The synthesis of novel, metastable materials has potential to affect areas of science and physics as such compounds can exhibit unrivaled structural complexity, unique bonding, and unusual properties. High-pressure synthesis is an especially powerful tool for isolating new intermetallic compounds that cannot be realized using traditional solid-state syntheses. In this presentation, we describe the synthesis and structural characterization of the first Cu–Bi binary intermetallic compounds, CuBi and Cu11Bi7, which are synthesized at ~4 GPa and ~250 °C and ~6 GPa and ~500 °C, respectively. Both compounds can be derived from the NiAs structure type by ordered vacancies of the Cu atoms. Cu11Bi7 features one-dimensional channels formed by Bi atoms, while CuBi adopts a layered structure where the layers are formed by Bi atoms. The distinguishing feature of the Cu–Bi binary intermetallic compounds is that of channels and layers formed by Bi atoms, which we attribute to nonbonding electrons, or sterochemically active lone pairs, on the Bi atom. In situ X-ray diffraction experiments performed at high-pressure and –temperature conditions in a diamond anvil cell allow for experimental mapping of phase stability at high-pressures. The presence of multiple high-pressure stabilized phases in the Cu–Bi binary system, which can be readily identified with in situ techniques, gives promise for other binary systems in which no ambient pressure phases exist.

Creating binary Cu–Bi compounds at high pressure

MnO2 has been widely applied as activation additives in capacitive deionization (CDI) technique due to its low cost and high performance. However, there is no unambiguous pattern concluded on which MnO2 phase could lead the highest CDI performance. To answer this question, different MnO2 phases were synthesized and associated to activated carbon supports to examine their CDI performances (percentage difference in the conductivity) in different pH by a simple batch mode. In addition, their surface chemistry was characterized using alkalimetric-acidimetric titration. Our preliminary results showed that in a first glimpse, beta-phase MnO2 seemed to exhibit the highest CDI performance over other phases did. However, when plotting the surface charge density of different MnO2 phases in different pH against the deionization efficiency, an interesting pattern appeared that the deionization efficiency decreased proportionally with increasing surface charge density. Importantly, this correlation was independent to the pH and the MnO2 phases. Accordingly, we speculate that the discrepancy in CDI efficiency caused by different MnO2 phases might be simply as a result of the structure induced surface charge effect where different MnO2 phases have its own distribution pattern of surface charge density over MnO2 surfaces.

MnO2 structure induced surface charge effect on the performance of capacitive deionization in different pH

A series of linear hydrophobic polymeric antioxidants has been synthesized and studied as active components of anticorrosion coatings on aluminum 2024 T3 substrates. This aluminum alloy is widely used for aircraft and aerospace applications. The polymers are composed of methacrylamide units carrying hydrophobic hexyl and antioxidant 3,4,5-trihydroxy or 3,4-dihydroxy benzyl moieties. Polyphenol groups provide excellent adhesion of the polymers to the pretreated mirror-polished aluminum substrates as shown by X-ray photoelectron spectroscopy (XPS). The anticorrosion efficiency of the coatings was studied using electrochemical impedance spectroscopy and open-circuit potential techniques when substrates were immersed in a corrosive environment provided by 3.5% sodium chloride solution exposed to ambient air. The coated aluminum substrates demonstrated an increase in impedance as compared to bare aluminum surfaces. The anticorrosion activity of the coatings is likely due to the formation of a protective layer of the oxidation products. The morphological and chemical changes induced by corrosion were analyzed by scanning electron microscopy (SEM) and XPS. The anticorrosion efficiency of the polymers, when used as additives to barrier epoxy coatings, will be discussed.

Linear antioxidant polymers for anticorrosion coatings: Adhesion and electrochemical performance

Inhibition of ketohexokinase (KHK, fructokinase) may ameliorate non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH) by decreasing fructose conversion to fructose-1-phosphate. Initial low-molecular weight hits were identified by fragment screening; subsequent file-mining provided multiple starting points for hit-to-lead chemistry. A combination of parallel synthesis and structure-based drug design yielded an in vivo tool compound that recapitulated the efficacy reported in a KHK-null rodent model on a high-fructose diet. Further optimization provided the clinical candidate, currently in clinical trials. This fragment-to-candidate story will present the fragment-based screen triage, compound optimization via structure-based drug design and parallel chemistry, in vivo target validation, clinical candidate selection and initial clinical data.

Discovery of a ketohexokinase inhibitor for the treatment of NAFLD/NASH: Fragment-to-candidate via structure-based drug design and parallel chemistry

Advances in experimental high-pressure techniques has recently led to the discovery of numerous new metastable materials with exciting properties, ranging from unexpected stoichiometries in simple systems to reports of record breaking superconductivity in hydride materials. Theoretical methods often play a central role in such efforts, since a thorough experimental in situ characterization of a material at extreme pressures is challenging. Crystal structure prediction methods such as the minima hopping algorithm in conjunction with ab initio calculations are essential tools to assess the composition, structure and properties of high-pressure compounds. I will present the discovery of high-pressure intermetallics in ambient-immiscible systems, and illustrate how novel high-pressure compounds can be predicted on a large scale.

