Arc-discharge In Solution: A Novel Synthesis Method For Carbon Nanotubes And In Situ Decoration Of Carbon Nanotubes With Nanoparticles

Nanotechnology has reached the status of the 21st century\u27s leading science and technology based on fundamental and applied research during the last two decades. An important feature of nanotechnology is to bridge the crucial dimensional gap between the atomic and molecular fundamental sciences and microstructural scale of engineering. Accordingly, it is very important to have an in-depth understanding of the synthesis of nanomaterials for the use of state-of-the-art high technological devices with enhanced properties. Recently, the \u27bottom-up\u27 approach for the fabrication of nanomaterials has received a great deal of attention for its simplicity and cost effectiveness. Tailoring the various parameters during synthesis of selected nanoparticles can be used to fabricate technologically important components. During the last decade, carbon nanotubes (CNTs) have been envisioned for a host of different new applications. Although carbon nanotubes can be synthesized using a variety of techniques, large-scale synthesis is still a great challenge to the researchers. Three methods are commonly used for commercial and bulk productions of carbon nanotubes: arc-discharge, chemical vapor deposition and laser ablation. However, low-cost, large-scale production of high-quality carbon nanotubes is yet to be reported. One of the objectives of the present research is to develop a simplified synthesis method for the production of large-scale, low-cost carbon nanotubes with functionality. Herein, a unique, simple, inexpensive and one-step synthesis route of CNTs and CNTs decorated with nanoparticles is reported. The method is simple arc-discharge in solution (ADS). For this new method, a full-fledged optoelectronically controlled instrumen is reported here to achieve high efficiency and continuous bulk production of CNTs. In this system, a constant gap between the two electrodes is maintained using a photosensor which allows a continuous synthesis of the carbon nanostructures. The system operates in a feedback loop consisting of an electrode-gap detector and an analogue electronic unit, as controller. This computerized feed system was also used in single process step to produce in situ-decorated CNTs with a variety of industrially important nanoparticles. To name a few, we have successfully synthesized CNTs decorated with 3-4 nm ceria, silica and palladium nanoparticles for many industrially relevant applications. This process can be extended to synthesize decorated CNTs with other oxide and metallic nanoparticles. Sixty experimental runs were carried out for parametric analysis varying process parameters including voltage, current and precursors. The amount of yield with time, rate of erosion of the anode, and rate of deposition of carbonaceous materials on the cathode electrode were investigated. Normalized kinetic parameters were evaluated for different amperes from the sets of runs. The production rate of pristine CNT at 75 A is as high as 5.89 ± 0.28 g.min-1. In this study, major emphasis was given on the characterizations of CNTs with and without nanoparticles using various techniques for surface and bulk analysis of the nanostructures. The nanostructures were characterized using transmission electron microscopy, high resolution transmission electron microscopy, scanning transmission electron microscopy, energy dispersive spectroscopy and scanning electron microscopy, x-ray photo electron spectroscopy, x-ray diffraction studies, and surface area analysis. Electron microscopy investigations show that the CNTs, collected from the water and solutions, are highly pure except the presence of some amorphous carbon. Thermogravimetric analysis and chemical oxidation data of CNTs show the good agreement with electron microscopy analysis. The surface area analysis depicts very high surface area. For pristine multi-walled carbon nanotubes, the BET surface area is approximately 80 m2.g-1. X-ray diffraction studies on carbon nanotubes shows that the products are clean. Nano-sized palladium decorated carbon nanotubes are supposed to be very efficient for hydrogen storage. The synthesis for in-situ decoration of palladium nanoparticles on carbon nanotubes using the arc discharge in solution process has been extensively carried out for possible hydrogen storage applications and electronic device fabrication. Palladium nanoparticles were found to form during the reduction of palladium tetra-chloro-square planar complex. The formation of such a complex was investigated using ultraviolet-visible spectroscopic method. Pd-nanoparticles were simultaneously decorated on carbon nanotubes during the rolling of graphene sheets in the arc-discharge process. Zero-loss energy filtered transmission electron microscopy and scanning transmission electron microscopy confirm the presence of 3 nm palladium nanoparticles. The deconvoluted X-ray photoelectron spectroscopy envelope shows the presence of palladium. Surface area measurements using BET method show a surface area of 28 m2.g-1. The discrepancy with pristine CNTs can be explained considering the density of palladium (12023 kg.m-3). Energy dispersive spectroscopy suggests no functionalization of chlorine to the sidewall of carbon nanotubes. The presence of dislodged graphene sheets with wavy morphology as observed with high-resolution transmission electron microscopy supports the formation of CNTs through the \u27scroll mechanism\u27

