8 research outputs found
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Molecular-Beam Mass-Spectrometric Analyses of Hydrocarbon Flames
Laminar flat flame combustion has been studied with molecular-beam mass-spectrometry (MBMS) for a fuel-rich cyclohexane (Ф = 2.003) flame, a fuel-lean toluene (Ф = 0.895), and a fuel-rich toluene (Ф = 1.497) flame. Different hydrocarbon species in these flames were identified, and their mole fraction profiles were measured. The information can be used to propose reaction mechanisms for the different hydrocarbon flames.
One MBMS apparatus located at Advanced Light Source (ALS) at Lawrence Berkeley National Laboratory was used to identify and measure the mole-fraction profiles of different species in these flames. The MBMS apparatus located at University of Massachusetts Amherst was used to measure the temperature profile of the cyclohexane flame. The temperature profile of two different fuel-rich toluene flames (Ф= 2.02 , Ф = 3.94) and a fuel-lean (Ф=0.452) methane flame were also measured with the UMass apparatus
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Discriminatory Bio-Adhesion Over Nano-Patterned Polymer Brushes
Surfaces functionalized with bio-molecular targeting agents are conventionally used for highly-specific protein and cell adhesion. This thesis explores an alternative approach: Small non-biological adhesive elements are placed on a surface randomly, with the rest of the surface rendered repulsive towards biomolecules and cells. While the adhesive elements themselves, for instance in solution, typically exhibit no selectivity for various compounds within an analyte suspension, selective adhesion of targeted objects or molecules results from their placement on the repulsive surface. The mechanism of selectivity relies on recognition of length scales of the surface distribution of adhesive elements relative to species in the analyte solution, along with the competition between attractions and repulsions between various species in the suspension and different parts of the collecting surface. The resulting binding selectivity can be exquisitely sharp; however, complex mixtures generally require the use of multiple surfaces to isolate the various species: Different components will be adhered, sharply, with changes in collector composition. The key feature of these surface designs is their lack of reliance on biomolecular fragments for specificity, focusing entirely on physicochemical principles at the lengthscales from 1 – 100 nm. This, along with a lack of formal patterning, provides the advantages of simplicity and cost effectiveness.
This PhD thesis demonstrates these principles using a system in which cationic poly-L-lysine (PLL) patches (10 nm) are deposited randomly on a silica substrate and the remaining surface is passivated with a bio-compatible PEG brush. TIRF microscopy revealed that the patches were randomly arranged, not clustered. By precisely controlling the number of patches per unit area, the interfaces provide sharp selectivity for adhesion of proteins and bacterial cells. For instance, it was found that a critical density of patches (on the order of 1000/m2) was required for fibrinogen adsorption while a greater density comprised the adhesion threshold for albumin. Surface compositions between these two thresholds discriminated binding of the two proteins. The binding behavior of the two proteins from a mixture was well anticipated by the single- protein binding behaviors of the individual proteins.
The mechanism for protein capture was shown to be multivalent: protein adhesion always occurred for averages spacings of the adhesive patches smaller than the dimensions of the protein of interest. For some backfill brush architectures, the spacing between the patches at the threshold for protein capture clearly corresponded to the major dimension of the target protein. For more dense PEG brush backfills however, larger adhesion thresholds were observed, corresponding to greater numbers of patches involved with the adhesion of each protein molecule. . The thesis demonstrates the tuning of the position of the adhesion thresholds, using fibrinogen as a model protein, using variations in brush properties and ionic strength. The directions of the trends indicate that the brushes do indeed exert steric repulsions toward the proteins while the attractions are electrostatic in nature. The surfaces also demonstrated sharp adhesion thresholds for S. Aureus bacteria, at smaller concentrations of adhesive surfaces elements than those needed for the protein capture. The results suggest that bacteria may be captured while proteins are rejected from these surfaces, and there may be potential to discriminate different bacterial types. Such discrimination from protein-containing bacterial suspensions was investigated briefly in this thesis using S. Aureus and fibrinogen as a model mixture. However, due to binding of fibrinogen to the bacterial surface, the separation did not succeed. It is still expected, however, that these surfaces could be used to selectively capture bacteria in the presence of non-interacting proteins.
