Browsing by Subject "block copolymer"
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Item Data for A soft crystalline packing with no metallic analogue(2024-04-08) Chen, Pengyu; Dorfman, Kevin D; dorfman@umn.edu; Dorfman, Kevin D; Dorfman Research Group - University of Minnesota Department of Chemical Engineering and Materials ScienceThis dataset contains the input and output files for self-consistent field theory (SCFT) simulations in the associate paper.Item Data for Deformation and failure of glassy polymer-polymer interfaces compatibilized by linear multiblock copolymers(2024-07-08) Collanton, Ryan P; Dorfman, Kevin D; dorfman@umn.edu; Dorfman, KevinUsing coarse-grained molecular dynamics simulations, we study the mechanical properties and stress transfer mechanisms of weakly entangled, glassy polymer blends compatibilized by diblock, triblock, or pentablock copolymers. For a given number of copolymer junctions per unit area, copolymer architecture is found to play a minimal role, whereas block degree of polymerization and copolymer loading qualitatively impact the interfacial mechanics. Explicitly, the stress-strain and density-strain curves reveal distinctly different deformation mechanisms at low and high compati- bilizer loading related to cavitation and fibril formation near the A/B interface. Furthermore, the competition between interfacial cavitation and chain pullout from the bulk leads to non-monotonic dependencies of the toughness and strain-at-break on copolymer loading. For sufficiently long copolymers, the simulations predict an optimum loading that produces mechanical properties that nearly match those of the homopolymer glass. These results imply that moderate loading of long block copolymers is ideal for effective compatibilization and stress transfer across the interface.Item Data for Surface Relief Terraces in Double Gyroid-Forming Polystyrene-block-Polylactide Thin Films(2023-09-28) Yang, Szu-Ming; Oh, Jinwoo; Magruder, Benjamin R; Kim, HeeJoong; Dorfman, Kevin D; Mahanthappa, Mahesh K; Ellison, Christopher J; cellison@umn.edu; Ellison, Christopher J; University of Minnesota Department of Chemical Engineering and Materials ScienceThis study describes the thin film self-assembly behavior of a polystyrene-block-polylactide (SL-G) diblock copolymer, which undergoes melt self-assembly in bulk into a double gyroid (DG) network phase with a cubic unit cell parameter a = 52.7 nm. Scanning electron microscopy (SEM) and grazing-incidence small-angle X-ray scattering (GISAXS) reveal that thermally annealing 140–198 nm thick copolymer films on SiO2 substrates below the morphological order-to-disorder transition temperature yields polydomain DG structures, in which the (422) planes are oriented parallel to the surface. Bright-field optical microscopy (OM) and atomic force microscopy (AFM) analyses further reveal the film thickness-dependent formation of topographical terraces, including islands, holes, and bicontinuous features. The occurrence of these features sensitively depends on the incommensurability of the as-prepared film thickness and the (211)-interplanar spacing (d211) of the DG unit cell. While the steps heights between adjacent terraces exhibiting characteristic “double wave” patterns of the DG (422) planes coincide with d211, previously unreported transition zones between adjacent terraces are observed wherein “boomerang” and “droplet” patterns are observed. These intermediate patterns follow the expected sequence of adjacent termination planes of the bulk DG unit cell along the [211] direction, as confirmed by comparisons with self-consistent mean-field theory calculations.Item Data for Threading-the-Needle: Compatibilization of HDPE/iPP blends with butadiene-derived polyolefin block copolymers(2023-07-31) Shen, Liyang; Diaz Gorbea, Gabriela; Danielson, Evan; Cui, Shuquan; Ellison, Christopher J; Bates, Frank S; bates001@umn.edu; Bates, Frank S; University of Minnesota Department Chemical Engineering and Material ScienceManagement of the plastic industry is a momentous challenge, one that pits enormous societal benefits against an accumulating reservoir of nearly indestructible waste. A promising strategy for recycling polyethylene (PE) and isotactic polypropylene (iPP), constituting roughly half the plastic produced annually worldwide, is melt blending for reformulation into useful products. Unfortunately, such blends are generally brittle and useless due to phase separation and mechanically weak domain interfaces. Recent studies have shown that addition of small amounts of semicrystalline