Magnetic nanoparticles coated with polymers hold great promise as materials for applications in biotechnology. In this body of work, magnetic fluids for the treatment of retinal detachment are examined closely in three regimes; motion of ferrofluid droplets in aqueous media, size analysis of the polymer-iron oxide nanoparticles, and calculation of interparticle potentials as a means for predicting fluid stability. The macromolecular ferrofluids investigated herein are comprised of magnetite nanoparticles coated with tricarboxylate-functional polydimethylsiloxane (PDMS) oligomers. The nanoparticles were formed by reacting stoichiometric concentrations of iron chloride salts with base. After the magnetite particles were prepared, the functional PDMS oligomers were adsorbed onto the nanoparticle surfaces. The motion of ferrofluid droplets in aqueous media was studied using both theoretical modeling and experimental verification. Droplets (~1-2 mm in diameter) of ferrofluid were moved through a viscous aqueous medium by an external magnet of measured field and field gradient. Theoretical calculations were made to approximate the forces on the droplet. Using the force calculations, the times required for the droplet to travel across particular distances were estimated. These estimated times were within close approximation of experimental values. Characterization of the sizes of the nanoparticles was particularly important, since the size of the magnetite core affects the magnetic properties of the system, as well as the long-term stability of the nanoparticles against flocculation. Transmission electron microscopy (TEM) was used to measure the sizes and size distributions of the magnetite cores. Image analyses were conducted on the TEM micrographs to measure the sizes of approximately 6000 particles per sample. Distributions of the diameters of the magnetite cores were determined from this data. A method for calculating the total particle size, including the magnetite core and the adsorbed polymer, in organic dispersions was established. These estimated values were compared to measurements of the entire complex utilizing dynamic light scattering (DLS). Better agreement was found for narrow particle size distributions as opposed to broader distributions. The stability against flocculation of the complexes over time in organic media were examined via modified Derjaguin-Landau-Verwey-Overbeek (DLVO) calculations. DLVO theory allows for predicting the total particle-particle interaction potentials, which include steric and electrostatic repulsions as well as van der Waals and magnetic attractions. The interparticle potentials can be determined as a function of separation of the particle surfaces. At a constant molecular weight of the polymer dispersion stabilizer, these calculations indicated that dispersions of smaller PDMS-magnetite particles should be more stable than those containing larger particles. The rheological characteristics of neat magnetite-PDMS complexes (i.e, no solvent or carrier fluid were present) were measured over time in the absence of an applied magnetic field to probe the expected properties upon storage. The viscosity of a neat ferrofluid increased over the course of a month, indicating that some aggregation occurred. However, this effect could be removed by shearing the fluids at a high rate. This suggests that the particles do not irreversibly flocculate under these conditions. / Ph. D.

Flotation is a process of separating particulate materials of different surface properties in a hydrodynamic environment, and is used extensively for separating different minerals from each other in the mining industry. In this process, air bubbles are introduced at the bottom of a particulate suspension (pulp), so that bubbles coated with hydrophobic particles rise to the top and form a froth phase while hydrophobic particles stay in suspension. The selectivity of the flotation process is determined by the hydrophobicity of the particulate materials involved, while the kinetics of the process is controlled by the hydrodynamic conditions and the disjoining pressures in the thin aqueous films between air bubbles and particles. In the present work, a mathematical model for the flotation process has been developed by considering both the hydrodynamic and surface chemical parameters. The model can describe the events occurring in both the pulp and froth phases of a mechanically-agitated flotation cell. The pulp-phase model is based on predicting the kinetics of bubble-particle attachment using the DLVO extended to include contributions from hydrophobic force and the theory of turbulent collision. The froth-phase model is based on predicting the rate of bubble-particle detachment by considering bubble coarsening and water recovery. The predictions from the overall flotation model are in general agreement with the results obtained in single-bubble flotation experiments and the flotation test results reported in literature. Since the model has been developed largely from first principles, it has predictive and diagnostic capabilities. / Ph. D.

