3. Electronic Theses and Dissertations (ETDs) - All submissions

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Photocatalytic degradation of methyl violet using modified radially aligned nano rutile TiO2-nanodiamonds composite
(2020) Mugadza, Farirai; Farirai, Mugadza
In this work, a hydrothermal method was used to synthesize the radially aligned nano rutile (RANR) TiO2,usingTiCl4as a precursor. The synthesis temperatures, as well as the time involved in the refluxing step of the synthesis were varied to obtain the optimum morphology of the resulting TiO2. The optimum refluxing time for RANR TiO2 synthesis was determined to be 16 hours at 180°C. The synthesized RANR TiO2 with dandelion-like shapes had diameters ranging from 300 nm to 800 nm and an average diameter of 560 nm. The RANR TiO2 had BET surface area of 68 m2/g, which is higher than that of the commercially available Degussa P25 (45 m2/g).The RANR TiO2-nanodiamond composites were all synthesized in situ using the hydrothermal method with detonation nanodiamonds ranging from 0.1 to 1% mass loading. BET surface area analysis showed an increase in the surface area of the RANR TiO2 with an increase in the amount of nanodiamonds used in its modification. Raman spectra confirmed the presence of graphitic carbon and rutileTiO2in all the composite samples. The results obtained from XPS analysis showed that oxygen, carbon and titanium were all present in the sample but there was no evidence showing bond formation between titanium and carbon. RANR TiO2 was the most effective in dye degradation due to their nano rod structure, which increases light harvesting properties due to multiple reflections of light. All the other composites did generally well with respect to dandelions in the first hour, but then the rate of degradation decreased which could be attributed to the reduction in photocatalytic active sites due to blockage by reactants. A good dispersion of the nanodiamonds and RANR TiO2(0.1% loading) helped to create strong electronic interphase interactions. This helps to separate the photogenerated electrons and positive holes, thereby increasing photocatalytic efficiency. Calcination increased photocatalytic efficiency because of the increase in crystallinity of materials which reduces electron/hole recombination, the increase in crystallinity was shown by results from Raman spectroscopy. The photocatalyst recyclability studies showed that the recovery of the catalyst after each cycle and the re-use was not effective as the degradation efficiency decreased from 80% to 60% after 3 cycles
Evaluation of metal nanocomposite polymer inclusion membranes (PIMs) for trace heavy metal extraction in natural waters
(2020) Maiphetlho, Kgomotso
The shortcomings of the conventional membranes in water applications such as low stability and the hydrophobic nature reduces the membrane productivity and lifespan. These result in expensive procedures that hinder membrane science technology. Hence, recent investigations have resulted in the synthesis of nanocomposite membranes as an alternative. In this work, silver nanocomposite polymer inclusion membranes (PIMs) were synthesized to evaluate the extraction of trace metal ions in natural waters. To characterise the PIMs, scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX), contact angle measurements and water uptake measurements were used. The contact angle and the water uptake measurements highlighted that the introduction of the silver nanoparticles (Ag NPs) into the membrane, modified the membrane hydrophobic/hydrophilic character. The evaluation of the synthesized PIMs demonstrated that the PIMs containing Ag NPs exhibit better extraction capacity as opposed to the bare PIMs and the PIM with (40 w.t% D2EHPA, 10 w.t% Ag NPs and 50 w.t% PVC) has the optimum composition. It was then used to optimise the parameters that are important for the extraction of trace metal ions and those were sample pH 5, 1 M HNO3 of the receiving solution and 120 hrs for the extraction time. The selectivity of the nanocomposite PIM was investigated and it was found that its affinity