Flory-Huggins Photonic Sensors

This Thesis focuses on the design of a simple optical method for the determination of molecular diffusion coefficients and for the quali-quantitative assessment of the diffusing species in polymer photonic sensors and in commercial polymer thin films used in packaging. This project arose to overcome the lack of methodologies related to the detection of hazardous vapor molecules both in air and in goods packaging. To tackle this task, this Thesis proposes simple optical spectroscopy coupled to photonic crystal sensors (called Flory-Huggins Photonic Sensors, FHPSs) and commercial polymer thin films to retrieve quali-quantitative information of polluted air and molecular diffusion coefficient in the polymers themselves. This is achieved studying the kinetics of optical variations in the diffraction and/or interference pattern of the sensors, which are opportunely designed to interact with the analyte species. In the first Chapters, after discussing the problematics related to the monitoring of vapor analytes and to the determination of diffusion coefficients, this Thesis explains the working principle of the FHPSs, and the optical set-up designed to the purpose. Then, commodity polymers FHPSs are used as proof of principle to create a receipt for the design of sensors suitable for any class of chemical compounds. This system also shows colorimetric response with sensitivity and lower detection limit approaching the part per million and label free selectivity to the tested analytes. Moreover, the study of the kinetics of the spectral response allow to evaluate the diffusion coefficients of the analytes within the photonic structure. The method is then tested for the detection of various pollutants. The possibility to use unstructured commercial films to the same purposes in also discussed and demonstrated. These results promise to simplify detection of volatile pollutants in atmosphere and a new simple tool to asses diffusion of hazardous molecules in packaging systems. The possibility to assess the colorimetric response of the FHPSs even by the naked eye, together with the capability to monitor diffusive processes in polymer packaging film directly on the shelf, promises also safety devices and continuous assessment of goods.