Design and Analysis of Air-Stiffened Vacuum Lighter-Than-Air Structures

Lighter-than-air (LTA) systems have been developed for numerous applications and have taken several forms. Airships, aerostats, blimps, and balloons are all part of this family of systems, which uses Archimedes principle to achieve neutral and positive buoyancy in air by replacing an air volume with LTA gases. These lifting gases stiffen the otherwise compliant envelope structures, allowing them to sustain the pressure difference brought by the displaced air. The compliance of these structures is a byproduct of the weight requirement, materials and geometrical arrangement of which these structures are built from, typically resulting in dimensionalities that exhibit low or virtually non-existent in-plane bending stiffness. The former has constrained the development of LTA structures that utilize an internal partial vacuum, rather than a lifting gas, to achieve positive buoyancy, where the structure would be subjected to a pressure differential near atmospheric pressure. Given the above limitation, this research presents the development trajectory and structural characterization of air stiffened designs, which utilize air to shape and serve as the core of a set of enclosing envelopes. The development trajectory established a simulation framework that enables the structural characterization of air-stiffened designs under a variety of geometric and loading conditions. Such framework allowed for the development of finite element solutions that included geometric, fluid-structure and contact nonlinearities, with capacity for further generalization. Given the developed framework, the structural characterization of the Helical Sphere and Icoron air-stiffened designs demonstrated a reduction of material modulus and strength requirements compared to membrane-over-frame designs, and showed the capability of air-stiffened designs to be tailored for specific material strength limits

SPIG2018

This Special Issue covers a wide range of topics from fundamental studies to applications of ionized gases. It is dedicated to four topics of interest: 1. ATOMIC COLLISION PROCESSES (electron and photon interactions with atomic particles, heavy particle collisions, swarms, and transport phenomena); 2. PARTICLE AND LASER BEAM INTERACTION WITH SOLIDS (atomic collisions in solids, sputtering and deposition, and laser and plasma interactions with surfaces); 3. LOW TEMPERATURE PLASMAS (plasma spectroscopy and other diagnostic methods, gas discharges, and plasma applications and devices); 4. GENERAL PLASMAS (fusion plasmas, astrophysical plasmas, and collective phenomena). This Special Issue of Atoms will highlight the need for continued research on ionized gas physics in different topics ranging from fundamental studies to applications, and will review current investigations

Localised conduction electrons in carbon nanotubes and related structures

Single localized polaron (quasiparticle) States are considered in structures relating to carbon nanotubes. The hamiltonian is derived in the tight-binding approximation first on a hexagonal lattice and later on a general carbon nanotube with specifiable chirality, and shares close links with the Davydov model of excitations of a one-dimensional molecular chain. First-order interactions of the lattice degrees of freedom with the electron on-site and exchange terms are included. The system equations are shown, under certain approximations, to share a close relationship with the nonlinear Schrödinger equation - an equation that is known to possess localised solutions. The ground state of system is investigated numerically and is found to depend crucially upon the strengths of the electron-phonon interactions

