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[WE C ]Chemical
Engineering Fundamentals Review
Colloids and Surface Behavior b y Arthur
L.
Draper,
b b
Department of Chemistry, Texas Technological College, Lubbock, Tex.
Foams continued to be of industrial importance Adsorption measurement has been automated
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RECEST listing prepared by the vice president of the Academy of Science of the LT.S.S.R.. .4.1'. Topchiev, gives the official Rusian opinion of the 30 most important chemical problems to be studied. Over half of the 30 deal either directly with colloids and surface behavior or bvere derivative and developed from colloids and surface behavior. This serves to focus the scope and position of colloid chemistrb- today. .4 field of study in itself. it enters many other aspects of chemistry. and from i t has developed many a fuIl-gro~\m.complete, and active pure or applied science. Revieiving this field thus presents problems. particularly those of volume. T h e review references deal with the field of colloids and surface behavior. during the period from late 1958 through early 1960. Approximately 18 months a r e covered. Both pure and applied articles are included. Several specific topics are excluded; these are ion exchange. chemisorption and catalysis. chromatography. polymers, and operations. Other fundamental and applied reviewss treat these subjects. A more comprehensive survey of the literature. a collated indexing of nearly 700 references in addition to those published here. is also available (see coupon).
General
During the period covered by this revieiz. two outstanding colloid chemists have been named the recipients of the Kendall Co. Award in colloid chemistry. In 1960. John D. Ferry received the award for his major contributions to the study of macromolecules. For 1961, Stephen Brunauer is to be the recipient for his basic work in adsorption. T h e annual colloid contest for undergraduate college students is achieving a notabie success as it moves into its sixth year in 1961. Under the direction of Karol J. Mysels and the sponsorship of the Continental Oil Co., many of our college students are meeting colloid research while they are still undergraduates. From this group may come some of our future scientists.
Colloids Research in colloids is usually related to the system or to a system propert!.
Thc: systems include sols and arrosols. gels. emulsions, foams. and macromolecules. T h e properties include those of a kinetic nature, like osmosis, diffusion, sedimentation: and viscosity. Other properties studied are electrokinetic and optical. Some of the typical \vork in these fields is covered only briefly here. In the field of sol behavior. Gregg (78; presented a review on the characteristic properties of highly disperse solids, and Zasepa (66) revieived the extensive work done in studving silver hydrosols. T h e polydispersity and particle size of gold sols \vas determined by small angle x-ray diffraction and electron microscopy (43).together ivith Tvork on carbon blacks and polystyrene latices. Douglas and Burden ( I d ) related the stability of Tho:! suspensions in acid. alkali, and salt solutions to the zetapotential. Theoretical studies included the development of a n equation expressing the potential about a charged colloidal sphere (73) and the application of the Boltzmann distribution la\v to the charge equilibrium in aerosols composed of particles < 100 A . ( 2 6 ) . \\'ark on the diffusion of electrolytes in gels and membranes \\-as reviewed by hfarignan (39). T h e gelation of polymethacrylic acid was studied in Lvatcr! acid. and methyl alcohol solutions ( , ? d ) . and Niemark and Slinyakova ( d , 5 )varied the preparation methods to produce ferrogels ranging in porosity from 0.1; to 1.88 cc. per gram, as measured by methyl alcohol and benzene adsorption. Emulsification by ultrasonic irradiation \vas investigated (57). and Rajagopal 57) reported that this method resulted
in a uniform droplet size. Stocckenius and others (60) revie1ved \cork done in determining Ehe structure of microemulsions by electron microscope esaminations. hlcredith (47)treated a t length the theory of the electrical conductivit) of emulsions and reported much experimental data. Albers and Overbeek ( 7 ) theoretically and experimentally related the stability of water in oil emulsions to the electrokinetic potential. Colloidal iron and nickel hydroxides \ v e x reported ( 7 j as very effective emulsifying agents in the benzene-water system, \vith the efficiency increasing as more of the sols were used. Foams continued to be oJ industrial imLmrtance. Michils (d2j discussed formation conditions and the stability of foams, and Kirsche ( 2 8 ) related the capacity of a solution to form foams to low surface tension. Osmosis in a thermal gradient \vas measured in the u'ater-cane sugar s>.stern using a copper ferrocyanide mcmbranc. the observed behavior fitting equations developed from thermodynamic theor)- ( 2 0 ) . Tikhomolova (0'2) observed discontinuities a t 111r solid change point in two-layer membranes of polystyrene and quartz pondcr in the osmotic and in the streaming potential behavior. Patal (-181 reviewed membranes used for osmotic measurements, and Beduneau 13) reviewed tlir industrial applications of dialysis. T h e nxthods and applications of eicctrophoresis \cere revirwed by Holler (27). and Proksch 150) compared electrophoretic theory \vith observrd results. T h e electrophoresis of gold and silvrr
