A. C. Zettlemoyer Lehigh University Bethlehem, Pennsylvania
Colloid and Surface Chemistry in the Physical Chemistry Course
A
visiting educator to the United States from another world would find a curious situation with regard to the position of colloid and surface chemistry in our modero society. On the other hand, he would notice that our experience with the world around us is largely dependent on the surfaces of things. The first sight that greets us on awakening is the color produced by the surface coating on our bedroom walls. We brush the surface of our teeth with colloidal preparations, wash the surfaces of our bodies with colloidal dispersions of detergents, and make use of colloidal cosmetic substances to alter various exposed surfaces. At breakfast we are concerned with colloid and surface chemistry in almost everything we eat: in milk, in coffee, in eggs, and even in the critical texture of the toast. And through the day almost everything we Presented as part of the Symposium on the Teaching of Colloid and Surface Chemistry before the Divisions of Collold and Surface Chemistry and Chemical Education s t the 140th ACS Meeting, Chicago, September, 1961.
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touch or use depends for its vital properties on colloid and surface chemistry: the newspaper and magazine which we read, the carbon black reinforced tires on which we ride to work, the inorganic colloidal concrete aggregate or asphaltic macadam roadbed, the highly filled plastic floor in the reception room, the paper and typewriter ribbon and dictaphone recording disk essential to the operation of the office, the electrical contacts that send our telephone calls on their way-all these and many many more. We indeed meet colloid and surface chemistry on every side. I n industrial practice, our visitor would find much of the same situation. Colloid and surface chemistry pervades many industrial activities, in production and in research and development. He would find examples in current research on oil recovery from the earth, in the catalytic cracking of petroleum, in the coatings for rocket nose cones, in emulsion polymerization of resins for the coating materials required for paints and printing
inks, and in a host of others. I n paints and inks, for example, our interstellar traveler would find that surface chemistry a t the pigment/vehicle interface cont,rols most of the finished properties, and that colloid and surface chemistry are centrally involved in every step of their application. What might stir our visitor a t this junction is the growing recognition by industry of the importance of the field. After all, many more practicing chemists are involved in surface and colloid chemistry problems than are involved in kinet,ic studies or in nuclear chemistry. What would astonish our visitor, therefore, is that even though our way of life is strewn with things colloidal and surface-chemical, we pay little or no at,tention t,o these subjects in the formal education of our scientists. Ignorance of t,he field is abominable, there is a paucity of the teaching of its principles, and very few graduate schools or research groups in colloid and surface chemistry exist in our colleges and universities. What is more, if our visitor would closely inspect our current scientific progress, he would learn that some of the most exciting fundamental developments of our t,ime fall in the field of colloid and surface chemistry. One of the most engaging concerns the main forces of atptractiou and repulsion between colloidal particles. That the long-range London-van der Waals force of a.t,t,raction between plane bodies should vary as the inverse fourth power of the gap distance was argued by Professors Dejaguin and Abricossova a t the Discussion of the Faraday Society on ''Coagulation and Flocculation"' in 1954. Their experimental findings were in accord with theoryz but in sharp contrast with the experiments of Professor Overbeek and Dr. Sparnaay' reported at the same meeting. The later experiment of Ritchener and Prossner3 confirmed the results of the Derjaguin school. At the 1954 Discussion, the priority on the development of the theory of electric double layer repulsion was also est,ablished. I t became clear that the Derjaguin school published similar conclusions to those of Verwey and Overbeek, but preceding the Western world by a few years. Lack of commimication during the years of World War I1 led t,o the independent developments. Certainly our visitor would conclude that t,hese fundamental achievements of the Russian scientists are of more basic value than that of Sputnik! The cont,rast between the Russian scene and the American sccne would appear most striking to our visit,or. These subjects are not expendable in the USSR, where courses in colloid and surface chemistq are part of the basic core of chemical education. Besides, some five research institutes devote major effort to t,he field. What then is responsible for the lowly place of colloid and surface chemistry in the chemistry curriculum in t.he USA? How can the situat,ion be remedied and in what directions? Answers to t,hese questions can now be given.
Discussions of the Faraday Sm'etg, N o . 18, "Coagulation and Flocculation" (1954). C. R., Acad. S e . USSR, 97,643 (1954). LIFSHITZ, a KITCRENER, J. A,, AND PROSSNER, A. P., PTOC. Royal Sac. London, (A), 242,403, (1957).
