Solubility properties of siloxane polymers for chemical sensors

Many chemical sensors rely on a sorbent material to collect and concentrate analyte molecules at the sensor's surface where they can be detected. Ideally, this sorbent material will impart the chemical sensor with both sensitivity and selectivity for the target species. If the sensor is to be reversible, then the species must also desorb from the material or be actively removed by some process such as catalytic destruction. Polymer materials offer many attractive features for chemical sensing. Organic compounds are readily sorbed in a reversible fashion, selectivity can be altered by varying the chemical structure, and polymer materials can be processed into thin films. In this paper, we discuss the factors that govern the sorption of vapors by organic polymers. The approach described has been applied in the past for the design and selection of polymers for acoustic wave sensors. However, the principles apply equally well to the sorption of vapors by polymers used on optical chemical sensors. For example, the polymer could be applied as a thin film to a planar waveguide as the cladding along the length of an optical fiber, or to the end of an optical fiber. Species sorbed into the polymer could then be detected by a change in an optical signal.