Mechanics of Piezoelectric Actuating Crystals

Tanari, S S Pratap (2022) Mechanics of Piezoelectric Actuating Crystals. Masters thesis, Indian Institute of Science Education and Research Kolkata.

Text (MS Dissertation of S S Pratap Tanari (17MS129)) 17MS129_Thesis_file.pdf - Submitted Version Restricted to Repository staff only Download (4MB)

Abstract

In 1989, Desiraju's defined crystal engineering as “understanding of intermolecular interactions in the context of crystal packing and application of such understanding in the design of new solids with desired physical and chemical properties.” The idea of enhancing desired properties simply by fine tuning the intermolecular interactions has resulted in a slew of single crystal discoveries in a variety of fields. One such area of research which is gaining traction is actuation in organic single crystals which has many applications in soft robotics. The field of soft robotics has advanced so far that there has been a significant shift in how we perceive robots in various applications. Following the introduction of hundreds of actuators (organic and inorganic, soft and hard), people all over the world began to recognise materials that had previously gone unnoticed, such as smart organic crystals. Designing smart crystals with potential actuation capabilities necessitates strong molecular engineering. Crystal engineering has aided in the development of new classes of responsive compounds that can be used in soft robotics, sensors, actuators, and piezoelectric devices, among other applications. Despite the fact that crystals are not as soft as gels or polymers, they have the unique ability to have long-range molecular order and a moderate softness due to weak intermolecular interactions inside them. Because of this ordered molecular packing, stimulus responsive single crystals can exhibit macroscopic interactions with the environment via actuation motions. And due to mechanically compliant nature in some crystals, the actuation could be complex at times. Currently, there are many reports on photoresponsive crystals, a few on thermoresponsive crystals and a little on other stimuli induced actuation. The reason for such responses has always been photochemistry and phase transition and these crystals cannot perform work, motility, or locomotion without the input energy. SAR1 (code name for dimethyl-4,4'-(methylenebis(azanediyl))dibenzoate) single crystal, on the other hand, when fractured by mechanical stress, travels towards the counter parts by means of mechanical actuation by itself. The distance of attraction varies from crystal dimensions as it solely depends upon the magnitude of charges generated on the broken surfaces. Piezoelectricity is the cause of charge development, and the molecule may be non-centrosymmetric to have this property. The mechanical motion observed is one of its kind and so far, no study has been reported on this phenomenon. Because any material must meet specific criteria in order to be considered an effective actuator, I chose to investigate the mechanics of actuation behaviour in order to calculate certain attributes. These attributes are known as performance parameters, and they can be used to compare a material to a practical actuator. In this study I presented two viable models that describe the motion of SAR1 single crystals when aligned in a desired way. And, using the models, one can derive some readily accessible parameters that describe the crystal's performance, which could then be compared directly with other smart material. To summarise, this thesis presents a preliminary investigation of mechanics in SAR1 single crystals in order to extract some actuation attributes that can be used to quantify its performance in comparison to other actuator classes as well as under the potential of piezoelectric molecular crystals in the field of soft robotics and micro actuators.

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