Presence Of Polymer Molecules Research Articles

Effect of hydrolyzed polyacrylamide used in polymer flooding on droplet–interface electro-coalescence: Variation of critical electric field strength of partial coalescence

Polymer flooding is widely used in petroleum industry to enhance oil recovery. However, presence of polymer molecules in produced liquids can influence the droplet coalescence at oil–water interface in electric dehydration separators. In this study, the influence of hydrolyzed polyacrylamide (HPAM) on droplet–interface coalescence was examined through high-speed recording and observation. Deformation of droplets of aqueous polymer solution under electric fields was experimentally observed. The images showed droplets collapsed to filament without pinch-off due to viscoelasticity. Meanwhile, fine secondary droplets erupted from the summit of filament, which was detrimental to dehydration efficiency. A critical electric field strength (Ecrit) beyond which partial coalescence occurred was identified. The effects of the initial droplet size, HPAM concentration, electric field waveform and frequency were explored. The results showed that Ecrit increased with the decrease in initial droplet radius or the increase in HPAM concentration. Four kinds of AC or pulsatile electric fields (PEFs) were used including sinusoidal AC (sine AC), square, pulsed DC (PUDC) and pulsed AC (PUAC) waveforms. The increase in frequency suppressed the electro-induced stretching of droplets in the vertical direction, inhibiting partial coalescence. For these different electric fields, the increase in Ecrit with elevated frequencies followed different ways. Overall, Ecrit of square waveform was larger than those of other waveforms; however, Ecrit of PUAC and sine AC waveforms may exceed that of square waveform at high frequencies. These findings are useful for the development of electro-dehydration separators for oils containing dissolved polymers in the dispersed aqueous phase.

Entrapped Styrene Butadiene Polymer Chains by Sol-Gel-Derived Silica Nanoparticles with Hierarchical Raspberry Structures.

A sol-gel transformation of liquid silica precursor to solid silica particles was carried out in a one-pot synthesis way, where a solution of styrene butadiene elastomer was present. The composites, thus produced, offered remarkable improvements of mechanical and dynamic mechanical performances compared to precipitated silica. The morphological analysis reveals that the alkoxy-based silica particles resemble a raspberry structure when the synthesis of the silica was carried out in the presence of polymer molecules and represent a much more open silica-network structure. However, in the absence of the polymer, the morphology of the silica particles is found to be different. It is envisaged that the special morphology of the in situ synthesized silica particles contributes to the superior reinforcement effects, which are associated with a strong silica-rubber interaction by rubber chains trapped inside the raspberry-like silica aggregates. Therefore, the interfaces are characterized in detail by low-field solid-state 1H NMR spectroscopy, 29Si solid-state NMR spectroscopy, and energy-dispersive X-ray spectroscopy. Low-field 1H NMR-based double-quantum experiments provide a quantitative information about the cross-link density of the silica-filled rubber composites and about the influence of silane coupling agent on the chemical cross-link density of the network and correlates well with equilibrium swelling measurements. The special microstructure of the alkoxy-based silica was found to be associated with the interaction between alkoxy-based silica and rubber chains as a consequence of particle growth in the presence of rubber chains.

Structural and magnetic properties of polymer-stabilized tetragonal Ni nanoparticles

Ni nanoparticles (Ni-NPs), with diameter (D) ranging 5–30 nm, were synthesized by reducing nickel chloride with NaBH4 in the presence of polymer molecules of poly-vinyl alcohol (PVA) in cold water. Nickel chloride was dispersed in the PVA molecules which stabilized the resulting Ni-NPs. Experiments were carried out with and without PVA to elucidate the effect of PVA molecules on the structural and magnetic properties of Ni-NPs. It was found that both uncoated (uc) and PVA-coated (pc) Ni-NPs exhibit a tetragonal (t) crystal structure, i.e. different from the cubic (fcc) structure of bulk nickel. pc Ni-NPs (paramagnetic in nature) converted to fcc Ni (spherical shape, D ∼ 12 nm) on annealing at 573 K in air, exhibiting a saturation magnetization M s = 20.5 emu/g, squareness ratio M r /M s = 0.48 and coercivity H c = 248 Oe, which is higher than the bulk Ni (0.7 Oe). uc Ni-NPs showed little improvement in M s and H c on air annealing. The core–shell structure resulted in a high H c value in stable pc Ni-NPs in air. Electron magnetic resonance revealed exchange interaction between the core and shell, which changes on annealing in air.

A 29Si MAS NMR study of modified C–S–H nanostructures

Abstract The sustainability of cement-based materials is a core technical issue of national importance. The serviceability of the concrete infrastructure, especially bridges, has recently received considerable media attention. Concurrently, the nanoscience of cements has emerged as a new discipline with the potential to positively manipulate the nanostructure of calcium silicate hydrate (C–S–H) in order to achieve sustainability objectives. Organic/inorganic C–S–H nanocomposites are being developed to enhance durability and long-term engineering behavior. Results of a 29 Si MAS NMR study of phase pure C–S–H (prepared with C/S ratios 0.6–1.6) modified by interaction with hexadecyltrimethyl ammonium (HDTMA), methylene blue (MB), polyethylene glycol (PEG), polyvinylalcohol (PVA) and polyacrylic acid (PAA) are reported. It is apparent that the degree of silica polymerization is affected by the presence of the various organic molecules and the C/S ratio of the C–S–H. Possible mechanisms responsible for this effect are described. The implications of these nanostructural changes for sustainability are discussed. It is suggested that the interaction of polymers with the nanostructure of C–S–H that increases silicate polymerization may improve volume stability and promote mechanical properties of such systems. The resistance of polymer-modified C–S–H systems in chemically aggressive environments is likely to be increased as the defect sites in the silicate structure are eliminated by the presence of polymer molecules.

