Executive Summary : | "The fragility of molecular crystals is well recognized. However, in very rare situations, the molecular crystals have been shown to exhibit considerable mechanical deformability. This deformability could be elastic or plastic in nature. Owing to its enormous potential applications in the materials science, this field has recently become an important focus of research in materials science. Therefore, to build new crystals with desired flexibility, it is vital to understand the basic
mechanism that produces various types of deformability in crystals. The major disadvantage of this plastic bending process is that after bending crystal loses its single crystallinity, making single crystal X-ray diffraction impossible to analyze its crystal structure. Microfocus synchrotron X-ray diffraction is an approach for solving this problem, however it is highly challenging. As a result, this method could only be utilized to investigate the structural changes generated by bending on two systems thus far. Other alternate approaches for determining structural changes in the bent region include µ-Raman, µ-infrared spectroscopy, and so on. These strategies, however, are deceptive and challenging at the same time. As a result, scientists are forced to make educated guesses about probable structural alterations based on the crystal structure of a straight crystal. Both thermal expansion and bending are anisotropic processes that are influenced by the strength of intermolecular interactions and molecular mobility. So, thermal expansion analysis could be a quick and easy way to anticipate the deformability in a molecular crystal, even if it was indirect. To the best of my knowledge there are only three system specific reports where the structure?property of thermal expansion and mechanically deformative crystal have been revealed. Having said that, there are several problems that need to be investigated further. The major thermal expansion principle axis is found to be along the bending axis in all three investigations reported so far. Is it feasible to have a bending axis that is not parallel to the predominant axis of substantial thermal expansion? Is it feasible to have negative or even zero thermal expansion along the
bending axis? If that is the case, what could be the correlation between the bending mechanisms and its thermal expansion? Also, there has never been a known occurrence of negative compressibility in the molecular crystal. After understanding the basic mechanism of mechanically deformable crystals, novel deformities crystals with varying degrees of deformability can be designed. Thermal expansion of self-healing crystals, in particular, will be thoroughly investigated in order to generate novel self-healing crystals with varying degrees of self-healing potential. Also, the synthesis and thermal expansion of new compounds with expected crystal deformability using the spacer idea will be performed." |