Effect of oscillatory shear on the interfacial morphology of a reactive bilayer polymer system

We investigated, via atomic force microscopy and transmission electron microscopy, the effect of oscillatory shearing amplitude (γ0) and frequency (ω) on the interfacial morphology of a reactive bilayer polymer system composed of end-functionalized polystyrene with carboxylic acid (PS-mCOOH) and poly(methyl methacrylate-ran-glycidylmethacrylate) (PMMA-GMA). It has been observed that in the absence of oscillatory shearing (or at very small values of γ0 and ω), the roughness of the interface increased with reaction period, while at large values of γ0 and ω it became less than that observed in the absence of oscillatory shearing. This observation may be attributable to the possibility that oscillatory shearing might have hindered the diffusion of polymer chains, which are located away from the interface, to the interface of the layers. However, the effect of γ0 and ω on the roughness of the interface of (PS-mCOOH)/(PMMA-GMA) bilayer is found to be quite different. Specifically, when a large γ0 was first applied to the bilayer, followed by application of a low γ0, the reactive polymer chains diffused into the interface of the (PS-mCOOH)/(PMMA-GMA) bilayer; and then the roughness of the interface increased. However, when a high ω of oscillatory shear flow was first applied to a specimen, followed by application of a low ω of oscillatory shear flow to the same specimen, a relatively low degree of roughness of the interface was observed. This is attributable to the fact that the oscillatory shear with a large ω generated a multilayer microstructure consisting of PS and PMMA layers, which apparently played the role of an obstacle (or diffusion barrier) that hindered the diffusion of both reactive polymer chains to the interface for chemical reactions.