Self-Assembly and Bioactivity of Peptides for Therapeutic Applications

Peptides are an attractive platform to make new and novel constructs for therapeutic applications due to their biocompatibility, biodegradability and biofunctionality. Peptides that self-assemble may have enhanced in vivo stability and may be able to self-deliver. Furthermore, peptides can be modified to enhance their in vivo stability through lipidation, PEGylation and other modifications. This thesis aims to explore the self-assembly and bioactivity of small oligopeptides, telechelic tyrosine functionalised PEGylated peptides and peptide hormones with potential therapeutic applications. With the rise in cases of antimicrobial resistance, there is a great amount of interest in the development of alternate medicines to combat these issues. Short cationic peptides are beginning to show great potential in this area, due to their ‘multi-hit’ strategy and relatively cheap cost of synthesis. The self-assembly and lipid interactions of a group of surfactant-like peptides (SLPs) and peptide bola-amphiphiles containing arginine and alanine are examined. It is apparent that the size of the hydrophobic block causes increased aggregation propensity and increased structural ordering. The cytocompatibility of the SLPs and bola-amphiphiles is measured, revealing that cytotoxicity is not linked to molecular weight. The SLPs are more cytocompatibile than the bola-amphiphiles. These peptides show activity at cytocompatibile concentrations against P.aeruginosa, a bacterial species on the World Health Organisations list of species that require new treatments. Further to this, the self-assembly and bioactivity of two short symmetrical AMPs, consisting of arginine and phenylalanine was examined. These peptides were found to have weak selfassembly behaviour, but strong interactions with many different Pseudomonas bacteria, with particularly strong interactions with P.aeruginosa. The peptides alter the structure of liposomes based on the composition of the P.aeruginosa membrane, with the most active peptide, R4F4, completely disrupting vesicle formation. The peptide R4F4 disrupts biofilm formation and interacts with cyclic diguanylate (c-di-GMP), a regulator of biofilm formation and dispersion in the species. Materials functionalised with tyrosine may be of interest for enzyme responsive materials. The self-assembly of tyrosine functionalised telechelic PEO-star conjugates at native pH and pH 12 was examined These conjugates were found to self-assemble into a mixture of spherical globules and fibres. The self-assembly of the lower molecular weight conjugate was disrupted by pH adjustment. The larger conjugate formed mixed long straight fibres and smaller globules when adjusted to pH 12. These conjugates did not form hydrogels and were proved to be cytocompatible at sufficiently high concentration. Self-assembled hormones may have prolonged half-lives and increased stability in vivo. Peptide hormone oxytocin has found to be heat unstable, affecting its performance in developing nations. Probing conditions for selfassembly may improve the stability. Thus, the assembly of the peptide hormone oxytocin and analogues was examined. The self-assembly of oxytocin was inconclusive when examined by biophysical techniques. Analogue carbetocin was found to not aggregate at native pH. Oxytocin was found to form a self-standing β-sheet gel at 2 wt% and pH 12, whereas carbetocin appeared slightly crystalline under these conditions. A lipidated variant of oxytocin was found to be insoluble and to assemble into irregular aggregates in ethanol. Overall, this thesis examines through biophysical techniques and bioassays, different peptides with a range of potential therapeutic applications, contributing to the understanding of short antimicrobial peptides

Molecular basis of membrane stability and dynamics

Dit proefschrift is onderverdeeld in vier verschillende delen, die overeenkomen met de vier verschillende onderwerpen die ik heb gewerkt . In hoofdstukken 2-4, bestudeerden we het werkingsmechanisme van antimicrobiële peptiden. We concentreerden ons op twee korte peptiden, de cyclische BPC194 en zijn lineaire analoge BPC193. Hoewel beide bezitten dezelfde aminozuursequentie, maar het cyclische peptide kan microbiële cellen te doden. Met behulp van een combinatie van fluorescentie-gebaseerde technieken met moleculaire dynamica simulaties, kwamen we erachter dat het cyclisch peptide plooien in de juiste conformatie op membraanbindende, inserts diep, vormt poriën en fuseren de membranen . In hoofdstuk 5, wij ontwerpen en gesynthetiseerd een DNA - peptide hybride te moduleren de oligomerisatie van een membraan kanaal met behulp van complementaire DNA-strengen of een G-quadruplex motief. In beide gevallen heeft de daaruit zender heeft voorkeur voor een specifieke oligomere toestand van een vaste grootte . In hoofdstuk 6 hebben we de effecten van koolhydraten op het membraan organisatie. We combineerden fluorescentie microscopie met moleculaire dynamische simulaties en ontdekte dat alleen de niet-reducerende koolhydraten, sucrose en trehalose, hebben een effect op de lipid raft organisatie. Die twee disachariden worden meestal gesynthetiseerd door verschillende organismen, om te overleven in extreme uitdroging omstandigheden. In hoofdstuk 7 bestudeerden we de lokalisatie, oligomerisatie en dynamiek van verschillende plasmamembraan aminozuur transporters van S. cerevisiae. De verdeling van deze eiwitten in het membraan niet homogeen. We kwamen erachter dat de reden dat de extreem trage verspreiding die we gemeten voor die eiwitten samen met hun lage bedragen zou kunnen zijn

