Browsing by Subject "Surfactant"

Now showing 1 - 8 of 8
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    Design and Production of High-Performance Hydrophobin Surfactant Proteins Using a Dual-Domain Fusion Strategy
    (2019-01) Calixto Mancipe, Natalia
    Biosurfactants are amphipathic molecules required for vital processes in all life forms. They help to reduce surface tension facilitating interfacial processes such as breathing and evaporative cooling, modulate environmental conditions, control surface wettability, interact with substrates, form protective layers, etc. Thus, nature has evolved a wide variety of biosurfactants combining hydrophilic building blocks such as acid groups, sugars or polar amino acids with hydrophobic ones such as lipids, creating an enormous pallet of possibilities. Among them, hydrophobins (hereafter HFBs) are a family of self-assembling surfactant proteins with the highest surface activity known to date and an intrinsic amphipathic structure that does not require additional functional groups such as lipids or sugars. These characteristics give them a great potential for their industrial use as interfacial stabilizers, dispersal agents, surface modifiers and molecular anchors for protein immobilization on solids. The unique sequences and folding structures of HFBs particularly promote interfacial and intermolecular interactions, along with robust self-assembling mechanisms and surface activity. Unfortunately, a lack of knowledge on their sequence-structure-function relationships hinders the optimal selection of proteins for specific applications as well as manipulation of their properties. For a specific consideration, the use of HFBs for standard coating processes usually results in irregular products; at the same time, such an application requires a large-scale production that has been difficult to achieve limited by the productivity of native organisms, the HFB toxicity for heterologous hosts and the challenges of their purification. These obstacles suggest the need to leverage HFBs’ interfacial behaviors to better fit a broader range of applications. Therefore, an HFB from the fungus Trichoderma reesei is taken as a model surfactant protein in this work to explore the variation of its characteristics by a modular fusion strategy, as an alternative approach to protein directed mutagenesis and engineering. We aim to combine its high surfactant activity with the functionalities of different fusion partners to enhance its productivity and interfacial properties. Our results show that the fusion with a small metal binding protein from Nitrosomonas eurepaea (SMBP) achieves much improved product solubility and easier purification without compromising the hydrophobin properties. SMBP-HFBII shows a critical micelle concentration (CMC) < 0.5 mg/l and is prone to form stable nanobubbles of 50-60 nm radius and thin films at liquid-air interfaces. The adsorption of SMBP-HFBII on hydrophilic substrates (mica and glass) generates homogeneous coatings that reverse their wettability increasing the water contact angle (WCA) 460% and 70%, respectively. Adsorbed SMBP-HFBII also demonstrated a slight increase of Botrytis cinerea spores’ adhesion to coated glass, dependent on pH and spore concentration. This work shows that fusion HFBs can expand the application potentials of their native parent proteins as the fusion provides a powerful avenue to manipulate their functionalities. The lack of knowledge on their structure-function relationships and uncontrolled self-assembling can be subsidized by the addition of domains that influence the overall protein performance. This fusion strategy also enhances HFB productivity, facilitating their use in research and industry.
