Browsing by Subject "Surface modification"

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Colloidal particles at fluid interfaces : from stabilizing emulsions to destabilizing them
(2019-05) Griffith, Christopher Adam; Daigle, Hugh; Lake, Larry W; Mohanty, Kishore; Balhoff, Matthew T; Werth, Charles J
This work uses silica nanoparticles to stabilize oil-in-water and water-in-water emulsions. These emulsions are called Pickering emulsions and have potential use for enhanced oil recovery. There are two challenges with using nanoparticles for subsurface applications which are the high salinities and elevated temperatures of reservoir brines. These conditions are problematic because nanoparticles without surface modification are unstable, because of nanoparticle charge screening, which leads to particle agglomeration. Additionally, much of the current research on particle stabilized emulsions focuses on using nanoparticles modified with hydrophobic molecules or surfactants with the sole intent of getting particles to the oil/water interface. Because of this, many of these particles are not applicable for subsurface applications due to their lack of stability in brine. To address these challenges, I functionalize silica nanoparticles with different concentrations of a hydrophilic silane called (3-glycidyloxypropyl)trimethoxysilane (glymo) and stabilize Pickering emulsions with these particles. Glymo was selected as a nanoparticle surface modifier because of its ability to sterically stabilize particles in brine. I characterized the static stability of different Pickering emulsion formulations by using a centrifuge and by calculating the emulsion demulsification pressure. I correlate a critical demulsification pressure to emulsions that show little change in emulsion drop size while flowing, which I define as dynamically stable. The critical demulsification pressure is applied to several untested Pickering emulsion formulations to verify its applicability as an emulsion pre-screening tool. I perform a rheological characterization on emulsions stabilized with low and high surface coverage glymo-coated particles to establish relationships between nanoparticle bridging and the extent of glymo surface modification with different ionic strength brines. I use cryo-scanning electron microscopy to visually assess the bridging behavior of these different Pickering emulsions. I use fumed silica particles, with different wettabilities, and assess their ability to destabilize a model Pickering emulsion. I determine there is a strong correlation between the wettability of a fumed silica particle and its ability to destabilize a model emulsion. This work is relevant because most of the current research on Pickering emulsions focuses primarily on how to tune the properties of colloidal particles to generate stable emulsions with less overall emphasis on methods to destabilize them. Lastly, an aqueous, two phase system is stabilized with 6 nm and 50 nm silica particles modified with 2-(methoxy(polyethyleneoxy)6-9propyl)trimethoxysilane (PEG-silane). Stabilization of the water/water interface results in emulsions that have relatively good stability to shear. Water-in-water emulsions do not contain any oil which is often considered a major limitation of Pickering emulsions for EOR, therefore these emulsions are potential candidates for enhanced oil recovery
Polyamide desalination membrane characterization and surface modification to enhance fouling resistance
(2010-05) Van Wagner, Elizabeth Marie; Freeman, B. D. (Benny D.); Sharma, Mukul M.; Paul, Donald R.; Bonnecaze, Roger T.; Lawler, Desmond F.; Mickols, William E.
The market for polyamide desalination membranes is expected to continue to grow during the coming decades. Purification of alternative water sources will also be necessary to meet growing water demands. Purification of produced water, a byproduct of oil and gas production, is of interest due to its dual potential to provide water for beneficial use as well as to reduce wastewater disposal costs. However, current polyamide membranes are prone to fouling, which decreases water flux and shortens membrane lifetime. This research explored surface modification using poly(ethylene glycol) diglycidyl ether (PEGDE) to improve the fouling resistance of commercial polyamide membranes. Characterization of commercial polyamide membrane performance was a necessary first step before undertaking surface modification studies. Membrane performance was found to be sensitive to crossflow testing conditions. Concentration polarization and feed pH strongly influenced NaCl rejection, and the use of continuous feed filtration led to higher water flux and lower NaCl rejection than was observed for similar tests performed using unfiltered feed. Two commercial polyamide membranes, including one reverse osmosis and one nanofiltration membrane, were modified by grafting PEGDE to their surfaces. Two different PEG molecular weights (200 and 1000) and treatment concentrations (1% (w/w) and 15% (w/w)) were studied. Water flux decreased and NaCl rejection increased with PEGDE graft density ([microgram]/cm2), although the largest changes were observed for low PEGDE graft densities. Surface properties including hydrophilicity, roughness and charge were minimally affected by surface modification. The fouling resistance of modified and unmodified membranes was compared in crossflow filtration studies using model foulant solutions consisting of either a charged surfactant or an oil in water emulsion containing n-decane and a charged surfactant. Several PEGDE-modified membranes demonstrated improved fouling resistance compared to unmodified membranes of similar initial water flux, possibly due to steric hindrance imparted by the PEG chains. Fouling resistance was higher for membranes modified with higher molecular weight PEG. Fouling was more extensive for feeds containing the cationic surfactant, potentially due to electrostatic attraction with the negatively charged membranes. However, fouling was also observed in the presence of the anionic surfactant, indicating hydrodynamic forces are also responsible for fouling.
