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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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