Important role of structural defects revealed in deformation of amorphous solids

Yellow and red areas in the image indicate structural defects, and white circles indicate particles damaged by external stress. These particles involved in the deformation process occur preferentially in regions containing structural defects. Credit: Dr. Vijayakumar Chikkadi’s Research Group
Researchers from Indian Institute of Science Education and Research (IISER) Pune and CSIR-National Chemical Laboratory (NCL) Pune have shown that macroscopic deformation in amorphous solids is controlled by structural defects within the material. Ta.
The collaboration, led by Dr. Vijayamar Chikkadi from IISER Pune and Dr. Sarika Bhattacharyya from CSIR-NCL, Pune, combines experimental studies on colloidal glasses (a model system for amorphous solids) with a theoretical framework based on structural order parameters. I am.
The findings, published in the Proceedings of the National Academy of Sciences, address a long-standing question in materials science and condensate physics.
All materials deform when subjected to external stress. In 1934, GI Taylor, M. Polanyi, and E. Olowan independently explained that macroscopic deformation results from the mechanics of defects in materials. In crystalline solids, these defects are relatively easy to identify due to lattice distortion.
However, the lack of long-range order in amorphous solids makes detecting defect-like regions much more difficult. Although several approaches have been proposed to identify soft defect-like regions within disordered solids, direct observation in experimental systems has been difficult.
To address this, Ratimanasee Sahu and Dr. Vijayamar Chikkadi from IISER Pune conducted experiments using dense colloidal suspensions, which serve as models for amorphous solids. Using advanced microscopy techniques to track the movement of approximately 100,000 individual colloidal particles over time in three dimensions, we gain unprecedented access to microscopic information that is difficult to obtain in atomic systems. I did.
These studies utilized structural order parameters developed by Mr. Mohit Sharma and Dr. Sarika Bhattacharyya of CSIR-NCL, Pune to quantify the soft and hard regions of amorphous suspensions and to identify structural defects. It led to
“The main advantages of this order parameter, developed from detailed microscopic theory, are its practical applicability in experimental settings and its ease of use compared to other theoretical quantities,” Sarika said. Dr. Bhattacharyya said.
The research team has experimentally demonstrated for the first time that macroscopic deformation in colloidal glass is due to local deformation and occurs preferentially in regions containing structural defects when subjected to external stress.
“This breakthrough significantly increases our understanding of how defects affect the mechanical properties of disordered solids. It also has applicability to a wide range of materials, including soft matter such as granular materials and emulsions. , it has also paved the way for the development of improved rheological models based on structural aspects ”, as well as for metallic glasses,” Dr. Vijaykumar Chikkadi said about the future prospects of this research.
Further information: Ratimanasee Sahu et al, Structural origins of relaxation in dense colloidal suspensions, Proceedings of the National Academy of Sciences (2024). DOI: 10.1073/pnas.2405515121
Provided by: Indian Institute of Science Education and Research Pune
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