Density functional theory (DFT) provides an affordable computational tool to understand electronic structure of various molecules and solids. However, the use of DFT is still challenging to investigate nanomaterials of intermediate size that are too small to assume translational symmetry and too large to be considered as molecules. This thesis focuses on developing cost-effective but accurate computational methods for nanomaterials and using the methods to rationalize and predict experimental behaviors. A notable difference of a nanomaterial from its bulk counterpart is that its properties are exceptionally sensitive to the dielectric environment, requiring a proper treatment of the surrounding dielectrics for an accurate understanding. The consequences of heterogeneous dielectric screening on transition metal dichalcogenides are studied by developing a new theory based on classical electrostatics, which closely reproduced the band gaps and optical gaps calculated by the ab initio GW approximation and the Bethe-Salpeter equation (BSE). The relative insensitivity of the first optical transition energy observed by experiments was explained for the first time in terms of the cancellation effect of changes of the band gap and the exciton binding energy. The theory of heterogeneous dielectric environments is further developed to be used in an atomistic calculation of layered hybrid organic-inorganic lead halide perovskites via a tight-binding GW-BSE method. The binding energies of trions and biexcitons were also calculated using the stochastic variational method to give spectrum peak energies that show a good agreement with reported experimental measurements. Lastly, the tight-binding GW-BSE method is generalized into an atomistic, semiempirical approach to calculate the electronic structure and optical spectra of arbitrary nanomaterials, termed semiempirical GW (sGW) and BSE (sBSE).

Semicrystalline polymers constitute the majority of the commercially manufactured polymers, mostly known as commodities with low modulus and inferior properties. A robust approach used in tailoring such commodity’s properties for more advanced applications is through the incorporation of inorganic nanoparticles (NPs). Over the past half century, polymer nanocomposites (PNCs) have attracted extensive interest in fundamental research and technological applications. However, NPs have been found to result in complicated alterations in the semicrystalline polymer crystallization kinetics, and their crystalline morphology, which could either synergistically or adversely affect the final composite properties. A comprehensive understanding of this topic is still lacking, which with one could tune the final polymer properties for various cutting-edge applications. In this dissertation, we focus on the crystallization kinetics of semicrystalline PNCs and the connection between the morphology and the mechanical (and rheological) properties of such hybrid systems. First, we control the NP dispersion and self-assembly in a semicrystalline poly(ethylene oxide) (PEO) matrix using both bare and polymer-grafted NPs. We show that bare NPs (with different sizes) and unimodal poly(methyl methacrylate) (PMMA)-g-SiO2 NPs uniformly disperse in a PEO matrix because of the favorable interaction between the matrix and the NP surface (or the PMMA brush). Grafting the latter NPs with a short dense polystyrene brush that is immiscible with PEO while varying the PMMA grafting parameters induces self-assembly and leads to various NP structures: well-dispersed, connected sheets, strings, and large aggregates. Next, we systematically investigate the role of bare and self-assembled grafted NPs on the spherulitic growth kinetics of semicrystalline polymers. In all cases, the incorporation of spherical NPs suppresses the polymer growth kinetics. Using rheological measurements, we show that the reduction in growth is mainly attributed to the NPs increasing the melt viscosity; whereas, they minimally alter the secondary nucleation process. Surprisingly, the PNC growth kinetics is suppressed in two apparently universal manners when plotted as a function of confinement: NP dominated and brush-controlled regimes. Bare NPs and large aggregates of polymer-grafted NPs appear to nearly follow the same dependence for the role of additives on polymer viscosity, weakly suppressing the growth kinetics. On the other hand, all the other self-assembled NP structures showed much stronger growth reductions because of the larger increase in the melt viscosity by the chemically bonded brush. Given our prior knowledge of the PNC growth kinetics, we then draw generalized trends for the role of bare and grafted NPs in nucleating semicrystalline polymers. This is achieved by comparing the polymer crystallization kinetics in the presence of large, asymmetric, immobile fillers (selected from the well-established literature) to those smaller, spherical, mobile NPs (examined throughout this thesis). Generally, NPs serve as heterogenous nucleation sites when incorporated at smaller amounts, leading to accelerated crystallization kinetics. At larger filler contents, NPs confine the polymer chains into smaller domains and become more susceptible to aggregation, which results in antinucleating effects and suppressing the crystallization rate. Such competing effects result in a