Ternary phase separation during spin casting

Lead Research Organisation: University of Sheffield
Department Name: Physics and Astronomy


Spin coating is a widely used tool in the manufacture of very smooth and very thin polymer films. For example, it is routinely used on a massive scale for making integrated circuits and colour filters for liquid crystal displays. It is likely to be a centrally important processing step in the emerging field of polymer electronics. The most common situation is the spin coating of a polymer solution (a polymer dissolved in a solvent). A flat disc, which has been flooded with the solution, is rotated at speeds of up to 10,000 revolutions per minute. This results in a uniform coating of solution. The solvent then rapidly evaporates to leave a very smooth and high quality film of pure polymer. A more complicated situation, that has great technological potential, occurs when two polymers are spun from a common solvent. Most chemically different polymers do not like to mix, but if diluted enough in a solvent favourable to both polymers a mixed solution forms. However, the two polymers will separate from each other as the solvent evaporates. Significantly, this can result in a wide variety of microstructures in the final films. These can range from two well defined layers to situations in which lateral phase separation takes place on a variety of length-scales, from nanometres to many micrometres. In thin films of, for example, semiconducting polymers used in light emitting diodes and photovoltaic devices, the device efficiency depends critically on the microstructure. Hence, if one understands how to control the microstructure, one can achieve an optimised film in a single, inexpensive processing step.


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Description Spin coating is a common means of creating thin films of reproducible and controlled quality, with uniform thickness and smoothness. It is used in common technologies such as compact discs. We have investigated the process of spin coating polymer films, in order to understand the physics of the technology. We have understood that inertial forces (due to the mass of solution) in the process and have characterised this. We have also been able to gain some understanding of the energy of the solution as the solvent evaporates, We have also applied this experimental knowledge to perovskite materials, a new means of creating solution processable solar cells.
Exploitation Route These technologies are useful for improving the means that we can coat surfaces. The output so far has been rather technical, but it remains nonetheless important.
Sectors Electronics

Description The student graduated last year; a first paper has just been published, and a second paper is ready for submission. The work is being continued with another student continuing this work. The first student, funded on the grant has since been employed at the Welsh Centre for Printing and Coating, and outcome that inherently recognises the training provided by the grant.
First Year Of Impact 2014
Sector Electronics,Other
Impact Types Societal

Description Swansea University 
Organisation Swansea University
Country United Kingdom 
Sector Academic/University 
PI Contribution Youmna Mouhamad met Jenny Baker from Swansea at a conference and suggested they try their perovskite experiments on the in situ light scattering in Sheffield. The experiments worked and the data were published.
Collaborator Contribution The partners supplied the perovskite samples
Impact One publication in IET Renewable Power Generation. The PhD student hired on this EPSRC grant is now working in Swansea
Start Year 2014