Browsing by Author "Jan Genzer, Committee Member"

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Affinity Adsorption of Viruses Using Small Peptide Ligands
(2008-07-11) Heldt, Caryn L; Robert M. Kelly, Committee Member; Jan Genzer, Committee Member; Lee-Ann Jaykus, Committee Member; Orlando J. Rojas, Committee Member; Ruben G. Carbonell, Committee Chair
Affinity Interaction between Hexamer Peptide Ligand HWRGWV and Immunoglobulin G Studied by Quartz Crystal Microbalance and Surface Plasmon Resonance.
(2010-05-03) Shen, Fei; Ruben Carbonell, Committee Chair; Jason Haugh, Committee Member; Jan Genzer, Committee Member; Orlando Rojas, Committee Member
Asphaltene Self-Assembly
(2008-11-07) Verruto, Vincent J.; Peter K. Kipatrick, Committee Chair; Jan Genzer, Committee Member; Orlin D. Velev, Committee Member; Saad A. Khan, Committee Member
Despite a strong push for alternative energy, fossil fuels remain an important energy source given an ever-increasing global energy demand. As crude oil prices continue to soar, petroleum producers and refiners are looking to â€œunconventionalâ€ crudes, such as bitumen and heavy crude oils, to meet their needs. Unlike light-sweet â€œconventionalâ€ feedstocks, heavy crudes are often rich in a fraction that is characteristically polydisperse, of high-MW, polyaromatic, polar, and surface-active. Consequently, asphaltenes present expensive challenges associated with aggregation, flocculation, precipitation, deposition, and emulsion stabilization. The scope of the work here focuses on two important aspects of asphaltene self-assembly: bulk phase aggregation and interfacial film formation. Using small-angle neutron scattering (SANS) we expand the description of these aggregates beyond their size (~50-100 Ã…), shape (discoidal), and degree of solvent entrainment (30-50% by volume), to also include the entrained solvent composition when dissolved in binary solvent mixtures. We then use SANS to evaluate the physical and chemical properties of the stabilizing interfacial films in water-in-model oil emulsions. In Part I of this SANS of emulsions investigation, we unravel the thickness and asphaltenic composition of the interfacial films from emulsions made in three solvents of varying aromaticity. We will show that for these three systems, emulsion stability depended on the asphaltenic composition in the films as opposed to the film thickness, which was nearly constant among the three solvents. In the Part II we seek a more thorough definition of the interfacial film composition by using neutron contrast variation to illuminate not just the asphaltenic makeup, but the solvent, water, and, when applicable, additive composition within the films. Finally, through the use of interfacial shear and dilatational rheology, we explore the various interactions at model oil/water interfaces that influence interfacial film assembly. We find that electrostatic interactions between charged adsorbed species largely dictate the transient evolution of the interfacial elasticity at acidic, neutral, and basic pH. Furthermore, through our comparisons of the interfacial rheological behavior of asphaltenes and model polycyclic compounds, we are able to better understand the physicochemical phenomena that contribute to asphaltene interfacial dynamics.
Broadband Polarization Gratings for Efficient Liquid Crystal Display, Beam Steering, Spectropolarimetry, and Fresnel Zone Plate.
(2009-11-30) Oh, Chulwoo; Philip J. Bos, Committee Member; Jan Genzer, Committee Member; David E. Aspnes, Committee Member; David Schurig, Committee Member; Michael J. Escuti, Committee Chair
We introduce achromatic polarization gratings (PGs) as broadband polarizing beam splitters, which exhibit practically ~100% efficient diffraction over a wide range of spectrum. We have experimentally demonstrated high-quality achromatic PGs fabricated using holographic photoalignment techniques for liquid crystal (LC) materials. Non-ideal diffraction behaviors of the PGs have been investigated beyond the paraxial limitations (i.e., small grating periods, oblique incidence, and finite gratings) via extensive numerical analysis based on the finite-difference time-domain method. Design and fabrication of small-period PGs are also discussed to show how to achieve high diffraction efficiency and large diffraction angles at the same time. Three key innovative technologies utilizing the unique diffraction properties of the PGs have been introduced and experimentally demonstrated. The first application for light-efficient LC displays is the polymer-PG display. We have developed a prototype projector based on the polymer-PG display as a viable solution for ultra-bright pico-projector applications. Second, two novel beam steering concepts based on the PG diffraction have been proposed: a non-mechanical, wide-angle beam steering system using stacked PGs and LC waveplates and the Risley grating as a thin-plate version of the Risley prism. The third PG application is in advanced imaging and non-imaging spectropolarimetry. In the last part of this Dissertation, we introduce a polarization-type Fresnel zone plates (P-FZPs), comprising of spatial-variant linear birefringence or concentric PG (CPG) patterns. We have experimentally demonstrated high-quality P-FZPs, which exhibit ideal Fresnel-type lens effects, formed as both LC polymer films and electro-optical LC devices. In summary, we have explored the fundamental diffraction behavior of the polarization gratings and their applications in various optics and photonics technologies. We conclude this Dissertation with our suggestions of a number of potential innovations and advances in technologies that can be enabled by polarization gratings and related technologies.