towards a range of divalent cations (Co2+, Ni2+, Cu2+, and Cd2+) in synthetic water solutions, based on the percentage recovery factor of the extracted metal ions, follow the order; Cd 2+ (94) > Cu2+ (87) > Ni2+ (78) > Co2+ (67), where the numerical data in the brackets correspond to the percentage recovery factor of metal ion extracted from the source solution, respectively. This order can be explained by the Hard and Soft Acids and Bases Theory and the hydration energy of the metal cations. However, the stability of the PIM was still compromised during repeated cycle operations despite an improvement of hydrophilicity with introduction of Ag NPs, this was indicated by an appreciable leaching of the carrier (D2EHPA) and Ag NPs in a 4:1 ratio (identical to the ratio of these components in the original membrane). This silver nanocomposite PIM was tested in dam water. No matrix effect was observed on metal ion transport efficiency in such waters. The obtained transport efficiencies for the metal ions were Cd2+ (88), Cu2+ (80) , Ni2+ (62) , Co2+ (70) and Fe2+ (37) respectively. The newly synthesized PIM could be used for future extraction of the target metals in water systems. The designed PIM system has also the potential to be used as passive sampler for in situ extraction of the target metals in water systems. However, further studies are needed to improve the stability of both the carrier and nanoparticles in the membrane
In vitro assessment of the toxicity of gold nanoparticles
(2019) Vetten, Melissa Anne
The hazard identification of gold nanoparticles forms an essential part of their risk assessment; however, the test methodologies used should be appropriate and applicable to ensure reliable results. In this study, various in vitro testing methodologies used for hazard identification were investigated for their applicability in the testing of gold nanoparticles. Preferable assays were identified, in particular, the use of label-free methodologies, such as the cell impedance based xCELLigence and the CytoViva HSI systems, were found to be ideal in order to avoid optical interference of the nanoparticles with the testing methodology. The recommended tests were then implemented to investigate the effect of size, surface charge and different functional groups in the bronchial epithelial cell line BEAS-2B. Two citrate stabilized gold nanoparticles of 14 nm and 20 nm in diameter were tested. Moreover, the 14 nm polyethylene glycol-liganded AuNPs with either hydroxyl, carboxyl, biotin, nitrilotriacetic acid, or azide negatively charged functional groups, and the positively charged 14 nm polyethylene glycol-liganded AuNP with amine functional group were investigated. The characterization of the physicochemical characteristics and sterility of these nanoparticles were performed prior to the assessment of their toxicity, intracellular uptake and localization, and the mechanism of uptake. The gold nanoparticles tested were not toxic or genotoxic to the BEAS-2B cells, regardless of cellular internalisation. These cellular effects were not influenced by their size or surface charge. On the other hand, surface functionalization influenced uptake, which was shown to be through a caveolin-mediated endocytosis pathway followed by accumulation within vesicles and in the cytosol. However, additional work needs to be conducted to establish the link between different functional groups and their role in endocytosis and subsequent localization and toxicity. In conclusion, the possibility exists for the interference of nanoparticles with in vitro assays and this should be tested prior to their implementation. However, most importantly, the physicochemical characterization of nanoparticles is of utmost importance, which should precede the hazard identification of nanomaterials using these in vitro assays. These in turn, will allow the establishment of the relationship between these characteristics and any observed toxicity, which will aid not only the risk assessment of nanomaterials but also in the establishment of predictive models in the toxicity of newly synthesised nanomaterials.
