The formulation of econazole nitrate liposomes was optimized by orthogonal design. The shape, size,viscosity and z potential of the liposomes were examined. The results showed that the prepared liposomes were spherical,Z-average diameter 118.1nm, and z potential +65.3mV. The viscosity of the liposomes solution and gel were 0.0033 and7.9166 Pa·s[(32±1)℃], respectively. There were no drug crystal adsorbed on liposomes surface.
Based on special antipolyelectrolyte effect of zwitterion polymer with same quantity of anionic and cationic charges, we developed two types of salt-responsive polyampholytes, one with high molecular weight and low charge density (HvL) and the other with low molecular weight and high charge density (LvH), by inverse emulsion polymerization. Molecular structure and salt-responsiveness of them were characterized by 1H-NMR and rheology measurement, respectively. HvL and LvH were evaluated in saturated-salt bentonite suspension and influences of their ratio on apparent viscosity and fluid loss were investigated as well. The results indicate that HvL is better at decreasing fluid loss while LvH is better at maintaining low viscosity. A saturated saltwater drilling fluid centering on HvL and LvH with simple formula was designed and applied. It is indicated that salt-responsive polyampholytes are fundamentally better than AM-AMPS anionic copolymer and AM-AMPS-DMDAAC amphoteric copolymer. The saturated saltwater drilling fluid has excellent thermal stability, tolerance to bentonite and shale cuttings, and certain resistance to CaCl2. Salt-responsive polyampholytes can be used in KCl-saturated drilling fluid, with universal adaptability.
The interfacial accumulation of PGS makes interfacial film gel-like and droplets attractive, resulting in mechano-responsive rheology modification for inverted emulsions.
The solubility parameter characterizes solubility in terms of simple numbers representing cohesive energy contribution within the molecular system and thus is considered a powerful approach for understanding highly complex systems such as asphaltenes. To obtain solubility parameters, compared with the traditional experimental method, molecular dynamics (MD) simulation provides an efficient approach and gives an explanation at the molecular level. In this study, we calculated the solubility parameters of asphaltenes using MD simulations with the digital oil model that we developed for a domestic oilfield. We have also computed the solubility parameters for more than 20 different solvents, including mixtures, to gain confidence. A new method to calculate asphaltene Hansen solubility parameters (HSPs) in solvents was proposed and implemented. This method uses a small solvent molecule as a probe. It considers different aggregation states and the potential to form hydrogen bonds in solvents, which successfully separate polar and hydrogen bonding contributions from the total cohesive energy. Six types of solvents, including heptane, toluene, isopropyl alcohol (IPA), pyridine, o-xylene, and toluene–IPA mixtures, were employed. For the toluene–IPA mixtures, different concentrations were considered. Utilizing the obtained asphaltene solubility parameters, we drew Hansen solubility sphere diagrams and estimated the solubility of asphaltenes in a solvent using the Flory–Huggins thermodynamic model, which gives results in line with expectations. Furthermore, an optimal toluene–IPA mixing solvent concentration ratio was found for asphaltenes of our target oilfield. This was achieved by tuning the polar and hydrogen bonding interaction contributions in the mixtures. Further onward, using the same method to calculate the solubility parameters for predicting asphaltene deposition risk during production, such as CO2-EOR, will be possible.
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