Dewetting Instabilities in Thin Block Copolymer Films:  Nucleation and Growth

We examined the dynamics of dewetting of a thin symmetric diblock copolymer film on a substrate above the bulk order−disorder transition temperature, T ODT, of the copolymer using atomic force microscopy. The dewetting mechanism proceeded with the formation of discrete holes without their characteristic peripheral rims. During this early stage, the hole radii R increased exponentially with time. This stage was followed by a narrow intermediate regime where the rim develops and R ∼ t . When the rim was fully developed, R increased as t 2/3 . The shape of the rim was highly asymmetrical and its width L increased as t 1/2 . At the final stage of the process, droplets of the copolymer, a few microns in diameter and with heights on the order of tens of nanometers, existed on a dense copolymer “brush” of uniform thickness 7 nm anchored to the substrate. This clearly indicates that the process is autophobic, a phenomenon first documented in small molecule liquids.