N. Hasan, T. M. H. Nguyen, A.-K. Flieger and J. Kressler
Faculty of Natural Sciences II, Martin Luther University Halle-Wittenberg, Von-Danckelmann-Platz 4, D-06120 Halle (Saale), Germany.
Perfect isotactic poly(methacrylic acid) (i-PMAA) was synthesized and characterized by NMR spectroscopy. Langmuir isotherms of i-PMAA were measured and compared with atactic PMAA. The crystallization of i-PMAA on the water surface strongly depends on the pH-value of the subphase. We found that i-PMAA solutions can immediately form crystalline nanoparticles upon spreading at the air-water interface at neutral pH value. They have diameters of approximately 14 nm to 40 nm and their size can be increased 60 nm to 100 nm without aggregation upon compression on the Langmuir trough. Helical structures are observed when i-PMAA is spread on water having pH value of 10. The morphology of i-PMAA was studied after transfer in LB films by AFM. i-PMAA can also be crystallized in thin films after treatment for several weeks with water. Wide-angle X-ray diffraction (WAXD) studies of these films show a new Bragg reflection at 2θ = 7° (d = 1.20 nm) indicating the crystallization of i-PMAA which might correspond to the helical pitch distance as known for isotactic poly(methyl methacrylate) (i-PMMA) [1-3]. The crystallization is also observed by polarized optical microscopy and AFM.
References
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[3] D. Kamei, H. Ajiro, C. Hongo and M. Akashi, Langmuir 25, 280 (2009) (link)