Matching Items (3)
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- All Subjects: Polymers
- All Subjects: Water--Purification--Vaporization.
- Creators: Dai, Lenore L
Description
The rheological properties at liquid-liquid interfaces are important in many industrial processes such as manufacturing foods, pharmaceuticals, cosmetics, and petroleum products. This dissertation focuses on the study of linear viscoelastic properties at liquid-liquid interfaces by tracking the thermal motion of particles confined at the interfaces. The technique of interfacial microrheology is first developed using one- and two-particle tracking, respectively. In one-particle interfacial microrheology, the rheological response at the interface is measured from the motion of individual particles. One-particle interfacial microrheology at polydimethylsiloxane (PDMS) oil-water interfaces depends strongly on the surface chemistry of different tracer particles. In contrast, by tracking the correlated motion of particle pairs, two-particle interfacial microrheology significantly minimizes the effects from tracer particle surface chemistry and particle size. Two-particle interfacial microrheology is further applied to study the linear viscoelastic properties of immiscible polymer-polymer interfaces. The interfacial loss and storage moduli at PDMS-polyethylene glycol (PEG) interfaces are measured over a wide frequency range. The zero-shear interfacial viscosity, estimated from the Cross model, falls between the bulk viscosities of two individual polymers. Surprisingly, the interfacial relaxation time is observed to be an order of magnitude larger than that of the PDMS bulk polymers. To explore the fundamental basis of interfacial nanorheology, molecular dynamics (MD) simulations are employed to investigate the nanoparticle dynamics. The diffusion of single nanoparticles in pure water and low-viscosity PDMS oils is reasonably consistent with the prediction by the Stokes-Einstein equation. To demonstrate the potential of nanorheology based on the motion of nanoparticles, the shear moduli and viscosities of the bulk phases and interfaces are calculated from single-nanoparticle tracking. Finally, the competitive influences of nanoparticles and surfactants on other interfacial properties, such as interfacial thickness and interfacial tension are also studied by MD simulations.
ContributorsSong, Yanmei (Author) / Dai, Lenore L (Thesis advisor) / Jiang, Hanqing (Committee member) / Lin, Jerry Y S (Committee member) / Raupp, Gregory B (Committee member) / Sierks, Michael R (Committee member) / Arizona State University (Publisher)
Created2011
Description
The horizontal desalination units belonging to the humidification-dehumidification family purify water using air as a carrier gas. The temperature required for separation can vary from ambient to 99 °C so waste heat, fuel combustion, or solar collectors can drive the process. A unit in which air flows horizontally affords several advantages over similar vertical “Dewvaporation” towers (as an example), including ease of construction and potentially increased efficiency. The objective was to build and test horizontal units and identify areas of potential efficiency improvements. The desalination units consisted of: 1.) A series of aligned, corrugated, polypropylene sheets covered on the outside with absorbent, water-wettable cloth. 2.) A basin that caught saline water flowing downward from the absorbent cloth. 3.) Ten pumps to cycle the basin water back onto the cloth. 4.) An air blower on the front of the unit that drove air horizontally across the cloth, increasing the humidity of the air. 5.) A steam generator on the back of the unit producing steam that mixed with the incoming air to increase the temperature and humidity. 6) A steam box that caused the air to mix with the steam and return to flow inside the corrugations in the plastic sheets, creating a countercurrent heat exchanger as the exiting air transferred its heat to the incoming air and causing purified water to condense from the cooling, oversaturated air. The tested unit produced distillate at a rate of 0.87 gallons per hour with 13 parts per million total dissolved solids and an energy reuse factor of 2.5. Recommendations include the implementation of a continuous longitudinal pump design, a modification of the basin to accommodate top and bottom unit center dividers, increase in insulation coverage, and optimization of air flow rate.
ContributorsJackson, Skyler (Author) / Beckman, James R. (Thesis advisor) / Krause, Stephen J (Committee member) / Dai, Lenore L (Committee member) / Arizona State University (Publisher)
Created2015
Description
Identification of early damage in polymer composite materials is of significant importance so that preventative measures can be taken before the materials reach catastrophic failure. Scientists have been developing damage detection technologies over many years and recently, mechanophore-based polymers, in which mechanical energy is translated to activate a chemical transformation, have received increasing attention. More specifically, the damage can be made detectable by mechanochromic polymers, which provide a visible color change upon the scission of covalent bonds under stress. This dissertation focuses on the study of a novel self-sensing framework for identifying early and in-situ damage by employing unique stress-sensing mechanophores. Two types of mechanophores, cyclobutane and cyclooctane, were utilized, and the former formed from cinnamoyl moeities and the latter formed from anthracene upon photodimerization. The effects on the thermal and mechanical properties with the addition of the cyclobutane-based polymers into epoxy matrices were investigated. The emergence of cracks was detected by fluorescent signals at a strain level right after the yield point of the polymer blends, and the fluorescence intensified with the accumulation of strain. Similar to the mechanism of fluorescence emission from the cleavage of cyclobutane, the cyclooctane moiety generated fluorescent emission with a higher quantum yield upon cleavage. The experimental results also demonstrated the success of employing the cyclooctane type mechanophore as a potential force sensor, as the fluorescence intensification was correlated with the strain increase.
ContributorsZou, Jin (Author) / Dai, Lenore L (Thesis advisor) / Chattopadhyay, Aditi (Thesis advisor) / Lind, Mary L (Committee member) / Mu, Bin (Committee member) / Yu, Hongyu (Committee member) / Arizona State University (Publisher)
Created2014