Reaction-induced pattern formation at the polymer-polymer interface

The interfacial structure of immiscible bilayer films of amorphous polyamid e (aPA)/polysulfone (PSU) was investigated by ellipsometry, atomic force mi croscopy (AFM), and transmission electron microscopy (TEM). The interfacial thickness of the annealed aPA/non-functionalized PSU sample was smaller th an the measurable limit of ellipsometry (ca. 2 nm). However, by grafting a maleic anhydride group to the PSU chain, the thickness increased to the ord er of 40 nm at 200 degrees C. It was also found from AFM measurements that the interface was undulated, with the scale of the lateral roughness being ca. 40 nm. Therefore, it is likely that, during the interfacial reaction be tween the amine-terminated aPA and the MAH-functionalized PSU, an undulated interface was formed. This is probably because in situ formed copolymers e ntropically destabilized the interface by adopting a tightly packed conform ation at high copolymer concentrations, which resulted in an increase of th e interfacial area. The interfacial thickness determined by ellipsometry se ems to include the contribution of the amplitude of the undulation.