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    Effects of Spray Surfactant and Particle Charge on Respirable Dust Control
    (2015-06) Tessum, Mei
    Great efforts have been taken in underground coal mines to prevent coal workers' pneumoconiosis by controlling respirable coal dust, but respirable coal dust levels in mines still often exceed occupational exposure limits. Water-based spray systems are one of the primary dust control methods in mines; studies have suggested a potential to improve spray dust collection efficiency by adding surfactants. This dissertation investigates the effectiveness of different surfactant-containing sprays in capturing lab-generated monodisperse polystyrene latex particles and polydisperse coal dust by analyzing the impact of particle diameter, aerosol charging condition, surfactant type, sign and magnitude of particle charge, spray solution surface tension, spray drop size, and sign and magnitude of spray drop charge on spray collection efficiency. In order to focus on how the electrical effects caused by adding surfactants to spray water impact spray collection efficiency, the spray surface tension and drop size were taken into account during statistical modeling. Results indicate that particle size had the most important impact on respirable dust capture by water-based spray. Most particles with a diameter greater than 2 �m can be removed by the spray regardless of other factors. The magnitude of particle charge affected spray efficiency in that highly-charged particles tended to be removed more efficiently than weakly-charged particles. The magnitude and sign of the charge on surfactant-containing spray drops depended on both surfactant classification and concentration. Pure water spray drops and spray drops with nonionic (Triton X-100) and cationic (DAH) surfactants tended to carry net positive charges on average, whereas spray drops with anionic (SDS) surfactant tended to carry a net negative charge on average. However, the magnitude of spray drop charge was independent from the concentration of surfactant in the spray water. After controlling the surface tension and drop size, test results indicated a positive correlation between the magnitude of spray drop charge and spray collection efficiency. Nonionic surfactant-containing spray performed better in capturing respirable dust than the other sprays tested here, especially for weakly-charged aerosols. This superiority may be due to the relatively low surface tension and high charge magnitude of drops containing nonionic surfactant as compared to the other sprays tested here. Although the predominant mechanisms for respirable dust capture by water-based spray are inertial impaction and interception, electrical effects are also an important factor, especially for highly-charged particles. Therefore, the electrical effects caused by adding surfactants to spray water should be a consideration for future research regarding surfactant effectiveness.
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    Manipulating colloids and surfactants as co-templates for porous nanostructures and nanocomposites.
    (2010-02) Li, Fan
    Templating is a general and efficient strategy for creating nanostructured, particularly nanoporous materials. Two commonly employed classes of templates are colloidal crystals and surfactants. Colloidal crystals typically have an opal-like structure and have been used to produce macroporous (>50 nm pores) solids; surfactants generate various mesoporous structures (2−50 nm pores) as a result of their versatile phase behavior. One aim of this study is to combine colloidal crystals and surfactants to realize simultaneous templating at two length scales. A series of hierarchically structured porous silica samples were synthesized under different synthetic conditions, comprehensive TEM characterization was conducted to reveal the detailed hierarchical porous structures, and simulation was performed to correlate the structures to the surfactant phase behavior within the colloidal crystal confinement. The dual templating approach was further extended to synthesize functional materials with composite porous architectures, in which functional cores were embedded in a hierarchically porous framework for optical ionsensing application. A second aim of this study is to develop a template-based strategy for sculpting nanoparticles of desired shapes and sizes. Owing to the ordered structure and symmetry of the template, a templating-disassembly process was found to produce uniform, nanometer-level, multipodal particles. This method is applicable to a variety of compositions, including oxides, phosphates and carbon, and it could further lead in-situ organization of particles following a self-reassembly process. In addition, through a coupled passivation-disassembly process, site-specific functionalization was achieved to modify only the tips of the multipods with a range of functional groups, and therefore to enable their directional bonding to other colloidal particles. (256 words)
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    The role of dynamic interfacial phenomena in marine crude oil spill dispersion
    (2016-12) Riehm, David
