In situ vacuum ellipsometry approach to investigation of glass transition behavior in ionic liquid thin films

Glass transition behavior of vacuum-deposited ionic liquid thin films was investigated by in situ ellipsometry. The glass transition temperatures of [omim][TFSA] thin films (≥50 nm) were determined from the temperature-dependent light ellipticity and found to be almost identical to the bulk value regardless of the thickness. Moreover, it was suggested that the sequentially deposited [omim][PF₆]/[omim][TFSA] bi-layer film became homogeneous and had one glass transition temperature close to the value of the corresponding bulk mixture for each weight fraction, which could be explained by the theoretical fast mutual diffusion of ILs within the film relative to the total deposition time.