The substrate roughness is a very important parameter that can influence the properties of supported thin films. In this work, we investigate the effect of surface roughness on the properties of a vapor-deposited glass (celecoxib, CXB) both in its bulk and in confined states. Using dielectric spectroscopy, we provide experimental evidence depicting a profound influence of surface roughness on the α-relaxation dynamics and the isothermal crystallization of this vapor-deposited glass. Besides, we have verified the influence of film confinement on varying values of surface roughnesses as well. At a fixed surface roughness value, the confinement could alter both the dynamics and crystallization of vapor-deposited CXB.

The physicochemical properties of polymers can be modified by spatial configuration. Here, dielectric spectroscopy (DS) was employed to investigate the effect of the tacticity on the glass-transition dynamics of confined polymer films. We have also carried out dielectric relaxation studies at ambient and elevated pressure conditions. High-pressure measurements provide information on the sensitivity of the glass-transition dynamics to density changes, which can be helpful to better understand the confinement effect. For our study, we have chosen a glass-forming polymer, poly(methyl methacrylate) (PMMA), with two different tacticities (isotactic and syndiotactic) and an approximately equal molecular weight. We have shown that the segmental relaxation for the bulk syndiotactic PMMA is observed at a higher temperature range compared to the bulk isotactic PMMA. The experimental data analysis has also revealed that the molecular order influences the behavior of the polymer under increased pressure. The glass-transition dynamics of isotactic PMMA is more sensitive to the pressure/density changes than syndiotactic PMMA. Finally, we have also demonstrated that tacticity has a significant impact on the segmental dynamics of the confined polymer films. Syndiotactic PMMA has a stronger interaction with the substrate than isotactic PMMA, which is indicated by the higher amount of irreversibly adsorbed polymer chains. For this reason, the segmental dynamics of s-PMMA thin films follows the bulk behavior. In contrast, for i-PMMA, the confinement effects are pronounced, and the glass-transition dynamics accelerate with the reduction of the thickness of thin films.

Geometric nanoconfinement, in one and two dimensions, has a fundamental influence on the segmental dynamics of polymer glass-formers and can be markedly different from that observed in the bulk state. In this work, with the use of dielectric spectroscopy, we have investigated the glass transition behavior of poly(2-vinylpyridine) (P2VP) confined within alumina nanopores and prepared as a thin film supported on a silicon substrate. P2VP is known to exhibit strong, attractive interactions with confining surfaces due to the ability to form hydrogen bonds. Obtained results show no changes in the temperature evolution of the α-relaxation time in nanopores down to 20 nm size and 24 nm thin film. There is also no evidence of an out-of-equilibrium behavior observed for other glass-forming systems confined at the nanoscale. Nevertheless, in both cases, the confinement effect is seen as a substantial broadening of the α-relaxation time distribution. We discussed the results in terms of the importance of the interfacial energy between the polymer and various substrates, the sensitivity of the glass-transition temperature to density fluctuations, and the density scaling concept.