Browsing by Subject "Emulsions"
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Item Biopharmaceutical classification and development of limonene-based self-nanoemulsified capsule dosage form of coenzyme Q10(Texas Tech University, 2004-05) Palamakula, AnithaCoenzyme QIO (CoQ) is a challenging micronutrient for oral formulation due to its low aqueous solubility and bioavailability. The present dissertation deals with a systematic approach to classify CoQ biopharmaceutically according to FDA biopharmaceutical classification system (BCS), and to develop a self-nanoemulsified capsule dosage form (SNCDF) with chiral limonenes. We have hypothesized that the oral bioavailability of CoQ may be enhanced by limonene based SNCDF. In vitro transport studies using Caco-2 cells and solubility studies indicated that CoQ is moderately permeable and has low solubility. However, CoQ exhibits substantial solubility in limonenes. The permeability of CoQ across isolated rat GI segments revealed regional differences with maximum absorption through duodenum. Based on these results, a limonene based self-nanoemulsified formulation of CoQ was prepared and evaluated by in vitro and in vivo methods. Dissolution studies in water have shown CoQ release of > 90% within 5 minutes. Thermal analysis showed no significant change in CoQ endotherm. FT-IR and X-ray diffraction studies revealed the preservation of CoQ structure, indicating no interactions. Particle size, turbidity and zeta potential measurements have indicated that R-(+)-limonene provided superior self-nanoemulsified formulation of CoQ when compared with S-(-)-limonene. A three-factor, three-level optimization design was used to evaluate the effect of critical process variables on the drug release characteristics. Mathematical relationships, contour plots and response surface methodology were employed with constrained optimization to predict levels of factors that provide maximum drug release. The predicted and observed responses were in good agreement. The long term stability of the formulation was ascertained by subjecting to various temperature and humidity conditions for 6 months. The results indicated no significant effect on turbidity, particle size, zeta potential, DSC, FT-IR and total drug release at room temperature. The in vivo performance of CoQ limonene based SNCDF and eutectic based self-nanoemulsified drug delivery systems (SNEDDS) was evaluated by assessing the pharmacokinetic parameters, Tmax, Cmax, and AUC in rats. The oral bioavailability of SNCDF and SNEDDS was found to increase by 650% and 730% respectively when compared with CoQ powder (control). Preliminary assessment in human volunteers indicated increased tendency of rate and extent and metabolism of nanoemulsified preparations as compared to control.Item Breaking and curing rates in asphalt emulsions(2012-12) Banerjee, Ambarish; Prozzi, Jorge Alberto; Bhasin, Amit; Korgel, Brian; Folliard, Kevin J.; Zhang, ZhanminThis PhD dissertation addresses a number of issues pertaining to the use and application of surface treatments using asphalt emulsions. The work conducted as part of this research study shows in detail the problems associated with the state-of-practice and how these issues can be addressed using a scientific and rational approach as opposed to the experience-based approach which is prevailing currently. The first objective of this research study focuses on developing a methodology to determine the total amount of evaporative water loss of an emulsion before the aggregates are placed. An algorithm is presented that can be used by field inspectors and practitioners for the optimal timing of chip placement. The second objective focuses on another key aspect associated with the constructability of surface treatments, i.e., the optimal time to open a new surface treatment to traffic. Laboratory tests were conducted on the emulsion and aggregates to measure the rate of moisture loss and the evolution of the rheological properties as function of time. This was related to the field measured evaporation rates to determine the minimum stiffness required for optimal performance of the chip seal towards adequate resistance to raveling. The final objective of this dissertation focuses on developing a theoretical understanding of the current flowing through a circuit when an emulsion separates into its constituent phases when placed in an electric field. The measured current depends on a set of material properties that include the emulsion’s viscosity, surface potential, and dielectric of the medium and the strength of the electric