Browsing by Subject "block polymer"
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Item 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 GroupData 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.Item Impact of Architecture on High-Performance Sustainable Aliphatic Polyester Thermoplastic Elastomers(2022-11) Liffland, StephanieThermoplastic elastomers (TPEs) are a class of reprocessable materials that behave like chemically crosslinked elastomers at their usage temperatures but can be processed like thermoplastic materials. This reprocessability is a result of the physical rather than chemical crosslinks present in the materials. Commercial TPEs are typically linear ABA triblock polymers with hard polystyrene endblocks and a soft polydiene midblock and have varied applications from adhesives to personal care products depending on composition . Unfortunately, these petrochemical-derived materials last long beyond their functional lifetimes and contribute to the growing problem of plastic waste. Aliphatic polyester-based TPEs (APTPEs) present an alternative to these non-renewable materials that can be sustainably derived from renewable biomass with enhanced degradation capabilities through recycling or composting. The best performing APTPEs consist of poly(L-lactide) and poly(γ-methyl-ε-caprolactone) and have shown to be competitive with commercial styrenic materials. The work presented in this thesis is focused on continued improvements to the mechanical properties of these APTPEs through alterations to the ABA triblock architecture. Chapter 1 provides an analysis of the methods in which we assess sustainable materials and background on thermoplastic elastomers. Chapter 2 investigates the influence of composite (i.e. glassy and semicrystalline) hard domains in ABCBA pentablock terpolymers. Chapters 3 details systematic investigations into the impact of symmetric multiarm star architectures on the mechanical performance of APTPEs. Chapter 4 further expands on the enhancements observed in the materials reported in Chapter 3 through the introduction of stereoblock PDLA-PLLA hard domains to star APTPEs. Chapter 5 details a study into the potential for high-performing star block APTPEs to act as sustainable medical devices.Item Imperfect" Block Polymers: Effects of Dispersity and Morphological Defects on Block Polymer Properties"(2020-07) Xu, HongyunThe chemically distinct segments of block polymers drive the formation of various microphase separated morphologies such as lamellae, cylinders packed on a hexagonal lattice and double gyroid. Previous experimental and computational studies have explored the phase behaviors of model, near-perfect block polymers with narrow molar mass distributions of the constituent blocks. However, recent reports have shown that broad block dispersity notably alters the thermodynamic phase behavior of block polymers and have explored the efficacy of using polymer dispersity to enhance performance in various applications such as nanolithography and thermoplastic elastomers. Lithium salt-doped polyether-based block polymers present an attractive system to combine desirable mechanical properties with high ionic conductivities to enable design of safe, high performance electrolytes in solid-state lithium batteries, while the effect of block dispersity in polymer electrolytes has not been studied. In this thesis, we investigate how Li salt-doped block polymer phase behavior and ion conductivities are affected by increased dispersity in the conductive poly(ethylene oxide) (PEO) domains of poly(styrene-block-ethylene oxide-block-styrene) (bSOS) polymers. We blend a series of bSOS triblock polymers with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and construct the corresponding morphology portraits as a function of Li+ loading using small-angle X-ray scattering analyses. We investigate the shift of the lamellar phase boundaries and dilation of the domain spacing caused by the increased O block dispersity. We observe that bSOS affords higher ionic conductivities than the narrow dispersity diblock control samples, as characterized by electrochemical impedance spectroscopy. We rationalize this observation based on a decreased extent of long-range ordering of the lamellar phase in the salt-doped bSOS that reduces ion diffusion pathway torturosity. In other words, the PEO domain continuity is preserved across morphological defects such as grain boundaries. We further explore the idea of continuity through grain boundaries by successfully fabricating mechanically stable nanoporous materials by etching away the matrix domain from a cylindrical phase. We utilize polystyrene/polylactide and polyisoprene/polylactide block polymers to establish the versatility of this matrix etching method, and find that highly interconnected cylinders are present in both cases. We further assess the continuity and size selectivity of the fibril network composed of cross-linked polyisoprene through a permeation experiment as a proof-of concept for future applications as ultrafiltration membranes. This thesis provides new insights into using the ‘imperfections’ in the block polymer architecture and microphase separated morphologies to realize real-world applications as Li-ion battery electrolytes and separation membranes.Item Molecular bottlebrushes: new routes to self-assembled morphologies with small periodicities(2021-09) Karavolias, MichaelLinear A/B block polymer self-assembly offers exciting opportunities for bottom-up nanostructured materials design. For any chemically incompatible A/B monomer pair, there is a minimum degree of polymerization (N) required for melt self-assembly that sets the smallest microdomain (d) periodicity