Hardness Alternation in α,ω-Alkanedicarboxylic Acids.

Area of Science:

• Materials Science
• Organic Chemistry
• Crystallography

Background:

• Dicarboxylic acids are organic compounds with diverse applications.
• Understanding their mechanical properties is crucial for material design.
• Previous studies noted variations in physical and thermal properties with chain length.

Purpose of the Study:

• To investigate the relationship between carbon chain length and hardness in α,ω-alkanedicarboxylic acids.
• To explore the influence of molecular structure on mechanical properties.
• To elucidate the plastic deformation mechanisms in these organic crystals.

Main Methods:

• Nanoindentation was performed on single crystals of α,ω-alkanedicarboxylic acids (C(N)H(2N-2)O4, 4≤N≤9).
• Hardness was measured as a function of the number of carbon atoms (N).
• Structural features like interplanar spacing and interlayer separation were correlated with indentation responses.

Main Results:

• Hardness exhibited an odd-even alternation: odd-numbered carbon acids were softer than even-numbered ones.
• The magnitude of this odd-even difference decreased with increasing carbon chain length.
• Discrete displacement bursts during nanoindentation were observed and related to structural features.

Conclusions:

• The observed odd-even hardness alternation is attributed to strained molecular conformations in odd-numbered acids, facilitating plastic deformation.
• Shear sliding of molecular layers is identified as the primary mechanism for plastic deformation.
• The findings correlate structural characteristics with mechanical responses in organic crystalline materials.