Brownian Motion in Polymer and Surfactant Solutions
(2007-07-04) Tanner, Shaun Anthony; Christopher Daubert, Committee Member; John van Zanten, Committee Chair; Saad Khan, Committee Member; Jan Genzer, Committee Member
The objective of this work is to investigate the dynamical behavior of aqueous polymer solutions, and aqueous poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide), commercially available as Pluronics™, triblock copolymer surfactant solutions at elevated temperatures and pressures. Diffusing wave spectroscopy is utilized to monitor the thermal motion of dispersed colloidal particles in the solutions. The measured mean squared displacement (MSD) of the colloidal particles is used to infer the microrheological properties of the solutions, since the MSD is directly proportional to the microscopic creep compliance. This technique allows for the motion of the colloidal particles to be resolved at times as short as ˜ 10-6 s, allowing access to the microrheological properties at frequencies as large as 1MHz. For the case of aqueous poly(ethylene oxide) (PEO) solutions, the MSD of the colloidal particles is shown to change with temperature and pressure variations, owing to modification of water hydrogen bonding properties. These colloidal sphere MSD variations reflect changes in the solvent quality of water for PEO The MSD of tracer particles is also used to study aqueous Pluronic™ F108 solutions, which exhibit rich phase behavior with concentration, temperature, and pressure. These solutions are shown to behave essentially as soft, repulsive spheres. Also, the effect of Pluronic-R™ 25R4 on the phase behavior and microrheological properties of F108 solutions is studied. The observed microrheological behavior of these systems is discussed within the context of theoretical descriptions of high-frequency colloidal dynamics.
Colloidal Gels of Fumed Silica: Microstructure, Surface Interactions and Temperature Effects
(2006-06-29) Sanchez, Angelica Maria; Wendy Krause, Committee Member; Peter S. Fedkiw, Committee Member; Jan Genzer, Committee Member; Saad A. Khan, Committee Chair; Orlin D. Velev, Committee Member
The interactions of fumed oxides with organic solvents, polymers and biological systems are of great interest as they can be utilized as viscosity modifiers, fillers or adsorbents when mixed in or in contact with such materials. Fumed silica is of particular interest due to the large surface area that its branched structure provides for establishing interactions with specific matrices or chemical reactive groups. If these small particles are dispersed in an adequate medium, they can form suspensions, flocculated systems or three-dimensional networks; thus an understanding of how to control this microstructure is of paramount importance. Extensive research involving fumed silica dispersions has been conducted in areas such as inks, cosmetics, and paints. More recently, alternative novel applications such as fiber optic cables and composite polymer electrolytes, our major research effort in the past years, have gained especial importance. In this work, various types of fumed silica particles have been dispersed in different oligoethers and poly(ethylene oxide) PEO and their properties evaluated with the aim to finely tune them for improved performance during end use. Rheology, a reliable, easy, and readily available technique has been employed not only to characterize the systems, but also to study their microstructure and establish correlations that can be subsequently employed to tailor the material for the particular application. In particular, we examined dispersions of hydrophobic and hydrophilic fumed silica in oligoethers of different molecular weights and end group composition at different temperatures by using dynamic rheology. We observed that hydrophilic fumed silica particles form gels in the less polar oligoethers, whereas the hydrophobic ones form a network in all the oligoethers employed. Increasing the temperature increases irreversibly the gel modulus of the system containing hydrophilic fumed silica and the oligoether with the largest end group content, poly(ethylene glycol)dimethyl ether PEGdm(250). We also studied the effect of fumed silica particle concentration in PEGdm(250); a larger relative change in the gel modulus was observed for the materials containing lower concentration of fumed silica. A "concentration" effect due to polymer adsorption and chemical reaction on the particles' surface seems to explain this anomalous observation. We also study how the hydrophobic group length attached on the fumed silica particles affects the rheological properties, in particular the yield stress of the dispersions. Additionally, we take advantage of a material instability known as wall slip to explore how chemical composition of the shearing surface modifies the flow behavior of gels containing particles with different surface functionalities. Dynamic stress sweep experiments with hydrophobic and hydrophilic surfaces suggest that specific interactions between the nanoparticles contained in the gel and the plates' surface control the extent of wall slip. By combining dynamic mechanical rheology and flow visualization, it was possible to accurately determine the yield stress of the gels and differentiate the observed rheological behavior from slippage. Mixtures