Network Phases in Block Copolymer Melts
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Network Phases in Block Copolymer Melts Frank S. Bates Abstract The following article is an edited transcript based on the David Turnbull Lecture given by Frank S. Bates of the University of Minnesota on December 1, 2004, at the Materials Research Society Fall Meeting in Boston. Bates received the award for “pioneering contributions to the fundamental understanding of structure and properties of complex polymeric materials, particularly block copolymers and polymeric vesicles, coupled with outstanding lecturing, writing, teaching, and educational leadership.” This article outlines the research accomplishments of a group of Bates’ students that provide fresh insights into the molecular factors governing complex self-assembly in block copolymers. Three triply periodic and multicontinuous network phases were discovered in poly(isoprene-bstyrene-b-ethylene oxide) (ISO) triblock copolymers. Two cubic phases (Q 230 and Q 214) and an orthorhombic phase (O70) were identified using small-angle x-ray scattering (SAXS), transmission electron microscopy (TEM), birefringence measurements, and dynamic mechanical spectroscopy, along with level-set modeling. These findings establish a concrete strategy for locating potentially valuable network morphologies in ABC triblock copolymer melts. Keywords: block copolymers, network phases, self-assembly.
Introduction It is a great privilege for me to carry David Turnbull’s name through this award. I would like to talk about networkforming block copolymers. The research project I am going to discuss represents the culmination of four PhD theses at the University of Minnesota. The work was started by Travis Bailey and continued by Cordell Hardy, Thomas Epps, and, most recently, Eric Cochran. Ryan Waletzko, an undergraduate student now at the Massachusetts Institute of Technology, participated in the work as well. Dave Morse and his student Chris Tyler, also at the University of Minnesota, completed additional work on the theoretical side of the project. The phenomenon we have pursued is the production of materials that are triply periodic (three-dimensionally ordered) and multicontinuous (i.e., each of the three or more domains is individually three-dimensionally connected). This area of research has some exciting applications, which I will mention later.
MRS BULLETIN • VOLUME 30 • JULY 2005
Block copolymers are large molecules with two or more sequences of chemically distinct repeating units. Almost all commercial products based on this class of macromolecules are formed from just two types of polymer, such as SIS, where S and I refer to polystyrene and polyisoprene, respectively. This pairing combines glassy (S) and rubbery (I) polymers, resulting in either tough plastics or resilient elastomers, depending on the relative amount of each polymer. More polymer blocks could lead to more functionality, provided that the resulting morphology is suitably controlled. My lecture describes the recent discovery of several network morphologies in linear ABC triblock copolymers. These materials co
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