Molecular dynamics simulation study of compatibility for the polyvinylmethylether/polystyrene mixture

摘要

We have performed molecular dynamics simulations for atomistic representations of polyvinylmethylether/polystyrene blends using the 'discover' module of the Materials Studio software platform with the COMPASS forcefield. The simulation boxes are constructed with the Amorphous Cell module, introducing polymer chains designed with the Visualiser building tools. The simulations yield trajectories files, whose coordinates have been employed to calculate the collective scattering structure factor. Comparison of the numerical data obtained for this property with the predictions of random phase approximation theory, depending on the Flory-Huggins parameter, has allowed us to obtain numerical results for this parameter, commonly accepted as a good indicator of compatibility. The results depend on the method used to assign partial charges though they are always reasonably close to existing data obtained through neutron scattering experiments. The charge equilibration method gives a correct prediction of compatibility in the studied temperature range. Moreover, it shows a positive variation of the Flory-Huggins parameter with temperature, in agreement with the phase behaviour of these blends that show a lower critical temperature. However, the parameter absolute values are too high. When forcefield assigned charges are introduced, the Flory-Huggins parameter are slightly positive and a non-monotonous variation with temperature is found. However, the values for the highest temperatures are remarkably close to the experimental data.