Reduced Plastic Dilatancy in Polymer Glasses

Amorphous solids in general exhibit a volume change during plastic deformation due to microstructure change during plastic relaxation. Here the deformation dilatancy of alkane polymer glasses upon shearing is investigated using molecular static simulations at zero temperature and pressure. The dilatancy of linear alkane chains has been quantified as a function of strain and chain length. It is found that the system densities decrease linearly with respect to strain after yield point. In addition, dilatability decreases considerably with increasing chain length, suggesting enhanced cooperation of different deformation mechanisms. An analytic model is introduced for dilatability based on the atomistic study. The entanglement chain length is predicted as 43 for alkane polymers from the model, agreeing well with experiments. The study provides insights of correlations of the physical properties and chain length of polymers which might be useful in material design and applications of structural polymers.