Molecule diffusion behaviours of waterproof sealants into silicone rubber insulation for submarine cable joint based on molecular dynamics simulations

The repair joints of high-voltage cables play a significant role in the urgent cable main-tenance,by recovering cable conductor,insulation,shielding layer and waterproof layer especially for submarine cables.However,the molecule diffusion and permeation pro-cesses from waterproof sealant into the cable joint insulation occur,leading to the insulation ageing and deterioration.In this article,the molecule diffusion behaviours of six typical molecules from the asphalt-based and polyurethane-based waterproof sealants into silicone rubber insulation are investigated.The results show that the order of diffusion coefficients is as follows,phenanthrene>fluoranthene>pyrene>benzo[k]fluoranthene>indeno[1,2,3-cd]pyrene>polyurethane(PU).The relative molecular mass and binding energy are pivotal factors affecting the diffusion behaviour,while there is a linear relationship between the logarithm of the diffusion coefficient and the ratio of binding energy to relative molecular mass.Besides,the rising ambient temperature in-creases the fraction of free volume of silicone rubber and decreases the binding energy,thus resulting in a higher diffusion coefficient and an enhanced permeation process of the asphalt-based sealant.In summary,the PU-based waterproof sealant,with a much lower permeability than the asphalt-based material,has a potential application in the waterproof layer for high-voltage submarine cable repair joints.