Experimental and Numerical Characterization of Interlaminar Properties of SWCNTs Doped PAN Nano-mats Strenthened Multiscale Hybrid Composites
(2019) Arif, Muhammad
Polymer composite reinforced with conventional macro size bres have taken a major role in various modern engineering applications and their demand is ever increasing due to their light weight and design exibility. Various im-provements in manufacturing methods, fabrication techniques and composite constituents have been made over the years to produce better polymer com- posites. However, the major challenge of the conventional polymer composites is that failure at the matrix rich interlaminar region still remains and limits their performance resulting in unreliable usage of these composites. A number of research attempts had little success due to various limiting factors have been carried out to rectify this problem. One of the potential methods expected to improve the strength of the interlaminar region is the incorporation of nano-size llers, such as electrospun Polyacrylonitrile (PAN) nano bres mat as an interalia into the matrix rich interlaminar region of the conventional polymercomposite. However, controlling the alignment and distribution of the PAN nano bres during the chaotic electrospinning process is a major hurdle for im-proving the interlaminor regions. The random orientation of electrospun PAN nano bres mat reduces their strengthening e ect and also the required material properties.Hence, the current study has focused on the design of electrospinning process for improving the orientation and distribution of the PAN nano bre mats. The developed electrospinning process was used to produce random and aligned PAN nano bres mat and also used for producing both pristine and function-alized single walled carbon nanotubes (SWCNTs) doped PAN nano bres mat. These nanomats were then sandwiched with the glass bre-epoxy matrix to produce nano strengthened multiscale hybrid composites. As part of the electrospinning procedure, electric elds of general electrospin- ning technique were manipulated using two position adjustable auxiliary ver- tical electrodes (AVEs) to produce aligned nano bres mat along with reduced diameter. So as to optimise the electrospinning parameters, the e ect of AVEs on the PAN nano bres mat orientation, distribution and diameter were ex- perimentally matrixed and analysed. The fractographic study showed that auxiliary vertical electrodes (AVEs) added to the electrospinning process re- duced the diameter, enhanced the alignment of the nano bres and improved molecular orientation. Among four di erent volume fractions of 0.1%, 0.2%, 0.5% and 1% randomly oriented PAN nano bre mats, the volume fraction of 0.5% PAN polymer was selected to manufacture aligned PAN nano bres mat strengthened hybrid composite based on the improved experimental randomly oriented PAN nano bre mats strengthened hybrid composites. A series of tests showed that glass bre composites (GFC) reinforced with the volume fraction of 0.5% aligned nano bre mats were better than those of 0.5% randomly distributed nano bre mats. The aligned nano bre mat with reduced diameter increased the tensile, exural, and impact properties of glass bre composite by 68.91%, 95.32% and 45.30% respectively. Aligned nano bres mat was further utilised to align and disperse the pristine and functionalized SWCNTs into the interlaminar region of breglass compos- ite. Alignment and a nano-range diameter of nano bres helped in improved distribution and alignment of pristine SWCNTs (p-SWCNTs), which was re- ected in an increase in tensile, exural and impact resistance by 89.30%, 105.48% and 107.17% respectively. A nondestructive functionalization method (Friedel craft alkylation) was used to improve the interface bonding of SWC- NTs with the host PAN polymer nano bre. PVA chains crafted to the surface of the SWCNTs without damaging the wall was con rmed using FTIR and Ra- man spectroscopy. The e ect of functionalized SWCNTs (f-SWCNTs) doped aligned PAN nano bre mats improved the properties of nano-hybrid multiscale composite up to 111.34%, 117.11% and 180.03% in tensile, exural and impact resistance respectively. A multiscale model was used to determine the properties of the multiscale nanohybrid composite strengthened with random and aligned PAN nano bre mats, PAN doped with p-SWCNTs and f-SWCNTs aligned nano bre mats. Three length scales, such as nano, micro and macro scales were modelled. At rst, a numerical model was developed to determine the elastic properties of di erent carbon nanotubes (CNTs) i.e. Pristine and defective single wall (SWCNTs), double wall (DWCNTs), and multiwall (MWCNTs) for zigzag and armchair con gurations. CNTs atomic geometry was