Study of Glassy and Rubbery States of Polymers Using Positronium

Described is the technique of observing the vacancies in glassy and rubbery polymers using positronium (Ps) which is formed when positrons are injected into polymers. First, two important fundamental aspects of Ps are introduced that 1) it is “a seeker and digger of holes” and that 2) the ortho-positronium (o-Ps) intensity cannot be simply correlated with the number density of holes since the Ps formation process, basically involving fast intra-spur reactions, is complicated. Three examples are given. The first example is the simple method of determining glass transition temperature, Tg. Due to the particular nature of Ps as “seeker and digger of holes”, the volume information is amplified in the rubbery state, which is a favorable condition for the determination of Tg. Second example is the study of gas sorption. It is shown that the o-Ps lifetime and intensity reflect the Langmuir-type and Henry-type sorption mechanisms in contrastingly different ways. Furthermore o-Ps brings forth information of the microscopic states at the very site of sorption, the information which cannot be obtained by any other macroscopic methods of sorption study. Last example is the study of irradiation effects of polymers by Ps. In the rubbery state it is difficult for Ps to see the radiation induced changes since the efficient segment motions smear out the differences of the hole. However in the glassy state, where the hole structure is frozen, the radiation effects can be observed by Ps. Ps appears to be particularly sensitive to those sites that has acquired less density by degradation. Ps is promising as a probe of holes in polymers provided that we are well aware of the unique nature of Ps and deepen our knowledge about it.