Glass Transition Dynamics of Poly(phenylmethylsiloxane) Confinedwithin Alumina Nanopores with Different Atomic Layer Deposition(ALD) Coatings

Dielectric spectroscopy (DS) and differential scanning calorimetry (DSC) were employed to study the effect ofchanges in the surface conditions on the segmental dynamics of poly(phenylmethylsiloxane) confined in alumina nanopores (AAO).The inner surface of the pores was modified by using the atomic layer deposition technique. Coated membranes include 5 nm thicklayers of hafnium oxide, titanium oxide, and silicon oxide, exhibiting different wetting properties. Modification of the surfaceconditions dramatically affects the interfacial interactions between the polymer and confining surface. The interfacial energycalculations indicate a decrease of gamma SLvalue from 18.7 mN/m in SiO2-coated to 0.5 mN/m in HfO2-coated nanopores. The results ofthe dielectric relaxation study demonstrate that the segmental relaxation time of confined PMPS 2.5k depends on the thermaltreatment protocol and the hydrophilic/hydrophobic character of the pore walls. From calorimetric measurements, we found thatthe two glass transitions events are still observed, even in the absence of strong interfacial interactions. Values of bothTgs do notdepend strongly on the chemical nature of the surface. In this way, changes in the glass-transition behavior of the tested polymerconfined in ALD-coated nanopores cannot be rationalized in terms of the polymer/substrate interfacial energy. Eliminating stronglyadhered surfaces does not eliminate the puzzling two-Tgseffect seen in cylindrical nanopores.