PE-iPP block copolymers (ca. 1 wt%) to mixtures of these polyolefns results in ductility comparable to the pure materials. However, current methods for producing such additives rely on expensive reagents, prohibitively impacting the cost of recycling these inexpensive commodity plastics. Here, we describe an alternative strategy that exploits anionic polymerization of butadiene into block copolymers, with subsequent catalytic hydrogenation, yielding E and X blocks that are individually melt miscible with PE and iPP, where E and X are poly(ethylene-ran-ethylethylene) random copolymers with 6% and 90% ethylethylene repeat units, respectively. Cooling melt blended mixtures of PE and iPP containing 1 wt% of the triblock copolymer EXE of appropriate molecular weight, results in mechanical properties competitive with the component plastics. Blend toughness is obtained through interfacial topological entanglements of the amorphous X polymer and semicrystalline iPP, along with anchoring of the E blocks through cocrystallization with the PE homopolymer. Significantly, EXE can be inexpensively produced using currently practiced industrial scale polymerization methods, offering a practical approach to recycling the world’s top two plastics.Item Development of Model Diblock Copolymer Surfactants for Mechanistic Investigations of Cell Membrane Stabilization(2015-08) Haman, KarenAmphiphilic triblock copolymers of poly(ethylene oxide) and poly(propylene oxide), generically referred to as poloxamers, have been identified for therapeutic use in cell membrane stabilization applications since the early 1990s. Historically, mechanistic investigations of block copolymer facilitated membrane stabilization have nearly exclusively featured poloxamers, commercially available in a wide range of molecular weights and hydrophobic/hydrophilic compositions. This work instead considers diblock copolymers of poly(ethylene oxide) and poly(propylene oxide), for which molecular properties can be easily tuned by living anionic polymerization. The diblock architecture simplifies the structure-function understanding of block copolymer interactions with membranes by eliminating a redundant hydrophilic block (A) from the poloxamer A-B-A architecture. Work presented here indicates that these diblock copolymers are capable of shielding liposome model membranes from harmful free radical-initiated peroxidation at lower loadings than analogous triblock copolymers. Besides the pharmacological advantages of lower required doses, the finding highlights the significance with respect to membrane interaction of differences in the chemical environments of the hydrophobic blocks between the triblock and diblock architectures. From this point, the roles of both hydrophobic block length and end-functionality were explored in liposome and in vitro model stresses, and the dependence of therapeutic benefit on each was established. Future systems to consider are discussed, and additional methods for investigation are detailed.Item Mechanisms of Chain Exchange in Block Copolymer Micelles(2015-11) Lu, JieMechanisms of equilibration in block copolymer micelles were investigated in detail using time resolved small angle neutron scattering (TR-SANS). The model polymers used in this study were polystyrene-b-polyethylenepropylene (PS-PEP) diblock copolymers and corresponding triblock copolymers (PS-PEP-PS, PEP-PS-PEP). When dissolved in squalane, the polymers self assembled into spherical micelles with the PEP blocks forming the solvated coronas, and undiluted PS blocks as the micelle cores. Normal and selectively deuterated equivalent polymers with controlled molecular weight, narrow molecular weight distribution and composition were synthesized by anionic polymerization of styrene and isoprene followed by the selective saturation of the polyisoprene blocks. The structure of polymer micelles were characterized using dynamic light scattering (DLS) and small angle X-ray scattering (SAXS). A contrast matching strategy was employed for the TR-SANS experiments, where separately prepared deuterated and protonated micelles were mixed at equal volume fractions in a solvent containing 42 vol% h-squalane and 58 vol% d-squalane. Chain exchange reduces the mean contrast of the micelle cores in the solvent mixture, thus reducing the SANS scattering intensity, providing a method to characterize the dynamics of the process as a function of time. In this thesis, several aspects of chain exchange mechanisms were investigated. The hypothesis of hypersensitivity of chain exchange rate to the core block