What is it about?
Amorphous solids relax via particle rearrangements driven by thermal fluctuations or applied stress. These rearrangements preferentially occur in soft, defect-like regions within the material. Using dense colloidal suspensions as model amorphous solids, we provide direct experimental evidence of the structural defects governing the rearrangements. These studies exploit a structural order parameter derived from microscopic theories, which effectively identifies weak defect-like regions in glasses and other amorphous materials.
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Why is it important?
Defects control the mechanical properties of materials. In 1934, E. Orowan, M. Polanyi, and G.I. Taylor proposed that macroscopic deformation in crystalline materials originates from the dynamics of defects, which can be easily identified from lattice distortions. However, in amorphous solids, the lack of long-range order makes detecting defect-like regions much more challenging. While various methods have been proposed to identify soft, defect-like regions in disordered solids that are susceptible to failure under external stress, direct observation in experimental systems has proven difficult. Through experiments on colloidal glasses and the use of a novel structural order parameter, we have demonstrated that macroscopic deformation in amorphous materials originates from the irreversible rearrangement of particles in regions with structural defects.
Perspectives
Deformation of materials and their failure are everyday experiences. However, the underlying physics of these phenomena in amorphous materials or glasses has remained a mystery. Our experiments deepen the understanding of how defects affect the mechanical properties of disordered solids. They also pave the way for developing improved rheological models applicable to a wide range of materials, including soft glasses like granular materials and emulsions, as well as metallic glasses.
VIJAYAKUMAR CHIKKADI
Indian Institute of Science Education and Research Pune
Read the Original
This page is a summary of: Structural origin of relaxation in dense colloidal suspensions, Proceedings of the National Academy of Sciences, October 2024, Proceedings of the National Academy of Sciences,
DOI: 10.1073/pnas.2405515121.
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