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Hayward, Ryan C.

Publications and source records attributed to Hayward, Ryan C..

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Interconnected Nanoporous Polysulfone by the Self-Assembly of Randomly Linked Copolymer Networks and Linear Multiblocks

Porous materials have attracted considerable attention due to their versatile applications, especially in water purification. Interconnected nanoporous structures are distinguished by their high degree of porosity and resistance to clogging, as well as their insensitivity to nanostructural orientation. Previous works on randomly linked copolymer systems have shown that they can effectively produce disordered cocontinuous nanostructures, which upon removal of one component yield interconnected nanoporous materials. However, the cocontinuous nanomaterials previously developed using polystyrene (PS) and poly(d,l-lactic acid) (PLA) strands, and the resulting interconnected nanoporous PS monoliths, were far too brittle to enable practical use as membranes. Here, we study the self-assembly of randomly linked copolymer networks prepared using blocks of the engineering polymer polysulfone (PSU). A wide cocontinuous regime (spanning 40 wt %) was found for randomly end-linked copolymer networks (RECNs) constructed from PSU and PLA strands, via a combination of mechanical testing, gravimetry, small-angle X-ray scattering, and scanning electron microscopy. The PSU/PLA cocontinuous nanomaterial with symmetric composition showed 2.4 times higher Young’s modulus and ~100 times greater toughness than the corresponding PS/PLA sample. The interconnected nanoporous PSU fabricated after etching of PLA even exhibited 1.6 times greater toughness than PS/PLA prior to PLA removal. To facilitate the production of thin films of cocontinuous nanomaterials, we applied solution-processable randomly linked linear PSU/PLA multiblock polymers onto ultrafiltration membranes. Here, the interconnected nanoporous PSU thin film generated by etching PLA was found to effectively reject 50 nm diameter particles without significantly compromising permeability. This discovery presents a valuable addition to the existing techniques used to fabricate PSU membranes. In contrast to traditional methods, which are sensitive to processing conditions, produce a wide range of pore sizes, and offer limited adjustability of pore size, the current technique is anticipated to enable interconnected PSU membranes with more uniform and tailorable porosity.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Cocontinuous Nanostructures by Microphase Separation of Statistically Cross-Linked Polystyrene/Poly(2-vinylpyridine) Networks

Cocontinuous polymeric nanostructures have drawn considerable attention due to their ability to combine distinct, percolation-dependent properties of two different polymer domains. Randomly end-linked copolymer networks (RECNs) have previously been shown to support the formation of disordered cocontinuous nanostructures across wide composition windows in a robust way. However, achieving highly efficient linking of telechelic polymers with excellent end-group fidelity often requires complex synthetic routes. As an alternative, we study here statistically cross-linked copolymer networks (SCCNs) composed of polystyrene and poly(2-vinylpyridine) (PS and P2VP) with cross-linkable allyl pendent groups that are conveniently synthesized by controlled radical copolymerization. Via selective extraction of P2VP, coupled with gravimetry, small-angle X-ray scattering, and electron microscopy, we find disordered cocontinuous phases across wide composition ranges (up to ≈ 35 wt %), approaching values previously determined for RECNs. Remarkably, even for samples that appear to exhibit full percolation, a substantial fraction of P2VP (≈ 20–30 wt %) cannot be removed, which we ascribe to short strands between nearby cross-linkers that are physically embedded within PS domains. Here, the resulting PS porous monoliths with residual surface P2VP layers enable facile surface modification to resist protein adsorption and templating of porous gold nanostructures.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Photo-actuators via epitaxial growth of microcrystal arrays in polymer membranes

Photomechanical crystals composed of three-dimensionally ordered and densely packed photochromes hold promise for high-performance photochemical actuators. However, bulk crystals with high structural ordering are severely limited in their flexibility, resulting in poor processibility and a tendency to fragment upon light exposure, while previous nano- or microcrystalline composites have lacked global alignment. Here we demonstrate a photon-fuelled macroscopic actuator consisting of diarylethene microcrystals in a polyethylene terephthalate host matrix. These microcrystals survive large deformations and show a high degree of three-dimensional ordering dictated by the anisotropic polyethylene terephthalate, which critically also has a similar stiffness. Overall, these ordered and compliant composites exhibit rapid response times, sustain a performance of over at least hundreds of cycles and generate work densities exceeding those of single crystals. In conclusion, our composites represent the state-of-the-art for photochemical actuators and enable properties unattainable by single crystals, such as controllable, reversible and abrupt jumping (photosalient behaviour).

