Letters Surface Behavior of Amphiphilic Heteroarm Star-Block Copolymers with Asymmetric Architecture S. Peleshanko, R. Gunawidjaja, J. Jeong, V. V. Shevchenko, # and V. V. Tsukruk* Department of Materials Science and Engineering, Iowa State University, Ames, Iowa 50011 Received March 20, 2004. In Final Form: August 21, 2004 We study the surface behavior of the asymmetric amphiphilic heteroarm poly(ethylene oxide) (PEO)/ polystyrene (PS) star polymer on solid substrate. These star polymers differ in both architecture (four- and three-arm molecules, PEO-b-PS3 and PEO-b-PS2) and in the length of PS chains (molecular weight from about 10 000 up to 24 000). We observed that, for a given chemical composition with a predominant content of hydrophobic blocks, the compression behavior of the PS domain structure controls the surface behavior and the final morphology of the monolayers. New features of the surface behavior of star-block copolymers are high stretching of the PS arms from the interface and enhanced stability of the circular PS domain structure, even at high compression. We suggest that for asymmetric star-block copolymers both architecture and chemical composition heavily favor the formation of highly curved interfaces and, thus, more stable circular domain structure with stretched PS arms. Introduction Functionalized amphiphilic block copolymers are widely explored for their ability to form organized micellar aggregates with different morphologies in polymer solu- tions, in the bulk state, and in thin polymer layers at surfaces and interfaces, which are critical for many modern applications. 1-5 One of the most-exploited types of am- phiphilic block copolymers is composed of poly(ethylene oxide) (PEO) and polystyrene (PS) blocks. The properties of these PEO-PS block copolymers, with variable mo- lecular weight and chemical composition, are widely studied in the terms of their micellar structures in water 6 and organic solvents of different qualities 7-9 The inter- facial behavior and the microstructure of PEO-PS block copolymers at both air-water and air-solid interfaces have been widely studied during the past few years. 10-19 The surface behavior of these block copolymers is mainly controlled by the volume ratio of hydrophilic and hydro- * Author to whom correspondence should be addressed. E-mail: vladimir@iastate.edu. # The Institute of Macromolecular Chemistry, Kiev, 02160, Ukraine. (1) (a) Hsieh, H. L.; Quirk, R. P. Anionic Polymerization: Principles and Practical Applications; Marcel Dekker: New York, 1996. (b) Mishra, M. K.; Kobayashi, S. Star and Hyperbranched Polymers; Marcel Dekker: New York, 1999. (c) Sperling, L. H. Introduction to Physical Polymer Science, 3rd ed.; Wiley-Interscience: New York, 2001. (2) (a) Koutos, V.; Van der Vegte, E. W.; Hadziioannou, G. Macro- molecules 1999, 32, 1233. (b) Green, P. F.; Christensen, T. M.; Russell, T. P.; Jerome, R. Macromolecules 1989, 22, 2189. (c) Xu, T.; Goldbach, J. T.; Russell, T. P. Macromolecules 2003, 36, 7296. (d) Hong, S.; MacKnight, W. J.; Russell, T. P.; Gido, S. P. Macromolecules 2001, 34, 2876. (3) (a) Tsukruk V. V. Adv. Mater. 2001, 13, 95. (b) Tsukruk, V. V.; Sidorenko, A.; Gorbunov, V. V.; Chizhik, S. A. Langmuir 2001, 17, 6715. (c) Julthongpiput, D.; Lin, Y.-H.; Teng, J.; Zubarev, E. R.; Tsukruk, V. V. J. Am. Chem. Soc. 2003, 125, 15912. (d) Zhai, X.; Peleshanko, S.; Klimenko, N. S.; Genson, K. L.; Vortman, M. Ya.; Shevchenko, V. V.; Vaknin, D.; Tsukruk, V. V. Macromolecules 2003, 36, 3101. (e) Julthongpiput, D.; Lin, Y.-H.; Teng, J.; Zubarev, E. R.; Tsukruk, V. V. Langmuir 2003, 19, 7832. (f) Ornatska, M.; Jones, S. E.; Naik, R. R.; Stone, M.; Tsukruk, V. V. J. Am. Chem. Soc. 2003, 125, 12722. (g) Tsukruk, V. V.; Ornatska, M.; Sidorenko, A. Prog. Org. Coat. 2003, 47, 288. (4) (a) Tsukruk, V. V. Prog. Polym. Sci. 1997, 22, 247. (b) Luzinov I.; Minko, S.; Tsukruk, V. V. Prog. Polym. Sci. 2004, 29, 635. (5) Zhao, B.; Brittain, W. J. Prog. Polym. Sci. 2000, 25, 677. (6) Cogan, K.; Gast, A. Macromolecules 1990, 23, 745. (7) Hickl, P.; Ballauff, M.; Jada, A. Macromolecules 1996, 29, 4006. (8) Yu, K.; Eisenberg, A. Macromolecules 1996, 29, 6359. (9) Seo, Y.; Kim, M.; Ou-Yang, D.; Peiffer, D. Polymer 2002, 43, 5629. © Copyright 2004 American Chemical Society OCTOBER 26, 2004 VOLUME 20, NUMBER 22 10.1021/la049269c CCC: $27.50 © 2004 American Chemical Society Published on Web 09/18/2004