Surface-Induced Ordering in Graft Copolymer Thin Films

Langmuir, 15 (8), 2911 -2915, 1999. 10.1021/la980556o S0743-7463(98)00556-3
Web Release Date: March 19, 1999

Surface-Induced Ordering in Graft Copolymer Thin Films

Shouren Ge, Lantao Guo, Miriam H. Rafailovich,* and Jonathan Sokolov

Department of Materials Science and Engineering, State University of New York at Stony Brook, Stony Brook, New York 11747-2275

Dennis G. Peiffer

Exxon Research and Engineering Company, Annandale, New Jersey 08801

Steven A. Schwarz

Department of Physics, Queens College, Flushing, New York 11367

Ralph H. Colby

Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802-5007

William D. Dozier

Fannie Mae, Washington, D.C. 20016

Received May 11, 1998

In Final Form: January 29, 1999

Abstract:

The surface-induced ordering of deuterated poly(ethyl acrylate)-polystyrene (dPEA-PS) graft copolymers with different average number x of graft chains per copolymer chain (dPEA-g-xPS, x = 1, 3, 5) was investigated using neutron reflection, secondary ion mass spectrometry, and atomic force microscopy. The ordering starts only at the vacuum surface and decays through the bulk of the film to the silicon surface. The dPEA-g-3PS thin films (f, fraction of styrene monomers = 0.28) appear to have dPEA-PS lamellar structures and a nearly pure dPEA layer next to the vacuum surface. The dPEA-g-5PS thin films (f = 0.48) are found to be cylindrical except for the top layer, adjacent to the vacuum surface, which is lamellar. On comparison with diblock copolymers, graft copolymers show a phase diagram shift and smaller micelle spacing. We find that long-range order in graft copolymers only occurs within ~15 lamellar spacings of the vacuum surface. Linear viscoelasticity of bulk samples reveals that none of the shear-history and low-frequency terminal response complications observed for diblock copolymers are observed for graft copolymers, owing to their lack of long-range order.

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