    Marine oil spill dispersants containing the surfactants Tween 80, Span 80, and dioctyl sodium sulfosuccinate (DOSS) have been widely used for decades, but their environmental impact remains controversial. The interfacial science behind their formulation has been studied in this work in order to develop new, equally effective dispersants using nontoxic components. The effectiveness of dispersants containing different Tween 80-Span 80-DOSS (T-S-D) blends was measured using a Stirred Flask Test and correlated with the dynamic oil-water interfacial tension (IFT) produced by each dispersant (Chapter 3). Very low IFT (<10-4 mN/m) was produced by both DOSS-rich dispersants and Span 80-rich dispersants, but DOSS-rich dispersants were significantly more effective and adsorbed to the oil-water interface faster than Span 80-rich dispersants. In order to investigate whether T-S-D dispersants form water-in-oil microstructures which influence dispersants’ interfacial adsorption rates, T-S-D blends were added to a transparent, low-viscosity model crude oil and studied using cryo-transmission electron microscopy and dynamic light scattering (Chapter 4). T-S-D blends formed spherical water-in-oil microstructures in the oil, and the microstructures formed by DOSS-rich T-S-D blends were much smaller than those formed by Span 80-rich T-S-D blends. This may explain why DOSS-rich T-S-D blends adsorb to the interface faster, and thus are more effective, than Span 80-rich T-S-D blends. Blends of Tween 80 and lecithin (L), a biosurfactant which also forms water-in-oil microstructures, were investigated as a substitute for T-S-D dispersants (Chapter 5). The most effective L-T dispersants performed comparably to the most effective T-S-D dispersants in the Baffled Flask dispersant effectiveness test. However, lecithin-rich L-T dispersants were significantly more effective than Tween 80-rich L-T dispersants which produced lower or comparable IFT, even though interfacial adsorption rates of L-T dispersants did not vary as a function of lecithin:Tween 80 ratio. This suggests that interfacial phenomena other than dynamic IFT influence L-T dispersants’ effectiveness. The interface between seawater and crude oil treated with L-T dispersants was therefore studied using light microscopy, cryogenic scanning electron microscopy, and droplet coalescence tests (Chapter 6). Tween 80-rich L-T dispersants caused oil-into-water spontaneous emulsification, indicating rapid dispersant leaching from oil into water. This may explain why Tween 80-rich L-T dispersants are less effective than lecithin-rich L-T dispersants which produce similar IFTs. Conversely, lecithin-rich L-T dispersants exhibited water-into-oil emulsification, indicating that such surfactant blends are stable in the oil and perhaps explaining why some lecithin-rich L-T dispersants are as effective as T-S-D dispersants which produce much lower IFT. Possible mechanisms for the spontaneous emulsification induced by L-T dispersants are discussed, based on images of the spontaneously emulsifying L-T dispersant-treated oil-water interfaces.
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    Structure-property relationship of synthetic lung surfactant films
    (2023-01) Valtierrez Gaytan, Cain
    Surfactants are ubiquitous in our daily lives as they are found in household, personal care, and pharmaceutical products. Surfactants also play an important in making life possible by helping essential cellular components organize and grow. Of particular interest is lung surfactant (LS), a lipid-protein mixture that makes breathing possible by reducing the interfacial tension of the air-liquid interface of the alveoli. This modulation of the interfacial tension enables effortless lung expansion and stabilizes the lung against collapse thus allowing for proper oxygenation of the bloodstream. The lack of LS or its inhibition leads to deadly respiratory illnesses. Various animal-based replacement lung surfactant (RLS) therapies currently exist that have decreased the mortality of neonatal and acute respiratory distress syndrome, however, these RLS therapies do not work as well as natural LS, are expensive, and vary widely in composition. This motivates the development of a synthetic LS formulation. One of the major challenges is that we do not know an ideal LS composition. Therefore, to better understand LS function and make progress towards a viable synthetic LS formulation we require a detailed study that considers both the fundamental science and physiologically relevant performance parameters. In this dissertation, we have elucidated the role of dihydrocholesterol (DChol) within the context of a simple model LS system composed of 2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1-hexadecanol (HD) in modulating film microstructure, phase behavior, interfacial rheology, and film nano-mechanics. Using confocal microscopy, we found that DPPC and HD phase separate into crystalline domains within a fluid matrix. The addition of DChol to our model LS system causes domains that are initially semi-circular to develop fingering instabilities and undergo a spontaneous and reversible shape transition to stripes of uniform width. The fingering instabilities follow a version of the classical Mullins-sekerka growth instability theory and depend on domain growth kinetics. The stripe morphology is found to be an equilibrium state governed by the competition between dipole-dipole interactions within the domains and the line tension at the domain boundaries and depends on film composition, temperature, and surface pressure. To study how LS spreads on an air-water interface, we use surface micro-rheology to show that HD causes the film to resist flow while DChol causes the film to be more fluid-like. We transfer our monolayers from the air-water interface onto a supported substrate and show using atomic force microscopy that the addition of DChol destabilizes the crystalline and liquid-like phases with highly dissipative nano-structures. Overall, we believe the work presented in this dissertation provides the building blocks for using fundamental and applied science to develop a synthetic replacement LS therapy.
