The increasing production and usage of engineered nanoparticles has raised concerns about potential ecological and human exposures and the risks these novel materials may pose. Nanoparticles are often manufactured with an organic macromolecular coating, and they will attain further coatings of adsorbed natural organic matter (NOM) in the environment. The overall objective of this thesis is to improve our ability to quantify the effects of adsorbed coatings on nanoparticle fate in the environment. The physicochemical properties of the coating or the adsorbing macromolecule are expected to strongly mediate the surface interactions, and hence the environmental fate, of coated nanoparticles. To this end, this research focuses on assessing a coating characterization method and applying extensive characterization of NOM coatings to enable the development of correlations to predict nanoparticle deposition onto model environmental surfaces and aggregation. The first objective is to assess the applicability of a soft particle electrokinetic modeling approach to characterize adsorbed layer thickness, which contributes to repulsive steric forces that will affect nanoparticle deposition. A statistical analysis determined that high uncertainty in fitted layer thicknesses will limit this approach to thin, low-charged coatings (for which it may be advantageous to typical sizing methods such as dynamic light scattering). Application of this method in experimental studies further confirmed the model limitations in estimating layer thicknesses and the inability of this measurement (and other commonly measured properties) to fully explain nanoparticle deposition behavior. These results demonstrated the need for improved detail and accuracy in coating characterization. The second objective is to correlate the properties of NOM to its effects on gold nanoparticle aggregation, with particular focus on the role of heterogeneity or polydispersity of the NOM molecular weight. Multiple types of NOM collected from representative water bodies and soils were used, both in whole and separated into molecular weight (MW) fractions, and characterized for chemical composition and MW distribution. While average MW of the NOM provided good correlation with aggregation rate, the highest MW components were found to contribute disproportionately in stabilizing nanoparticles against aggregation, highlighting the importance of measuring and accounting for high MW components to explain nanoparticle aggregation. However, an outlier from the MW trend was identified, emphasizing the need for additional characterization (e.g. of reduced sulfur content or the conformation of the adsorbed NOM) to fully explain the effects of NOM on nanoparticle aggregation. Altogether, this research provides novel knowledge that will guide future application of characterization methods to predict attachment processes for coated nanoparticles in the environment.

The application of an electric field to contaminated soil specimens and the resulting electrokinetic phenomena have been combined with the degradative actions of bacteria to create a novel method for the remediation of contaminated land. Currently, the vast majority of remediation projects involve disposing of contaminated soil in landfill. With the introduction of, and increases in, landfill tax in the UK, this option is becoming less desirable, and so robust, more sustainable techniques are required, such as bioremediation. A major problem with the implementation of bioremediation is the bioavailability of contaminating chemicals. Reduced accessibility of bacteria to the chemical(s) they are attempting to degrade can lead to significant increases in required remediation times, as well as the possibility of significant residual contamination, the levels of which cannot be easily further reduced. This thesis addresses the problem of bioavailability of contaminants in soils, and has investigated the use of electrokinetic phenomena as tools to bring about an increase in this factor, leading to improved biodegradation. Soil contaminated with pentachlorophenol (sodium salt) was subjected to an electric field in a number of experiments, with significant transport of the initially ionic chemical noted. The transport and fate of this chemical were tracked throughout each experiment, along with properties of the soil pore fluid. Significant changes in soil chemistry were noted (particularly pH or moisture content, depending on the experiment). The effect of pH change was found to be particularly important in this respect, with acidic conditions hindering both movement and bioavailability. A method of applying an electric field to contaminated soil containing degrading bacteria was developed which minimised the changes to these parameters within the soil. A significant increase in the effectiveness of the remediation was noted with this technique, with substantially faster degradation found to occur.

Thesis (M.S.) -- Mississippi State University. Dave C. Swalm School of Chemical Engineering. / Title from title screen. Includes bibliographical references.

