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Molecular‐weight factors affecting formation of the OBDD morphology in block copolymer blends
Author(s) -
Spontak Richard J.,
Smith Steven D.,
Ashraf Arman
Publication year - 1994
Publication title -
microscopy research and technique
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.536
H-Index - 118
eISSN - 1097-0029
pISSN - 1059-910X
DOI - 10.1002/jemt.1070270507
Subject(s) - copolymer , morphology (biology) , lamellar structure , materials science , transmission electron microscopy , styrene , polymer chemistry , phase diagram , phase (matter) , chemistry , nanotechnology , composite material , polymer , genetics , biology , organic chemistry
Block copolymers undergo self‐organization when the blocks are sufficiently incompatible, and generate a variety of periodic morphologies in the limit of strong segregation. An equilibrium morphology only recently added to the diblock copolymer phase diagram is the ordered bicontinuous double‐diamond (OBDD) morphology, which possesses a Pn3m space group. It has been observed over a very narrow composition range (ca. 4 vol%), thereby making it difficult to obtain in pure copolymers. This obstacle can, however, be surmounted by blending a copolymer with one of the parent homopolymers. In the present study, several symmetric poly(styrene‐ b ‐isoprene) diblock copolymers varying in molecular weight (M) have been blended with homopolystyrene to produce the OBDD morphology. Transmission electron microscopy is employed here to identify the morphologies in cryosections of each blend and reveals that, at intermediate molecular weights, the OBDD morphology is indeed observed. At low M, near the order‐disorder transition, however, a lamellar catenoid or disordered morphology is preferred. At the other extreme, high‐M blends are frustrated by molecular entanglements and adopt a cylindrical morphology. © 1994 Wiley‐Liss, Inc.