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REMOVAL OF BACTERIAL CONTAMINANT FROM MODEL SUBSTRATES USING A MICELLAR NANOFLUID FORMULATION
Title
REMOVAL OF BACTERIAL CONTAMINANT FROM MODEL SUBSTRATES USING A MICELLAR NANOFLUID FORMULATION
Creator
Shim, Jiyoung
Date
2017, 2017-05
Description
The oscillatory structural force (OSF) of a micellar film of sodium dodecyl sulfate (SDS) was monitored with atomic force microscope (AFM)...
Show moreThe oscillatory structural force (OSF) of a micellar film of sodium dodecyl sulfate (SDS) was monitored with atomic force microscope (AFM) using an attached glass microsphere against a smooth flat and energy homogenous solid substrate. The force versus distance measurements for the 0.03M and 0.06 M SDS micellar solutions were monitored. The force versus distance had an oscillatory decay profile with a period of oscillation which was the same as the micellar diameter. The number of periodic oscillations increased with an increase in the micellar concentration. The OSF in the SDS micellar film confinement was also proved by a thinning single foam film formed from a micellar solution. It was observed that, due to micellar layering, the film thinned in a multiple regular stepwise manner promoted by the OSF. The results obtained by the AFM and thinning single foam film were used in the application of the OSF to remove bacteria from a model solid substrate. The experimental data for the OSF was complemented with modeling research. The theoretical OSF curves were obtained using the statistical mechanics approach. The experimental data and theoretical results for OSF for SDS micellar film were analyzed and found to be in fair agreement with each other. Based on the model prediction calculation, the structural film interaction energy barrier for the both the 0.03 M and 0.06 M SDS micellar solutions was calculated; the estimated structural film interaction energy barrier due to the presence of the OSF was about 10 3 kT / 􀝉􀬶 for the 0.03 M SDS micellar solution and about 5 x 10􀬷 kT /􀝉􀬶for the 0.06 M SDS micellar solution in film with micellar layers at about 25 ºC. Understanding the interactions between bacteria and solid surfaces that result in bacterial adsorption and removal is of immense importance for reducing foodborne illness outbreaks. Here, we used fluorescence microscope in conjunction with the concept of the diffusion of bacteria from the bulk suspension to the substrate and the adsorption isotherm to estimate the adsorption energy for E.coli K12; we obtained a value of about 2.5 kT. This value compares favorably with the value of 2.1 kT reported previously for E.coli NCTC 9002 [49]. We also used the dynamic light scattering method to estimate the radius of gyration of E.coli K12, which has a diameter of about 1 m and a length of 2 m to estimate the effective volume. The radius of gyration was also used to estimate the surface area covered by the bacterium and compared it to the surface area measured from the image taken with fluorescence microscope. A nanofluid formulation comprised of a sodium dodecyl sulfate (SDS) micellar aqueous solution in the presence of an organic acid (as a pH controller) was used to test the E. coli K12 removal from two substrates, polyvinylchloride (PVC) and partially hydrophobic glass. We investigated the bacterial removal efficacy based on the combined effect of the nanofluid’s structural forces and bacterial isoelectric point. We predicted the nanofilm oscillatory structural energy (NOSF) against the E.coli K12 adsorption energy by applying the statistical mechanics approach. Based on the model prediction, the NOSF was estimated at the vertex of three phase contact angle between a bacterium and the substrate (i.e., the wedge film’s interaction energy at one particle layer). The evaluated film’s repulsive energy due to the NOSF was about 15.6  4.4 kT of the 0.02 M SMNF (the SDS micellar nanofluid formulation) and several times higher than the bacterial adsorption energy, 2.5  0.2 kT. These findings suggest that the NOSF is capable of bacteria/microorganism removal from contaminated substrates. Here, we present a methodology based on NOSF to optimize the nanofluid formulation for bacterial substrate removal and bulk inactivation. The results of this study will assist the food industry with the design of proper sanitation and will enhance microbial removal and inactivation strategies.
Ph.D. in Chemical Engineering, May 2017
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RISE OF A SINGLE BUBBLE IN A VERTICAL TUBE FILLED WITH NANOFLUIDS
Title
RISE OF A SINGLE BUBBLE IN A VERTICAL TUBE FILLED WITH NANOFLUIDS
Creator
Cho, Heon Ki
Date
2018, 2018-05
Description
The motion of air bubbles in tubes filled with nanofluids is of practical interests. Thus, this study focuses on the dynamics of air bubbles...
