Polymer-coated PtCo nanoparticles deposited on diblock copolymer templates: chemical selectivity versus topographical effects.

Metal-polymer hybrid films are prepared by deposition of polymer-coated PtCo nanoparticles onto block copolymer templates. For templating, a thin film of the lamella-forming diblock copolymer poly(styrene-b-methyl methacrylate) P(S-b-MMA) is chemically etched and a topographical surface relief with 3 nm height difference is created. Two types of polymer-grafted PtCo nanoparticles are compared to explore the impact of chemical selectivity versus the topographical effect of the nanotemplate. A preferable wetting of the polystyrene (PS) domains with poly(styrenesulfonate) (PSS)-coated PtCo nanoparticles (instead of residing in the space between the domains) is observed. Our investigation reveals that the interaction between PSS-coated nanoparticles and PS domains dominates over the topographical effects of the polymer surface. In contrast, a non-selective deposition of poly(N-vinyl-2-pyrrolidone) (PVP)-coated PtCo nanoparticles and the formation of large metal-particle aggregates on the film is observed.

Surface processes during sorption of aromatic molecules on medium pore zeolites.

The elementary steps of sorption and transport of benzene, toluene, and o- and p-xylene from the gas phase to hydroxy groups of zeolite H/ZSM-5 on the outer surface (SiOH groups) and in the pores (SiOHAl groups) were studied using pressure modulations followed by fast time-resolved IR spectroscopy. Sorption on these acid sites occurs via a common physisorbed state on the outer surface. The equilibration of the molecules in this state is fast compared to the sorption rates on SiOH and SiOHAl groups. The relative rates of equilibration of functional groups with the aromatic molecules suggest that the aromatic molecules move freely on the surface of the outer surface before reversibly binding to OH groups, entering the micropores or desorbing. Molecules able to enter into the pores (benzene, toluene, p-xylene) adsorb faster on SiOHAl groups than on SiOH groups. If the access of the molecules into the pores is sterically constrained (o-xylene), the rate of adsorption on the remaining accessible SiOH groups is strongly enhanced.