Browsing by Subject "micelle"

Now showing 1 - 3 of 3
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    Data for "The disordered micelle regime in a conformationally asymmetric diblock copolymer melt"
    (2021-10-21) Cheong, Guo Kang; Dorfman, Kevin D; dorfman@umn.edu; Dorfman, Kevin D; Dorfman Research Group
    Data appearing in the publication "The disordered micelle regime in a conformationally asymmetric diblock copolymer melt". This paper reports Monte Carlo Field Theoretic Simulation (MC-FTS) results for diblock copolymers in the sphere-forming region of the phase diagram. The archived data are the post-processed trajectories. Owing to their size, the raw trajectories for the fields are not stored.
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    Structure and Dynamics of Compositionally Asymmetric Block Polymers and Their Blends
    (2021-09) Lindsay, Aaron
    Over the past two decades, investigation of nanoscale, particle-forming amphiphiles has revealed a wealth of previously unanticipated packings, including multiple Frank–Kasper phases and a dodecagonal quasicrystal. These complex periodic and aperiodic packings are characterized by multiple particle volumes and geometries ordered onto massive unit cells consisting of ≥7 particles, making them promising platforms for applications ranging from lithography to photonics. However, such phase behavior has largely been limited to a narrow set of length scales and chemistries, significantly hindering these applications. To address this challenge, this thesis is devoted largely to an exploration of new strategies by which Frank–Kasper phases can be made more broadly accessible. Multiple routes to these fascinating packings were discovered, including the use of bidisperse AB/ABʹ or AB/AʹBʹ diblock copolymer blends, AB/Aʹ-diblock copolymer/homopolymer blends, and asymmetric BABʹ-triblock copolymers. Crucially, these strategies are simple, largely invariant to chemistry, and effective at stabilizing Frank–Kasper phases with unit cell dimensions exceeding 100 nm. In a second focus, the phase behavior of a poly(ethylene-alt-propylene)-block-poly(ethylene-alt-propylene) diblock copolymer first investigated in 1999 was reevaluated by small-angle X-ray scattering (SAXS). A rich phase space was uncovered including dodecagonal quasicrystal and Frank–Kasper σ phases, which, had they been identified in the initial 1999 report, would have preceded their discovery in block polymers by more than a decade. On subjecting the material to large amplitude oscillatory (LAOS) shear at temperatures well-below the order-disorder transition temperature, SAXS evidenced the development of a twinned BCC crystal that, on heating underwent an unusual, epitaxial transformation to an oriented dodecagonal quasicrystal. Surprisingly, no evidence for this epitaxy was observed on heating or cooling through an equilibrium, high temperature BCC-σ OOT and LAOS resulted in a loss of long-range order when applied directly to well-ordered σ and dodecagonal quasicrystal packings. These results were rationalized in relation to shear deformation behavior identified in metals (e.g., Fe-Cr and β-U) and an apparent transition to micelle translation-mediated ordering dynamics far below the order–disorder transition temperature.
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    Transition State of Single Chain Expulsion from a Diblock Copolymer Micelle
    (2023-06) Seeger, Sarah
    The presence of a selective solvent induces self-assembly of block copolymers into a myriad of micellar nanostructures, offering great versatility for utilization in a wide range of technological applications such as viscosity modification and drug delivery. In order to fully harness their use in practical application, it is necessary to gain a comprehensive understanding of the mechanisms underlying micellization and equilibration of block copolymer micelles. The process of single chain exchange holds significant importance in equilibration of block copolymer micelles. While existing techniques offer insights into the ensemble behavior of chain exchange, the molecular-level details of the process remain insufficiently understood. To address this, a simulation framework combining dissipative particle dynamics with umbrella sampling to study chain exchange in diblock copolymer micelles in dilute solution was introduced. In this thesis, umbrella sampling was employed to probe the free energy trajectory of single chain expulsion from a diblock copolymer micelle. Using dissipative particle dynamics simulations, a biasing potential was applied to hold the chain at various distances from the micelle center-of-mass and the weighted histogram analysis method was utilized to extract the free energyprofile. By capturing the full free energy landscape of chain expulsion, this approach diverges from previous methods, providing access to the experimentally unobservable expulsion mechanism. The investigation focuses on exploring the dependence of the free energy barrier on the interaction energy between the core block and the solvent, or the core block length of the expelled chain. It was found that there is a monotonic increase in the free energy barrier for chain expulsion as either the interaction energy or the block length of the expelled chain increases, aligning with experimental results. Interesting, the effect of the core block length of the expelled chain was independent of the micelle characteristics. Examination of the radius of gyration of the core block during expulsion revealed a remarkable feature of the transition state: the core block exhibited partial stretching, allowing specific core beads to remain within the micelle core until the chain was completely expelled. This stretching mechanism effectively minimized unfavorable contacts by ensuring that only a fraction of the core block was exposed to the solvent at any given point along the expulsion trajectory, challenging previous models of chain exchange. Finally, a model consistent with the scaling behavior observed in both simulation and experimental data was put forward, offering an alternative perspective on the process of single chain exchange.