that such a material can form. This thermodynamic limitation impacts some block polymer applications, especially sub-10 nm templating for microelectronic device manufacture. Nonlinear polymer architectures offer opportunities to manipulate A/B block polymer self-assembly thermodynamics without resorting to new monomer chemistries. This thesis compares the morphologies and self-assembly thermodynamics of parent poly(lactide)-block-poly(𝜀-decalactone)-block-poly(lactide) (LDL) polymers bearing a midchain norbornene functionality to those of daughter core-shell bottlebrushes (csBBs) with varied backbone degrees of polymerization (Nbb), which derive from living “grafting through” polymerization of the norbornyl moieties. We specifically quantify how the d-spacings and order-disorder transition temperatures of the parent LDL triblocks change on enchainment into csBBs using small-angle X-ray scattering. Across lactide volume fractions fL = 0.27–0.73, we demonstrate that the csBB architecture thermodynamically stabilizes microphase separated melts and that it can drive ordering of disordered parent LDL triblocks. On this basis, we develop general phenomenological relationships for the composition-dependent critical degree of polymerization of the LDL triblock arms (Narm) for melt self-assembly in terms of Nbb, which enable new materials designs with ever smaller d-spacings. In compositionally asymmetric LDL triblocks and their daughter csBBs, we establish that the csBB architecture also alters the observed microphase separated morphologies. When the total volume fraction of the L block is fL = 0.27-0.34, the parent LDL polymers form hexagonally-packed cylinders and micellar Frank-Kasper A15, σ, and dodecagonal quasicrystal phases. However, enchainment into csBBs induces a spheres-to-cylinders transition with increasing Nbb. When fL = 0.73, the parent LDL triblocks form hexagonally-packed cylinders yet the csBBs form both double gyroid and metastable modulated lamellar phases. Thus, the csBB architecture induces an interfacial curvature reduction in the observed morphology relative to the parent triblock. Thus, this work establishes that the csBBs of A/B block polymers offer new opportunities to tune both the accessible morphologies and their thermodynamic stabilities.Item Molecular Simulation and Design of High-χ Low-N Block Oligomers for Control of Self-Assembly(2022-02) Shen, ZhengyuanMulti-component oligomer systems are exciting candidates for nanostructured functional materials, due to the wide variety of their self-assembled morphologies with extremely small feature size. However, experimentally screening through the vast design space of molecular architectures can be extremely laborious. Therefore, guidance from predictive modeling is essential to reduce the synthetic effort. This dissertation discusses the predictive design of self-assembling block oligomer systems using molecular simulations, and the development of computer vision models for automated morphology detection for simulation trajectories. Work presented in this thesis creates a roadmap for efficient computational screening of shape-filling molecules, thus accelerating the design and discovery of nanostructured functional materials. First, with the aid of experimentally-validated force fields, molecular dynamics simulations were exploited to design: 1) a series of symmetric triblock oligomers that can self-assemble into ordered nanostructures with sub-1 nm domains and full domain pitches as small as 1.2 nm, 2) Blends of a lamellar-forming diblock oligomer and a cylinder-forming miktoarm star triblock oligomer leading to stable gyroid networks over a large composition window. Similarities and distinctions between the self-assembly phase behavior of these block oligomers and block polymers are discussed. Second, existing simulation data were used to train deep learning models based on three-dimensional point clouds and voxel grids. The pretrained neural networks can readily detect equilibrium morphologies, and also give rich insights of emerging patterns throughout new simulations with different system sizes and molecular dimensions.Item Solid-State Block Polyelectrolytes(2020-07) Goldfeld, DavidWhile polyelectrolytes are, in general, hydrophilic and soluble in water, there are many applications that benefit from immobilized solid-state charged materials, including membrane separations and batteries. One convenient method to immobilize polyelectrolytes in a solid-state configuration is using block polymer materials self-assembled to contain charged polyelectrolyte domains immobilized by neutral supporting domains. We used this strategy to work towards charge mosaic materials, a proposed design for a piezodialysis-based water desalination system. In a charge mosaic membrane, there are both positively and negatively charged polymer domains that are spatially separated and independently cross the thickness of the material. In Chapter 2, we first developed a new technique to integrate this design into thin films. Through the synthesis of neutral ABC triblock polymers, we casted thin films with three microphase separated domains. We then demonstrated the functionalization of these materials in a mild, 2-in-1 postpolymerization modification that converted the A domain (poly(n-propyl styrene sulfonic ester)) to a negatively charged polyanion and the C domain (poly(vinylbenzyl chloride)) to a positively charged polycation in a mild, single step vapor exposure. While these materials demonstrated successful microphase separation with a simple functionalization that maintained morphology, they had poor long-range order and suffered from brittle mechanical properties that prevented their effective use