Froth floatation is an important process used in the mining industry for separating minerals from each other. The separation process is based on rendering a selected mineral hydrophobic using an appropriate hydrophobizing reagent (collector), so that it can selectively attach onto the surfaces of a rising stream of air bubbles. Thus, controlling the hydrophobicity of the minerals to be separated from each other is of critical importance in flotation. If one wishes to separate plastics from each other by flotation, however, it would be necessary to render a selected plastic hydrophilic and leave the others hydrophobic. In the present work, the possibility of separating common plastics from each other by flotation has been explored. While water contact angle is the most widely used measure of the hydrophobicity of a solid, it does not give the information on the kinetics of flotation. Therefore, the forces acting between the surfaces coated with different hydrophobic polymers (or plastics) in water were measured using the Atomic Force Microscope (AFM). The results obtained with polystyrene, polymethylmethacryrate (PMMA), polypropylene (PP), and Teflon showed the existence of long-range attractive forces (or hydrophobic force) that cannot be explained by the classical DLVO theory. The surface force measurements were conducted in pure water and in solutions of surfactant (alkyltrimethylammonium chloride) and a salt (NaCl). In pure water, the attractive forces were much stronger than van der Waals force. In the presence of the surfactant and NaCl, the long-range attraction decreased with increasing concentration and the alkyl chain length. A series of contact angle measurements were conducted to determine the hydrophobicity of polystyrene (PS), polyvinyl chlorite (PVC), and polymethylmethacrylate (PMMA) in the presence of different wetting agents (surfactants). The results show the possibility of separating plastics from each other by flotation, and a series of microflotation tests conducted on PS and PVC showed promising results. / Master of Science

No labirinto dos gotejadores ocorrem diferentes interações entre as partículas de argila e as características do escoamento, sendo que essas interações interferem no potencial de obstrução dos mesmos. Considerando que os principais fatores que interferem no processo de obstrução causado por partículas de argila estão relacionados à natureza das argilas, ao regime de escoamento, à força iônica e ao pH da solução, e à concentração de partículas em suspensão. Esta pesquisa apresentou como objetivo identificar como esses fatores podem influenciar o desempenho dos gotejadores. Além disso, visando a caracterização do processo de obstrução causado por partículas desta natureza, buscou-se: relacionar o potencial de agregação das partículas com o desempenho dos gotejadores; e, analisar o comportamento da deposição de partículas no interior dos labirintos dos gotejadores. Para isso, além da realização dos ensaios em bancada utilizando diferentes dispersões de argila, foram realizadas análises sobre o potencial de agregação das partículas, e, utilizando um dispositivo milifluidico, foi realizada uma análise de deposição de partículas. Durante a pesquisa foram utilizados dois tipos de argilas, caulinita e montmorilonita. A força iônica da solução e a natureza dos materiais de argila apresentaram efeito sobre o desempenho dos gotejadores, enquanto que a caulinita em solução salina de sódio proporcionou incremento máximo de vazão de 5%, a montmorilonita causou redução máxima de vazão de 15%. No geral, as partículas de argila começaram a causar redução de vazão significativas com concentrações iguais ou superiores a 1000 mg L-1. Observou-se que as partículas de argila estão sujeitas ao fenômeno de autolimpeza que ocorre no interior dos labirintos após o acionamento do sistema. Não foi possível encontrar uma relação entre o potencial de agregação das partículas de argila e o desempenho dos gotejadores. Possivelmente, o índice de agregação utilizado pela teoria DLVO clássica não seja o mais adequado para obter esta relação. Em relação a deposição de partículas, as regiões que apresentaram maiores deposições de partículas coincidem com aquelas que apresentam menores valores de intensidade de turbulência e energia cinética turbulenta. A deposição de partícula ocorre principalmente nas regiões de vórtices e estagnação, localizadas nos dois primeiros defletores dos labirintos. Não foi observado acúmulo de partículas na região do fluxo principal. Por isso, sugere-se que partículas de argila, como agente isolado de obstrução, não apresentam potencial para causar obstrução completa dos gotejadores. / In the drippers labyrinth different interactions occur between the clay particles and the flow characteristics, and these interactions interfere in the clogging potential of the particles. Considering the main factors that affect the process of clogging caused by clay particles are related to the type of the clays, the flow regime, the ionic strength and pH of the solution, and the concentration of suspended particles. This research aims to identify how these factors can influence the performance of drippers. In addition, aiming to characterize the clogging process caused by particles of clay, it was sought to relate the potential of particles aggregation with the performance of drippers; and, to analyze the behavior of particles deposition inside the labyrinths of drippers. For this, in addition to performing bench tests using different clay dispersions, analyzes were carried out on the particle aggregation potential, and a particle deposition analysis was performed using a microfluidic device. During the research two types of clays were used, kaolinite and montmorillonite. The ionic strength of the solution and the type of the clay materials had an effect on the drippers performance. Whereas the kaolinite in sodium saline provided a maximum flow rate increase of 5%, the montmorillonite caused a maximum flow rate reduction of 15%. In general, clay particles began to cause significant flow rate reduction with concentrations equal to or greater than 1000 mg L-1. It was observed that clay particles are subject to the phenomenon of self-cleaning which occurs inside the labyrinths after turn on the system. It was not possible to find a relation between the potential of clay particles aggregation and the drippers performance. Possibly, the aggregation index used by the classical DLVO theory is not the most adequate to obtain this relation. In relation to the particles deposition, the regions of greatest deposition coincide with those that present lower values of turbulence intensity and turbulent kinetic energy. Particles deposition occurs mainly in the vortex and stagnation regions, located in the first two baffles of the labyrinths. In addition, no particle accumulation occurs in the main stream region, it suggested that clay particles, as an isolated clogging agent, do not have the potential to cause total clogging of drippers.

