The relationship between diffusion and dynamically accessible volume in polymer chain dynamics simulated with the bond fluctuation model

The dependence of the diffusion coefficient, D, of polymer systems on the Dynamically Accessible Volume (DAV) was calculated in the framework of the Bond Fluctuation Model. The quadratic relationship between dynamically accessible volume and diffusion coefficient, which has been observed for some other models, has been confirmed for high values of DAV, whereas smaller diffusion coefficients than those predicted by the model were shown for DAV values lower than 0.1 independently of the chain length. This critical value is related to the loss of connectivity of the holes of the system and the consequent diminution of the diffusion of the system. The influence of the chain length on this behaviour has been established, showing that there is a linear relationship between the γ parameter (the proportionality constant between D and the squared DAV) and the reciprocal of the chain length.