Study of Soft Photonics Materials using an Optical Shear Cell

(supervisor: Chris Finlayson)

Nature of project: experimental, software

Available to full-time physicists or joint students.

Project description and methodology

All the laws of optics that you know are based on the assumption that optical media are fairly uniform. These laws break down completely when we make materials which are structured on the sub-micron size-scale of the wavelength of light often called "photonic crystals".[1] New effects are then possible such as photonic bandgaps, super-prisms, slow light, and optical switching. Most photonic crystals are made using extremely expensive fabrication equipment and cover areas less than 1mm^2. However, we use a new process for making photonic crystals which depends on the self-assembly of sub-micron sized plastic spheres, and allows us to make sheets of "polymer opals" which are metres long.[2] Iridescence is produced which comes only from the structural order rather than absorption by a dye; this is known as structural colour and has a number of important analogues in nature.[3]

In this project, the student will study the ordering of viscoelastic polymer opal samples in real time, using a recently commissioned Optical Shear Cell instrument to make spectroscopic measurements on samples.[4]

A successful project will develop beyond the above in one/some of the following directions:
Development of simple coding routines to handle data sets of multiple spectra. Imaging and video recording of the development of structural colour in polymer opals under shearing, using the integral dark-field optical microscope.

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: Expanding parametric study of shear-ordering processes to explore effect of temperature, viscosity, shear-rate and -amplitude. At Y4 level, this could potentially feed into the development of intuitive theoretical models.

Initial literature for students:

  1. http://en.wikipedia.org/wiki/Photonic_crystal
  2. C. E. Finlayson et al., Adv. Mater., vol. 23, p1540 1544 (2011)
  3. P. Vukusic and J. R. Sambles, Nature, vol. 424, p852 855 (2003)
  4. D.R.E.Snoswell et al., Phys. Rev. E, vol.92, 052315

Novelty, degree of difficulty and amount of assistance required

Students will need to be trained on a number of new pieces of lab equipment relating to spectroscopic techniques. Appropriate assistance and training will be given.

Project milestones and deliverables (including timescale)

milestoneto be completed by
Equipment familiarisationChristmas
Data collectionend of February
Collation and data processingmid-March
Analysis/result phaseEaster

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