No labirinto dos gotejadores ocorrem diferentes interações entre as partículas de argila e as características do escoamento, sendo que essas interações interferem no potencial de obstrução dos mesmos. Considerando que os principais fatores que interferem no processo de obstrução causado por partículas de argila estão relacionados à natureza das argilas, ao regime de escoamento, à força iônica e ao pH da solução, e à concentração de partículas em suspensão. Esta pesquisa apresentou como objetivo identificar como esses fatores podem influenciar o desempenho dos gotejadores. Além disso, visando a caracterização do processo de obstrução causado por partículas desta natureza, buscou-se: relacionar o potencial de agregação das partículas com o desempenho dos gotejadores; e, analisar o comportamento da deposição de partículas no interior dos labirintos dos gotejadores. Para isso, além da realização dos ensaios em bancada utilizando diferentes dispersões de argila, foram realizadas análises sobre o potencial de agregação das partículas, e, utilizando um dispositivo milifluidico, foi realizada uma análise de deposição de partículas. Durante a pesquisa foram utilizados dois tipos de argilas, caulinita e montmorilonita. A força iônica da solução e a natureza dos materiais de argila apresentaram efeito sobre o desempenho dos gotejadores, enquanto que a caulinita em solução salina de sódio proporcionou incremento máximo de vazão de 5%, a montmorilonita causou redução máxima de vazão de 15%. No geral, as partículas de argila começaram a causar redução de vazão significativas com concentrações iguais ou superiores a 1000 mg L-1. Observou-se que as partículas de argila estão sujeitas ao fenômeno de autolimpeza que ocorre no interior dos labirintos após o acionamento do sistema. Não foi possível encontrar uma relação entre o potencial de agregação das partículas de argila e o desempenho dos gotejadores. Possivelmente, o índice de agregação utilizado pela teoria DLVO clássica não seja o mais adequado para obter esta relação. Em relação a deposição de partículas, as regiões que apresentaram maiores deposições de partículas coincidem com aquelas que apresentam menores valores de intensidade de turbulência e energia cinética turbulenta. A deposição de partícula ocorre principalmente nas regiões de vórtices e estagnação, localizadas nos dois primeiros defletores dos labirintos. Não foi observado acúmulo de partículas na região do fluxo principal. Por isso, sugere-se que partículas de argila, como agente isolado de obstrução, não apresentam potencial para causar obstrução completa dos gotejadores. / In the drippers labyrinth different interactions occur between the clay particles and the flow characteristics, and these interactions interfere in the clogging potential of the particles. Considering the main factors that affect the process of clogging caused by clay particles are related to the type of the clays, the flow regime, the ionic strength and pH of the solution, and the concentration of suspended particles. This research aims to identify how these factors can influence the performance of drippers. In addition, aiming to characterize the clogging process caused by particles of clay, it was sought to relate the potential of particles aggregation with the performance of drippers; and, to analyze the behavior of particles deposition inside the labyrinths of drippers. For this, in addition to performing bench tests using different clay dispersions, analyzes were carried out on the particle aggregation potential, and a particle deposition analysis was performed using a microfluidic device. During the research two types of clays were used, kaolinite and montmorillonite. The ionic strength of the solution and the type of the clay materials had an effect on the drippers performance. Whereas the kaolinite in sodium saline provided a maximum flow rate increase of 5%, the montmorillonite caused a maximum flow rate reduction of 15%. In general, clay particles began to cause significant flow rate reduction with concentrations equal to or greater than 1000 mg L-1. It was observed that clay particles are subject to the phenomenon of self-cleaning which occurs inside the labyrinths after turn on the system. It was not possible to find a relation between the potential of clay particles aggregation and the drippers performance. Possibly, the aggregation index used by the classical DLVO theory is not the most adequate to obtain this relation. In relation to the particles deposition, the regions of greatest deposition coincide with those that present lower values of turbulence intensity and turbulent kinetic energy. Particles deposition occurs mainly in the vortex and stagnation regions, located in the first two baffles of the labyrinths. In addition, no particle accumulation occurs in the main stream region, it suggested that clay particles, as an isolated clogging agent, do not have the potential to cause total clogging of drippers.

