Are polymers glassier upon confinement?

Glass forming systems are characterized by a stability against crystallization upon heating and by the easiness with which their liquid phase can be transformed into a solid lacking of long-range order upon cooling (glass forming ability). Here, we discuss on the the thickness dependence of the thermal phase transition temperatures of poly(L-lactide acid) thin films supported onto solid substrates [1]. The determination of the glass transition (T$_{g}$), cold crystallization (T$_{CC}$) and melting (T$_{m}$) temperatures down to a thickness of 6 nm via ellipsometry, permitted us to build up parameters describing glass stability and glass forming ability. We observed a strong influence of the film thickness on the latter, while the former is not affected by 1D confinement. Remarkably, the increase in T$_{g}$/T$_{m}$ ratio, a parameter related to glass forming ability, is not accompanied by an increase in T$_{CC}$-T$_{g}$, as observed on the contrary, in bulk metallic glasses. We explained this peculiar behavior of soft matter in confinement considering the impact of irreversible adsorption on local free volume content [2]. [1] J. Spiece et al. Soft Matter, 2015,11, 6179-6186 [2] Non-equiibrium Phenomena in Confined Soft Matter, S Napolitano (ed.) Springer, 2015