Dewetting and microphase separation in symmetric polystyrene-block-polyisoprene diblock copolymer ultrathin films

The kinetics of surface structure evolution in ultrathin films of low-molecular-weight polystyrene-block-polyisoprene (M-w: 7300 g mol(-1) - 7300 gmol(-1)) diblock copolymer at temperatures below the bulk order-to-disorder transition temperature are presented. Films with two different thicknesses were studied as a function of annealing temperature using atomic force microscopy. These film thicknesses enabled the investigation of the competition between microphase separation and dewetting that resulted in two different morphologies: long-range bicontinuous structures and random holes. Three distinctive stages of structure evolution were observed in bicontinuous structure, with the underlying mechanism compared with spinodal dewetting. Thicker films presented holes on their surfaces upon annealing at elevated temperatures, and kinetics of formation of the holes were discussed. We found that the molecular mobility determined the rates of dewetting, while the microphase separation hardly affected the dewetting process. (C) 2015 Society of Chemical Industry