Charge Trapping in Polymers

An investigation is described of the role of unsaturated groups in the molecular structure on charge trapping in synthetic polymers. An attempt has also been made to quantify the effect on carrier migration of doping these materials with halogens. Using a surface charge decay technique carrier mobility has been determined in vacuo for a number of synthetic polymers and also for both high‐ and low‐density polyethylenes doped with halogens. These data are presented together with an account of concurrent measurements of optical absorption in the same materials. The data indicate a tendency for "pure polymers" with known higher unsaturation content to exhibit a lower carrier mobility. Increased mobility was observed with either bromine or iodine impregnation of polyethylene. The optical data show that the iodine enters the polymer as neutral molecules most of which emerge under atmospheric conditions. The remainder, however, form charge exchange complexes at unsaturation sites in the polymer. The role of complexes in carrier transport is discussed.