Mechanical Properties of Molecular Crystals: Self-Healing Materials for Nonlinear Optics and Electronics

Mondal, Saikat (2023) Mechanical Properties of Molecular Crystals: Self-Healing Materials for Nonlinear Optics and Electronics. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Saikat Mondal (17RS006)) 17RS006.pdf - Submitted Version Restricted to Repository staff only Download (99MB)

Abstract

Industrial applications in the fields of optics and electronic devices largely depend on the durability of the constituent materials. Molecular crystals, due to their typical brittle nature, are ignored for potential applications as they develop micro-cracks during their fabrication and prolonged applications. Crystal engineering has evolved to a point where it is now feasible to develop flexible and durable molecular crystals strategically. Therefore, to overcome some of these common problems, I have synthesized some organic molecular crystals and demonstrated their mechanical flexibility, self-healing properties, and device performances. Some of the materials discussed in the thesis may be useful as potential candidates for future durable device applications purposes. In Chapter 2, I have demonstrated a design strategy to prepare a crystal with 2D elastic bending and elastic twisting nature in a non-trivial hydrogen-bonded structure starting from a same structure type which shows plastically bendable nature. In Chapter 3, I have demonstrated an autonomous self-healing organic crystal that shows excellent selfhealing in mechanically damaged broken shards, which is associated with an ultrafast actuation motion. SEM, SPM, and SCXRD studies confirmed the healing behavior. Further I demonstrated its healing efficacy using second harmonic generation studies as the crystals are non-centrosymmetric in nature. Using two classical actuation motions I have determined their ultrafast actuation response time and a few more performance parameters that are comparable to some real-world actuators. In Chapter 4, I have shown an autonomous self-healing organic crystal for durable conductive devices. The SEM, SCXRD, and confocal imaging studies confirmed the healing behavior. The microcrystals of the same compound deposited on the flexible devices via an in-air sublimation technique were used for studying the performance of the conductivity which confirmed that the performance of the devices is not reduced even after bending for 100 cycles, demonstrating the durability of the devices. In Chapter 5, I have used the same non-centrosymmetric polar crystal from Chapter 4 for piezoelectric and pyroelectric energy harvesting and also for ferroelectric applications. The self-healing crystals show superior ferroelectric response with a very low coercive field. The piezoelectric and pyroelectric energy harvesting experiments on the composite of the crystals show excellent performances and device durability. In summary, I have made durable molecular crystals and demonstrated some of their proof-of-concept durable device performances for future technological applications.

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