Structural study of a poly(methylmethacrylate) Langmuir–Blodgett film on a graphite surface by scanning tunneling microscope

Abstract

In this study, molecular configurations of three different stereoregular poly(methylmethacrylate) (PMMA) (isotactic, atactic, and syndiotactic PMMA) monolayers, which were transferred onto graphite substrates by the Langmuir–Blodgett (LB) technique, were investigated using scanning tunneling microscope (STM). STM images of monolayer films taken in air in the constant height mode showed various types of film structures. First, polymer films in their different forms always showed long-range ordered chain structures. Second, these polymer chains were generally observed to arrange themselves in parallel chains with no backbone crossovers. However, the packing density of polymer chains on the surface varied with change of scanning area presumably due to the nonuniformity of the LB film and the effect of thermal fluctuation of polymer chains on the film. Third, a monolayer film of isotactic PMMA film showed the coexistence of helical and linear chains in most of the film areas suggesting that the structural transition from the linear chains to 51 single stranded helices occurs at the surface pressure of 8 mN/m.