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Abstract
Volatile organic compounds (VOCs) are organic chemicals that could cause health effects on short-term and long-term exposure. Therefore, the detection of VOCs is important for early monitoring of hazards. However, current technologies for VOC detection have drawbacks such as relying on expensive instruments and skilled operators, and are time-consuming. To overcome these challenges, this thesis aims to develop an easy-to-use VOC sensor that could potentially be used on-sites by employing polydiacetylenes (PDAs), a class of conjugated polymers which are excellent materials for colorimetric sensors due to their chromatic properties visible by the naked eye.
There have been many developments in PDA-based sensors, however, shortcomings still exist. On one hand, the conventional method to fabricate PDA hinders its scalability for large-scale PDA production. On the other hand, although PDA-based VOC sensors recently developed lead to excellent detection performance, these approaches can only be realized by tedious monomer synthesis procedures. This thesis focuses on overcoming these two problems.
In this thesis, the first application of the solvent injection method for large-scale PDA synthesis was presented. The formation of PDA particles similar to those formed by the conventional film hydration method was confirmed by a study on particle size and morphology using dynamic light scattering and electron microscopy. The functionality of the PDA was confirmed via ammonia detection. Large-scale production of PDA vesicles (0.1 L and 0.25 L) was achieved. The results indicate that the solvent injection method is a viable alternative to the conventional method for large-scale PDA production.
Next, a simple approach to fabricate a paper-based PDA/polymer VOC sensing array using a drop-casting technique was developed. Compared with pure PDAs, the incorporation of polymers led to an enhanced sensitivity towards acetone vapor. The rationale of polymer incorporation was based on the solubility and affinity of polymers to different VOCs, which creates varying molecular interactions between polymers and VOCs. Length of diacetylene monomers, polymer molecular weight, and the ratios of PDA/polymer were investigated to tune the system. In the last section, the colorimetric behavior of the PDA sensor was investigated in response to vapors of five VOCs. The work presented in this thesis highlights new opportunities for the development of large-scale PDA materials and PDA-based VOC sensors.