field. A theoretical formulation was developed that relates the current flowing through the circuit with the mobility of the charged particles and the bulk charge density. The proposed theory was further utilized in developing a test procedure to quantify the breaking characteristics of asphalt emulsions. Results demonstrated that the parameters obtained from these tests were repeatable and different for different types of asphalt emulsions. It was also noticed that for a given type of emulsion the test method is sensitive to factors such as water content and partial breaking due to mechanical agitation.Item Carbon dioxide and water emulsion stability and rheology with nonionic hydrocarbon surfactants or particles(2009-05) Adkins, Stephanie Sue; Johnston, Keith P., 1955-For the first time the interfacial properties of nonionic hydrocarbon surfactants at both the air-water and CO₂-water interfaces are investigated in terms of surfactant structure to determine the changes in surfactant efficiency (negative of the logarithm of the surfactant concentration to create a surface pressure of 20 mN/m). At the air-water interface, linear surfactant tails are more efficient due to the higher packing ability of the straight chains in the dense surfactant monolayer. However, at the CO₂-water interface, surfactant adsorption is small and tails can be solvated. Thus, branching which increases both tail solvation and tail hydrophobicity also enlarges the hard disk area of the surfactant to ultimately increase the efficiency of the surfactant at the CO₂-water interface. CO₂-in-water concentrated emulsions (foams) are studied over short and long times to evaluate the foam stability as a function of both surfactant structure and foam conditions using in-situ optical microscopy. The surface pressure measured at the CO₂- water interface is correlated with the short time stability of coalescing foams with very small cell sizes (under 0.4 [mu]m in diameter). Long time stability of bubbles to coalescence is shown under a variety of conditions. The rheology of these bulk CO₂-in-water foams under high-pressure conditions are also evaluated through measurements of the pressure drop over a capillary tube. Viscosities in excess of 200 cP are measured, an increase of over 1000 time that of pure CO₂ (0.09 cP at 24 °C and 2000 psia). The viscosity of the C/W foams are found to correlate with bubble size, continuous phase viscosity, shear rate, and interfacial tension. Hydrophobic silica particles adsorbed at the interface are also used to stabilize water-in-CO₂ emulsions as an alternative to surfactant stabilizers. The difficulties of tail solvation associated with many hydrocarbon surfactants in CO₂ can be removed by using particles instead of surfactant. A porous cross-linked shell is formed about the hydrophilic (colloidal and fumed) silica to render the particles CO₂-philic and the crosslinking removes ligand tails from the particle surface.Item Emulsions and microemulsions of water and carbon dioxide: novel surfactants and stabilization mechanisms(2005) Ryoo, Won Sun; Johnston, Keith P., 1955-Item Enhanced Heavy Oil Recovery by Emulsification With Injected Nanoparticles(2013-11-26) Martinez Cedillo, Arturo ReyIn-situ oil-in-water emulsion generation, using modified silica hydrophilic nanoparticles as emulsifier, has been proposed as an enhanced oil recovery process. The nanoparticles are injected as an aqueous dispersion; its hydrophilic character allows emulsifying the immobile heavy oil, and transports it out of the reservoir as a low viscosity fluid. Generating the emulsions in the reservoir was suggested because it offers numerous advantages. The first advantage is low injectivity pressures due to the low dispersion viscosity. Also, the size of nanoparticles (5 nm) yields a better emulsion stability. Furthermore, complex injection facilities are not required, which reduces operational costs. In this research, 12 nanoparticle dispersions were created using nanoparticle concentrations of 0.5, 2.0 and 5.0 wt%, deionized water or brine made with 0.5 wt% of Sodium Chloride. These dispersions were tested to investigate their ability to generate oil-in-water emulsions. Emulsion generation experiments included interfacial tension measurements between heavy oil and nanoparticle dispersions, microscopy analysis to determine the amount of emulsion generated, and emulsion viscosity measurements. Results obtained from these experiments indicated that the nanoparticles lead to a reduction of the interfacial tension of the heavy oil and the dispersion. In addition, the