Interfadal tension

Reduction in interfadal tension of a homopolymer Mend by addition of block copolymer... 

When surfactants concentrate in an adsorbed monolayer at a surface the interfacial film may provide a stabilizing influence in thin films and foams since they can both lower interfadal tension and increase the interfacial viscosity. The latter provides a mechanical resistance to film thinning and rupture. 

Enzymes can be liberated from enteric-coated formulations by the neutral to slightly alkaline pH caused by secretions front die pancreas, the gall bladder, and the intestinal mucosa. They have a hydrogen carbonate concentration of about SS mM, which causes an increase in pH. Bile salts decrease the interfadal tension, promoting the liberation of drugs from solid dosage forms. 

Fig. 1. Qualitative representation of the interfadal tension at a planar oil-water interface against HLB...

The Stability of the Spherical Shape When a Hicroemu1 si on Coexists with an Excess Dispersed Phase When an excess dispersed phase coexists with a microemulsion, P2 - p = 0. However, p2 - pi is always positive. To prove this, it is convenient to use the interfadal tension y defined via Eq. (17). Using expressions (21) for tf and the corresponding expressions for C provided by Eqs. 27, one obtains, in the same order ... 

The first attempts of Bidlingmeyer and co-workers [15,16] to formulate an ion interaction model quantitatively [21-23] did not provide a rigorous description of the system. Stranahan and Deming [22] accounted for electrostatic effects via a simplified activity coefficient in the stationary phase. An interfadal tension decrease with increasing IPR concentration was considered responsible for the appearance of maxima in the plot of retention factor, k versus IPR concentration, but experimental results were at odds with known surfactant chemistry. 

The structure of the liquid- liquid interfadal layer depends on the difference in polarity between the two liquids (Kaeble, 1971). Asymmetric molecules of some liquids display a molecular orientation on the interface which is indicative of their structure. Thus, interfacial tension at the octane-water interlace is SO.S nm/m whereas at the octanol-water interne it is only 8.8 nm/m. Reduction of inter dal tension in the latter case points to the orientation of octanol hydroxyl groups toward water, in other words to the structure and polarity of the interfadal layer. Because of such an orientation, the stimulus for adsorption of other asymmetric molecules on the interface is decreased. A similar pattern is typical of the homologous series of lower attcy] acrylates at the interface with water the carbonyl groups of their asymmetrical molecules are oriented toward water this orientation is more eSective the higher the polarization of the carbonyl, i.e the smaller the alkyl. Interfadal tension decreases in the same order from 27.2 nm/m for hexyl acrylate (Yeliseyeva et at, 1978) to 8 nm/m for methyl acrylate (datum from our laboratory by A, Vasilenko). 

Interfadal tension, however, cannot serve as the only criterion of adsorption. Typical sui ctants with asymmetric molecules or ions consisting of a polar group and a sufficiently long hydrocarbon chain are always active at water-hydrocarbon interfaces. The greater the difference in polarity between bounda ry phases the steeper the orientation of surfactant molecule at the interface and the larger the reduction in free energy of the system due to adsorption. 

Flooding, holdup, and mass transfer rates are highly interdependent and are not simply related. Reissinger and Schrflter (1978) state that tray towers in comparison with other types have good efficiencies at 60 m /m hr at frequencies of 60-90/min and amplitudes of 10 mm. Packed towers have about 2/3 the capacities of tray towers. Also in comparison with unagitated towers, which are limited to interfacial tensions below lOdyn/cm, pulsed towers are not limited by interfadal tension up to 30-40 dyn/cm. Some... 

The polymer-phase system composed of PEG and potassium phosphate has a relatively large difference in density between the two phases, so that it can be retained well in both XL and XLL column positions which provide efficient mixing of the two phases. On the other hand, the viscous PEG-dextran system, with an extremely low interfadal tension and a small density difference between the two phases, has a high tendency of emulsification under vigorous mixing. Therefore, the use of either the XLLL or L column position, which produces less violent mixing and an enhanced lateral force field, is required to achieve satisfactory phase retention of the PEG-dextran system. 

Packed towers may be employed when 5-10 stages suffice. They are not satisfactory at interfadal tensions above lOdyn/cm. Even at this condition, sieve trays have greater efficiency, and at much higher interfacial tensions some form of agitated tower is required. 

Chen, T.-R, Pu, C.-S., 2006. Study on ultralow interfadal tension chemical flooding in low permeability reservoirs. Journal of Xi an Shiyou University 21 (3), 30-33. 

Figure 5.2 Variation of surface and interfadal tension with log (C ) at the air/water and oil/water interface.

In addition to the Gibbs equation, three other equations have been suggested that relate the surface excess Tj, surface or interfadal tension and equilibrium concentration in the liquid phase C . The Langmuir equation [3] relates Tj to Cj... 

For a stable interface y is positive that is, if the interfadal area increases G increases. Note that y is energy per unit area (mj m ), which is dimensionally equivalent to force per unit length (mN m ), the unit usually used to define surface or interfadal tension. 

Single surfactants lower the interfadal tension y, but in most cases the critical micelle concentration (cmc) is reached before y is close to zero. The addition of a second surfactant of a completely different nature (i.e., predominantly oil-soluble, such as an alcohol) then lowers y further and very small, even transiently negative, values may be reached [9]. This is illustrated in Figure 15.7, which shows the effect of addition of the cosurfactant on the y-log curve. It can be seen that addition of cosurfaclant shifts the whole curve to low y-values, while the cmc is shifted to lower values. 

Shinoda and coworkers [20] found that many O/W emulsions (based on ethoxylated surfactants) undergo a process of inversion to W/O at a critical temperature (PIT). The PIT can be easily measured by following the conductivity of the emulsion as a function of temperature (a small amount of electrolyte, e.g., NaCl is added to increase the sensitivity of measurement). The conductivity of the O/W emulsion increases with increase of temperature until the PIT is reached, above which there is a rapid reduction in conductivity (a W/O emulsion is formed with low conductivity as the continuous phase is now oil). Figure 15.12 shows a schematic representation of the variation of conductivity with temperature increase for an O/W emulsion. At the PIT, the interfadal tension y reaches a minimum, as illustrated in Figure 15.13 for an O/W emulsion. 

The contact angle 6 depends on the balance between the sohd/vapour (ygy) and solid/liquid (yg ) interfadal tensions. The angle which a drop assumes on a solid surface is the result of the balance between the adhesion force between solid and liquid and the cohesive force in the liquid,... 

Glucopon. [Henkel/Emery] Alkyl polyglycoside surfactant detergent wetting agent surface/interfadal tension reducer, persant for laundry detergents, liq. cleaners, hard surface cleaners, institutional and industrial cleaners. 

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