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Langmuir 1985,l, 278-281
Influence of Surfactant Vapor on the Spectrum of Cloud Drops Forming in the Process of Condensation Growth B. V. Derjaguin,* Yu. S. Kurghin, S. P. Bakanov, and K. M. Merzhanov Department of Surface Phenomena, Institute of Physical Chemistry of the USSR Academy of Sciences, Moscow 117915, USSR Received October 24, 1984. In Final Form: January 9, 1985 Introduction of a highly disperse aerosol of higher fatty alcohols into the zone of an ascending current under cumuli results in that a greater part of droplets are passivated, and in cumuli there are provided conditions for the preferred growth of large drops. One has numerically solved a system of equations describing variations in the supersaturation of a cloud system, condensationalgrowth of drops, and kinetics of adsorption of surfactant vapor on the surface of drops. The calculation results indicate that small droplets are passivated, the number of growing drops increases, and the growth of large drops is accelerated. Of considerable interest for meteorology would be a method of acting upon warm cumuli and fogs based not on heating or using hygroscopic substances but on controlling the growth of drops on the atmospheric condensation nuclei. As is known, Langmuir that the presence of monolayers of cetyl alcohol on the surface of water retards ita evaporation. The influence of the monolayers of cetyl alcohol and other higher fatty alcohols on the evaporation and growth of water drops is much more drastic. This was proved in ref 3 and 4. The fundamentals of the theory of passivation of the growth of a single drop by condensation in the atmosphere with the use of surfactants were developed by Derjaguin, Fedoseyev, Rosenzweig, and K ~ r g h i n .It~ was found that the growth of fog drops was strongly retarded in the presence of surfactant vapor. This fact was used for preventing the formation of radiation fog. The field supported the theory. The present paper is concerned with our studies of the use of the vapors of fatty alcohols adsorbed on the condensation nuclei for the purpose of acting upon the forming of clouds. In his research on the modification of clouds Langmuir used other means, such as, for example, introduction of silver iodide and dry ice.13 Warm clouds and fogs are characterized by a high internal stability and their direct disintegration would involve tremendous energy consumption. Therefore, one of the suggested the following approach one should (1)Langmuir, I.; Langmuir, D. B. J. Phys. Chem. 1927,31, 1719. (2)Langmuir, I.; Schaeffer, V. J. J. Franklin Inut. 1943,235, 119. (3)Derjaguin, B. V.;Fedoseyev, V. A.; Rosenzweig, L. A. Dokl. Akad. Nauk SSSR 1966,167(3),617-620. (4)Derjaguin, B. V.;Fedoseyev, V. A.; Rosenzweig, L. A. J. Colloid Interface Sci. 1966,22,45-50. (5)Rosenzweig, L. A,; Derjaguin, B. V.; Fedoseyev, V. A. Dokl. Akad. Nauk SSSR 1967,176,636438. (6)Derjaguin, B. V.; Rosenzweig, L. A.; Fedoseyev, V. A. Proc. Int. Congr. Surf. Act., 5 t h 1968,87. (7)Derjaguin, B. V.; Kurghin, Iu. S. Proc. Int. Con/. Condem. Ice Nucleation 7th 1969,pp 461. (8)Derjaguin, B. V.;Kurghin, Iu. S. Dokl. Akad. Nauk SSSR 1970, 192 (5). 1067-1070. .-,,---. (9) Derjaguin, B. V.; Kurghin, Iu. S.; Fedoseyev, V. A.; Rosenzweig, L. A. Aerosol Sci. 1971,2,261-274. (IO)Bigg, E. R.; Brownscombe, J. L.; Thompson, W. J. J. Appl. Meteorol. 1969,8, 75-82. (11)Fedoseyev, V. A.; Ershov, V. A,; Shagly, E. I.; Shustov, V. A. 'Physics of Aerodisperse Systems", Kiev University: Kiev, 1972;No. 7,
-
n2 4 -. r
(12)Derjaguin, B. V.;et al. Proc. WMOIIAMAP Sci. Con/.Weather Modif. 1973,29-33. (13)"The Collected Works of I. Langmuir"; Suits, G., Ed.; v.10, Pergamon Press: Oxford, 1962;Vols. 10, 11. (14)Izmailova, G. I.; Prokhorov, P. S.: Deriamin. - - B. V.: Kolloidn. Zh. 1957,I9 556-561.
