Browsing by Author "Wu, Yan"
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Item Drying and Cracking Behavior of Aqueous Particulate Coatings(2018-03) Wu, YanThe goal of this work is to understand the connections between stress, structural and mechanical property development during the drying of particulate coatings containing rigid particles, and the how these conditions are impacted by coating formulation variables and processing conditions. The motivation is to better predict and control the coating performance by optimizing the formulation design and drying condition. Characterizing drying behavior and correlating the stress development with microstructure evolution are critical in this research. In Chapter 3, drying characterization approaches are introduced. To extend the capability of stress measurement, walled substrates with different dimensions and materials were designed. And a shrinkage measurement method allowing convenient correlation of the microstructure change with stress development was developed using laser profilometry technique. Chapters 4-6 focus on investigating the role of formulation variables on the drying and cracking of coatings prepared with micron-sized particles. Chapter 4 focuses on studying the effect of particle size distribution. The study showed that with similar average particle size, coatings prepared from particles with a wide particle size distribution form a more compact microstructure, but are prone to cracking due to high tensile stress development on drying. Chapters 5 and 6 study the effect of particle shape on coatings cracking resistance. Different levels of clay particles were added to particulate coating systems prepared from the irregular-shaped ground calcium carbonate (GCC) particles and the spherical-shaped silica particles. The different geometry constraints of the mixed particles have altered impacts on the drying shrinkage and mechanical strength of the coatings, thus different cracking behaviors were observed. Finally, in Chapter 7 attention is shifted from the particulate coatings with the micron-sized particle to those prepared from nano-sized particles. Formulation variables of particle size and shape were characterized using coatings of nano-silica particles, nano-zinc oxide particles, and fumed-silica.Item Microbial separation from a complex matrix by a hand-held microfluidic device(Chemical Communications (Cambridge, England), 2017) Singh, Renu; Brockgreitens, John; Saiapina, Olga; Wu, Yan; Abbas, AbdennourThrough a simple chemical activation of biomolecules present in the outer structures of microbial cells, microorganisms can be rapidly isolated on gold-coated surfaces in a microfluidic device with over 99% capture efficiency. Bacterial and fungal cells can be selectively captured, concentrated and retrieved for further analysis.Item Produce Safety in the United States: Epidemiological Trends and Risk Management Utilizing a Novel Screening Method for Shiga-Toxin Producing E. coli and Salmonella in Irrigation Water(2019-12) Wu, YanDespite significantly improved technologies in food science and public health and tremendous efforts being put by governments to ensure food safety, foodborne outbreaks are still abundant worldwide. Produce products have been frequently implicated in foodborne illness outbreaks in recent years due to changes in consumer demands, consumption habits and production practices. A better understanding on epidemiology changes of produce outbreaks is needed to evaluate current risks associated with produce supply chain and to understand safety regulations regarding produce safety. In addition, it is evident that water used in produce production plays an important role in potentially introducing microbial contaminations. Therefore, its risk management is crucial for safety assurance of the produce supply chain. The goal of this thesis research is to analyze the epidemiological trends of produce outbreaks and to improve the risk management of microbial quality of irrigation water. It summarizes the changing epidemiology of produce outbreaks in the United States from 1998-2007, establishes the baseline to further evaluate the potential impact from the recently implemented Food Safety Modernization Act (FSMA). The study also describes the development, optimization, and evaluation of a novel selective medium for sensitive enrichment and screening of Shiga-toxin producing E. coli and Salmonella in irrigation water. The developed enrichment-indicator system meets the increasing demand of method for multi-pathogen enrichment and detection in a single assay format allowing cost effective detection of STEC and Salmonella within 24 hours.