Seeing how polymer chains organise with torsional tapping atomic force microscopy

Our understanding of semicrystalline polymers, the class of polymers that by far and away dominates usage in modern society, is surprisingly poor. At a molecular scale we rely on cartoons and inference, unable to reach the certainty obtained in other areas of material science by direct, atomic or molecular scale imaging, and by diffraction from macroscopic crystals. Yet in polymers the structure at this level is arguably more important as it determines the properties from mechanical behaviour to the oxygen barrier performance through the adhesive behaviour to the aesthetic appeal. Recently we developed a new form of atomic force microscopy, torsional tapping AFM (TTAFM) capable of robustly and routinely obtaining images with true molecular resolution on the most frequently used polymers (polyolefins, that include polyethylene and polypropylene) in essentially any sample. This step change in performance is based on the improved dynamics and signal-to-noise performance that comes from the cantilever geometry and drive mechanism. Perfecting the cantilever design is predicted to lead to even greater performance, and to allow the technique to be used in a wide range of instruments. At the same time as developing the technology we will use it to answer a string of questions that underpin our understanding of polymer crystals, questions that will lead to both greatly enhanced fundamental understanding and real application from the development of new materials and applications to problem solving during processing. We aim to directly reveal how crystallization temperature, variations in chain chemistry, chain branching, re-enforcing fibres and particles, control the organisation of polymer chains within the crystal and at the interface between the crystal and the non-crystalline material. While doing this we will perfect the sample preparation methods for molecular scale imaging, and enhance the cantilever design to improve performance, allowing the technique to be widely adopted both in polymer science and across molecular nanoscience.

Semicrystalline polymers are ubiquitous in modern life. Further property enhancements will be built upon new knowledge and understanding. The proposed project will develop a revolutionary new technique to provide insight at the fundamental level of the individual chain. The new knowledge this will provide will impact on polymer manufacturers and users (e.g. in the packaging market) through their ability to develop new applications and enhanced properties. By directly providing information at the chain level a deep understanding of fundamental questions that underpin properties and applications will be obtained, ultimately leading to enhanced product development. This will clearly benefit industry, but also have potential societal benefits as new material/application development is increasingly driven by the societal need for sustainability and reduced environmental impact.

The technique itself will be developed with the aim of being widely adopted. By optimising cantilevers etc it should be possible to push down on the specification of the base AFM necessary to obtain molecular resolution, maximising the potential for uptake of the technique. It will take time for the technology to be adopted and will require input from microscopy companies. Here the AFM companies will benefit considerably. Direct imaging at the molecular scale allows microscopy to solve problems usually addressed by scattering and spectroscopy, so growing the market for the technique and opening up whole new areas for application. Once the technique is widely used we expect it to have a real impact on improved research, development and problem solving in an industrial context. The technique itself will also have application beyond semicrystalline polymer science, with the potential to have a substantial impact across molecular nanoscience. If similar resolution can be widely obtained on soft condensed matter systems then there will be up-take in other industrial sectors such as pharma, personal care, etc. Across materials science models are based on 'understanding' at the molecular scale, and used to develop and perfect applications. Enabling microscopy to provide this information in a relatively routine manner even on soft systems could have a transformative effect on future developments.