Abstract
Free volume characteristics in three samples of monodisperse polystyrene were investigated by positron annihilation technique over a temperature range from 300 to 380 K. The number-average molecular weight of the samples ranged from 5730 to 1,524,000. The observed lifetime spectra were resolved into three components, where the longest lifetime, τ 3 , was associated with the pick-off annihilation of ortho-positronium (o-Ps) trapped by free volumes. The change of the temperature coefficient of τ 3 was observed at around 350 K, at which the value of τ 3 was a constant value of 2.3 ns for all specimens with different molecular weights. There was no discrete change of τ 3 in intensity, which is corresponding to the number of free volumes. The size of free volume at glass transition was evaluated to be 0.1 nm 3 .
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