Browsing by Subject "Colloid"
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Item Generation and stabilization of emulsions and foams with nanoparticles and surfactants(2015-12-03) Worthen, Andrew Jay; Johnston, Keith P., 1955-; Truskett, Thomas M; Bonnecaze, Roger T; Huh, Chun; Bryant, Steven LInteractions between nanoparticles and surfactants are shown to improve the formation and stability of emulsions of dodecane-in-water and foams of carbon dioxide (CO2)-in-water. The initial work focuses on establishing a fundamental understanding of the interfacial properties of nanoparticle-surfactant combinations as novel dispersants for oil-in-water emulsions. Using the synergy between nanoparticles and surfactants, highly stable emulsions stabilized by with very low concentrations of amphiphiles are demonstrated. Additionally, amphiphilic polymers are grafted to nanoparticles to investigate their delivery to oil-water interfaces. Concepts developed in oil-in-water emulsion systems are then extended to design stabilizers for CO2-in-water foams. In this work, the first examples of viscous and opaque white foams stabilized solely with nanoparticles are demonstrated. This remarkable result was explained in terms of the nanoparticle interactions with the CO2 and water phases, which are tuned with small hydrophobic groups or amphiphilic polymers covalently grafted to the particle surfaces. Then the concept of nanoparticle-surfactant synergy is applied for the first time to CO2-in-water foams to create foams with both high stability and high viscosity. Finally, nanoparticles with grafted ligands on their surfaces are synthesized to give long-term colloidal stability in high salinity aqueous phases. These nanoparticles are then shown to improve CO2-in-water foam formation and stability. These new technologies may open new applications of nanoparticles in both seawater and reservoir brine.Item Intra-meander groundwater-surface water interactions in a losing experimental stream(2010-08) Nowinski, John David; Cardenas, Meinhard Bayani, 1977-; Sharp, John M.; Bennett, Philip C.Groundwater-surface water interactions between streams and shallow alluvial aquifers can significantly affect their thermal and chemical regimes and thus are critical for effective management of water resources and riparian ecosystems. Of particular significance is the hyporheic zone, an area delineated by subsurface flow paths that begin and end in surface water bodies. Although detailed work has examined hyporheic flow in the vertical dimension, some studies have suggested that the drop in a stream’s elevation as it flows downstream can laterally extend the hyporheic zone. This study examines intra-meander hyporheic flow using extensive field measurements in a full-scale experimental stream-aquifer system. Synoptic head measurements from 2008 and 2009 and a lithium tracer test were conducted to determine the extent and nature of hyporheic flow within the meander. Permeability was measured and sediment cores were analyzed from 2008 to 2009 to assess aquifer properties. Finally, transient head and temperature measurements were collected during flooding events to assess the sensitivity of intra-meander hyporheic flow and temperature to stream discharge. Results verify that hyporheic flow through meanders occurs, but show that it is sensitive to whether a stream is gaining or losing water to the subsurface overall. In addition, permeability and core grain size results indicate moderate heterogeneity in permeability can occur in aquifers composed of relatively uniform sediment. Results also demonstrate that permeability in alluvial aquifers can evolve through time. Such evolution may be driven by groundwater flow, which transports fine particles from areas where porosity and permeability are relatively high and deposits them where they are relatively low, thus creating a positive feedback loop. Finally, measurements during flooding indicate that steady-state hyporheic flow and the thermal regime within the aquifer are largely insensitive to stream discharge. Together, these results expand upon previous field studies of intra-meander hyporheic flow and verify previous modeling work, although they demonstrate a level of complexity within these systems that should be considered in future work.Item Reaction controlled kinetic assembly of small gold nanoclusters with high NIR extinction(2011-08) Willsey, Brian William; Johnston, Keith P., 1955-; Milner, Thomas ENanoclusters with sizes of ~50nm with high NIR extinction at wavelengths beyond 800 nm are of interest in various fields including biomedical optical imaging, microelectronics, plasmonic sensors, and catalysis. Herein we report gold nanoclusters with hydrodynamic diameters of ~50 nm composed of ~10 nm primary particles. The kinetically controlled assembly of clusters occurs simultaneously with the reaction to synthesize the primary particles. The clustering is induced by attractive van der Waals forces that dominate over the steric and electrostatic repulsive forces present. Stability is provided using a single, biocompatible polysaccharide in either carboxymethyl dextran or dextran. High NIR shifts of the surface Plasmon resonance are achieved through close interparticle spacings of primary particles, deviations in morphology from that of a sphere of primaries, and the surface roughness that results from the clustering process. The cluster size is mediated by controlling the relative nucleation and growth rates of primary particles using a moderate reducing agent in NH2OH and glucose at pH 8.7. It will be shown that cluster size is also dependent on Au concentrations in solution. Maintaining low Au concentrations will allow for smaller clusters. In particular, the small size and high NIR extinction at longer wavelengths (800-1100 nm) makes these particles of interest for optical imaging applications in biology, as particles with a hydrodynamic diameter of ~50 nm have long blood lifetimes.