Methane and carbon dioxide hydrate crystals were formed on nearly spherical water droplets at 274.6 K and 2,150 kPa or 1,000 kPa above the corresponding three‐phase hydrate equilibrium pressure. Each experiment was performed with two... more
Methane and carbon dioxide hydrate crystals were formed on nearly spherical water droplets at 274.6 K and 2,150 kPa or 1,000 kPa above the corresponding three‐phase hydrate equilibrium pressure. Each experiment was performed with two droplets 5 mm and 2.5 mm in diameter or three droplets with a diameter of 2.5 mm. At the higher pressure the water droplets quickly became jagged and exhibited many needlelike or hairlike crystals extruding from the droplet, whereas at the lower pressure the surface was smooth. In almost all experiments, a depression or collapse of the hydrate layer was observed to occur. This collapse was interpreted as evidence of a continuing hydrate formation after the droplet surface was covered by the hydrate layer. The type of hydrate‐forming gas and the size of the droplet was observed not to influence the macroscopic hydrate crystal morphology. The decomposition of the methane and carbon dioxide hydrate layers was also observed. Reformation was also experimented, and the effect of memory on the morphology of hydrate crystal growth was determined.
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This review presents theory and simulation of liquid crystal phase ordering in biological fibrous materials, solutions, and composites in the presence of elastic fields, second phase inclusions, and transport phenomena, including complex... more
This review presents theory and simulation of liquid crystal phase ordering in biological fibrous materials, solutions, and composites in the presence of elastic fields, second phase inclusions, and transport phenomena, including complex shear-extensional flow and mass transfer. Liquid crystal self-assembly through phase ordering on elastic deformable membranes is first applied to characterize the mechanisms that control the structures in plant cell walls, highlighting how curvophobic and curvophilic effects introduce new structuring fields beyond hard-core repulsion. Then chiral nematic self-assembly is simulated in a mesophase containing fibrillar colloidal inclusions (liquid crystal-fibre composites) to demonstrate how the inclusion positional order generates defects and disclinations as shown in the plant cell wall. Coupling phase ordering to tuned transport phenomena is shown how and why it leads to self-organization such as paranematic states of dilute acidic aqueous collagen ...
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Nanotubes may provide interfacial effects for viscosity reduction and align in the flow direction. However, the graphene nanoflake surface area is only limited by its mean free path while nanotubes can entangle with each other.
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Abstract Clathrate hydrate promotion research has often focused on hydrate growth rate differentiation, however little work has been done to understand the kinetics of dissolution. The dissolution of gas into the bulk liquid phase is of... more
Abstract Clathrate hydrate promotion research has often focused on hydrate growth rate differentiation, however little work has been done to understand the kinetics of dissolution. The dissolution of gas into the bulk liquid phase is of great importance to hydrate growth, as it is the first step in hydrate formation. Furthermore, understanding the influence of additives on hydrate systems may provide significant insight into the mechanisms of their function. The effect of the hydrate promoter sodium dodecyl sulphate (SDS) on methane dissolution was thus investigated at the three-phase (H-Lw-V) equilibrium condition of 275.1 K and 3145 kPa. Experiments with concentrations of SDS ranging from 0.01 mM to 4 mM were conducted. The purpose of this study was to investigate the effects on the methane equilibrium saturation values as well as the kinetics of dissolution. The effects on saturation were found to be negligible. The rate of dissolution was measured using a first-order response model and the time constant tau (τ). It was found that the values of τ for SDS increased with an increasing loading of 0.01 mM–0.75 mM and then plateaued for concentrations ranging between 0.75 and 4 mM producing a sigmoidal trend.
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The vibrational characteristics of gas hydrates are key identifying molecular features of their structure and chemical composition. Density functional theory (DFT)-based IR spectra are one of the efficient tools that can be used to... more
The vibrational characteristics of gas hydrates are key identifying molecular features of their structure and chemical composition. Density functional theory (DFT)-based IR spectra are one of the efficient tools that can be used to distinguish the vibrational signatures of gas hydrates. In this work, ab initio DFT-based IR technique is applied to analyze the vibrational and mechanical features of structure-H (sH) gas hydrate. IR spectra of different sH hydrates are obtained at 0 K at equilibrium and under applied pressure. Information about the main vibrational modes of sH hydrates and the factors that affect them such as guest type and pressure are revealed. The obtained IR spectra of sH gas hydrates agree with experimental/computational literature values. Hydrogen bond’s vibrational frequencies are used to determine the hydrate’s Young’s modulus which confirms the role of these bonds in defining sH hydrate’s elasticity. Vibrational frequencies depend on pressure and hydrate’s O···...
