Dimensional metrology at the nanoscale: quantitative characterization of nanoparticles by means of metrological atomic force microscopy

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Establishing the role of surface chemistry and topography in determining wettability and the development of a novel assessment methodology for repellent surfaces

Coatings and surfaces with repellence to a range of liquids can find application in aerospace, marine, construction, energy industries and many more. The reported research provides understanding of the relative roles of surface chemistry and surface roughness on repellence and has allowed the development of a new methodology for assessing wettability. A review on surface treatments and how they affect solid-liquid interaction by measuring the static and dynamic contact angle with a variety of polar and non-polar probe liquids has been presented. During this research, eleven coating systems (including fluorinated and non-fluorinated ones) were assessed for promoting repellence on planar/smooth surfaces and on substrates grit blasted to micro-level roughness (roughness average of 1 "# to 4 "#). To assess the impact of nano-scale and dual-scale roughness on repellence, the functionalised silica nanoparticles (fumed and synthesised by sol-gel) were incorporated into the coating system to build up the desired nano-scale topography (roughness average of 56 nm). This approach was undertaken in efforts to decouple the effects of surface roughness/topography on repellence from the surface chemistry contributions. The nano-scale topography provided high static contact angles, 128° and 93° with water and diiodo-methane respectively as probe liquids, this scale of roughness however, also exhibited high roll-off angles/or no roll- off even at 80° tilt. The micro-scale topography provided similar results. The combination of both nano and micro-scale topographies provided both high static contact angles (above 150°), low contact angle hysteresis and low roll-off tilts (below 10°) for water. However, this same combination of surface characteristics does not satisfy the conditions to achieve super repellence for probe liquids with lower surface tensions and different surface tension components (polar part/disperse part). The results in this study show that a high static contact angle with a probe liquid does not guarantee the abhesive behaviour. A novel assessment methodology has been proposed for the evaluation of repellence of surfaces. This approach helps to classify coatings and surface roughness characteristics according to their ability to repel various liquids not only in terms of static contact angles but also in terms of contact angle hysteresis, roll off tilt and film forming behaviour. It is proposed that droplet diameter is used as an indicator of a tendency of specific liquids to film formation. Whilst the critical parameters to achieving omniphobicity are still unclear, this work sheds light on the parameters that have to be considered and the methods to elucidate them

Frontiers in Ultra-Precision Machining

Ultra-precision machining is a multi-disciplinary research area that is an important branch of manufacturing technology. It targets achieving ultra-precision form or surface roughness accuracy, forming the backbone and support of today’s innovative technology industries in aerospace, semiconductors, optics, telecommunications, energy, etc. The increasing demand for components with ultra-precision accuracy has stimulated the development of ultra-precision machining technology in recent decades. Accordingly, this Special Issue includes reviews and regular research papers on the frontiers of ultra-precision machining and will serve as a platform for the communication of the latest development and innovations of ultra-precision machining technologies

Surface Wetting and Friction Studies of Nano-Engineered Surfaces on Copper Substrate

Nano-engineered-textures on a material surface can dramatically improve the wetting and non-wetting properties of a surface, and they also show promise to address friction issues that affect surfaces in contact. In this work, aluminum-induced crystallization (AIC) of amorphous silicon (a-Si) was used to produce nano-textures on copper (Cu) substrates. A study was performed to examine the effects of changing the annealing conditions and a-Si thickness on nano-texture formation. The creation of various nano-topographies and chemically modifying them using octafluorocyclobutane (C4F8) was performed to control hydrophilicity, hydrophobicity, and oil affinity of nano-textured surfaces. A video-based contact angle measurement system was used to measure the surface wetting properties. Scanning electron microscopy (SEM) was employed to characterize the surface nano-topographies and provide a basis for qualitative and quantitative analysis of the nano-texture formations. Scratch testing was performed using a TriboIndenter to assess the potential of the nano-textured Cu substrates to lower the coefficient of friction (COF). It was found that the thicker a-Si layer generated larger textures overall which contributed to water contact angle (CA) results ranging between superhydrophilic and superhydrophobic, as well as increased oil affinity of Cu substrate. The nano-textured surfaces also achieved COF values that were 40 % lower than as-received (AR) Cu

Structural, Magnetic, Dielectric, Electrical, Optical and Thermal Properties of Nanocrystalline Materials: Synthesis, Characterization and Application

This book is a collection of the research articles and review article, published in special issue "Structural, Magnetic, Dielectric, Electrical, Optical and Thermal Properties of Nanocrystalline Materials: Synthesis, Characterization and Application"

Improvement of Thermoelectric Properties Through Manipulation of their Microstructure: the Effect of Graphene Reinforcement