replicated with an equivalent space frame structure (SFS). Co-ordinates de nition of SFS of CNTs was developed in MATLAB code and transferred to the nite element analysis (FEA) software 'ANSYS'. The basic entity of SFS, C-C chemical bond was designed as a circular beam of orthotropic properties. The properties were determined by linking the energy equation of molecular mechanics to structural mechanics along with the parametric study. The van der Waals forces between inter-shell of DWCNTs and MWCNTs were modelled as linear elastic springs in a simpli ed way. The simpli ed model avoided the problems due to the nonlinear behaviour of van der Waals forces and improved the performance of the FEA software by computational resources. The e ect of chirality, vacancy defects, di erent diameters and numbers of walls on elastic properties of CNTs were calculated, tabulated and compared with each other. The result of the proposed SFS model with orthotropic properties was compared with others result. The SFS model is found better than the equivalent shell model as the defects can be placed at the exact location and a more realistic behaviour could be predicted. The SFS models could be developed with any type of defects, a number of walls, van derWaals and agglomerated forms with variable geometries. Using the space frame structures (SFS) of SWCNTs, the nanoscale RVE of PAN nano bre doped with SWCNTs was modelled. Simulated results of nanoscale RVEs were used to determine the equivalent properties of p-SWCNTs and f-SWCNTs doped nano bres, which were further used in microscale RVE models. Four micro scale RVEs were developed to represent the random and aligned PAN nano bres mats, PAN nano bres mat doped with p-SWCNTs and f-SWCNTs aligned PAN nano bres mat in epoxy matrix. Analysed micro scale RVEs provided equivalent properties of interlaminar regions developed with random and aligned PAN nano bres mat, PAN doped with p-SWCNTs and f-SWCNTs aligned nano bres mat. At the macro scale, MNHCs were de- veloped with equivalent interlaminar regions and analysed. The results of the simulated MNHCs were compared with experimentally obtained results. The results of the experimental study suggested that aligned nano bres with reduced diameter improved the properties of interlaminar region noticeably than the random nano bres mat of the same volume fraction. Aligned nano - bres successfully placed the pristine and functionalized SWCNTs within the multiscale hybrid composites which signi cantly improved the properties of the multiscale hybrid composite. Results of the multiscale modelling were in line with the experimental results, which could be useful in extending the small- scale theoretical results to the real-life applications.
Improving polysulfone membrane resistance to carbon dioxide induced plasticization during natural gas separation using functionalized carbon nanotubes
(2019) Aberefa, Oluseyi Adebisi
Commercial natural gas, generally methane (CH4), is described as the most efficient energy source with a calorific value per mass of approximate 50.1 MJ/kg. However, raw natural gas is made up of mostly methane and a considerable quantity of other components like C2+, CO2, water and hydrogen sulphide (H2S) in varying composition from well to well depending on the geographical location and condition. Membrane technology for gas separation technology has become an acceptable method for CO2 removal from natural gas. Majority of commercial natural gas separation membrane systems are polymeric due to processing feasibility and low cost. However, conventional polymeric membranes have reached a trade-off threshold between permeability and selectivity, and of great concern is CO2 induced plasticization due to harsh industrial conditions such as high feed pressure. The addition of carbon nanotubes (CNTs) into polymers appears to offer a unique solution to the deficiencies of conventional polymeric membrane systems. In this study, carbon nanotubes (CNTs) were produced using a catalyst-assisted chemical vapour deposition method. Ferrocene was used as the catalyst. Effects of carbon sources (acetylene and methane) and production conditions (temperature and type of carrier gas) on the physicochemical property of as-produced CNTs were investigated using field emission scanning electron microscopy (FESEM), energydispersive X-ray spectroscopy (EDS), electronic precision balance (EPB) and Raman spectroscopy. The best of as-produced CNTs was purified and functionalized using carboxylation protocol. The surface chemistry, thermal stability, textural property and crystallinity of the functionalized CNTs (FCNTs) were obtained using Fourier transform infrared spectroscopy (FTIR), thermo-gravimetric analysis (TGA), N2 