What is it about?
How do you measure the strength of a powder when each grain is about the width of your hair? We used nanoindentation on isolated grains of molecular crystals to measure the onset of plastic deformation and the hardness of materials with three different crystal structures, and our results suggest the defects formed during powder processing lead to similarities in the strength to stiffness ratio that overwhelm differences based on crystal structures in these limited slip system forms.
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Why is it important?
Molecular crystals are used in both pharmaceutical and energetic applications. We showed here that the strength of a wide range of these materials in the as-used condition (small powders) is similar and can be estimated based on the stiffness, and does not correspond to well-curated and carefully grown model single crystals. This suggests the structural defects during processing greatly influence the resulting strength. Tableting and other powder forming processes can now use some first order estimates of properties for new materials development as new molecules are crystallized.
Perspectives
This was a great experience for collaborating with experts from across fields and around the country to carry out a set of measurements that was very challenging. Matt has recently graduated, and this was the capstone of his MS degree at Purdue. We'll be continuing the collaboration with new students on a wide range of this class of materials.
David F Bahr
Purdue University System
Read the Original
This page is a summary of: The mechanical properties of as-grown noncubic organic molecular crystals assessed by nanoindentation, Journal of Materials Research, June 2017, Cambridge University Press,
DOI: 10.1557/jmr.2017.219.
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