Interdependence of ammonia and water sorption in polyacrylic acid layers

Based on gravimetric measurements, a model describing the interdependence between the ammonia and water sorption in polyacrylic acid (PAA) is developed. The starting point is the fact that PAA-coated quartz microbalances (QMBs) show significant frequency shifts under exposure to ammonia and humidity. The response of the devices suggests that the mass increase under ammonia exposure, in humid air, is due to both the absorbed ammonia and the additionally absorbed water. At low humidity levels the ammonia changes the polymer matrix so that more water molecules can be absorbed. If the humidity is increased a glassy-to-rubbery state transition occurs that leads to a complex response of PAA-QMBs. (C) 2007 Elsevier B.V. All rights reserved.