Topological coarsening of low-molecular-weight block copolymer ultrathin films by environmental AFM

Topological coarsening of block copolymer ultrathin films is well-understood for copolymers exhibiting intermediate or strong segregation and differing in film thickness or molecular weight at temperatures above the upper glass transition temperature (Tg), but below the order–disorder transition (TODT), of the copolymers. More recent studies suggest that the stability and topology of such films differ at temperatures above TODT. In this work, we use environmental atomic force microscopy to examine the effect of temperature on the coarsening of block copolymer ultrathin films in situ. Films measuring ca. 25 nm thick consist of a low-molecular-weight poly(styrene-b-isoprene) diblock copolymer for which the upper Tg and TODT in the bulk are about 42 and 70 °C, respectively. Time-resolved image sequences illustrating surface reorganization are obtained at temperatures below, above and near 70 °C. At temperatures very close to 70 °C, coarsening is found to slow markedly, by almost an order of magnitude relative to what is observed at higher and lower temperatures, suggesting that thermal factors may provide a means by which to inhibit the dewetting of block copolymer ultrathin films.