Ph.D. (Chemistry) / This study focuses on the morphology and crystal-growth behaviour of polyactide (PLA)-based blends and blends modified with organoclay thin films. The study further examined the effect of blending and the incorporation of organoclays on the enzymatic degradation behaviour. Thin films of unmodified and nanoclay-modified PLA/poly(butylene succinate) (PBS) blends were cast on a glass substrate by a spin coater, while thin films of biodegradable PLA/poly[(butylene succinate)-coadipate] PBSA blends and blends containing organoclays were cast on a silicon (100) wafer substrate. The morphology and crystal growth behaviour of the thin films crystallized at different temperatures were examined with an atomic force microscopy (AFM) equipped with a hot-stage scanner. In PLA/PBS blend thin films, AFM images showed that the size of the dispersed PBS phase was influenced by C30B clay loading on the blends. The dispersed size reduced on the addition of C30B clay up to 2 wt%, beyond which, dispersed size began to increase. Transmission electron microscopy studies indicated that this behaviour was due to the preferential location of silicates in the PBS phase than in the PLA phase. For thin films annealed at 60 °C, the additi on of organoclays to the blend quenched the growth of edge-on lamellae. The crystalline morphologies at 120 °C were dominated by edge-on lamellae grown, around the PBS phase to form spherulites. Morphologies of thin films crystallized at 120 °C from melt were dominated by the flat-on lamellae, while those crystallized at 70 °C from melt were dominated by the edge-on lamellae. In the case of PLA/PBSA blend thin films, the results indicated that the size and distribution of the dispersed phase were directly related to the blend composition. The crystal growth behaviours indicated the presence of homogeneous and heterogeneous nucleations, and the nature of nucleation was directly related to the blend ratio and the temperature at which crystallization occurred. Therefore, this study will facilitate the understanding of crystal growth behaviour in a confined environment and will enable the modulation of the blend properties.

Orientador: Liliane Maria Ferrareso Lona / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-24T08:44:00Z (GMT). No. of bitstreams: 1 Botan_Rodrigo_D.pdf: 8541673 bytes, checksum: fc88cab0852acd3cb9bf0b6052e4458d (MD5) Previous issue date: 2014 / Resumo: Ao longo da última década, nanocompósitos poliméricos vêm atraindo grande atenção da comunidade científica e industrial. Este fato se deve à notável melhora em inúmeras propriedades destes novos materiais, proporcionado pelo uso de uma pequena quantidade de nanoreforços. Entre as propriedades melhoradas é possível citar com maior destaque as propriedades mecânicas e térmicas. Buscando alcançar melhores propriedades para o poli(estireno) (PS), o objetivo deste trabalho foi o de sintetizar nanocompósitos in situ de PS com hidróxidos duplos lamelares (HDLs) e hidroxissal lamelar (HSL). Para isto, foram sintetizados dois tipos de HDLs e um tipo de HSL, os HDLs foram modificados com ácido láurico, ácido palmítico e uma mistura destes dois ácidos e o HSL foi modificado com ácido palmítico. Os HDLs e HSL sintetizados foram caracterizados por difração de raios x (DRX), microscopia eletrônica de varredura (MEV), espectroscopia no infravermelho por transformada de Fourier (FTIR) e análise termogravimétrica (TGA). Os nanocompósitos foram sintetizados in situ por polimerização em massa e foram caracterizados por DRX, FTIR, TGA, calorimetria exploratória diferencial (DSC), microscopia eletrônica de transmissão (MET), ensaio de flexão, análise da fratura e teste de flamabilidade. Os resultados obtidos demostram que estes novos nanocompósitos foram sintetizados, apresentando, de uma forma geral, uma boa interação polímero ¿ reforço com morfologia variando da intercalada/esfoliada a esfoliada. A estabilidade térmica e, principalmente, a propriedade mecânica apresentaram ganhos significativos em todos os materiais estudados quando comparadas com o polímero puro, fato que possibilita uma vasta gama de aplicação destes novos materiais em diversos campos da pesquisa e engenharia / Abstract: Over the past decade, polymer nanocomposites have attracted interest, both in the industry and in the academia. They often exhibit remarkable improvement in their properties when compared with neat polymer or conventional micro and macrocomposites using low levels of reinforcements, usually maximum 5% by weight. The improvements mainly include mechanical, thermal, and physical properties. Seeking to achieve better properties for poly(styrene) (PS), the purpose of this work was to in situ synthesize PS with layered double hydroxides (LDHs) and layered hydroxide salt (LHS) nanocomposites. Thus, two types of LDH and a type of LHS was synthesized, the LDHs were modified with lauric acid, palmitic acid and a mixture of both, and LHS was modified with palmitic acid. The LDHs and LHS synthesized were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). The nanocomposites were synthesized by in situ bulk polymerization and were characterized by XRD, FTIR, TGA, differential scanning calorimetry (DSC), transmission electron microscopy (TEM), bend test, fracture analysis and flammability test. The obtained results show that indeed these new nanocomposites were synthesized. These nanocomposites have in general good interaction polymer ¿ reinforcement with morphology varying from intercalated/exfoliated to exfoliated. The thermal stability and mechanical property mainly, showed significant improvement in all materials studied, when compared with the neat polymer, a fact that enables a wide range of application of these new materials in various fields of research and engineering / Doutorado / Engenharia Química / Doutor em Engenharia Química

