An high sensitivity optical sensor for chloroform vapours detection based on nanometric film of delta-form syndiotactic polystyrene

A film of syndiotactic polystyrene (sPS) in the nanoporous crystalline 8 form has been used for the detection of chloroform in the vapor phase at very low concentration The variation of the refractive index due to the chloroform sorption within the polymer has been used as transduction property. Reflectivity measurements by a fiber optic refractometer, coated with a nanometric (73 nm) film has been performed at very low pressure of chloroform (between 0.2 and 5 Torr) at three different temperatures (35, 49 and 56 degrees C). Mass sorption experiments have been concurrently performed with an electronic microbalance operating in the same conditions of the optical sensor. Major result from the gravimetric tests is that the analyte is mainly adsorbed into the nanoporous phase where the penetrant molecules can be hosted with a certain selectivity based on both size exclusion and host guest interactions. The quantitative correlation between the mass of analyte sorbed within the polymer layer and the refractive index variation has been observed to be temperature independent. A phenomenological equation based on the Lorentz-Lorenz law has been proposed to describe the effect of the chloroform uptake including both concentration and polarizability, changes on the refractive index of the sensible layer. (c) 2004 Elsevier B.V. All rights reserved.