Block copolymer self-assembly in solution: structure and dynamics.
2010-08
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Block copolymer self-assembly in solution: structure and dynamics.
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2010-08
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Abstract
Block copolymers can self-assemble into micelles or vesicles when dispersed in a
selective solvent. In this study, spherical micelles were formed by poly(styrene-bethylene-
alt-propylene) (PS-PEP) in squalane, highly selective to PEP blocks, leading to
PS cores and swollen PEP coronas. The micelle structure was characterized by dynamic
light scattering (DLS) and small-angle x-ray scattering (SAXS). The experimental results
provide a detailed picture of micelle structure and intermicelle interaction as a function of
block copolymer molecular weight and composition, concentration, and temperature.
Based on this structural information, the single molecular exchange kinetics between the
spherical micelles in dilute solution was examined by time-resolved small-angle neutron
scattering (TR-SANS). Two pairs of structurally matched partially protonated and deuterated micelles were prepared and each pair was blended to provide an initially
isotopically segregated state in solution. The SANS intensity is directly related to the
concentration of protonated chains in the micelle cores. Therefore, a reduction in the
measured scattering intensity can be quantitatively correlated with the exchange of
chains. This measurement was aimed at probing the dependence of molecular exchange
kinetics on temperature, molecular weight, and concentration. The temperature
dependence of the chain exchange rate R(t) can be explained based on the core block
dynamics, while the documented quasi-logarithmic decay of R(t) is shown to be
consistent with single chain exchange that is hypersensitive to the core degree of
polymerization and therefore polydispersity. Complementary measurements were also conducted with concentrated solutions where the micelles pack onto a body-centered
cubic lattice. Based on a first-principles model, the exchange kinetics are expected to be
independent of micelle concentration. However, slower dynamics in ordered micelles were observed. These results suggest that contributions from factors other than core block
dynamics can come into play in the exchange kinetics for ordered micelles.
Description
University of Minnesota Ph.D. dissertation. August 2010. Major: Chemical Engineering. Advisors: Frank S. Bates and Timothy P. Lodge. 1 computer file (PDF); xviii, 198 pages.
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Choi, Soo-Hyung. (2010). Block copolymer self-assembly in solution: structure and dynamics.. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/96027.
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