Polymeric sensing films absorbing organic guests into a nanoporous host crystalline phase

Syndiotactic polystyrene (s-PS) semicrystalline films, including the nanoporous crystalline δ phase, have been tested as sensing elements of resonant sensors for vapors of volatile organic compounds (VOCs). In particular, the response to chloroform vapor of quartz crystal microbalance (QCM) sensors, coated with films of semicrystalline δ form of s-PS have been analyzed and compared to analogous systems coated with films of amorphous atactic polystyrene (a-PS). The sensitivity of sensors based on s-PS films was found markedly higher than those based on a-PS, particularly for low chloroform pressures. The higher sensitivity of the semicrystalline s-PS films is associated with a peculiar sorption mechanism: in fact, the organic compound, rather than being dissolved only into the amorphous phase, as it is generally the case for semicrystalline polymers, is mainly absorbed into the nanoporous crystalline phase, each molecule being confined into regularly spaced crystalline nanocavities, thus leading to a clathrate structure.