Probing the dynamics and structure of soft matter and out-of-equilibrium materials using 3D-photon correlation spectroscopy

The aim of this proposal is to set up a state-of-the art so called 3D photon correlation light scattering spectroscopy (3D-PCS) facility, unique to the UK, that will be accessible the UK research community. The use of light scattering to study both the motions and structure of material building blocks is a powerful way to learn about materials. However, in order to investigate a material using light the material normally needs to be highly transparent to light. Unfortunately, most materials are not transparent, but show various degrees of optical turbidity. If one attempts to study such a turbid material using light scattering, the result is normally very difficult or even impossible to interprete. However, the particular light scattering technique termed 3D-photon correlation spectroscopy gets around this problem by using a trick.
Generally, when studying a material by the use of light, a laser beam is focused upon your material of interest, light is scattered and you detect the scattered light for some particular scattering angle. By analyzing the time-varying intensity of the scattered light you can work out how the units within your samples that are responsible for the scattering move and by studying how the time-averaged intensity of scattered light varies with the scattering angle you can work out how the scattering units are arranged or what shape they have. The problem comes, as mentioned above, if the sample is turbid. This means that light is generally scattered many times before it exits the sample and the information about the scattering event gets lost. The trick utilized in the 3D-PCS technique, is that the incoming beam is divided into two and each of these two beams is focused into the same sample volume. Here, they both undergo scattering and by analyzing both these scattering events simultaneously, one can find those scattering events where light was only scattered once within the volume and thus no confusion will remain in terms of interpretation.
This powerful light scattering technique is thus excellent for studying turbid materials such as many gels, emulsions, biological materials. In fact, materials where it is important to understand the motions and structure of the building blocks over a wide range of time- and length-scales, but where the materials are not optically clear are so common that researchers within physics, chemistry, biology, medicine, engineering etc are interested in having access to this technique. Moreover, since industrially relevant materials are perhaps even more likely to be turbid than the more 'purified' materials used in university labs, the interest in applying this technology to study materials relevant for industrial products such as plastics, pharmaceuticals, personal care products, or advanced materials for drug delivery or batteries is huge.

The 3D-Photon correlation system will be unique to the UK and only a small number of these systems have been manufactured world-wide. Moreover, the particularly strong capabilities of the Leeds set-up, with the latest options installed for optimal accuracy and high signal-to-noise ratio, with excellent hardware for proper measurements on systems such as gels or glasses that are out-of-equilibrium, and with high class polarization optics enabling measurement of both translational and reorientational motions makes this kit one out of a handful world-wide. Access to this system should impact a long range of different scientific and industrial discisplines within physics, chemistry, biology, medicine, food science, engineering etc and the equipment will be of significant strategic importance due to its impact on our understanding of turbid materials such as colloids, surfactant systems, polymers, gels, glasses, microgels, emulsion or bio-macromolecules. These types of materials are essential to a range of key focus areas for UK technology such as medical, pharmaceutical and food technologies and the ability of 3D-PCS to study such materials where other techniques fail will impact key sectors of our society and economy, including personal care, pharmaceuticals (aging population), nuclear and renewable energy (sustainability) and agrochemicals and advanced engineering materials technology (manufacturing the future). The strong support received for this proposal from industry already highlights the potential this technique has to revolutionise our understanding of may difficult to study materials, which have hitherto remained properly investigated. In the industrial Letters of support, it is e.g. stressed how important and difficult it is to try to understand the formation and breakage of non-equilibrium gel structures, where formulation testing is a key bottleneck in progressing new products to the market; to have access to this unique technology which can study the detailed dynamics and structure in these highly turbid materials could lead to a significant move forward not just in the fundamental sciences, but also in a wide range of practical applied problems. It is also pointed out that there are a wide range of UK companies for example within the food, petrochemical, dye and pharmaceutical sector that have very similar interests. This is further illustrated by the strong interest in a UK-based 3D-PCS set-up from Chamelic, Escubed, Infineum and Unilever. Moreover, The fact that 3D-PCS is ideal for studies on slow dynamics, dynamic arrest and out-of-equilibrium behaviour strongly adds to its importance; this research area was recently highlighted by the EPSRC signposting "Matter far from equilibrium". The strategic case is further strengthened by the fact that 3D-PCS is an excellent and unique research tool in 3 out of 4 of the recently identified EPSRC Physics Grand Challenges: "Emergence and Physics Far from Equilibrium", "Nanoscale Design of Functional Materials" and "Understanding the Physics of Life". ". It is also important to point out the close relation between the physics of non-equilibrium solids and non-equilibrium behaviour in large-scale systems such as traffic systems, animal populations, human societies or financial markets, all of which are areas of significant importance to the UK society.