Study of free volume parameters of polystyrenes of different molecular architecture by positron annihilation lifetime measurement

Differences of size, content and size distribution of free volumes in linear branched and three-armed polystyrenes, synthesized by radical and anionic processes, were observed by positron annihilation lifetime measurements. The temperature dependence of an average free volume radius was quite similar among polystyrenes of different architectures and molecular weight distributions. The free volume radius increased with temperature, from 0.27 nm (T:60 K) to 0.29 nm (T:260 K) and 0.30 nm (T _g:363 K), then to 0.35 nm (423 K), showing turning at and transition temperature. The free volume content decreased from 60 K to 220 K to 300 K showing peculiar minimum at 220 K to 300 K depending on the molecular shape, increased above 320 K, upto 340 to 360 K. The free volume contents decreased with an increase of molecular weight and by an addition of oligomer or plasticiser, suggesting differences in relaxation time or molecular motion between the edge and middle portions of molecular chain and filling effect of smaller molecules in free volumes, respectively. The apparent free volume fraction showed clear variations atT andT _g. Size distribution of free volumes suggested more complicated behavior of free volume upon the molecular relaxations and filling effect.     

The radioisotopic battery based on radio-voltaic effect

The radio-voltaic effect is investigated to be applied radioisotopic batteries in this work. The collection rates of the electron-hole pairs are 94 percent for the alpha particles emitted by²³⁹Pu source and 65 percent for the beta particles emitted by⁹⁰Sr-⁹⁰Y source. The maximum energy conversion efficiency got by the silicon element is about 16%. A prototype radioisotopic battery with¹⁴⁷Pm beta sources is constructed. Its maximum short-circuit current and off voltage are about 2 A and 190 mV respectively. The experimental data suggest that the life of the prototype battery may be more than three years.