of fumed silica particles, hydrophobic and hydrophilic, were dispersed in PEGdm(250) and the effects of temperature in the rheological properties of the systems evaluated. The mixtures showed a negative deviation from the log-additive mixing rule within the temperature range studied. This indicates that the two types of particles form independent networks that provide less mechanical stability than each individual component in the system. In order to explore the effects of adding a low-molecular weight oligoether to PEO containing hydrophobic and hydrophilic fumed silica, blends of high- and lo- molecular weight (MW) PEOs were prepared by melt and solution mixing. In the composition range studied, the blends containing hydrophilic fumed silica showed to be more susceptible to the presence of the low-MW component. Blends containing larger amounts of the high-MW component behave liquid-like as the low-MW concentration in the blend increases. This behavior reverses at the 50⁄50 high- to low-MW composition, where the gel formation mechanism of the fumed silica in the low-MW component dominates and a gel-like behavior is observed. Both hydrophobic and hydrophilic fumed silica showed the same trend. Our results are encouraging and establish a new approach for designing methods that facilitate processing of these particulate materials and the control of their flow and ?at rest? properties while establishing the underlying mechanisms dictating such behavior.
Controlling Sub-Microdomain Structure in Microphase-Ordered Block Copolymers and Their Nanocomposites
(2008-08-08) Bowman, Michelle Kathleen; Richard Spontak, Committee Chair; Jan Genzer, Committee Member; Russell Gorga, Committee Member; Carl Koch, Committee Member; Mark Luo, Committee Member; Steve Smith, Committee Member
Distribution of Liquid Drops on Solid Surfaces between Flat Surface and Fibers.
(2010-05-26) Du, Jinmei; Stephen Michielsen, Committee Chair; Hoon Joo Lee, Committee Chair; Keith Beck, Committee Member; Jan Genzer, Committee Member; Brian Matthews, Committee Member; Orlando Rojas, Committee Member
Formation of Organic-Inorganic Nano/Microcomposites using Environmentally Benign Solvents or Processes
(2006-08-07) Frankowski, David John; Jan Genzer, Committee Member; Juan P. Hinestroza, Committee Member; Richard J. Spontak, Committee Co-Chair; Saad A. Khan, Committee Co-Chair
This dissertation involves development of organic/inorganic hybrids utilizing supercritical carbon dioxide (scCO₂), wherein at least one component has a characteristic length scale below 10 µm. One of the systems studied is a block copolymer (BC) comprising CO₂-philic (polydimethylsiloxane) and metallated (polyferrocenylsilane) (PFS) blocks. The BC dissolves into the CO₂-phase and forms soft nanostructures of varying size, shape and complexity depending on the pressure, temperature and time of exposure. The nanostructures were "harvested" upon depressurization and analyzed via transmission electron microscopy. Systems such as these are of particular relevance to the microelectronics sector, and this work is intended to open new avenues to novel materials that can be used therein. Another composite system focused not on the CO₂-rich phase, but the polymer-rich phase and CO₂-induced swelling and plasticization. Thin films of functionalized PFS homopolymer, a ceramic precursor, were exposed to scCO₂ in a high-pressure batch vessel at varying temperatures and pressures and for differing saturation times. Isotropic microcellular polymeric foams were produced similar to that for commodity polymers like poly(methylmethacrylate) and polystyrene (PS). Additionally, judicious parameter selection produced bimodal distributions of pore cells and anisotropic pore cells termed "V-directional" cells from the neat homopolymer. The final composite system comprised silicate (clay) platelets that serve as hard fillers with either nano- or micro-size scales depending on the platelet dispersion. Various fabrication techniques and formulations were explored and this dissertation describes a mechanism for producing intercalated or exfoliated nanocomposites (NCs) from an immiscible system. Exposure of the immiscible NC to an oxidative environment (i) breaks up polymer chains bridging the edges of the silicate platelets allowing a less obstructed pathway for intercalation and (ii) induces chain scission near the periphery of the platelets to provide chains of reduced molecular weight that have more favorable intercalation capability. scCO₂ treatment of an immiscible NC system may be postulated to increase the diffusion of chains into the clay gallery, change interfacial tensions or swell the interlayer spacing to increase the d-spacing, all of which might promote intercalation. However, our results indicate that scCO₂ behaves similar to inert environments like vacuum and nitrogen for our particular system comprising PS and organically-modified montmorillonite (OM-MMT). To better understand our system, an analysis of the individual polymer and clay properties and stability were undertaken. Insight was gained on the limited thermal stability of OM-MMT and the extreme alignment of clay platelets after processing. The latter may help in the development of impermeable membranes when the platelets are aligned with their surface normal parallel to the diffusive direction.