Two years ago, the Division of Colloid and Surface Chemistry, a t the direction of Professors Mysels and Beebe4, conducted a survey of the teaching of these subjects in the colleges and universities across our nation. The 172 useful replies from physical chemistry teachers were most revealing. Typical statements included: "Most colloid and surface chemistry has been crowded out for more nuclear chemistry." "We gave six lectures on the subject last year, but will probably only give three next year." Very commonly, only three to six lectures are given on colloid and surface chemistry, even when a physical chemistry sequence is three semesters long. And only a few colleges offer a separate course as an elective in the senior year.
Coverage in Physical Chemistry Texts
The treatment. of the subject in our colleges and universities ultimately depends on the treatment given in the available physical chemistry textbooks. Especially is this true in the liberal arts college where t,he size of the faculty does not provide a broad spectrum of training. What then is the record with regard to the contents of our textbooks? (It should be emphasized in what is to follow that the discussion applies to the subject a t hand and not to the many excellent features of the books in question.) Historically, t,he treatments were largely descriptive and the physical chemistry student and teacher were led to believe that colloid chemistry was the simplest portion of the subject, not requiring the rigor of derivations and mathematical analysis needed elsewhere. Surface chemistry was scarcely discussed at all. Among the older books, Getman and Daniels (Wiley) exemplified the topic-by-topic presentation without leading the student to any appreciation of the integrated whole. Millard (McGraw-Hill), which was often used for a first course in physical chemistry, gave a purely qualitatative account. Eastman and Rollefson (McGrawHill), in a final chapter, also gave a purely qualitative treatment much as an afterthought. Needless to say, teachers seldom get to final chapt,ers anyway. With this background, it is of interest to examine the tcxtbooks in current use. Table 1 presents a survey of the topics treated in current physical chemistry textbooks. Included in the first column is the total number of pages so that the number devoted to colloid and surface chemistry, given in the third column, can be compared. From the Divisional survey, it was learned that 85y0 of the colleges and universities reporting were then using one of the first three textbooks. I n the third column are listed the main chapter or section titles under which colloid and surface chemistry topics are discussed. I n the last cohrmns, the specific topics covered are listed. In many cases, five per cent or less of the book is devoted to colloid and surface chemistry. Many books do not present an orderly account of the subject. Sometimes the subject is treated only under catalysis and macromolecules. I n fact, there seems to be a trend toward devoting a separate chapter or section to
' MYSEL~, K. J., J. CHEW.EDUC., 37,355 (1960). Volume
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Table 1.
Textbook
Survey of Colloid and Surface Chemistry in Current Physical Chemistry Textbooks
Adoptions (of 172 reporting)
Daniels b- Alherty, Wiley, 744 pages (total)
66
Maron b- Prutton, Macmillan, 1958, 789 pages
54
Moore, Prentiee-Hall, 1955, 633 pages
26
Sheehan, Allyn& Bacon, 1961,618 pages
Chapter or section titles
Surfaces
Colloids
Surface chemistry, macramoleoules Surface tension, Gibhs eqna- General (41 pages colloids and surfaces) tion, gas isotherms, heats, Polymers: mol. wt., optical chromatography, lyophobie properties, light scattering, dihsion, sediment., electrokinetics, 'gels Surface chemistry, colloids, hetero- Isotherms, solution, insoluble General, optical, sediment., stability, gels, preparation, kinetfilms, applications geneous catalysis (62 pages) ics. electrokinetics. emulsions. m&romolecules, mol. wt., light scattering, viscosity Surface chemistry, heterogeneous Surfaces, Gihbs equation, in- Colloidal state, stability catalysis (29 pages) soluble films. ess isotherms. solution adsorhion, ion exchange, eleho., catalysis Industrial oatalysis, biological Kinetics, electrokinetics Catalysis (8 pages) catalysis Insoluble frlms, gsr isotherms, General solutionadsorption, adsorp Polymers: mol. wt., optical tion state. eatdvsis orooerties, diffusion. sediment., ele&okin&tics, viscosity,
Barrow, MeGraw-Hill, 1961, 694 pages
Adsorption, catalysis, cules (57 pages)
Glasstone & Lewis, D. Van Nostrand, 1960, 758 pages
Colloids and surface ohemistry (43 pages)
Hamill & Williams, Prentice-Hall, 1959, 590 pages
Colloid and surface chemistry (32 pages)
Surfme tension, films, adsorption
MaeDougdl, Macmillan, 1952, 750 pages
Colloids, heterogeneous catalysis (53 pages)
Rutgers, Interscience, 1954,804 pages
Thermodynamics, isotherms, electrokinetics (36 pages)
Meolwyn-Hughes, Pergamon, 1957, 1295 pages
Interfaces, eatdysis (90 pages)
