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Permeability, diffusion, and solubility coefficients for H2O vapor in four different 6FDA‐based polyimides were determined at temperatures between 25 and 45°C and over a wide range of relative humidities. The solubility of H2O vapor in some of the polyimides studied can be described by the “dual‐mode sorption” model whereas in other polyimides it is represented by the Flory‐Huggins equation, which suggests that the latter polymers are plasticized by H2O. The solubility of H2O vapor in the polyimides decreases as the temperature is raised and increases with increasing polarity of the polymer. The diffusion coefficients for H2O in the polyimides studied either increase or pass through a weak maximum with increasing H2O activity, or concentration in the polymers. The latter behavior is probably due to a clustering of H2O molecules in the polyimides at higher H2O activities or concentrations. The diffusion coefficients for H2O decrease as the chain‐packing density of the polyimides increases. The permeability coefficients for H2O vapor in 6FDA‐based polyimide membranes either increase slightly or are constant as the H2O activity is increased. The experimental values of the permeability coefficients are consistent with the values determined from diffusion and solubility coefficients. The permeability of the polyimides to H2O vapor appears to be controlled by the solubility of H2O in the polymers. The polyimides studied exhibit a very high selectivity for H2O vapor relative to CH4, and therefore are potentially useful membrane materials for the dehydration of natural gas. ©1995 John Wiley & Sons, Inc.

SummaryInterventions to improve water quality, particularly when deployed at the household level, are an effective means of preventing endemic diarrhoeal disease, a leading cause of mortality and morbidity. Following a national survey indicating widespread faecal contamination of drinking water in Indian cities, a point-of-use water treatment unit was developed, which combines filtration and disinfection, does not require power or water pressure and has an operating cost of Rs. 0.25 (US$0.0057) per litre.We assessed the microbiological performance of the unit in the laboratory over the full 1500 l design life of the unit's consumable components. Geometric mean reductions for the units were more than 6 logs (99.9999%) for bacteria, more than 7 logs (99.99999%) for viruses and more than 3 logs (99.9%) for the test surrogate for protozoan cysts. Geometric mean reductions exceeded levels established for microbial water purifiers. The product water was free of detectable chlorine. If these results are validated in field trials, the deployment of the unit on a wide scale among vulnerable populations may make an important contribution to public health efforts to control intractable waterborne diseases.

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