Free Meniscus Coating Using Compressed Carbon Dioxide
(2003-07-16) Novick, Brian Jeffery; Gregory Parsons, Committee Member; Ruben Carbonell, Committee Co-Chair; Jan Genzer, Committee Member; Joseph DeSimone, Committee Co-Chair; Orlin Velev, Committee Member; Peter Kilpatrick, Committee Member
This thesis investigates the use of compressed carbon dioxide as a replacement solvent for web based coating processes including the free meniscus based devices. We use theory, such as Tallmadge's Four Force Inertial Theory, to show why carbon dioxide based free meniscus coaters are advantageous over normal coating processes. We show theoretically that thinner films can be formed at faster rates, that important deposition forces can be controlled, that there is better penetration into porous materials, that there are less capillary forces, that films may have increased uniformity, and that there is better process control. This research also details how coatings can be applied by using a novel high pressure free meniscus coater (hFMC) to deposit thin films of important perfluorpolyether lubricants for microelectronics. The coater was designed as part of this thesis. We have investigated what substrates can be coated by showing that compressed gaseous carbon dioxide induces the wetting of low enery surfaces by low Mw coating precursors. We have shown that the hFMC device can be used to take advantage of the induced wetting. Biocompatible precursors have been coated onto porous PTFE and polymerized at high pressure. The coating process results in porous PTFE with significantly different properties than uncoated samples. We have also investigated what materials can be coated from carbon dioxide by studying the rheological effects of carbon dioxide on coating precursors. We find that changing the backbone structure, end groups, or side groups on the precursor affect the mixture viscosity. The results of this investigation open up new potential applications of this environmentally benign coating process.
How Asphaltenes Aggregate: Role of Chemistry and Solvent
(2005-05-26) Gawrys, Keith Louis; Saad A. Khan, Committee Member; Jan Genzer, Committee Member; Stefan Franzen, Committee Member; Richard J. Spontak, Committee Member; Peter K. Kilpatrick, Committee Chair
Asphaltenes were separated into several subfractions by sequential precipitation from n-heptane and toluene. Three distinct solubility regimes were indicated where the subfraction chemical and colloidal behaviors varied significantly with total precipitated asphaltenes. The earliest fractions precipitated had lower than average aromaticity and atomic N/C ratios and contained significant inorganic solids contents. Subfractions isolated in the second regime varied significantly in aromaticity and had systematically decreasing N/C ratios and increasing O/C ratios with increasing asphaltene yield. The most aromatic subfractions formed the largest aggregates in solution. Subfractions in the most soluble regime were more 'resin-like' in chemical composition and aggregation behavior. Application of various geometric form factors to the SANS scattering spectra of asphaltenes suggested the aggregates are polydisperse radius oblate cylinders. A polydisperse cylinder model provided ranges of average particle thicknesses (5-32Å), radii (25-125Å), and polydispersity (~30%). Calculation of aggregate molar masses suggested solvent entrainment within the aggregates from 30-50% (v/v) that was consistent with previous viscosity measurements. Changes in the apparent aggregate mass with concentration indicated deviations from ideal solutions that were quantified through the calculation of second virial coefficients (A2). A2 values varied significantly with solvent conditions, concentration, and chemical composition of the solute. Results suggested that interactions of asphaltenes, resins, and solvent are dominated by dispersion and p-bonding interactions. Experimentally measured A2 values under-predicted those calculated on an excluded volume basis, suggesting energetic interactions of the solute and entrained solvent are significant. UV-vis spectroscopy was used to determine the solubility of poly-nuclear aromatics in binary solvent mixtures with the intention of extending the methods to asphaltenic systems. Binary solvent mixtures were selected to probe specific intermolecular solvent-solute interactions (i.e., dispersion, polar, and hydrogen bonding). Solubility data were fit to a three-dimensional solubility parameter model that provided accurate solubility predictions in some solvents with less than 30% error. The predictive capability of the model decreased as one or more contributions to the solvent solubility parameter deviated from the solute. Experiments measuring solubility in a multi-component solute mixture suggested a need to incorporate aggregation in the model.