maximum nucleation efficiency at moderate filler contents. It is also worth noting that the degree of nucleation enhancement and subsequent suppression depends on the system and is controlled by NP dispersion, geometry, and surface chemistry. For example, one- and two-dimensional NPs usually result in a higher nucleation power compared to spherical NPs. Another major difference between mobile and immobile fillers is that when slowly crystallizing from the melt, the smaller diffusive NPs can be segregated and ordered into hierarchal structures (interlamellar sheets and interfibrillar and interspherulitic aggregates). This provides a much richer class of materials with a kinetics route in controlling NP assemblies. Finally, we create robustly toughened semicrystalline polymers by confining the PEO crystallization using a densely grafted PMMA brush (i.e., PMMA-g-SiO₂) with different molecular weights. For comparison, we prepare linear PMMA/PEO blends with equivalent PMMA molecular weights and volume fractions to those of the nanocomposites. We show that PMMA-g¬-SiO₂ NPs surpass linear PMMA homopolymers in terms of toughening the PEO matrix, with the grafted system experiencing relatively higher connectivity and lower crystallinity. At moderate confinement, the nanocomposite sustains a maximum modulus increase of 42%, with around a 200-fold increase in the PEO toughness. This provides a novel route for toughening semicrystalline polymers using noncrystallizable polymer-grafted NPs.

Polymer nanocomposites (PNCs) have found their way into our everyday lives in a long list of applications, including airplane parts and car tires. This is due to their unique properties of combining the strengths of their constituents – elasticity and stiffness – while mitigating their weaknesses – softness and brittleness. In the past few decades, they have generated more interest due to the discovery that the PNCs’ optical, electrical, and a host of other properties can be tuned for specific use by controlling the assembly and dispersion of nanoparticles (NPs) within the host polymer matrix. The grafting of some of the matrix chains onto the surface of the NPs not only improves NP miscibility but also grants an additional handle tocontrol the self-assembly of NPs. However, at present, there remains many open questions in the field of these novel PNCs. For instance, it is commonly believed that long enough matrix polymers of length P will spontaneously dewet a chemically identical polymer layer, comprised of sufficient chains of length N , end-grafted to a flat surface (”brush”). This entropically driven idea is frequently used to explain experiments in which 10-20 nm diameter polymer-grafted NPs are observed to phase separate from homopolymer matrices for P/N⪆4. At lower grafting densities, these entropic effects are also thought to underpin the self-assembly of grafted NPs into a diverse set of structures. To explore the validity of this picture, a two-pronged approach is used in this thesis, exploring such systems from both a single NP and a multi-NP point of view in order to find novel methods for understanding and controlling NP dispersion in polymers. In each of the chapters, we employ coarse-grained Molecular Dynamics (MD) simulations to understand the self-assembly and dispersion behavior in PNCs, with the experimental analog being primarily polystyrene (PS) grafted silica NPs in PS matrices. We start by investigating the entropic effects of P/N on the brush of a single grafted NP, taking advantage of an indirect umbrella sampling method (INDUS) to quantify matrix density fluctuations. This method essentially makes use of an external biasing potential to mimic the dewetting of the brush. We find for the first time that entropic P/N effects can be identified at the single NP level and is primarily surface driven. INDUS is later extended to two-body and many-body NP systems, to understand the role of NP surfactantcy in the self-assembly of grafted NPs and create free-energy profiles for a range of inter-NP separations. Finally, results from a comprehensive series of large-scale multi-NP simulations, where we consider NPs in the ≈ 5nm and ≈ 10nm size range. For the smaller NPs, we find no evidence of phase separation even for P/N = 10 in the absence of attractions. Instead, we discover that we are able to recreate most of the experimentally observed structures when allthe polymer chain monomers are equally attractive to each other but repel the NPs. Only when the NPs are in the ≈ 10nm size range that we are able to access the phase separated morphologies. Our results thus imply that experimental situations where the grafting density is low are dominated by the surfactancy of the NPs, which is driven by the chemical mismatch between the inorganic core and the organic ligands (the graft and free chains are chemically identical). Entropic effects, i.e. the translational entropy of the NPs and the matrix, the entropy of mixing of the grafts and the matrix, and the conformational entropy of the chains appear to thus play a second order effect even in the context of these model systems. Each of these insights provides details around controlling the organization and assembly of NPs in polymers for the purpose of improving their mechanical properties, all while changing the way in which the material is designed.