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The complete bibliography for the 1959-60 Fundamentals Review of Colloids and Surface Behavior b y Draper
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NO. 2
FEBRUARY 1961
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Chemical Engineering Fundamentals Review
sols was successfully treated by electrokinetics when the particles were assumed to be nonconductors (27). Biefer and Mason ( 6 )measured the electrokinetic streaming of KCl and TlC13 solutions in Dacron, nylon, cellulose acetate: viscose, and cotton. A theory of electrosedimentation related the applied field to the capacity change during settling ( 4 9 ) . Light scattering equipment was described (56) rchich measured scattering and sedimentation. Surface Behavior
Research in surface behavior is usually related to phenomena on the surface or to properties of the surface. .Adsorption is characteristic of the first of these, including adsorption equipment, theory. gas adsorption, liquid adsorption, and special methods of study. Surface properties are surface tension, monolayer spreading. wetting? and f l o ~ .in capillary systems. Adsorption equipment has now been automated. Ballou and Doolen (2) described a volumetric nitrogen assembly whose measurements are fed directly to a digital computer for calculation of the results. A high-precision instrument, capable of measuring to 1 to 2 parts per 10,000 and incorporating a n adiabatic calorimeter and a gas thermometer: was used in studying the interactions between gases and the surface of a graphitized carbon black (70). A mono- and multilayer adsorption equation was derived by Ishida (23) using Markov processes for a binomial probability distribution that is equivalent to the B.E.T. equation. Sandomirskii and Kogan (37: 53) derived the adsorption isotherm and the heat of adsorption theoretically for a Fermitype electron level distribution. An equation for computing the differential heats and entropies of vapors on active charcoals was developed. with the equation reportedl!. good to 1% (5). T h e validity of the Gibbs adsorption isotherm has been widely questioned recently. For instance, one objection has been raised by d e TYitte (72), who maintains that the equation is invalid
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because it is not an exact differential, as the chemical potential is equivalent only on an area to area basis, not on a surface to bulk basis; an exchange potential term must be included. Johnson (25) found the Gibbs treatment satisfactory for treating the sessile drop on a solid, so long as surface tension is the only variable considered and the surface energy is excluded. Kogan (30) used the method to develop a statistical mechanical theory of chemisorption, Sumerous gas-solid adsorption data were reported. These range from a comparison of argon and nitrogen adsorption o n A1203: SiOZ? Ti02, F e p 0 3 , and carbon black ( 7 7 ) to the calculation of adsorption thermodynamic values from isobaric plots of the adsorption of nitrogen. methane, CO,.ethylene, and n-monocarboxylic acids on the same sugar charcoal ( 6 3 ) . hlacEivan and others (37) reported that titre types of complex adsorption were observed in the interlamellar sorption of amines in graphitic acid and montmorillonite. I n liquid-solid adsorption systems, the effects of branching and steric hindrance on the amount adsorbed were investigated. McKee (38) found that hexane: heptane, and octane filled the same pore volume on silica gel at 25' C. as did branched hexanes, heptanes. and octanes. \\'heeler and Levy (65) observed that increases in the steric hindrance of phenols and benzenes decreased their adsorption from cyclohexane solutions on Dacro G-60 carbon. Dye adsorption was also used. St'ith a nonporous carbon black of known nitrogen area, Kipling and IYilson (27) measured the area or' the methylene blue molecule a t 102 to 108 AZ. T h e number of active centers on Al(OH)3 surfaces activated \vith cobalt ions was determined using indigo carmine dye adsorption ( 3 2 ) . I n adsorption from binary liquid mixtures: Klinkenberg ( 2 9 ) developed an equation expressing preferential adsorption of one component, and Nagy and Schay ( 4 4 ) found an extrapolation method for simple, totally miscible systems to determine the surface area of the adsorbent.
