Microemulsions as Emerging Electrolytes: The Correlation of Structure to Electrochemical Response.

We describe the structural studies of microemulsions (µEs) prepared from water, toluene, butanol, and polysorbate 20 (PS20) that we recently used as electrolytes. Small-angle neutron scattering was used to monitor the development of the bicontinuous system as a function of the water-to-surfactant mass ratio on a constant oil-to-surfactant dilution line, revealing how the domain size, correlation length, amphiphilicity factor, and bending moduli change with composition. Kratky and Porod analyses are also employed, providing further structural detail of the scattering domains. We demonstrate that controlling the water-to-surfactant ratio with a constant oil-to-surfactant dilution affects the bicontinuous phase, reveals a sizeable compositional region with structural similarities, and provides insight into the correlation of structure to physical properties. Voltammetric results are presented to examine how the evolution of the bicontinuous structure formed in a µE prepared from water, toluene, butanol, and PS20 contributes to the electrochemical response. These findings, therefore, provide essential information that will guide the formulation of µEs as electrolytes for energy storage.

Microemulsions: Breakthrough Electrolytes for Redox Flow Batteries.

Aqueous and non-aqueous redox flow batteries (RFBs) have limited energy and current densities, respectively, due to the nature of the electrolytes. New approaches to electrolyte design are needed to improve the performance of RFBs. In this work, we combined a highly conductive aqueous phase and an organic redox-active phase in a microemulsion to formulate a novel RFB electrolyte. As a proof-of-concept, we demonstrate an RFB using this microemulsion electrolyte with maximum current density of 17.5 mA·cm-2 with a 0.19 M posolyte and 0.09 M negolyte at a flow rate of only ∼2.5 ml·min-1, comparable to early vanadium electrolyte RFBs at similar flow rates on a per molar basis. The novel active negolyte component is an inexpensive oil-soluble vitamin (K3). By combining aqueous and organic phases, the solvent potential window and energy density may be increased without sacrificing current density and new redox couples may be accessed. Microemulsion electrolytes show great promise for improved performance and increased energy densities in aqueous RFBs but the path forward is complex. We end with discussion of areas that need work to achieve the potential of these electrolytes.

Dynamic Mixing Behaviors of Ionically Tethered Polymer Canopy of Nanoscale Hybrid Materials in Fluids of Varying Physical and Chemical Properties.

An emerging area of sustainable energy and environmental research is focused on the development of novel electrolytes that can increase the solubility of target species and improve subsequent reaction performance. Electrolytes with chemical and structural tunability have allowed for significant advancements in flow batteries and CO2 conversion integrated with CO2 capture. Liquid-like nanoparticle organic hybrid materials (NOHMs) are nanoscale fluids that are composed of inorganic nanocores and an ionically tethered polymeric canopy. NOHMs have been shown to exhibit enhanced conductivity making them promising for electrolyte applications, though they are often challenged by high viscosity in the neat state. In this study, a series of binary mixtures of NOHM-I-HPE with five different secondary fluids, water, chloroform, toluene, acetonitrile, and ethyl acetate, were prepared to reduce the fluid viscosity and investigate the effects of secondary fluid properties (e.g., hydrogen bonding ability, polarity, and molar volume) on their transport behaviors, including viscosity and diffusivity. Our results revealed that the molecular ratio of secondary fluid to the ether groups of Jeffamine M2070 (λSF) was able to describe the effect that secondary fluid has on transport properties. Our findings also suggest that in solution, the Jeffamine M2070 molecules exist in different nanoscale environments, where some are more strongly associated with the nanoparticle surface than others, and the conformation of the polymer canopy was dependent on the secondary fluid. This understanding of the polymer conformation in NOHMs can allow for the better design of an electrolyte capable of capturing and releasing small gaseous or ionic species.

Electron Transfer in Microemulsion-Based Electrolytes.

The use of flowing electrochemical reactors, for example, in redox flow batteries and in various electrosynthesis processes, is increasing. This technology has the potential to be of central significance in the increased deployment of renewable electricity for carbon-neutral processes. A key element of optimizing efficiency of electrochemical reactors is the combination of high solution conductivity and reagent solubility. Here, we show a substantial rate of charge transfer for an electrochemical reaction occurring in a microemulsion containing electroactive material is loaded inside the nonpolar (toluene) subphase of the microemulsion. The measured rate constant translates to an exchange current density comparable to that in redox flow batteries. The rate could be controlled by the surfactant, which maintains partitioning of reactants and products by forming an interfacial region with ions in the aqueous phase in close proximity. The hypothesized mechanism is evocative of membrane-bound enzymatic reactions. Achieving sufficient rates of electrochemical reaction is the product of an effort designed to establish a reaction condition that meets the requirements of electrochemical reactors using microemulsions to realize a separation of conducting and reactive elements of the solution, opening a door to the broad use of microemulsions to effect controlled electrochemical reactions as steps in more complex processes.

