Interdiffusion of short chain oligomers into an entangled polymer film

The crossover from a simple liquid to an unentangled oligomer diffusing into liquid and glassy entangled polymer matrices is studied by molecular dynamics simulations. The oligomer film is described by a bead-spring model of chain length No = 10 and 50 while the polymer matrix consist of chains of length Np = 500. Results are compared to interdiffusion into an unentangled polymer matrix of chain length Np = 50. Diffusion of the oligomer into the polymer is observed in all cases as evidenced by t1/2 scaling of both the mass uptake of the oligomer by the polymer and oligomer density profiles on the polymer-rich side of the interface as a function of time t. On the oligomer-rich side, the scaling exponent is less than 1/2 due to the swelling of the polymer film and depends on the chain length of both the oligomer and polymer. Oligomer diffusivities into the entangled polymer matrix are highly concentration dependent, in contrast to a nearly constant diffusivity for penetration into the unentangled polymer. The roughness of the polymer film evolves as t0,2 for both liquid and glassy films. © 2009 American Chemical Society.