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No description available.

Many intervention methods theoretically have the potential to eliminate microorganisms. However, they do not perform efficiently once applied to fruits and vegetables. In this study Salmonella Typhimurium LT2 and hydrogen peroxide (H2O2) were used as model systems on 6 different types of produce to determine the effect of produce surface characteristics on sanitizer effectiveness. Microbial attachment on produce surfaces was induced after 3 h of drying at 24°C and high relative humidity (RH). Afterwards, produce was stored for 3 subsequent days and washed with sterilized tap water for 5, 10 and 15 minutes to separate weakly from strongly attached microorganisms from the produce surface. The strongly attached microorganisms were then treated with 3% H2O2 for 1, 3, and 5 minutes. These results were compared to the log reduction curves obtained with a pure liquid culture and 3% H2O2. Additionally, contact angle of water and diiodomethane on each type of surface were measured and used as indicator of wettability, and for calculating surface tension characteristics of the produce surfaces. Then these surface characteristics were related to the bacterial attachment and population reduction values obtained after applying the treatments. In general, the geometric mean equation was the most useful in predicting the surface tension values of produce surface and the polar and non-polar components of produce surface tension. Our results suggest that surface properties, such as roughness and surface tension of fruits and vegetables are important factors limiting decontamination. These surface properties allow the formation of micro-air pockets within the rough surface, thus contributing to create a protective environment for microorganisms and reducing the effectiveness of the chemical aqueous based intervention methods applied. Wettable surfaces (water contact angle < 90°) allowed more bacteria to attach after the washing and H2O2 chemical treatments. Roughness and surface polarity are intrinsic characteristics of produce surfaces which affect wettability and the spreading and penetration of the sanitizer treatment on the produce surface. Rough surface and porosity, considered an extreme case of roughness, enhance a deeper cell internalization and a protective environment for bacteria.

The condition of no relative velocity of fluid past solid is termed as ‘no-slip boundary condition’. This condition is a general observation in fluid mechanics. However, several research groups have recently reported slip of water for surfaces with water repelling chemistry (referred to as hydrophobic surfaces). The effect has been attributed to disruption of H-bonding network of water molecules at such surfaces and resulting nucleation of dissolved gases and even reduced water density locally in absence of dissolved air. Slip of water on hydrophobic surfaces has been demonstrated to get amplified by high degree of roughness and patterning. Trapping of air in the surface asperities has been cited as the possible reason. The present work focuses on the study of effect of surface chemistry and roughness on flow behavior close to solid surfaces. Superhydrophobic surfaces have been generated by novel methods and wet-etching has been used to generate well-defined patterns on silicon surfaces. For flow characterisation, a micrometre resolution Particle Image Velocimetry (micro-PIV) facility has been developed and flow measurements have been carried out with a spatial resolution of less than 4 µm. It has been found from the experiments that flow of water on smooth surfaces, with or without chemical modification, conforms to the no-slip within the resolution limits of experiments. Deviation is observed in case of rough and patterned hydrophobic surfaces, possibly because of trapped air in asperities. Total Internal Reflection experiments, used to visualise the air pockets, confirmed the trapping of air at asperities. Diffusion of air out of the crevices seems to be the limiting factor for the utility of these surfaces in under-water applications.

Texte remanié de--Leiden (Pays-Bas)--Université de Leiden, 2003. / Thèse en anglais avec un résumé et une page de garde en néerlandais. Bibliogr. en fin de chap.

Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references (leaves 87-91). Also available on the Internet.

Thesis (M.S.)--Boise State University, 2009. / Includes abstract. Includes bibliographical references (p. 46-49).

Thèse de doctorat : sciences. Mécanique : Ecully, Ecole centrale de Lyon : 2005. / 124 réf.

Thèse de doctorat : sciences. Mécanique : Ecully, Ecole centrale de Lyon : 2005. / Titre provenant de l'écran-titre. 124 réf.

Thèse de doctorat : Chimie et physico-chimie des polymères : Paris 12 : 2005. / Titre provenant de l'écran-titre. Bibliogr. en fin de chapitres.