Exploration of sub-diffusive motion in high-value polymers

Some complex polymers have been found to possess anomalous sub-diffusive motion. The question of whether sub-diffusive motion is a feature of high-value polymers more generally has not been addressed (they are normally assumed to have diffusive motion), and yet their motional properties are absolutely central to how they behave. This project aims to understand the molecular basis of this sub-diffusive motion and to understand whether it is a universal feature of these polymers. Understanding this motion will provide fundamental breakthroughs in our ability to predict the properties of synthetic high-value polymers and drive their adoption in new products and processes, such as sensors, coatings, hydrogels and pharmaceuticals.

The objectives are to:

1. Produce experimental model systems based on peptide, phophodiester and ether-based polymer chemistries, including polymers with isotopic enrichment and photo-labile linkers to enable accurate analytical measurements to be performed.
2. Use advanced analytical techniques (such as nuclear magnetic resonance: NMR and laser photolysis) to study the equilibrium and non-equilibrium (time dependent) 3-dimensional properties of these polymers in order to measure and determine the extent of sub-diffusive motion in each polymer type.
3. Develop and test new computational techniques for modelling the 3-dimensional properties of these polymers both at equilibrium and non-equilibrium (time dependent) and use these models to explain the experimental results and provide a molecular interpretation of the sub-diffusive motion.

In order to investigate sub-diffusion, chemistry approaches will be used to make defined polymers, both with isotopic enrichment and photo-labile chemical cross-linkers. The isotopically enriched polymers will be used in advanced physical experiments using NMR and laser spectroscopy. In particular, NMR experiments will be used to confirm chemical composition and determine the 3-dimensional equilibrium arrangement of the polymers. Laser photolysis experiments will cleave photo-labile cross-linked polymers to explore the subsequent rapid non-equilibrium time-dependent motion. Computer physics models of the polymers will be underpinned by accurate molecular dynamics simulations rather than the coarse-grained approaches used previously. These molecular dynamics simulations have previously been shown to have the ability to accurately simulate sub-diffusive motion.

The experiments will be analyzed empirically, to measure the sub-diffusive motion, by calculating that the scaling behavior of the time dependence of motion. Results from simulations will be directly tested against these experiments to confirm that the amount of sub-diffusive motion predicted is accurate. The simulations will then be used to analyze the amount of and nature of sub-diffusive motion in detail to provide a molecular-level interpretation and understanding for each polymer.

The project has direct relevance to EPSRCs Manufacturing and Healthcare Technologies themes, since these polymers are used widely across the manufacturing sector and specifically in healthcare as drugs and drug delivery systems. The project will also provide training and experience in Information and communication technologies (ICT), and in the Mathematical and Physical sciences.