David R. Salem

Effect of silica particle surface chemistry on the shear thickening behaviour of concentrated colloidal suspensions

We have found that heat treating silica particles can have a large effect on the shear thickening properties of suspensions comprised of 550?nm silica particles in ethylene glycol (EG). The shear thickening effect becomes stronger after heat treating the particles at the temperatures studied (120 and 220??C) especially at the higher temperature, indicating that the interparticle interactions in these suspensions are changed by heat treatment. Having confirmed the existence of hydroxyl groups on the surface of the silica particles using differential scanning calorimetry, x-ray photoelectron spectroscopy showed that heat treatment increases the valence of the Si element on the surface, resulting in a higher density of hydroxyl groups. We believe that a denser solvation layer on the surface of heat-treated particles, formed by adsorbing EG molecules to the particle surface through hydrogen bonds between EG and hydroxyl groups, results in a higher short-range repulsive force, which is responsible for the enhanced shear thickening behaviour.

Flexoelectric effect in PVDF-based polymers

Flexoelectricity is a gradient electromechanical coupling effect that exists in all dielectrics and is important for the understanding of a variety of gradient-induced physical phenomena and the design of new electromechanical devices. At present, the flexoelectric effect in polymer materials has not been well studied. In this work, thick rectangular poly(vinylidene fluoride) (PVDF)-based polymer samples were fabricated and the flexoelectric coefficient was measured. Our results show that the flexoelectric coefficient of the PVDF, which is on the order of several nC/m, is more than twice higher than that of P(VDF-CTFE) and P(VDF-HFP) polymers. All these materials exhibited a non-polar α phase, but the copolymers showed much smaller crystallinity values than the PVDF homopolymer. The difference in the flexoelectric response in these polymers is believed to be related to the crystallinity of the polymers.

Rewiring the microbe-electrode interfaces with biologically reduced graphene oxide for improved bioelectrocatalysis

The aim of this work was to study biologically reduced graphene oxide (RGO) for engineering the surface architecture of the bioelectrodes to improve the performance of Bioelectrochemical System (BES). Gluconobacter roseus mediates the reduction of graphene oxide (GO). The RGO modified bioelectrodes produced a current density of 1 mA/cm2 and 0.69 mA/cm2 with ethanol and glucose as substrates, respectively. The current density of RGO modified electrodes was nearly 10-times higher than the controls. This study, for the first time, reports a new strategy to improve the yield as well as efficiency of the BES by wrapping and wiring the electroactive microorganisms to the electrode surfaces using RGO. This innovative wrapping approach will decrease the loss of electrons in the microbe-electrolyte interfaces as well as increase the electron transfer rates at the microorganism-electrode interfaces.

Biohydrogen production from space crew’s waste simulants using thermophilic consolidated bioprocessing

Human waste simulants were for the first time converted into biohydrogen by a newly developed anaerobic microbial consortium via thermophilic consolidated bioprocessing. Four different BioH2-producing consortia (denoted as C1, C2, C3 and C4) were isolated, and developed using human waste simulants as substrate. The thermophilic consortium C3, which contained Thermoanaerobacterium, Caloribacterium, and Caldanaerobius species as the main constituents, showed the highest BioH2 production (3.999 mmol/g) from human waste simulants under optimized conditions (pH 7.0 and 60 °C). The consortium C3 also produced significant amounts of BioH2 (5.732 mmol/g and 2.186 mmol/g) using wastewater and activated sludge, respectively. The developed consortium in this study is a promising candidate for H2 production in space applications as in situ resource utilization.

Single pot bioconversion of prairie cordgrass into biohydrogen by thermophiles

The aim of the present work was to use a thermophilic consortium for H2 production using lignocellulosic biomass in a single pot. The thermophilic consortium, growing at 60 °C utilized both glucose and xylose, making it an ideal source of microbes capable of utilizing and fermenting both hexose and pentose sugars. The optimization of pH, temperature, and substrate concentration increased the H2 production from 1.07 mmol H2/g of prairie cordgrass (PCG) to 2.2 mmol H2/g PCG by using the thermophilic consortium. A sequential cultivation of a thermostable lignocellulolytic enzyme producing strain Geobacillus sp. strain WSUCF1 (aerobic) with the thermophilic consortium (anaerobic) further increased H2 production with PCG 3-fold (3.74 mmol H2/g PCG). A single pot sequential culturing of aerobic and anaerobic microbes can be sustainable and advantageous for industrial scale production of biofuels.

