@article{smith_mcgillivray_genzer_losche_kilpatrick_2010, title={Neutron reflectometry of supported hybrid bilayers with inserted peptide}, volume={6}, ISSN={["1744-683X"]}, DOI={10.1039/b915800f}, abstractNote={The insertion of a synthetic amphiphilic, α-helical peptide into a supported hybrid bilayer membrane (HBM) was studied by neutron reflectometry to elucidate the resulting nanostructure. The HBM consisted of a self-assembled monolayer of perdeuterated octadecanethiol on gold and an overlying leaflet of acyl-deuterated phosphatidylcholine (d-DMPC). Using contrast variation, several reflectivity spectra were recorded for each step of film fabrication, and simultaneously modeled. This analysis indicated that peptide insertion into the DMPC lipid leaflet is the likeliest mode of incorporation.}, number={5}, journal={SOFT MATTER}, author={Smith, Matthew B. and McGillivray, Duncan J. and Genzer, Jan and Losche, Mathias and Kilpatrick, Peter K.}, year={2010}, pages={862–865} } @article{verruto_le_kilpatrick_2009, title={Adsorption and molecular rearrangement of amphoteric species at oil-water interfaces}, volume={113}, number={42}, journal={Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces & Biophysical}, author={Verruto, V. J. and Le, R. K. and Kilpatrick, P. K.}, year={2009}, pages={13788–13799} } @article{turgman-cohen_fischer_kilpatrick_genzer_2009, title={Asphaltene Adsorption onto Self-Assembled Monolayers of Alkyltrichlorosilanes of Varying Chain Length}, volume={1}, ISSN={["1944-8244"]}, DOI={10.1021/am900203u}, abstractNote={The adsorption of asphaltenes onto flat silica surfaces modified with self-assembled monolayers (SAMs) of alkyltrichlorosilanes of varying thickness due to a variable number of carbon atoms (N(C)) has been studied by means of contact angle measurements, spectroscopic ellipsometry, and near-edge X-ray absorption fine structure spectroscopy. The extent of asphaltene adsorption was found to depend primarily on the ability of the SAM layer to shield the underlying silicon substrate from interacting with the asphaltenes present in solution. Specifically, asphaltene adsorption decreased with an increase in N(C) and/or an increase in SAM grafting density, sigma(SAM), (i.e., number of SAM molecules per unit area). The effect of the solvent quality on the extent of asphaltene adsorption was gauged by adsorbing asphaltenes from toluene, 1-methylnaphthalene, tetralin, decalin, and toluene-heptanes mixtures. The extent of asphaltene adsorption was found to increase proportionally with a decrease in the Hildebrand solubility parameter of the solvent.}, number={6}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Turgman-Cohen, Salomon and Fischer, Daniel A. and Kilpatrick, Peter K. and Genzer, Jan}, year={2009}, month={Jun}, pages={1347–1357} } @article{turgman-cohen_smith_fischer_kilpatrick_genzer_2009, title={Asphaltene Adsorption onto Self-Assembled Monolayers of Mixed Aromatic and Aliphatic Trichlorosilanes}, volume={25}, ISSN={["0743-7463"]}, DOI={10.1021/la9000895}, abstractNote={The adsorption of asphaltenes onto flat solid surfaces modified with mixed self-assembled monolayers (SAMs) of aliphatic and aromatic trichlorosilanes with varying wettabilities, aromaticities, and thicknesses is tested. The mixed SAMs are characterized by means of contact angle to assess hydrophobicity and molecular and chemical uniformity, spectroscopic ellipsometry to measure the thickness of the films, and near edge X-ray absorption fine structure (NEXAFS) spectroscopy to assess chemical and molecular composition. The molecular characteristics of the adsorbed asphaltene layer and the extent of asphaltene adsorption are determined using NEXAFS and spectroscopic ellipsometry, respectively. The SAMs are formed by depositing phenyl-, phenethyl-, butyl-, and octadecyl- trichlorosilanes from toluene solutions onto silica-coated substrates; the chemical composition and the wettability of the SAM surface is tuned systematically by varying the trichlorosilane composition in the deposition solutions. The adsorption of asphaltenes on the substrates does not correlate strongly with the SAM chemical composition. Instead, the extent of asphaltene adsorption decreases with increasing SAM thickness. This observation suggests that the leading interaction governing the adsorption of asphaltenes is their interaction with the polar silica substrate and that the chemical composition of the SAM is of secondary importance.}, number={11}, journal={LANGMUIR}, author={Turgman-Cohen, Salomon and Smith, Matthew B. and Fischer, Daniel A. and Kilpatrick, Peter K. and Genzer, Jan}, year={2009}, month={Jun}, pages={6260–6269} } @article{gupta_alargova_kilpatrick_velev_2008, title={On-chip electric field driven assembly of biocomposites from live cells and functionalized particles}, volume={4}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-41149160380&partnerID=MN8TOARS}, DOI={10.1039/b717850f}, abstractNote={Live cells and surface-functionalized synthetic microparticles are co-assembled on electrically controlled chips to yield permanent chains and one cell layer thick membranes that can be freely manipulated in external magnetic fields.}, number={4}, journal={Soft Matter}, author={Gupta, S. and Alargova, R.G. and Kilpatrick, P.K. and Velev, Orlin}, year={2008}, pages={726–730} } @article{tombokan_aguda_danehower_kilpatrick_carbonell_2008, title={Three-component phase behavior of the sclareol-ethyl lactate-carbon dioxide system for GAS applications}, volume={45}, ISSN={["0896-8446"]}, DOI={10.1016/j.supflu.2007.12.007}, abstractNote={This paper focuses on the extraction of sclareol from the leaves of Salvia sclarea Lamiaceae, more commonly known as Clary sage. The process involves the extraction of sclareol using a CO2-soluble GRAS solvent such as ethyl lactate, followed by GAS anti-solvent precipitation from ethyl lactate solution with carbon dioxide. The three-component phase behavior of the sclareol–ethyl lactate–CO2 system at various pressures has been determined and indicates a slight cybotactic effect. The ability of thermodynamic models to predict the complex three-component phase behavior of this system is discussed, together with the implications of the thermodynamic behavior of the system on process design.