length, and the single chain exchange mechanism, were first tested and confirmed in the PS-PEP model micelle system. The chain exchange mechanisms in PEP-PS-PEP and PS-PEP-PS micelles were then investigated, and a remarkable effect of molecular architecture on the chain exchange rate is documented. In addition, this study explores the facilitating role of the corona chains in molecular exchange. It was found that adding PEP homopolymers of size comparable to the PEP blocks into dilute PS-PEP micelle solutions can significantly retard the chain exchange rate. Decreasing the corona block fraction in the PS-PEP polymers also reduced the chain exchange rate, and the concentration dependence of the chain exchange relaxation time constant. Finally, we extended our scope to chain exchange between micelles away from equilibration, i.e., micelle hybridization of two populations of PS-PEP micelles of different sizes. The results of this work suggested quantitatively different mechanisms when the micelle systems are away from equilibration, and a concentration effect was found, even when the micelles are still dilute.Item Nanoporous and Functionalized Polymer Thermosets by Polymerization-Induced Microphase Separation in Bulk, Dilution, and Suspension(2021-10) Peterson, ColinThe microphase separation of diblock polymers allows for excellent control over the nanostructuring of polymer-based materials. Polymers are also readily functionalized and chemically manipulated to alter their chemical properties. Therefore, block polymers represent an important tool in the preparation of precision nanostructured functional materials. Polymerization-induced microphase separation (PIMS) is a convenient and powerful strategy towards the development of such materials. In PIMS, the diblock polymer is simultaneously grown while one block is crosslinked. This captures a non-equilibrium percolating morphology. In this thesis, the morphology is used as a host for photochromic dyes, diluted with solvent to increase the possible porosity, and prepared in suspension to give uniform mesoporous beads.Chapter 1 is a brief overview of key topics relevant to the entire thesis. Chapter 2 describes the incorporation of photochromic dye molecules into a variety of materials from liquid solvent to rigid polymer. PIMS thermosets were created using a liquid-like polycaprolactone derivative and crosslinked polymethylmethacrylate. The liquid-like domains provide an environment for the dye where fast structural relaxation allows for fast dye decoloration while being encased in a rigid matrix. Chapter 3 shifts focus to porous PIMS derivatives. In particular, the effect on the pore size distribution of diluting the monomer solution with solvent to create an organogel is explored. Chapter 4 presents a new synthetic method to prepare beads from PIMS thermosets by performing the chain-growth and cross-linking steps in aqueous suspension. The size of the particles is tuned independently from the size of the pores. Also, functionality is incorporated into the pore walls using a diblock precursor. Chapter 5 provides general conclusions and possible future directions for research relating to disordered diblock thermoset materials.Item Structure and Thermodynamics of Salt-Doped Polymer Blends(2020-08) XIE, SHUYIA central challenge in designing novel polymeric materials is to find a broadly applicable strategy to systematically tailor microstructures in order to simultaneously optimize two or more orthogonal properties. For example, polymeric materials with high ion transport and mechanical stiffness are highly desired in water treatment membranes, ion battery electrolytes, fuel cell membranes etc. To achieve this goal, at least two components with distinct properties are usually needed, and a co-continuous microstructure, where one domain is responsible for ion transport while the other imparts mechanical strength, is favored. In this thesis, we propose that the salt-doped A/B/AB ternary system that consists of A and B homopolymer and a corresponding AB diblock copolymer is an attractive platform in accessing the bicontinuous microemulsion (BμE), where the introduction of salt improves the ionic conductivity. To help design such materials with desired properties, the influence of salt ions on the thermodynamics of mixing and phase behaviors needs to be elucidated. We start with one limit of the salt-doped ternary system that no copolymer is added. In Chapter 2, we investigated the phase behavior of LiTFSI-doped poly(ethylene-alt-propylene)/poly(ethylene oxide) (PEP/PEO) and