Liquidlike Morphological Transformations in Monolamellar Polymer Crystals

We performed annealing experiments on monolamellar polyethyleneoxid crystals. Even well below the melting point, local relaxations of metastable folded states led to pronounced liquidlike morphological changes on a micron scale of shape and perimeter of the crystalline domains, similar to dewetting of liquids. First, a rim of less folded molecules was formed around the lamellae, making relaxations of the interior difficult. On longer time scales, hole formation within these domains was observed. Our experiments showed that, due to such spatial anisotropy in relaxations, polymer crystal morphology depends on the thermal pathway taken, implying that a time-temperature superposition principle does not apply.