J. Phys. II France
Volume 5, Numéro 3, March 1995
Page(s) 377 - 396
DOI: 10.1051/jp2:1995139
J. Phys. II France 5 (1995) 377-396

Surface Topography of Symmetric and Asymmetric Polyolefin Block Copolymer Films

Navjot Singh, Andrew Kudrle, Mohan Sikka and Frank S. Bates

Departments of Chemical Engineering and Materials Science, University of Minnesota, Mineapolis, MN 55455, U.S.A.

(Received 13 September 1994, accepted 28 November 1994)

Finite film thickness constraints result in the formation of islands and holes on the surface of block copolymer films when the film thickness deviates from a conformal number of layers. This paper describes a comprehensive study of surface topography in model polyolefin diblock copolymers. We present results on the evolution of surface topography from the spun cast state, changes in the topology accompanying the thermal expansion/contraction of the film during annealing, and the influence of internal microstructure on the long term stability of the surfaces. Two distinct mechanisms of evolution and coarsening of islands and holes from the as cast state were observed. In one case the islands slowly nucleate and grow, while the other mechanism is characterized by a spontaneous evolution of surface structure followed by rapid coarsening. One of the most significant results of this work is the identification of a distinct asymmetry in the long term stability of the surface topography with respect to the block copolymer composition. Diblock copolymers containing a majority of the wetting component form islands and holes more readily, while those having a minor fraction remain flat for long periods of time (i.e., months) after annealing.

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