Enhanced mass transport in carbon-based nanoscale conduits (e.g. carbon nanotubes, graphene nanochannels/capillaries, graphene/graphene oxide membranes) has attracted tremendous interest over the last decade due to its significant implications for water desalination/purification, nanofiltration, electronic cooling, battery/fuel cells, and lab-on-a-chip. Further development of carbon-based nanoscale conduits for practical applications relies on understanding fundamental mechanisms of transport through individual conduits, which have not been well studied due to challenges in fabrication and measurement. In this thesis, the construction of two-dimensional planar graphene nanochannel devices and the studies of enhanced water and ion transport inside the graphene nanochannels are reported for the first time. The graphene nanochannels are fabricated by conformally covering high-quality graphene on the surfaces of silica nanochannels. A new fabrication scheme consisting of graphene wet transfer, graphene patterning and vacuum anodic bonding is developed to create such graphene nanochannels with heights ranging from 24 to 124 nm. Using these nanochannels and a new hybrid nanochannel based capillary flow measurement technique, we successfully measured the hydraulic resistance (water permeability) of single graphene nanochannels. Our results demonstrate that the frictionless surface of graphene induces a boundary slip and enhances water flow inside the graphene nanochannel. The measured slip length of graphene in the graphene nanochannels poses a median value around 16 nm, albeit with a large variation from 0 to 200 nm regardless of the channel height. The small-yet-widely-varying values of the graphene slip length are attributed to the surface charge of graphene and the interaction between graphene and underneath silica substrate, which are in good agreement with the prediction of our molecular dynamics (MD) simulation. In addition, we also investigated enhanced ion transport inside the graphene nanochannels. Higher electroosmotic conductance at low electrolyte concentrations (10-6 M~10-2 M) is observed in graphene nanochannels when compared with silica nanochannels with the same geometry. Our results suggest that the enhanced electroosmotic flow is also due to the boundary slip at the graphene/electrolyte interface. Besides, our analysis shows that the surface charge on the graphene, originating from the dissociation of oxygen-containing functional groups, is crucial to the enhanced electroosmotic flow inside nanochannels.

This dissertation presents the design and implementation of a 16-channel sinusoidal generator to stimulate microfluidic devices that use electrokinetic forces to manipulate particles. The generator has both, independent frequency and independent amplitude control for each channel. The stimulation system is based upon a CMOS application specific (ASIC) device developed using 0.35¦Ìm technology. Several generator techniques were compared based on frequency range, total harmonic distortion (THD), and on-chip area. The best alternative for the microfluidic applications is based in a triangle-to-sine converter and presents a frequency range of 8kHz to 21MHz, an output voltage range of 0V to 3.1VPP, and a maximum THD of 5.11%. The fabricated device, has a foot- print of 1560¦Ìm¡Á2030¦Ìm. The amplitude of the outputs is extended using an interface card, achieving voltages of 0V to 15VPP. The generator functionality was tested by performing an experimental set-up with particle trapping. The set-up consisted of a micromachined channel with embedded electrodes configured as two electrical ports located at different positions along the channel. By choosing specific amplitude and frequency values from the generator, different particles suspended in a fluid were simultaneously trapped at different ports. The multichannel stimulator presented here can be used in many microfluidic experiments and devices where particle trapping, separation and characterization is desired. / This dissertation presents the design and implementation of a 16-channel sinusoidal generator to stimulate microfluidic devices that use electrokinetic forces to manipulate particles. The generator has both, independent frequency and independent amplitude control for each channel. The stimulation system is based upon a CMOS application specific (ASIC) device developed using 0.35¦Ìm technology. Several generator techniques were compared based on frequency range, total harmonic distortion (THD), and on-chip area. The best alternative for the microfluidic applications is based in a triangle-to-sine converter and presents a frequency range of 8kHz to 21MHz, an output voltage range of 0V to 3.1VPP, and a maximum THD of 5.11%. The fabricated device, has a foot- print of 1560¦Ìm¡Á2030¦Ìm. The amplitude of the outputs is extended using an interface card, achieving voltages of 0V to 15VPP. The generator functionality was tested by performing an experimental set-up with particle trapping. The set-up consisted of a micromachined channel with embedded electrodes configured as two electrical ports located at different positions along the channel. By choosing specific amplitude and frequency values from the generator, different particles suspended in a fluid were simultaneously trapped at different ports. The multichannel stimulator presented here can be used in many microfluidic experiments and devices where particle trapping, separation and characterization is desired.

