A Solvent-Vapor Approach toward the Control of Block Ionomer Morphologies

Materials descriptors for advanced water dissociation catalysts in bipolar membranes

The voltage penalty driving water dissociation (WD) at high current density is a major obstacle in the commercialization of bipolar membrane (BPM) technology for energy devices. Here we show that three materials descriptors, that is, electrical conductivity, microscopic surface area and (nominal) surface-hydroxyl coverage, effectively control the kinetics of WD in BPMs. Using these descriptors and optimizing mass loading, we design new earth-abundant WD catalysts based on nanoparticle SnO2 synthesized at low temperature with high conductivity and hydroxyl coverage. These catalysts exhibit exceptional performance in a BPM electrolyser with low WD overvoltage (ηwd) of 100 ± 20 mV at 1.0 A cm-2. The new catalyst works equivalently well with hydrocarbon proton-exchange layers as it does with fluorocarbon-based Nafion, thus providing pathways to commercializing advanced BPMs for a broad array of electrolysis, fuel-cell and electrodialysis applications.

Preventing the spread of life-threatening gastrointestinal microbes on the surface of a continuously self-disinfecting block polymer

Highly persistent, drug-resistant and transmissible healthcare pathogens such as Clostridioides difficile (C. difficile) and Candida auris (C. auris) are responsible for causing antibiotic-associated fatal diarrhea and invasive candidiasis, respectively. In this study, we demonstrate that these potentially lethal gastrointestinal microbes can be rapidly inactivated on the solid surface of a self-disinfecting anionic block polymer that inherently generates a water surface layer that is highly acidic (pH < 1) upon hydration. Due to thermodynamic incompatibility between its chemical sequences, the polymer spontaneously self-organizes into a nanostructure that enables proton migration from the interior of a film to the surface via contiguous nanoscale hydrophilic channels, as discerned here by scanning electron and atomic force microscopies, as well as X-ray photoelectron spectroscopy. Here, we report that two strains of C. difficile in the vegetative state and two species of Candida, Candida albicans (C. albicans) and C. auris, are, in most cases, inactivated to the limit of minimum detection. Corresponding electron and optical microscopy images reveal that, upon exposure to the hydrated polymer, the outer microbial membranes display evidence of damage and intracellular material is expelled. Combined with our previous studies of rapid bacterial and viral inactivation, these antimicrobial results are highly encouraging and, if translatable to clinical conditions in the form of self-standing polymer films or coatings, are expected to benefit the welfare of patients in healthcare facilities by continuously preventing the spread of such potentially dangerous microbes.

Rapid and Repetitive Inactivation of SARS-CoV-2 and Human Coronavirus on Self-Disinfecting Anionic Polymers

While the ongoing COVID-19 pandemic affirms an urgent global need for effective vaccines as second and third infection waves are spreading worldwide and generating new mutant virus strains, it has also revealed the importance of mitigating the transmission of SARS-CoV-2 through the introduction of restrictive social practices. Here, it is demonstrated that an architecturally- and chemically-diverse family of nanostructured anionic polymers yield a rapid and continuous disinfecting alternative to inactivate coronaviruses and prevent their transmission from contact with contaminated surfaces. Operating on a dramatic pH-drop mechanism along the polymer/pathogen interface, polymers of this archetype inactivate the SARS-CoV-2 virus, as well as a human coronavirus surrogate (HCoV-229E), to the minimum detection limit within minutes. Application of these anionic polymers to frequently touched surfaces in medical, educational, and public-transportation facilities, or personal protection equipment, can provide rapid and repetitive protection without detrimental health or environmental complications.

Proton conducting ABA triblock copolymers with sulfonated poly(phenylene sulfide sulfone) midblock obtained via copper-free thiol-click chemistry

The synthesis and characterization of novel proton conducting ABA triblock copolymers are reported. Structure-properties relationship of the block copolymers has been investigated at both the microscopic and macroscopic levels.

Ionic complexation of endblock-sulfonated thermoplastic elastomers and their physical gels for improved thermomechanical performance

Thermoplastic elastomers (TPEs) composed of nonpolar triblock copolymers constitute a broadly important class of (re)processable network-forming macromolecules employed in ubiquitous commercial applications. Physical gelation of these materials in the presence of a low-volatility oil that is midblock-selective yields tunably soft TPE gels (TPEGs) that are suitable for emergent technologies ranging from electroactive, phase-change and shape-memory responsive media to patternable soft substrates for flexible electronics and microfluidics. Many of the high-volume TPEs used for these purposes possess styrenic endblocks that are inherently limited by a relatively low glass transition temperature. To mitigate this shortcoming, we sulfonate and subsequently complex (and physically crosslink) the endblocks with trivalent Al³⁺ ions. Doing so reduces the effective hydrophilicity of the sulfonated endblocks, as evidenced by water uptake measurements, while concurrently enhancing the thermomechanical stability of the corresponding TPEGs. Chemical modification results, as well as morphological and property development, are investigated as functions of the degree of sulfonation, complexation and TPEG composition.

