Thermal and UV stability of organic glasses under extreme nanoconfinement

Extreme nanoconfinement of organic glasses can be achieved by Capillary Rise Infiltration onto self-assembled films of nanoparticles (NPs). Here we investigate thermal and UV degradations of highly confined indomethacin (IMC, T_g = 316 K) in silica NPs (3 – 30 nm average pore sizes). Upon confinement in ~ 3 nm pores, a T_g increase of ~ 30 K is observed along with a factor of ~ 7 slow-down of thermal degradation rate at elevated temperatures (T_g +137 K) under N₂. These observations are consistent with previous measurements in polystyrene, where thermal stability was correlated with T_g increase. UV degradation under both low O₂ and ambient conditions was explored at room temperature (T_g - 20 K). We show that the interplay between entropic and enthalpic effects under extreme nanoconfinement also leads to substantial stability towards UV degradation, however the details highly depend on the specific reaction pathways under these two conditions, both of which are kinetically limited by the transport of O₂ and/or CO₂. UV degradation mass loss rate is slowed down by a factor of ~ 20 (at 365 nm) under ambient conditions, while mass loss is only observed at the near surface region of the composites at low O₂ condition (at 254 nm).