A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, in fulfilment of the requirements for the degree of Master of Science in Engineering. Johannesburg, 21 July 2016 / The use of supercapacitors for energy storage is an attractive approach considering their ability to deliver high levels of electrical power, unlimited charge/discharge cycles, green environmental protection and long operating lifetimes. Despite the satisfactory power density, supercapacitors are yet to match the energy densities of batteries and fuel cells, reducing the competitiveness as a revolutionary energy storage device. Therefore, the biggest challenge for supercapacitors is the trade-off between energy density and power density. This presents an opportunity to enhance the electrochemical capacitance and mechanical stability of an electrode. Previous attempts to get around the problem include developing porous nanostructured electrodes with extremely large effective areas. One of the emerging high-power supercapacitor electrode materials is molybdenum disulfide (MoS2), a member of the transition-metal dichalcogenides (TMDs). Its higher intrinsic fast ionic conductivity and higher theoretical capacity have attracted a lot of attention, particularly in supercapacitors. In addition to double-layer capacitance, diffusion of the ions into the MoS2 at slow scan rates gives rise to Faradaic capacitance. Analogous to Ru in RuO2, the Mo center atom displays a range of oxidation states from +2 to +6. This plays an important role in enhancing charge storage capabilities. However, the electronic conductivity of MoS2 is still lower compared to graphite, and the specific capacitance of MoS2 is still very limited when used alone for energy storage applications. As evident in several literature reports, there is a need to improve the capacitance of MoS2 with conductive materials such as carbon nanotubes (CNT), polyaniline (PANI), polypyrrole (PPy), and reduced graphene (r-GO). Carbon nanospheres (CNS) have, in the past, improved the conductivity of cathode material in Li-ion batteries, owing to their appealing electrical properties, chemical stability and high surface area. The main objective of this dissertation research is to develop nanocomposite materials based on molybdenum sulphide with carbon nanospheres for pseudocapacitors with simultaneously high power density and energy density at low production cost. The research was carried out in two phases, namely, (i) Symmetric pseudocapacitors based on molybdenum disulfide (MoS2)-modified carbon nanospheres: Correlating physico-chemistry and synergistic interaction on energy storage and (ii) The effects of morphology re-arrangements on the pseudocapacitive properties of mesoporous molybdenum disulfide (MoS2) nanoflakes. The physico-chemical properties of the MoS2 layered materials have been interrogated using the surface area analysis (BET), scanning electron microscopy (SEM), transmission electron microscopy (TEM), x-ray diffraction (XRD), Raman, fourier-transform infrared (FTIR) spectroscopy, and advanced electrochemistry including cyclic voltammetry (CV), galvanostatic cycling with potential limitation (GCPL), repetitive electrochemical cycling tests, and electrochemical impedance spectroscopy (EIS). In the first phase, Molybdenum disulfide-modified carbon nanospheres (MoS2/CNS) with two different morphologies (spherical and flower-like) have been synthesized using hydrothermal techniques and investigated as symmetric pseudocapacitors in aqueous electrolyte. The two different MoS2/CNS layered materials exhibit unique differences in morphology, surface areas, and structural parameters, which have been correlated with their electrochemical capacitive properties. The flower-like morphology (f-MoS2/CNS) shows lattice expansion (XRD), large surface area (BET analysis), and small-sized nanostructures (corroborated by the larger FWHM of the Raman and XRD data). As a contrast to the f-MoS2/CNS, the spherical morphology (s-MoS2/CNS) shows lattice contraction, small surface area with relatively large-sized nanostructures. The presence of CNS on the MoS2 structure leads to slight softening of the characteristic Raman bands (E12g and A1g modes) with larger FWHM. The MoS2 and its CNS-based composites have been tested in symmetric electrochemical capacitors in aqueous 1 M Na2SO4 solution. CNS improves the conductivity of the MoS2 and synergistically enhanced the electrochemical capacitive properties of the materials, especially the f-MoS2/CNS-based symmetric cells (most notably, in terms of capacitance retention). The maximum specific capacitance for f-MoS2/CNS-based pseudocapacitor show a maximum capacitance of 231 F g-1 with high energy density 26 Wh kg-1 and power density 6443 W