Computational discovery of high-pressure materials

Polymer composite materials, adhesives, and coatings are derived from non-renewable petroleum sources, making their use unsustainable and causing their cost to be highly volatile. Furthermore, these polymer materials often contain toxic components or produce toxic emissions. To address these issues, we have used plant-derived renewable resources to develop a number of polymer technologies with properties and performance similar to that of petroleum-derived polymers. We formulated and developed fatty acid-based vinyl ester resins derived from plant oils and successfully demonstrated and validated them on weapons platforms across the DoD. We have been addressing toxicity issues associated with bisphenol, a component used in the production of many high performance polymers. Through use of polymers from lignin-derived chemicals, such as guaiacol, and carbohydrate-derived isosorbide and furans, we have created a number of polymers with properties similar or superior to that of commercial polymers. Furthermore, we have shown that these bio-derived chemicals and polymers have reduced toxicity relative to the baseline commercial polymers. As a result, we are currently preparing diamines derived from carbohydrates and lignin to reduce the toxicity and improve the sustainability of polyimides and epoxies.

Environmentally friendly high performance bio-derived polymers for DoD applications

The purpose of the presented work is to provide society with alternative polyphenolic molecules that are derived from xylochemicals (wood-derived building blocks). The xylochemicals utilized are molecules that we currently obtain, or have the potential to obtain, from a variety of lignocellulosic biorefineries, from pulp and paper mills to fermenters. As lignin is known as Earth’s most prevalent aromatic biopolymer, our approach has focused on strategically designing, synthesizing, and testing polyphenolic molecules, monomers, oligomers, and resins containing aromatic lignin units, such as guaiacyls, coniferyls, and courmaryls, and other bio-based molecules, such as cardanol, carvacrol, and betulin. Similar to nature, we strive to engineer materials that aid in sustaining life, withstand environmental stress factors, and serve multiple needs. Testing has included spectroscopic, rheological, thermomechanical, thermogravimetric, mechanical, and toxicity measurements to fundamentally understand the structure-processing-property-toxicity relationships of these novel systems. As a result of this work, we are generating a valuable library of xylochemical-based polyphenolics and their functionalized derivatives for use in high-performing polymer applications, including coatings, adhesives, and composites.

Strategic assemblies of functionalized xylochemicals for new bio-based polymers

In order to understand the mechanics and chemistry of silicon electrodes and to prevent undesirable effects such as cracking in and dendrites formation of the anode, research have been performed using nanoscale approaches to a full nanobattery. We studied the graphite as a control calculation first and then the silicon nanocrystal anodes, performing ab initio calculations and classical molecular dynamics atomistic simulations. In this effort in progress, we are focusing on the mechanical properties, such as swelling, alloying mechanism, amorphization, cracking, and dendriting of the anode material during the charging cycle and also the electrical properties such as polarization as well as ionic and electronic conductance. The nanobattery includes LiCoO2 cathode; the electrolyte solution contains ethylene carbonate, as well as hexafluorophosphate and Li-ions. An external electric field is applied to emulate the charging process causing the migration of the Li-ions from the cathode, diffusing through the electrolyte to finally get into the anode. We immediately observe during charging (i.e., when an external electric field is applied) of the nanobattery, the Si anode changes gradually into a LiSi alloy at temperatures below 360 K. We obtained the drift velocity of the Li-ions during the amorphization of the silicon nanocrystal as the original volume of the anode increases. For the graphite anode, the full lithiated state is achieve when the initial structure C changes into LiC6, storing the Li-ion between the layers of the graphite, thus we were able to compare energy, temperature, and electrical properties such as current, resistance, current density, conductivity and resistivity. Our model can be used to study the mechanisms taking place in the electrolyte, cathode, and anode; especially, for new materials such as solid electrolytes.

Analysis, design and simulation of nanobatteries: Silicon anodes and beyond

By designing metallo-supramolecular materials with specific metal-coordination moieties, we can integrate the unique photochemistry of metal-coordination complexes into polymeric materials. Our group has shown that ligand design is critical to tune the overall mechanical properties of metallo-supramolecular materials. In addition, materials made from metal-coordination groups that show photo-labilization showed softening of the material with light irradiation. New work has focused on tuning the excited state dynamics and photochemical mechanisms of the metal-coordination bonds to change the overall properties and photo-response of the metallo-supramilecular materials. Such photoresponsive metallo-supramolecular materials have been used to create advanced materials that show photo-healing, and for next-generation tissue engineering scaffolds with patterned interfaces in mechanical properties.

Harnessing photochemistry and photophysics for responsive metallo-supramolecular materials

In this talk, I will present an update on the current status of our ability to design and discover quantum materials, and discuss their relevance to transforming our society. Specific examples will be pulled from recent work by the Institute for Quantum Matter and the Platform for the Accelerated Realization, Analysis, and Discovery of Interface Materials, including: (a) the successful electron doping of a prototypical two dimensional spin liquid, (b) a rational design strategy for the tuning of direct and indirect band gaps, and (c) the interplay of bonding and topology in samarium hexaboride. Particular focus will be placed on the current abilities and limitations in selectively making and breaking bonds in the solid state.

