylazobenzenes cause homeotropic alignments and tilted alignments with high pretilt angles, respectively. The level of photoisomerization and surface free energy of the CRA-CM monolayers are not a sufficient condition to cause the contrasting alignment behaviors. We conclude that the molecular-level morphology and/or fluidity of the monolayer surfaces of CRA-CMs, which is deduced from the contact angle hysteresis of anisotropic liquids for the surfaces, is the most significant factor to induce the LC alignment alterations observed.