Saturation of the interface

Addition of poly(styrene-block-butadiene) block copolymer to the polystyrene-polybutadiene-styrene ternary system first showed a characteristic decrease in interfacial tension followed by a leveling off. The leveling off is indicative of saturation of the interface by the solubilizing agent. 

Equation (5.46) shows a further difference relative to Eq. (5.34). Equation (5.46) indicates a zero reaction order relative to [BH] in the forward extraction rate, reflecting the complete saturation of the interface with the extracting reagent. 

As far as water/toluene interfacial tension is measured, it appears that the saturation of the interface is reached more quickly with PTBS (P0)2 star-shaped block copolymers (Table VII) this molecular architecture seems to be more efficient to fill in the interface (3 0 ... 

This indicates that saturation of the interface occurs just below the one. Above the break point (C > cmc), the slope is zero. 

Teyssie and coworkers have studied the surface, interfacial, and emulsifying properties of AB2 stars where A is a polydiene or polyvinyl block and B polyethylene oxide)(PEO) [297,298]. The miktoarm stars were shown to be better emulsifying agents for water-organic solvent mixtures than linear block copolymers. Saturation of the interface is reached more quickly with the miktoarm stars. Their results are in agreement with the results of Xie and Xia on PS2PE02 stars [228]. 

SSHG measurements have also been performed at ion-selective membrane electrodes (ISE) in presence of the cations Li", and Na dissolved in the aqueous phase and several ionophores like dibenzo-24-crown-8 in a poly(vinyl chloride) (PVC) membrane [49]. In these experiments, the nonlinear optical signal has been observed as a function of the analyte concentration in the aqueous phase and has been ascribed to the oriented cation-ionophore complexes at the aqueous phase/liquid membrane. Langmuir isotherms were built from the data and the results suggested that a saturation of the interface was achieved at high analyte concentration. 

If the derivative, dy/d log c, is identified with the maximum slopes of the plots in Figure 1, then the surface excess T may to a good approximation be identified with the surface concentration of adsorbed solute at saturation of the interface. The slope is found to be 7.3 dynes/cm., from which T is calculated to be 3.05 x 10 moles/cm ... 

The data in Figure 9.27 show an obvious correlation between the structure of the double layer and kinetics of Sn(II) reduction both ig and C j vary in the same manner. The decrease in C j with time seems to arise from the progressive saturation of the interface with an adsorbed TEG, causing an increasing inhibition of tin reduction. This manifests itself in the respective lowering of the exchange current density. A more than 10-fold decrease in ig is observed after 2 h, as compared with the surfactant-free solution. 

There is a large reduction in the mean size of the domains. The corresponding large increase in interfacial area becomes possible because of the reduction in interfacial tension at the domain boundaries. In this respect the compatibilizers act in an analogous way to emulsifiers in oil/water systems. Indeed, the reduction in domain size levels off with increasing additive concentration, possibly indicating saturation of the interface. 

In the intermediate stage of the reaction or t < t < t the time at which saturation of the interface by copolymer remains negligible, but the interfacial concentrations of A and B reactive chains, pAi(t) and PBj(t), are reduced below their bulk concentrations, PAi(t) = pBi(t) = Po( Ap) - I other words, within this time interval, there is a depletion hole of reactive chains with spatial extension (DcomO - The reaction rate is dominated by the flux of reactive chains to the interface and is independent of the reaction kinetics, kinto- The copol5nner coverage grows as the square root of time... 

In the late stage of the reaction corresponding to t > t< the copolymer coverage has reached the point, S, that saturation of the interface by the copolymer layer presents a significant chemical potential barrier to the reactive chains. T e reaction rate is then reduced drastically in an exponential manner, i.e.,... 

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