Analysis of self-cleaning and float glass: a comparative study of pollution on the glass surfaces under real life conditions

In order to investigate the self-cleaning efficiency two commercial self-cleaning TiO2 coated glasses and an uncoated float (reference) glass were exposed to the environment under two different sets of experimental conditions. The first experiment involved the exposure of glass panels in unsheltered conditions for 16 months in France and England. Macroscopic observations were performed monthly by panels of ten end users and a visual ranking of the samples was given according to standardised guidelines. Haze values were also measured by means of a haze meter. A good correlation between the haze and the visual evaluation of samples was obtained. In general, a lower level of soiling was detected on the self-cleaning glasses. The second exposure experiment was carried out in Paris (France); samples were exposed to sheltered and unsheltered conditions and a survey of particulate pollutants was also performed by means of air filtration. Microscopic characterisation of the deposit was performed by means of different analytical techniques. The relative abundance of deposited carbonaceous species as compared to sulphates, and nitrates was determined as well as the nature of the organic compounds deposited on the glass samples. Frequent dry droplets, observed on the traditional float glass samples, demonstrate the hydrophobicity of the glass surface due to the presence of organic contaminants, while different patterns of dirt deposits were identified on the hydrophilic self-cleaning surfaces. Inorganic salts and organic compounds were identified as the 'glue' that hampers the removal of the particles by rain.