Regulation of the Interfacial Effects of Thin PolystyreneFilms by Changing the Aromatic Group Structure on Substrate Surfaces

In this article, interfacial π–π interactions of polystyrene (PS) chains next to aromatic-modified substrates were investigated. The results show that the glass transition temperature (Tg) and the modulus of the supported thin PS films increased gradually from phenyltrimethoxysilane-, naphthalenetrimethoxysilyl- to 9-anthracenyltrimethoxysilane-modified substrates with the increasing number of π electrons. For the p-tolyltrimethoxysilane (p-tolyl)-modified substrates, a very weak interfacial effect was observed. As revealed by sum frequency generation (SFG), the phenyl rings in the deuterated PS (dPS) side chains were perpendicular to the interface, which was induced by the anchored aromatic groups on the surface via the parallel-displaced configuration of the π–π interactions. Enhanced interfacial interactions with an increasing number of π electrons on the surface were revealed in which the peak area of the redshifted wavenumber of the ν2 C–D stretching vibration in dPS caused by π–π interactions increa...