kg-1. For the s-MoS2/CNS-based pseudocapcitor, the equivalent values are 108 F g-1, 7.4 Wh kg-1 and 3700 W kg-1. The high-performance of the f-MoS2/CNS is consistent with its physico-chemical properties as determined by the spectroscopic and microscopic data. In the second phase, Mesoporous molybdenum disulfide (MoS2) with different morphologies has been prepared via a hydrothermal method using different solvents, water or water/acetone mixtures. The MoS2 obtained with water alone gave graphene-like nanoflakes (g-MoS2) while the other with water/acetone (1:1 ratio) gave a hollow-like morphology (h-MoS2). Both materials are modified with carbon nanospheres as conductive materials and investigated as symmetric pseudocapacitors in aqueous electrolyte (1 M Na2SO4 solution). Interestingly, a simple change of synthesis solvents confers on the MoS2 materials different morphologies, surface areas, and structural parameters, correlated by electrochemical capacitive properties. The g-MoS2 exhibits higher surface area, higher capacitance parameters (specific capacitance of 183 F g-1, maximum energy density of 9.2 Wh kg-1 and power density of 2.9 kW kg-1) but less stable electrochemical cycling compared to the h-MoS2. These findings have opened doors for further exploration of the synergistic effects between MoS2 graphene-like sheets and CNS for energy storage. / MT2017

FePt/B4C multilayer thin films are deposited on silicon substrates using magnetron sputtering with different B4C layer thickness. Experimental results suggest that the B4C layers effectively serve as spacers to separate the FePt layers, making the multilayer configuration stable even after film annealing at elevated temperatures. On the other hand, B and C are found to be incorporated into the FePt layer, which is responsible for the FePt grain growth confinement and grain separation, and eventually affects the properties of the composite film. Based on the experimental results of multilayer composite film, particle (FePt)/matrix (B4C) monolayer composite thin films on Si substrate are synthesized, in which a record coercivity of 2200 Oe is achieved compared to similar system. The size uniformity of the FePt nanoparticles, the well-defined particle-particle separation, together with the good magnetic property and high temperature thermal stability of the overall composite film, make it a very promising candidate for the ultrahigh density magnetic storage media. / Functional nanostructures serve as the basic building blocks for nanodevices and significant efforts have been devoted to their morphology control and properties optimization. In present study, four functional nanostructures, i.e., FePt/B4C multilayer composite film, particle (FePt)/matrix (B4C) monolayer composite film, Ga-doped ZnO nanowire arrays, and CdSe nanotube arrays are designed, synthesized and characterized in detail, in which the first two are expected to be prominent candidates for ultrahigh-density magnetic storage media while the later two have potential applications in solar energy conversion. / Semiconductor based one-dimensional nanostructures are investigated as promising building blocks for solar energy conversion devices. Two aspects are explored, aiming at increasing the energy conversion efficiency, i.e., facilitating electron transport and enhancing photon absorbing. In the first case, large area Ga-doped ZnO nanowire arrays are grown on transparent conducting substrate. Experimental results reveal the well-aligned array morphology and the uniform Ga concentration in these nanowires. In particular, direct I-V measurements performed on single nanowire-on-ITO substrate disclose its Ohmic contact with the conducting substrate and the significant conductivity improvement compared to undoped ZnO nanowire, In the second case, a novel synthesis strategy for nanotube arrays is developed and CdSe is used for demonstration, which material possessing more appropriate band gap as effective light harvester compared to that of materials for existing semiconductor nanotube arrays. The controllable tube wall thickness that can be increased until continuous CdSe porous network is obtained. The experimental results suggest a nanotube array formation mechanism that can be generally applied to a wide range of materials. / Zhou, Minjie = 功能纳米结构在磁性和能源方面的应用 / 周民杰. / Adviser: Li Quan. / Source: Dissertation Abstracts International, Volume: 72-11, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2009. / Includes bibliographical references (leaves 91-100). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [201-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese. / Zhou, Minjie = Gong neng na mi jie gou zai ci xing he neng yuan fang mian de ying yong / Zhou Minjie.

