Positron Annihilation Spectroscopy of Polystyrene Filled with Carbon Nanomaterials

Positron annihilation lifetime spectroscopy (PALS) was employed to study the free volume properties of polystyrene (PS) containing three different types of carbon nanoparticles: polystyrene-grafted single wall carbon nanotubes (SWCNTs-g-PS), single wall carbon nanotubes (SWCNTs), and carbon nanofibers (CNFs). The glass transition temperature measured via PALS was significantly lower than that from differential scanning calorimetry (DSC), although qualitatively the two methods agreed in that the T-g measured increased as nanotubes were added to the material. There were some specific differences between the two measurements which may have been related to the fact that DSC does not measure T-g of a portion of the material which is immobilized on the surface of the particle, while PALS measures all polymer, whether immobilized or not. PALS was also used to measure the thermal expansion coefficient and distributions of the free volume of the polystyrene.