physisorption at 77 K and X-ray diffraction (XRD), respectively. CNT produced from methane and argon at 900 oC displayed the best quality with ID/IG ratio of 0.17 while the CNT produced from acetylene and mixture of argon and hydrogen at 1000 oC has the highest yield of 1.78 mg/s. FTIR confirms successful functionalization of CNTs. The degree of functionalization obtained from TGA is consistent with that of EPB. N2 physisorption at 77 K indicates an increase in pore volume and average pore size of the FCNTs indicating more adsorption sites for the adsorbate. Thereby suggesting that FCNT could be a good filler in membrane synthesis for gas separation. Dense mixed matrix membranes (MMMs) were synthesized by incorporating functionalized CNTs (FCNTs) at different wt. % (0.2, 0.5, 1.0, and 1.5) into polysulfone (PSF) using evaporation method. The MMMs were characterized using field emission scanning electron microscopy (FESEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), atomic force microscopy (AFM) and texture analysis (TA). Single gas permeation experiment was conducted using a custom-built permeation set-up via constant volume variable pressure technique while mixed gas permeability was measured on a constant pressure variable volume gas permeation apparatus. Surface and cross-section morphology of the MMMs as depicted by FESEM show that the membranes are dense, indicating that the membranes consist of dense structure whose porosity is not observable under an electron microscope. Depth-at-max analysis of AFM images of the synthesized membranes further supports that the pores of the MMMs possess dense structure. TGA indicates improved thermal stability of the MMMs with increasing wt. % loading of FCNTs. DSC results show that the glass transition temperature (Tg) of the MMMs was also improved with the addition of FCNTs. However, the increase in wt. % loading of FCNTs does not significantly increase the Tg of the MMMs. Tensile strength and Young’s modulus of the MMM obtained from TA show an increase in these mechanical properties with the addition of FCNTs. Single gas permeation results indicate an increase in CO2 permeability as the wt. % loading of FCNTs increases up to 1.0 wt. % loading. Mixed gas separation shows similar trend without sacrificing CO2/CH4 selectivity. CO2 induced plasticization of the membranes was investigated experimentally and by phenomenological modelling. The sorption isotherms showed a typical dual-mode sorption model behaviour for all the types of synthesized membranes with the CO2 concentration increasing rapidly at low pressures, which indicated a hole-filling of the Langmuir sites. At higher pressure, the rate of increase in the concentration declines due to the saturation of the Langmuir sites, the further increase in the concentration at higher pressure is because of the penetrant sorption in Henry’s law sites. The permeation isotherm of pure PSF indicated plasticization onset at CO2 pressure of 12 bar. The MMMs showed no sign of plasticization over the pressure range tested (0-20 bar). This indicated an improvement in the CO2 plasticization resistance of PSF by the addition of FCNTs. The developed model assumed three possible interface interactions in the MMMs; polymer matrix – polymer matrix, CNT – polymer matrix, and aligned CNT – CNT interface interactions. The model also accounted for the plasticization of the membrane. The model equation was solved by using the Levenberg-Marquardt algorithm in the Matlab environment to obtain the plasticization potential and the fraction of the gas held in Langmuir sites that have mobility within the membrane. The model CO2 permeability is in good agreement with CO2 permeability obtained experimentally. The PSF plasticization potential obtained is similar to ones reported in the literature. The fraction of the gas held in Langmuir sites that have mobility within the membrane increases with an increase in FCNT wt. % loading which shows high diffusivity through the microvoids with respect to diffusivity through the polymer matrix. This is an indication of an increase in Langmuir sorption sites for the penetrant thereby improving gas permeabilit
Synthesis, characterization and application of 2d semiconducting layered inorganic nanostructures of In2S3 and WS2 in gas sensing
(2018) Gqoba, Siziwe Sylvia
