Macroscopically oriented lamellar microdomains created by “cold zone-heating” method involving OOT

The zone-heating method, which involves ordering of materials under moving temperature gradient ∇ T , has been widely used as a technique to create macroscopically oriented ordered structures of various kinds of materials. We applied this method to a large molecular weight symmetric polystyrene-block-polyisoprene diblock copolymer (dibcp) at a temperature where the ∇ T field exists below its order–disorder transition temperature TODT of the dibcp. In this method we first prepared the solvent-cast bulk films of the dibcp having a nonequilibrium morphology of hexagonally packed cylindrical microdomains (hex-cyl) by using a solvent selectively good for polyisoprene blocks. Then the zone-heating method was applied to the order–order transition process from the nonequilibrium hex-cyl to equilibrium lamellae. The “cold zone-heating” method, “cold” in the sense of the ∇ T field existing below TODT, successfully created macroscopically oriented lamellae with their normals preferentially oriented parallel to the ∇ T axis and their edges preferentially standing with respect to the bulk film surfaces. It was also found that the initial orientation of the (100) plane of hex-cyl normal to the ∇ T axis prefers to that parallel to the ∇ T axis for a better macroscopic alignment of lamellae. A possible model for the cold zone-heating-induced lamellar orientation will be discussed in the text.