Hardness Alternation in α,ω-Alkanedicarboxylic Acids.
The variation of hardness as a function of the number of carbon atoms in α,ω-alkanedicarboxylic acids, C(N)H(2N-2)O4 (4≤N≤9), was examined by recourse to nanoindentation on the major faces of single crystals. Hardness exhibits odd-even alternation, with the odd acids being softer and the even ones harder; the differences decrease with increasing chain length. These variations are similar to those seen for other mechanical, physical, and thermal properties of these diacids. The softness of odd acids is rationalized due to strained molecular conformations in them, which facilitate easier plastic deformation. Relationships between structural features, such as interplanar spacing, interlayer separation distance, molecular chain length, and signatures of the nanoindentation responses, namely, discrete displacement bursts, were also examined. Shear sliding of molecular layers past each other during indentation is key to the mechanism for plastic deformation in these organic crystals.
Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore, 560 012, India.
Manish Kumar
MK
Mishra
Department of Materials Engineering, Indian Institute of Science, Bangalore, 560 012, India. ramu@materials.iisc.ernet.in.|Center of Excellence for Advanced Materials Research, King Abdulaziz University, Jeddah, 21589, Saudi Arabia. ramu@materials.iisc.ernet.in.
Upadrasta
U
Ramamurty
Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore, 560 012, India. desiraju@sscu.iisc.ernet.in.
Gautam R
GR
Desiraju
carboxylic acids; crystal engineering; hardness; mechanical properties; nanoindentation