FREE-VOLUME STUDIES IN MISCIBLE POLYMER BLEND SYSTEMS

This paper summarises the currently available literature concerned wit h measurement of free volume in miscible, amorphous polymer blends usi ng positron annihilation lifetime spectroscopy (PALS) which probes exc luded volume at the angstrom level. Previously reported data is compar ed with new data from a range of different blend systems. Miscible ble nds tend to show a negative deviation of free volume size (and to a le sser degree free volume fraction) on mixing due to the intimacy of pac king of the blend component macromolecules. A largely immiscible syste m is also reported and shows a different behaviour (positive deviation of free volume size) and this is ascribed to additional free volume a t the interface.