title: Visualization of two-dimensional single chain conformations solubilized in a miscible polymer blend monolayer by atomic force microscopy.
abstract: Polymer Langmuir monolayers spread on a water surface are one of the best models for two-dimensional (2D) polymer and have been extensively studied. However, the most fundamental issue in understanding a 2D film, the polymer chain packing in the film, is still not well-understood, especially from the experimental point of view. Direct observation of the chain packing by microscopy at a molecular level, such as by atomic force microscopy (AFM), might be one of the most promising ways to study this issue; however, because of the limited resolution of the method, the chain packing of polymer cannot be resolved by AFM, except for especially large polymers. Here, we show that a mixed monolayer of vinyl polymers, poly(methyl methacrylate) (PMMA) and poly(n-nonyl acrylate) (PNA), was miscible at a low surface pressure, and if a small amount of PMMA chains was solubilized in a PNA monolayer, the isolated PMMA chains in the PNA monolayer were, for the first time, successfully visualized by AFM with a clear contrast, which originated from a difference of rigidities of the polymers due to their different glass transition temperatures (105 °C(PMMA) and -89 °C(PNA)). The PMMA chains were found to strongly interpenetrate into the PNA monolayer, with a radius of gyration (R(g(PMMA))) that was several times larger than that of the 2D ideal chain (segregated-chain). Furthermore, the radius scaled with the molecular weight of the PMMA (M(PMMA)) as R(g(PMMA)) ∝ M(PMMA)(0.63), which was between the scaling of the 2D ideal chain (segregated chain), R(g) ∝ M(0.5), and the 2D chain in good solvent, R(g) ∝ M(0.75). On the other hand, R(g(PMMA)) was independent of the molecular weight of the PNA matrix over a wide range. These results indicate that the PNA/PMMA monolayer is a strongly miscible system, although the R(g(PMMA)) scaling with M(PMMA) (0.63) is somewhat smaller than that expected for a 2D chain in good solvent systems (0.75). The generation of molecular level information by direct observation of polymer chains in 2D blend films should improve our understanding of polymer 2D films.
authors.affiliation: Department of Polymer Science and Engineering, Graduate School of Science and Engineering, Yamagata University, Yonezawa, Yamagata 992-8510, Japan.
authors.forename: Kouki
authors.initials: K
authors.lastname: Sugihara
authors.forename: Jiro
authors.initials: J
authors.lastname: Kumaki
mesh_terms: D000179:Acrylates / Q000737:chemistry*; D008567:Membranes, Artificial; D018625:Microscopy, Atomic Force; D008968:Molecular Conformation; D019904:Polymethyl Methacrylate / Q000737:chemistry*; D012995:Solubility
chemical_list: D000179:Acrylates; D008567:Membranes, Artificial; C575300:poly(n-nonyl acrylate); D019904:Polymethyl Methacrylate