Figure 2

A series of AFM images [row (I)] show the morphologies of the PMMA-air interface with varying Mw of the PS film before annealing. A series of optical micrographs [row (II)] and AFM images [row (III)] illustrating the morphologies of the PMMA-air interface with varying Mw of the PS film when heated to 160 °C. Images (A–E) in both the rows correspond to PS Mw = 13 kg/mol (annealing time: 1.5 min), 31 kg/mol (annealing time: 5 min), 97 kg/mol (annealing time: 20 min), 390 kg/mol (annealing time: 180 min) and 2000 kg/mol (annealing time: 240 min), respectively, when PMMA Mw = 50 kg/mol (1.75 × 10⁷ Pa s)^51,52,53, h _PMMA  = 18 ± 2 nm and h _PS  = 174 ± 5 nm. A series of AFM images [row (IV)] show the morphologies of the PMMA-air interface with varying Mw of the PS film when heated to 160 °C for the same systems in row (II and III) with an annealing time of 20 min. The size of the bar on the optical micrographs is 20 µm.