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hfinerd adsorption characteristics were also examined; Novikova (J6) measured peroxide adsorption on clays and X 1 2 0 3 . Slabaugh (58) measured the heats of immersion of preheated and pretreated calcium and hydrogen clays, and bfacarus (36) followed the kinetics of the adsorption of 1-hexene, acetic acid, and hexyl acetate on bauxite. Several special methods were employed to study adsorption and surface characteristics. Low energy electron diffraction was used to follow the adsorption of nitrogen and oxygen on the (ooolj face of titanium crystals (77). Field emission electron microscopy was used to measure the adsorption of S r O vapor on tungsten, in the 900' to 2200'K. temperature range (Sj. Low pressure glow discharges ivere used to stud) solid surfaces (24). The adsorption of "3. methyl chloride, butane, and water on silica gel was studied by perrnittivit! at 10,000 megacycle frequencies (75). The nuclear magnetic resonance determinations of 10 to 180% water sorbed on cellulose showed a discontinuity on1)a t 20% ( d 7 ) . Three general reviews should be mentioned. Zettlemoyer ( 6 7 ) discussed the modern techniques of adsorption study, Low (35) reviewed the kinetics of chemisorption, and Fries (76)covered methods for particle size determination. T'Vith respect to surface properties, it was found that surface active agents changed the interfacial tension during falling drop liquid-liquid extraction of o-nitrophenol in a water-carbon tetrachloride system. but did not affect the net mass transfer (8). Rusanov (53) treated surface tension and other surface phenomena from the viewpoint of thermodynamics. assuming the surface to be of finite thickness. and Reich (52) developed a n empirical equation to calculate the surface tension from liquid density and vapor pressure d a t a ; the equation best fitted liquids whose vapor pressures were 1400 mm. of mercury. Monolayer spreading was examined on different substrates. Trurnit (61) studied the theory of protein monolayers spreading on water, and Xlathieson (40) used the electron microscope to observe islands of stearic acid 25 A. thick when the acid was spread on a mica substrate. T h e adhesion of surfaces was reviewed (33), and Benjamin and Weaver (1) studied the adhesion of films of gold, aluminum, iron, and silver to glass, mica, and plastics. I n vermiculite flotation, linoleic acid soap \vas found superior to other soaps (5'). Capillary flow conditions were treated by Greinacher (791, including the vertical gravity effects. and Street (67) developed a n equation for two-phase flow in capillaries. Schwartz and Minor (55) deduced from theory the thermo-
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an dynamics of capillarity, including flow, contact angle. \vetting. and spreading properties. literature Cited (1) Albers, T.\'., Overbeek, J. Th. G., J . CoiloidSci. 14, 501-9, 510-18 (1959). (2) Ballou, E. V.. Doolen: 0. K., Anal. Chem. 32, 532-6 (1960). (3) Bedumau, H., Rev. prods. chim. 62, 443-51 (1959). (4) Benjamin. P., L\:eaver, C., Proc. Roy. SOG. (Londoti) 254, 163-76, 177-83 (1 960). (5) Bering, B. P., Dubinin, M. M.: Scrpinskii. V. V., Inest. Akad. .Vmk .C. .$. S. R . . Otdrl. Khim. 'Vauk 1959, pp. 981-8. (6) Biefer. G. J.. Mason. S. G.. T~.r a..n..r . Faradaykoc. 55, 1239-45 (1959); ' (7) Borisikhina. V. I., Mokrushin, S. G., h e s f . Vwshikh Ucheb. Zavendenii, Khim. I' Khim. Tekhnol. 2, 541-4 (1959). (8) Boye-Christensen, G.. Terjesen, S. G., Cheni. En
