Hierarchical Rearrangement of Self-Assembled Molecular Bundle Strands from Poly(oxyethylene)-Segmented Amido Acids

We observed the arrays of molecular bundle strands in ribbon shape and their perpendicular arrangement between the bundle strands from the molecules that consist of symmetrical structure of poly(oxyethylene)-segmented bisamido acid (POE-amido acid). The molecules enabled to self-assemble into bundle strands of 5―10 nm width, 1-7 nm height, and 5-120 nm length, which further self-arranged into secondary bundle clusters. By varying the conditions of spin-coating or dip-coating (immersion) on polyethersulfone film surface and drying temperature (26 or 19 °C), the morphologies of the bundle clusters were controllable. Lengthy rattan-like strands with multiple "side-armed" short bundle strands were observed from tapping-mode atomic force microscopy. Different arrays of parallel bundle strands in cluster (by spin-coating method) and rattan-like strands with side arms (by dip-coating method) were observed, with the same bundle units of 5-10 nm in width but varying in height from 0.5 to 7 nm. The bundle height of 0.5 nm obtained by carefully controlled dip-coating into film implies a "self-assembled monolayer (SAM)" formation. The perpendicular bundle side arm arrangement is attributed to the complementary noncovalent bonding forces of POE and -COOH interaction. The presence of a POE crystalline segment (T m = 22.6 °C, ΔH = 85.6 J/g) in the molecules contributed predominately to the formation of bundles and hierarchical parallel clusters or perpendicular "side arms".