Many phase transitions exhibit ordering transitions at the boundary of the material that are distinct from the interior where the intermolecular interactions can be significantly different. The present result considers the existence of a reversible surface thermodynamic transition between two distinct morphologies in thin block copolymer (BCP) films that are of interest in nanomanufacturing applications. Specifically, we find a thermally reversible morphology transition between two distinct ordered states (spheres and cylinders) in flow coated films of poly (styrene-block-methyl methacrylate) (PS-b-PMMA) where the BCP forms a cylinder microphase in the bulk. This transition occurs only at the outer polymer-air interface of the film, the film interior remaining in the cylinder state. Moreover, we find this order-order transition to be insensitive to film thickness over the thickness range investigated (40 nm to 170 nm). This transition is of importance in characterizing the thermodynamics and dynamics of thin BCP films used in manufacturing applications where these films are used as templates.
Citation: Nano Letters
Pub Type: Journals
block copolymer, residual stress