Orientador: Leinig Antônio Perazolli / Resumo: O presente trabalho buscou desenvolver fotocatalisadores cerâmicos por meio da produção de heterojunções inovadoras à base de SrTiO3, TiO2 e CaO, que tiveram suas fotoatividades avaliadas pela descoloração do corante Rodamina B (RhB) e pela obtenção de biodiesel, utilizando luz ultravioleta. As amostras TiO2, CaO e SrTiO3 foram obtidas pelo método de precursores poliméricos, método Pechini, e as heterojunções TiO2/SrTiO3, CaO/SrTiO3 e CaO/CaTiO3 foram preparados por rota sol-gel. Após síntese e tratamento térmico, as amostras foram caracterizadas por difração de Raios-X (DRX) para verificar as fases cristalinas formadas, por espectroscopia de infravermelho com transformada de fourier (FT-IR) e termogravimetria/análise térmica diferencial (TG/DTA) para verificar e quantificar a formação de CaCO3 e Ca(OH)2, por espectroscopia de refletância difusa (UV/Vis/NIR DRS) para determinar a energia de band gap, por Brunauer, Emmett e Teller (B.E.T.) para determinar a área específica, por microscopia eletrônica de varredura acoplada a espectroscopia de energia dispersiva de Raios-X (FE-SEMEDS) para estimar o tamanho das partículas, sua morfologia e composição elementar, por espectroscopia de fotoelétrons excitados por Raios-X (XPS) para conhecer a composição elementar presente na superfície da amostra e seus estados de oxidação, por espectroscopia de fotoluminescência (PL) para verificar a formação de defeitos estruturais, por microscopia eletrônica de transmissão de alta resolução (HRTE... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The present work aimed to develop ceramic photocatalysts through the production of innovative SrTiO3, TiO2 and CaO based heterojunctions, which had their photoactivities evaluated by the discoloration of Rhodamine B (RhB) dye and by obtaining biodiesel using UV light. TiO2, CaO and SrTiO3 samples were obtained by polymeric precursor method, Pechini method, and TiO2/SrTiO3, CaO/SrTiO3 and CaO/CaTiO3 heterojunctions were prepared by sol-gel route. After synthesis and heat treatment, the samples were characterized by X-ray diffraction (XRD) to verify the crystalline phases formed, fourier transform infrared spectroscopy (FT-IR) and thermogravimetry/differential thermal analysis (TG/DTA) to verify and quantify the formation of CaCO3 and Ca(OH)2, diffuse reflectance spectroscopy (UV/Vis/NIR DRS) to determine band gap energy, Brunauer, Emmett e Teller (B.E.T.) to determine specific area, field emission scanning electron microscopy coupled X-ray dispersive energy spectroscopy (FE-SEM-EDS) to estimate particle size, morphology and elemental composition, X-ray photoelectron spectroscopy (XPS) to know the elemental composition present on the sample surface and oxidation states, photoluminescence spectroscopy (PL) to verify the formation structural defects, high resolution transmission electron microscopy (HRTEM) to confirm the formation of heterojunction. Rhodamine B discoloration was measured by UV/Vis molecular absorption spectroscopy and the conversion of oil to biodiesel was analyz... (Complete abstract click electronic access below) / Doutor