Environmental changes and extreme climate-related events are mainly attributed to greenhouse gas (GHG) emissions and are becoming a growing concern. The reported scientific evidence, highlighting such interrelationships, has convinced researchers to look for clean energy sources and improve operational efficiencies, and capture and convert the waste heat into electricity. Since almost two-thirds of energy is converted to heat and wasted, the recovery of waste heat will boost savings in fossil fuel consumption as an abundant source of energy. In this regard, thermoelectric (TE) compounds can be employed to convert the waste heat into electricity, thereby increasing the efficiencies of energy generating operations. Such an approach is even applicable to renewable energy (RE) sources. However, the applications of the thermoelectric converters necessitate the development of advanced, efficient thermoelectric materials with a high level of thermomechanical stability. This doctoral research project aims to develop and modify thermoelectric compounds by manipulating their microstructure and improving their mechanical properties by reinforcement with graphene nanoplates (GNPs). To the best of our knowledge, there is no specific report in the open literature to determine the reinforcing effects of graphene nanofillers (e.g., GNPs) on thermoelectric products. There is a lack of a comprehensive assessment in the scientific and industrial communities in evaluating the advantages and drawbacks of GNPs, as the reinforcing agent on TE compounds. In this dissertation, to assess the performance of the GNPs, three potential thermoelectric compounds, namely MnTe, CoVSn, and CuSbTe2, have been investigated. These designated compounds address the requirements for covering an extended working temperature range from low to high, examining various crystal structures (e.g., Chalcogenides and half-Heusler), and developing environmentally-friendly (i.e., lead-free) TE products. The bulk samples with the addition of small quantities of GNPs (0.25, 0.5, 0.75, and 1 wt. %) were synthesized using powder metallurgy and fabricated by spark plasma sintering (SPS). The thermoelectric factors, magnetic behavior, microstructure, and mechanical properties of the samples were evaluated and analyzed. Grain growth inhibition is the main consequence of the reinforcing GNPs, which results in an enhancement in the thermoelectric and mechanical characteristics of the nominated TE products. Scattering of electrical carriers and phonons due to the precipitation of the reinforcing GNPs in the matrix, thus providing a higher density of microstructural boundaries, improves the thermoelectric properties. Furthermore, microstructural manipulation, such as crystal/particle size reduction caused by the segregation of the reinforcing GNPs as a second phase in the matrix, enhances the mechanical characteristics of TE compounds, for example, the fracture toughness () and hardness.Thesis (Ph.D.) -- University of Adelaide, School of Mechanical Engineering, 202

Analytical spectroscopy method development to study mechanisms of Alzheimer's and tuberculosis diseases

2020 Spring.Includes bibliographical references.This dissertation covers the analytical method development created to study and enhance the knowledge of two specific disease mechanisms important to Alzheimer's disease and Mycobacterium tuberculosis. There are two parts in this dissertation where Part 1 is entitled Measurement of The Kinetic Rate Constants of Interpeptidic Divalent Transition Metal Ion Exchange in Neurodegenerative Disease. Part 2 is entitled The Electrochemistry of Truncated Menaquinone Electron Transporters with Saturated Isoprene Side Chains Important in Tuberculosis. These diseases appear on the World Health Organization's top 10 leading causes of death worldwide. The amyloid-beta (Aβ) peptides are associated with Alzheimer's disease, where neurodegeneration is caused by the aggregation of the peptide into senile plaques within neuronal synaptic cleft spaces. Alzheimer's disease currently has no cure due to its multi-causative pathology. One disease mechanism is the coordination of divalent metal ions to the peptide. Specifically, Aβ coordinates Cu(II) and Zn(II) ions that can enhance the aggregation of Aβ into plaques. These metal ions are highly regulated within the human body and are usually found bound to peptides and not as free ions. Therefore, the Aβ must sequester the metals from other proteins and peptides. The primary research in this dissertation advances fluorescence method development to measure interpeptidic Cu(II) exchange kinetics to be able to measure this type of disease mechanism. The small peptides GHK (Gly – His – Lys) and DAHK (Asp – Ala – His – Lys) both chelate Cu(II) with nM affinity, have biological relevance as they are motifs found in human blood like Aβ, and chelate Cu(II) with similar nitrogen-rich binding ligands as Aβ. By substituting non-coordinating lysine residues with fluorescent tryptophan, the interpeptidic exchange rates can be measured since tryptophan fluorescence is statically quenched when within 14 angstroms of a paramagnetic bound Cu(II). Thus Cu(II) transfer from Cu(H-1GHW) to either GHK or DAHK can be monitored by recovered GHW fluorescence as the Cu(II) is exchanged and second-order kinetic rate constants were determined. This methodology was then used to monitor the Cu(II) exchange from truncated Cu(Aβ1-16) and Cu(Aβ1-28) complexes to GHW and DAHW, where second-order reaction kinetic rate constants were determined. While in the exchanges between Cu(H-1GHW) with GHK/DAHK the second-order rate constants were on the magnitude of 102 or 101 M-1s-1, respectively, the exchanges from Cu(Aβ) complexes were 2-3 orders of magnitude larger, 104 M-1s-1 (to GHW and DAHW). These differences in rate constant magnitude arise from the fact that the affinity of GHW (KA = 1013 M-1) for Cu(II) is larger than Aβ (KA =1010 M-1). This method development is an important step to an accurate measurement of the interpeptidic exchange between Aβ peptides, including in their fibril and plaque formations. Since senile plaques are found in synaptic cleft spaces with nanometer distances between neurons, a model system was generated to study coordination reactions at the nanoscale. In order to do this, the metal ion would need to be released in a controlled manner. Studies of metal ion burst reactions through the use of photocages can simulate bursts of ions like those seen in the synaptic cleft. Zn(II) is often released in its ionic form within the synapse in its function as a neurotransmitter, so we simulated a burst of Zn(II) ions by using a photocage, [Zn(NTAdeCage)]- which releases Zn(II) when irradiated with light. The photocage was irradiated to release Zn(II) then we followed its reaction progress with an in situ chelator, Zincon, in reverse micelles and in bulk aqueous buffer. The coordination reaction was 1.4 times faster in an aqueous buffer than in reverse micelles, despite the Zn(II) and Zincon being closer in the nanoparticle. These observations suggested that there is an impact on coordination reactivity within a highly heterogeneous environment with a cell-like membrane, which is due to the partitioning of each ligand. We observe that the photocage stays in the water pool of the reverse micelle and the Zincon partitions into the membrane interface. Thus, the coordination reactivity is diminished, likely due to the need for Zn(II) to diffuse to the Zincon, crossing a highly organized Stern layer to encounter the Zincon. Whereas in aqueous buffer, these are free to encounter each other despite being hundreds of nanometers apart. These proof of concept studies are integral to studying initial binding dynamics of metal ions with peptides at the nanoscale present in cells and neuronal synapses. Tuberculosis is a pathogenic bacterium which despite having a curable medication, can be drug-resistant. Menaquinone (MK) analogs with regiospecific partial saturation in their isoprenyl side chain, such as MK-9(II-H2), are found in many types of bacteria, including pathogenic Mycobacterium tuberculosis and function as electron transport lipids cycling between quinone and quinol forms within the electron transport system. While the function of MK is well established, the role of regiospecific partial saturation in the isoprenyl side chain on MK remains unclear and may be related to the redox function. Recently, an enzyme in M. tuberculosis called MenJ was shown to selectively saturate the second isoprene unit of MK-9 to MK-9(II-H2). The knockout expression of this enzyme was shown to be essential to the survival of the bacterium. A series of synthesized truncated MK-n analogs were investigated using a systematic statistical approach to test the effects of regiospecific saturation on the redox potentials. Using principal component analysis on the experimental redox potentials, the effects of saturation of the isoprene tail on the redox potentials were identified. The partial saturation of the second isoprene unit resulted in more positive redox potentials, requiring less energy to reduce the quinone. While full saturation of the isoprene tail resulted in the most negative potentials measured, requiring more energy to reduce the quinone. These observations give insight into why these partially saturated menaquinones are conserved in nature

