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ABSTRACT: This paper describes the influence of interactions of poly(ethylene oxide) (PEO) with cationic cetyltrimethylammonium bromide (CTAB) micelles on drag reduction. Since the interactions between PEO and CTAB micelles alone are weak, salicylate ions were used as CTAB counterions. They facilitate formation of polymer-micelle aggregates by screening the electrostatic repulsions between the charged surfactant headgroups. The influence of polymer-surfactant interactions on drag reduction is of biomedical engineering importance. Drag reducing additives introduced to blood produce beneficial effects on blood circulation, representing a novel way to treat cardiovascular disorders. PEO is a blood-compatible polymer. However, it quickly mechanically degrades when subjected to high shear stresses. Thus, there is a need to search for other additives able to reduce drag, which would be more mechanically stable, e.g. polymer-surfactant aggregates. Numerical simulations of the flow were performed using the CFX software. Based on the internal structure of the polymer-surfactant solution, a hypothesis explaining the reason of increase of drag reduction and decrease in dynamic viscosity with increasing shear rate was proposed. It was suggested that the probable reason for the abrupt increase in friction factor, observed when the critical Reynolds number was exceeded, was the disappearance of the difference in the dynamic viscosity.
Bioelectrochemistry (Amsterdam, Netherlands) 02/2012; 87:42-9. · 2.65 Impact Factor
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ABSTRACT: In this study, the effect of prazosin on the molecular interactions between cholesterol and 1,2-dipalmitoylphosphatidylcholine (DPPC) within a monolayer at an air-water interface was studied. A mixed cholesterol/DPPC monolayer was employed as a model lipid membrane. From a detailed analysis of surface pressure-area isotherms, it was concluded that DPPC and cholesterol were miscible and formed non-ideal monolayers on prazosin solution. The thermodynamic stability of the mixed monolayers was investigated by analyzing the free energy of mixing. It was found that the mixed monolayers were more stable than the single component monolayers. Monolayers spread over a subphase with prazosin were more compressible than those spread on pure water. To quantify the effect of prazosin on the monolayer stability, the Gibbs free energy due to the presence of prazosin in the water subphase was calculated. It was found that prazosin penetrated and destabilized mixed cholesterol/DPPC monolayers. However, a comparison of the drug penetration into the pure DPPC monolayer and the mixed cholesterol/DPPC monolayer showed that the presence of cholesterol in the DPPC monolayer considerably restricted the drug penetration.
Bioelectrochemistry (Amsterdam, Netherlands) 12/2011; 87:96-103. · 2.65 Impact Factor
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ABSTRACT: When a water-soluble polymer and surfactant with addition of salt are mixed in water solution, the specific structures (aggregates) are formed, in which polymer film is formed around micelle. In a pipe flow, such aggregates take preferred orientation, according to minimum resistance principle. When the Reynolds number increases, the aggregates elongate.In this work, poly(ethylene oxide) (PEO)–cetyl trimethyl ammonium bromide (CTAB) complex formation and its effect on drag reduction was studied. It was found that PEO–CTAB aggregates reduced drag much more efficiently than these substances alone. Structure degradation appeared later and the drag reduction existed longer. Moreover, damaged structure could be partly rebuilt.
Thin Solid Films 516(24):8848-8851. · 1.89 Impact Factor
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ABSTRACT: The behaviour of dipalmitoyl phosphatidylcholine (DPPC)/cholesterol monolayers on pure water and on water with phenytoin was studied by performing Langmuir monolayer technique experiments. Surface pressure–area isotherms were measured for pure DPPC, cholesterol films and their mixtures. The changes of the limiting molecular area, collapse pressure and maximum compressional modulus show that phenytoin can modify the structure of lipid aggregates. The introduction of phenytoin to the subphase reduces the deviations of mean molecular areas from additivity rule observed for mixed DPPC/cholesterol monolayers. Thermodynamic stability of the mixed monolayers, as compared to that of pure monolayers, was determined by analysis of the excess Gibbs free energy of mixing. Results indicate an increase of thermodynamic stability with increasing surface pressure and decrease of thermodynamic stability in the presence of phenytoin in the system. The existence of a minimum indicates that the mixed monolayers are thermodynamically more stable than the monolayers with separation between individual components, especially around xDPPC = 0.6, on both subphases.
Colloids and Surfaces A: Physicochemical and Engineering Aspects.
