Effect of Nanoparticle Surfactants on the Breakup of Free-Falling Water Jets during Continuous Processing of Reconfigurable Structured Liquid Droplets

Structured liquids, whose 3-D morphology can adapt and respond to external stimuli, represent a revolutionary materials platform for next-generation energy technologies, such as batteries, photovoltaics, and thermoelectrics. Structured liquids can be crafted by the jamming of interfacial assemblies of nanoparticle (NP) surfactants. Due to the interactions between functional groups on nanoparticles dispersed in one liquid and polymers having complementary end-functionality dissolved in a second immiscible fluid, the anchoring of a well-defined number of polymer chains onto the NPs leads to the formation of NP surfactants that assemble at the interface and reduce the interfacial energy. Microfluidic techniques provide a simple and versatile route to produce one liquid phase in a second where the shape of the dispersed liquid phase can range from droplets to tubules depending on the flow conditions and the interfacial energies. In this study, the effect of NP surfactants on Plateau–Rayleigh (PR) instabilities of a free-falling jet of an aqueous dispersion of carboxylic acid functionalized silica NPs into a toluene phase containing amine-terminated polydimethylsiloxane (PDMS–NH₂) is investigated. NP surfactants were found to significantly affect the breakup of laminar liquid jets, resulting in longer jet breakup lengths and dripping to jetting flow transitions

Minute-MOFs: Ultrafast Synthesis of M₂(dobpdc) Metal–Organic Frameworks from Divalent Metal Oxide Colloidal Nanocrystals

The material demands for metal–organic frameworks (MOFs) for next-generation energy-efficient CO₂ capture technologies necessitate advances in their expedient and scalable synthesis. Toward that end, the recently discovered expanded MOF-74, or M₂(dobpdc), where M = divalent metal cation and dobpdc = 4,4′-dioxido-3,3′-biphenyldicarboxylate, can now be prepared in minutes via a controlled dissolution–crystallization route from divalent metal oxides as precursors. We show that the available surface area of the metal oxide plays a critical role in the precursor dissolution, which was found to be rate-limiting. Based on this understanding of the reaction trajectory, we pushed the chemical transformation to its fringe kinetic limit by configuring the metal oxide precursors as ligand-free colloidal metal oxide nanocrystals, which allowed MOF formation in less than 1 min. MOFs prepared by this strategy were highly crystalline, with BET surface areas on par with conventional multihour syntheses from metal halide salts. This method was also applied successfully in the synthesis of M₂(dobdc) MOFs, highlighting its generality. Our work challenges the conventional wisdom that plurality of steps in MOF formation is inherently time-intensive

Redox-Active Supramolecular Polymer Binders for Lithium–Sulfur Batteries That Adapt Their Transport Properties in Operando

π-Stacked perylene bisimide (PBI) molecules are implemented here as highly networked, redox-active supramolecular polymer binders in sulfur cathodes for lightweight and energy-dense Li–S batteries. We show that the in operando reduction and lithiation of these PBI binders sustainably reduces Li–S cell impedance relative to nonredox active conventional polymer binders. This lower impedance enables high-rate cycling in Li–S cells with excellent durability, a critical step toward unlocking the full potential of Li–S batteries for electric vehicles and aviation

Aqueous-Processable Redox-Active Supramolecular Polymer Binders for Advanced Lithium/Sulfur Cells

Lithium/Sulfur (Li/S) cells are a promising chemistry with potential to deliver a step-change in energy density compared to state-of-the-art Li-ion batteries. To minimize the environmental impact of the Li/S cell manufacturing and to compete with Li-ion cells in both performance and cost, electrodes cast using an aqueous process are highly desirable. Here we describe the discovery and application of a lithiated redox-mediating supramolecular binder based on the well-known n-type semiconductor, perylene bisimide, that forms high-fidelity sulfur electrodes from water-processed slurries. A 1.4-fold improvement in sulfur utilization at 3.0 C and 58% increase in capacity retention after 250 cycles at 1.5 C are reported for the prelithiated, supramolecular binder compared to control samples. These improvements are attributed to the self-assembly of lithiated perylene bisimide binders in water to yield nanowire web morphologies that increase interfacial area between electrode components and exhibit enhanced electrode-current collector adhesion

Influence of Surface Composition on Electronic Transport through Naked Nanocrystal Networks

Influence of Surface Composition on Electronic Transport through Naked Nanocrystal Network

Diamine-Appended Mg₂(dobpdc) Nanorods as Phase-Change Fillers in Mixed-Matrix Membranes for Efficient CO₂/N₂ Separations

Despite the availability of chemistries to tailor the pore architectures of microporous polymer membranes for chemical separations, trade-offs in permeability and selectivity with functional group manipulations nevertheless persist, which ultimately places an upper bound on membrane performance. Here we introduce a new design strategy to uncouple these attributes of the membrane. Key to our success is the incorporation of phase-change metal–organic frameworks (MOFs) into the polymer matrix, which can be used to increase the solubility of a specific gas in the membrane, and thereby its permeability. We further show that it is necessary to scale the size of the phase-change MOF to nanoscopic dimensions, in order to take advantage of this effect in a gas separation. Our observation of an increase in solubility and permeability of only one of the gases during steady-state permeability measurements suggests fast exchange between free and chemisorbed gas molecules within the MOF pores. While the kinetics of this exchange in phase-change MOFs are not yet fully understood, their role in enhancing the efficacy and efficiency of the separation is clearly a compelling new direction for membrane technology