Si-based anodes have recently received considerable attention for use in Li-ion batteries, due to their extremely high specific capacity - an order of magnitude beyond that offered by conventional graphite anode materials. However, during the lithiation process, Si-based anodes undergo extreme increases in volume, potentially by more than 300 %. The stresses produced within the electrode by these volume changes can damage the electrode binder, the active Si particles and the solid electrolyte interphase (SEI), causing the electrode to rapidly fail and lose capacity. These problems can be overcome by producing new anode materials incorporating both Si and C, which may offer a favorable combination of the best properties of both materials, and which can be designed with internal porosity, thereby buffering the high strains produced during battery charge and discharge with minimal overall volume changes. However, in order to develop useful anode materials, we must gain a thorough understanding of the structural, microstructural and chemical changes occurring within the electrode during the lithiation and delithiation process, and we must develop new processes for synthesizing composite anode particles which can survive the extreme strains produced during lithium intercalation of Si and exhibit no volume changes in spite of the volume changes in Si. In this work we have developed several novel synthesis processes for producing internally porous Si-C nanocomposite anode materials for Li-ion batteries. These nanocomposites possess excellent specific capacity, Coulombic efficiency, cycle lifetime, and rate capability. We have also investigated the influence of a range of different parameters on the electrochemical performance of these materials, including pore size and shape, carbon and silicon film thickness and microstructure, and binder chemistry.

It is common knowledge that water is one of the basic needs for human beings. However, the consumption of contaminated water can lead to waterborne diseases and fatalities. It is, therefore imperative to constantly monitor the quality of potable water. There are numerous technologies used for water quality monitoring. These technologies are relatively effective however these tests are expensive and complex to use, which then require experienced technicians to operate them. Other tests are not rapid, making consumers of water susceptible to waterborne diseases. In this study, dye-doped, surface functionalized silica nanoparticles (SiNPs) and surface-functionalized magnetic nanocomposites (MNCs) were proposed as materials that can be applied in order to reduce the time taken to get results as well as to make the processes less complex and portable. The aim of this study was to synthesize and characterize surface functionalized dye-doped SiNPs and surface functionalized MNCs for detection and preconcentration of in water. Additionally, proof of concept had to be shown using the synthesized materials. SiNPs were the materials of choice due to their easily functionalized surfaces and their strong optical properties. SiNPs are photostable and they do not leach in solution due to the inert nature of the silica matrix in aqueous media. MNCs were chosen as materials of choice for preconcentration of E. coli in water because they are easy to synthesize and they can be applied in various biological applications due to their functional groups. SiNPs were synthesized using the water-in-oil microemulsion. The SiNPs were further functionalized with amine and carboxyl groups and avidin. Thereafter, they were bioconjugated with biotinylated anti-E. coli antibodies. The pure and surface functionalized SiNPs were characterized using ATR-FTIR spectroscopy, FE-SEM, HR-TEM, Zeta Sizer, UV-vis spectroscopy and spectrofluorometry. The application of the dye—doped surface functionalized SiNPs in E. coli detection was characterized using the fluorescence plate reader. The SiNPs were spherical and uniform in size. They increased in size as they were being functionalized, ranging from 21.20 nm to 75.06 nm. The SiNPs were successfully functionalized with amine and carboxyl groups as well as with avidin and antibodies. Two methods were investigated for carboxyl group attachment (direct and indirect attachment) and the direct attachment method yielded the best results with a surface charge of -31.9 mV compared to -23.3 mV of the indirect method. The dye loading was found to be 1% after particle synthesis. The optical properties of the Ru(Bpy) dye were enhanced 3 fold when they were encapsulated in the Si matrix. The SiNPs were binding to the E. coli cells and enabled detection. MNCs were synthesized through in-situ polymerization. The MNCs were characterized using ATR-FTIR spectroscopy, SEM, TEM and XRD. The MNCs were successfully functionalized with carboxyl groups. The increase in size of the nanocomposites as seen in SEM images proved that the Fe3O4 was successfully encapsulated in the polymer matrix. The MNCs were proven to be magnetic by a simple magnetism test whereby they were separated in an aqueous solution using an external magnetic field. The antibody-labelled MNCs were binding to the E. coli cells as shown in TEM images. E. coli cells were removed from water at varying concentrations of 1x106 CFU/mL to 1x109 CFU/mL at 10 mL volumes. This study has demonstrated that dye-doped SiNPs amplify the signal of E. coli cells using fluorescence. The study has also demonstrated that the MNCs can be applied in sample preconcentration and enrichment for E. coli detection. However, further studies should investigate and optimize the combination of the two techniques in a point of use device for water quality testing of 100 mL-samples as per the requirement of the SANS 241 standard. / Civil and Chemical Engineering / M. Tech. (Chemical Engineering)

In this dissertation, algorithms for creating estimated potentials for metals and modeling of nano composites are developed. The efficacy of the algorithms for estimated potentials were examined. The algorithm was found to allow molecular dynamic and Monte Carlo modeling to be included in the potential building process. Additionally, the spline based equations caused issues with the elastic constants and Young’s modulus due to extra local minima. Two algorithms were developed for improved modeling of nano composites: one was a random number generation algorithm for initializing polymer, second was a bonding algorithm for controlling bonds between polymer and nano particle. Both algorithms were effective in their tasks. Additionally, the algorithms for improved nano composite modeling were used for preliminary material design of PMMA metal oxide nano composite systems. The results from the molecular dynamic simulations show the bonding between polymer matrix and nanoparticle has a large effect on the Young’s modulus and if this bonding could be controlled, the tensile properties of PMMA-metal oxide nano composites could be tailored to the applications’ requirements. The simulations also showed bonding had caused changes in the density of the material which than effected the energy on the polymer chain and the Young’s modulus. A model was than developed showing the relationship between density and the chain energy, and density and the Young’s modulus. This model can be used for a better understanding and further improvement of PMMA-metal oxide nano composites.

Thesis (PhD)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Novel silicone nanocomposites were prepared using poly(acrylonitrile) (PAN) based reinforcing fibres as well as multi-walled carbon nanotubes (MWCNTs). Compatibility of the fibre fillers with the silicone matrix required the synthesis of novel amphiphilic, organic–inorganic graft copolymers of PAN and poly(dimethylsiloxane) (PAN-g-PDMS). These fibre precursor materials were synthesised via the “grafting through” technique using conventional free radical copolymerisation. The PDMS macromonomer content in the feed was varied from 5 wt% to 25 wt% and the molecular weights of the macromonomer were 1000 g.mol-1 and 5000 g.mol-1. The solvent medium of the precipitation reaction was optimised at a volume ratio of 98% benzene to 2% dimethylformamide (DMF). Successful incorporation of PDMS yielded graft copolymer blend materials of PAN-g-PDMS, blended with PAN homopolymer and unreacted PDMS macromonomer. A gradient elution profile was developed to track the successful removal of the PDMS macromonomer via hexane extraction. The gradient profile showed that as the PDMS content in the feed increased, the number of graft molecules in the blend increased relative to the number of PAN homopolymer molecules. The crystallisability of the PAN segments was shown to decrease as the PDMS content increased. The synthesised polymer was used as precursor material for the electrospinning of fibre fillers. The electrospinning of the precursor material was successfully achieved using 100% DMF as electrospinning solution medium. The amphiphilic nature of the precursor material in DMF resulted in self-assembled aggregate structures in the electrospinning solution. An increasing PDMS content was shown to affect the aggregation of the precursor material, and resulted in an increase in the solution viscosity. The “gel-like” solutions limited the achievable fibre morphological control when altering conventional