polystyrene/poly(ethylene oxide) (PS/PEO) binary blends and observed a significant reduction of miscibility and an asymmetric phase diagram. Chapter 3 details the symmetric isopleth phase diagram of LiTFSI-doped PS/PEO/PS-b-PEO ternary blends, where a robust and wide BμE channel has been found. Chapter 4 extends the research reported in Chapter 3 to off-symmetric isopleths, where an unexpected C15 Laves phase has been observed, and isothermal phase diagrams have also been mapped out. Finally, Chapter 5 describes the influence of salts on the single-chain dimensions of PEO melts by small-angle neutron scattering and the difficulties in data analysis. Throughout the whole thesis, the main goal is to comprehensively understand salt-polymer interactions and explore the change of phase behavior compared to the salt-free system, which may help to prepare polymer electrolytes with tunable structures and properties.Item Toughen and recycle plastics with strategically designed polyolefin copolymers(2018-09) Xu, JunThe goal of fabricating materials with better properties and understanding the underlying structure-property-performance relationship has continuously driven research efforts and motivated our work in this thesis. Unique block copolymers have been strategically designed and employed in concert with commercially available resins to achieve blend materials with well-controlled nano-structures and excellent mechanical properties. We first carried out a model system study of the phase behavior between iPP and a series of synthesized copolymers that are potentially miscible with iPP according to the conformation asymmetry theory. Though they are not miscible with iPP as predicted by theory because of density mismatch, their marginal immiscibility imparted very low interfacial tensions with iPP, producing blends with nano-sized dispersed droplets and excellent optical transparency. More interestingly, 5 wt% of these copolymers raised the elongation at break from 20% for neat PP to more than 300%, which is attributable to greatly reduced interparticle distance and cavitation induced shear yielding as evidenced in electron microscopy studies. With the knowledge learned from the model study, we proceeded to strategically design ‘amphiphilic’ block copolymers (BCPs) to explore the application of block copolymer micelles for toughening of semi-crystalline iPP matrix. When melt blended with iPP, these polyolefin block copolymers were uniformly dispersed as sub-100nm micelles. Moreover, these excellent toughening agents increased the tensile toughness by 20 times with merely 5 wt% addition and improved the impact strength by 12 times with 10 wt% addition, and more importantly, no significant deterioration in the elastic modulus or tensile strength was observed. Electron microscopy revealed coexistence of the cavitated micelles and shear band structure in the matrix of the BCP modified blends, suggesting a cavitation induced shear yielding toughening mechanism. A well-established theory was employed to model the dependence of toughening performance on the modifier size and an optimal size range was identified where particle cavitation and matrix shear yielding can occur simultaneously so that maximum toughness can be achieved. Lastly, we targeted the grand PP/PE recycling challenge faced by the global society using iPP-PE block copolymers synthesized by our Cornell collaborators. The compatibilizing performance of the iPP-PE block copolymers was evaluated from two perspectives: blend morphology studied with electron microscopy and interfacial adhesion studied with model T-peel testing. Then the mechanical properties of compatibilized blends were measured with tensile testing. The iPP-PE diblock copolymers with high molecular weights and multiblock copolymers with moderate molecular weights are shown to be exceptional compatibilizers, significantly reducing the droplet size in the blend morphology and leading to PE cohesive failure during peel testing. To explain the molecular weight and architecture dependence, we have invoked two mechanisms concerning cocrystallization in diblocks and interlocked entanglements in multiblocks. The finer blend morphology and enhanced interfacial adhesion translate into excellent blend mechanical properties. Tough blends can be obtained with as little as 0.5 wt% BCP, an amazing result that demonstrates the amazing interfacial activity of these BCP species.Item Transition State of Single Chain Expulsion from a Diblock Copolymer Micelle(2023-06) Seeger, SarahThe 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.