act not on already formed clouds and fogs but on the very process of their formation-the kinetics of heterogeneous condensation on the atmospheric nuclei. This can be done through the surface passivation of nuclei, thereby retarding drastically the water vapor condensation process. The "activity" of nuclei can change owing to adsorption of surfactant vapors on them. The mechanism of the phenomenon obviously resides in a change in the properties of the surface of nuclei, which entails a variation in the condensation rate associated with a change in the coefficient of condensation. Thus, monolayers of cetyl alcohol and other higher fatty alcohols are able to reduce the coefficient of condensation of water by a fador of lo00 and more. In the present report an attempt is made to investigate theoretically the influence of surfactant vapor on the growth of the hygroscopic nuclei population with a view of using it for man-made rainfall from warm clouds. The following model was taken as a subject of investigation: air upflowing with the updraft speed u', having a suffiently wide size distribution spectrum of water-containing condensation nuclei, is saturated with surfactant vapor. The saturation degree amounts to 100% and is maintained constant during the whole process. The growing cloud is supposed to be a closed one; i.e., there is neigher mass nor heat exchange with the surrounding atmosphere. The cloud characteristics are supposed to depend only on the vertical coordinate and to be uniform in the horizontal direction. The dependence of the coefficient of condensation of water vapor a(Z) on the monolayer surface coverage is taken from the experimental data obtained for cetyl alcohol by Nutting and Harkins,15Trapeznikov and Avetisyan,le Barnes and La Mer (Figure 1),17Derjaguin et a1.,18 Rubel and Gentry,lg and La Mer et a1.20-22 The dependence of the surface tension u on the monolayer surface coverage 2 is represented in Figure 2. We considered the kinetics of the variation (caused by vertical displacement of the system) in the following (15)Nutting, G. C.;Harkins, W. D. J. Am. Chem. SOC.1939,61, 1180-1187. (16)Trapeznikov, A. A.; Avetisyan, R. A.; Zh. Fiz. Khim. 1970,44, 2873-2878. (17)Barnes, G . T.; La Mer, V. K. In 'Retardation of Evaporation by Monolayers: Transport Proceeaes"; La Mer, V. K., Ed.; Academic Press: New York and London, 1962;p 278. (18)Derjaguin, B. V.;Leonov, L. F.; Mogilat, S. V.; Borisova, V. M. Kolloidn. Zh. 1982,44,877-883. (19)Rubel, G. 0.; Gentry, J. W. J.Phys. Chem. 1984,88,3142-3148. (20)Archer, B. J.; La Mer, V. K. J. Phys. Chem. 1955,59,200. (21)Rosano, H. L.; La Mer, V. K. J . Phys. Chem. 1956,60,348. (22)La Mer, V. K.; Healy, T. H.; Aylmore, L. A. G. J. Colloid Sci. 1964,19,673.
0743-7463/85/2401-0278$01.50/00 1985 American Chemical Society
Langmuir, Vol. 1, NO.3, 1985 279
Influence of Surfactant Vapor on Cloud Drops where
’I
2 lo”
’I E 0,5 0,6 47 0 8
0.1 I O
Figure 1. Coefficient of condensation of water in the presence of an adsorption layer, a,as a function of the monolayer surface . ~ ~ ~ ~ coverage, z
0.5 0;6 i 7
d8 i9
I;O
z
Figure 2. Surface tension, u, of water modified by surfactants, as a function of the monolayer surface coverage, Z.1b17
characteristics: the water vapor supersaturation S, the spectrum of cloud drops, the monolayer surface coverage, and the growth of drops in size r. For comparison, the variation in the characteristics of the cloud system was calculated in the absence of surfactants. A wide spectrum of condensation nuclei participates in the formation of cloud drops, and the adsorption of surfactant vapors can influence in different ways the nuclei of different sizes. Introduction of a highly disperse aerosol of cetyl alcohol or other higher fatty alcohols into the zone of an ascending air current just under a cumuli can result in passivation of a greater part of the nuclei and drops. Thus, conditions will be provided for the preferred growth of a few but large drops, thereby assuring artificial rainfall. Let us consider the influence of surfactants on the population of drops growing on hygroscopic nuclei. The process is described by the following system of basic equations (for S
