Dr Richard Thompson, (Senior Research Fellow)

Personal web page

(email at r.l.thompson@durham.ac.uk)

Research Interests

The small mixing entropy of polymer blends means that even weak interactions can have a profound effect on the phase behaviour and surface segregation of components. We exploit this process and prepare new materials with specific surface properties such as hydrophobicity or chemical reactivity without detriment to bulk properties such as physical strength or optical clarity. Clear analogies can be drawn between the behaviour of surface-modifying polymers in blends and surfactants in solution. Both exhibit a critical micelle concentration at the point of maximum surface coverage, and micelle size is clearly linked to amphiphilic strength.¹

Figure 1. (left) Our ion beam accelerator facility and (right) nuclear reaction analysis data obtained using this equipment to establish the concentration profile of deuterium labelled polymers in blended films.

Influence of solvents on polymer adsorption and diffusion

Polymer processing frequently makes use of organic solvents and we have used ion beam and optical techniques to explore for the first time the relationship between the ingress of a penetrating solvent vapour or nonsolvent and the interdiffusion of polymer chains that can accompany this process.^2,3  Not only does this allow us to understand how to make efficient use of organic solvents, but is leads to new opportunities in polymer self-organisation. We have also shown that it is possible to anneal polymers under high surface-energy non-solvents including some ionic liquids to promote surface segregation of polar groups to a polymer surface.^3,4

Figure 2. Volume fraction versus depth profiles obtained for thin films of blends containing functional polymers determined by ⁴He(¹H,¹H)⁴He ERDA. The organisation of these polymers was attained by exposure of samples to solvent vapour. 

Semi-crystalline polymer films

Many polymers are partially crystalline, including most conducting polymers. It is known that self-organisation of conducting polymers in devices is vital to their performance, but it is not trivial to characterise this behaviour. We have shown that ion beam analysis is a versatile technique that can readily determine the near-surface and interfacial distributions of conducting polymers in semi-crystalline blends.⁵

Figure 3. AFM image of the crystalline surface of a thin (100 nm) PEO. The structure seen is due to the spontaneous crystallisation of this polymer, which is acutely sensitive to film thickness and humidity.

Research group members make use of our unique combination of in-house experimental facilities, including ion beam analysis and AFM, which are supplemented by beamtime allocations at the national ion beam and neutron facilities. There are strong collaborative links with the members of the Durham Centre for Soft Matter and North East Polymer Association.

References

1. I. A. Ansari, N. Clarke, L. R. Hutchings, A. Pillay-Narrainen, A. E. Terry, R. L. Thompson, J. R. P. Webster, Langmuir, 2007, 23, 4405-4413.
2. R. L. Thompson, M. T. McDonald, J. T. Lenthall, L. R. Hutchings, Macromolecules, 2005, 38, 4339-4344.
3. L. R. Hutchings, C. J. R. Douglas, C. L. Rhodes, W. D. Carswell, M. W. A. Skoda, J. R. P. Webster, and R. L. Thompson; Langmuir, 2010, 26, 19, 15486-15493,
4. A. P. Narrainen, N. Clarke, S. M. Eggleston, L. R. Hutchings, R. L. Thompson, Soft Matter, 2006, 2, 981-985.
5. S. Goffri, C. Mueller, N. Stingelin-Stutzmann, D. W. Breiby, C. P. Radano, J. W. Andreasen, R. Thompson, R. A. J. Janssen, M. M. Nielsen, P. Smith, H. Sirringhaus, Nature Materials, 2006, 5, 950-956.