The stability or wettability of thin polymer films on solids is of vital interest in traditional technologies as well as in new emerging nanotechnologies. We report here that nanoscale structures of polymer chains adsorbed onto a solid surface play a crucial role in the thermal stability of the film. In this study, polystyrene (PS) spin-cast films (20 nm in thickness) with eight different molecular weights prepared on silicon (Si) substrates were used as a model. When low molecular weight (Mw≤ 50 kDa) PS films were subjected to thermal annealing at temperatures far above the bulk glass transition temperature, dewetting occurred promptly, while high molecular weight (Mw≥ 123 kDa) PS films were stable for at least 6 weeks at 150 °C. We reveal a strong correlation between the film stability and the two different interfacial structures of the adsorbed polymer chains: their opposing wettability against chemically identical free polymer chains results in a wetting-dewetting transition at the adsorbed polymer-free polymer interface. This is a unique aspect of the stability of polymer thin films and may be generalizable to other polymer systems regardless of the magnitude of solid-polymer attractive interactions.

Silver orthophosphate (Ag 3 PO 4 ) had been reported as an excellent candidate to split water or decompose pollutants with high efficiency in visible light region, yet is not stable due to the reduction of silver ion. In this work, an easy-fabricated method (in situ photoinduced reduction) was provided to enhance the stability of Ag 3 PO 4 for its possible application as a visible-light sensitive photocatalyst. The as-prepared samples were characterized by X-ray diffraction (XRD), UV-vis diffuse reflectance spectra, photoluminescence spectra (PL) and Photoelectrochemical measurements. The Ag 3 PO 4 /Ag photocatalysts showed strong photocatalytic activity for decomposition of RhB dye or phenol-X-3B mixture under visible light irradiation (λ> 420 nm) and can be used repeatedly. The possible mechanism for the enhanced photocatalytic properties of the Ag 3 PO 4 /Ag hybrid was also discussed. It was found that •OH and holes take priority over •O 2 ‾ radicals in serving as the main oxidant in the Ag 3 PO 4 /Ag photocatalytic system. Especially, the experimental results indicate that the surface plasmon resonance of Ag nanoparticles and a large negative charge of PO 4 3-ions as well as high separation efficiency of e--h + pairs, facilitated the enhancement of the photocatalytic activity of the Ag 3 PO 4 /Ag composite. The results indicated that Ag 3 PO 4 /Ag is an efficient and stable visible-light-driven photocatalyst.

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