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Title: Controlling the morphology of spin coated polymer blend films
Author: Mokarian-Tabari, Parvaneh
ISNI:       0000 0004 2702 0706
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2010
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Thin films of polymer mixtures made by spin-coating can phase separate in two ways - by forming lateral domains, or by separating into two distinct layers. The latter situation - self-stratification or vertical phase separation - could be advantageous in a number of practical applications, such as polymer photovoltaics. In our experiments, we have used time-resolved small-angle light scattering and light reflectivity during spin coating to study the structure development in PS/PMMA and PFB/F8BT blends, solution cast in toluene. A sample cell was designed, made and mounted on the apparatus to manipulate the evaporation rate. Having solved the Meyerhofer equation for thinning rate and by fitting the model to the experimental data, we are able to extract the evaporation rate of toluene during spin coating. We demonstrate that, by controlling the evaporation rate during the spin-coating process, we can obtain either selfstratification or lateral phase separation in the same system. We relate this to a previously hypothesised mechanism for phase separation during spin coating in thin films, according to which a transient wetting layer breaks up due to a Marangoni-type instability driven by a concentration gradient of solvent within the drying film. Our results show that a high evaporation rate leads to a laterally phase separated structure, while reducing the evaporation rate suppresses the interfacial instability and leads to a self-stratified final film. Using the set up we developed to control the morphology through evaporation rate, we made preliminary photovoltaic devices. It is possible to control the efficiency of the polymer photovoltaics by means of process parameters such as evaporation rate.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available