With the availability of nanoparticles with controlled size and shape, there has been renewed interest in the mechanical properties of polymer/nanoparticle blends. Despite the large number of theoretical studies, the effect of branching for nanofillers tens of nanometers in size on the elastic stiffness of these composite materials has received limited attention. Here, we examine the Young's modulus of nanocomposites based on a common block copolymer (BCP) blended with linear nanorods and nanoscale tetrapod Quantum Dots (tQDs), in electrospun fibers and thin films. We use a phenomenological lattice spring model (LSM) as a guide in understanding the changes in the Young's modulus of such composites as a function of filler shape. Reasonable agreement is achieved between the LSM and the experimental results for both nanoparticle shapes-with only a few key physical assumptions in both films and fibers-providing insight into the design of new nanocomposites and assisting in the development of a qualitative mechanistic understanding of their properties. The tQDs impart the greatest improvements, enhancing the Young's modulus by a factor of 2.5 at 20 wt.%. This is 1.5 times higher than identical composites containing nanorods. An unexpected finding from the simulations is that both the orientation of the nanoscale filler and the orientation of X-type covalent bonds at the nanoparticle-ligand interface are important for optimizing the mechanical properties of the nanocomposites. The tQD provides an orientational optimization of the interfacial and filler bonds arising from its three-dimensional branched shape unseen before in nanocomposites with inorganic nanofillers.three-dimensional nanoparticle branching | polymer fibers | nanocomposite films | lattice spring model | tetrapod quantum dot P olymer−nanoparticle composites have become a highly active topic of research with rapidly expanding applications (1), in part because of their high polymer−particle interfacial area and the unique shape-and size-dependent, tunable properties of nanoparticle reinforcements. For example, new polymer nanocomposites have been developed that can optically sense stress concentration (2), are responsive to magnetic, electrical, and thermal actuation (3, 4), and exhibit large changes in elastic modulus and glass transition temperature at low nanoparticle concentrations (5).While theoretical studies show that the Young's modulus of such polymer nanocomposites depends on nanoparticle shape (6), experimental studies are limited. Experimental studies on polymers (7) include the synergistic reinforcement effects of multiple nanocarbons (8) and the shape-dependent reinforcement effects of micrometer-sized tetrapods (9), microscale ceramic needles (10), carbon nanotubes (11), clay-based nanocomposites (12, 13), and others (14). Computational studies include the effects of nanoparticle packing and size on the nanocomposite Young's modulus (15-17). However, the effects of increasing nanoparticle branching on the mechanical behavior of nanocomposite...

The Tafel slope is a key parameter often quoted to characterize the efficacy of an electrochemical catalyst. In this paper, we develop a Bayesian data analysis approach to estimate the Tafel slope from experimentally-measured current-voltage data. Our approach obviates the human intervention required by current literature practice for Tafel estimation, and provides robust, distributional uncertainty estimates. Using synthetic data, we illustrate how data insufficiency can unknowingly influence current fitting approaches, and how our approach allays these concerns. We apply our approach to conduct a comprehensive re-analysis of data from the CO2 reduction literature. This analysis reveals no systematic preference for Tafel slopes to cluster around certain "cardinal values” (e.g. 60 or 120 mV/decade). We hypothesize several plausible physical explanations for this observation, and discuss the implications of our finding for mechanistic analysis in electrochemical kinetic investigations.