2D semiconductor nanostructure based chemical sensors hold the promise of portable, fast, low power, simple and low cost technologies for the detection of volatile organic compounds (VOCs) and gases. Detection, monitoring and quantification of these analytes are important for the improvement of the quality of human life, safety and the surrounding environment. Their electrical conductance is extremely sensitive to changes in the local chemical environment and can be chemically modified to increase selectivity. Nanostructures have tunable band gaps and exhibit new and improved properties at the quantum confinement limit. The band gap is affected by the size, shape, dimensionality and chemical composition of the nanostructures. So, precise control of these factors is achieved by manipulating reaction parameters like time, temperature, choice of precursors and choice of capping agent as well as concentration. In this study, we unravel the effect of reaction parameters on the structural, optical and morphological properties of In2S3 and WS2 nanostructures during colloidal synthesis. The reaction parameters under investigation were time, concentration, solvent or capping agent and precursor. For instance, different shapes of ß-In2S3 were obtained for mono- and bi-ligand systems, reaction time, concentration of the precursor and solvent. Capping agents influence the growth kinetics and the shape of nanostructures. Well defined hexagonal ß-In2S3 nanostructures of the tetragonal phase were obtained as a function of time with elemental S and indium chloride reacted at 1:1 mole ratio in oleylamine (OLA) medium. OLA, an alkylamine played the triple role of the reducing agent, solvent and capping agent. An increased amount of S to In3+ proved to be an unfavourable condition for the formation of the hexagonal shape as seen with the 1:2 mole ratio. Hexadecylamaine (HDA) and octadecylamine (ODA), alkylamines like OLA were also used in separate experiments. The hexagonal shape like with OLA evolved with time for ODA while it never materialized for HDA. Dodecanethiol (1-DDT), a thiol ligand produced microspheres as a function of time. These alkylamines were then each used in bi-ligand systems with a controlled amount of 1DDT at a 1:1 mole ratio of In3+ and S. For OLA/1-DDT, the hexagonal morphology was favoured and retained regardless of the duration of the reaction time. However, the hexagonal shape transformed into nanorods with prolonged reaction time for the ODA/1-DDT combination. The morphology was rather elusive for HDA/1-DDT system even at extended reaction time. HDA and ODA yielded the cubic phase of ß-In2S3 in both the mono- and biligand systems. An increased amount of 1-DDT to OLA resulted in mixed morphologies regardless of the reaction time, once again proving the importance of concentration. It is interesting to note that hexagonal nanostructures were retained when 1-DDT was used as a source of S (1:1) with OLA serving a triple role. In the case of WS2, only OLA was used as a capping agent and the variation of reaction of time yielded nanoflowers, nanoflake-like and nanorod-like structures. The nanostructures of these semiconductors were used as components in chemi-resistive sensors for the detection and identification of NH3 gas and selected VOCs. Unlike their oxide counterparts, their gas sensing potential has been largely overlooked despite their capability of operating at room temperature. Preliminary studies on ß-In2S3 sensors based on the 330 min nanostructures showed gas sensing potential towards formaldehyde vapour. In the case of WS2 nanostructures, all the sensors regardless of the reaction time exhibited gas sensing potential. However, the percentage of that response was based on the morphology which was associated with the reaction time. For instance, the microflower morphology obtained at 15 and 45 min displayed the best response compared to 60, 180 and 240 min. However, 45 min had a higher response than 15 min because the ‘petals’which make up the microflowers had opened up. This meant that the reaction not only took place on the surface of the microflower but also in between the ‘petals’. It is well known that humidity is an interferant and can either reduce or improve a sensor’s performance. The sensor’s performances towards NH3 varied depending on the relative humidity they were operating under. Annealing of the sensors showed improved performance at lower temperatures while higher temperatures led to reduced performance. OLA, a long chain ligand renders the semiconductor an insulator thereby reducing its performance. Effect of replacement of OLA with shorter chain ligands on the gas response was also investigated. Mercaptoethanol (ME) and ethanedithiol (1, 2EDT) were used as the short chain ligands and showed improved response towards a lower concentration of NH3. Application of the OLA/WS2 sensors in a tristimulus analysis proved that they can be used in chemical sensor arrays despite the fact that they are made of the same chemical composition. The various morphologies obtained at different time intervals provided the distinguishing factor between the nanostructures.