}, number={2}, journal={JOURNAL OF SUPERCRITICAL FLUIDS}, author={Tombokan, Xenia C. and Aguda, Remil M. and Danehower, David A. and Kilpatrick, Peter K. and Carbonell, Ruben G.}, year={2008}, month={Jun}, pages={146–155} } @article{gupta_huda_kilpatrick_velev_2007, title={Characterization and optimization of gold nanoparticle-based silver-enhanced immunoassays}, volume={79}, ISSN={["1520-6882"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-34249093580&partnerID=MN8TOARS}, DOI={10.1021/ac062341m}, abstractNote={Silver-enhanced nanoparticle-labeled immunoassays provide a simple, low-cost, and effective way of detecting antigens in dilute solutions. The physical mechanisms behind their operation, however, have not been fully investigated. We present a semiquantitative approach for optimizing sandwich nanoparticle immunoassays using an adsorption-controlled kinetic model. Primary antibodies were immobilized on a solid substrate to bind the target antigens in solution. An optical signal was measured by secondary labeling of antigens with gold nanoparticles and their enhancement by silver nucleation. The opacity of the silver-enhanced spots was quantified by densitometry. The selectivity of the sandwich immunoassays was adequately high, and antigen concentrations as low as 0.1 microg cm(-3) (4 ng total) were detected reproducibly. The role of mass transfer was investigated, and a model was developed to optimize the performance of immunoassays by correlating the opacities of silver spots to the concentration and incubation times of antigens and gold nanoparticles. The results could allow the development of more rapid and reliable nanoparticle immunoassays.}, number={10}, journal={ANALYTICAL CHEMISTRY}, author={Gupta, Shalini and Huda, Sabil and Kilpatrick, Peter K. and Velev, Orlin D.}, year={2007}, month={May}, pages={3810–3820} } @article{yang_verruto_kilpatrick_2007, title={Dynamic asphaltene-resin exchange at the oil/water interface: Time-dependent W/O emulsion stability for asphaltene/resin model oils}, volume={21}, ISSN={["1520-5029"]}, DOI={10.1021/ef060465w}, abstractNote={The critical electric field (CEF) technique was used to determine the time-dependent stability of water-in-oil emulsions in which asphaltenes stabilize the film. Stabilizing films comprising purely...}, number={3}, journal={ENERGY & FUELS}, author={Yang, Xiaoli and Verruto, Vincent J. and Kilpatrick, Peter K.}, year={2007}, pages={1343–1349} } @article{verruto_kilpatrick_2007, title={Preferential solvent partitioning within asphaltenic aggregates dissolved in binary solvent mixtures}, volume={21}, ISSN={["0887-0624"]}, DOI={10.1021/ef060456n}, abstractNote={The heaviest fraction of crude oils, asphaltenes, has been shown to play a central role in the stabilization of troublesome water-in-crude oil emulsions. In previous model oil systems, emulsion stability was observed to depend notably on the properties of self-assembled interfacially active asphaltenic aggregates. Thus, careful characterization of these aggregates is of great importance for better understanding of asphaltene-stabilized emulsions. Small-angle neutron scattering (SANS) has proven to be a powerful tool for such characterization. Described here is the application of SANS on asphaltenes from Hondo crude oil dissolved in binary solvent mixtures of toluene with n-heptane, decalin, or 1-methylnaphthalene. A polydisperse oblate cylinder (POC) form factor model was used to fit the aggregate scattering data, and subsequent calculations of minimum error were performed to ascertain the entrained solvent composition within the aggregates. When toluene was paired with either a weak solvent (decalin) or ...}, number={3}, journal={ENERGY & FUELS}, author={Verruto, Vincent J. and Kilpatrick, Peter K.}, year={2007}, pages={1217–1225} } @article{smith_efimenko_fischer_lappi_kilpatrick_genzer_2007, title={Study of the packing density and molecular orientation of bimolecular self-assembled monolayers of aromatic and aliphatic organosilanes on silica}, volume={23}, ISSN={["0743-7463"]}, DOI={10.1021/la062475v}, abstractNote={Bimolecular self-assembled monolayers (SAMs) of aromatic and aliphatic chlorosilanes were self-assembled onto silica, and their characteristics were established by contact angle measurement, near-edge X-ray absorption fine structure spectroscopy, and Fourier transform infrared spectroscopy. Three aromatic constituents (phenyltrichlorosilane, benzyltrichlorosilane, and phenethyltrichlorosilane) were studied in combination with four aliphatic coadsorbates (butyltrichlorosilane, butyldimethylchlorosilane, octadecyltrichlorosilane, and octadecyldimethylchlorosilane). Our results demonstrate that whereas SAMs made of trichlorinated organosilanes are densely packed, SAMs prepared from monochlorinated species are less dense and poorly ordered. In mixed systems, trichlorinated aromatics and trichlorinated aliphatics formed SAMs with highly tunable compositions; their surfaces were compositionally homogeneous with no large-scale domain separation. The homogeneous nature of the resulting SAM was a consequence of the formation of in-plane siloxane linkages among neighboring molecules. In contrast, when mixing monochlorinated aliphatics with trichlorinated aromatics, molecular segregation occurred. Although the two shortest aromatic species did not display significant changes in orientation upon mixing with aliphatics, the aromatic species with the longest polymethylene spacer, phenethyltrichlorosilane, displayed markedly different orientation behavior in mixtures of short- and long-chain aliphatics.