ac electrical investigation of polysilsesquioxanic films used as humidity sensors

We tested the ac electrical properties of dielectric poly(propylmetacril heptaisobutyl-POSS)-co-(N-butylmethacrylate) thin films in order to better understand their working mechanism as relative humidity sensing devices. Samples with a 15% and 25% of cage content in weigh have been characterized as a function of temperature and frequency. The different frequency responses are reported and discussed in terms of the existing models. The temperature glass transition (T-g) has been measured by means of an electrical method on films in the same sensor configuration and correlated with the electronic transport properties. Furthermore, the interest of the material with a 15% of cage content is discussed in the contest of basic studies concerning water confinement effects at the molecular scale, i.e., the supercooling of water. (C) 2008 American Institute of Physics.