Experimental assessment of emulsification stability during enhanced oil recovery in the presence of polymer (PMMA) and nanoparticles (ZnO)
(2018) Muzang, Emmaual Ndakwe
Among several methods proposed as secondary or tertiary recovery techniques, water flooding has proven to be less costly in terms of operating costs but often results in lower recovery value and sweep efficiency. Water flooding may be preferred when limited economic resources exist and/or for the displacement of oils with similar mobility to water. In heavy oil reservoirs the low mobility of the oil makes this method inefficient as water mobility is much greater than the oil leading to unfavorable mobility ratio, large viscosity difference which may cause channeling or fingering in the reservoir sweep and an early water breakthrough. Surfactant injection has been considered as an attractive alternative in order to attain higher oil recovery volumes. For instance when a stable oil-in-water emulsion is injected in a reservoir after a secondary recovery with water flooding, it tend to flow through the same high permeable water-wet zone previously covered by water flooding and the oil droplets get trapped in the pore throats changing the wettability of the rock surface and decreasing the permeability of the invaded zone. As a result water injected afterwards is forced to flow through less permeable zones that were not swept previously and lead to an oil recovery increase. Often surfactant injection is useful for improving the sweep in the reservoir. It has been found that polymer injection may decrease further water mobility, thus contributing to a favorable mobility ratio and optimized volumetric sweep efficiency. Though injection of polymer may not reduce the residual oil saturation in the reservoir, it results in an improvement of displacing front stability and better oil recovery compared to other techniques such as water flooding. Polyacrylamide copolymers or hydrolyzed polyacrylamide (HPAM) polymers are by viii far the most widely used polymer for EOR but they are still expensive. Poly (methyl methacrylate) or PMMA was considered for this work since it’s relatively cheaper and readily available. On the other hand emulsions can be typically stabilized by the use of emulsifiers that are usually added in volumes (up to less than 1%wt) in order to lower the operational cost of the recovery process. In particular, emulsions stabilized by solid particles (nanoparticles) have become recently an attractive alternative that provides stabilization in oil-in-water and water-in oil emulsions by reducing the interfacial tension and the capillary pressure, but are still relatively less covered in open literature. Therefore this dissertation considers oil-in-water/water-in-oil emulsions stabilized by nanoparticles and polymers to extent knowledge in this area. Therefore; this study investigates the stability of crude oil/water emulsions in the presence and absence of polymer and nanoparticles using crude oil blend received from NATREF with average API gravity of 35 and in particular assess the influences of the temperatures, brine concentration, polymer/nanoparticle concentration, oil/water ratio and stirring mechanism. It further investigates whether or not the combination of polymers and nanoparticle can provide a more stable emulsion than polymers only. Poly (methyl methacrylate) or PMMA polymer and zinc oxide (ZnO) nanoparticle were used. Furthermore droplet size distribution was analyzed using a microscope to see how tight the emulsions are and the droplets distribution.
Noise in nanosystems
(2018) Mehay, Timothy Patrick
With the increasing interest in nanosystems in various branches of science, the question naturally arises as to whether such systems will have practical applications. At the nano-scale all physical measurements are fundamentally constrained by the Heisenberg uncertainty relations. In addition to these fundamental limitations, ﬂuctuations or noise arising from various physical processes act so as to further obscure the accuracy with which we can perceive the physical world. The goals of this thesis are to investigate the consequences of these ﬂuctuations in physical systems, and to develop methods enabling the study of physical processes associated with these ﬂuctuation phenomena. I begin by developing the necessary framework with which to describe these random ﬂuctuations. After discussing the necessary prerequisites, I develop a probabilistic model of charge-density ﬂuctuations. This model draws on results from kinetic theory and Eulerian perturbation theory. It is found that under certain assumptions regarding the nature of the ﬂuctuations, the equation of motion governing charge-density ﬂuctuationsmaybesolvedanalytically. Ithendevelopamethodenablingthestudy of the statistical correlation of density ﬂuctuations using the ﬂuctuationdissipation theorem. This approach is then applied to the study of density ﬂuctuations in graphene using the electron energy-loss spectrum (EELS) of ideal graphene. It is found that the autocorrelation function (ACF) of density ﬂuctuations contains information related to both plasmonic resonance and to the noise present in the EELS. I conclude this thesis by developing a formalism which allows for the calculation of the dephasing rate of a systemusingonlytheEELS.Thisapproachhasthebeneﬁtofenablingauniformtreatmentofdephasinginbothhigh-temperatureandlow-temperature regimes, and contains both electron-electron and electron-phonon interactions by virtue of the EELS, which are the primary contributions to the dephasing rate in low-dimensional semiconductor systems. The use of this approach is then illustrated using the EELS of ideal graphene. Given the generality of the ﬂuctuation-dissipation theorem, many of the methods discussedinthisworkmaybeextendedtostudyarbitraryﬂuctuationphenomena in a wide variety of systems.