}, number={2}, journal={LANGMUIR}, author={Smith, Matthew B. and Efimenko, Kirill and Fischer, Daniel A. and Lappi, Simon E. and Kilpatrick, Peter K. and Genzer, Jan}, year={2007}, month={Jan}, pages={673–683} } @article{sullivan_zaki_sjoblom_kilpatrick_2007, title={The stability of water-in-crude and model oil emulsions}, volume={85}, number={6}, journal={Canadian Journal of Chemical Engineering}, author={Sullivan, A. P. and Zaki, N. N. and Sjoblom, J. and Kilpatrick, P. K.}, year={2007}, pages={793–807} } @article{smith_tong_genzer_fischer_kilpatrick_2006, title={Effects of synthetic amphiphilic alpha-helical peptides on the electrochemical and structural properties of supported hybrid bilayers on gold}, volume={22}, ISSN={["0743-7463"]}, DOI={10.1021/la051104w}, abstractNote={Amphiphilic alpha-helices were formed from designed synthetic peptides comprising alanine, phenylalanine, and lysine residues. The insertion of the alpha-helical peptides into hybrid bilayers assembled on gold was studied by a variety of methods to assess the resulting structural characteristics, such as electrical resistance and molecular orientation. Self-assembled monolayers (SAMs) of dodecanethiol (DDT); octadecanethiol (ODT); and 1,2-dipalmitoyl-sn-glycero-3-phosphothioethanol (DPPTE) were formed on gold substrates with and without incorporated peptide. Supported hybrid bilayers and multilayers of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) were formed on SAMs by the "paint-freeze" method of bilayer formation. Modeling of electrochemical impedance spectroscopy data using equivalent electrochemical circuits revealed that the addition of peptide decreased dramatically the resistive element of the bilayer films while maintaining the value of the capacitive element, indicating successful incorporation of peptide into a well-formed bilayer. Near-edge X-ray absorption fine structure spectroscopy data provided evidence that the molecules in the SAMs and hybrid multilayers were ordered even in the presence of peptide. The peptide insertion into the SAM was confirmed by observing the pi* resonance peak correlating with phenylalanine and a peak in the nitrogen K-edge regime attributable to the peptide bond.}, number={4}, journal={LANGMUIR}, author={Smith, MB and Tong, JH and Genzer, J and Fischer, D and Kilpatrick, PK}, year={2006}, month={Feb}, pages={1919–1927} } @article{gawrys_blankenship_kilpatrick_2006, title={On the distribution of chemical properties and aggregation of solubility fractions in asphaltenes}, volume={20}, ISSN={["1520-5029"]}, DOI={10.1021/ef0502002}, abstractNote={Asphaltenes from B6, Canadon Seco (CS), and Hondo (HO) crude oils were separated on a preparatory scale into 20−30 so-called “fine fractions” by sequential precipitation from mixtures of n-heptane and toluene. Chemical analyses were performed to measure the carbon, hydrogen, nitrogen, sulfur, oxygen, and trace metals contents of the fractions. Small-angle neutron scattering (SANS) was performed on fractions dissolved or dispersed in mixtures of toluene-d (or methylnaphthalene-d) and methanol-d to determine the average aggregate size. Statistical analyses were performed to calculate the weighted moments of each elemental parameter assuming that the data were “normally” distributed. High values of the standard deviation and skewness because of the early precipitation of metal oxides and inorganic salts suggested that a Gaussian distribution was inappropriate to describe the behavior of most metals. H/C, N/C, and S/C ratios in B6 and HO asphaltenes appeared to obey a Gaussian distribution, with mean values a...}, number={2}, journal={ENERGY & FUELS}, author={Gawrys, KL and Blankenship, GA and Kilpatrick, PK}, year={2006}, pages={705–714} } @article{gawrys_blankenship_kilpatrick_2006, title={Solvent entrainment in and flocculation of asphaltenic aggregates probed by small-angle neutron scattering}, volume={22}, ISSN={["0743-7463"]}, DOI={10.1021/la052509j}, abstractNote={While small-angle neutron scattering (SANS) has proven to be very useful for deducing the sizes and masses of asphaltenic aggregates in solution, care must be taken to account for solvation effects within the aggregates so as to not err in the characterization of these important systems. SANS measurements were performed on solutions of asphaltenes dispersed in deuterated solvents in which a broad spectrum of solute and solvent chemical compositions was represented. Fits to the scattering intensity curves were performed using the Guinier approximation, the Ornstein-Zernike (or Zimm) model, a mass-fractal model, and a polydisperse cylinder model. The mass-fractal model provided apparent fractal dimensions (2.2-3) for the aggregates that generally decreased with increasing aggregate size, indicating increased surface roughness for larger aggregates. The polydisperse cylinder model provided typical values of the particle thicknesses from 5 to 32 angstroms, the average particle radius from 25 to 125 angstroms, and approximately 30% radius polydispersity. Subsequent calculation of average aggregate molar masses suggested a range of solvent entrainment from 30 to 50% (v/v) within the aggregates that were consistent with previous viscosity measurements. Additional calculations were performed to estimate the proportion of microparticle to nanoparticle aggregates in the solutions. The results indicate that the inclusion of solvation effects is essential for the accurate determination of aggregate molecular weights and fractal dimensions.