Germanium cantilever nanoelectromechanical resonators were fabricated using chemically grown nanowires with diameters ranging from 50 to 140 nm. Single nanowires were mechanically positioned at the edge of a copper transmission electron microscope (TEM) grid and then pinned to the grid with local platinum deposition. Oscillating cantilevers were induced into electromechanical resonance with an applied AC voltage, and the frequency response of the vibrational amplitude was measured. From this data, the Young’s modulus of the nanowires was determined to be insensitive to diameter in this size range with an average value of 106 GPa (with 95% confidence limits of ±19 GPa), which is on par with the literature values for bulk Ge (100−150 GPa). The mechanical quality factors (Q) of the nanowire cantilevers were also measured and found to decrease with decreasing diameter. The data indicate that energy dissipation from the oscillating cantilevers occurs predominantly via surface losses, which increase in magnitude with increasing surface area-to-volume ratio of the nanowires.
The Faraday rotation spectrum of composites containing magnetite nanoparticles is found to be dependent on the interparticle spacing of the constituent nanoparticles. The composite materials are prepared by combining chemically synthesized Fe3O4 (magnetite) nanoparticles (8-nm diameter) and poly(methylmethacrylate). Composites are made containing a range of nanoparticle concentrations. The peak of the main spectral feature depends on nanoparticle concentration; this peak is observed to shift from approximately 470 nm for (dilute composites) to 540 nm (concentrated). We present a theory based on the discrete-dipole approximation which accounts for optical coupling between magnetite particles. Qualitative correlations between theoretical calculations and experimental data suggest that the shifts in spectral peak position depend on both interparticle distance and geometrical configuration.
Hemp fiber was used untreated and treated with sodium hydroxide or (3-aminopropyl)triethoxysilane (APTES) as an additive in polylactic acid (PLA) for fused filament fabrication (FFF) of tensile test specimens. Composites granules were produced by solvent processing with 10 wt. % of hemp fiber to use as feedstock for the extrusion of filaments compatible with commercial FFF printers. The dataset shows the thermal properties of the various composites, which were used to determine the appropriate temperatures required for extrusion of filaments and FFF printer settings. Microcomputed tomography imaging was performed and tensile mechanical properties of FFF-printed tensile test specimens were determined as a function of hemp fiber surface treatment. The data provides an assessment of the use of minimally processed hemp fiber as a filler or mechanical enhancer of thermoplastic materials for additive manufacturing.
Manufacturers that produce products using fused filament fabrication (FFF) 3D printing technologies have control of numerous build parameters. This includes the number of solid layers on the exterior of the product, the percentage of material filling the interior volume, and the many different types of infill patterns used to fill their interior. It is important that manufacturers understand how these choices affect the mechanical properties of the product, the amount of material needed, and how long it will take to print the part. This study tested the hypothesis that as the density of the part increases, the mechanical properties will improve at the expense of build time and the amount of material required. The mechanical strength and stiffness of printed test specimens in this study increased with increasing density. In addition, we found that adding more solid external layers to the specimens increased the strength-to-weight ratio. The ductility was much greater in the specimens with a rectilinear infill pattern possibly due to better pattern alignment of the object and better adhesion to the outer solid layers. This study supported our hypothesis and provides a guide for designers and engineers seeking to optimize tensile mechanical behavior, print time, and material usage for FFF applications through the selection of optimal infill parameters.
Development of new additive manufacturing materials often requires the production of several batches of relatively large volumes in order to print and test objects. This can be difficult for many materials that are expensive or difficult to produce in large volumes on the laboratory scale. Bioprinter systems are advantageous in this regard, however, commercial systems are expensive or do not have the ability to use photopolymers. Herein, we outline a Syringe Pump Extruder and Curing System (SPECS) modification for inexpensive filament-based 3D printers which enables the use of standard bioplotter materials and photopolymers. The system is capable of using multiple syringe volumes and needle sizes that can be quickly and easily exchanged. The SPECS modification is demonstrated using a Prusa i3 mk3 fused filament fabrication printer to print several 3D objects and films using stereolithography (SLA) photopolymer resin. Geometric accuracy in the X, Y, and Z directions was ±0.1 mm using a 5 ml syringe, 22-gauge needle, and commercial SLA resin. The SPECS system could be of great benefit for laboratories pursing material development in the area of additive manufacturing.
Shrimp shell waste obtained from Louisiana Gulf shrimp (Litopenaeus setiferus) was heat-treated at varying temperatures and ground into a powder by ball-milling. The powder was used with and without surface treatment with maleic anhydride or stearic acid to form shrimp shell - polylactic acid (PLA) composite granules by solution processing and mechanical grinding. These granules were used as feedstock for the extrusion of composite filaments. The dataset shows the thermal properties of the shrimp shells and the presence of covalent bonding for surface treatment with maleic anhydride. The thermal properties of the composite granules and the influence of the use of surfactants on the morphology, density, and die swell of the extruded filaments are also collected to assess their use as a manufacturing material.
The room temperature optical absorbance spectra of polymer-embedded and solvent-dispersed germanium (Ge) nanowires are reported. Homogeneous blends of Ge nanowires in a polymer (Kraton) were enabled by hydrophobic organic monolayer passivation of the nanowires, and stable dispersions of nanowires in a solvent were achieved by grafting poly(ethylene glycol) onto Ge nanowires. The nanowires exhibit enhanced light absorption compared to bulk Ge near the band edge, with a linear dependence on photon energy. An absorbance peak was also observed at about 600 nm, resulting from enhanced light trapping due to the high index of refraction of Ge at this wavelength. Discrete dipole approximation calculations revealed that the light trapping within the nanowires depends also on the nanowire size and incident light polarization. These optical effects are useful for applications requiring low reflectivity and strong light absorption, such as photovoltaics and antireflective coatings.
Chapter 2 addresses the impact of diseases on wheat and the nature of infectious diseases, the types of pathogens that cause them, and general options for managing them. The nature of noninfectious disorders is also addressed, including the factors that indicate them. The stages of wheat plant development are outlined, as well, and recommendations are made for when to scout for various types of diseases. The text is illustrated with numerous color photographs.