presence of Sodium Chloride in the dispersion reduced still more of that interfacial tension, generating the largest amount of emulsions. Six core flooding experiments were conducted to study the effect of the nanoparticle dispersion flooding on the final recovery under different settings. Two types of core plugs with permeabilities of 150 mD and 2,300 mD, and two heavy oils with viscosities of 600 cP and 3500 cP were combined to establish the original experiment conditions. Tertiary heavy oil recoveries ranged from 20% to 64 % of OOIP were obtained. The results throughout these experiments suggest that if the reservoir conditions (e.g. permeability, porosity and oil viscosity) are adequate, the nanoparticle dispersion flooding may be a reliable alternative to the thermal recovery processes.Item Laboratory investigation of the influence from aggregate and climate on stiffness development in seal coat asphalt emulsions(2010-12) Tubb, Andrew A; Senadheera, Sanjaya; Won, Moon C.Emulsified asphalt is widely used in many highway maintenance and construction applications, and their effectiveness is greatly influenced by the construction process and climatic conditions at the time of application and soon thereafter. This research studied the rate of residue formation of emulsified asphalts over time, with particular emphasis on two key construction-related factors; the aggregate it is in contact with, and the climatic conditions. Emulsified asphalts were sampled both from a plant location as well as three construction sites. Test specimens were prepared by pouring asphalt emulsion directly on aggregate substrates and then cured under different climate regimes in an environmental chamber. These climate regimes were selected to simulate field conditions and anticipated laboratory test environments. The stiffness of the asphalt was measured at specified time intervals by a Dynamic Shear Rheometer (DSR) using a strain-sweep test protocol.Item Relationship between interfacial properties and formation of microemulsions and emulsions of water and supercritical carbon dioxide(2001-08) Psathas, Petros; Johnson, Keith P.The utilization of supercritical (SC) CO2 as an alternative green solvent has attracted significant research devotion in the last decade. Its uniqueness lies on the fact that CO2 is a non-FDA regulated solvent mainly generated as the sideproduct of industrial process, is easily recyclable, readily available, non flammable and essentially non toxic. Dense CO2 is non-polar (unlike water), has weak van der Waals forces (unlike oils) and as such may be considered a third type of fluid phase in nature, somewhat similar to fluorocarbons. The use of SC CO2 has expanded into broad technological areas one of which is the stabilization of water-in-CO2 dispersions that offer new possibilities for separations on the basis of polarity, and as media for reactions between polar and nonpolar molecules. The formation of stable emulsions of water-in-CO2 (W/C) so far has been hampered by the lack of suitable surfactants. The synthesis of various molecularly engineered surfactants is demonstrated in this study, among which are polydimethylsiloxane (PDMS)-based block copolymer ionomers, ionic and nonionic perfluoropolyether (PFPE) and nonionic perfluorooctylmethacrylate (PFOMA)-based ones. The concentrated W/C emulsions are characterized with electrical conductivity, optical microscopy and multiwavelength turbidity technique. The emulsion stability is assessed as a function of formulation variables that influence the surfactant monolayer curvature, such as temperature, pH, salinity and pressure. The response of the interfacial activity of the surfactant to changes in the variables above is monitored with interfacial tension (γ) measurements and is correlated to emulsion stability. Moreover, salinity is used to tune the surfactant aggregation characteristics, resulting in spontaneous microemulsion formation upon crossing the critical microemulsion concentration (cµc). Based on guidelines provided by γ versus temperature, stable concentrated (50:50 by mass) C/W miniemulsions consisting of 200 nm droplets are formed with the phase inversion temperature (PIT) method. Finally, the formation of unflocculated and stable dilute W/C emulsions is studied with a homologous series of PFOMA-based nonionic surfactants, and mapping of γ with surfactant hydrophilicity provide useful pathways for the synthesis of the optimum structure.Item Stabilization of dispersions in carbon dioxide and in other low-permittivity media(2006) Smith, Peter Griffin; Johnston, Keith P., 1955-