Design and synthesis of functional materials for smart label devices

Abstract

Maintaining the quality of temperature-sensitive products across the cold-supply chain is critical in preventing food waste and loss. Time temperature indicators (TTIs) are a type of smart label that can offer part of the solution to this complex problem. Unlike conventional “use-by date” labels, TTIs monitor the cumulative effects of time and temperature, and provide a visual indication to the consumer when the product is no longer safe for consumption. Providing the end user with this information can greatly reducing waste by presenting a real-time evaluation of food freshness. The aim of this project is to identify and develop functional materials that can be integrated into a TTI smart label device as either a) the visible indicator, or b) as a functional component that provides autonomous activation via light-sensitive microfluidic valves. In the first section of this work, polyoxometalate-polymer hybrids were synthesised for use as redox-active colour indicators. N-vinylimidazole and N-vinylimidazolium monomers were co-polymerised with poly(ethylene glycol) diacrylate crosslinkers to yield highly crosslinked polymer networks. [PMo12O40](TBA)3 was immobilised onto the polymer supports and reduction of the resulting composite materials with aqueous ascorbic acid resulted in vivid colour changes. The hybrid materials were then integrated into prototype diffusion-based TTIs. Temperature and ascorbic acid concentration was varied, and it was found that the prototype systems exhibited time-temperature dependent colour changes, although there were inconsistencies between repeated device experiments. More elaborate device designs are needed in any future work to address this issue. In the latter section of this thesis, an array of spiropyran derivatives were synthesised via palladium catalysed Suzuki-Miyaura cross coupling reactions between bromo-substituted spiropyrans and arylboronic acids. Conversions of up to 99 % were recorded under mild reaction conditions and with low catalyst loadings. Phenol- (SpOH) and pyridine- (SpPy) substituted spiropyran derivatives were shown to possess photochromic and acidochromic properties. Interestingly, SpPy derivatives also displayed solid-state photochromism. SpOH compounds were further transformed into spiropyran-acrylates (SpA) for covalent incorporation into poly(N-isopropylacrylamide)-based hydrogels as light-responsive microfluidic valves. However, light actuation was not observed as smaller-scale testing methods were required.