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The ideal strength of methane hydrates or clathrates is investigated and quantified from first principles calculations. Methane hydrates are crystalline compounds in which hydrogen-bonded water molecules entrap methane at high pressures... more
The ideal strength of methane hydrates or clathrates is investigated and quantified from first principles calculations. Methane hydrates are crystalline compounds in which hydrogen-bonded water molecules entrap methane at high pressures and/or low temperatures [1]. Although they exist abundantly almost all over the world, their mechanical properties are still under investigation. This is essential for detection and for risk assessment during production. Specifically, the ideal strength, defined as the stress at the elastic instability of a perfect crystal, sets an upper limit for strength, can be observed near crack tips, and is important in plastic deformation in terms of width of dislocations and stresses near dislocation sites [2,3]. Using Density Functional Theory (DFT), the linear and nonlinear elastic properties of methane hydrates are studied. Tests are performed to compute the ideal strength in characteristic lattice directions and under different modes of uniaxial, triaxial...
Several industries have steadily gained interest in gas hydrate technologies for their potential use in natural gas transport and storage applications. Additives which optimize the efficiencies of ...
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In this work, we investigate the fabrication of stainless-steel substrates decorated with laser-induced periodic surface structures (LIPSS) of both hydrophilic and hydrophobic wettability through different post-processing manipulation. In... more
In this work, we investigate the fabrication of stainless-steel substrates decorated with laser-induced periodic surface structures (LIPSS) of both hydrophilic and hydrophobic wettability through different post-processing manipulation. In carrying out these experiments, we have found that while a CO2-rich atmosphere during irradiation does not affect final wettability, residence in such an atmosphere after irradiation does indeed increase hydrophobicity. Contrarily, residence in a boiling water bath will instead lead to a hydrophilic surface. Further, our experiments show the importance of removing non-sintered nanoparticles and agglomerates after laser micromachining. If they are not removed, we demonstrate that the nanoparticle agglomerates themselves become hydrophobic, creating a Cassie air-trapping layer on the surface which presents with water contact angles of 180°. However, such a surface lacks robustness; the particles are removed with the contacting water. What is left beh...
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Abstract The melting of frozen water droplets is a fundamental and ubiquitous process and the study of the transport processes occurring within the system during phase change is essential to understanding the forces that govern it.... more
Abstract The melting of frozen water droplets is a fundamental and ubiquitous process and the study of the transport processes occurring within the system during phase change is essential to understanding the forces that govern it. Multiwall carbon nanotubes (MWCNTs) can be added to liquid systems prior to crystallization in order to modify the properties of the phase change process and of the liquid or solid systems themselves. In this study, the melting behavior of frozen sessile droplets composed of water and 50 ppm of either functionalized or non-functionalized aqueous MWCNTs is investigated. Droplets are thawed from their base on a hydrophobic substrate set to temperatures between 1 and 30 °C. Tracking of MWCNT clusters during melting shows convective fluid motion occurring within the liquid melt at temperatures above 5 °C. This circulation is contingent on the presence of the ice phase above. The internal fluid dynamics are attributed predominantly to thermocapillary effects as a result of temperature-induced surface tension gradients along the air/liquid interface in the melt. Further, the melting times of MWCNT-containing systems were longer than pure water samples. These results highlight new and important mechanisms driving the melting processes within water droplet systems.
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Abstract Polymer based kinetic hydrate inhibitors are increasingly used in the oil and gas industry to prevent hydrate formation. It is well known that the effectiveness of inhibitors decreases as the driving force for hydrate formation... more
Abstract Polymer based kinetic hydrate inhibitors are increasingly used in the oil and gas industry to prevent hydrate formation. It is well known that the effectiveness of inhibitors decreases as the driving force for hydrate formation increases. The current study assesses whether the inhibitory effect of polyvinylpyrrolidone (PVP) can be completely masked by high driving forces for hydrate growth. Methane hydrate kinetic experiments were performed with solutions of pure water and 0.007 wt% PVP in water at 277 K and pressures ranging from 23.83 MPa to 31.33 MPa. Results showed that as the driving force for hydrate formation increases, the effect of PVP as a hydrate growth inhibitor diminishes and may be entirely masked for a significant amount of time. With the current system, hydrate growth appeared uninhibited at subcoolings greater than 17.4 K (26.33 MPa). The time of uninhibited growth was found to increase linearly with subcooling to a maximum of 537 s at a 19 K subcooling (31.33 MPa). Under such high driving forces, inhibitory effects have been shown to take time to manifest themselves, indicating that under these conditions additives have no effect on hydrate nucleation but solely on hydrate growth following nucleation.
