Effects of Nanoscale Confinement and Interfaces on the Structural Relaxation of Amorphous Polymers Monitored at the Molecular Scale by Fluorescence and Dielectric SpectroscopyPublic Deposited
Over the past decade and a half, there has been considerable interest in the effect confinement and interfaces have on the properties of glass forming materials. With the emergence of nanotechnology, some glass formers, in particular polymeric glass formers, will be used at increasingly smaller length scales. An understanding of how polymeric properties are impacted by confinement and interfaces is essential to their full utilization in nanotechnology applications. The focus of this work was to investigate how confinement and interfaces impact the alpha-relaxation dynamics, the glass transition temperature (Tg), and physical aging of polymers. In this work, a unique fluorescence / multilayer method was employed to investigate confinement and interfacial effects on the Tg of a series of poly(n-methacrylate) films. Fluorescent probe-labeled polymer was selectively placed at known locations within a multilayer film. It was demonstrated that there exists a correlation between the observed deviation in Tg with confinement for single layer films and the relative strength of the deviation in Tg of free surface and substrate interface layers of the films. In addition, a novel dielectric / multilayer technique was developed allowing for measurements of the alpha-relaxation dynamics at surfaces and interfaces. The technique is analogous to the fluorescence / multilayer technique except for the choice of probe. It was illustrated that the reorientation and rotational dynamics of molecular dipole probes were coupled to the alpha-relaxation dynamics of polymer. Studies show for the first time that the alpha-relaxation dynamics at the aluminum-polymer interface are faster and broader compared to the film interior. Lastly, work presented within the dissertation investigated confinement and interfacial effects on physical aging. It was shown for the first time that physical aging could be strongly suppressed via attractive interactions between a polymer and an inorganic interface. Dielectric relaxation spectroscopy provided evidence that the suppression of physical aging with confinement is related to the reduction of alpha-relaxation dynamics with confinement. In summary, this work investigated confinement and interfacial effects on the relaxation dynamics of polymer at the glass transition (Tg), above the glass transition (alpha-relaxation dynamics), and below the glass transition (physical aging).
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