}, number={10}, journal={LANGMUIR}, author={Gawrys, KL and Blankenship, GA and Kilpatrick, PK}, year={2006}, month={May}, pages={4487–4497} } @article{yang_kilpatrick_2005, title={Asphaltenes and waxes do not interact synergistically and coprecipitate in solid organic deposits}, volume={19}, ISSN={["1520-5029"]}, DOI={10.1021/ef050022c}, abstractNote={Waxes and asphaltenes are the major components in organic deposits from petroleum fluids. A key unresolved issue is whether there are significant intermolecular interactions between wax and asphaltene molecules during precipitation that would lead to synergy and coprecipitation, i.e., the phase change of one class inducing the precipitation of the other class. To address this, we studied six organic deposits in great chemical and physical detail:  three that we categorized as predominantly wax deposits, two that were asphaltenic deposits, and one that seemed to be an organic acid deposit. Chemical analyses included elemental analysis, Fourier transform infrared (FTIR) spectroscopy, high-temperature simulated distillation, melting range measurement, and solubility experiments, performed on both parent crude oils and their corresponding deposits. The wax deposits contain in excess of 44 wt % waxes, and the complement of the deposits was occluded oil, water, and inorganic solids. Less than 6.2% (w/w) of thes...}, number={4}, journal={ENERGY & FUELS}, author={Yang, XL and Kilpatrick, P}, year={2005}, pages={1360–1375} } @article{gawrys_kilpatrick_2005, title={Asphaltenic aggregates are polydisperse oblate cylinders}, volume={288}, ISSN={["1095-7103"]}, DOI={10.1016/j.jcis.2005.03.036}, abstractNote={Small-angle neutron scattering (SANS) has proven to be very useful for deducing the sizes and morphologies of asphaltenic aggregates in solution. A wide variety of intra-particle structure factors have previously been applied to SANS scattering spectra, but the studies often provided limited information concerning the quality of the fits and the Q range over which the models were applied. Selection of an appropriate form factor that closely approximates the structure of asphaltenic aggregates is important for determining the properties of asphaltenic aggregates, such as the radius of gyration (RG), molar mass, and apparent fractal dimension. This study evaluates various mono- and polydisperse intra-particle structure factor models as applied to four asphaltene scattering spectra. Agreement of the model fit parameters (I0 and RG) with those obtained from Guinier analyses suggests that such a form factor model is physically reasonable. Reduced χ2 values for each non-linear least squares fit indicates how well a given model fits to the entire Q range studied for the scattering intensity distribution. In the polydispersity analyses, an analytical function is introduced to model the scattering behavior of oblate cylinders with a Schultz distribution of radii. Results indicate that the polydisperse radius oblate cylinder model best approximates the shape of asphaltenic aggregates.}, number={2}, journal={JOURNAL OF COLLOID AND INTERFACE SCIENCE}, author={Gawrys, KL and Kilpatrick, PK}, year={2005}, month={Aug}, pages={325–334} } @article{akbarzadeh_bressler_wang_gawrys_gray_kilpatrick_yarranton_2005, title={Association behavior of pyrene compounds as models for asphaltenes}, volume={19}, ISSN={["1520-5029"]}, DOI={10.1021/ef0496698}, abstractNote={Asphaltene association in solution has been studied extensively using methods such as vaporpressure osmometry and neutron scattering. These methods give relative data on association as a function of solvent strength, temperature, and concentration, but interpretation of the results is hampered by the polyfunctional nature of asphaltenes and the distribution of molecular weight. In this work, we present data on association of representative model structures for asphaltenes, as measured using vapor-pressure osmometry in o-dichlorobenzene at 75-130 °C, and using smallangle neutron scattering in toluene. A series of compounds were synthesized based on the fourring aromatic compound pyrene. The synthetic compounds were designed to give interactions between aromatic rings, alkyl chains, and selected functional groups through aromatic interactions, hydrogen bonding, and polar interactions. Even in this strong solvent, polar interactions between oxygen functional groups gave average molecular weights of up to twice the true value, indicating dimer formation. An alkyl pyrene compound, dipyrenyl decane, gave much less significant association. Pyrene itself exhibited little or no self-association.}, number={4}, journal={ENERGY & FUELS}, author={Akbarzadeh, K and Bressler, DC and Wang, JN and Gawrys, KL and Gray, MR and Kilpatrick, PK and Yarranton, HW}, year={2005}, pages={1268–1271} } @article{gawrys_kilpatrick_2004, title={Asphaltene aggregation: Techniques for analysis}, volume={32}, ISSN={["1525-6030"]}, DOI={10.1081/CI-120030536}, abstractNote={Abstract The study of asphaltene colloidal properties is motivated by their propensity to aggregate, flocculate, precipitate, adsorb onto interfaces and, hence, pose considerable challenges for the petroleum industry. Asphaltenes are defined as the toluene (or benzene) soluble, yet n‐heptane (or n‐pentane) insoluble, portion of crude oil. The “solubility class” definition of asphaltenes generates a broad distribution of molecular structures that vary greatly among crude sources. Asphaltenes are generally characterized by fused ring aromaticity, small aliphatic side chains, and polar heteroatom‐containing functional groups (e.g., carboxylic acids, carbonyl, phenol, pyrroles, and pyridines) capable of donating or accepting protons inter‐ and intra‐molecularly. Molar H/C ratios between 1.0–1.2 and N, S, and O content of a few weight percent suggest that the asphaltene backbone mostly contains fused aromatic carbon interspersed with occasional polar functional groups. The most plausible mechanisms of asphaltene aggregation involve dispersion interactions between aromatic rings, polar and hydrogen bonding interactions between heteroatoms, and other charge transfer interactions. Understanding asphaltene chemistry and the fundamental mechanisms of colloid formation has been the driving force behind much petroleum research of the last half‐century.