ATTITUDES IN THE TEACHING OF COLLOID CHEMISTRY ROBERT D. VOLD University of Southern California, Los Angeles, California COLLOID CHEMISTRY IN THE TRAINING OF CHEMISTS
be so designed as to give the student su5cient acquaintance with the generally important principles, techniques, and properties of illustrative types of colloidal Undergraduate. At the undergraduate level it would systems to permit him to learn on the job and to recogseem desirable to require at least a one-semester survey nize colloidal phenomena when he comes across them, course as a graduation requirement for all chemists and or to undertake more serious study of the subject a t the chemical engineers. This can be justified 6 r s t of all by graduate level. If at all possible, physical chemistry the nearly universal occurrence and frequent controlling should be a prerequisite for this course, although only importance of colloidal phenomena in industrial and one semester rather than a full year may be required if biological processes. A further consideration is the it is necessary to service considerable numbers of preunlikelihood that the average student will he able to medical students, biochemists, . and other marginal achieve a satisfactory understanding of colloid chemis- groups. Graduate. At the graduate level colloid chemistry try through independent study, in view of the complexity of the subject matter and the contradictions in should be recognized as a distinctive field in itself in which it is possible to specialize for the Ph.D. degree. the interpretations of dierent authorities. Regardless of detail, it is obvious that such a course This organization is actually realized at the University will necessarily be largely descriptive and necessarily of Southern California, with three stafi members somewhat dogmatic, although still critical. It should directly active in this field, supplemented by two physi-
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cal chemists and one organic chemist some of whose problems are directly of a colloidal nature. It is unsatisfactory to treat cblloids solely as a branch of physi, cal chemistry because of the tendency of most classical physical chemists to be so insistent on precise mathematical formulation that many important colloidal phenomena are likely to be neglected, since they are insufficiently understood to specify the ~ariablesprecisely enough to make them amenable to successful mathematical treatment. I t certainly is not classifiable under organic chemistry, since by and large it is the physical-chemical approach which has led to the present rapid rate of development of the subject. By its very nature colloid chemistry tends to be a bridging science of great importance ifl most other branches. This is one of the difficulties which teachers of colloid chemistry must face; their subject tends to be. cannibalized by its offspring. Topics such as adsorption, catalysis, and capillarity are frequently claimed by physical chemistry. High polymers and their behavior are often regarded as being within the province of organic chemistry or chemical engineering. Study of proteins, starch, and the like, is often concentrated under biochemistry. In the applied fields of chemical engineering there is a great tendency to subdivide primarily colloidal topics under material groups. Thus, a t American Chemical Society meetings one frequently finds important colloidal papers classified as rubber chemistry, or high polymer chemistry, or petroleum chemistry. Still, in all these varied instances there is a common characteristic which permits identification of. the given topic as colloid chemistry, i. e., the dominant role of an interface, or of particle size and shape, or particle aggregation or orientation. It would be desirable to group all these topics together and teach them from a unified viewpoint as colloid chemistry, rather than permitting them to become important but singular parts of other disciplines. At the University of Southern California this has been done to a considerable extent by means of a three-semester general sequence, together with a seminar and two courses in special topics (high polymers and surface chemistry). OBJECTIVES OF A TWO-SEMESTER GRADUATE COURSE IN COLLOIDS
A course of this type should prepare a student to undertake either library or experimental investigation of any problem involving colloidal phenomena on his own initiative and with a minimum of external direction. To further this end the courses' should therefore strive to develop the ability to use information rather than merely to practice the memory, to promote a critical evaluation of the literature and of the 'results obtained or obtainable, to develop skill in the preparation of concise and critical reports, to emphasize the frontier or research aspects of the science, and to develop familiar-
ity with a variety of the more important techniques and laboratory instruments. Upon completion of this course a student should have a critical understanding of the general laws which govern the behavior of colloidal systems. He should be acquainted with the properties of important types of colloidal systems, and aware of existing difficulties in our present theories of their behavior. He should have an understanding of, and at least potential ability to use, the various important experimental techniques and be familiar with the limitations in the results obtained. For example, particle size measurements are meaningless without proper control of peptization effects; electron microscope photographs cannot be evaluated without due regard for the influence of the method of preparation of samples and the presence of possible artifacts; and monodispersity in the ultracentrifuge cannot be accepted as proof of the homogeneity of a protein without confirmation by electrophoresis determinations over a range of pH's. Our hypothetical student should therefore have had practice in selecting the various factors bearing on a specific problem and in evaluating theirrelativeimportance. As a further accomplishment, one might expect a general acquaintance with several of the currently most active fields of investigation within the subject. Here one might think of the intensive study of macromolecular colloids (high polymem) using a battery of physical-chemical techniques, of proteins in both the native and denatured states (of importance, respectively, in irnmunochemistry and in the study of fibers and plastics such as silk, wool, casein, etc.), of the role of colloidal electrolytes in problems of detergency, solubilization and emulsion polymerization, and of the many investigations of the relation of colloidal structure to physical properties as in the characterization of lubricating greases or the relation between clay structure and catalytic and adsorptive activity. The student should understand exactly how colloid science has been applied to solve a number of practical problems, so that he acquires a feeling for its use as well as a regard for its beauty as an abstract subject. Finally, he should certainly have cultivated the ability to prepare and present intelligible, critical reports on assigned topics, making good use of the pertinent literature. MEANS OF ATTAINING THE DESIRED OBJECTIVES
A primary means for accomplishing the desired end is to make extensive use of the literature as an integral part of the course. It can be assumed that the student will have an acquaintance with the language of the subject and an elementary understanding of the general principles from the preliminary survey course. In the advanced work, then, it is possible to start at the level of selected readings in specialized treatises dealing with the various topics taken up. Examples include books of the type of Brunauer on Physical Adsorption, Schwab, Taylor, and Spence on Catalysis, Adam on This formulation is an adaptstion and extension of that preSwface Chemistry, Svedburg and Pederson On the sented in a report of the American Chemical Society Committee Ultracentrifuge, Mark on the Physical Chemistry of on Professional Training, Chem. Eng. N m . Jan. 9 (1948).
