The relation between free volume and relaxation behavior studied by positron annihilation

用热机械法（TMA）和核磁共振法研究了聚合物的松弛行为。近年来正电子湮没寿命谱（帕尔斯）被用于研究聚合物的弛豫行为。帕尔斯是利用电子偶素（Positronium，Ps）的寿命来测量自由体积的大小。Ps是由正电子和电子组成的类氢原子。自由体积中与聚苯乙烯有关的长寿命组分的强度可以作为研究聚合物的化学结构、三维结构、自由基、电子结构等诸多因素的一个很好的尺度，因此，如果我们能够制备样品或实验条件，可以从强度上讨论聚合物的特性。我们观察到低温下的强度随时间的增加而增加。这可以通过以下事实来解释：由辐射效应引起的被捕获的电子随着经过的时间而增加。由于结构的冻结，被捕获的电子被保持在聚合物结构之间产生的电势中。随着样品温度的升高，强度逐渐降低，达到最小值后又开始增加。低温下的这种降低与聚合物结构运动引起的松弛行为有关。

Relaxation behavior of polymers has been studied by the thermo mechanical method (TMA) and NMR. Recently positron annihilation lifetime spectroscopy (PALS) has been applied to study the relaxation behavior of polymers. PALS is utilizing the lifetime measurement of positronium (Ps), which is hydrogen like atom composed of positron and electron. From the lifetime of PS, the size of free volume can be deduced. The intensity of the long lived component related to the PS in the free volume can be a good measure to study many factors such as chemical structure, three dimensional structure, radicals, electronic structure, etc.Hence from the intensity we can discuss characteristics of polymers, if we can prepare samples or experimental condition. We have observed the increase in the intensity at low temperature with the elapsed time. This can be explained by the fact that trapped electrons, which are induced by the radiation effect, increase with the elapsed time. The trapped electrons are kept in the potential created among polymer structures because of the freezing of the structure. Increasing the temperature of samples, the intensity gradually decreases and the after minimum, it starts increasing again. This decrease at low temperature is related to the relaxation behavior, which is originated from the movement of polymer structures.