Show moreThe motion of air bubbles in tubes filled with nanofluids is of practical interests. Thus, this study focuses on the dynamics of air bubbles rising in tubes in nanofluids. Many authors experimentally and analytically proposed the rising air bubble velocity in vertical tubes in common liquids when Capillary number is large. We report here a systematic study of an air bubble rising in vertical tube filled with nanofluids when the Capillary number is small. The presence of the nanoparticles creates a significant change in the bubble velocity compared with the bubble rising in the common liquids. We observed a novel phenomenon of a step-wise decreases in the bubble rising velocity vs. bubble length for small Capillary number. The step-wise velocity increases is attributed to the nanoparticles self-layering phenomenon in the film adjacent to the tube wall. The effect of volume fraction of the nanoparticles and the tube diameters are investigated. Also, we measured the film thickness and calculated the film structural energy isotherm vs. the film thickness from the film meniscus contact angle measurement using the reflected light interferometric method. Based on the experimental measurement of the film thickness and the calculated values of the film structural energy barrier, we estimated the structural film viscosity vs. the number of nanoparticles/micelles. Due to thenanoparticle film self-layering phenomenon, we observed a gradual increasing the film viscosity with the decrease in the film thickness. But, we found a significant increase in the film viscosity accompanied by a step-wise decrease in the bubble velocity when the number of nanoparticles/micelles decreased from three to two particle layers due to the structural transition in the film. Bretherton analyzed the rise of a single long air bubble at a very small Capillary number under the effect of gravity in a vertical tube filled with common liquids with a thick and stable film. However, Bretherton equation cannot accurately predict the rate of the rise of the slow-moving long bubble in the vertical tube in nanofluids because it is valid only for very thick films and uses the bulk viscosity of the fluid. But, we demonstrate that the Bretherton equation can indeed be used for predicting the rate of the rise of the long single bubble through the vertical tube filled with the nanofluids by simply replacing the bulk viscosity with the proper structural nanofilm viscosity of the fluid.
Ph.D. in Chemical Engineering, May 2018
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Capillary Rise of Common Liquids and Nanofluids: Experiments and Modeling
Title
Capillary Rise of Common Liquids and Nanofluids: Experiments and Modeling
Creator
Wu, Pingkeng
Date
2018
Description
Capillary dynamics of common liquids and nanofluids is a ubiquitous everyday phenomenon. It has practical applications in diverse fields,...
Show moreCapillary dynamics of common liquids and nanofluids is a ubiquitous everyday phenomenon. It has practical applications in diverse fields, including ink-jet printing, lab-on-a-chip, biotechnology, and coating. Important as it is, this phenomenon has not been fully understood and requires tremendous effort in theoretical analysis and experimental investigations to gain further knowledge and guide the design of practical precesses whenever capillarity is essential.The rise of the main meniscus in rectangular capillaries is important in interpreting the phenomenon of fluid flow in porous media. This thesis presents an experimental study on the rise of the main meniscus in rectangular borosilicate glass and plastic (polystyrene) capillaries using three different liquids (water, ethanol, and hexadecane). A universal model (an extended two-wall model) based on the Laplace equation was developed to predict the equilibrium height of the main meniscus in rectangular capillaries. In capillary dynamics, it is crucial to understand the interaction between fluid molecules and a solid substrate (the wall) in molecular scale. Recent studies reveal that a layered molecularly thin wetting film (LMTWF) will develop ahead of the apparent three-phase contact line for the spreading of a wetting liquid on solid surfaces. Based on this fact, a novel molecular self-layering model is proposed to explain the dynamic wetting considering the role of the molecular shape on self-layering and its effect on the molecularly thin film viscosity in regards to the advancing (dynamic) contact angle. The proposed molecular self-layering model is then incorporated into the Lucas-Washburn-Rideal (LWR) equation to explain the capillary rise dynamics of fluids of spherical, cylindrical, and disk shape molecules in borosilicate glass capillaries. The abilities of the other popular dynamic contact angle models to correct the dynamic contact angle effect in the capillary rise process were also investigated. The LWR equation modified by molecular self-layering model predicts well the capillary rise of carbon tetrachloride, octamethylcyclotetrasiloxane and n-alkanes with the molecular diameter or measured solvation force data. The molecular self-layering model modified LWR equation also has good predictions on the capillary rise of silicone oils covering a wide range of bulk viscosities with the same key parameter W(0), which results from the molecular self-layering. Besides the open capillaries, the proposed molecular self-layering model is applied to explain the spontaneous rise of Newtonian liquids in closed-end capillaries. Contribution of the compressed air inside the closed capillaries is also modeled and experimentally verified. Finally, the research is extended to a liquid phase displacing another immiscible liquid in capillaries with the focus on surfactant solutions containing polymeric nanoparticles (nanofluids), which have been shown to have an improved wetting and spreading on solid surfaces. The polymeric nanoparticles can reduce the frictional coefficient by as much as four times by forming structured layers in the confined wedge film. The role of the interfacial tension on the frictional coefficient is also demonstrated.In summary, this thesis presents the physics of liquid rise in rectangular capillaries, effect of molecular self-layering in capillary dynamics in open and closed-end capillaries, and the contribution of nanofluids in the two-phase displacement dynamics.
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