Confinement-Induced Changes in the Glassy Dynamics and Crystallization Behavior of Supercooled Fenofibrate

Abstract

Here, we have studied the effect of spatial restrictions on the molecular dynamics and crystallization behavior of modeled lipophilic drug fenofibrate incorporated into nanoporous aluminum oxide membranes of different pore size. Our measurements demonstrate that, on subsequent cooling, dynamics of confined liquid split up into two distinct fractions, due to the presence of core and interfacial layers. At the temperature, at which vitrification of the interfacial layer takes place ( T g_interface ), departure from the bulk-like behavior occurs, and molecules in the center of the pores enter quasi-isochoric conditions. Depending on the thermal protocol and pore size, the volume fixed at T g_interface might be a bit different so as the core liquid’s dynamics. Interestingly, below that temperature, the nanoconfined liquid can still obey the fundamental density scaling relation (1/ TV γ ), just like in the bulk phase, while not necessarily isochronal superposition. This is in contrast to a common observation that the validity of the density scaling in bulk glass-forming systems always goes together with isochronal superposition of the α-relaxation, and vice versa. Finally, our careful analysis of the crystallization kinetics as a function of lowering pore diameter indicates for systematic slowing down crystallization progress, the shift of the maximum crystallization rate toward higher undercooling and decrease in the dimensionality of growing crystals.