Cryo-FIB-SEM-CT: a 'three-in-one' imaging facility for opaque soft matter

Lead Research Organisation: University of Edinburgh
Department Name: Sch of Physics and Astronomy

Abstract

The University of Edinburgh (UoE) is an international centre for soft matter research. Soft matter scientists study complex liquids in which there are structures intermediate in size between the small molecules making up the solvent and the macroscopic world of structures visible to the naked eye. The structures may be pigment particles in paint (colloids), self-assembled aggregates of soap molecules in washing-up liquid (surfactant micelles), bubbles (say, in whipped cream) or long-chain molecules (polymers) such as DNA (as used in gene transfection). The field is of fundamental interest because the properties of these materials are controlled by many competing length and time scales, and can change dramatically under everyday conditions. Such materials are also ubiquitous in formulations of all kinds, such as medicines (CALPOL is a suspension of colloidal paracetamol) and personal care products (a shampoo is a surfactant-polymer mixture). They are also key intermediates in many sectors: all ceramics, for example, begin as soft pastes (think potter's clay) that are pumped into moulds or extruded before they are sintered at high temperatures to form the final hard products.

A fundamental challenge in soft matter is to figure out the way these intermediate structural elements are organised, and how such organisation changes in response to external forces. Most of such materials are opaque to light, so that optical microscopies of all kinds are not useful except to give surface information. As a result, scientists sometimes resort to various kinds of electron microscopy, which, however, operate in a vacuum, so that wet samples are desiccated and their native structures destroyed.

A major development in the last decades is cryogenic scanning electron microscopy (cryo-SEM). A native, wet soft sample is frozen in liquid nitrogen, using special techniques to ensure rapidity of cooling to preserve intricate microstructures. Then these frozen samples are fractured, exposing internal structures to be imaged by SEM. (One disadvantage is that samples fracture more or less randomly, so that what is exposed to view is haphazard.) A single cryo-SEM instrument exists at UoE. This decade-old instrument is limited in both resolution (ten times worse than the best instruments today) and in access for soft matter scientists, as it requires laborious conversion of the system to cryogenic mode. We propose to purchase a state-of-the-art cryo-SEM to enable this cutting-edge technique to become routinely available for day-to-day work.

This purchase is timely, because cryo-SEM has recently been revolutionised for soft matter researchers by the addition of focussed ion beam (FIB). This powerful technique uses a focused beam of charged atoms (ions) to cut and section specimens very accurately inside the SEM. This not only allows the user to expose desired sections at will, but also to build up a complete 3D picture (literally) by imaging the sample section by section to a resolution of 10 nm (100 times the size of atoms). We propose to purchase a cryo-FIB SEM. The technique is so new that we know of only two current instruments in the UK, neither of which is dedicated to the study of soft matter. We propose to add X-ray tomography capability to our cryo-FIB SEM. This allows us to build up a 3D picture non-destructively to 350 nm resolution, much like the way X-ray CT scanners build up 3D images of the body in hospitals. The availability of this combined suite of instruments will transform the ability of soft matter scientists to see inside their samples routinely. A host of exciting applications immediately follow. One example is 'designer electrodes' based on novel soft materials that minimise expansion/shrinkage during charge/discharge cycles. A programme of outreach and training will make this facility available to academic and industrial researchers UK-wide.

Planned Impact

The equipment will contribute to four areas with national societal and economic significance, which are also EPSRC priorities:
1) Formulations: industrial formulations include complex fluids as the final product (e.g. shampoos, foods), or products with complex-fluid stages during their processing and manufacturing (e.g. polymer composites and nanocomposites). Formulations contribute £180bn mark value in the UK, but their production to date is largely based on empirical formulas and past experience. Innovation and creation of new markets require a radical change to predictive models for new formulations. Obtaining an accurate picture of nano/microscale structures is of paramount importance in transitioning formulations 'from art to science' (terminology used by the UK's National Formulation Centre), because it is the response of these structures to external forcing that underpin all applications of soft matter. Our instrument allows scientists to probe the 3D structure of soft samples at the 10 nm to 10 micrometre scale, which is the most relevant for applications. By making this technique routinely available, it will therefore transform our understanding of many industrial products and processes, and therefore contribute directly to reaching to goal of 'predictive formulations' by validating models and simulations.
2) Energy: the instrument will enable new work by our hard-matter scientists studying hydrogen under extreme conditions, creating improved solar energy solutions and synthesising novel solid-state hydrides. Our soft matter scientists are using a new material they patented, bijels, as novel solid electrolytes with improved safety, and as new-generation electrodes minimising cracking and therefore improved lifetime. The new instrument will transform their work in collaboration with some of the top battery scientists in the country (e.g. Peter Bruce, Oxford). For example, it will enable them to survey cracks non-destructively (CT), and then study sectios near the crack at high resolution (FIB).
3) Health: living cells are 'soft matter come alive'; synthetic soft matter also finds many applications as biomedical materials (catheters, implants, etc.). Again, detailed structural information underpins all advances in these fields. Thus, e.g., UoE scientists will use the new instrumentation to help find new ways of synthesizing organic-inorganic composites that may be useful for enamel repair. Separately, SoPA hosts one of the biggest bacterial biophysics research efforts in the UK, where the new instrument will enable researchers to study the structure of bacterial colonies and biofilms at a new level of detail. The information obtained should give insights in the continued effort to find new ways of stopping bacterial adhesion, which offer a different pathway to impact on the global problem of antimicrobial resistance (by reducing the need for antibiotics).
4) Food security: As many foods are soft matter systems, the new instrument will have the capacity to be used in this key area of societal and economic importance. UoE scientists will use it to help in the discovery of new ingredients, e.g. to modify ice melting, which can significantly decrease food spoilage and therefore wastage. Discovering the nano/microstructure of food ingredients can also lead to more efficient ways of enabling one industry to use wastes from another, from animal-skin-derived collagens to cellulose from plant materials (fruit peels, etc.).

Publications

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Radacsi N (2018) Spontaneous formation of nanoparticles on electrospun nanofibres. in Nature communications

 
Description Using the cryo-FIB/SEM we were able to study the cross-section of nanoscale electrospun fibres. As the fibres cool nanocrystals emerge on their surface, creating a large surface area. By observing in cross-section we have a better understanding about the distribution and emergence of these nanocrystals. These systems can be used where nanomaterials with high surface area are required, such as in fuel cells. This is how the instrument was used in the publication DOI: 10.1038/s41467-018-0724-5.

We hope this is the first of many examples where the microscope reveals something previously hidden.
Exploitation Route As we have shown the distribution of nanocrystals in the cross-section of electrospun nanofibres, others might be interested in tweaking and controlling this and observing how that changes the behaviour of the system.
Sectors Aerospace, Defence and Marine,Chemicals,Electronics,Energy,Environment

 
Description So far images taken using the microscope have been used by an industrial food company as part of a larger research project. The exact findings are confidential but we know that they were interested and pleased with the findings and are in the process of finding further funding for another research project. We expect these findings to contribute to changes in their food products in the next few years.
First Year Of Impact 2019
Sector Aerospace, Defence and Marine,Agriculture, Food and Drink,Chemicals,Electronics,Energy,Environment
Impact Types Economic