Interfacial tension concentration effects

PA-12 or PA-1212 or PA-612 or PA-610 or PA-69 or PA-46 /SEES (0-20) / SEBS-g-MA (1.8% MA) (0-20) properties / TEM / ductile-brittle transition temperatures / interfacial tension estimates / effects of PA amine end-group concentration on copolymer formation (titration before and after extrusion) / torque rheometry ... 

The measurement of interfacial tension revealed that it was markedly decreased by all the three Eucarol emulsifiers. The boundary tension was lower than 10 mN m even with 0.1%. The boundary-tension-decreasing effect of the three surfactants did not show a significant difference. When the interfacial tension concentration functions were plotted separately in a semilogarithmic coordinate system, a linear relationship was found between the logarithm of concentration and interfacial tension in the case of Eucarols in the concentration range of 0.00001 and 0.1. 

In the presence of liquid flow, the situation becomes more complicated due to the creation of a surface concentration gradients [20]. These gradients, described by the Gibbs dilational elasticity [5], initiate a flow of mass along the interface in the direction of the higher surface or interfacial tension (Marangoni effect). This situation can happen, for example, if an adsorption layer is compressed or stretched (Figure 11.18). 

Mass transfer to and from drops affects coalescence. Mass transfer creates concentration gradients in the region of the thinning film. Depending on the interfacial tension-concentration characteristics of the system, this can lead to Marangoni effects, causing surface flows and internal circulation within the drops. Such movement accelerates film drainage and increases the probability of coalescence. 

Surface Tension. Interfacial surface tension between fluid and filter media is considered to play a role in the adhesion of blood cells to synthetic fibers. Interfacial tension is a result of the interaction between the surface tension of the fluid and the filter media. Direct experimental evidence has shown that varying this interfacial tension influences the adhesion of blood cells to biomaterials. The viscosity of the blood product is important in the shear forces of the fluid to the attached cells viscosity of a red cell concentrate is at least 500 times that of a platelet concentrate. This has a considerable effect on the shear and flow rates through the filter. The surface stickiness plays a role in the critical shear force for detachment of adhered blood cells. 

Larch gum is readily soluble in water. The viscosity of these solutions is lower than that of most other natural gums and solutions of over 40% soHds are easily prepared. These highly concentrated solutions are also unusual because of their Newtonian flow properties. Larch gum reduces the surface tension of water solutions and the interfacial tension existing in water and oil mixtures, and thus is an effective emulsifying agent. As a result of these properties, larch gum has been used in foods and can serve as a gum arabic substitute. 

In the 1990s, the thmst of surfactant flooding work has been to develop surfactants which provide low interfacial tensions in saline media, particularly seawater require less cosurfactant are effective at low concentrations and exhibit lower adsorption on rock. Nonionic surfactants such as alcohol ethoxylates, alkylphenol ethoxylates (215) and propoxylates (216), and alcohol propoxylates (216) have been evaluated for this appHcation. More recently, anionic surfactants have been used (216—230). 

FIG. 16 Effect of LAS/AES ratio on dishwashing foam stability and interfacial tension. Conditions 46°C, 0.05% concentration, 50 ppm hardness, Keen soil. (From Ref. 33.)... 

The log of the reciprocal of the bulk concentration of surfactant (C in mol/ L) necessary to produce a surface or interfacial pressure of 20 raN/m, log( 1 / On= 20 i e > a 20 mN/m reduction in the surface or interfacial tension, is considered a measure of the efficiency of a surfactant. The effectiveness of surface tension reduction is the maximum effect the surfactant can produce irrespective of concentration, (rccmc = [y]0 - y), where [y]0 is the surface tension of the pure solvent and y is the surface tension of the surfactant solution at its cmc. 

Decreasing the pH of 3% NaCl (entries 2 and 3, Table 14) could decrease neutralization of crude oil organic acids. This neutralization increases both aqueous phase salinity and effective surfactant concentration. A lower effective surfactant concentration at pH 8 could account for the increased interfacial tension value. However, a similar pH change does not reduce IFT when the surfactant is AOS 1618 with a much lower di monosulfonate ratio (entries 6 and 7, Table 14). 

The electrolyte concentration also has an effect on the co-areas. An increase in the ionic strength from 0.01 to 0.04 M causes a considerable decrease in the interfacial tension [56]. 

For long-chain alcohol esters it is interesting to see that the interfacial tension between a 0.01 wt % aqueous solution and octane or xylene has a minimum for ester sulfonates with a total 22 carbon atoms in the fatty acid chain and the ester chain [60]. The balance in length between the two chains has only a poor effect. Thus, a-sulfonated fatty acid esters with a total number of 22-26 carbon atoms in the molecule have excellent interfacial activities. To attain the same magnitude in the interfacial tension between linear alkylbenzenesulfonate (LAS) solution and octane, the required concentration of LAS is 0.1 wt %. This is 10 times the concentration needed for a-sulfonated fatty acid esters [60]. 

The effect, which arises in cases where the interfacial tension is strongly dependent on the concentration of diffusing solute, will generally be dependent on the direction (sense) in which mass transfer is taking place. 

Eq. (132) states that the interfacial tension has to be balanced by a pressure difference between the two phases. The terms containing derivatives of crin Eqs. (133) and (134) are non-zero only if there are local variations of the interfacial tension, which might be due to differences in concentration or temperature. The flow induced by such an effect is known as Marangoni convection. 