36 MATERIALS SCIENCE↗
DOE OSTI2022

Self-assembly of cocontinuous nanostructured copolymer templates with compositional and architectural dispersity. Final Report

Cocontinuous nanostructured materials in which multiple domains of different materials simultaneously span three dimensional space offer opportunities to achieve combined properties not possible with a single homogeneous material. These architectures have importance in a broad range of energy-relevant technologies including batteries, supercapacitors, fuel cells, separation membranes, and catalysts. Achieving such structures in polymeric materials has been of long-standing interest in the field, due to both the inherently attractive properties of cocontinuous polymer morphologies as well as their ability to serve as templates for other functional nanostructured materials. Our work on this project has established that randomly-linked polymer architectures constructed from two immiscible polymer strands provide robust and highly tunable approaches to disordered cocontinuous nanostructures. In particular, we developed a detailed understanding of how the parameters (linker functionality and strand length, asymmetry, and dispersity) of randomly-linked networks controlled the breadth of the cocontinuous window over which both phases remain percolated. We further characterized how these nanostructures undergo orientation, while retaining cocontinuity, under mechanical deformation. We also compared their behavior to that of random multi-block polymers of linear architecture, which show similar propensity to form disordered nanostructures, albeit over narrower ranges of parameter space. Finally, we have explored the development of functional polymer nanostructures and composites based in part on the fundamental understanding obtained via this project.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Assembly of Disordered Cocontinuous Morphologies by Multiblock Copolymers with Random Block Sequence and Length Dispersity

Among the wide variety of nanostructures accessible by self-assembly of block copolymers, cocontinuous morphologies are of great interest for separations, catalysis, sensing, and energy storage due to their ability to integrate distinct properties of the constituent polymers. Furthermore, we investigate the tendency to form disordered cocontinuous phases of multiblock copolymers (MBCs) with random block sequence and length dispersity prepared by step-growth polymerization of pre-made telechelic polymers, specifically using thiol-Michael addition between diacrylate functionalized polystyrene (PS) and poly (D,L - lactide) (PLA) chains and a small molecule dithiol. In the phase diagram so established, disordered cocontinuous nanostructures occupy a wide window (≈ 25 % vol) at a modest segregation strength of χN = 15, close to the critical value for microphase separation. At a higher segregation strength of χN = 30, only a moderately wide (≈ 10 vol %) cocontinuous window is found, with MBCs instead tending to form ordered nanostructures. Although the breadth of the cocontinuous widow is less than that found in prior work on analogous randomly end-linked copolymer networks (RECNs), the MBC architecture offers offsetting advantages in terms of solution and melt processability.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Polymer Zwitterions for Stabilization of CsPbBr 3 Perovskite Nanoparticles and Nanocomposite Films

Abstract Functional polymers with sulfobetaine or phosphorylcholine zwitterions as pendent groups are demonstrated as both ligands and host matrices for CsPbBr 3 perovskite nanoparticles (PNPs). These polymers produce nanocomposite films with excellent NP dispersion, optical transparency, and impressive resistance to NP degradation upon exposure to water. Multidentate interactions of the zwitterion‐containing copolymers with the PNPs induce dispersed or weakly aggregated nanocomposite morphologies, depending on the extent of zwitterionic functionality in the polymer. Incorporating additional functionality into the polymers, such as benzophenone pendent groups, yields lithographically patternable films, while time‐resolved photoluminescence measurements provide insight into the electronic impact of PNPs in zwitterionic polymer matrices.

Kim, Hyunki↗
DOE OSTI2020

Polymer Zwitterions for Stabilization of CsPbBr 3 Perovskite Nanoparticles and Nanocomposite Films

Functional polymers with sulfobetaine or phosphorylcholine zwitterions as pendent groups are demonstrated as both ligands and host matrices for CsPbBr 3 perovskite nanoparticles (PNPs). These polymers produce nanocomposite films with excellent NP dispersion, optical transparency, and impressive resistance to NP degradation upon exposure to water. Multidentate interactions of the zwitterion-containing copolymers with the PNPs induce dispersed or weakly aggregated nanocomposite morphologies, depending on the extent of zwitterionic functionality in the polymer. Incorporating additional functionality into the polymers, such as benzophenone pendent groups, yields lithographically patternable films, while time-resolved photoluminescence measurements provide insight into the electronic impact of PNPs in zwitterionic polymer matrices.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Tuning Metastability of Poly(3-hexyl thiophene) Solutions to Enable in Situ Atomic Force Microscopy Imaging of Surface Nucleation

