Audible Sound Controlled Chemical Patterns and Hydrogel Patterning

Abstract

This thesis presents a method of generating and controlling chemical patterns in solution through the application of audible sound. These patterns arise from the diffusion of colored chemical species from networks operating under non-equilibrium conditions. Despite the known ability of various chemical reactions to form patterns, consistent replication is challenging due to the inherently uncontrollable nature of diffusion. However, sound, a known regulator of biological processes and pattern generation in materials, is harnessed here to introduce a controllable variable. Chladni figures and Faraday instability exemplify the pattern formation potential of sound on solid and liquid mediums, respectively. The faraday waves occur at the air-liquid interface when a low-frequency vertical vibration is applied to a liquid placed in a dish. The waves generated on the surface of the solution by applying audible sound result in the nonuniform dissolution of atmospheric gases such as oxygen or carbon dioxide at the nodal and antinodal positions. Based on this phenomenon, we reported that chemical pattern created in a Petri dish can be easily regulated by controlling the diffusion according to the frequency and intensity of the audible sound waves applied. In this study, we have demonstrated the utilization of audible sound-induced liquid vibrations to obtain spatiotemporal chemical patterns in a solution. We explored the influence of audible sound on the generation of spatiotemp oral chemical patterns, focusing on the effects of sound frequency and amplitude. Utilizing the blue bottle experiment and phenolphthalein reaction within a Petri dish, we were able to observe a spatiotemporal pattern comprising well-defined concentric rings that formed within a specific temporal window. Our findings included a reduction in the spacing of these ring patterns with increasing sound frequency. Additionally, we investigated the effect of the shape of the dish, another important factor that has an impact on the shape of these chemical patterns. Experiments in a square dish revealed that the pattern is optimized and ring pattern spacing decreased with higher frequencies as with the circular dish. However, there was a notable variance in pattern formation based on the applied frequency. The experimental results demonstrated a strong correlation with the theoretical predictions of a two-dimensional (2D) standing wave model. Beyond theoretical exploration, we developed a new methodology to localize gelation and manipulate the structure and porosity of hydrogels by sound. We have applied our strategy to the synthesis of patterned hydrogels using bovine serum albumin solution and glutaraldehyde vapor. Synthesized patterned hydrogels has potential applications such as biomedical microdevices, soft machines, microfluids, optical devices, drug delivery systems and artificial muscles. Also, the patterns in hydrogels could also be advantageous in biological modelling for in vitro models, dynamic systems and biomimetic tissue engineering scaffolds. This work not only elucidates the role of audible sound in chemical pattern formation but also introduces a new avenue for the spatiotemporal regulation of chemical reactions, with broad applications in science and engineering.