}, number={3}, journal={INSTRUMENTATION SCIENCE & TECHNOLOGY}, author={Gawrys, KL and Kilpatrick, PK}, year={2004}, pages={247–253} } @article{spiecker_kilpatrick_2004, title={Interfacial rheology of petroleum asphaltenes at the oil-water interface}, volume={20}, ISSN={["0743-7463"]}, DOI={10.1021/la0356351}, abstractNote={A biconical bob interfacial shear rheometer was used to study the mechanical properties of asphaltenic films adsorbed at the oil-water interface. Solutions of asphaltenes isolated from four crude oils were dissolved in a model oil of heptane and toluene and allowed to adsorb and age in contact with water. Film elasticity (G') values were measured over a period of several days, and yield stresses and film masses were determined at the end of testing. The degree of film consolidation was determined from ratios of G'/film mass and yield stress/G'. Asphaltenes with higher concentrations of heavy metals (Ni, 330-360 ppm; V, 950-1000 ppm), lower aromaticity (H/C, 1.24-1.29), and higher polarity (N, 1.87-1.99) formed films of high elasticity, yield stress, and consolidation. Rapid adsorption kinetics and G' increases were seen when asphaltenes were near their solubility limit in heptane-toluene mixtures (approximately 50% (v/v) toluene). In solvents of greater aromaticity, adsorption kinetics and film masses were reduced at comparable aging times. Poor film forming asphaltenes had yield stress/G' values ((1.01-1.21) x 10(-2)) more than 4-fold lower than those of good film forming asphaltenes. n-heptane asphaltenes fractionated by filtering solutions prepared at low aromaticity (approximately 40% toluene in mixtures of heptane and toluene) possessed higher concentrations of heavy metals and nitrogen and higher aromaticity. The less soluble fractions of good film forming asphaltenes exhibited enhanced adsorption kinetics and higher G' and yield stress values in pure toluene. Replacing the asphaltene solutions with neat heptane-toluene highlighted the ability of films to consolidate and become more elastic over several hours. Adding resins in solution to a partially consolidated film caused a rapid reduction in elasticity followed by gradual but modest consolidation. This study is among the first to directly relate asphaltene chemistry to adsorption kinetics, adsorbed film mechanical properties, and consolidation kinetics.}, number={10}, journal={LANGMUIR}, author={Spiecker, PM and Kilpatrick, PK}, year={2004}, month={May}, pages={4022–4032} } @article{ese_kilpatrick_2004, title={Stabilization of water-in-oil emulsions by naphthenic acids and their salts: Model compounds, role of pH, and soap: Acid ratio}, volume={25}, ISSN={["1532-2351"]}, DOI={10.1081/DIS-120038634}, abstractNote={Abstract Increasingly, crudes of high acidity are observed in production of petroleum reserves. Naphthenic acids, which are generally cyclic and branched aliphatic carboxylic acids, are interfacially active and adsorb at water–oil interfaces to form monolayers, liquid crystalline films, and other colloidal structures. A serious challenge in petroleum production is the resulting stabilization of water‐in‐oil emulsions, which can cause problems in topside and subside separators, and in refining processes. A variety of acids and their corresponding soaps have been thoroughly studied in order to investigate how these compounds interact in aqueous solutions at different pH, and how these association structures relate to emulsion formation and stability. The formation of aggregates and hence, the stabilizing properties of this class of material are strongly sensitive to the relative proportion of uncharged acid and charged soap anion. In this paper, we review our experimental results on naphthenic acid/naphthenate stabilized emulsions utilizing several model compounds, including heptylbenzoic acid (HB), trans‐4‐pentylcyclohexane‐carboxylic acid (PCA), and 5‐β‐cholanic acid (CA). #A special tribute to Dr. Jan Czarnecki on the occasion of his 65th birthday.}, number={3}, journal={JOURNAL OF DISPERSION SCIENCE AND TECHNOLOGY}, author={Ese, MH and Kilpatrick, PK}, year={2004}, month={May}, pages={253–261} } @article{zaki_carbonell_kilpatrick_2003, title={A novel process for demulsification of water-in-crude oil emulsions by dense carbon dioxide}, volume={42}, ISSN={["0888-5885"]}, DOI={10.1021/ie0303597}, abstractNote={CO2 was used to break several water-in-crude oil and water-in-model oil emulsions stabilized by asphaltenic films. The stability of asphaltenic films in model oils having varying H/C ratios (aromaticities) was also studied upon contact with liquid or supercritical CO2. The efficacy and kinetics of demulsification appeared to be enhanced with increased CO2 density and mole fraction. The proposed mechanism by which CO2 destabilizes water-in-crude oil emulsions involves asphaltene flocculation and precipitation. The emulsions break by flocculating the adsorbed asphaltenes, leading to film defects, film thinning, film rupture, and water coalescence. The various factors influencing asphaltene precipitation and emulsion destabilization were studied in model solvent systems containing asphaltenes and resins. Increasing CO2 pressure, residence time, temperature, and degree of mixing were found to increase the rate of asphaltene precipitation. Asphaltene precipitation by CO2 was found to increase in the presence o...