Temperature Dependence of Mechanical Properties in Molecular Crystals

Abstract

Quantitative evaluation of the mechanical behavior of molecular materials by nanoindentation technique has gained prominence recently. However, all the reported data has been on room temperature properties despite many interesting phenomena observed in them with variations in temperature. In this paper, we report the results of nanoindentation experiments conducted as a function of temperature, T, between 283 and 343 K, on the major faces of three organic crystals: saccharin, sulfathiazole (form 2), and L-alanine, which are distinct in terms of the number of strength of intermolecular interactions in them. Results show that elastic modulus, E, and hardness, H, decrease markedly with increasing T. While E decreases linearly with T, the variations in H with T are not so, and were observed to drop by ~50% over the range of T investigated. The slope of the linear fits to E vs. T the organic crystals was found to be around 1, which is considerably higher than the values of 0.3 to 0.5 reported in literature for metallic, ionic and covalently bonded crystalline materials. Possible implications of the observed remarkable changes in H for pharmaceutical manufacturing are highlighted.

A large anisotropic plasticity of L-leucinium hydrogen maleate preserved at cryogenic temperatures

“…Most studies of organic crystals that can be deformed plastically to a large extent were carried out at room temperature. Variable-temperature studies are less common; they are usually related to heating and using nanoindentation techniques for probing mechanical properties (Mohamed et al, 2015;Sidelnikov et al, 2016;Rather & Saha, 2018). However, to the best of our knowledge, there are few, if any, research articles on high plasticity of molecular organic crystals preserved to cryogenic temperatures.…”

Synthesis, crystal growth and characterizations of bis (l-proline) cadmium iodide: a new semi-organic nonlinear optical material

“…The mechanical properties of crystalline materials, particularly hardness depend on the crystal structure as well as nature of the chemical bonds. With an increase in temperature, the lattice thermal vibrations get amplified, which in turn change the lattice energy and reduce the curvature of the potential energy curve (the intermolecular interactions in crystal become much weaker) [34]. The variation of Vickers microhardness values of BLPC with load is shown in the Fig.…”

Crystal Indentation Hardness

“…Here, we mention, first, an important hardness connection with material compaction behaviors that arise for softer organic crystals relating to pharmaceutical tableting [21] and formulated energetic material processing [5]. Research effort on the former topic has been carried on to investigating temperature [22] and strain rate [23] influences on molecular crystal hardness. In the latter energetic crystal case, a recent report on hardness and molecular dynamics aspects of RDX (cyclotrimethylenetrinitramine) crystals has dealt with concern for their mechanical and tribological properties [24].…”