Physics projects for Y3 and Y4 students

Project description

Quantitative imaging of polymer blend films

(supervisor: Rudi Winter)

Nature of project: data analysis, experimental

Available to students on full-time physics degree schemes only.

Project description and methodology

Polymer blends consist of two phases with chemically opposite functionalisation, i.e. they can be dissolved differentially in various solvents. This means the two phases don't mix, which gives rise to a wide variety of morphologies from micelles, cylinders, lamellae, inter-penetrating gyroid structures to disordered forms. We try to utilise phase transitions between these forms to push embedded inorganic nano-particles into desirable configurations, e.g. to align photovoltaic absorber particles to avoid short circuiting a thin-film solar cell.

This undergraduate project aims to explore the phase diagram of simple polymer blends with and without embedded nano-particles and to identify external stimuli which can trigger phase transitions, such as film thickness, solvent vapour atmosphere or strain in the film. It uses optical microscopy and other techniques to determine the morphology of the films under various conditions.

A successful project will develop beyond the above in one/some of the following directions:
For a successful project, relevant morphologies will be analysed quantitatively using the Gwyddion image analysis software to find correlation lengths and internal surface areas. Some straightforward Python coding may be required to combine and plot data.

A potential development of the project could include using atomic force microscopy to extend the size range of features investigated. The AFM images need to be analysed in the same comprehensive way as the optical micrographs described above.

Another potential development would use ellipsometry to study film thickness. This would entail setting up a model of the layer structure of the film and writing Python code to fit the model to the ellipsometer data.

When considering where to take your project, please bear in mind the time available. It is preferable to do fewer things well than to try many and not get conclusive results on any of them. However, sometimes it is useful to have a couple of strands of investigation in parallel to work on in case delays occur.

Additional scope or challenge if taken as a Year-4 project: For a Y4 project, the student will be expected to model the phase diagram of the chosen polymer blend in terms of molar weight ratio and Flory-Huggins parameter (encompassing temperature and the polarity of both phases) based on initial experiments in order to predict morphologies prevalent in other areas of the phase diagram by extrapolation. Some of these predictions should be tested in a final experimental period at the end of the project.

Please speak to Rudi Winter if you consider doing this project.

Initial literature for students:

  1. Xinchang Pang et al.; Nanoscale 5 (2013) 8695
  2. http://gwyddion.net/
  3. R Toomey et al.; Macromolecules 37 (2004) 905

Novelty, degree of difficulty and amount of assistance required

Partial phase diagrams of various polymer blend systems are already available in the literature but typically do not cover the entire parameter space. The response to external stimuli is genuinely open-ended research.

Project milestones and deliverables (including timescale)

milestoneto be completed by
familiarise with microscope and Gwyddionend of November
parameter space finalisedChristmas
complete set of images takenend of February
Gwyddion analysis completeEaster

Students taking this project will have to submit a full risk assessment form