Micro-properties of coal aggregates: Implications on hyperbaric filtration performance for coal dewatering

The recovery of ultrafine coal can be enhanced significantly by flocculating the particles prior to dewatering. It is thus crucial to be able to quantify the effects of aggregated particles on the separation efficiency, of which they are still not fully understood. This study focused on the relationship between the micro-properties (size, structure, and strength) of flocculated coal particles and the characteristics of filter cakes obtained through hyperbaric filtration. Tools such as small angle light scattering and confocal scanning laser microscopy were used to determine the aggregate structure. The comparative bond strength of aggregates generated under different flocculation conditions was measured through a non-dimensional approach. The effects of these properties on specific cake resistance, saturation, and moisture content, as indicative of the filtration performance, were observed. It was found that flocs generated using a moderate amount of flocculant dosage (60–100 g of polymer/tonne of coal) for this ultrafine coal (97% < 35 μm) optimised the properties of dewatered filter cakes. Although cakes composed of larger and stronger aggregates with more flocculant were found to have higher porosity, the effects on specific cake resistance and cake saturation were detrimental, possibly due to the increasing proportion of intra-aggregate pores that were harder to dewater. The trend was less noticeable at low filtration pressures where most of the dewatering occurred within the larger capillaries of the inter-aggregate zones. In addition, the presence of polymer molecules was responsible in absorbing residual moisture that could not be removed through mechanical means. Through a series of tests using pre-formed filter cakes, the amount of moisture retained by the flocculant was quantified to be approximately 10.2 mg of water for every addition of 1 g of polymer/tonne of coal, calculated per 100 g of filter cake produced from hyperbaric filtration in this case.

Solubilization of Nonionic Polymers in a Lyotropic Lamellar Mesophase: Lecithin-Water-Polyethylene Oxide System

Soybean lecithin forms a homogeneous lamellar liquid crystalline phase with water at concentrations of less than 33 wt% water. The solubilization of water-soluble polyethylene oxide polymer into the lamellar phase is studied by 2 H and 31P NMR and polarizing microscopy methods. Between 20 and 33 wt% of water, the liquid crystalline phase is unable to solubilize any appreciable amounts of polymer and the mesophase is destabilized by the addition of about 0.5% of polymer, whereas the solubilization of the polymer increases drastically in the lamellar phase (e.g., 18% polymer at 10% water) with water content less than 10%. The 2H NMR quadrupole splitting values, as well as the 31P NMR chemical shift anisotropy, remain unaffected by replacement of lecithin or water with polymer. The results indicate that the binding of water to the interface and the molecular organization of the choline headgroup are little affected by the presence of polymer molecules in the mesophase.

Polymer-induced wormlike-to-spherical micelle transition in surfactant solutions

In various applications important to chemical, pharmaceutical, petroleum, and mineral processing industries, surfactant molecules are present in solution not alone but along with synthetic or biological macromolecules. The presence of polymer molecules gives rise to changes in the solution and its interfacial properties as compared to the corresponding polymer-free systems.The interaction between surfactant and polymer results in association of the two, which affect many properties of the system, especially the rheological ones. Recently, a polymer induced transition from non-Newtonian to Newtonian behavior was observed in the CTAB/NaSal system. This effect was attributed to a polymer-induced break-up of the worm-like micelles into spherical ones. This interpretation can be tested directly by microscopic observation.In this study, interactions between poly(vinylmethylether) (PVME) or poly(propyleneoxide) (PPO) (Aldrich, WI) and the nonionic surfactant pentaethylene glycol mono-dodecyl ether (C12E5) (Nikkol, Japan) or the cationic surfactant cetyltrimethylammonium bromide (CTAB) (Aldrich) with presence of sodium salicylate (NaSal) (Mallinkordt, MO) were examined by cryo-TEM and rheometry.

Rotational diffusion in solvents with large characteristic lengths

A theory, based upon mode coupling, is given for the rotational diffusion constant of a tagged particle in a solvent characterized by a large macroscopic length. The theory is used to explain rotational diffusion near a critical point or in the presence of polymer molecules.

A study of solvent motion in acetone-PMMA solutions using 13C and 1H spin-lattice relaxation measurements

The 13C and 1H spin-lattice relaxation times of acetone in solutions containing from 0 to 20% poly(methyl methacrylate) have been measured from −55°C to 120°C. The 13C measurements show that except at low temperature and the higher polymer concentrations, solvent rotation is little affected by the presence of polymer molecules. By assuming that the 13C relaxation time is entirely intramolecular in origin, and by progressive deuteration of the acetone, the 1H relaxation time has been separated into intramolecular, acetone-acetone intermolecular and acetone-polymer intramolecular contributions. These results show that up to 10% of polymer or so does not affect solvent diffusion, but for 20% polymer, solvent diffusion is perceptibly slowed down, and the activation energy increased by 50%. The data give no indication of polymer conformational transitions in this temperature range, as suggested by others elsewhere, but this may be because of the very short-range sensitivity of n.m.r. measurements.