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    Surfactant Effects On Pool Boiling Of Dilute Emulsions On A Horizontal Surface
    (2020-05) Proper, John
    Previous research has demonstrated that heat transfer of water may be enhanced by either the addition of surfactants or through emulsifying the water with a small volume of volatile disperse phase. However, the combination of surfactant and emulsion has not yet been thoroughly investigated. To accomplish this, experiments of boiling heat transfer were conducted with dilute FC-72 in water emulsions and Tween-20 surfactant. Boiling occurred over a flat upward-facing aluminum nitride heater in a vessel nearly 1 L in volume. FC72-in-water emulsions with volume fractions of 0.1, 0.5, and 1.0 % were tested with concentrations of 0, 10, 60, and 100 ppm Tween-20 surfactant. Turbulent mixing induced by pumping through a check valve caused the fluid to emulsify. Size distributions of oil droplets in the emulsions were measured via laser diffraction. The resulting boiling curves for emulsion without surfactant confirmed previously observed trends, with an increase in heat transfer occurring near 80 °C. Boiling with Tween-20 surfactant did not show any increase in heat transfer, in both aqueous surfactant systems and emulsions with surfactant. Laser diffraction imaging showed that emulsions with different volume fractions can have different particle size distributions even though the emulsification process was the same. Addition of surfactant to the emulsion tended to cluster the droplet diameter distribution around a mean of 2 µm. The similarity of boiling behavior between mixtures of water and Tween-20 and emulsions with Tween-20 suggests that the boiling behavior is characterized mostly by interface chemistry unique to Tween-20, rather than a secondary effect of droplet size distribution. However, there is considerable variety in surfactants, and there is still value in testing the effect of other surfactants on the boiling behavior of dilute oil-in-water solutions.
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    Thermodynamics of Micellar Lyotropic Liquid Crystals
    (2020-06) Jayaraman, Ashish
    Aqueous lyotropic liquid crystals (LLCs) comprise a class of ordered morphologies formed by self-assembly of amphiphiles in water. LLCs assume a variety of concentration- and temperature-dependent structures including lamellae (bilayers), bicontinuous networks, hexagonally-packed cylindrical micelles, and spherical micelles packed on a lattice. Typically, LLC sphere packings include high-symmetry body-centered cubic (BCC), face-centered cubic (FCC), and hexagonally closest-packed (HCP) structures. Recently, a giant tetragonal σ phase containing 30 micelles of five different sizes was discovered in the aqueous LLC self-assembly of dianionic alkylphosphonate surfactants. The σ phase belongs to a class of tetrahedrally close-packed structures called Frank-Kasper (FK) phases, which possess ≥ 7 particles of two or more types situated at 12-, 14-, 15-, or 16-fold coordination environments in low-symmetry unit cells. Ubiquitous in intermetallic alloys, FK phases have been recapitulated in other soft materials including dendritic thermotropic liquid crystals, giant-shape surfactants, and block polymers. The observation of these complex morphologies across different soft material classes stabilized by varying non-covalent interactions begs the question of universality in the principles that govern FK phase formation. The formation of the σ phase in LLCs of ionic surfactants was rationalized based on maximizing counterion-mediated intermicellar cohesion, while minimizing expensive local variations in headgroup-counterion solvation. However, molecular design principles guiding FK phase selection in LLCs are lacking. FK phases are periodic approximants of dodecagonal quasicrystals (DDQCs), structures which possess 12-fold rotational symmetry yet lack translational symmetry. DDQCs have been observed in self-assembled micelles of neat, neutral amphiphiles in regions of phase space adjacent to FK morphologies. However, quasiperiodic ordering of micelles in LLC self-assembly is surprisingly unknown given the pervasiveness of the periodic approximants. This thesis elucidates the amphiphile structural motifs that stabilize FK phases and related DDQCs in aqueous LLCs. We first establish the molecular design criteria for the formation of σ phases in ionic amphiphiles by investigating the LLC phase behavior of alkylmalonate dianionic surfactant analogous to the alkylphosphonate amphiphiles. FK phase formation was observed to depend on the nature of the