Piezoelectric materials have had widespread application since their discovery both in bulk crystal and thin film applications, but thin film piezoelectrics have unlocked key applications like acoustic filtering and energy harvesting. [1] This work investigates a small subset including energy harvesting, multifunctional nanocomposites, acoustic wave resonators, and gravimetric and infrared sensing. Electroactive polymers such as PVDF-TrFE have a unique combination of characteristics including a high dielectric constant, piezoelectricity, pyroelectricity, biocompatibility, and mechanical flexibility. [2, 3, 4, 5, 6] This unique combination gives them a wide potential application space including energy harvesting, biomedical devices, drug delivery, flexible electronics, and tactile sensing. [7] In recent years, there has been significant work investigating potential composite materials based on electroactive polymers and nanoparticles. [8] This interest has been primarily driven by the increased commercial availability, tunability, and available functionalities of nanoparticles. In this work, nanocomposites of PVDF-TrFE, barium titanate (BTO), and europium barium titanate (EBTO) are investigated. EBTO is an optically active material which can add optical functionality to these active polymer composites. [9] Acoustic wave resonators including bulk acoustic wave resonators and surface acoutstic wave resonators are widely used for front end filtering technologies, but their high quality factor, small size, and low power makes them good candidates for sensing technologies. [10, 11, 12] In this work, FBARs are applied to VOC sensing and infrared sensing sucessfully.

A thesis submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Engineering. Johannesburg, May 2016 / In this study, hybrid multiscale epoxy composites were developed from woven glass fabrics and PAN nanofibers embedded with short ECNFs (diameters of ~200nm) produced via electrospinning. Unlike VGCNFs or CNTs which are prepared through bottom-up methods, ECNFs were produced through a top-down approach; hence, ECNFs are much more cost-effective than VGCNFs or CNTs. Impact absorption energy, tensile strength, and flexural strength of the hybrid multiscale reinforced GFRP composites were investigated. The control sample was the conventional GFRP composite prepared from the neat epoxy resin. With the increase of ECNFs fiber volume fraction up to 1.0%, the impact absorption energy, tensile strength, and flexural strength increased. The incorporation of ECNFs embedded in the PAN nanofibers resulted in improvements on impact absorption energy, tensile strength, and flexural properties (strength and modulus) of the GFPC. Compared to the PAN reinforced GRPC, the incorporation of 1.0% ECNFs resulted in the improvements of impact absorption energy by roughly 9%, tensile strength by 37% and flexural strength by 29%, respectively. Interfacial debonding of matrix from the fiber was shown to be the dominant mechanism for shear failure of composites without ECNFs. PAN/ECNFs networks acted as microcrack arresters enhancing the composites toughness through the bridging mechanism in matrix rich zones. More energy absorption of the laminate specimens subjected to shear failure was attributed to the fracture and fiber pull out of more ECNFs from the epoxy matrix. This study suggests that, the developed hybrid multiscale ECNF/PAN epoxy composite could replace conventional GRPC as low-cost and high-performance structural composites with improved out of plane as well as in plane mechanical properties. The strengthening/ toughening strategy formulated in this study indicates the feasibility of using the nano-scale reinforcements to further improve the mechanical properties of currently structured high-performance composites in the coming years. In addition, the present study will significantly stimulate the long-term development of high-strength high-toughness bulk structural nanocomposites for broad applications. / MT2016