Acid flooding can be successful in formations that are dissolvable in the particular acid mixture, thus opening the pores. Hydrochloric acid is common, in a concentration of 6% to 30%, sometimes also with hydrofluoric acid and surfactants added (e.g., isononylphenol) [130,723]. The acidic environment has still another effect on surfactants. It converts the sulfonates into sulfonic acid, which has a lower interfacial tension with oil. Therefore a higher oil forcing-out efficiency than from neutral aqueous solution of sulfonates is obtained. Cyclic injection can be applied [4,494], and sulfuric acid has been described for acid treatment [25,26,1535]. Injecting additional aqueous lignosulfonate increases the efficiency of a sulfuric acid treatment [1798]. 

Modem oil spill-dispersant formulations are concentrated blends of surface-active agents (surfactants) in a solvent carrier system. Surfactants are effective for lowering the interfacial tension of the oil slick and promoting and stabilizing oil-in-water dispersions. The solvent system has two key functions (1) to reduce the viscosity of the surfactant blend to allow efficient dispersant application and (2) to promote mixing and diffusion of the surfactant blend into the oil film [601]. 

Oil/water interfacial tensions were measured for a number of heavy crude oils at temperatures up to 200°C using the spinning drop technique. The influences of spinning rate, surfactant type and concentration, NaCI and CaCI2 concentrations, and temperature were studied. The heavy oil type and pH (in the presence of surfactant) had little effect on interfacial tensions. Instead, interfacial tensions depended strongly on the surfactant type, temperature, and NaCI and CaCL concentrations. Low interfacial tensions (<0.1 mN/m) were difficult to achieve at elevated temperatures. 

Effect of NaCI Concentration. The presence of surfactant in brine can have a dramatic effect on crude oil-aqueous surfactant tensions even at elevated temperatures r5,211. Figure 5 shows that the effect of sodium chloride concentration on Athabasca bitumen-D20 interfacial tensions measured at constant surfactant... 

In n-octane/aqueous systems at 27°C, TRS 10-80 has been shown to form a surfactant-rich third phase, or a thin film of liquid crystals (see Figure 1), with a sharp interfacial tension minimum of about 5x10 mN/m at 15 g/L NaCI concentration f131. Similarly, in this study the bitumen/aqueous tension behavior of TRS 10-80 and Sun Tech IV appeared not to be related to monolayer coverage at the interface (as in the case of Enordet C16 18) but rather was indicative of a surfactant-rich third phase between oil and water. The higher values for minimum interfacial tension observed for a heavy oil compared to a pure n-alkane were probably due to natural surfactants in the crude oil which somewhat hindered the formation of the surfactant-rich phase. This hypothesis needs to be tested, but the effect is not unlike that of the addition of SDS (which does not form liquid crystals) in partially solubilizing the third phase formed by TRS 10-80 or Aerosol OT at the alkane/brine interface Til.121. 

Figure 5 Effect of NaCI concentration on the Athabasca bitumen/DJ) interfacial tension for Enordet C18 18, Sun Tech IV and TRS 10-80. Closed triangle represents the data measured for Enordet C16 18 at concentrations up to 160 g/L NaCI.

Figure 8 shows the effect of Ca 2 on the interfacial tensions of two oils (Karamay and Clearwater) in Sun Tech IV (5 g/L) and NaCI (10 g/L) solutions at 150°C. The interfacial tension values for the two oils were very similar with as much as an 8-fold reduction, depending on concentration. Interfacial tension minima in the range of 0.06 to 0.1 mN/m were observed at 0.05 and 0.5 g/L CaCI2 for both oils. 

The interfacial tension-temperature relationships at various CaCL concentrations for Karamay crude in a Sun Tech IV (5 g/L) and NaCI (10 g/L) solution are shown in Figure 9. For 0, 0.025 and 0.1 g/L Ca, an increase in interfacial tension with temperature was observed. The interfacial tension values above 150°C were about the same for these concentrations. At temperatures below 100°C, the effect of Ca was to increase interfacial tension, probably by hindering the formation of a surfactant-rich phase. This is consistent with the detrimental effect or light oil/brine interfacial tensions (increase from about 10 3 to about 10 1) reported by Kumar et al. T371. ... 

Figure 8 Effect of CaCI2 concentration on the interfacial tension of oil/D20 systems containing Sun Tech IV and NaCI for Karamay and Clearwater crudes at 150°C.

Bansal, V.K. Chan, K.S. McCallough, R. Shah, D.O. The Effect of Caustic Concentration on Interfacial Charge, Interfacial Tension and Droplet Size A Simple Test for Optimum Caustic Concentration for Crude Oils, J. Canadian Petrol. Tech. 1978,17(1), 69. 

The rheological properties of a fluid interface may be characterized by four parameters surface shear viscosity and elasticity, and surface dilational viscosity and elasticity. When polymer monolayers are present at such interfaces, viscoelastic behavior has been observed (1,2), but theoretical progress has been slow. The adsorption of amphiphilic polymers at the interface in liquid emulsions stabilizes the particles mainly through osmotic pressure developed upon close approach. This has become known as steric stabilization (3,4.5). In this paper, the dynamic behavior of amphiphilic, hydrophobically modified hydroxyethyl celluloses (HM-HEC), was studied. In previous studies HM-HEC s were found to greatly reduce liquid/liquid interfacial tensions even at very low polymer concentrations, and were extremely effective emulsifiers for organic liquids in water (6). 

In precipitation studies (4 7, 4 ) it has been shown that, below a certain Mg/Ca concentration ratio in the aqueous solution, the rate of nucleation of calcite was faster than that of aragonite. Above that Mg/Ca ratio the order was reversed. This was explained by the effect of Mg2+ ions on the interfacial tension between the solution and precipitate, which apparently is larger for calcite than for aragonite (49). At still higher Mg/Ca ratios dolomite can be formed (50). Such low temperature precipitates of dolomite contain ordering defects. The number of defects increases when precipitation proceeds in a shorter time interval or at lower temperatures C51 ). 

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