Molekulardynamik-Simulationen von amyloidogenen Proteinen in Lösung: Stabilitätsuntersuchungen und Weiterentwicklung einer Kontinuumsmethode

Viele neurodegenerative Erkrankungen, wie die transmissiblen spongiformen Enzephalopathien (TSE), die Alzheimer- und die Huntington-Krankheit, sind durch charakteristische Ablagerungen im Gehirn, sogenannte Amyloide, gekennzeichnet. Amyloide sind oftmals fibrilläre Aggregate von normalerweise löslichen Proteinen, deren dreidimensionale Strukturen sich bei der Aggregation verändern. Bedauerlicherweise waren hochauflösende Methoden biophysikalischer Strukturaufklärung bislang auf Amyloide nicht anwendbar. Dagegen können Molekulardynamik (MD)-Simulationen amyloidogener Proteine und Peptide in ihrer Lösungsmittelumgebung dazu beitragen, die Mechanismen der auftretenden Konformationsänderungen zu verstehen und die Strukturen amyloider Fasern aufzuklären. Die korrekte und effiziente Beschreibung der Lösungsmittelumgebung spielt dabei eine entscheidende Rolle. Im ersten Teil dieser Arbeit wird die Konformationsdynamik Amyloid bildender Peptide und Proteine in expliziter wässriger Umgebung untersucht. In MD-Simulationen des zellulären Prion Proteins (PrPC) werden durch Einführung der Punktmutationen M205S und M205R entscheidende Faktoren für die korrekte Faltung und strukturelle Stabilität des Proteins identifiziert. Ferner wird für die Grundstruktur der bei TSE auftretenden pathogenen Isoform PrPSc ein Modell basierend auf dem Strukturmotiv einer parallelen beta-Helix entwickelt. Analog dazu werden Peptide aus poly-Glutamin, die den mutmaßlichen Aggregationskeim bei der Huntington-Krankheit darstellen, als parallele beta-Helizes unterschiedlicher Formen und Größen modelliert. In MD-Simulationen ermitteln wir aus diesen Strukturen thermodynamisch stabile monomere und dimere Aggregationskeime. Da die erreichbaren Simulationszeiten in expliziten Lösungsmitteln verglichen mit den Zeitskalen der Proteindynamik zu kurz sind, wird im zweiten Teil dieser Arbeit eine effiziente Kontinuumsmethode für Proteine in polaren Lösungsmitteln weiterentwickelt. In dieser Methode wird das durch die Polarisation des Lösungsmittels hervorgerufene Reaktionsfeld (RF) durch normalverteilte RF-Dipoldichten an den Orten der Proteinatome beschrieben. Die sich daraus ergebenden RF-Kräfte auf die Proteinatome berücksichtigen aber nicht den Druck an den dielektrischen Grenzflächen, der vom Kontinuum auf das Protein ausgeübt wird, und verletzen damit das 3. Newtonsche Gesetz. Dies führt in MD-Simulationen zu erheblichen Artefakten. In dieser Arbeit wird diese Kontinuumsmethode so umformuliert und erweitert, dass die resultierenden RF-Kräfte dem Prinzip Actio=Reactio gehorchen. Die modifizierte Kontinuumsmethode wird in ein MD-Programm implementiert und an Hand geeigneter Systeme parametrisiert. In ausgedehnten MD-Simulationen des Alanin-Dipeptids wird die Korrektheit und Effizienz der Methode demonstriert