The commodity plastics industry is dominated by semicrystalline polymers, which generally display high toughness relative to amorphous polymers but typically suffer from low strength and modulus. Researchers have shown that the addition of nanoparticles (NPs) to these semicrystalline matrices can result in materials with enhanced properties relative to the neat systems. The arrangement of these NPs into anisotropic sheet-like structures appears to endow these processed polymer nanocomposites (PNCs) with further improved mechanical properties relative to PNCs where the NP morphology remains well-dispersed. However, there is currently no appropriate methodology in the literature with which to quantitatively correlate the extent of NP organization to the enhancement in mechanical properties. Additionally, isothermal crystallization (the current processing technique of choice for this class of PNCs) results in numerous grain boundaries. While entanglements across grains can limit issues associated with failure, grain boundaries can also be undesirable for the modulus of the material. In this dissertation, we methodically investigate several key topics related to the above. We first present our modifications to the correlation function approach of Strobl and Schneider, which was originally developed to characterize the structural parameters of neat semicrystalline polymers and their blends, that allow us to apply it to isothermally crystallized poly(ethylene oxide) (PEO) PNCs. We select PEO due to the relative ease with which mobile silica NPs can be dispersed within the matrix. Next, we characterize these materials using the generally used large beam size typical of laboratory-scale and synchrotron X-ray scattering instruments. In this study, we show that our adaptations to the correlation function approach allow for the quantitative evaluation of the NP ordering process as a function of isothermal crystallization temperature. The same systems are then characterized with a microfocus synchrotron X-ray scattering beam guided by an autonomous experimentation protocol, which allows for a detailed, granular mapping of the structural parameters of these materials. The much smaller beam reveals spatial morphological heterogeneity in both the neat and PNC systems due to the grain size being on the order of the dimensions of the microbeam as opposed to those of the larger beam. Hence, the combination of the large and microfocus beam provides a comprehensive view of these systems, with varying degrees of granularity. We also find quantitative evidence that demonstrates that NPs organize parallel to the direction of polymer crystal growth, a phenomenon which has previously only been shown in the literature in a qualitative fashion. Having established the physics of the NP ordering process in isothermally crystallized PNC systems, we turn to the zone annealing (ZA) technique as inspiration to approach more uniform, unidirectionally oriented NP morphologies. ZA, which has found extensive use in the production of ultra-pure semiconductors for electronics applications, proceeds by translating a sample at a constant velocity over a well-defined temperature gradient. This directional processing technique has been shown to result in the reduction of grain boundaries when applied to semicrystalline polymers. Since the PNC is a more complicated system than the neat matrix, we first perform studies of zone annealed neat PEO. Our experimental, analytical, and numerical investigations validate a crucial directional crystallization theory proposed by Lovinger and Gryte, who were among the first to apply ZA to semicrystalline polymers; our experimental evidence confirms the existence of a critical ZA velocity (v_crit) below which directional crystallization occurs and above which the process is closer in spirit to isothermal crystallization. Having determined the mechanism driving the ZA of neat PEO, we then turn to the ZA of PEO-based PNCs. Through our studies, we find that it is imperative to minimize or eliminate sample flow during the procedure, as otherwise the NPs order in disparate directions. Our subsequent redesign of the sample preparation protocol, such that the material is pressed between two glass coverslips separated by Teflon spacers, leads to extensive unidirectional organization of NPs that persists throughout the film at slow enough ZA velocities, as evidenced from X-ray scattering experiments. Hence, this dissertation systematically examines questions relevant to understanding how to obtain uniform, unidirectional NP organization in semicrystalline PNCs, with relevance to applications requiring enhanced properties.

A non-invasive method to quantify the stress distribution in polymer-based materials is presented through the piezospectroscopic calibration of alumina-epoxy nanocomposites. Three different alumina volume fraction nanocomposites were created and loaded under uniaxial compression in order to determine the relationship between applied stress and the frequency shift of the R-lines produced by alumina under excitation. Quantitative values for six piezospectroscopic coefficients were obtained which represent the stress-sensing property of the nanocomposites. The results were applied to an alumina-filled adhesive in a single lap shear configuration demonstrating the capability of the technique to monitor R-line peak positions with high spatial resolution and assess the stress distribution within the material prior to failure. Additionally, particle dispersion and volume fraction were confirmed with spectral intensities, introducing a novel experimental method for the assessment of quality in manufacturing of such nanocomposites. Results were further used to initiate studies in determining the load transfer to the nanoparticles and assessing the fundamental driving mechanisms.

Soft materials are indispensable components of energy storage and conversion technologies necessary for the renewable energy transition. Two key examples are electrolytes used in solid-state batteries and ion-exchange membranes used in electrolysis and electrodialysis. The figures of merit for these applications are often summarized using upper-bound relationships, which define the best possible combination of performance metrics for a given material. A promising route to break the upper-bound and to improve upon the state-of-the-art is engineering materials at the nanoscale. Two commonly employed strategies are the use of block copolymers and polymer nanocomposites. In the former, the sequence of different monomers along the backbone of the polymer chain is varied; in the latter, ceramic nanoparticles are mixed with polymers and processed to achieve different dispersion states. In both of these classes of materials, the self-assembly of molecular and colloidal components controls the structure and function of the resulting material. This dissertation investigates these structure-property relationships in model soft nanomaterials, namely colloids, polymer nanocomposites, and ion-exchange membranes, using experiments, molecular dynamics simulations, and theory. The dissertation can be divided into three parts. The first, Chapters 2 and 3, investigates polymer and polymer nanocomposite electrolytes for applications in solid-state Li batteries. Chapter 2 investigates the coarse-graining and force field parameterization of polymer electrolytes for molecular dynamics simulations. Chapter 3 reports the experimental characterization of polymer nanocomposite electrolytes, with a key focus on understanding how the particle dispersion state affects the ionic conductivity and mechanical reinforcement of the composite. The second part, Chapters 4 and 5, studies fundamental structure-property relationships in two types of polymer nanocomposites. In Chapter 4, the surface chemistry of hydrophilic silica nanoparticles is altered to promote miscibility in organic solvents and in semicrystalline polymers. In these "bare" nanocomposites, the particles are stabilized against aggregation via the adsorption of a polymer bound layer, which is quantitatively studied via small angle X-ray scattering. In Chapter 5, the surface-modified particles are densely grafted with polymer chains via surface-initiated polymerization to obtain matrix-free polymer grafted nanoparticle films. The collective dynamics of the nanoparticle cores in these self-supporting films, where all of the polymer is grafted to the particle surface, is then measured using X-ray photocorrelation spectroscopy at a variety of temperatures. In Chapters 6 and 7, random copolymer chemistries are used to create cation- and anion-exchange membranes, respectively, with controlled ion-exchange capacity and swelling behavior. The key finding of Chapter 6 is that water-lean cation-exchange membranes selectively transport ions with low free energies of hydration, allowing the design of specific-ion selective electrodialysis stacks for Li+ recovery applications. The analogous properties of anion-exchange membranes are suggested as an avenue for future research.

