Interfacial tension, reduction

The theory of Leibler holds for mainly compatible systems. Leibler developed a mean field formalism to study the interfacial properties of two polymers, A and B with an A-B copolymer. An expression for interfacial tension reduction was developed by Noolandi and Hong [ 18] based on thermodynamics to explain the emulsifying effect of the A-b-B in immiscible A-B blends (A-A-b-B-B). [18,19]. The expression for interfacial tension reduction Ar) in a binary lend upon the addition of divalent copolymer is given by ... 

According to this theory, the interfacial tension reduction should decrease linearly with copolymer content at low concentrations followed by a leveling off at higher concentrations. The theory of Noolandi and Hong [18]... 

ATBN - amine terminated nitrile rubber X - Flory Huggins interaction parameter CPE - carboxylated polyethylene d - width at half height of the copolymer profile given by Kuhn statistical segment length DMAE - dimethyl amino ethanol r - interfacial tension reduction d - particle size reduction DSC - differential scanning calorimetry EMA - ethylene methyl acrylate copolymer ENR - epoxidized natural rubber EOR - ethylene olefin rubber EPDM - ethylene propylene diene monomer EPM - ethylene propylene monomer rubber EPR - ethylene propylene rubber EPR-g-SA - succinic anhydride grafted ethylene propylene rubber... 

TABLE 19 Efficiencies and Effectiveness of Water-Air Interfacial Tension Reduction of Alcohol and Alcohol Ether Sulfates... 

This chapter describes recent work in our laboratories examining density modification of DNAPLs through a combination of batch non-equilibrium rate measurements and DNAPL displacement experiments in 2D aquifer cells. The objective of this work was to evaluate the applicability of nonionic surfactants as a delivery mechanism for introducing hydrophobic alcohols to convert the DNAPL to an LNAPL prior to mobilizing the NAPL. Three different nonionic surfactants were examined in combination with n-butanol and a range of DNAPLs. Overall, it was found that different surfactants can produce dramatically different rates of alcohol partitioning and density modification. However, for some systems interfacial tension reduction was found to be a problem, leading to unwanted downward... 

The work presented here illustrates that surfactant selection can have a substantial impact on the rates of alcohol partitioning and associated reduction of DNAPL density. More work is needed to develop surfactant/alcohol systems which can minimize interfacial tension reduction while still providing acceptable density conversion rates. Because the potential benefits of in situ density modification are substantial, future work will be directed at system design to minimize interfacial tension reduction. 

The emulsifying properties of these polymeric surfactants demonstrate that the chemical structure influences the kinetic behaviour of interfacial tension reduction. An increase of sulfopropyl moieties reduces the interfacial tension slower while an increase in 2-hydroxy-3-phenoxy propyl moieties reduces the interfacial tension faster. The ionic strength of the emulsion appears to increase the rate of tension reduction. The average droplet size of oil-in-water emulsions in presence of previously dissolved 2-hydroxy-3-phenoxy propyl sulfopropyl dextran is around 180 nm immediately after preparation and increases with time. The presence of ionic moieties appeared to facilitate emulsification at low polymer concentrations due to electrostatic repulsions between the oil droplets [229]. 

Surfactants fulfil many functions, such as detergency, micelle stabilization, interfacial tension reduction, wetting, and so on. In hydrocarbons, however, surfactants are not capable of lowering the surface tension, because these solvents... 

W. Hu, J. T. Koberstein, J. P. Lingelser, and Y. Gallot, Interfacial Tension Reduction in Polystyrene/Poly(dimethylsiloxane) Blends by the Addition of Poly(styrene-b-dimethylsilox-ane), Macromolecules, 28, 5209-5214 (1995). 

HuW et al. (1995) Interfacial tension reduction in polystyrene/poly(dimethyl-siloxane) blends by the addition of poly(styrene-b-dimethylsiloxane). Macromolecules 28(15) 5209—5214... 

We can see from this simple model why a necessary but not sufficient condition for surface or interfacial tension reduction is the presence in the surfactant molecule of both lyophobic and lyophilic portions. The lyophobic portion has two functions (1) to produce spontaneous adsorption of the surfactant molecule at the interface... 

Since surface or interfacial tension reduction depends on the replacement of solvent molecules at the interface by surfactant molecules, the efficiency of a surfactant in reducing surface tension should reflect the concentration of the surfactant at the interface relative to that in the bulk liquid phase. A suitable measure for the efficiency with which a surfactant performs this function would therefore be the ratio of the concentration of surfactant at the surface to that in the bulk liquid phase at equilibrium, both concentrations being expressed in the same units, e.g., [Cj]/Ci, where both concentrations are in moles/liter. 

The reduction of the tension at an interface by a surfactant in aqueous solution when a second liquid phase is present may be considerably more complex than when that second phase is absent, i.e., when the interface is a surface. If the second liquid phase is a nonpolar one in which the surfactant has almost no solubility, then adsorption of the surfactant at the aqueous solution-nonpolar liquid interface closely resembles that at the aqueous solution-air interface and those factors that determine the efficiency and effectiveness of surface tension reduction affect interfacial tension reduction in a similar manner (Chapter 2, Section IIIC,E). When the nonpolar liquid phase is a saturated hydrocarbon, both the efficiency and effectiveness of interfacial tension reduction by the surfactant at the aqueous solution-hydrocarbon interface are greater than at the aqueous solution-air interface, as measured by pC2o and IIcmc, respectively. The replacement of air as the second phase by a saturated hydrocarbon increases the tendency of the surfactant to adsorb at the interface, while the tendency to form micelles is not affected significantly. This results in an increase in the CMC/C2o ratio. Since the value of rm, the effectiveness of adsorption (Chapter 2, Section IIIC), is not affected significantly by the presence of the saturated hydrocarbon, the increase in the... 

Integrating the area under the plot of adsorption, rS versus In C (or log C) (Figure 11-2) below the CMCs of the respective solutions, yields the value of IIs , the amount of solid-aqueous solution interfacial tension reduction. This is plotted (Figure 11-3) against In (or log) C and values of Cj, Cf, and C 2 selected, at the largest common value of 1 ISv, for substitution into equations 11.1 and 11.2 to evaluate ( (). 1Isv can also be evaluated (Zhu, 1991) directly from adsorption isotherm data by use of equations... 

III.A. Synergism or Antagonism (Negative Synergism) in Surface or Interfacial Tension Reduction Efficiency... 

Analogous expressions have been derived for the existence of synergism in interfacial tension reduction efficiency at the liquid-liquid interface (Rosen, 1986)... 

At the point of maximum synergism or maximum antagonism in surface or interfacial tension reduction effectiveness, the composition of the mixed interfacial layer equals the composition of the mixed micelle, i.e., X E = the mole... 

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