Poly(3-hexyl thiophene) (P3HT), a workhorse material for the study of organic electronic devices, assembles into nanofibers (NFs) upon crystallization from solution, providing the means to tailor morphology and improve device performance. We investigate how P3HT regioregularity, molecular weight, and concentration influence the hysteresis between crystallization and melting temperatures of NFs. Hysteresis is found to increase with molecular weight and reach an asymptote for polymer chains above the chain folding threshold (Mn > 12 kg/mol). Regioregularity does not substantially affect the hysteresis above a level of 88%, while increasing polymer concentration is found to reduce hysteresis. This insight facilitates in situ high-resolution atomic force microscopy measurements that provide better understanding of the mechanism of NF crystallization on graphite. We find an interchain distance (along the a crystallographic axis) of 16.7 ± 0.7 Å, and a spacing of 7.7 ± 0.2 Å along the c axis, suggesting that the crystals on graphite are form I.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effects of Randomly End-Linked Copolymer Network Parameters on the Formation of Disordered Cocontinuous Phases

Randomly end-linked copolymer networks (RECNs) provide a robust route to cocontinuous nanoscale structures, yielding opportunities to integrate desirable and distinct properties of the constituent materials. In this report, we rely on gravimetric and mechanical analysis of polystyrene (PS)/poly(dl-lactide) (PLA) RECNs to characterize the continuity of both phases as a function of four key network parameters. (1) For symmetric (M n,PS ≈ M n,PLA ) RECNs, variations in strand length reveal a critical segregation strength of χ(N PS + N PLA ) ≈ 11 required for microphase separation, above which the disordered cocontinuous phase spans roughly 30 wt % in composition, with dispersed domains of the minority phase residing on either side. Increasing the strand length above this threshold increases the characteristic d spacing but has little effect on the boundaries of the cocontinuous phase. (2) For asymmetric strand lengths, M n,PS ≠ M n,PLA , the d spacing is shifted to adopt the preferred size set by the minority domains, but the breadth and location of the cocontinuous window are not altered. (3) An increase in the dispersity Ð of PLA strands widens the cocontinuous window and shifts it toward the PLA-rich end of the phase diagram. (4) Finally, an increase in the dispersity in junction functionality f expands the cocontinuous window toward both sides of the phase diagram, yielding an overall width of roughly 45 wt %. The understanding provided on how network parameters influence self-assembly of RECNs offers guidelines for the robust design of cocontinuous nanostructures.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Functional polymers for growth and stabilization of CsPbBr 3 perovskite nanoparticles

We introduce an approach to synthesize polymer-stabilized CsPbBr 3 perovskite nanoparticles (NPs) using ammonium bromide-functionalized polymers as both bromide precursors and stabilizing ligands. The polymer-passivated NPs exhibit significant advantages over conventional perovskite NPs owing to their facile dispersion in polymer matrices and enhanced optoelectronic stability.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Stress-Induced Orientation of Cocontinuous Nanostructures within Randomly End-Linked Copolymer Networks

Randomly end-linked copolymer networks (RECNs) provide a robust route to self-assembled cocontinuous nanostructures. Here, we study the orientation of cocontinuous polystyrene/poly(D,L-lactide) (PS/PLA) RECNs induced by uniaxial stretching above the glass transition temperatures of the components. Small-angle X-ray scattering (SAXS) reveals that the domains initially undergo nonaffine stretching at low strain (ε < 0.4), followed by domain rotation at larger strains, yielding a “soft elastic” response and providing a high degree of orientation. Transmission electron microscopy (TEM) tomography confirms that stretching leads to topological changes in the nanostructure, corresponding to reorganization of domain interfaces. The combination of orientation at the molecular and nanostructural levels provides substantial improvements in yield strength, toughness, and stiffness. In addition to possibilities for improving mechanical properties, cocontinuous nanostructures with controlled levels of orientation have potential in a variety of contexts including directional ion transport and energy absorption.

