Nanoconfinement of Ionic Liquid and Polymers in Supported Thin Films: A Time-of-Flight Secondary Ion Mass Spectrometry Study of Surface Diffusion

Abstract

To gain insights into properties of a room-temperature ionic liquid in confined geometry, 1-ethyl-3-methylimidazolium bis[trifluoromethanesulfonyl]imide ([emim][Tf2N]) adspecies interacting with various substrates was investigated as a function of temperature by using time-of-flight secondary ion mass spectrometry. The monolayer of adspecies is incorporated into substrates of porous Si, self-assembled monolayers, and Li[Tf2N] at 180–190 K that is slightly greater than the bulk glass transition temperature, Tg, of [emim][Tf2N]. In contrast to simple glass formers, no surface diffusivity is observed for [emim][Tf2N] in the sub-Tg region. The uptake of [emim][Tf2N] into polymer films is associated with the surface mobility of polymer segments rather than adspecies. The mobility of poly(methyl methacrylate) is not quenched by hydrogen bonds with the substrate, as evidenced by that the uptake onset of [emim][Tf2N] is almost independent of the polymer film thickness.