Hard gold thin films and coatings are widely used in electronics as an effective material to reduce the friction and wear of relatively less expensive electrically conductive materials while simultaneously seeking to provide oxidation resistance and stable sliding electrical contact resistance (ECR). The main focus of this dissertation was to synthesize nanocrystalline Au films with grain structures capable of remaining stable during thermal exposure and under sliding electrical contact stress and the passing of electrical current. Here we have utilized a physical vapor deposition (PVD) technique, electron beam evaporation, to synthesize Au films modified by ion implantation and codeposited ZnO hardened Au nanocomposites. Simultaneous friction and ECR experiments of low fluence (< 1x10^17 cm^-2) He and Ar ion implanted Au films showed reduction in friction coefficients from ~1.5 to ~0.5 and specific wear rates from ~4x10^-3 to ~6x10^-5 mm^3/N·m versus as-deposited Au films without significant change in sliding ECR (~16 mΩ). Subsurface microstructural changes of He implanted films due to tribological stress were analyzed via site-specific cross-sectional transmission electron microscopy (TEM) and revealed the formation of nanocrystalline grains for low energy (22.5 keV) implantation conditions as well as the growth and redistribution of cavities. Nanoindentation hardness results revealed an increase from 0.84 GPa for as-deposited Au to ~1.77 GPa for Au uniformly implanted with 1 at% He. These strength increases are correlated with an Orowan hardening mechanism that increases proportionally to (He concentration)1/3. Au-ZnO nanocomposite films in the oxide dilute regime (< 5 vol% ZnO) were investigated for low temperature aging stability in friction and ECR. Annealing at 250 °C for 24 hours Au-(2 vol%)ZnO retained a friction coefficient comparable to commercial Ni hardened Au of ~ 0.3 and sliding ECR values of ~35 mΩ. Nanoindentation hardness increases of these films (~2.6 GPa for 5 vol% ZnO) are correlated to microstructure via high resolution TEM and scanning electron microscope cross-sections to both Hall-Petch and Orowan strengthening mechanisms. Also presented is a correlation between electrical resistivity and grain size in the oxide dilute range based on the Mayadas-Shatzkes (M-S) electron scattering model. Using the M-S model in combination with a model describing solute drag stabilized grain growth kinetics we present a new technique to probe grain boundary mobility and thermal stability from in-situ electrical resistivity measurements during annealing experiments.

Polymer nanocomposites are a going part of Materials Science and Engineering. These new composite materials exhibit dimensional and thermal stability of inorganic materials and toughness and dielectric properties of polymers. Development of nanocomposites become an important approach to create high-performance composite materials. In this study silica, fly ash, silica nanotubes and carbon black particles have been added to modify polyurethane foam and thermoplastic polyurethanes. It has been found that the addition of silica can diminish the size of foam bubbles, resulting in an increased stiffness of the material, increase of the compressive strength, and greater resistance to deformation. However, the uniformity of bubbles is reduced, resulting in increased friction of the material. Fly ash added to the foam can make bubbles smaller and improve uniformity of cells. Therefore, the material stiffness and compressive strength, resistance to deformation, and has little impact on the dynamic friction of the material. Adding nanotubes make bubble size unequal, and the arrangement of the bubble uneven, resulting in decreased strength of the material, while the friction increases. After the addition of carbon black to the polyurethane foam, due to the special surface structure of the carbon black, the foam generates more bubbles during the foaming process changing the foam structure. Therefore, the material becomes soft, we obtain a flexible polyurethane foam. The results of mechanical properties determination of the thermoplastic polyurethane that adding particles may increase the stiffness and wear resistance of the thermoplastic polyurethane, while the tensile properties of the material are reduced. This phenomenon may be due to agglomeration of particles during the mixing process. Possibly the particles cannot be uniformly dispersed in the thermoplastic polyurethane.