electrospinning parameters such as voltage, tip-to-collector distance, and solution concentrations. The rapid evaporation and stretching of the solution during electrospinning, combined with the phase segregated amphiphilic molecules in solution and the crystallisation of the PAN segments resulted in (non-equilibrium morphology) fully porous fibres. The crystallinity was shown to decrease after electrospinning of the fibre precursor materials. Successful incorporation of surface oxidised MWCNTs into the electrospun fibres was achieved. The content of nanotubes was varied from 2 wt% to 32 wt%. The MWCNTs reduced the mean fibre diameters by acting as cross-linkers between the PAN segments and increasing the solution conductivity. The nanotubes dispersed well throughout the porous structure of the fibres and aligned in the direction of the fibre axis. Fabrication of silicone composites containing nonwoven and aligned fibre mats (with 8 wt% MWCNTs in the fibres, and without) was successfully achieved. The compatibilisation of the PDMS surface segregated domains allowed excellent dispersion and interaction of the PAN based fibre fillers with the silicone matrix. Mechanical analysis showed improved properties as the PDMS content in the fibre increased. The highest PDMS content fibres did, however, exhibit decreased properties. This was ascribed to increased PDMS (soft and weak) content, decreased crystallinity and increased fibre diameter (lower interfacial area). Dramatic improvements in strength, stiffness, strain and toughness were achieved. The most significant result was an increase in strain of 470%. The mechanical results correlated with results of SEM analysis of the fracture surfaces. The dramatic improvements in properties were a result of the fibre strength and ductility, as well as the mechanism of composite failure. / AFRIKAANSE OPSOMMING: Nuwe silikonnanosamestellings is berei deur gebruik te maak van poli(akrilonitriel) (PAN) gebaseerde versterkende vesels wat multi-ommuurde koolstof nanobuisies bevat het. Versoenbaarheid van die vesels met die silikonmatriks het die sintese van nuwe amfifiliese, organies–anorganiese ent-kopolimere van PAN en poli(dimetielsiloksaan) (PAN-g-PDMS) benodig. Die vesel voorlopermateriaal is deur middel van ‘n “ent-deur” vryeradikaalkopolimerisasie gesintetiseer. Die inhoud van die PDMS makromonomeer in die reaksie het gewissel vanaf 5% tot 25%. Die gebruik van twee verskillende molekulêre massas makromonomere is bestudeer (1000 en 5000 g.mol-1). Die optimale oplosmiddelmengsel vir die neerslagreaksie was 'n volume verhouding van 98% benseen tot 2% dimetielformamied (DMF). Suksesvolle insluiting van PDMS het versnitmateriale van PAN-g-PDMS kopolimere gemeng met PAN homopolimere en ongereageerde PDMS makromonomere gelewer. 'n Gradiënteluering- chromatografiese profiel is ontwikkel om die suksesvolle verwydering van die PDMS makromonomere via heksaanekstraksie te bepaal. Die gradiëntprofiel het aangetoon dat indien die PDMS inhoud in die reagense verhoog is, die aantal entmolekules relatief tot PAN homopolimeermolekules ook verhoog het. 'n Toename in PDMS inhoud het egter 'n afname in kristallisasie van die PAN segmente tot gevolg gehad. Die gesintetiseerde polimeer is gebruik as die beginmateriaal vir die elektrospin van veselvullers. Die elektrospin van die beginmateriaal was suksesvol wanneer 100% DMF as elektrospinoplosmiddel gebruik is. Die amfifiliese aard van die beginmateriaal in DMF lei tot outokonstruksie van aggregaatstrukture in die elektrospinoplossing. Toenemende PDMS inhoud beïnvloed die outokonstruksie van die molekules in oplossing en het gelei tot 'n toename in die oplossings se viskositeit. Die "gelagtige" oplossings beperk die haalbare vesel se morfologiese beheerbaarheid wanneer konvensionele elektrospin parameters soos elektriese spanning, punt-tot-versamelaar afstand, en oplossingkonsentrasies gewysig word. Die vinnige verdamping en strek van die oplossing tydens elektrospin, gekombineer met die fase-geskeide amfifiliese molekules in oplossing en die kristallisasie van die PAN segmente, het gelei tot (nie-ewewig morfologie) volledige poreuse vesels. Die kristalliniteit van die veselbeginmaterial het afgeneem nadat elektrospin toegepas is. Die insluiting van die oppervlak-geoksideerde multi-ommuurde koolstof nanobuisies in die elektrogespinde vesels was suksesvol. Die inhoud van die nanobuisies het gewissel van 2 wt% tot 32 wt%. Die MWCNTs het die gemiddelde veseldeursnit verminder deur op te tree as kruisbinders tussen die PAN segmente van die molekules. Die nanobuisies was goed versprei deur die poreuse struktuur van die vesels en dit was gerig in die rigting van die