Diffusion of ions into polymers

Not only have ionic solutions been used to initiate water treeing in polyethylene under laboratory conditions, but evidence has been obtained that ions enhance the absorption of water into polyethylene [1] and also enhance the growth of water trees [2, 3, 4, 5]. It has also been shown that ions are present in the treed region of the polymers [6]. Given and Crichton [7, 4] have shown that there is an inverse relationship between the growth rate of trees and the ionic radius on the anion. Given et al. [7] also suggest that the penetration of ions into the polymer will distort its structure by forcing apart the polymer chains in the amorphous region. This in turn is seen as a mechanism for en hancing the rate of water migration into the polymer where the water is held in part by the hydration sphere around the anion. In a cable, the insulating polyethylene is surrounded by a semiconducting jacket. If ions are going to penetrate into the polyethylene insulation, it must first diffuse through the semiconducting jacket and traverse the interface between the semicon and insulation before diffusing into the polyethylene. This paper will describe the experiments designed to study the diffusion of ions through the semicon.