}, number={25}, journal={INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH}, author={Zaki, NN and Carbonell, RG and Kilpatrick, PK}, year={2003}, month={Dec}, pages={6661–6672} } @article{spiecker_gawrys_kilpatrick_2003, title={Aggregation and solubility behavior of asphaltenes and their subfractions}, volume={267}, ISSN={["0021-9797"]}, DOI={10.1016/S0021-9797(03)00641-6}, abstractNote={Asphaltenes from four different crude oils (Arab Heavy, B6, Canadon Seco, and Hondo) were fractionated in mixtures of heptane and toluene and analyzed chemically, by vapor pressure osmometry (VPO), and by small angle neutron scattering (SANS). Solubility profiles of the asphaltenes and their subfractions indicated strong cooperative asphaltene interactions of a particular subfraction that is polar and hydrogen bonding. This subfraction had lower H/C ratios and modestly higher N, V, Ni, and Fe contents than the less polar and more soluble subfraction of asphaltenes. VPO and SANS studies indicated that the less soluble subfractions formed aggregates that were considerably larger than the more soluble subfractions. In general, asphaltene aggregate size increased with decreasing solvent aromaticity up to the solubility limit, beyond which the aggregate size decreased with heptane addition. The presence of a low wavevector Q feature in the scattering curves at 25 degrees C indicated that the individual aggregates were flocculating; however, the intensity of the feature was diminished upon heating of the samples to 80 degrees C. The solubility mechanism for Canadon Seco asphaltenes, the largest aggregate formers, appears to be dominated by aromatic pi-bonding interactions due to their low H/C ratio and low nitrogen content. B6 and Hondo asphaltenes formed similar-sized aggregates in heptol and the solubility mechanism is most likely driven by polar interactions due to their relatively high H/C ratios and high nitrogen contents. Arab Heavy, the least polar asphaltene, had a H/C ratio similar to Canadon Seco but formed the smallest aggregates in heptol. The enhancement in polar and pi-bonding interactions for the less soluble subfraction indicated by elemental analysis is reflected by the aggregate size from SANS. The less soluble asphaltenes contribute the majority of species responsible for aggregation and likely cause many petroleum production problems such as pipeline deposition and water-in-oil emulsion stabilization.}, number={1}, journal={JOURNAL OF COLLOID AND INTERFACE SCIENCE}, author={Spiecker, PM and Gawrys, KL and Kilpatrick, PK}, year={2003}, month={Nov}, pages={178–193} } @article{spiecker_gawrys_trail_kilpatrick_2003, title={Effects of petroleum resins on asphaltene aggregation and water-in-oil emulsion formation}, volume={220}, number={03-Jan}, journal={Colloids and Surfaces. A, Physicochemical and Engineering Aspects}, author={Spiecker, P. M. and Gawrys, K. L. and Trail, C. B. and Kilpatrick, P. K.}, year={2003}, pages={27-} } @misc{zaki_kilpatrick_carbonell_2003, title={Methods of demulsifying emulsions using carbon dioxide}, volume={6,566,410}, number={2003 May 20}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Zaki, N. N. and Kilpatrick, P. K. and Carbonell, R. G.}, year={2003}, month={May} } @article{gawrys_spiecker_kilpatrick_2003, title={The role of asphaltene solubility and chemical composition on asphaltene aggregation}, volume={21}, ISSN={["1091-6466"]}, DOI={10.1081/LFT-120018533}, abstractNote={Abstract Asphaltenes from four different crude oils (Arab Heavy, B6, Canadon Seco, and Hondo) were fractionated in mixtures of heptane and toluene and analyzed by small angle neutron scattering (SANS). Fractionation appeared to concentrate the most polar species into the least soluble sub-fraction as indicated by elemental analysis. SANS results indicated a wide spectrum of asphaltene aggregate sizes and molecular weights; however, the less soluble (more polar) fraction contributed the majority of the species responsible for asphaltene aggregation in solution. This more polar, less soluble fraction is likely the major cause for many petroleum production problems such as deposition and water-in-oil emulsion stabilization. A comparison of molecular weight and aggregate size indicated that asphaltenes formed fractal aggregates in solution with dimensions between 1.7 and 2.1. This was consistent with the “archipelago” model of asphaltene structure. Resins were shown to effectively solvate asphaltene aggregates as observed by an increase in asphaltene solubility, reduction in aggregate size and molecular weight, and an increase in the fractal dimension to ˜ 3.}, number={3-4}, journal={PETROLEUM SCIENCE AND TECHNOLOGY}, author={Gawrys, KL and Spiecker, PM and Kilpatrick, PK}, year={2003}, pages={461–489} } @article{poindexter_zaki_kilpatrick_marsh_emmons_2002, title={Factors contributing to petroleum foaming. 1. Crude oil systems}, volume={16}, ISSN={["1520-5029"]}, DOI={10.1021/ef010224i}, abstractNote={Gas/oil separation can often be accompanied by unwanted foaming. To study this phenomenon, 20 crude oils were subjected to low-pressure foaming experiments. Eleven of the crudes were from offshore platforms where foaming occurs regularly. Two foaming parameters, foam volume (or foamability) and collapse slope (i.e. the rate of foam collapse in the absence of sparge gas), were compared with several crude oil properties, namely, density, bulk viscosity, surface tension, asphaltene and resin content, asphaltene and resin molecular weight, and asphaltene and resin heteroatom content. For asphaltenic crudes, collapse slope was found to correlate with asphaltene content as well as several other crude oil properties:  density, viscosity, and surface tension. Foam volume did not relate to any asphaltenic crude oil property. However, for crudes having little to no asphaltenes, foam volume, not collapse slope, strongly related to crude oil surface tension. For low asphaltenic crudes, results further indicate that r...