Hydrophobically Modified Associative Polymers: Solution Rheology and Applications in Electrospinning
(2008-03-25) Talwar, Sachin; Saad A. Khan , Committee Chair; Benham Pourdeyhimi , Committee Member; Jan Genzer, Committee Member; Juan P. Hinestroza, Committee Member
Hydrophobically modified associative polymers are generating considerable research interest owing to their ability to be used in a variety of applications ranging from paints and coatings to drug delivery. These polymers have pendant hydrophobic groups that form a reversible physical network in an alkaline solution comprising of both intra- and inter-molecular hydrophobic junctions resulting in a unique thickening mechanism. The present study can essentially be divided into two parts. In the first part, we discuss how nonionic surfactants, both individually and in binary surfactant mixtures, can be effectively used to modify the rheology of associative polymers via formation of free as well as bound micelles incorporating polymer hydrophobes. We also demonstrate the applicability of nonionic surfactants in modulating hydrophobic associations in these polymers in the presence of inclusion compounds called cyclodextrin. Electrostatic spinning or electrospinning of nanofibers has drawn considerable research attention in recent years. It involves the application of an electric filed to a polymer solution or melt to facilitate production of fibers in the sub-micron range. The scope and utility of associative polymers can be broadened further by incorporating them in precursor electrospinning solutions due to their ability to alter solution rheology. In the second part of this study, we focus on gaining insights into the role of rheology on fiber formation by including associative polymers in electrospinning solutions. We further illustrate how the concept of using surfactants to control viscoelasticity of these polymers can be extended to fabricate electrospun nanofibers. Finally, we establish the utility of associative polymers in improving the morphology of electrospun fibers through significant changes in viscosity and viscoelasticity of precursor solutions. This concept of using associative polymers is extended further to other associative polymers that interact via mechanisms other than hydrophobic associations.
Investigation of Synthetic and Natural Lubricants
(2008-08-19) Liang, Jing; Sam M. Hudson, Committee Member; Jan Genzer, Committee Member; Alan E. Tonelli, Committee Co-Chair; Wendy E. Krause, Committee Chair
Nanoindenter-based scratch tests are simple, rapid, and reliable method to evaluate the tribological properties of materials at the microscale. It not only works well on dry polymer surfaces, but also can evaluate thin fluid film lubrication on polymer surfaces. By using different experimental tips (different shape and radius) on the same polymer surfaces, different coefficient of friction results are obtained. Because of the different molecular structures, different polymer surfaces show different tribological properties. Furthermore, the relationship between the adsorption of lubricant and the lubricity of lubricant has been studied. Lubrication is an extremely complex phenomenon and it can be influenced dramatically by the lubricant, including the lubricants'molecular weight, molecular structure (both its chemical structure and its geometry (et al., di-block versus tri-block) and chain length, the solvent, the substrates, including the substrates' roughness and chemistry, the number of lubrication layers, the sliding velocity, and applied load. In addition, the lubrication properties of synovial fluid and its components (sodium hyaluronate (HA), proteins, and phospholipids) have also been studied. The concentration and molecular weight of sodium hyaluronate both have great effect on its lubricity. The concentrations of gamma-globulins and albumin also have effect on their lubricating properties. With just one type of protein or with excessive proteins, the solutions looses lubricity. Addition of HA can improve the lubricating properties of some protein solutions. DPPC (dipalmitoyl phosphatidylcholine) also shows some lubricity for polyethylene. However, without HA, the concentration of DPPC has no effect on its lubricity at the microscale. Addition of HA can improve the lubricity of DPPC solution when the concentration of DPPC is high. Depending on the concentration, every component has some lubricity, but working synergistically at the concentrations found in typical, healthy synovial fluid can greatly improve their lubricity. Indeed, the Synovial fluid model, which has gamma-globulins at 7 mg⁄mL, albumin at 11 mg⁄mL, HA (MW: 2.0 MDa) at 3 mg⁄mL, showed the best lubricity.