Controlling Interfacial Dynamics: Covalent Bonding versus Physical Adsorption in Polymer Nanocomposites.

It is generally believed that the strength of the polymer-nanoparticle interaction controls the modification of near-interface segmental mobility in polymer nanocomposites (PNCs). However, little is known about the effect of covalent bonding on the segmental dynamics and glass transition of matrix-free polymer-grafted nanoparticles (PGNs), especially when compared to PNCs. In this article, we directly compare the static and dynamic properties of poly(2-vinylpyridine)/silica-based nanocomposites with polymer chains either physically adsorbed (PNCs) or covalently bonded (PGNs) to identical silica nanoparticles (RNP = 12.5 nm) for three different molecular weight (MW) systems. Interestingly, when the MW of the matrix is as low as 6 kg/mol (RNP/Rg = 5.4) or as high as 140 kg/mol (RNP/Rg= 1.13), both small-angle X-ray scattering and broadband dielectric spectroscopy show similar static and dynamic properties for PNCs and PGNs. However, for the intermediate MW of 18 kg/mol (RNP/Rg = 3.16), the difference between physical adsorption and covalent bonding can be clearly identified in the static and dynamic properties of the interfacial layer. We ascribe the differences in the interfacial properties of PNCs and PGNs to changes in chain stretching, as quantified by self-consistent field theory calculations. These results demonstrate that the dynamic suppression at the interface is affected by the chain stretching; that is, it depends on the anisotropy of the segmental conformations, more so than the strength of the interaction, which suggests that the interfacial dynamics can be effectively tuned by the degree of stretching-a parameter accessible from the MW or grafting density.

Understanding the Impact of Poly(ethylene oxide) on the Assembly of Lignin in Solution toward Improved Carbon Fiber Production.

Carbon fiber produced from lignin has recently become an industrial scalable product with applications ranging from thermal insulation to reinforcing automobile bodies. Previous research has shown that mixing 1-2 wt %, of poly(ethylene oxide) (PEO) with the lignin before fiber formation can enhance the properties of the final carbon fibers. The research reported here determines the impact of adding PEO to a lignin solution on its assembly, focusing on the role of the lignin structure on this assembly process. Results indicate the addition of PEO anisotropically directs the self-assembly of the hardwood and softwood lignin by lengthening the cylindrical building blocks that make up the larger global aggregates. On the other hand, results from an annual lignin exhibit a shapeless, more complex structure with a unique dependence on the PEO loading. These results are consistent with improved carbon fibers from solutions of lignin that include PEO, as the local ordering and directed assembly will inhibit the formation of defects during the carbon fiber fabrication process.

In vivo oxidative degradation of polypropylene pelvic mesh.

Commercial polypropylene pelvic mesh products were characterized in terms of their chemical compositions and molecular weight characteristics before and after implantation. These isotactic polypropylene mesh materials showed clear signs of oxidation by both Fourier-transform infrared spectroscopy and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDS). The oxidation was accompanied by a decrease in both weight-average and z-average molecular weights and narrowing of the polydispersity index relative to that of the non-implanted material. SEM revealed the formation of transverse cracking of the fibers which generally, but with some exceptions, increased with implantation time. Collectively these results, as well as the loss of flexibility and embrittlement of polypropylene upon implantation as reported by other workers, may only be explained by in vivo oxidative degradation of polypropylene.

Accurate thermochemistry for transition metal complexes from first-principles calculations.

The "correlation consistent Composite Approach" or ccCA is an ab initio model chemistry based on the single reference MP2 level of theory. By adjusting the basis set and level of theory of the core valence additive correction, ccCA is capable of reliable thermochemical predictions of inorganic and organometallic transition metal-containing molecules, as well as achieving chemical accuracy on main group species, with a mean absolute deviation of 0.89 kcal mol(-1) against the 147 enthalpies of formation in the G2/97 test set. For a set of 52 complexes containing elements Sc-Zn, ranging in size from diatomics to Ni(PF(3))(4) and Fe(C(5)H(2))(2), ccCA on average predicts enthalpies of formation to within +/-3 kcal mol(-1) of the experimental result with a mean absolute deviation of 2.85 kcal mol(-1) and a root mean square deviation of 3.77 kcal mol(-1). The ccCA methodology is a significant step toward quantitative theoretical modeling of transition metal thermodynamics.