Integrated Consolidated Bioprocessing for Conversion of Lignocellulosic Feedstock to Biofuels and Value-Added Bioproducts

This chapter will provide basic information about consolidated bioprocessing (CBP), including native and recombinant strategies and their application in biofuel production. It will address the integrated CBP process to produce biopolymers (e.g., polyhydroxyalkanoates, extracellular polysaccharides), organic compounds (e.g., 1,3-propanediol), and biogas (methane). The chapter will also discuss the production of biofuels by integrating the CBP process with fuel cells and other bioelectrochemical systems. A detailed discussion will be provided on the thermophilic anaerobic digestion (TAD) process to produce methane from agricultural biomass using thermophilic microorganisms as well as biological oxidation of methane to methanol using methanotrophic bacteria. The chapter will conclude with presenting different approaches in modeling CBP processes for existing applications.

Production and characterization of epoxy syntactic foams highly loaded with thermoplastic microballoons

Glass microballoon syntactic foams consisting of 60–70 vol% hollow glass microballoons and epoxy resin matrix have gained considerable attention in recent years due to their unique combination of mechanical properties and low density, with applications in the naval and aerospace industries. An important limitation of these materials is the volume fraction ceiling (∼0.74) and subsequent density limit (0.36 g/cm3). Utilizing thermoplastic microballoons, syntactic foams were produced with densities as low as 0.067 g/cm3, achieved by developing a method that produces epoxy/microballoon compositions comprising an unusually high volume fraction of microballoons (0.75–0.95). The resulting morphology features microballoons which, having expanded in a restricted volume, are deformed into irregular shapes that efficiently pack together and are encapsulated by a thin coating of epoxy. The compressive yield strength, tensile strength and initial modulus of these highly loaded syntactic foams exhibit a non-linear decrease with increasing microballoon volume fraction to values typical of highly porous polymers, but display a high degree of recovery, or rebound, from large compressive strain compared with glass microballoon syntactic foams.

Extremophilic exopolysaccharides: A review and new perspectives on engineering strategies and applications

Numerous microorganisms inhabiting harsh niches produce exopolysaccharides as a significant strategy to survive in extreme conditions. The exopolysaccharides synthesized by extremophiles possess distinctive characteristics due to the varied harsh environments which stimulate the microorganisms to produce these biopolymers. Despite many bioprocesses have been designed to yield exopolysaccharides, the production of exopolysaccharides by extremophiles is inefficient compared with mesophilic and neutrophilic exopolysaccharide producers. Meanwhile, the industrial development of novel extremophilic exopolysaccharides remains constrained due to the lack of exploration. In this review, we summarize the structure and properties of various exopolysaccharides produced by extremophiles, and also discuss potential metabolic and genetic engineering strategies for enhanced yield and modified structure of extremophilic exopolysaccharides. Special focus is given to the applications of extremophilic exopolysaccharides in the areas of biomedicine, food industry, and biomaterials via nano-techniques, casting and electrospinning.

The effect of nano-additive reinforcements on thermoplastic microballoon epoxy syntactic foam mechanical properties

Syntactic foams comprising glass microballoons have gained considerable attention over the past several years due to mechanical and thermal properties that are advantageous for use as a core material in naval and aerospace applications. Recent advancements in the production of thermoplastic microballoon syntactic foams have allowed for an increase in microballoon volume fraction (up to 0.9 volume fraction), with correspondingly lower densities but reduced mechanical properties. In this work, carbon nanofibers and halloysite nanotubes were incorporated in thermoplastic microballoon-based syntactic foam to enhance the mechanical properties and the relative effects of these two nanoscale reinforcements were compared. X-ray micro-computed tomography was employed to analyze the microstructure of the materials produced, and scanning electron microscopy was used to assess the dispersion of nano-additives within the resin. Compressive strength and modulus enhancements as large as 180% and 250% respectively were achieved with a 0.25 wt% addition of carbon nanofiber and increases of 165% and 244% respectively were achieved with a 0.5 wt% addition of halloysite nanotube. Tensile strength and modulus enhancements as large as 110% and 165% respectively were achieved with a 0.125 wt% addition of carbon nanofiber and increases of 133% and 173% respectively were achieved with a 0.125 wt% addition of halloysite nanotube.

Topology Optimization of Lightweight Lattice Structural Composites Inspired by Cuttlefish Bone

Lattice structural composites are of great interest to various industries where lightweight multifunctionality is important, especially aerospace. However, strong coupling among the composition, microstructure, porous topology, and fabrication of such materials impedes conventional trial-and-error experimental development. In this work, a discontinuous carbon fiber reinforced polymer matrix composite was adopted for structural design. A reliable and robust design approach for developing lightweight multifunctional lattice structural composites was proposed, inspired by biomimetics and based on topology optimization. Three-dimensional periodic lattice blocks were initially designed, inspired by the cuttlefish bone microstructure. The topologies of the three-dimensional periodic blocks were further optimized by computer modeling, and the mechanical properties of the topology optimized lightweight lattice structures were characterized by computer modeling. The lattice structures with optimal performance were identified.