Optimum design parameters and mechanical properties of polymeric nanocomposites using NSGA-II optimization method
(2018) Rabothata, Mahlatse Solomon
The aim of this work was to develop a method for optimizing both design parameters and mechanical properties of polymer based nanocomposites using numerical multi-objective optimization (MOO) methods. The main objective was to simultaneously maximize the elastic modulus and the tensile strength of nanocomposites. The rationale behind focusing on these particular properties is that they play a signiﬁcant role in designing of materials for structural applications. Ji and Zare models of determining the elastic modulus and tensile strengths of polymeric nanocomposite materials were respectively used for the formation of the objective functions for numerical optimization. The design variables (i.e major factors aﬀecting the given mechanical properties) were identiﬁed as the diameter of nanoﬁllers, thickness of the interphase region, nanoﬁllers loading as weight fraction, elastic modulus of the interphase, interfacial shear stress and the orientation factor of the nanoﬁllers. The Fast Non-dominated Sorting Genetic Algorithm (NSGA-II) approach in MATLAB was used to maximize the objective functions by obtaining the optimum solutions of the given design variables. The optimization model was able to successfully ﬁnd optimum solutions of the design variables. Furthermore, the overall optimization results were found to be in good agreement with the available experimental results from literature. The proposed optimization model was found to be signiﬁcantly accurate in ﬁnding the optimum values of the design variables for improving the mechanical properties of nanocomposites. The optimum values of the design variables were determined to be 2.12 – 2.96 nm for the thickness of the interphase, 5.41 – 7.01 nm for the diameter of the nanoﬁllers, 2.95 – 4.69 wt.% for the nanoﬁllers loading, and 1 for the nanoﬁllers orientation factor. In addition, the results further showed that nano-reinforcements such as multi-wall car-bonnanotubes(MWCNTs)yields high elastic modulus of the interphase and interfacial shear stress.
CNT Doped PAN Nanofibre strengthened Aramid-pp composites: Improved interlaminar properties
(2018) Ncube, Mkhulili
This study focused on the strengthening of aramid polypropylene hybrid composites using both electrospun PAN and CNT doped PAN nanomat. The strengthening of the aramid-polypropylene (PP) composites with both aligned and randomly distributed nano bres resulted in the improvement of the tensile strength, exural strength, impact energy absorption and interlaminar shear strength (ILSS). However, compared to the randomly distributed 0.5% PAN nano bre strengthened aramid-PP composites, the aligned PAN nano bre strengthened aramid-PP composites had higher mechanical properties with improvements in tensile strength by 6%, exural strength by 5%, impact energy absorption by 7% and ILSS by 3%. The doping of PAN nanomat with pristine and functionalized CNTs resulted in an improved mechanical properties of the hybrid composites with those strengthened with functionalized CNTs achieving higher mechanical properties. With the increase in CNT concentration in the CNT doped PAN nanomat strengthened hybrid composite the mechanical properties increased. Compared with PAN reinforced aramid-PP composites, the addition of PAN doped with 0.5% functionalized CNTs resulted in an increase in tensile strength by 15%, exural strength by 35%, impact absorption energy by 26% and ILSS by 32%. It was found that the dominant mechanism of failure for aramid-PP composites without PAN/CNT reinforcement was due to interfacial debonding. This study shows that the use of aligned electrospun nano bres help to improve the imterlaminar properties of the the hybrid composites. Functionalization of CNTs greatly improves the bre-matrix interaction and thus greatly reducing failure by interfacial debonding. Overall, the doping of aligned PAN nano bres with functionalized CNTs resulted in improvement in interlaminar and mechanical properties of the hybrid composites

3. Electronic Theses and Dissertations (ETDs) - All submissions

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