Surface Modification of a Titanium Alloy via Electrospraying for Biomedical Engineering Applications

Hydroxyapatite (HA) coated titanium (Ti) based dental and orthopaedic implants are widely utilised owing to their bone-bonding capability. However, the longevity of such implants is restricted by poor HA-Ti interfacial adhesion. In contrast, alternative coating materials such as titania (TiO2) and zirconia (ZrO2) have superior mechanical properties but are generally bioinert. Therefore, the performance of coated implants has been optimised by combining highly bioactive HA with mechanically superior TiO2 or ZrO2. This thesis investigated the deposition of novel electrosprayed bioceramic films with enhanced bioactivity and mechanical properties. Sol-gel derived TiO2 and ZrO2 nano-particles were synthesized using a range of precursors and solvents whereas nano-sized HA was synthesized by precipitation. Composite suspensions with a range of HA:TiO2 and HA:ZrO2 compositions were prepared by mixing. The liquid physical properties such as electrical conductivity and surface tension were affected by suspension composition which in turn influenced the electrospray process. Film morphology was dependent on deposition parameters such as needle-to-substrate distance and suspension flow rate as well as post deposition annealing. The in vitro bioactivity was generally enhanced by post deposition annealing temperature and was further improved by the presence of HA. However, the TiO2/HA composite films were more bioactive than the ZrO2/HA composite films. The mechanical integrity of the electrospray films was assessed by scratch testing. The scratch hardness improved with an increase in the post deposition annealing temperature and declined with an increase in HA content. Furthermore, the scratch resistance was affected by materials composition and was in the order ZrO2>TiO2>HA. The scratch resistance was further enhanced by the deposition of HA-based bi-layer and functionally graded films with a comparable in vitro response to the electrosprayed HA films. Thus the electrospray process is a promising route for the deposition of bioceramic composite films for biomedical applications

Recent Trends in Coatings and Thin Film–Modeling and Application

Over the past four decades, there has been increased attention given to the research of fluid mechanics due to its wide application in industry and phycology. Major advances in the modeling of key topics such Newtonian and non-Newtonian fluids and thin film flows have been made and finally published in the Special Issue of coatings. This is an attempt to edit the Special Issue into a book. Although this book is not a formal textbook, it will definitely be useful for university teachers, research students, industrial researchers and in overcoming the difficulties occurring in the said topic, while dealing with the nonlinear governing equations. For such types of equations, it is often more difficult to find an analytical solution or even a numerical one. This book has successfully handled this challenging job with the latest techniques. In addition, the findings of the simulation are logically realistic and meet the standard of sufficient scientific value