End-Effects in Diblock Copolymer Melts
2018-01
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End-Effects in Diblock Copolymer Melts
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2018-01
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Modern understanding of block copolymer systems relies heavily on coarse-grained models and mean-field theories such as self-consistent field theory (SCFT) and Fredrickson-Helfand (FH) theory. These models simplify the system, ignoring the finer structural details of the underlying polymers. One often ignored detail is the difference in the chemistry of the last monomer on the chain. Polymer synthesis re- quires the end-monomer to have a different chemistry than the other monomers in the chain. The effect that this difference has on equilibrium properties of the system has not been thoroughly explored. This work is an attempt to quantify these effects using course-grained simulations. We report on a number of simulation measurements designed to characterize the local environment of the end-monomer. The local composition distributions of monomers around the end-monomer was measured and compared to the other monomers. Additionally the composition profile of all monomer types was measured and compared to 1-dimensional SCFT simulations. Our second focus was to quantify the shift in position of the Order-Disorder Tran- sition (ODT) due to an end-monomer that was more repulsive than the other beads in the chain. Upper and lower bounds on the new position of the ODT were calculated using conventional scattering structure factor hysteresis loop methods. A subsequent Claperyon-style approximation of the new position of the ODT agreed nicely with the range that was measured. The precise location of the ODT was then obtained using well-tempered metadynamics simulations. Finally, we estimated the effective interaction parameter χe by fitting disordered phase scattering measurements to Renormalized One Loop (ROL) theory predictions. This was used to determine the effect that the repulsive end-monomer had on the value χeN at the ODT. Our results indicate that the effect is small enough to go unnoticed when the calibration of χe is constrained to scattering data from a single chain-length.
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University of Minnesota M.S. thesis.January 2018. Major: Physics. Advisor: David Morse. 1 computer file (PDF); vi, 51 pages.
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Mackey, Mark. (2018). End-Effects in Diblock Copolymer Melts. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/194649.
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