Christopher M. Hoffman

Microbially-induced corrosion is the acceleration of corrosion induced by bacterial biofilms. The bacteria in the biofilms oxidize metals on the surface, especially evident with iron, to drive metabolic activity and reduce inorganic species such as nitrates and sulfates. Coatings that prevent the formation of these corrosion-inducing biofilms significantly increase the service life of submerged materials and significantly decrease maintenance costs. One species in particular, a member of the Roseobacter clade, Sulfitobacter sp., has demonstrated iron-dependent biofilm formation in marine environments. We have found that compounds that contain the galloyl moiety can prevent Sulfitobacter sp. biofilm formation by sequestering iron, thus making a surface unappealing for bacteria. Herein, we have fabricated surfaces with exposed galloyl groups to test the effectiveness of nutrient reduction in iron-rich media as a non-toxic method to reduce biofilm formation.

Gel polymer electrolytes (GPEs) hold great promise for next-generation Li-ion batteries as they combine the high ionic conductivity and facile transport properties of liquid electrolytes with the improved safety and mechanical properties of solid polymer electrolytes. The selection of appropriate non-flammable solvents as well as polymer matrices with good electrochemical stability and robustness is a critical step in the design of efficient and safe GPEs. Here, we show that integration of an easy-to-make deep eutectic solvent (DES) based on N-methylacetamide and lithium bis(trifluoromethanesulfonyl)imide, in a versatile acrylate polymer host comprising 2-hydroxyethyl acrylate (HEA) and polyethylene glycol methyl ether acrylate (MPEGA), results in various GPE formulations with improved electrochemical stability compared to the liquid DES alone. At optimized HEA to MPEGA ratios, eutectic GPEs achieve ionic conductivities exceeding 0.4 mS cm⁻¹ and 1.2 mS cm⁻¹ at 20 °C and 40 °C respectively. When tested in Li₄Ti₅O₁₂/LiMn₂O₄ full cells, these GPEs outperform the liquid DES at 0.45C rate in terms of cycling stability. More impressively, the eutectic GPEs exhibit substantially improved non-flammability as well as remarkable robustness and stability to water compared to the liquid DES. The self-extinguishing time of the eutectic GPEs when exposed to a flame is suppressed by over a factor of seven. Regarding water stability, while the cycle life of full cells with a liquid DES is dramatically impacted by the presence of water, eutectic GPEs are significantly more tolerant, enabling more stable cycling and even the assembly of cells in fully ambient laboratory conditions. These findings provide useful insights into the design of novel, safe, robust GPEs based on environmentally friendly solvents.

We report UV-photopolymerized “water-in-bisalt” electrolytes that expand the electrochemical stability window, improving “water-in-bisalt” cycle life in lithium titanate full cells.

Scalable, bottom‐up chemical synthesis and electrospinning of novel Cl‐substituted poly(para‐phenylene terephthalamide) (PPTA) nanofibers are herein reported. To achieve Cl‐PPTA nanofibers, the chemical reaction between the monomers was precisely controlled, and dissolution of the polymer into solvent was tailored to enable anisotropic solution formation and sufficient entanglement molecular weight. Electrospinning processing parameters were studied to understand their effects on fiber formation and mat morphology and then optimized to yield consistently high quality fibers. Importantly, the control of relative humidity during the fiber formation process was found to be critical, likely because water promotes hydrogen bond formation between the PPTA chains. The fiber and mat morphologies resulting from different combinations of chemistry and spinning conditions were observed using scanning electron microscopy, and observations were used as inputs to the optimization process. Tensile properties of single Cl‐PPTA nanofibers were characterized for the first time using a nanomanipulator mounted inside a scanning electron microscope (SEM), and fiber moduli measuring up to 70 GPa, and strengths exceeding 1 GPa were achieved. Given the excellent mechanical properties measured for the nanofibers, this chemical synthesis procedure and electrospinning protocol appear to be a promising route for producing a new class of nanofibers with ultrahigh strength and stiffness. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 563–573

The synthesis and electrospinning of novel N‐substituted aramid nanofibers (ANFs) prepared from basic dispersions of commercial microscale Kevlar fibers are herein reported. The functionalized ANFs were characterized via Fourier transform infrared spectroscopy, ¹³C solid‐state nuclear magnetic resonance spectroscopy, and X‐ray diffraction to confirm proper N‐substitution of the side groups and to determine changes to the polymer crystallinity and stability. These analyses suggested that the electrospun ANFs consisted of numerous crystalline domains in the transverse fiber direction with large amorphous regions that were void of defects commonly found in commercial Kevlar fibers. A semi‐empirical study of the variations in the solubility parameter due to various side chain moieties was conducted to facilitate solvent selection and to elucidate the enhanced solubility effects with selected organic solvents. These initial findings suggest a promising route for obtaining a new class of nanofibers with ultrahigh strength and stiffness. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44082.

A general method for the gram scale resolution of 2-substituted and 2,8-disubstituted Tröger’s base (TB) derivatives in 63–91% yield has been achieved through the application of crystallization-induced asymmetric transformation (CIAT). Enantiomeric ratios of the resolved TB derivatives range from 99.1:0.9 to >99.5:0.5. Among the Tröger’s base compounds resolved are four synthetically valuable bromo and iodo derivatives.

An efficient molybdenum-catalyzed asymmetric allylic alkylation (Mo-AAA) of cyanoester nucleophiles is reported. A number of highly functionalized branched cyanoesters containing a quaternary carbon stereocenter with a vicinal tertiary stereocenter are obtained. This method generates a number of functionalized cyanoesters in excellent yield and chemoselectivity in good to excellent diastereoselectivity and enantioselectivity.