No description available.

The fast growing production of carbon based nanomaterials (CNMs) and their potential widespread use in consumer products raise concerns regarding their potential risks to human health and ecosystems. The present study investigated the role of photochemical transformation and natural organic matter (NOM) in the fate, transport, and toxicity of fullerenes and carbon nanotubes (CNTs) in natural aquatic systems, providing fundamental information for risk assessment and management. Photochemical transformation of aqueous fullerene nanoparticles (nC60) and CNTs occurs at significant rates under UVA irradiation at intensity similar to that in sunlight. The transformation processes are mediated by self-generated ROS, resulting in changes of surface structure depending on the initial surface oxidation state of CNMs. UVA irradiation leads to oxygenation of nC60 surface and decarboxylation of carboxylated multi-walled carbon nanotubes (COOH-MWNTs). The environmental transport of CNMs is significantly affected by their surface chemistry, concentration and species of electrolytes, and concentration and properties of co-existing NOM. In electrolyte solutions without NOM, the mobility of CNMs is largely decided by their surface chemistry, primarily the oxygen-containing functional groups. In NaCl solutions, UVA irradiation remarkably enhanced the mobility of nC60; conversely, it reduced nC60 stability in CaCl2 solutions. The mobility of COOH-MWNTs in NaCl solutions correlated well with the abundance of surface carboxyl groups. Humic acid, once adsorbed on the nC60 surface, can significantly enhance its stability through steric hindrance. The extent of stabilization depends on the amount and properties of humic acid adsorbed. Humic acid has limited adsorption on UVA-irradiated nC60. Soil humic acid is more efficient in stabilizing nC60 than aquatic humic acid due to its higher molecular weight. Humic acid immobilized onto the silica surface can potential enhance or hinder nC60 deposition, depending on the complex interplay of attractive and repulsive forces. MWNTs are more toxicity to bacteria, Escherichia coli, than COOH-MWNTs due to their higher bioavailability and oxidative capacity. Surface oxidation induced by •OH reduced the toxicity of MWNT while reactions with •OH have little effect on the COOH-MWNT toxicity. Antioxidants such as glutathione can effectively inhibit the antibacterial activity of MWNTs.

