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Title: The film formation and phase separation of spin coated polymer blends
Author: Dougherty, Eleanor Grace
ISNI:       0000 0004 7651 8017
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2019
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Polymer spin coating is a popular technique in adhering a thin film to a substrate as it can quickly produce a uniform film. The properties of a thin film can generally be controlled but the spin coating of a polymer blend solution induces phase separation, which causes morphological variations. Radial features have been noted many times but to date, a model that quantifies the film thinning away from the film centre does not exist. This could be problematic when using spin coating to make larger films. This thesis explores the film formation of poly(methyl methacrylate) and polystyrene blends cast from a toluene based solution as a function of time and radius using in situ light scattering experiments. The specularly reflected laser light is indicative of the film thickness and the off-specularly reflected light can be used to determine phase separation length scale. This experimental method is known as optospinometry. Specular data sets from numerous film radii were compared with a spin coating model that assumes no radial dependence, in order to test the validity of its assumptions. The off-specular results were compared with optical microscopy data in order to quantify the phase separation in the blended films. The results of the experiments indicate that radial variations in film thickness and structure are not always negligible and should be considered when deriving spin coating models. Numerous different effects such as a temperature gradient, varying solution flow, three-dimensional Ekman spirals and the Marangoni effect affect the film in a radial manner. The morphology of high concentration solution films (6% and 8%) clearly changes with radius yet this is not seen in lower concentration solution films (2% and 4%), that exhibit a non-uniform non-monotonic evaporation rate at different radii. This thesis also explores the interfaces between polymer trilayers after annealing. The boundaries between layered polymer structures have an interfacial width which exhibits a volume fraction gradient. Experimental interfacial widths are larger than theoretically predicted and capillary waves are theorised to contribute to this discrepancy. The disruption caused by capillary waves was investigated in polymer trilayers where the central layer was comparatively very thin. Fully disrupted central layers were observed after long annealing times, supporting the theory of capillary waves effect on the interfacial width.
Supervisor: Geoghegan, Mark ; Mears, Matthew Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available