Dr Nigel Clarke

(email at nigel.clarke@durham.ac.uk)

Research Interests

I have research interests in both experimental and theoretical aspects of soft condensed matter, a field of research that is concerned with materials that range from liquid crystals for display technology to biological membranes. My current work focuses on the phase behaviour of multi-component systems and the effects of flow on structure.

Phase Separation and Target Morphologies in Polymer Blends

Can we improve the properties of polymers by combining two or more different starting materials? It has been known for a long time that the answer is yes. However, it isn't easy to persuade polymers with different chemical structures to mix at a molecular scale; but rather than deterring scientists, many have actually used this fact to their advantage. Unusual, elegant and, more importantly (economically speaking), technologically useful structures emerge when polymer blends phase separate. We have recently proposed a novel method for targeting unusual morphologies^1,2. As shown in the figure, by controlling the routes to phase separated structures, it is possible to generate complex morphologies. To further extend these ideas, we are also working on the coupling between dewetting and phase separation in technologically significant thin-film binary mixtures³.

Reaction Induced Phase Separation

An area of fascination for me is reaction induced phase separation in polymer and polymer based blends. This process is used in many systems from high-tech composites for the aerospace industry to adhesives for bus panels. The mechanical properties of such materials are known to be dependent on both the length-scale of the final morphology and the interfacial adhesion between phases. It is therefore important to understand the static and dynamic processes that control the length-scales and the strength of the interface, as the morphology develops during the phase separation process⁴. A range of techniques, including rheology, light scattering and microscopy are used to study the structural development in these blends. A current focus of my work is the interplay between morphology and the chemistry of polymerisation.

Effects of Flow on Structure

We have recently developed techniques for probing the effect of flow on structure and morphology in polymer melts, solutions and blends. Many polymeric systems are subjected to quite complex flows during processing. We aim to address, both theoretically and experimentally, how flow induces or suppresses de-mixing in blends, the structures develop during flow, and the extent to which polymer molecules are stretched by flow. Experimental techniques include scattering (mainly using neutrons), and rheology⁵ - the science of how materials flow - properties. Theoretical techniques⁶ are based on tools developed for non-equilibrium statistical mechanics, both analytical and computational.

References

1. N. Clarke, Physical Review Letters, 2002, 89, 215506.
2. I.C. Henderson and N. Clarke, Macromolecules, 2004, 37, 1952.
3. N. Clarke, European Physical Journal E, 2004, 14, 207.
4. Y. Ishii, A.J. Ryan, N. Clarke, Polymer, 2003, 44, 3641.
5. J. Sharma,and N. Clarke, J.Phys. Chem., 2004, 108, 13220.
6. D. Miroshnychenko and N. Clarke, Physical Review E, 2002, 66, 041802.