Altobelli, Rosaria (2017) Assembly, Elasticity, and Structures of Nanoparticles in Immiscible Polymer Blends. [Tesi di dottorato]

Preview

Text Altobelli_Rosaria_30_completa.pdf Download (6MB) | Preview

Collection description

Introducing nanoscale fillers into polymer matrices can serve as a means to compatibilize polymer blends and represents a clever way to manipulate their morphology at the micro-scale. Such a novel “compatibilization” strategy represents a viable route for optimizing the performance of polymer systems, which are ubiquitous in the modern society. The effects of nanoparticles on the micrometer-sized arrangement of the polymer phases, however, are difficult to predict, and most of the recent literature on this topic lack in terms of generality. Many issues remain unclear, and even well-established phenomena are actually far from being fully understood. Is the origin of the uneven distribution of the filler in a multiphase host matrix merely dictated by thermodynamic arguments? Is it possible to drive the systems towards desired non-equilibrium configurations? How the filler affects the blend microstructure? And how the fluids in turn affect the nanoparticle assembly? This dissertation addresses these matters from both a theoretical and a practical point of view, shedding light on the sequence of events which determine the final morphology of nanoparticle-containing polymer blends through a combination of morphological and rheological analyses. In the first experimental part of this study, the physical mechanisms that govern the melt-state microstructural evolutions of polymer blends in the presence of nanoparticles are elucidated through a combination of several analyses and measurements. Using ternary blends of polystyrene (PS), poly(methyl methacrylate) (PMMA), and clay nanoplatelets we prove the generality of the mechanism of morphology stabilization by interfacial crowding of the nanoparticles, which keeps working in spite of the high viscosity of the liquid phases and the plate-like shape of the nanoparticles. The effect of the co-continuous morphology of the host matrix is highlighted through a comparative analysis with systems based on the same polymers and nanoparticles, but in which the matrix is either a single polymer or a drop-in-matrix blend. This allows us to emphasize the role of the multiphase nature of the host medium in driving the nanoparticle assembly. In particular, the elasticity and structure of the three-dimensional filler network which forms above Φc were studied in detail by resorting to the percolation theory. As regards the second part of the study the attention was paid to systems in which the filler gathers inside either of the polymer phases. Nanoclays with different hydrophobicity were selected to evaluate their localizations and consequently their effect on the blend. According to the research findings, it was emerged that the refinement ability of the filler was slightly better in the case of bulk localization, but interfacial nanoplatelets were more effective in stabilizing co-continuous morphologies against phase coarsening in the melt state. Foreground arising from the work carried out, regarding the nanoparticle-induced morphological modifications in multiphase systems, preliminary analyses were exploited for assessing the effect of nanoparticle morphology on the beginning systems.

Downloads

Actions (login required)

View Item