42 ENGINEERING↗
DOE OSTI2017

Anisotropic and Interconnected Nanoporous Materials from Randomly End-Linked Copolymer Networks

Microphase separation within randomly end-linked copolymer networks (RECNs) provides access to disordered bicontinuous morphologies over a wide composition range of the constituent network strands. Here, we rely on end-linking of telechelic hydroxyl-terminated polystyrene (PS) and poly(D,Llactide) (PLA) chains of equal molecular weight, with a tetrafunctional isocyanate cross-linker in a good solvent for both strands, followed by solvent removal to induce microphase separation, and finally etching of the PLA phase to yield nanoporous materials. Transmission electron microscopy (TEM) tomographic reconstructed 3D images along with gravimetric measurements and small-angle X-ray scattering (SAXS) indicate the formation of highly interconnected structures over a range of ~40-70 vol % of PLA, while N2 adsorption measurements indicate narrowly distributed pore sizes that can be tuned by varying the strand molecular weights. Stretching of the PS/PLA copolymer networks above the glass transition temperatures of both components prior to etching the PLA phase provides a straightforward means to introduce controlled anisotropy into the 3D interconnected porous materials.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Ion transport properties of mechanically stable symmetric ABCBA pentablock copolymers with quaternary ammonium functionalized midblock

Anion exchange membranes (AEMs) are a promising class of materials for applications that require selective ion transport, such as fuel cells, water purification, and electrolysis devices. Studies of structure–morphology–property relationships of ion-exchange membranes revealed that block copolymers exhibit improved ion conductivity and mechanical properties due to their microphase-separated morphologies with well-defined ionic domains. While most studies focused on symmetric diblock or triblock copolymers, here, the first example of a midblock quaternized pentablock AEM is presented. A symmetric ABCBA pentablock copolymer was functionalized to obtain a midblock brominated polymer. Solution cast films were then quaternized to obtain AEMs with resulting ion exchange capacities (IEC) ranging from 0.4 to 0.9 mmol/g. Despite the relatively low IEC, the polymers were highly conductive (up to 60 mS/cm Br- at 90 °C and 95%RH) with low water absorption (<25 wt %) and maintained adequate mechanical properties in both dry and hydrated conditions. X-ray scattering and transmission electron microscopy (TEM) revealed formation of cylindrical non-ionic domains in a connected ionic phase.

Ertem, SP↗
DOE OSTI2016

Crystallization-driven assembly of conjugated-polymer-based nanostructures

The goal of this project has been to improve our ability to simultaneously control the organization, and therefore the opto-electronic properties, of conjugated-polymer based materials across three different length-scales: 1) the molecular scale, in the sense of controlling growth and functionalization of highly crystalline semiconducting organic materials capable of efficient charge transport, 2) the nanoscale, in terms of positioning n- and p-type materials with domain sizes comparable to exciton diffusion lengths (~ 10 nm) to facilitate charge separation, and 3) the colloidal scale, such that well-defined crystalline nanoscale building blocks can be hierarchically organized into device layers. As described in more detail below, the project was successful in generating powerful new approaches to, and improved fundamental understanding of, processing and self-assembly of organic and hybrid semiconducting materials across all three length-scales. Although the goals of the project were formulated with primarily photovoltaic architectures in mind, the outcomes of the project have significant implications for a variety of conjugated-polymer-based devices including field-effect-transistors for sensors and logic devices, as well as potentially thermoelectrics and battery electrode materials. The project has resulted in 10 peer-reviewed publications to date [1-10], with several additional manuscripts currently in preparation.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Using Janus Nanoparticles To Trap Polymer Blend Morphologies during Solvent-Evaporation-Induced Demixing

Using ternary blends of polystyrene (PS), poly(methyl methacrylate) (PMMA), and Janus particles (JPs) with symmetric PS and PMMA hemispheres, we demonstrate the stabilization of dispersed and bicontinuous phase-separated morphologies by the interfacial adsorption of Janus particles during demixing upon solvent removal. The resulting blend morphology could be varied by changing the blend composition and JP loading. Increasing particle loading decreased the size of phase-separated domains, while altering the mixing ratio of the PS/PMMA homopolymers produced morphologies ranging from PMMA droplets in a PS matrix to PS droplets in a PMMA matrix. Notably, bicontinuous morphologies were obtained at intermediate blend compositions, marking the first report of highly continuous domains obtained through demixing in a polymer blend compatibilized by Janus particles. The JPs were found to assemble in a densely packed monolayer at the interface, allowing for the stabilization of bicontinuous morphologies in films above the glass transition temperature by inhibiting coarsening and coalescence of the phase-separated domains. In conclusion, the rate of solvent evaporation from the drop-cast films and the molecular weights of the homopolymers were found to greatly affect blend morphology.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