Characterization of Industrial and Biological Complex Fluids Using ConfocalMicroscopy.

Confocal Microscopy;Lithographic Ink;Biofilms;Chemical Engineering;Engineering;Chemical Engineering

Hohne, Danial N.Younger, John G. ;

University of Michigan

关键词: Confocal Microscopy;    Lithographic Ink;    Biofilms;    Chemical Engineering;    Engineering;    Chemical Engineering;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/61778/dnhohne_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Complex fluids are materials that respond to applied stresses in a way that isintermediate between that of a purely viscous fluid or a fully elastic solid. Thecharacterization of material properties depends upon the ability to both apply variablestresses or strains to the complex fluid and to measure the resulting response. Often themacroscopic response of these materials depends upon the microscale structure. In thisdissertation, confocal laser scanning microscopy is used to analyze microscopic changesin complex fluids. We developed methods to apply the stress or strain that matches theapplication or environment of the material to be characterized. For instance, confocalimages of the emulsion structure of fountain solution in ink exposed to oscillatory shearflow on model substrates were acquired. We found that surfactants inhibit aqueousdroplet wetting on hydrophobic substrates. Without surfactants, surface coverage of theaqueous fountain solution on the hydrophobic substrate became quite high. This result isrelevant to defects in lithographic printing. To characterize the material properties of biofilms a tunable small-scale device was needed. We developed a flexible microfluidicrheometer to apply a compressive force of ~200 pL volume. We used confocalmicroscopy to detect the deformation of a membrane in contact with a test material whencompressive stresses were applied. This measurement allowed us to characterize materialproperties including elastic modulus and relaxation time of soft viscoelastic solids,biofilms in particular. We report evidence of strain hardening in biofilms; a result thatcould have implications for the understanding of clearance of biofilms in industrial andphysiological environments. To understand the source of this phenomenon we appliedconfocal microscopy to characterize the structure of bacteria aggregated in apolysaccharide matrix. Interestingly, while aggregated bacteria and bacteria in biofilmsare held together by ostensibly the same material we find their inter-bacterial distance to be quite different. Once this tool was developed the origin of strain-hardening inbiofilms could be addressed. The strain-induced trajectories of individual bacteria foundusing image processing of confocal micrographs were analyzed to show that strainhardening occurs without an increase in volume fraction.