}, number={3}, journal={ENERGY & FUELS}, author={Poindexter, MK and Zaki, NN and Kilpatrick, PK and Marsh, SC and Emmons, DH}, year={2002}, pages={700–710} } @article{zaki_poindexter_kilpatrick_2002, title={Factors contributing to petroleum foaming. 2. Synthetic crude oil systems}, volume={16}, ISSN={["0887-0624"]}, DOI={10.1021/ef010225a}, abstractNote={The influence of petroleum asphaltenes and resins on stabilizing model oil foams comprised of light mineral oil mixed with toluene (minerol) was investigated. Two factors contribute significantly to foam volume and stability:  bulk viscosity and asphaltene state of aggregation. An increase in bulk viscosity was found to increase foam stability as gauged by the total time required for a foam to collapse. Asphaltene aggregation is governed primarily by the solvent aromaticity and resin/asphaltene (R/A) ratio. There is a threshold size in the state of asphaltene aggregation above which the ability of these aggregates to stabilize foams is markedly reduced. This appears to be closely related to asphaltene flocculation and precipitation at compositions beyond the solubility limit of the asphaltenes. Solvent systems generating the highest foam volume were found to reduce the air-oil surface tension to the greatest extent. Addition of an asphaltene dispersant increased the foamability of asphaltenes in minerol a...}, number={3}, journal={ENERGY & FUELS}, author={Zaki, NN and Poindexter, MK and Kilpatrick, PK}, year={2002}, pages={711–717} } @misc{sullivan_kilpatrick_2002, title={The effects of inorganic solid particles on water and crude oil emulsion stability}, volume={41}, ISSN={["0888-5885"]}, DOI={10.1021/ie010927n}, abstractNote={Small inorganic particles strongly enhance water−crude oil emulsion stability when interactions with asphaltenes promote particle adsorption at the oil−water interface. A variety of particle types have been studied to investigate the controlling factors for particle-stabilization effectiveness. Emulsion stabilities were determined by the extent of water resolved after centrifugation and the electric field required for emulsion breakdown. All particles used were hydrophilic and stabilized oil-in-water emulsions if small enough to be interfacially active. When dried and exposed to asphaltene-containing oil phases, the particles stabilized water-in-oil emulsions. Decreased extents of preadsorbed water, decreased particle sizes, and increased particle concentrations enhanced water-in-oil emulsion stability. Investigations with model emulsions showed that an intermediate state of asphaltene aggregation, near the point of incipient precipitation, is required for particle modification and emulsion stabilization....}, number={14}, journal={INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH}, author={Sullivan, AP and Kilpatrick, PK}, year={2002}, month={Jul}, pages={3389–3404} } @misc{roberts_kilpatrick_2001, title={Methods and apparatus for separating Fischer-Tropsch catalysts from liquid hydrocarbon product}, volume={6,217,830}, number={2001 April 17}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Roberts, G. W. and Kilpatrick, P. K.}, year={2001} } @misc{roberts_kilpatrick_2000, title={Methods and apparatus for separating Fischer-Tropsch catalysts from liquid hydrocarbon product}, volume={6,114,399}, number={2000 Sept. 5}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Roberts, G. W. and Kilpatrick, P. K.}, year={2000} } @misc{mullerat_curby_hazlett_kilpatrick_2000, title={Therapeutic, production and immunostimulatory uses of biocidal compositions}, volume={6,099,855}, number={2000 Aug. 8}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Mullerat, J. and Curby, W. A. and Hazlett, D. A. and Kilpatrick, P.}, year={2000} } @article{singh_mclean_kilpatrick_1999, title={Fused ring aromatic solvency in destabilizing water-in-asphaltene-heptane-toluene emulsions}, volume={20}, ISSN={["1532-2351"]}, DOI={10.1080/01932699908943792}, abstractNote={Abstract The role of asphaltenes in stabilizing water-in-crude oil emulsions is extremely well established. The mechanism appears to be one in which planar, disk-like asphaltene molecules aggregate through lateral intermolecular forces to form primary aggregates or micelles which are interfacially active. These aggregates — upon adsorbing at the oil-water interface — crosslink through physical interactions to form a viscoelastic network, which has been characterized by some as a “skin” or a “plastic film”. The strength of this film, as gauged by shear and elastic moduli, seems to correlate well with water-in-oil emulsion stability. What is still relatively unknown is the role of chemistry in governing the strength of these lateral inter-asphaltene interactions. The candidate interactions include π-bonding between the delocalized electrons in the fused aromatic ring core, H-bonding between proton donors and acceptors imbedded in the asphaltenic cores, and metal-electron interactions between, for example, h...}, number={1-2}, journal={JOURNAL OF DISPERSION SCIENCE AND TECHNOLOGY}, author={Singh, S and McLean, JD and Kilpatrick, PK}, year={1999}, pages={279–293} } @article{biales_di wan_kilpatrick_roberts_1999, title={Separation of Fischer-Tropsch wax from catalyst using near-critical fluid extraction: Analysis of process feasibility}, volume={13}, ISSN={["0887-0624"]}, DOI={10.1021/ef980208u}, abstractNote={The technical feasibility of a near-critical fluid extraction (NCE) process for the recovery of heavy normal paraffins from a Fischer−Tropsch slurry reactor has been analyzed. Process simulations were carried out using the ASPEN PLUS program, considering 100 individual compounds from C1 to C100. Four light solvents were evaluated:  n-pentane, n-hexane, n-heptane, and n-octane. These four compounds are major products of the F−T reaction. Most of the analysis was concentrated in two regions:  (1) high solvent/product ratios (ca. 20/1), such that product could be recovered by temperature-retrograde condensation; and, (2) low solvent/product ratios (ca. 3/1). The latter region appeared to require higher extraction temperatures and higher slurry flowrates, but had several attractive features such as lower vapor flowrates, lower solvent makeup rates, and lower energy requirements. The concentration of solvent in the product from the NCE process was never low enough for the process to be self-sufficient in solve...