Investigation of the utility of islands-in-the-sea bicomponent fiber technology in the spunbond process
(2007-10-02) Fedorova, Nataliya Vasylivna; Donald Shiffler, Committee Member; Stephen Michielsen, Committee Member; Trevor Little, Committee Co-Chair; Behnam Pourdeyhimi, Committee Co-Chair; Jan Genzer, Committee Member
Life Cycle Inventory Analysis of Medical Textiles and Their Role in Prevention of Nosocomial Infections
(2009-12-07) Ponder, Celia Steward; Jan Genzer, Committee Member; Marian McCord, Committee Member; Stephen Michielsen, Committee Member; Christine Grant, Committee Chair
Biocidal finishes grafted onto medical textiles are a potential technology to reduce nosocomial infection transmission. But is the application and use of biocidal finishes worth the environmental cost? Life cycle inventories (LCI) are a tool to show the resources used and emissions generated over the life cycle of a product. In this research, life cycle inventories are utilized in the design of a reusable medical garment with a biocidal finish to: assess options for the biocidal chemical, compare the reusable garment with a disposable garment, and assess the use of a biocidal finish in a hospital setting. The cradle-to-gate life cycle inventories of two biocidal halamines Ã¢â‚¬â€œ 3-allyl-5,5-dimethyl hydantoin (ADMH) and dimethylol-5,5-dimethyl hydantoin (DMDMH) Ã¢â‚¬â€œ are compared to allow the manufacturer to select the chemical that consumes less energy and raw materials and generates fewer emissions. The reusable garment is then compared with a disposable gown of similar use to determine, cradle-to-use, which has the better environmental performance. Life cycle inventory analysis is also used to determine the resources and emissions saved by the hypothetical use of a biocidal patient gown and the subsequent reduction in nosocomial infections. This is a novel area for LCI, as no LCI has been studied for treating an infection previously. When a patient contracts an infection while in the hospital, additional materials are used to test the patient, to provide contact isolation, and to treat the patient. Inventories were analyzed for each phase of this treatment using MRSA (Methicillin-resistant Staphylococcus aureus) as the nosocomial infection contracted and treated. In this research study, the drug therapy consists of vancomycin hydrochloride. While previous life cycle inventory studies have determined that solvent usage is the largest user of resources for pharmaceutical production, the current study shows that fermentation is actually the largest consumer of raw materials and energy in the cradle-to-gate (CTG) manufacture of vancomycin hydrochloride. Of the phases in infection treatment studied, contact isolation utilizes the most raw material and energy resources and generates the most emissions due to the use of disposable gowns and gloves. Finally, the LCI for treating an infection was compared with the LCI for using the biocidal finish. If the usage of the biocidal patient gown reduces the nosocomial infection rate more than 2%, the resulting reduction in raw material consumption, energy consumption, and emissions generated is enough to overcome that of using a biocidal garment. In addition, the impact of dyeing processes on the cradle-to-gate inventory of a textile product is investigated using carpet as a case study. Using a life cycle approach, gate-to-gate inventories for five nylon coloring processes are performed and compared to the cradle-to-gate life cycle inventory of the carpet. This analysis shows that dyeing can be a large contributor to the carpet cradle-to-gate energy usage.
Ligands from Combinatorial Peptide Libraries for Virus Removal
(2004-09-22) Salm, Jeffrey R; Jan Genzer, Committee Member; Dennis T. Brown, Committee Co-Chair; Ruben G. Carbonell, Committee Chair; Peter K. Kilpatrick, Committee Member
Small peptides were investigated as affinity ligands for virus removal from human blood plasma. Sindbis virus (SV) was radiolabeled with ³⁵S and screened against a solid phase peptide library. The screening identified 9 hexapeptides that were synthesized on a TosoBioseparations Toyopearl 650M Amino Resin. The peptide sequences SGKPVA and IATDGG were found to remove approximately 3 logs and 2.4 logs of SV from buffer respectively and approximately 1.5 logs of SV from 50% human blood plasma (HBP). Toyopearl Amino resin was used as a control and bound only 0.6 logs of SV in both buffer and 50% HBP. Good agreement was seen between infectious quantification methods and quantification of the virus using radiation. Injections of several batches of SV showed variations between the batches. A similar screening procedure was also applied to radiolabeled canine parvovirus (CPV). Screening against a solid phase library identified 25 leads through to be specific to CPV. Tests with a portion of these leads found less than 0.5 logs of CPV clearance in both buffer and 50% HBP. Electron microscopy of the CPV used in these experiments showed that large aggregates of virus were present in the radiolabeled virus. Infectious assays for CPV were also problematic and inconsistent. Work done in collaboration with the American Red Cross (ARC) identified several leads capable of binding porcine parvovirus (PPV) and human B-19 parvovirus (B-19). Selected leads were tested for viral clearance from 1 ml samples of spiked buffer and 50% HBP. The resins were shown to bind at least 4 logs of PPV and B-19 but less than 0.5 logs of CPV. Experiments with 10 ml samples of spiked buffer and 7.5% HBP showed that the resins were capable of 6 logs of PPV clearance. 10 ml experiments performed in 50% HBP showed an initial clearance of 6 logs of virus. Subsequent fractions showed decreasing clearance with complete breakthrough occurring by the 9th 1 ml fraction. Experiments that compared three different column systems showed that each system produced identical log clearance results. This work shows that screening a solid phase library can identify peptide ligands and that the leads can be used for viral clearance from HBP.