The processing of Kevlar to certain strengths by hot-drawing can benefit by quantitative understanding of the correlation between structural and mechanical properties during the pre-drawing process. Here, we use a novel continuous dynamic analysis (CDA) to monitor the evolution in storage modulus and loss factor of Kevlar 49 fibers as a function of strain via a quasi-static tensile test. Unlike traditional dynamic mechanical analysis, CDA allows the tracking of straindependent mechanical properties until failure. The obtained dynamic viscoelastic properties of Kevlar 49 are correlated with structural data obtained from synchrotron radiation analysis and with Raman scattering frequencies. Ratedependent stress-strain results from Kevlar are compared to Nomex, spider silk, polyester and rubber, and provide insight into how the mechanical properties of Kevlar originate from its characteristic structural features. We find that as the storage modulus of Kevlar is essentially equal to the Young's modulus, the measured quantitative relationships between storage modulus and strain can provide insights into the tuning of the mechanical properties of aramid materials for specific applications. On the other hand, the technique of continuous dynamic analysis (CDA) combines the advantages of dynamic mechanical analysis with those of the quasi-static tensile test to quantify the evolution of viscoelastic properties as a continuous function of strain [4]. This is achieved through application of a small harmonic (20 Hz) strain during the tensile deformation. Because the harmonic strain is much smaller in magnitude than the applied quasi-static strain, it remains within the limits of linear viscoelasticity and does not affect the behavior of a quasi-static tensile test. Here, using a specialized electromechanical load cell capable of applying small but continually increasing periodic forces, we employ CDA to monitor the dynamic properties of Kevlar 49 fibers as a function of their strain to failure. We then quantitatively correlate our results to the structural tensile data of Kevlar from previous studies utilizing wide-angle X-ray diffraction (WAXD) [5] and Raman spectroscopy [6], to provide insight into the molecular mechanisms by which Kevlar tolerates stress. The dynamic mechanical behavior of Kevlar is further compared to those of other key structural polymers to quantitatively discern its dynamic responses against known benchmarks. As such, this study presents quantitative information on how the drawing of Kevlar changes its mechanical properties, thereby providing guidelines for the systematic optimization of this important engineering fiber.

Lactones serve as key synthetic intermediates for the large-scale production of several important chemicals, such as polymers, pharmaceuticals, and scents. Current thermochemical methods for the formation of some lactones rely on molecular oxidants, which yield stoichiometric side products that result in a poor atom economy and impose safety hazards when in contact with organic substrates and solvents. Electrochemical synthesis can alleviate these concerns by exploiting an applied potential to enable the possibility of a clean and safe route for lactonization. In this study, we investigated the mechanism of electrochemical lactone formation from cyclic ketones. When using a platinum anode and cathode in acetonitrile with 10 M H 2 O and 400 mM cyclohexanone, we found that non-Baeyer−Villiger products, δhexanolactone and γ-caprolactone, are formed with a total Faradaic efficiency of ∼20%. Isotope labeling experiments support that water is the oxygen atom source for this reaction. In addition, electrochemical kinetic data suggest a first-order dependence on water at low water concentrations (<2 M H 2 O) and a zeroth order dependence on the substrate, cyclohexanone. A Tafel slope of 139 mV/decade was measured at 400 mM cyclohexanone and 10 M H 2 O, implying an initial electron transfer as the ratedetermining step. Literature-proposed mechanisms for similar transformations suggest an outer-sphere pathway. However, on the basis of the collected electrochemical kinetic data, we propose the possibility that Pt reacts with water in an initial electron transfer that forms Pt−OH, which can subsequently react with the ketone substrate. A subsequent electron transfer forms a ring-opened carboxylic acid cation that can reclose to form either of the observed fiveor six-membered ring lactone products.

Methods to produce ammonia from air, water, and renewable electricity are necessary to transition ammonia production away from the CO2-emitting Haber-Bosch process. In this vein, a fully electric process in which water-splitting-derived hydrogen and air-separation-derived nitrogen are reacted in an electrochemical process to produce ammonia is attractive. Such a process has the potential to be highly flexible and utilize intermittent renewable energy well. Here, we evaluated the cost-effectiveness of large-scale fully electric ammonia production relying on renewable electricity sources in conjunction with different types of storage and flexible operation, using a mixed-integer linear programming framework. The approach incorporates a first-principle, chemistry-independent representation of reactor power consumption and its dependence on reactor sizing and electrochemical parameters, the impact of product separation and recycling unconverted reactants, and plant dynamics in response to temporal variability in renewable energy availability. Given the emerging nature of electrochemical ammonia synthesis from nitrogen and hydrogen, we used the model to identify the reaction descriptors and their threshold values that enable cost parity between fully electric ammonia production with commercially viable production using thermochemical synthesis coupled with electrolytic hydrogen powered by renewable energy. We found that ammonia can be produced in an economically competitive manner, i.e. at costs <1 $/kg, at large scales if the electrochemical reactor can produce ammonia at partial currents exceeding 400 mA cm -2 , energy efficiencies exceeding 30%, and process lifetimes of several years. In light of this, novel chemistries that can reduce nitrogen at high rates and moderate (<2.5 V) overpotentials are necessary for economic, large-scale ammonia production.