Microstructure studies in synthetic and bio-colloids, imaging and applications

Ashish Kumar Jha, University of Rhode Island

Abstract

The mean size of CTAB/HDBS mixed surfactant vesicles confined into the three-dimensional voids generated by the random close packing (RCP) of polystyrene beads, shows a systematic decrease as the characteristic confinement length scale is reduced. The RCP of polystyrene beads of radius Rb = 1.5μm, 0.25μm and 0.1μm, creates voids of characteristic dimensions R ∼ 0.22 Rb = 3300Å, 550Å and 220Å respectively. These void length scales are comparable to or less than the radii of vesicles formed in the system under conditions of no confinement. A simple thermodynamic model was developed accounting for the balance between increased enthalpy when vesicles formed have higher than preferred curvature and increased free volume entropy for smaller vesicles. The model supports the observed trend in the experimental data. The results of this study are potentially important for understanding the flow of drug delivery vehicles through microcapillaries, in the recovery of oil from fine pores in rocks using surfactant containing fluids, micellar enhanced ultrafiltration, or in other situations where the size of surfactant aggregate structures approach the length scales between the confining walls. ^ Microstructural tuning of CTAB/HDBS mixed surfactant vesicles has been accomplished via interaction with surface functionalized polystyrene (PS) spheres. Cryogenic transmission electron microscopy (cryo-TEM) has been used for the artifact free visualization of the microstructures. The key premise is that selective adsorption on to the spheres, driven primarily by charge interactions, impacts surfactant concentrations in the solutions, thus driving structures to different, concentration-dependent states. A concurrent effect is the role played by adsorption on the clustering of the PS spheres. These effects can potentially be useful when surfactant composition must be changed without additional surfactant consumption, for rheology modification, in templated material synthesis, as well as in understanding situations where surfactant could potentially be adsorbed by neighboring solid boundaries, such as surfactant mediated oil recovery from porous rocks and detergency. ^ Differences in microstructures of aggregates present in serum from healthy individuals and age-matched prostate cancer (PC) patients have been identified using cryogenic transmission electron microscopy (cryo-TEM) and dynamic light scattering. Two predominant structures—vesicles and globules—are observed in cryo-TEM images. Image analysis reveals both the vesicle-to-globule ratio and the mean globule size in the serum from PC patients, lower than that in the serum from healthy individuals. The results from dynamic light scattering experiments complement those from cryo-TEM. These structural differences caused by the presence of the disease and associated variations in the secretion level of serum components, can be viable serum level biomarkers for prostate cancer. The use of structure-based biomarkers represents a paradigm shift away from biochemical assay based markers for disease. ^ A microfluidic device has been demonstrated that is capable of accurately monitoring bacteria levels in aqueous suspensions. The device uses nanoliter samples, thus providing very rapid, highly quantitative measurements. This method uses immunogenicity of bacteria to stain them with fluorescently labeled antibody specific to the target. Bacteria are then quantified by the fluorescence emission causing spikes in the output signal as they pass through the detection zone inside the microchip. This method has also been optimized to work where bacterial cells are not required to be washed after staining to make the process automated. The potential application of this device may be in continual monitoring of the harmful bacteria in coastal ocean waters that pose threat to the marine ecosystems. ^

Subject Area

Engineering, Chemical

Recommended Citation

Ashish Kumar Jha, "Microstructure studies in synthetic and bio-colloids, imaging and applications" (2008). Dissertations and Master's Theses (Campus Access). Paper AAI3328722.
http://digitalcommons.uri.edu/dissertations/AAI3328722

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