Surface modification of recycled tire rubber to enhance mechanical properties of rubberized cement mortar
(2023-08-10) Ahsan, Sanjida; Ferron, Raissa; Juenger, Maria; Folliard, Kevin J; Han, Dongyeop
The incorporation of recycled tire rubber in cement composite has shown potential as an environmentally sustainable approach to managing the increasing volumes of scrap tires. Due to the excellent shock absorbance and flexibility properties of rubber, the inclusion of discarded tire rubber in portland cement concrete has advantages like an increase in flexibility, toughness, and impact resistance. However, the inclusion of recycled tire rubber results in a significant decrease in compressive strength. This research explores using a new rubber chemical treatment process to modify the surface of discarded rubber. This new process is a two-step chemical treatment that entails halogenation of the rubber followed by amine functionalization. The effect of using rubber treated with this chemical treatment process in mortar was investigated. The results showed that the beneficial effects of adding rubber on impact resistance remained, and the adverse effects on strength were partially overcome when treated rubber was used. Specifically, it was seen that mortars containing treated rubber had higher compressive strength than mortars containing untreated rubber. This increase was attributed to the chemical surface treatment increasing the hydrophilicity of the rubber through the introduction of favorable functional bonds on the surface of the rubber with cement composite. Additionally, no adverse effect was observed on the early hydration kinetics of mortars containing treated rubber. Overall, the two-step chemical treatment showed promising results for the valorization of scrap rubber tires for use in cement-based composites. Furthermore, this study makes significant contributions to the current state of the art in several key areas. It shows that rubber hydrophilicity is a significant factor impacting the strength of Portland cement composites containing crumb rubber and highlights the potential for underestimation of the hydrophilicity of rubber when measured with deionized water. Additionally, the study sheds light on the efficacy of using halogenation and amine functionalization processes for the treatment of crumb rubber and provides valuable insights on which bond functionalization groups to target for the use of treated rubber in cement composites. The study also brings forth a new understanding of the behavior of concrete containing crumb rubber and indicates that there is an optimum treated rubber content at which further increases do not result in increasing impact resistance. Thus, design concrete at this optimum content to maximize compressive strength and impact resistance of concrete containing treated rubber.
Surface modification of water purification membranes to improve fouling resistance in oily water filtration
(2015-12) Kasemset, Sirirat; Freeman, B. D. (Benny D.); Sharma, Mukul M.; Paul, Donald R; Sanchez, Isaac C; Ellison, Christopher J; Emrick, Todd S
One of the biggest challenges in using water purification membranes is fouling. Surface modification using hydrophilic materials can reduce hydrophobic interactions between membrane surface and hydrophobic foulants, thereby alleviating fouling. In this Ph.D. research, polydopamine (PDA), a highly hydrophilic and universal coating agent, was used to surface-modified reverse osmosis (RO) and ultrafiltration (UF) membranes. PDA modification conditions (e.g., dopamine coating solution concentration, coating time, and pH of coating solution) control PDA deposition and can directly influence the modified membrane properties. Thus, the influence of PDA modification conditions on membrane physical, permeation, selective, and fouling properties were investigated systematically. A fundamental understanding relating the physical and permeation properties and the fouling characteristics of PDA-modified membranes was established. The RO membranes were modified with PDA at various modification conditions. Permeate fluxes during pure water and oil/water emulsion filtrations were studied. The PDA modification increased the permeate fluxes during oil/water emulsion filtration (thus, improved membrane fouling resistance) relative to unmodified membranes regardless of the initial dopamine concentration or deposition time used. However, these changes were only observed for the membranes coated under alkaline conditions, suggesting that the PDA did not deposit well under acidic condition. For UF membranes, molecular weight cutoff (MWCO) and pure water permeance decreased with increasing initial dopamine concentration or deposition time. A permeability and selectivity tradeoff was also observed. Membrane mean pore size and pore size distribution (modeled using log-normal pore size distribution) were investigated via modelling using a hindered solute transport model, Hagen-Poiseuille equation, and a stagnant film model. The PDA modification increased UF membrane surface hydrophilicity regardless of the coating conditions used, but it did not clearly change surface roughness or zeta potential (i.e., surface charge). Membrane fouling propensity was characterized using threshold flux. Compared to unmodified membranes, the threshold flux increased at minimal PDA coatings, but decreased at excessive PDA coatings. These threshold flux changes were likely governed by a tradeoff between surface hydrophilicity increase and pure water permeance decrease. Excessive PDA coatings resulted in decreased pure water permeance and possibly, pore blockage and pore size reduction, leading to higher local permeate flux causing severe fouling and decreased threshold flux.