Liquid-Phase Deoxygenation of Free Fatty Acids to Hydrocarbons Using Supported Palladium Catalysts
(2010-04-30) Immer, Jeremy Glen; Jerry L. Whitten, Committee Member; Steven W. Peretti, Committee Member; Jan Genzer, Committee Member; H. Henry Lamb, Committee Chair
Hydrocarbon biofuels that are drop-in replacements for traditional petroleum-derived liquid fuels can be produced from edible and inedible fats and oils (triglyceride sources) via thermocatalytic processes. Liquid-phase deoxygenation of stearic acid (SA) in dodecane at 300Â°C and 15 atm was employed to screen supported noble metal catalysts for decarboxylation of free fatty acids to hydrocarbons. Commercial samples of Pt/C, Pd/C (4), Pd/Al2O3, and Pd/SiO2 catalysts and an in-house prepared Pd/SiO2 catalyst (each containing 5 wt.% metal) were screened under flowing 0, 5, and 10% H2 (balance He). Under flowing He, most of the catalysts studied failed to achieve 100% SA conversion after 4 h under reaction conditions due to rapid deactivation. The exception was a uniformly impregnated Pd/C catalyst that gave >99% conversion in ~1 h with 99% CO2 selectivity. All of the catalysts were far more stable under H2 yielding nearly complete SA conversion after 4 h; however, they differed markedly in their CO2 selectivities. Pd/SiO2 and Pt/C catalysts were selective toward decarbonylation (CO production), and Pd/C and Pd/Al2O3 catalysts were selective toward decarboxylation. Even under H2, the uniformly impregnated Pd/C catalyst was the most active and selective for the hydrogen-neutral decarboxylation pathway. Semi-batch deoxygenation of SA employing this 5 wt.% Pd/C catalyst was investigated further using on-line quadrupole mass spectrometry. With fresh catalyst, SA deoxygenation under He occurred rapidly with very high CO2 selectivity; however, reuse of the catalyst showed an orders of magnitude loss of decarboxylation activity and high decarbonylation selectivity. Experiments employing smaller amounts of fresh catalyst evidenced that decarboxylation activity under He is limited to ~220 turnovers. Attempts to reactivate the used Pd/C catalyst by H2 treatment were only modestly effective. Increased catalyst lifetime (>2200 turnovers) was achieved by employing a H2-containing purge gas; however, the decarboxylation rate decreases with increasing H2 partial pressure resulting in lower CO2 selectivity. Increasing the initial SA concentration also inhibited decarboxylation, substantially prolonging the batch time and yielding lower overall CO2 selectivity. The origin of this effect was traced to catalyst poisoning by endogenous CO from the decarbonylation pathway. Catalyst poisoning experiments demonstrated that CO strongly inhibits the decarboxylation pathway and that the inhibitory effects of CO and H2 are additive. Under conditions of strong decarboxylation inhibition, the decarbonylation rate was unaffected, and we infer that decarboxylation occurs over different catalytic sites than decarbonylation. An elementary reaction sequence for Pd-catalyzed decarboxylation is proposed which accounts for our observations. Fed-batch deoxygenation of SA and oleic acid was demonstrated in a 50-mL stirred autoclave reactor with continuous feeding for run times up to 24 h. The maximum quasi-steady state decarboxylation rate observed under 5% H2 was 0.43 mmol/gcatâ€¢min (0.078 s-1 turnover frequency). When higher H2 partial pressures were employed, an abrupt switchover in product selectivity from CO2 to CO was observed. Higher CO selectivity leads to increased H2 consumption due to hydrogenation of heptadecene, the primary product of the decarbonylation pathway. The on-stream time at which this switchover occurs was found to increase with decreasing H2 pressure. We infer that the switchover phenomenon arises from H2 inhibition of the decarboxylation pathway resulting in SA accumulation. SA accumulation increases the decarbonylation rate leading to further inhibition of the decarboxylation pathway by endogenous CO. Parametric studies involving SA feed rate, H2 partial pressure and exogenous CO partial pressure support the proposed switchover mechanism. Inhibition of decarboxylation activity was reversible at least in the short term by lowering the H2 or CO partial pressure or stopping SA injection; however, if a catalyst was aged >10 h under reaction conditions favoring decarbonylation, decarboxylation activity could not be recovered.