}, number={3}, journal={ENERGY & FUELS}, author={Biales, JM and Di Wan, Y and Kilpatrick, PK and Roberts, GW}, year={1999}, pages={667–677} } @misc{mullerat_curby_hazlett_kilpatrick_1999, title={Therapeutic, production and immunostimulatory uses of biocidal compositions}, volume={6,004,587}, number={1999 Dec. 21}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Mullerat, J. and Curby, W. A. and Hazlett, D. A. and Kilpatrick, P.}, year={1999} } @article{musser_kilpatrick_1998, title={Molecular characterization of wax isolated from a variety of crude oils}, volume={12}, ISSN={["0887-0624"]}, DOI={10.1021/ef970206u}, abstractNote={Petroleum waxes from sixteen different crude oils were analyzed after isolation from the crude in a two-step process. These waxes were characterized molecularly to aid in the investigation of the effect of wax type and quantity on water-in-crude oil emulsion stability. The techniques used to gather information about the waxes included elemental analysis, FTIR spectroscopy, field desorption mass spectroscopy, 1H NMR spectroscopy, 13C NMR spectroscopy, gel permeation chromatography, and differential scanning calorimetry. Two distinctly different types of petroleum waxes were discerned, microcrystalline and paraffinic. Microcrystalline waxes are aliphatic hydrocarbon compounds containing a substantial amount of branches and rings. They have large molecular weight ranges from 300 to 2500 amu and are gel-like in appearance. The rings give rise to a decreased H/C ratio relative to paraffinic waxes, often as low as 1.85. Because of the large number of different compounds and the lack of large-scale crystallinity...}, number={4}, journal={ENERGY & FUELS}, author={Musser, BJ and Kilpatrick, PK}, year={1998}, pages={715–725} } @misc{mullerat_curby_hazlett_kilpatrick_1998, title={Therapeutic, production and immunostimulatory uses of biocidal compositions}, volume={5,830,511}, number={1998 Nov. 3}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Mullerat, J. and Curby, W. A. and Hazlett, D. A. and Kilpatrick, P.}, year={1998} } @article{mclean_kilpatrick_1997, title={Comparison of precipitation and extrography in the fractionation of crude oil residua}, volume={11}, ISSN={["0887-0624"]}, DOI={10.1021/ef9601125}, abstractNote={Four different crude oilsArab Heavy (AH), Arab Berri (AB), Alaskan North Slope (ANS), and San Joaquin Valley (SJV)were characterized by separating the crudes into compound classes by two different fractionation methodsextrography (ext) and asphaltene precipitation followed by extrographic isolation of the resins (ppt + ext). The fractions derived from these two methods of separation were characterized and compared in order to determine the most complete and discriminating compositional analysis for subsequent use in studies concerning the stability of emulsions or sludges which are produced by these crudes in refinery processing. The resin and asphaltene fractions are of primary interest due to their polar, surface-active nature, the central role these fractions play in stabilizing emulsions and sludges, and their resulting influence on crude processability. Preparatory-scale separations were developed and utilized to provide sufficient amounts of the polar fractions of these crudes for further studies. T...}, number={3}, journal={ENERGY & FUELS}, author={McLean, JD and Kilpatrick, PK}, year={1997}, pages={570–585} } @article{mclean_kilpatrick_1997, title={Effects of asphaltene aggregation in model heptane-toluene mixtures on stability of water-in-oil emulsions}, volume={196}, ISSN={["0021-9797"]}, DOI={10.1006/jcis.1997.5177}, abstractNote={As part of an ongoing investigation into the stability of water-in-crude oil emulsions, model oils have been utilized to further probe the effects of crude solvency as well as specific resin-asphaltene interactions on emulsion stability. These model oils were constructed by dissolving varying amounts of resins and/or asphaltenes in a mixture of heptane and toluene. The resins and asphaltenes used in this study were isolated from four different crude types-Arab Berri (AB), Arab Heavy (AH), Alaska North Slope (ANS), and San Joaquin Valley (SJV)-and characterized in a previous study using heptane precipitation of the asphaltenes followed by an extrographic separation of the resins from silica gel. Asphaltenes dissolved in heptol at concentrations of just 0.5% were shown to generate emulsions which were even more stable than those generated from their respective whole crude oils. Some types of resins (e.g., from AH and SJV) also demonstrated an ability to stabilize emulsions although these resin-stabilized emulsions were considerably less stable than those prepared with asphaltenes. The primary factors governing the stability of these model emulsions were the aromaticity of the crude medium (as controlled by the heptane:toluene ratio), the concentration of asphaltenes, and the availability of solvating resins in the oil (i.e., the resin/asphaltene or R/A ratio). The model emulsions were the most stable when the crude medium was 30-40% toluene and in many cases at small R/A ratios (i.e., R/A