<p>Od primenjenih elektrokinetičkih tehnika:<br />konvencionalna, elektrodijalitička (uz primenu CEM), zatim tretman<br />uz izmenu polariteta na elektrodama, primena pomeranja anode ka<br />katodi, bipolarnih elektroda kao i povećane dužine katodnog prostora,<br />na uzorku Ni zagađenog kaolina (model matriks) najveću efikasnost<br />uklanjanja Ni pokazale su primena pomeranja anode ka katodi (51%<br />odnosno 82% bez uračunavanja katodnog regiona kaolina) i primena<br />bipolarnih elektroda uz povećani katodni prostor (45%).<br />Primenom bipolarnih elektroda uz povećan katodni prostor kao<br />unapređene EK tehnike preči&scaron;ćavanja sedimenta sa visokim ANC<br />postignute su efikasnosti od 44% za uklanjanje Ni odnosno 36%,<br />42% i 43% za uklanjanje Ni, Cd i Pb u sme&scaron;i, redom. Ove efikasnosti<br />su približno dvostruko veće u odnosu na efikasnosti konvencionalnih<br />tretmana, a uviđa se neznatni uticaj prisustva Cd i Pb na efikasnost<br />uklanjanja Ni. Procena rizika na osnovu različitih kriterijuma utvrdila<br />je da je sediment zagađen Ni nakon tretmana siguran za okolinu.<br />Sediment zagađen Ni, Cd i Pb je prema sadržaju Ni i Pb siguran po<br />okolinu, ali se poređenjem različitih kriterijuma procene rizika koji su<br />kori&scaron;ćeni u toku rada dobijaju informacije koje se u manjoj ili većoj<br />meri potvrđuju &scaron;to ukazuje na neophodnost postojanja jedinstvenih i<br />sveobuhvatnih kriterijuma procene rizika. Navedeno potvrđuje da je<br />primena bipolarnih elektroda uz povećan katodni prostor efikasna<br />tehnika preči&scaron;ćavanja sedimenta koji je zagađen Ni i Pb pri<br />koncentracijama koje su navedene u radu.<br />Primenom pomeranja anode ka katodi uz povećan katodni<br />prostor kao unapređene EK tehnike preči&scaron;ćavanja sedimenta sa<br />niskim ANC postignute su efikasnosti od 25% za uklanjanje Ni<br />odnosno 17%, 24% i 62% za uklanjanje Ni, Cd i Pb u sme&scaron;i, redom.<br />Ove efikasnosti su približne za Ni odnosno dvostruko i trostruko veće<br />za Cd i Pb, redom u odnosu na efikasnosti konvencionalnih tretmana.<br />Može se utvrditi da je efikasnost unapređenog procesa značajno<br />povećana, ali poređenjem krajnih koncentracija metala u sedimentu<br />nakon tretmana sa kriterijumima procene rizika, utvrđeno je da jedino<br />prema sadržaju Pb sediment se može smatrati sigurnim po akvatičnu<br />sredinu dok prema sadržaju ostalih metala spada u visoko rizičnu<br />klasu (&gt;50%).</p> / <p> As the result of applying electrokinetic techniques:<br /> conventional, electrodialytic, treatment with electrode polarity<br /> exchange, moving anode, using bipolar electrodes and increased<br /> cathodic compartment length, on Ni contaminated kaolin (model<br /> matrix) the most efficient were moving anode technique (51% or<br /> 82% without calculating the cathode region of kaolin) and using<br /> bipolar electrodes and increased cathodic compartment length (45%).<br /> Using bipolar electrodes and increased cathodic compartment<br /> length as enhanced EK technique for remediation of sediment with<br /> high ANC resulted in 44% of Ni removal and 36%, 42% i 43% for<br /> removal of Ni, Cd and Pb, respectively. This technique nearly<br /> doubled efficiency after conventional treatment and there is slight<br /> influence of Cd and Pb on Ni removal. Risk assessment based on<br /> different criteria determine that Ni contaminated sediment is safe for<br /> the environment after EK treatment. According to Dutch standards it<br /> is classified as Class 1/2. Ni, Cd and Pb contaminated sediment is<br /> safe for the environment according to Ni and Pb content after EK<br /> treatment according to Dutch standards but comparing the risk<br /> assessment arise from different criteria in some cases it do not<br /> provide the same information. This indicates that it is of great<br /> importance to develop unique risk assessment criteria. According to<br /> the results using bipolar electrodes and increased cathodic<br /> compartment is efficient EK remediation technique of Ni and Pb<br /> contaminated sediment at the concentrations used for these<br /> investigations.<br /> Using the moving anode technique and increased cathodic<br /> compartment length as enhanced EK technique for remediation of<br /> sediment with low ANC resulted in 25% of Ni removal and 17%,<br /> 24% and 62% for removal of Ni, Cd and Pb, respectively. It can be</p> <p> concluded that efficiencies after enhanced technique compare to<br /> conventional treatments are significantly increased but the final metal<br /> concentrations (except Pb) in sediment after treatment according to<br /> risk assessment criteria are highly hazardous for the environment<br /> (&gt;50%).</p>

