Diffusion Behavior of Waterproof Glue into Silicone Rubber Insulation of Submarine Cable Joints Based on Molecular Dynamics Simulation

Silicone rubber (SiR) is widely used in submarine high-voltage cable joint insulation due to its outstanding electrical, mechanical and thermal endurance properties. Current research showed that the organic molecules of waterproof layer for submarine cable joints diffused into the SiR insulation during prequalification tests, which led to the insulation aging and deterioration. In this paper, in order to reveal the diffusion mechanism of waterproof glue into SiR insulation, the diffusion behavior of asphalt- and polyurethane-based waterproof glue is studied based on molecular dynamics simulation. The simulation parameters, including interaction energy, diffusion displacement and mean square displacement, are employed to evaluate the diffusion behavior of waterproof glue. The results show that the interaction energy between polyurethane and SiR is more powerful than that of asphalt, which indicates intense attraction between polyurethane and SiR, and lead to a weak diffusion coefficient for polyurethane. The order of diffusion coefficients is as follows, naphthalene > phenanthrene > pyrene > polyurethane, which is proportional to the relative molecular mass. Moreover, it is inferred that the interaction energy and the relative molecular mass are the key factors that influence the diffusion behavior of waterproof glue. The stronger interaction energy and greater relative molecular mass make it difficult for small molecules to diffuse in the free volume of SiR. It is concluded that the polyurethane-based waterproof glue has a great potential for the waterproof layer of submarine high-voltage cable joints.