Development of novel indicators

Two indicating systems for measuring the dose of erythmal UV light have been developed. The first system is of a viologen salt, preferably benzyl viologen chloride, dissolved in poly(vinyl alcohol). This viologen dosimeter responds clearly to different wavelengths and intensities of UV light, although the colour change is hampered by the presence of oxygen, and completely reversed in the absence of UV light. Attempts are made to enhance the rate of the reaction of the viologens with UV light by changing the halide of the salt or adding electron donating species. There is no positive effect noted with the addition of these materials, but changing the halide does alter the UV spectrum of the viologen species, resulting in a slower reaction and thus providing a way of retarding the dosimeter if required. This dosimeter shows a demonstrable reaction to both artificial and natural sources of erythemal light. The second UV dosimeter is based on the tetrazolium salts and is shown to behave in a similar way to the viologen dosimeter, with the neotetrazolium chloride salt as a preferred material for use in the dosimeter. This tetrazolium system is shown to respond clearly to different wavelengths and intensities of light, and shows a demonstrable response to erythemal levels of UV. A solvatochromic indicator is developed, using Reichardt's dye adsorbed onto fumed silica to identify and measure the concentration of various solvent vapours. The fumed silica films are shown to be faster in response than polymer systems and have been shown to distinguish between different solvent vapours, but do not do so in a way that correlates with Reichardt's dye in the pure solvent. These films are shown to be more reliable in identifying alcohol vapours in a predictable manner. A review is also carried out on existing methods of assessing the performance of photocatalytic films, comparing them with a new method developed within the Mills group.