Molecular motions at low temperature observed by positron annihilation

作者：He CQ^*; Suzuki T; Ma L; Matsuo M; Shantarovich VP; Kondo K; Ito Y

来源：Physics Letters A, 2002, 304(1-2): 49-53.

DOI：10.1016/S0375-9601(02)01318-X

• positron annihilation
• irradiation
• trapped electron
• molecular motion

Positron annihilation lifetime spectroscope (PALS) was applied to low-density polyethylene (LDPE) and ethylenemethylmethacrylate (EMMA) copolymers with various MMA contents. The experiments were conducted in the dark as well as under visible light condition, In the dark at a low temperature of about 30 K, the o-Ps intensity was observed to increase with the elapsed time. and the increasing rate depended on the MMA content. After being kept for a long time at low temperature. the sample temperature was increased. The o-Ps intensity and its lifetime were found to change as a function of temperature. In the light, no significant change was found for the o-Ps intensity below the glass transition temperature. However. a dramatic variation of the o-Ps intensity Was found to correspond to a change of its lifetime in the dark. The observations showed that not only the variation of the o-Ps lifetime could be related to the structural change and molecular motions of polymers, but also the change of the o-Ps intensity. particularly at low temperature in the dark. could be related to the activation of molecular motions. The results indicated that PALS could be used as a novel probe for molecular motions at low temperature.

• 出版日期2002-11-4