Morphological imaging of single methylcellulose chains and their thermoresponsive assembly on a highly oriented pyrolytic graphite surface

Individual methylcellulose (MC) chains and their thermoresponsive assembly were successfully visualized on a highly oriented pyrolytic graphite (HOPG) surface by atomic force microscopy (AFM). Momentary contact of a dilute MC solution at 4 °C onto the HOPG substrate permitted clear imaging of individual MC chains having a molecular thickness of ca. 0.5 nm and a hexagonal orientation. By increasing the solution temperature from 4 to 80 °C, it was possible to bring about significant changes in the MC nanomorphology from stretched molecular chains to disordered massive aggregates. It was presumed that the hydrophobic interaction between the MC chains and the HOPG π-conjugated system led to the successful visualization of thermally responsive changes in the MC conformations. These results imply that HOPG substrates could be used for clear nanoimaging of cellulosic polymers and other structural polysaccharides.