Electrochemical Manipulation of Aligned Block Copolymer Templates

Block copolymers have a wide range of functions in advanced electrochemistry because of their ability to self-assemble into ordered nanometer-sized structures, resulting in their extensive usage as nanoporous templates that can be electrochemically manipulated. These highly ordered nanoporous templates are used as working electrodes for electrodeposition and electropolymerization to build nanoelectrode arrays and can serve as models to study the diffusion pathway of redox-active units with regard to chemical modification of pores. The block copolymer system allows different morphologies to be utilized, but the most exploited structures are standing cylinders of the minority block that are etched to expose highly aligned porous nanoelectrode array templates. This review starts with introducing alumina and track-etched membranes as pioneer porous templates transitioning to the production of block copolymer films as succeeding templates, with a particular focus on both poly(styrene)-block-poly(methylmethacrylate) (PS-b-PMMA) and poly(styrene)-block-poly(lactide) (PS-b-PLA). The aim is to give fundamental insights of electrochemistry where functionality extends beyond to applications in the nanoscience field of biosensors and plastic electronics.

Self-Assembly of a Midblock-Sulfonated Pentablock Copolymer in Mixed Organic Solvents: A Combined SAXS and SANS Analysis

Ionic, and specifically sulfonated, block copolymers are continually gaining interest in the soft materials community due to their unique suitability in various ion-exchange applications such as fuel cells, organic photovoltaics, and desalination membranes. One unresolved challenge inherent to these materials is solvent templating, that is, the translation of self-assembled solution structures into nonequilibrium solid film morphologies. Recently, the use of mixed polar/nonpolar organic solvents has been examined in an effort to elucidate and control the solution self-assembly of sulfonated block copolymers. The current study sheds new light on micellar assemblies (i.e., those with the sulfonated blocks comprising the micellar core) of a midblock-sulfonated pentablock copolymer in polar/nonpolar solvent mixtures by combining small-angle X-ray and small-angle neutron scattering. Our scattering data reveal that micelle size depends strongly on overall solvent composition: micelle cores and coronae grow as the fraction of nonpolar solvent is increased. Universal model fits further indicate that an unexpectedly high fraction of the micelle cores is occupied by polar solvent (60-80 vol %) and that partitioning of the polar solvent into micelle cores becomes more pronounced as its overall quantity decreases. This solvent presence in the micelle cores explains the simultaneous core/corona growth, which is otherwise counterintuitive. Our findings provide a potential pathway for the formation of solvent-templated films with more interconnected morphologies due to the greatly solvated micellar cores in solution, thereby enhancing the molecular, ion, and electron-transport properties of the resultant films.

Incorporation of Metallic Species into Midblock-Sulfonated Block Ionomers

Block ionomers can, in the same fashion as their neutral block copolymer analogs, microphase-order into various nanoscale morphologies. The added benefit of a copolymer possessing a charged species is that the resultant block ionomer becomes amphiphilic and capable of imbibing polar liquids, including water. This characteristic facilitates incorporation of metallic species into the soft nanostructure for a wide range of target applications. In this study, the nonpolar and polar constituents of solvent-templated midblock-sulfonated block ionomers (SBIs) are first selectively metallated for complementary morphological analysis. Next, four different salts, with cationic charges ranging from +1 to +3, are introduced into three hydrated SBIs varying in their degree of sulfonation (DOS), and cation uptake is measured as a function of immersion time. These results indicate that uptake generally increases with increasing salt concentration, cationic charge, and specimen DOS. Swelling and nanoindentation measurements conducted at ambient temperature demonstrate that water uptake decreases, while the surface modulus increases, with increasing cationic charge. Chemical spectra acquired from energy-dispersive X-ray spectroscopy (EDS) confirm the presence of each of the ion-exchanged species, and corresponding EDS chemical maps reveal that the spatial distribution of these species is relatively uniform throughout the block ionomer films.

Effect of Systematic Hydrogenation on the Phase Behavior and Nanostructural Dimensions of Block Copolymers

Unsaturated polydienes are frequently hydrogenated to yield polyolefins that are more chemically stable. Here, the effects of partial hydrogenation on the phase behavior and nanostructure of polyisoprene-containing block copolymers are investigated. To ensure access to the order-disorder transition temperature (T_ODT) over a wide temperature range, we examine copolymers with at least one random block. Dynamic rheological and scattering measurements indicate that T_ODT increases linearly with increasing hydrogenation. Small-angle scattering reveals that the temperature-dependence of the Flory-Huggins parameter changes and the microdomain period increases, while the interfacial thickness decreases. The influence of hydrogenation becomes less pronounced in more constrained multiblock copolymers.

Olefinic Thermoplastic Elastomer Gels: Combining Polymer Crystallization and Microphase Separation in a Selective Solvent

Since selectively swollen thermoplastic elastomer gels (TPEGs) afford a wide range of beneficial properties that open new doors to developing elastomer-based technologies, we examine the unique structure-property behavior of TPEGs composed of olefinic block copolymers (OBCs) in this study. Unlike their styrenic counterparts typically possessing two chemically different blocks, this class of multiblock copolymers consists of linear polyethylene hard blocks and poly(ethylene-co-α-octene) soft blocks, in which case, microphase separation between the hard and the soft blocks is accompanied by crystallization of the hard blocks. Here, we prepare olefinic TPEGs (OTPEGs) through the incorporation of a primarily aliphatic oil that selectively swells the soft block and investigate the resultant morphological features through the use of polarized light microscopy and small-/wide-angle X-ray scattering. These features are correlated with thermal and mechanical property measurements from calorimetry, rheology, and extensiometry to elucidate the roles of crystallization and self-assembly on gel characteristics and establish useful structure-property relationships.