Herein we show that the nanostructured interface obtained via modulation of the pore size has a strong impact on the segmental and chain dynamics of two poly(propylene glycol) (PPG) derivatives with various molecular weights (Mn = 4000 g/mol and Mn = 2000 g/mol). In fact, a significant acceleration of the dynamics was observed for PPG infiltrated into ordinary alumina templates (Dp = 36 nm), while bulklike behavior was found for samples incorporated into membranes of modulated diameter (19 nm < Dp < 28 nm). We demostrated that the modulation-induced roughness reduces surface interactions of polymer chains near the interface with respect to the ones adsorbed to the ordinary nanochannels. Interestingly, this effect is noted despite the enhanced wettability of PPG in the latter system. Consequently, as a result of weaker H-bonding surface interactions, the conformation of segments seems to locally mimic the bulk arrangement, leading to bulklike dynamics, highlighting the crucial impact of the interface on the overall behavior of confined materials.
Keywords: aluminum oxide porous templates; confinement effect; dielectric spectroscopy; glass transition; interface roughness; surface effect.