Polymers

Synthetic polymers can be found in food additives, composite materials, drug packaging, artificial organs and solar cells. Biopolymers, such as DNA, actin, collagen and fibrin, play important roles in the body. Aside from the widely used, technical polymers have been designed or processed with particular properties in mind, irrespective of their chemical composition. Functional polymers, on the other hand, are usually selected based on specific chemical groups rather than physical properties. These tend to be exploited for novel optical and electronic applications, such as gas sensors.

At the ESRF, polymers have been one of the main subjects of research since its early days. Thanks to the ESRF, researchers can now:

Carry out time-resolved studies to monitor molecular chains and hydrogen bonds in polymers.
Use of microfocus X-ray beams to characterise nanostructure of fibre-reinforced composites and high performance fibres.
On axis scanning microdiffraction for skin-core morphologies.
Measurements of the strains in metal and ceramic phases separately and simultaneously in metal matrix composites using X-ray diffraction.
Following the internal failure mechanisms of composites using X-ray tomography.
Determination of the spatial distribution of defects at polymer interfaces.
Study of polymer crystallisation at elevated temperatures using nano-calorimeter and nanobeam diffraction.
Combination of wide-angle X-ray scattering and fluorescence data to assess the position, size and orientation of particles in carbon nanotube fibres.
Study of the influence of temperature and deformation on the molecular scale to reveal physical mechanisms behind macroscopic phenomena such as thermal expansion.

CASE STUDY

MICRO COMPUTED TOMOGRAPHY TO STUDY FILLER DISPERSION IN RUBBER

Company

Continental Reifen Deutschland GmbH

Challenge

The challenge was to accurately estimate the size distribution of the macro-dispersion of carbon black filler in a rubber matrix through a synchrotron experiment. This was to provide a high-accuracy 3D reference scan of the bulk material with which to compare the size distribution of the filler particles obtained from a new optical microscopy technique, radiometric stereo microscopy, used to examine the surface of freshly made planar sections, i.e. “fresh cuts”, of rubber, for future use in quality control.

Sample

The sample was a rubber in an early state of carbon black filler incorporation.

Solution

Tomographic data sets were acquired at beamline ID19 using propagation-based phase contrast to enhance contrast between the filler and the rubber matrix.

Tomographic image showing carbon black filler particles in rubber: volume rendering of a sub‐volume of 1100 × 1000 × 1300 pixels out of the complete 3D data set with 2560 × 2560 × 2160 pixels of size 0.65 μm. Filler particles (or particle agglomerates) of a volume larger than 100 μm³ are highlighted in red. Credit: J. Ohser et al., Journal of Microscopy 274, 32–44 (2019); doi: 10.1111/jmi.12782.

Benefits

Partially-coherent illumination and phase-retrieval techniques made it possible to exploit the full (complex-valued) refractive index of the materials. The contrast obtained was an order of magnitude better in sensitivity to material changes than the plain attenuation signal. This allowed the different material components to be identified directly in the grey-scaled tomographic image: the rubber matrix as well as the filler particles.

Macro-dispersion of globular filler particles (e.g. carbon black or silica) in a rubber matrix is an important quantity that depends on manufacturing parameters and influences various rubber properties. Therefore, it must be carefully adjusted during the incorporation process and investigated by industrial quality control. The synchrotron experiment provided a benchmark used to gauge the accuracy of radiometric stereo microscopy which would be used for manufacturing quality control of rubber products such as vehicle tyres.

Reference

Estimation of filler macro-dispersion in rubber matrix by radiometric stereo microscopy, J. Ohser, J. Lacayo-Pineda, M. Putman, A. Rack & D. Dobrovolskij, Journal of Microscopy 274, 32–44 (2019); doi: 10.1111/jmi.12782.

STUDYING CRACK PROPAGATION IN COMPOSITES AT HIGH PRESSURES

Company

University of Manchester and Rolls-Royce

Challenge

Crack propagation in metallic materials is well understood. But aircraft manufacturers are increasingly turning to more complicated composite materials that are lighter, stronger and can operate at higher temperatures. Lower weight reduces fuel consumption, while higher engine operating temperatures allow aeroengines to be more efficient. The challenge is to understand how cracks propagate in such materials.

Sample

Titanium reinforced with silicon carbide fibres. This composite material can operate at higher temperatures than titanium alone, making it a promising candidate for jet engine parts.

Solution

Electron microscopy reveals the surface features of micro-cracks, but synchrotron X-rays penetrate tens of millimetres into a sample where the behaviour of cracks can be very different. On beamline ID15, scientists can use imaging, to see how cracks grow, and diffraction, which tells them about the local stresses that the cracks grow under.

Benefits

The ability to monitor cracks under load at high temperatures allows researchers to evaluate the potential of these materials under realistic conditions. It also helps to make realistic estimates

of the lifetime of existing components and to design safer, more crack-resistant materials for the future.

Better knowledge of crack propagation transfers directly to other industries in which failure is unacceptable, notably the nuclear industry.

Proc. R. Soc. A 468 2722.

Acta Materialia 60 958.

3D crack-tip microscopy shows a crack (purple) growing in a composite material containing silicon carbide fibres.