Contact charging and small-scale charge migration in polymers

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Abstract
The authors describe a novel technique for investigating the motion of free charge in insulators. It involves measurements of the charge transfer in a series of contacts with a (preferably liquid) metal and, simultaneously, the mean distance of the charge from the insulator surface. The technique can detect charge migration over very small distances and it provides a powerful means of elucidating mechanisms of conduction; there is no possibility of confusing free-charge motion with polarisation changes due to e.g. dipole orientation. Their experiments on polymers reinforce previous suggestions that the polymers contain both permanent traps and 'shallow' traps which retain charge for a relatively short time. They suggest, however that this distinction may reflect different degrees of isolation of the electron traps in a relatively loose and mobile network of polymer molecules, rather than differences in their energy.