Interfacial Modification as a Route to Novel Bilayered Morphologies in Binary Block Copolymer/Homopolymer Blends.
Addition of a relatively low-molecular-weight parent homopolymer to a lamellar AB diblock copolymer constitutes a reliable means by which to induce, in controllable fashion, transitions to other morphologies. In this study, we examine the effect of interfacial modification on such transitions in "extended" A(A/B)B copolymer/homopolymer blends in which (i) the A/B midblock fraction (relative to the copolymer molecular weight) is varied from 0.0 to 0.4 in 0.1 increments and (ii) the overall concentration of A ranges from 0.50 to 0.95. As this A/B fraction is increased at constant blend composition, the extent of homopolymer-induced lamellar swelling becomes measurably less pronounced, indicating that the A/B midblock serves to delocalize repulsion along the interphase separating adjacent lamellae. At higher homopolymer concentrations, an increase in the A/B fraction results in the formation of either unilamellar vesicles or a randomly connected bilayered membrane, rather than micelles. These membranes become unstable and transform to micelles at high copolymer dilution. The results presented here are discussed in terms of the complex morphologies observed in, and predicted for, low-molar-mass (co)surfactant systems.
Laurer
JH
Departments of Materials Science & Engineering and Chemical Engineering, North Carolina State University, Raleigh, North Carolina 27695, Corporate Research Division, The Procter & Gamble Company, Cincinnati, Ohio 45239, Department of Physics, Institute for Energy Technology, N-2007 Kjeller, Norway, and Department of Condensed Matter Physics & Chemistry, Risø National Laboratory, DK-4000 Roskilde, Denmark.
Smith
SD
Samseth
J
Mortensen
K
Spontak
RJ