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Browsing by Subject "SCFT"

Now showing 1 - 6 of 6
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    A Computational Approach to the Stability of Complex Sphere Forming Phases in Block Polymer Melts
    (2021-05) Cheong, Guo Kang
    Block polymers spontaneously self-assemble into a variety of morphologies upon cooling below their order-disorder temperature. Owing to this behavior, block polymers have various potential applications ranging from semiconductors fabrication to filtration devices. Recent discovery of the stable Frank-Kasper phases in diblock copolymer melts resulted in a shift of focus from high-symmetry morphologies to low-symmetry tetrahedrally close-packed phases. While experimentalists have been able synthesize block polymers that exhibit stable Frank-Kasper phases, they could not predictably determine the observed phases a priori. Computational tools can aid in prediction but are rooted in well-developed theories and experimental results. In this dissertation, we aim to develop theoretical understanding of the stability of Frank-Kasper phases that could aid in prediction through a computational study of block polymers guided by experimental data. To this end, we take a three-pronged approach in the dissertation. First, we examined an experimental diblock copolymer/homopolymer system which produces a variety of Frank-Kasper phases. Our computational study reproduced the salient behavior of the system and unveiled a new mechanism for the stabilization of Frank-Kasper phases. Next, we studied the disordered micelle regime, which has consequence in stabilizing metastable Frank-Kapser phases in thermal processing experiments, for conformationally asymmetric diblock copolymer melts. We uncovered a reduction in the window of stability for the disordered micelle regime with increasing conformationally asymmetric. Finally, we compared computational prediction of binary blends of high molecular weight diblock copolymer to experimental results and demonstrated their utility in accessing Frank-Kasper phases. Along with our analysis, we unveiled a potentially new mechanism that may be important in the stabilization of Frank-Kasper phases. We believe that our work in this dissertation provides additional understanding to the behavior of diblock copolymer, specifically in stabilizing Frank-Kasper phases. This work also opens up potential avenues of interest that may further our ability to tailor block polymers for specific applications.
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    Computational Study and Design of Self-Assembling Block Polymers
    (2023-01) Case, Logan
    Upon cooling below the order-disorder transition temperature, block polymers self-assemble into a wide variety of nanostructured morphologies. When paired with advances in synthetic chemistry that allow unprecedented control over the size and architecture of these block polymers, these self-assembly characteristics make block polymers excellent candidates for use in specialty materials with highly tunable properties. Potential applications of block polymers range from filtration membranes to photonic crystals. As it happens, however, the source of this exemplary potential is also one of the great barriers to its realization. The vast design spaces available for block polymers (through numbers and permutations of chemistries, and architectural features) make possible a potentially limitless variety of morphologies. At the same time, these design spaces combined with the subtlety of mechanisms driving morphology selection make finding systems which adopt those morphologies a daunting task.In this dissertation, we take a computational approach to address the challenge of designing block polymer specialty materials through two broad approaches. First, we directly address the challenges posed by these vast design spaces by developing an open-source software to automate the exploration of polymer parameter space. This software uses a particle swarm optimization algorithm to guide a search through polymer parameter space for positions where self-consistent field theory predicts a targeted morphology will be most stable compared to a set of competing phases. Second, we use computational studies of two classes of diblock blends seeking to understand the mechanisms that stabilize the low-symmetry Frank-Kasper phases in block polymers with the goal of improving the intuition that guides future efforts to design block polymer materials. In the first of these studies, we use an AB/B`C diblock ``alloy'' with miscible corona and immiscible core blocks to probe the effect of conformational asymmetry on the stability of Frank- Kasper Laves phases when the conformational asymmetry is confined to only particular particle positions. This study finds that conformational asymmetry can be either stabilizing or destabilizing for the Laves phases, depending on which particles are impacted. In the second of these studies, we attempt to identify the balance of core and corona bidispersity in AB/A`B` blends which can still enable formation of Frank-Kasper phases. Unfortunately, this latter study was complicated by a series of methodological flaws limiting its utility in the furtherance of block polymer design. Regardless, the flawed study serves as a lesson in proper study design, and the importance of carefully considering complicating factors.
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    Data for "Stability of Cubic Single Network Phases in Diblock Copolymer Melts"
    (2022-07-25) Chen, Pengyu; Mahanthappa, Mahesh K; Dorfman, Kevin D; dorfman@umn.edu; Dorfman, Kevin D; Dorfman Research Group
    This dataset contains the self-consistent field theory (SCFT) simulation results and data for geometric analysis in "Stability of cubic single networks in diblock copolymer melts" by Chen et. al. (DOI: 10.1002/pol.20220318). SCFT was used to investigate the stability of cubic single and double network phases. Geometric analysis, including the calculations of mean curvatures and interfacial areas per unit volume of the domain interface, was used to understand the metastability of the single network phases. With this dataset, users should be able to regenerate the calculations and figures that appeared in the paper.
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    Data from: Accelerating self-consistent field theory of block polymers in a variable unit cell
    (2017-12-04) Arora, Akash; Morse, David C; Bates, Frank S; Dorfman, Kevin D; dorfman@umn.edu; Dorfman, Kevin D
    The data contain the results of all the SCFT calculations used to demonstrate the performance of the new algorithm that we devised in our paper: https://doi.org/10.1063/1.4986643
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    Modeling of diblock copolymers in selective solvents.
    (2012-06) Thiagarajan, Raghuram
    Phase behavior and micellization kinetics of diblock copolymer surfactants in selective solvents influence many processes. We study the driving forces behind the self-assembly of a diblock copolymer AB, consisting of a solvent-philic block (B) and a solvent-phobic block (A), in selective solvents (S). We investigate this system using self-consistent field theory (SCFT), which is a coarse-grained, approximate theory with a proven track record for polymer mixtures. It discards the effects of fluctuations. Micellar transformations between spherical, cylindrical, and bilayer curvatures are tracked in the dilute regime. We determine thermodynamic and structural properties of these isolated aggregates such as the critical micelle concentration (CMC), the critical micelle temperature (CMT), the solvent penetration of the core, and the core radius of micellar morphologies within the context of SCFT. We also investigate the morphological variation from ordered phases, found in the concentrated regime, to isolated aggregates upon copolymer depletion. Depleting this blend of surfactant causes these stable structures to swell and ultimately unbind. The unbinding transition of the ordered phases is compared with the morphology transformations observed in the dilute regime. We also delineate two phase coexistence regions between ordered phases, and ordered phases and a solvent rich macrophase. Furthermore, we quantify the effective interactions between the aggregates themselves. Intriguingly, for spherical micelles, the free energy of BCC, and FCC phases can be described in terms of a single effective pair potential that depends on micellar aggregation number, however, this aggregation number changes significantly with the concentration and temperature. The kinetic barriers to association and dissociation of diblock copolymers in various selective solvents are calculated. We study the variation of these kinetic barriers for both block copolymers in small molecule solvents and block copolymers in a homopolymer matrix. The kinetic barriers are found to be very sensitive to temperature and surfactant concentration. They also become prohibitive except in a modest range of temperature near the CMT, or in sufficiently highly supersaturated or subsaturated solutions near the equilibrium CMC. The dependence of kinetic barriers upon the chain lengths and solvent quality is also studied.
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    Phase Behavior of Multiblock Polymers: Comparison of Theory and Experiments
    (2017) Pillai, Naveen; Arora, Akash; Dorfman, Kevin D