Tadpole Conformation of Gradient Polymer Brushes

Abstract

Cylindrical molecular brushes, each with a gradient of grafting density along the backbone, demonstrated a transition from rodlike to tadpole conformations. Using atomic force microscopy (AFM), a coexistence of two conformational phases was observed within individual molecules adsorbed on a mica substrate. These observations were made by compressing monolayers on the surface of water and then transferring a sample of this monolayer to a mica substrate for AFM studies. Upon compression, the rod−globule transition occurs at the end where the brush is densely grafted, leaving a molecule with a globular "head" and an extended "tail"a so-called tadpole conformation. This research demonstrates the asymmetric changes in the molecular conformation, which is one of the prerequisites for directed motion.