The interaction of these brushes with two different cationic species PLL and lysozyme were studied. The thesis documents rapid and complete brush displacement by PLL, highlighting a major limitation of using such brushes in some applications. Also unanticipated, lysozyme, a small cationic protein, was found to adhere to the brushes in increasing amounts with the PEG content of the brush. This finding contradicts current understanding of protein-brush interactions that suggests increases in interfacial PEG content increase biocompatibility
Modified Asphaltene Capillary Deposition Unit: A Novel Approach to Inhibitor Screening
Asphaltene
deposition in capillaries is a tool that has been used
in an attempt to better understand asphaltene deposition in the field.
However, data reproducibility and inhibitor ranking present some challenges
with this technique. An improved asphaltene capillary deposition unit
and a novel experimental protocol were developed to address these
problems and are presented here. Using untreated Gulf of Mexico oil,
the current study generated reproducible amounts of asphaltene deposit
inside the capillary. It further identified the fact that residual
oil inside the capillary tube can be a limitation to inhibitor selection.
Evaluating the amount of asphaltene depositing in the capillary as
a function of time proved successful in addressing this issue and
led to inhibitor performance differentiation
Bacterial adhesion on hybrid cationic nanoparticle–polymer brush surfaces: Ionic strength tunes capture from monovalent to multivalent binding
The influence of ethanol addition on premixed fuel-rich propene-oxygen-argon flames
Kohse-Höinghaus K, Oßwald P, Struckmeier U, et al. The influence of ethanol addition on premixed fuel-rich propene-oxygen-argon flames. PROCEEDINGS OF THE COMBUSTION INSTITUTE. 2007;31(1):1119-1127.The role of ethanol as a fuel additive was investigated in a fuel-rich, non-sooting (C/O = 0.77) flat premixed propene-oxygen-argon flame at 50 mbar (5 kPa). Mole fractions of stable and radical species were derived using two different in situ molecular beam mass spectrometry (MBMS) set-ups, one located in Bie-lefeld using electron impact ionization (EI), and the other at the Advanced Light Source (ALS) at Berkeley using vacuum UV photoionization (VUV-PI) with synchrotron radiation. A rich propene flame, previously studied in detail experimentally and with flame model calculations, was chosen as the base flame. Addition of ethanol is believed to reduce the concentrations of benzene and small aromatic compounds, while augmenting the formation of other regulated air toxics such as aldehydes. To study the chemical pathways responsible for these effects, quantitative concentrations of about 35 species were determined from both experiments. This is also the first time that a detailed comparison of quantitative species concentrations from these independent MBMS set-ups is available. Effects of ethanol addition on the species pool are discussed with special attention on benzene precursor chemistry and aldehyde formation. (C) 2006 The Combustion Institute. Published by Elsevier Inc. All rights reserved
Using Flow to Switch the Valency of Bacterial Capture on Engineered Surfaces Containing Immobilized Nanoparticles
Toward an understanding of nanoparticle–bacterial
interactions
and the development of sensors and other substrates for controlled
bacterial adhesion, this article describes the influence of flow on
the initial stages of bacterial capture (<i>Staphylococcus aureus</i>) on surfaces containing cationic nanoparticles. A PEG (poly(ethylene
glycol)) brush on the surface around the nanoparticles sterically
repels the bacteria. Variations in ionic strength tune the Debye length
from 1 to 4 nm, increasing the strength and range of the nanoparticle
attractions toward the bacteria. At relatively high ionic strengths
(physiological conditions), bacterial capture requires several nanoparticle–bacterial
contacts, termed “multivalent capture”. At low ionic
strength and gentle wall shear rates (on the order of 10 s<sup>–1</sup>), individual bacteria can be captured and held by single surface-immobilized
nanoparticles. Increasing the flow rate to 50 s<sup>–1</sup> causes a shift from monovalent to divalent capture. A comparison
of experimental capture efficiencies with statistically determined
capture probabilities reveals the initial area of bacteria–surface
interaction, here about 50 nm in diameter for a Debye length κ<sup>–1</sup> of 4 nm. Additionally, for κ<sup>–1</sup> = 4 nm, the net per nanoparticle binding energies are strong but
highly shear-sensitive, as is the case for biological ligand–receptor
interactions. Although these results have been obtained for a specific
system, they represent a regime of behavior that could be achieved
with different bacteria and different materials, presenting an opportunity
for further tuning of selective interactions. These finding suggest
the use of surface elements to manipulate individual bacteria and
nonfouling designs with precise but finite bacterial interactions