title: Self-assembly of the triblock copolymer 17R4 poly(propylene oxide)₁₄-poly(ethylene oxide)₂₄-poly(propylene oxide)₁₄ in D₂O.
abstract: Our recent investigation of the three regions of the phase diagram of 17R4 in D2O (Huff et al., 2011) has led us to study the copolymer structure in this system by small-angle neutron scattering, rheometry, and dynamic light scattering. In region I at low temperatures and copolymer concentrations (0-30°C, 0.1-0.2 mass fraction ω), the cloudy solution contains the copolymer in large clusters made of hydrophobic PPO-rich "knots" bridged by dissolved hydrophilic PEO chains. These clusters vanish in region I at the lower temperatures and concentrations (below 39°C and ω=0.01). In region I over long times (weeks) at 25°C, a white liquid/gel film forms at the air-D2O interface. In region II at temperatures above the micellization line (above about 35°C, at ω=0.22) the large clusters dissipate and unimers coexist with "flower micelles," where the PPO blocks are the centers of the micelles and the PEO blocks loop into the solvent. In region III at still higher temperatures (above about 40°C at ω=0.2), the solution separates into coexisting liquid phases, where the upper phase of higher copolymer concentration is in region II, and the lower phase is in region I. The concentrated upper phase may contain micelles so crowded as to form a network.
authors.affiliation: Department of Chemistry and Biochemistry, The University of Maryland, College Park, College Park, MD 20742, United States. Electronic address: bryna.kumi@gmail.com.
authors.forename: Bryna C
authors.initials: BC
authors.lastname: Kumi
authors.affiliation: Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899, United States.
authors.forename: Boualem
authors.initials: B
authors.lastname: Hammouda
authors.affiliation: Department of Chemistry and Biochemistry, The University of Maryland, College Park, College Park, MD 20742, United States; Department of Chemical and Biomolecular Engineering, The University of Maryland, College Park, College Park, MD 20742, United States.
authors.forename: Sandra C
authors.initials: SC
authors.lastname: Greer
keywords: Block copolymers; Micelles; Poly(propylene oxide)–poly(ethylene oxide)–poly(propylene oxide); SANS