Abstract
The diffusion in a polymer couple composed of glassy PPO and rubbery PS was explored by using SIMS and AFM to study the polymer chain diffusion across a glassy state interface. The diffusion across the interface was found to follow a typical Case-II diffusion in which the PS chains plasticize the glassy PPO chains in a thin intermixing layer (ca. 20 nm) at the interface. Once the PPO chains diffused out the intermixing layer, they quickly disperse themselves in the PS region forming a completely miscible blend. It was also found that the interface diffusion speed increases with the spin coating speed of the PPO thin film, implying an effect due to chain conformation and the residue stress in the glassy region. In addition, the propagation speed of the diffusion front in the glassy PPO region significantly slowed down in the vicinities of an internal interface created by separate spin coatings. The AFM surface topography of the diffusion couple clearly shows a roughening process associated with the polymer chain diffusion, indicating a nano-scale non-uniform distribution in the lateral directions of the diffusion front.