Abstract Flotation is a well-known and widely used technique for the separation of particles smaller than 250 µm, but efficient performance requires the use of various synthetic chemicals which can potentially damage the health of humans and animals and pollute the environment. Consequently, their replacement through a more environment-friendly and sustainable alternative has been demanded. One promising candidate is cellulose, which is an abundant natural polymer that is environment-friendly and can be treated chemically and physically to yield tailored properties and thus a potential for use in processes such as flotation. This work focuses on the use of cellulose-based reagents in flotation processes to replace the often harmful conventional reagents derived from mineral oil, plant oils or animal fats. The physico-chemical properties of cellulose differ from those of conventional reagents, leading to differences in performance during flotation. In particular, the chemical and morphological heterogeneity of cellulose affects its properties and thus its interaction with minerals and water. Consequently, its use requires the study of the fundamentals of flotation and their application including the physico-chemical heterogeneity of cellulose to determine the optimum conditions and enable efficient performance. This work focuses on the determination of the thermodynamic surface energetics of solid particles and changes in this after reagent adsorption, using the inverse gas chromatography technique in a dry atmosphere. Furthermore, interactions between cellulose and minerals immersed in water are investigated using the DLVO theory, the interaction forces between cellulose and the minerals being derived and correlated with flotability. The importance of free surface charges is then considered by investigating the electric surface potential of cellulose-coated minerals in connection with particle-bubble attachment efficiency. At the same time, conventional amphiphilic reagents are used and its performances are related to cellulose-based reagents. / Tiivistelmä Vaahdotus on kaivannaisteollisuudessa laajasti käytössä oleva prosessi, jonka avulla saadaan erotettua tehokkaasti pieniä, alle 250 µm kokoisia partikkeleita. Vaahdotuksen apuaineena käytetään erilaisia synteettisiä kemikaaleja, jotka voivat aiheuttaa harmia ympäristölle. Siksi niiden korvaaminen ympäristöystävällisemmillä vaihtoehdoilla on tärkeää. Yksi lupaava vaihtoehto korvaavaksi materiaaliksi on selluloosa. Selluloosa on uusiutuva ja ympäristöystävällinen luonnonpolymeeri, josta voidaan valmistaa kemiallisesti ja fysikaalisesti käsittelemällä erilaisia biokemikaaleja. Näitä voidaan soveltaa erilaisissa prosesseissa, myös vaahdotuksessa. Tässä työssä keskitytään selluloosapohjaisten kemikaalien käyttöön vaahdotuksessa tavanomaisten, usein haitallisten synteettisten kemikaalien korvaamiseksi. Selluloosan fysikaaliskemialliset ominaisuudet eroavat synteettisten vaahdotuskemikaalien ominaisuuksista, mikä vaikuttaa niiden vuorovaikutukseen mineraalien ja veden kanssa. Erityisesti selluloosan kemiallinen ja morfologinen heterogeenisuus on keskeinen tekijä. Selluloosan hyödyntäminen tulevaisuuden vaahdotuskemikaalina edellyttää selluloosan ja mineraalien vuorovaikutuksen syvällistä ymmärtämistä. Tässä työssä tutkitaan selluloosan ja mineraalien vuorovaikutusta sekä IGC-menetelmän avulla, että DLVO-teorian että pintavarausmittausten avulla. Lisäksi tutkitaan selluloosan ja mineraalien vuorovaikutusvoimien yhteyttä vaahdotusprosessin onnistumiseen ja saavutettuja tuloksia verrataan kaupallisten reagenssien toimintaan.

Carbon –based engineered nanoparticles have been widely used due to their small size and uniquephysical and chemical properties. They can dissolve in water, transport through soil and reach drinkingwater resources. The toxic effect of engineered nanoparticles on human and fish cells has beenobserved; therefore, their release and distribution into the environment is a subject of concern. In thisstudy, two types of engineered nanoparticles, multi-walled carbon nano-tubes (MWCNT) and C60 withcylindrical and spherical shapes, respectively, were used. The aim of this study was to investigatetransport and retention of carbon-based engineered and natural nanoparticles through saturated porousmedia. Several laboratory experiments were conducted to observe transport behavior of thenanoparticles through a column packed with sand as a representative porous media. The columnexperiments were intended to monitor the effect of ionic strength, input concentration and the effect ofparticle shape on transport. The results were then interpreted using Derjaguin-Landau-Verwey-Overbeak (DLVO) theory based on the sum of attractive and repulsive forces which exist betweennanoparticles and the porous medium. It was observed that as the ionic strength increased from 1.34mM to 60 mM, the mobility of the nanoparticles was reduced. However, at ionic strength lower than10.89 mM, mobility of C60 was slightly higher than that of MWCNTs. At ionic strength of 60 mMMWCNT particles were significantly more mobile. It is rather difficult to relate this difference to theshape of particle and further studies are required.The effect of input concentration on transport of MWCNTs and C60 was observed in bothmobility of the particle and shape of breakthrough curves while input concentration was elevated from7 mg/l to 100 mg/l. A site-blocking mechanism was suggested to be responsible for the steep andasymmetric shape of the breakthrough curves at the high input concentration.Furthermore inverse modeling was used to calculate parameters such as attachment efficiency,the longitudinal dispersivity, and capacity of the solid phase for the removal of particles. The inversionprocess was performed in a way that the misfit between the observed and simulated breakthroughcurves was minimized. The simulated results were in good agreement with the observed data.