Materials Science and Sensing Applications of Surface Plasmon Resonance in Conducting Metal Oxides
(2008-06-15) Rhodes, Crissy Lynette; Jan Genzer, Committee Member; Stefan Franzen, Committee Chair; Lin He, Committee Member; Edmond Bowden, Committee Member
Meniscus-Directed Assembly of Biologically Active Coatings of Cells, Microparticles, and Nanoparticles
(2009-04-23) Stamm, Lindsey Brooks Jerrim; Orlin Velev, Committee Chair; Anne Lazarides, Committee Member; Jan Genzer, Committee Member; Christine Grant, Committee Member; Carol Hall, Committee Member
Convective assembly principles and techniques were used in two complementary studies for depositing close packed yeast-coated surfaces and gold nanoparticle wires. Convective assembly at high volume fraction was used for the rapid deposition of uniform, close-packed coatings of Saccharomyces cerevisiae onto glass slides. A computational model was developed to calculate the thickness profiles of such coatings for various experimental conditions. Both experimentation and numerical simulations demonstrated that the deposition process is strongly affected by the presence of sedimentation. The deposition device was inclined to increase the uniformity of the coatings by causing the cells to sediment toward the three-phase contact line. In accordance with the simulation, the experiments showed that both increasing the angle of the device and decreasing the angle between the slides increased the uniformity of the deposited coatings. Finally, the Ã¢â‚¬Å“convective-sedimentationÃ¢â‚¬Â assembly method was used to deposit composite coatings of live cells and large latex particles as an example of biologically active composite coatings. These coatings were allowed to proliferate and demonstrate a proof-of-concept of a self-cleaning surface. Two methods were developed for the deposition of micro- and nanoparticles into linear assemblies that could be used in biosensors and biomaterials. In capillary-guided deposition, a capillary is withdrawn across a wettable substrate, resulting in the assembly of a particle line. We characterized the effects of particle concentration and withdrawal speed and correlated them to structure of the deposited assemblies. The particles are assembled into one of three different structures, depending on the particle volume fraction and deposition speed. We demonstrate that the metallic nanoparticle lines are Ohmically conductive. Using wedge-templated deposition, linear assemblies were deposited from sessile droplets on moderately hydrophobic surfaces. The particles convectively assemble at the freely-receding three-phase contact line and are pulled into a line against the wedge. The deposited lines can be long and narrow with a few breaks or significantly wider and shorter but unbroken. These methods could be used for engineered patterning of nanoparticle structures on surfaces.
Modification of Nylon 6 Structure via Nucleation
(2009-08-12) Mohan, Anushree; Bruce Novak, Committee Member; Jan Genzer, Committee Member; Alan E. Tonelli, Committee Chair; Richard Kotek, Committee Co-Chair
For nearly two decades inclusion compounds (ICs) have been formed by threading polymer chains into the cyclic starches, cyclodextrins (CDs). Non-covalently bonded crystalline ICs have been formed by threading CDs, onto guest nylon-6 (N6) chains. When excess N6 is employed, non-stoichiometric (n-s)-N6-CD-ICs with partially uncovered and dangling N6 chains result. We have been studying the constrained crystallization of the N6 chains dangling from (n-s)-N6-CD-ICs in comparison with bulk N6 samples, as a function of N6 molecular weights, lengths of uncovered N6 chains, and the CD host used. While the crystalline CD lattice is stable to ~ 300Ã‚Â° C, the uncovered and dangling, yet constrained, N6 chains may crystallize below, or be molten above ~225Ã‚Â° C. In the IC channels formed with host ÃŽÂ±- and ÃŽÂ³-CDs containing 6 and 8 glucose units, respectively, single and pairs of side-by-side N6 chains can be threaded and included. In the ÃŽÂ±-CD-ICs the ~ 0.5nm channels are separated by ~ 1.4nm, while in ÃŽÂ³-CD-ICs the ~ 1nm channels are ~ 1.7 nm apart, with each ÃŽÂ³-CD channel including two N6 chains. The constrained dangling chains in the dense (n-s)-N6-CD-IC brushes crystallize faster and to a greater extent than those in bulk N6 melts, and this behavior is enhanced as the molecular weights/chain lengths of N6 are increased. Furthermore, when added at low concentrations (n-s)-N6-CD-ICs serve as effective nucleating agents for the bulk crystallization of N6 from the melt. Because of the biodegradable/bioabsorbable nature of CDs, (n-s)-polymer-CD-ICs can provide environmentally favorable, non-toxic nucleants for enhancing the melt crystallization of polymers and improving their properties.