<p>Microfluidics has established itself as a key technology in a wide range of fields including pharmaceuticals, point-of-care diagnostics, thermal management, and space technology. Most of these applications involve manipulation of small quantities (micro – nanoliters) of fluids and various particles or biological cells suspended in them. These platforms employ mechanical, thermal, acoustic, magnetic, optical, electric and many other means for creating particle and fluid motion. Many biological applications require handling cells that are vulnerable to getting damaged if proper physiological conditions are not maintained or if excessive force is applied on them. The non-invasive nature of optical and electrical micro-manipulation techniques such as rapid electrokinetic patterning (REP) has proven to be of great importance in such applications. These techniques enable handling, transportation, sorting and arrangement of fragile synthetic micro/nanoparticles and biological cells without compromising their structure and surface properties.</p> <p>REP is a recently developed micro-manipulation tool that employs optically induced electrothermal vortices to create custom flow patterns. Particle suspensions are entrained in these vortices and are trapped on an electrode surface through AC electrokinetic mechanisms. This work focuses on characterizing a REP trap and discusses its potential applications in handling biological cells. Polystyrene microparticles are confined in a REP trap and a MATLAB program is used to track their motion inside the trap. The tracked particle trajectory reveals that the potential energy of the trapped particle is parabolic and hence the trap is Hookean in nature. The trap is modelled as a spring-mass system and the stiffness coefficient of that system is found to be of the order of 10^-15 N/μm. The origin of the restoring force in the spring-mass model is found to be the drag force created by the electrothermal vortex. The ability to exert ultra-small forces in a stable trap enables REP to be used in various non-invasive particle manipulation applications.</p> <p>The transient nature of REP is studied using numerical modeling and particle image velocimetry (PIV) analysis of a vortex created by a moving laser spot. A numerical model suggests that custom-shaped steady state REP vortices can be created via superposition of multiple axisymmetric circular shaped vortices. However, the method of superposition cannot be extended to transient traps and a more involved 3D model is required to simulate them. The laser spot is scanned back-and-forth in a line with different speeds to create transient REP vortices. The PIV analysis, in agreement with the numerical model, shows that the location of the moving vortex is undiscernible at high speeds. Moreover, the circular shaped vortex is stretched out into a line when the laser scanning frequencies are more than 15 Hz.</p> <p>The particle-electrode attraction force, which entraps the particles at the electrode surface, is characterized using particle diffusometry (PD) and defocusing particle tracking. PD is used to measure the diffusion coefficient of polystyrene particles under different electric field parameters near an electrode surface. It is found that the particle diffusivity decreases with a decrease in the electric field frequency from 150 – 30 kHz and with an increase in the applied voltage from 4 – 8 V_pp. A MATLAB program is used to track the number of in-focus particles and their distance from the electrode surface. A histogram of the particles’ distance from the electrode surface shows an increase in the particle concentration near the electrode at low frequencies (30 – 60 kHz). These observations suggest that the average height of an entrapped particle decreases with a decrease in applied field frequency and an increase in applied voltage. This suggests that the attractive trapping force is significant at 30 kHz but diminishes at around 150 kHz.</p> <p>Salt and sugar-based isotonic media used for cell suspensions pose several challenges for electrokinetic mechanisms such as REP. Various solutions to overcome these challenges for bio-manipulation applications are discussed in this work. The presence of DC offset in the AC electric field is found to enhance particle entrapment in sugar-based media. The effect of DC offset on trapping performance in bio-relevant media is assessed by measuring the stability of the REP trap. This work also shows entrapment and manipulation of Mice pancreatic cancer cells (KPC2) suspended in the sugar-based isotonic media using REP. The biological applications of the REP technology are highly promising, but they have not yet been well-explored. This work lays the foundation of understanding how REP can be operated in high osmolarity media for bio-manipulation applications.</p>

The application of Cerium oxide nanoparticles (CNPs) for therapeutic purposes requires a stable dispersion of nanoparticles in biological environment. The objective of this study is to tailor the properties of polyelectrolyte coated CNPs as a function of molecular weight to achieve a stable and catalytic active dispersion. This was achieved by coating CNPs with polyacrylic acid (PAA) which increased the dispersion stability of CNPs and enhanced the catalytic ability. The stability of PAA coating was analysed using the change in the Gibbs free energy computed by Langmuir adsorption model. The adsorption isotherms were determined using soft particle electrokinetics which overcomes the challenges presented by other techniques. The Gibbs free energy was highest for PAA coated CNPs by 250 kg/mole indicating the most stable coating. The free energy for PAA 100 kg/mole coated CNPs is 85% lower than the PAA250 coated CNPs. This significant difference is caused by the strong adsorption of PAA100 on CNPs. Catalytic activity of PAA-CNPs is accessed by the catalase enzymatic activity of nanoparticles. The catalase activity was higher for PAA coated CNPs as compared to bare CNPs which indicated preferential adsorption of hydrogen peroxide induced by coating. Apart from PAA coating the catalase activity is also affected by the structure of the coating layer.

No description available.

No description available.