[pt] Um dos maiores problemas encontrados na indústria mineral é a perda de material ultrafino em processos convencionais de separação. A operação de floculação seletiva vem sendo estudada para a recuperação destes materiais. Por outro lado, o uso de biossurfactantes no processamento mineral, extraídos de microrganismos, vem apresentando bons resultados para a recuperação deste tipo de material, além de serem biodegradáveis e possuírem baixa toxicidade. Nesta pesquisa, tem-se como objetivo o estudo da floculação seletiva de partículas ultrafinas de hematita contidas em rejeito de minério de ferro usando o biossurfactante extraído da levedura Cândida stellata. Foi realizado um estudo de caracterização envolvendo análise granulométrica, análise química e difração raio-X (DRX). Para avaliar a interação do biossurfactante na superfície dos minerais de hematita e quartzo, foram desenvolvidos estudos de espectroscopia de infravermelho com transformada de Fourier (FTIR), potencial Zeta, microscopia eletrônica de varredura (MEV) e tensão superficial. Para os testes de floculação, realizados por jar test – teste de proveta, avaliou-se a influência do pH, concentração de sólidos e concentração de biossurfactante. A energia de interação foi avaliada através das teorias DLVO e DLVO Estendida (X-DLVO). As análises de espectroscopia no infravermelho (FTIR) e potencial zeta indicaram uma forte adsorção do biossurfactante na superfície da hematita, sendo que o ponto isoelétrico da hematita foi alterado de 5,35 para 3,25. No estudo de tensão superficial do biossurfactante indicou uma concentração micelar crítica (CMC) de 150 mg/L em pH 3, alcançando um valor próximo de 30 mN/m. Durante os ensaios de floculação foi alcançada uma recuperação de 99 por cento de hematita em pH 3, usando 75 mg/L de biossurfactante e uma concentração de sólidos de 0,50 por cento (1,25 g/500 mL). Pelo estudo da energia de interação entre as partículas, devido ao sinal negativo das interações de ácido-base de Lewis, as partículas de hematita flocularam após o contato com o biossurfactante, indicando que houve uma forte interação hidrofóbica entre elas. Os resultados obtidos neste trabalho indicam que o biossurfactante extraído da levedura Cândida stellata possui uma boa seletividade para a aglomeração das partículas ultrafinas de hematita. / [en] One of the biggest problems encountered in the mineral industry is the loss of ultrafine material in conventional separation processes. The selective flocculation operation has been studied to recover these materials. On the other hand, the use of biosurfactants in mineral processing, extracted from microorganisms, has been showing good results for the recovery of this type of material, in addition to being biodegradable and having low toxicity. In this research, the objective is to study the selective flocculation of ultrafine hematite particles contained in iron ore tailings using the biosurfactant extracted from the yeast Candida stellata. A characterization study was carried out involving particle size analysis, chemical analysis and X-ray diffraction (XRD). In order to evaluate the interaction of the biosurfactant on the surface of hematite and quartz minerals, studies of Fourier transform infrared spectroscopy (FTIR), Zeta potential, scanning electron microscopy (SEM) and surface tension were developed. For the flocculation tests, performed by jar test, the influence of pH, solids concentration and biosurfactant concentration was evaluated. The interaction energy was evaluated using the DLVO and DLVO Extended (X-DLVO) theories. The infrared spectroscopy (FTIR) and zeta potential analyzes indicated a strong adsorption of the biosurfactant on the hematite surface, with the hematite isoelectric point being changed from 5,35 to 3,25. In the surface tension study of the biosurfactant, it indicated a critical micellar concentration (CMC) of 150 mg/L at pH 3, reaching a value close to 30 mN/m. During the flocculation tests, a recovery of 99 percent of hematite at pH 3 was achieved, using 75 mg/L of biosurfactant and a solids concentration of 0,50 percent (1,25 g). By studying the interaction energy between the particles, due to the negative sign of the Lewis acid-base interactions, the hematite particles flocculated after contact with the biosurfactant, indicating that there was a strong hydrophobic interaction between them. The results obtained in this work indicate that the biosurfactant extracted from the yeast Candida stellata has a good selectivity for the agglomeration of ultrafine hematite particles.