Effect of surface activity

As mentioned in Section IX-2A, binary systems are more complicated since the composition of the nuclei differ from that of the bulk. In the case of sulfuric acid and water vapor mixtures only some 10 ° molecules of sulfuric acid are needed for water oplet nucleation that may occur at less than 100% relative humidity [38]. A rather different effect is that of passivation of water nuclei by long-chain alcohols [66] (which would inhibit condensation note Section IV-6). A recent theoretical treatment by Bar-Ziv and Safran [67] of the effect of surface active monolayers, such as alcohols, on surface nucleation of ice shows the link between the inhibition of subcooling (enhanced nucleation) and the strength of the interaction between the monolayer and water. 

See also Sections IJIA and 11IB for the effect of surface-active agents on bubble velocity. 

III. Effect of Surface-Active Agents A. Experimental Studies... 

Effect of surface activity 4.1 Tests for bacteriostatic activity... 

O. B. Kutergin, V. P. Melnikov, and A. N. Nesterov. Effect of surface-active agents on the mechanism and kinetics of hydrate formation of gases. Dokl Akad Nauk Sssr, 323(3) 549-553, 1992. 

Ledwidge, M. T. Corrigan, O. I., Effects of surface active characteristics and solid state forms on the pH solubility profiles of drug-salt systems, Int. J. Pharm. 174, 187-200 (1998). 

M Gibaldi, S Feldman, ND Weiner. Hydrodynamics and diffusional considerations in assessing the effects of surface active agents on the dissolution rate of drugs. Chem Pharm Bull 18 715-723, 1970. 

Grieser F, Ashokkumar M (2001) The effect of surface active solutes on bubbles exposed to ultrasound. Adv Colloid Interface Sci 89-90 423 138... 

M. Gibaldi, S. Feldman, N. D. Weiner. Hydrodynamic and diffu-sional considerations in assessing effects of surface active agents on the... 

Polystyrene latices used as an adsorbent were prepared by the Kotera-Furusawa-Takeda method(8 to reduce the spurious effects of surface active substances. The average diameter(D) and the surface gharge density(ao) of the latex particles were determined D=2000 A and 0O = 1.5 uC/cm. A silica sample was prepared by the method described by Stttber et al.(9), and was composed of highly mono-disperse spherical particles of 1900 X in diameter. These colloids were used after dialyzing exhaustively against distilled water to remove the ionic impurities. 

Bertole, C. J., Kiss, G., and Mims, C. A. 2004. The effect of surface-active carbon on hydrocarbon selectivity in the cobalt-catalyzed Fischer-Tropsch synthesis. J. Catal. 223 309-18. 

There are no solutions for transfer with the generality of the Hadamard-Rybczynski solution for fluid motion. If resistance within the particle is important, solute accumulation makes mass transfer a transient process. Only approximate solutions are available for this situation with internal and external mass transfer resistances included. The following sections consider the resistance in each phase separately, beginning with steady-state transfer in the continuous phase. Section B contains a brief discussion of unsteady mass transfer in the continuous phase under conditions of steady fluid motion. The resistance within the particle is then considered and methods for approximating the overall resistance are presented. Finally, the effect of surface-active agents on external and internal resistance is discussed. 

These flow transitions lead to a complex dependence of transfer rate on Re and system purity. Deliberate addition of surface-active material to a system with low to moderate k causes several different transitions. If Re < 200, addition of surfactant slows internal circulation and reduces transfer rates to those for rigid particles, generally a reduction by a factor of 2-4 (S6). If Re > 200 and the drop is not oscillating, addition of surfactant to a pure system decreases internal circulation and reduces transfer rates. Further additions reduce circulation to such an extent that shape oscillations occur and transfer rates are increased. Addition of yet more surfactant may reduce the amplitude of the oscillation and reduce the transfer rates again. Although these transitions have been observed (G7, S6, T5), additional data on the effect of surface active materials are needed. 

The effects of surface-active agents on the motion of and transfer from bubbles and drops have been discussed in earlier chapters. The main effect is to reduce the mobility of all or part of the interface. In this section we consider briefly two other interfacial phenomena interfacial convection during mass transfer and interfacial barriers to mass transfer. 

One set of observations exists for the effect of surface-active agents on A Tc and The values are somewhat incomplete because the A Tc for pure water could not be obtained with the equipment used. The accompanying table summarizes the results (M9). The results indicate that a decrease in a causes a decrease in the maximum heat flux. Addi-... 

Mel nikova (Ref 6) investigated the effect of surface active agents on the physicochemical and explosive properties of Igdanit. To Insure full utilization of the expl props of Igdanit, the Diesel oil. must be uniformly distributed on granules or crysts of AN. 

Hwang H J, Stenstrom M K (1979) Effects of surface active agents on oxygen transfer, Water Resources Program Report 79-2, University of California Los Angeles. 

El-Nahta, A. 1963. In-vitro studies on the effect of surface-active materials and of oestro-gens on lipase activity. Milchwiss. Berichte 13, 139-166. (German). 

---