counterions and length of the alkyl tail. Using real-space electron density reconstructions, we find that the preference for local micellar symmetry in the σ phase is dictated by the extent of headgroup-counterion association. We next report the formation of a well-ordered DDQC in oil-swollen micelles of alkylphosphonate surfactants, and we use high-resolution small-angle X-ray scattering data to determine the space group symmetry of this quasiperiodic structure. The formation of the DDQC was contingent on the sample-processing protocols employed, indicating the metastability of this mesophase. We further illustrate the non-specific nature of FK phase formation in soft materials by the discovery of a σ phase on self-assembly of hydrated non-ionic polyethylene-block-poly(ethylene oxide) surfactants. For the hydroxyl terminated surfactant, access to the σ phase depends on sample thermal history, indicating its metastability with respect to the A15 structure. Finally, the hydroxyl end-group of the amphiphile was synthetically modified with ionic and strongly H-bonding moieties. We find that strongly interacting terminal groups provide increased temperature- and composition-windows of σ phase stability. Moreover, cationically-terminated oligomers surprisingly self-assembled into a DDQC. These findings are rationalized based on the drive to minimize local variations in intramicellar chain-chain interactions, while maximizing intermicellar cohesion. These fundamental studies of the thermodynamics of micellar morphologies in solvated amphiphiles provide insights into the general underlying principles which stabilize these complex packings of soft reconfigurable particles.
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    Tunable Synthesis and Characterization of Oleo-Furan Sulfonate Surfactants from Renewable Furan and Fatty Acids
    (2018-05) Joseph, Kristeen Esther
    An important advance in fluid surface control was the amphiphilic surfactant composed of coupled molecular structures (i.e., hydrophilic and hydrophobic) to reduce surface tension between two distinct fluid phases. Surfactants are widely used in household detergents, cleaners, emulsifiers, foaming agents, and personal care products. Anionic surfactants constitute 50% of the $30 billion global surfactant industry and are widely used in household detergents, and personal care products. Linear alkylbenzene sulfonates (LAS) are widely used due to their low cost and high detergency. Current LAS production methods rely on toxic catalysts and petrochemical-based constituents, such as benzene and long chain hydrocarbons. The reaction has low selectivity to the prescribed linear structure thereby rendering minimal control over the desired composition and properties. Additionally, implementation of simple surfactants such as LAS has been hindered by the broad range of applications in water containing alkaline earth metals (i.e., hard water), which disrupt surfactant function and require extensive use of undesirable and expensive chelating additives. Despite years of technology development, most large-volume surfactants are made from petrochemical sources, while efforts to make renewable surfactants are focused on making existing surfactant structures from renewable sources. In this work, we demonstrate a new surfactant based on the natural structure and chemistry of plant-based oils and sugars with superior function and suitability as a replacement to petrochemicals. Furans obtained from lignocellulosic biomass can be acylated with triglyceride-derived fatty acids and anhydrides in the presence of a heterogenous zeolite catalyst. The results obtained for the reaction of lauric anhydride with furan show that different pore sizes, structures and acidity of zeolites result in varying acylation activity. Preliminary kinetic studies of the indirect acylation using anhydrides provide insight into reaction orders and product inhibition resulting in lowering of catalytic activity. Following acylation, the molecule can be upgraded via several independent and sequential chemistries such as etherification, hydrogenation and aldol condensation and finally subjected to sulfonation to yield surfactant molecules termed as oleo-furan sulfonates (OFS) in high yield. Evaluation of surfactant performance of OFS revealed hundredfold better detergency and stability in hard water conditions in comparison with petroleum-derived counterparts. The synthesis of OFS molecules is, highly tunable and selective where the number of carbon atoms in the linear or branched chain can be easily varied without compromising on reaction yields to achieve desired surfactant properties.