Crystallization of Layers of Strongly Adsorbed Poly(ethylene terephthalate) on Silicon Substrates

We examined the crystallization behavior of ultrathin layers of strongly adsorbed poly(ethylene terephthalate) (PET) chains on silicon substrates, yielding a characteristic morphology of uniquely curved dendritic polymer crystals. The observed curvature resulted from bent edge-on lamellar crystals from which terraced flat-on branched lamellar crystals grew essentially from the convex outer side. The degree of bending increased with decreasing crystallization temperature and increasing strength of polymer/substrate interactions. We propose that unbalanced stresses acting on the fold surfaces of PET lamellar crystals, probably induced by strong interactions with the substrate, were responsible for the observed curvature of the lamellar crystals. We present observations which indicate relations between curvature and lamellar thickness and between strength of adsorption and probability of nucleation for strongly adsorbed polymers under extreme confinement.