How natural materials behave across multiple length scales

By combining three advanced techniques, new insights can be uncovered into how natural materials behave across multiple length scales.

A rheometer, an optical visualisation system and synchrotron X-rays are all used to inspect natural materials © Roland Kádár

Researchers at Chalmers University and the MAX IV Laboratory, Sweden, can now observe how hierarchical materials like wood behave under flow conditions at different length scales.

The method, called Rheo-PLI-SAXS, combines rheology, polarised light imaging (PLI) and small-angle X-ray scattering (SAXS) – the latter involves synchrotron radiation experiments.

The method allows researchers to examine materials in simple shear – a type of deformation where parallel layers of material slide past each other.

Natural materials like wood are hierarchical and, as such, are structured and behave differently across various length scales.

For example, wood is built up of several different layers of structures, starting with cellulose chains that bundle into fibrils, forming fibres that create cell walls and wood tissue, ultimately creating a full tree. The molecular-to-macroscopic organisation gives wood its lightweight and mechanical properties.

Understanding the structure of natural materials like wood can enable similar hierarchies to be replicated in synthetic materials.

'Previously, we could only observe one scale at a time, which meant losing simultaneity and important details about how the different layers orient in relation to each other,' says Roland Kádár, Professor of Rheology at the Department of Industrial and Materials Science at Chalmers.

'For the first time, we can determine how orientation, which is a most important parameter for material properties, propagates across nano-macro length scales in the hierarchy.'

Rheology shows how materials flow and deform under an applied stress or deformation.

Polarised light imaging uses visual light to examine the alignment and orientation of a material’s internal structures. While SAXS studies nanoscale structures, revealing how the smallest structural layers of a material behave.

Through the partnership between Chalmers and the MAX IV Laboratory, work will continue to gain an even deeper understanding of how materials behave across multiple scales.