Advances in quantum materials synthesis and application

The Bureau of Reclamation is a Federal Government Agency in charge of maintaining large dams and water supply projects in the western United States. The Materials and Corrosion Laboratory use protective coatings and cathodic protection to maintain metal infrastructure at these facilities. Many of the original coatings are still providing corrosion protection today which include coal tar enamel and vinyl resin coatings. These coatings can provide 80 year service life in the harshest conditions in penstocks, the pipeline that connects the reservoir to the hydroelectric generators. The conditions inside the penstocks have high water flow rates 20-30 ft/s and pressures from 200-500 psi. This presentation will discuss these old coatings technologies and provide an explanation of why these technologies provided an extremely long service life in some of the most extreme conditions. Sometimes learning from the past can provide scientists new ideas. The ultimate goal would be that scientists could use this knowledge to develop coatings with superior corrosion protection.

Learning from the past, protective coatings that provided a 50-year service life for penstock linings

By taking advantage of the broad photochemistry of metal-coordination complexes, we have created metallo-supramolecular materials with tunable response to light. For example, materials created from a hydrophobic polymeric backbone linked by coordination to Cr(III) ions through a pyridine-modified termini showed reversible changes in mechanical stiffness with light irradiation. We have shown that by changing the metal-ligand moiety, to one with different photochemistry and photophysical properties (like Fe(III) coordinated to carboxylate groups), we can create materials with other specific mechanical properties that can be controlled with light irradiation. In addition, we have shown that the excited state lifetime of the metal-coordination interactions was influenced by the local mechanical properties of the metal-coordination interactions, and can also be used a sensor for the local stiffness in the material. Such studies provide important structure-function relationships that show how metal-coordination interactions can be exploited to create advanced materials with properties beyond the limit of traditional polymeric materials.

Tuning photochemistry and photophysics in metallo-supramolecular materials

The utilization of wood-derived building blocks (xylochemicals) to replace fossil-based precursors is an attractive research subject of modern polymer science. The continuing development of new bio-based feedstocks opens opportunities to increase the resource base from which chemical and materials engineers can draw to meet specific polymer property requirements. Recently, significant efforts have transpired to obtain bio-based polymers and copolymers with enhanced thermomechanical properties for a wide variety of applications. In continuing these efforts, we have prepared and examined novel linear polyesters and polycarbonates derived from xylochemicals. Bio-based bisphenolic analogues were synthesized via electrophilic aromatic condensations of lignin-based building blocks. These bisphenolics were subsequently polymerized with multiple diacid chlorides/diacids to prepare a series of polyesters with varied and well-defined thermomechanical properties. Additionally, the same monomers were used for the synthesis of polycarbonates. These novel thermoplastics were characterized to assess their structure-property relationships and compared to industrial, fossil-based “equivalents”. The results of our study illustrate that these new polymers are valid alternatives to petroleum-based materials currently employed in the plastics industry.

Preparation and characterization of bio-based polyesters and polycarbonates derived from xylochemicals

The geometric, electronic and chemical properties of Au nanoparticles supported by TiO2 have been the subject of much work since the discovery by Haruta that Au is a low temperature oxidation catalyst. Despite this earlier work there is no definitive evidence for the binding site or the direction of charge transfer associated with gold atoms and nanoparticles on the model substrate TiO2(110). In this work we have used STM to examine the nucleation properties of Au nanoparticles dispersed over a reduced rutile TiO2 (110) surface. From comparisons of the surface before and after Au deposition, and using atomic manipulation, the nucleation site of single Au atoms was directly observed to be at oxygen vacancies on the substrate (Ob-vacs). Statistical analysis of the atomic manipulation method applied provides some insight into the nature of the bonding between Au and Ob-vac sites. In an attempt to gauge the degree of Au/TiO2 charge transfer, synchrotron based X-ray photoelectron emission microscopy (XPEEM) was used in conjunction with STM and low energy electron microscopy (LEEM) to probe the electronic character of Au nanoparticles as a function of particle size and coverage. Core-level binding energy measurements reveal a two stage shift in Au 4f binding energy as the nanoparticle size increased in line with electron transfer from Ob vacs to Au for small nanoparticles (&lt;4 nm) on TiO2 (110). To reduce experimental error, a method was developed to precisely pattern the substrate with discrete regions of varying Au coverage on the nanometer scale. High resolution electron energy loss spectroscopy (HREELS) was used to measure the vibrational spectrum of an Au/TiO2 sample before and after ethanol exposure. After exposure, loss features appear that correspond to acetate, however, this is not observed for Au coverages less than 0.1-0.3 MLE. From this, it is suggested that Au nanoparticle size affects the reactivity of TiO2 towards ethanol oxidation, which is likely related to the degree of charge transfer.

Au nanoparticle interactions with TiO2(110) and their modification of the reactivity

254th National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.