Adsorption, isotherms, soh. General, preparation, kinetic adsorption, Gihbs equation, theory, optical properties, surface tension diffusion, sediment., electrokin., viscosity, gels, emulsions Sediment., Dannm equil., Surface energy, isotherms thermodynamics, electrocapillary eqn., electrokinetics, double layer theory Surface tension, Gihhs eqn., Diflusion, sediment. monolayers, double layer, isotherms, heats of adsorption, protein, oatalysis
macromolecules in physical chemistry textbooks. The trend seems incongruous. Pigments and dyes would also provide a fine topic for physical chemistry; it could be argued that their importance to our society is a t least equal to that of macromolecules. Both topics would appear to fit more harmoniously under the main physical chemistry heading of colloid chemistry. I n all fairness, it must be noted that the rigor of treatment of those topics taken up is on a higher level than was the case in the earlier hooks. If any of the books listed were to be chosen as superior in its coverage of colloids and surfaces, it would be Maron and Prutton. I t also excels as an integrated presentation. Alternative Treatments
There appear to be two ways to present colloid and surface chemistry in the physical chemistry textbook. The first is to have chapters or sections devoted to the two portions. I n Table 2, the subjects which might be taken up in an integrated way are listed. The last line a t the end of each section gives a few suggested applied topics which are selected by prejudice; others might be chosen. The excitement and importance of the modern studies have already been cited in regard to forces of attraction and repulsion between particles. A sophisticated 182 / Journal of Chemical Education
c6romatopraohv
Table 2.
lvodhil. solns., em;lsions. gels PoiyGers: optical propertiis, Ilonnan equil., ultra, light seatterine. viscositv General, osical prdperties, viscosity, diffusion, sediment., electrokinetics
Proposed Outline for Integrated Treatment of Surface and Colloid Chemistry
Surface Chemistry General, . J)efin~txan,surface us. colloid Imoortanee
Subjects Surface tension, surface free energy, capillarity Films on liquids, Gihbs equation Surfaces of solids, gas adsorption, isotherms Wetting Double Layer theory Adsorption from solution Lubrication, chromatography, ion exchange, heterogeneous catalysis Colloids General Occurrence Types Preparation Repulsion and attraction farces Eleotrokinetics Kinetic properties: diffusion, viscosity, sedimentation Optical properties and light scattering Emulsions, gels, macromolecules
analysis of this state of affairs is nowhere apparent% present textbooks. Similar statemenh can be made for a number of other topics. For example, adsorption from solution is usually treated as obeying the Langmnir or Freundlich equation without regard to competition for the adsorbent surface by t~hesolvent and with slight
mention of the composite or net aspect,sof the measurements being made. The student would never suspect that the solution adsorption isotherms, as plotted, would have t,o proceed to zero adsorbed a t pure solute if this point could be reached. Perhaps a second method of presentation would be more desirable. Here, the surface chemistry topics would be covered as they arose in the sequence of physical chemistry snbject,~. For example, after introducing the Gibbs functions, they could be applied to the liquid/air interface to investigat,e surface tension and capillarity. The thermodyuamic treatment could extend direct,ly to phase boundary phenomena by examining the nature of adsorption isotherms. The development of the Debye-Hiickel theory could be followed by a treatment of the diffuse double layer. The analysis of reaction kinetics could lead directly to elementary mechanisms a t the surface of catalysts (as many books already do). Then, a chapter on colloid chemistry could be presented. The book by Rntgers accomplishes much of this task, but probably a t a level too difficnlt for most undergraduates.
The field of colloid and surface chemistry is a part of physical chemistry, and to make it an effective integral part would seem to he most desirable. Some topics from the field have been absorbed into physical chemie try through the years. Physical chemists, for example, would probably all agree that the relation between specific viscosity and volume fraction of dispersed particles, which was initiated by Einstein" is a proper part of physical chemistry and it is included in many text,& So are these other subjects referred to here. The way seems clear to raise the status of colloid and surface chemistry in academic and industrial affairs. First we need textbooks which recognize the importance of the subject matter to the work chemists do and to our national life. When these texts are adopted, more adequate course treatments are likely to come. Our students will then be made aware of the field before the exigencies of the t,imes demand that at,tent,ionbe given it. 'EINSTEIN, A,., Ann. Phpsik, 19, 289 (1906); 34, 591 (1911); v. Smoluchowski, Kolloid Zrit., 18, 190 (1916).
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