vesel-as. Bereiding van die silikonsamestellings bestaande uit nie-geweefde en gerigte veseloppervlakke (met en sonder 8 wt% multi-ommuurde koolstof nanobuisies in die vesel) was suksesvol. Die versoenbaarheid tussen die oppervlak van die PDMS-geskeide gebiede en die silikonmatriks laat uitstekende verspreiding en interaksie van die PAN-gebaseerde veselvullers met die silikonmatriks toe. Meganiese analise het aangetoon dat die fisiese eienskappe verbeter het namate die PDMS inhoud in die vesel vermeerder het. Die vesels met die hoogste PDMS inhoud het egter verswakte eienskappe getoon. Dit is toegeskryf aan ‘n verhoogde PDMS inhoud (sag en swak), ‘n afname in kristalliniteit en ‘n verhoogde veseldeursnit (laer grensoppervlakke). Dramatiese verbeterings in sterkte, styfheid, verlengbaarheid, vervorming en taaiheid is bereik. Die mees betekenisvolle gevolg was 'n toename in die verrekking van 470%. Die meganiese resultate is gekorreleer met SEM ontleding van die brekingsoppervlakke. Die veselkrag en vervormbaarheid, sowel as die meganisme van die splyting van die samestellings, het tot die dramatiese verbeterings in die meganiese eienskappe gelei.

Thesis (MSc)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Polymer composites have been gaining more importance in our daily lives because of the favorable properties that can be provided by these types of material. A polymer composite consists of improved properties when compared to the individual polymers that it is compiled of. The reason that composites are better than the individual polymers is mainly because composites are a combination of all the bene cial properties from the individual materials that was used to make the polymer composite. High impact polypropylene (HiPP) is a complex copolymer that was developed to overcome the restrictions of polypropylene (PP). Although PP have excellent properties at lower temperatures, it loses these advantages at elevated temperatures. High impact polypropylene has a much better impact strength and is processable at high temperatures. High impact polypropylene has been studied in depth for its applications and its superior properties such as an improved impact strength. The tensile properties, after the incorporation of a nano ller, have however not been investigated to our knowledge. Nano llers have reinforcing abilities due to the nano-scale diameters. Particles that have sizes on a nanometer range are mostly devoid of defects. Nano llers that are biopolymers have additional advantages such that can consist of antimicrobial abilities, renewability, biocompatibility and biodegradability. Composites reinforced with chitin nanowhiskers (chnw) have shown to have valuable applications in the latest medical, industrial and environmental developments. Di erent loadings of chnw were incorporated into a HiPP matrix in order to investigate the e ects that this nano ller will have on the tensile properties of HiPP. There were two challenges that required attention during the incorporation of chnw into HiPP. The rst major challenge was the poor interaction that exist between chnw and HiPP due to the hydrophobic nature of the HiPP matrix and the hydrophilic nature of chnw. The second problem was the agglomeration that can occur because of the hydrogen bonding between the chnw that is caused by the structure of the chnw chains. In order to gain the best dispersion of chnw within the HiPP matrix it was necessary to use compatibilizers and di erent methods of incorporation. The two types of compatibilizers that were chosen to improve the compatibility between the HiPP matrix and chnw were polypropylenegraft- maleic anhydride (PPgMA) and poly(ethylene-co-vinyl alcohol)(EVOH). Injection molding is typically used to process HiPP and was chosen as one of the methods for incorporating chnw into the HiPP matrix. A second method of incorporation was used speci cally for the nancomposites containing EVOH known as electrospinning combined with meltpressing. Tensile testing, DSC, TGA and FTIR were used to investigate the changes in the mechanical and thermal properties of the nanocomposites. SEM and TEM were employed to investigate the morphology of the electrospun ber mats and to characterize the chnw. FTIR as well as TGA were used to characterize the chitin nanowhiskers and to identify the individual components within the nanocomposites after incorporation took place. The incorporation of chnw along with the compatibilizer did show improvement in some mechanical properties of the polymer matrix. However, the in uence that each type of compatiblizer had on this e ect varied depending on the content of the chnw and compatibilizer with regards to the polymer matrix.