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The solubility of carbon dioxide in pure water in the presence of CO2 gas hydrate has been measured at temperatures between 273 and 284K and pressures ranging from 20 to 60bar. It was found that the solubility decreases with decreasing... more
The solubility of carbon dioxide in pure water in the presence of CO2 gas hydrate has been measured at temperatures between 273 and 284K and pressures ranging from 20 to 60bar. It was found that the solubility decreases with decreasing temperature in the hydrate formation region. In the absence of gas hydrate, the gas solubility increases with decreasing temperature, but
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Evaluating gas hydrates properties contributes valuably to their large-scale management and utilization in fundamental science and applications. Noteworthy, structure-H (sH) gas hydrate lacks a comprehensive characterization of its... more
Evaluating gas hydrates properties contributes valuably to their large-scale management and utilization in fundamental science and applications. Noteworthy, structure-H (sH) gas hydrate lacks a comprehensive characterization of its structural, mechanical, and anisotropic properties. Anisotropic and pressure dependent properties are crucial for gas hydrates’ detection and recovery studies. The objective of this work is the determination of pressure-dependent elastic constants and mechanical properties and the direction-dependent moduli of sH gas hydrates as a function of guest composition. First-principles DFT computations are used to evaluate the mechanical properties, anisotropy, and angular moduli of different sH gas hydrates under pressure. Some elastic constants and moduli increase more significantly with pressure than others. This introduces variations in sH gas hydrate’s incompressibility, elastic and shear resistance, and moduli anisotropy. Young’s modulus of sH gas hydrate i...
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Macrosurfactants consisting of water-soluble poly(vinylcaprolactam) (PVCap) or poly(vinylpyrrolidone) (PVP) segments with comparatively shorter hydrophobic poly(styrene) (PS) or poly(2,3,4,5,6-pentafluorostyrene) (PPFS) segments were used... more
Macrosurfactants consisting of water-soluble poly(vinylcaprolactam) (PVCap) or poly(vinylpyrrolidone) (PVP) segments with comparatively shorter hydrophobic poly(styrene) (PS) or poly(2,3,4,5,6-pentafluorostyrene) (PPFS) segments were used as kinetic hydrate inhibitors (KHIs). These were synthesized with 2-cyanopropan-2-yl N-methyl-N-(pyridin-4-yl)dithiocarbamate switchable reversible addition–fragmentation chain transfer (RAFT) agent at 60 °C or 90 °C for 1-P(S/PFS) or 1-PVCap, respectively, followed by chain extension at 90 °C or 70 °C with PVCap or PVP, respectively. The addition of PVCap to the pure methane-water system resulted in a 53% reduction of methane consumption (comparable to PVP with 51% inhibition) during the initial growth phase. A PS-PVCap block copolymer comprised of 10 mol% PS and 90 mol% PVCap improved inhibition to 56% compared to the pure methane-water system with no KHIs. Substituting PS with a more hydrophobic PPFS segment further improved inhibition to 73%. B...
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This paper presents theory and simulation of viscous dissipation in evolving interfaces and membranes under kinematic conditions, known as astigmatic flow, ubiquitous during growth processes in nature. The essential aim is to characterize... more
This paper presents theory and simulation of viscous dissipation in evolving interfaces and membranes under kinematic conditions, known as astigmatic flow, ubiquitous during growth processes in nature. The essential aim is to characterize and explain the underlying connections between curvedness and shape evolution and the rate of entropy production due to viscous bending and torsion rates. The membrane dissipation model used here is known as the Boussinesq-Scriven fluid model. Since the standard approaches in morphological evolution are based on the average, Gaussian and deviatoric curvatures, which comingle shape with curvedness, this paper introduces a novel decoupled approach whereby shape is independent of curvedness. In this curvedness-shape landscape, the entropy production surface under constant homogeneous normal velocity decays with growth but oscillates with shape changes. Saddles and spheres are minima while cylindrical patches are maxima. The astigmatic flow trajectorie...
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Biomimetic hierarchical surface structures that exhibit features having multiple length scales have been used in many technological and engineering applications. Their surface topographies are most commonly analyzed using scanning... more
Biomimetic hierarchical surface structures that exhibit features having multiple length scales have been used in many technological and engineering applications. Their surface topographies are most commonly analyzed using scanning electron microscopy (SEM), which only allows for qualitative visual assessments. Here we introduce fractal and lacunarity analyses as a method of characterizing the SEM images of hierarchical surface structures in a quantitative manner. Taking femtosecond laser-irradiated metals as an example, our results illustrate that, while the fractal dimension is a poor descriptor of surface complexity, lacunarity analysis can successfully quantify the spatial texture of an SEM image; this, in turn, provides a convenient means of reporting changes in surface topography with respect to changes in processing parameters. Furthermore, lacunarity plots are shown to be sensitive to the different length scales present within a hierarchical structure due to the reversal of l...
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In addition to being the largest natural source of hydrocarbons on Earth, natural gas hydrates have been extensively investigated because they are known to plug oil/gas pipelines. Experiments have been carried out to find ways of... more
In addition to being the largest natural source of hydrocarbons on Earth, natural gas hydrates have been extensively investigated because they are known to plug oil/gas pipelines. Experiments have been carried out to find ways of preventing or slowing the formation of gas hydrates. In this study, kinetics of formation of methane hydrate film were compared in deionized water and
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