as active layers in membrane separations. During the synthesis of an ABC triblock polymer for charge mosaic applications, we found a previously unreported miscibility between polystyrene and poly(vinylbenzyl chloride). Although both polymers had been used together in a number of previous applications, their solid-state structure had never been adequately explored. In Chapter 4, we attempted to characterize the Flory-Huggins interaction parameter between these two polymers using small-angle X-ray scattering of homogeneous polymer blends. We then synthesized a vinylbenzyl chloride derivative, vinylbenzyl nitrate, that demonstrated both microphase separation from polystyrene as well as facile postpolymerization modification and explosive properties. Chapter 3 attempted to solve the mechanical problems associated with the triblock polymers by integrating poly(styrene sulfonic ester) and poly(vinylbenzyl chloride) into a system that undergoes polymerization-induced microphase separation (PIMS). PIMS monoliths were made through a simple radical polymerization initiated in a homogeneous mixture of a macroinitiator dissolved in mono- and di-functional monomers. The PIMS technique results in strong materials that contain a bicontinuous structure comprising a percolating macroinitiator domain crossing the thickness of the crosslinked matrix. We used PIMS to produce solid monoliths using the neutral polyelectrolyte precursors previously used in the ABC triblock polymers. The macroinitiator domain was then functionalized to yield either a positively charged polycation material or a negatively charged polyanion material, confirmed using oppositely charged dyes and infrared characterization. The integration of both positive and negative charges into a PIMS system is approached in Appendix A. Simply mixing macroinitiators, a procedure based on previous literature, showed unexpected macrophase separation in the monolith. The use of block polymer macroinitiators to overcome solubility differences between the segments is presented as a potential solution and the synthesis of the first block polymer PIMS is demonstrated. Finally, we introduced the potential of using a polyelectrolyte as the matrix domain. Appendix B presents a proposed model for controlling swelling in the PIMS polyelectrolyte domain. By adding a poly(lactide) block to the poly(styrene sulfonic ester) macroinitiator, a degradable domain is introduced that can be selectively removed to free swelling space for the polyelectrolyte. We hypothesize that control over the swelling will provide a model system for the systematic variation of ion conductivity and provide insights into the fundamental effects of ion density, water content, and morphology. A slightly different project is explored in Chapter 5, where we develop a poly(lactide) based foam for use in floral foam applications. We formulate a mix of surfactants that make the hydrophobic, low melt-strength poly(lactide) into a rigid, low density (<0.02 g·cm–3), hydrophilic foam that readily absorbs water and supplies it to inserted flowers. The foam is compostable and made from renewable materials, making it a significant improvement over the petroleum based, non-degradable materials that are currently commercially available.Item Structure and Dynamics of Compositionally Asymmetric Block Polymers and Their Blends(2021-09) Lindsay, AaronOver 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.Item Supporting data for "Physical Aging of Polylactide Based Graft Block Polymers"(2019-11-08) Haugan, Ingrid; Lee, Bongjoon; Maher, Michael; Zografos, Aristotelis; Schibur, Haley; Jones, Seamus; Hillmyer, Marc; Bates, Frank; bates001@umn.edu; Bates, Frank; University of Minnesota Bates and Hillmyer research labsThese files contain primary data along with associated output from instrumentation supporting all results reported in Haugan et al. Physical Aging of Polylactide Based Graft Block Polymers. In Haugan et al. we found: Graft block polymers (BCPs) with poly(4-methylcaprolactone)-block-poly(lactide) (P4MCL-PLA) side chains containing 80 to 100% PLA content were synthesized with the aim of producing tough and sustainable plastics. These graft BCPs experience physical aging and become brittle over time. For short aging times, ta, the samples are ductile and shear yielding is the primary deformation mechanism. A double yield phenomenon emerges at intermediate ta where the materials deform by crazing followed by shear yielding. At long ta the samples become brittle and fail after crazing. PLA content strongly governs the time to brittle failure, where a 100% PLA graft polymer embrittles in 1 day, an 86% PLA graft BCP embrittles in 35 days, and at 80% PLA the material remains ductile after 210 days. Molecular architecture is also a factor in increasing the persistence of ductility with time; a linear triblock ages three times faster than a graft BCP with the same PLA content. SAXS and TEM analysis reveal the role of the rubbery P4MCL domains in initiating crazing by cavitation. Pre-straining the graft BCPs also significantly toughens these glassy materials. Physical aging induced embrittlement is eliminated in all the pre-strained polymers, which remain ductile after aging for 60 days. The pre-strained graft BCPs also demonstrate shape memory properties. When heated above Tg the stretched polymer within seconds returns to its original shape and recovers the original mechanical properties of the unstrained material. These results demonstrate that graft BCPs can be used to make tough, durable, and sustainable plastics and highlight the importance of understanding the mechanical performance of sustainable plastics over extended periods of time following processing.