Polysulfide-Blocking Microporous Polymer Membrane Tailored for Hybrid Li-Sulfur Flow Batteries

Redox flow batteries (RFBs) present unique opportunities for multi-hour electrochemical energy storage (EES) at low cost. Too often, the barrier for implementing them in large-scale EES is the unfettered migration of redox active species across the membrane, which shortens battery life and reduces Coulombic efficiency. To advance RFBs for reliable EES, a new paradigm for controlling membrane transport selectivity is needed. We show here that size- and ion-selective transport can be achieved using membranes fabricated from polymers of intrinsic microporosity (PIMs). As a proof-of-concept demonstration, a first-generation PIM membrane dramatically reduced polysulfide crossover (and shuttling at the anode) in lithium–sulfur batteries, even when sulfur cathodes were prepared as flowable energy-dense fluids. The design of our membrane platform was informed by molecular dynamics simulations of the solvated structures of lithium bis­(trifluoromethanesulfonyl)­imide (LiTFSI) vs lithiated polysulfides (Li₂S_<i>x</i>, where <i>x</i> = 8, 6, and 4) in glyme-based electrolytes of different oligomer length. These simulations suggested polymer films with pore dimensions less than 1.2–1.7 nm might incur the desired ion-selectivity. Indeed, the polysulfide blocking ability of the PIM-1 membrane (∼0.8 nm pores) was improved 500-fold over mesoporous Celgard separators (∼17 nm pores). As a result, significantly improved battery performance was demonstrated, even in the absence of LiNO₃ anode-protecting additives

Mechanistic Insight into the Formation of Cationic Naked Nanocrystals Generated under Equilibrium Control

Cationic naked nanocrystals (NCs) are useful building units for assembling hierarchical mesostructured materials. Until now, their preparation required strongly electrophilic reagents that irreversibly sever bonds between native organic ligands and the NC surface. Colloidal instabilities can occur during ligand stripping if exposed metal cations desorb from the surface. We hypothesized that cation desorption could be avoided were we able to stabilize the surface during ligand stripping via ion pairing. We were successful in this regard by carrying out ligand stripping under equilibrium control with Lewis acid–base adducts of BF₃. To better understand the microscopic processes involved, we studied the reaction pathway in detail using in situ NMR experiments and electrospray ionization mass spectrometry. As predicted, we found that cationic NC surfaces are transiently stabilized post-stripping by physisorbed anionic species that arise from the reaction of BF₃ with native ligands. This stabilization allows polar dispersants to reach the NC surface before cation desorption can occur. The mechanistic insights gained in this work provide a much-needed framework for understanding the interplay between NC surface chemistry and colloidal stability. These insights enabled the preparation of stable naked NC inks of desorption-susceptible NC compositions such as PbSe, which were easily assembled into new mesostructured films and polymer-nanocrystal composites with wide-ranging technological applications

Materials Genomics Screens for Adaptive Ion Transport Behavior by Redox-Switchable Microporous Polymer Membranes in Lithium–Sulfur Batteries

Selective ion transport across membranes is critical to the performance of many electrochemical energy storage devices. While design strategies enabling ion-selective transport are well-established, enhancements in membrane selectivity are made at the expense of ionic conductivity. To design membranes with both high selectivity and high ionic conductivity, there are cues to follow from biological systems, where regulated transport of ions across membranes is achieved by transmembrane proteins. The transport functions of these proteins are sensitive to their environment: physical or chemical perturbations to that environment are met with an adaptive response. Here we advance an analogous strategy for achieving adaptive ion transport in microporous polymer membranes. Along the polymer backbone are placed redox-active switches that are activated in situ, at a prescribed electrochemical potential, by the device’s active materials when they enter the membrane’s pore. This transformation has little influence on the membrane’s ionic conductivity; however, the active-material blocking ability of the membrane is enhanced. We show that when used in lithium–sulfur batteries, these membranes offer markedly improved capacity, efficiency, and cycle-life by sequestering polysulfides in the cathode. The origins and implications of this behavior are explored in detail and point to new opportunities for responsive membranes in battery technology development

Assembly of Ligand-Stripped Nanocrystals into Precisely Controlled Mesoporous Architectures

The properties of mesoporous materials hinge on control of their composition, pore dimensions, wall thickness, and the size and shape of the crystallite building units. We create ordered mesoporous materials in which all of these parameters are independently controlled. Different sizes (from 4.5 to 8 nm) and shapes (spheres and rods) of ligand-stripped nanocrystals are assembled using the same structure-directing block copolymers, which contain a tethering domain designed to adsorb to their naked surfaces. Material compositions range from metal oxides (Sn-doped In₂O₃ or ITO, CeO₂, TiO₂) to metal fluorides (Yb,Er-doped NaYF₄) and metals (FePt). The incorporation of new types of nanocrystals into mesoporous architectures can lead to enhanced performance. For example, TiO₂ nanorod-based materials withstand >1000 electrochemical cycles without significant degradation