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siderations which have led to the present concept of each topic included. This tends to develop the useful characteristic of weighing all the evidence both pro and con on each question. An an example, it would scarcely be satisfactory merely to teach the generalization that coagulation of lyophobic colloids is determined by the valence of the oppositely charged ion. Instead it would be preferable to consider the experimental evidence on limiting concentrations, on the composition of the coagulum, the variations in the limiting values of different ions of equal but opposite charge to that on the colloid, the effect of different ions with the same charge, the data concerning replacement of one ion by another in the double layer, and &ally, the various theories that have been developeii in an dttempt to explain these observations with some discussion of the degree of validity of each. A second problem is that of relative emphasis on fundamental principles and on applications of either an industrial or biological nature. Most teachers and industrialists are agreed that the major emphasis must be on generally applicable laws and theories of behavior. However, some understanding of how such principles have been effectively used in the solution of actual practical problems should certainly not be omitted. On the one hand a chemical engineer might lecture for a semester on plastics and still leave a stndenK ignorant of how to control behavior through an understanding of the nature of the colloidal structures involved. At the .opposite extreme a physical chemist might lecture a semester on capillarity and surface films and leave a student unable to go about solving a problem in bonndary lubrication, and even unaware that such problems exist. It is necessary to choose a middle ground between these extremes. W i t h Respect to Students. One problem here, by no means confined to colloid chemistry alone, is that of recruitment of high caliber graduate students interested in this branch of chemistry. There are fashions in science as in dress, and colloid chemistry does not appear as glamorous to the average new graduate student as nuclear structure or radiochemistry. Moreover, most graduating seniors have little or no comprehension of the types of problems involved in modern colloid chemistry, since their only previous exposure has usually consisted merely of a few lectures in a physical SOME PRACTICAL PROBLEMS chemistrv course. usuallv concerned only with the In the Nature of the Course. The first difficulty here physics of colloidai partiel& and their charge and hydrais that of striking a proper balance between adequate tion. Under such circumstances it is scarcely surprising breadth of coverage of the whole field and sufficiently that they are unaware of the scope of the subject and intensive treatment of each topic. On the one hand it select their thesis problems in other fields. A more is undesirable to omit too many important topics. On general requirement of an undergraduate course as a the other, one can easily try to cover so many sub- graduation requirement would go far toward solving jects that the course becomes superficial. Rather than this problem. A second di6iculty is the great resistance of the avera facile acquaintance with limited subject matter, such as the lists of methods of preparation and typical reac- age graduate student-outside the organic field-to tions memorized by all undergraduate students of taking courses involving laboratory work. This is organic chemistry, it is more valuable to develop an probably the reason why colloid chemistry is so often understanding of the experimental and theoretical con- given as a lecture course only. The problem is a real High Polymers, the excellent articles in Vols. I-VI of Alexander's monumental work, and a variety of review articles in Chemical Reviews, Cold Spring Harbor Symposia on Quantitative Biology, etc. If necessary, an elementary text or combination of elementary texts (we use Weiser the fist semester and Lewis, Squires, and Bronghton the second semester) can be used to pull the material together and serve as an introduction to the more involved treatments. However, the proper spirit of a truly graduate course cannot be achieved without frequent use of pertinent, significant current articles on important topics, which serve to introduce the uncertainties, the contradictions, and the limitations both of the data obtained and of their interpretation. Actual laboratory work is absolutely indispensable to the proper study of colloid chemistry. It serves in the first place to develop an appreciation of the available techniques and a knowledge of how to use them. No amount of reading about such topics as coagulation by electrolytes, thixotropic properties, activation of adsorbent~or determination of contact angle can be a substitute for discovering by direct personal experience just exactly what is involved in getting a significant result. Proper use of laboratory work also serves as a useful stimulant of a creative attitude, since it is possible to design experiments as minor research problems still making a selection such that a broad range of instruments and types of measurements are employed, and the properties of the more important types of systems are illustrated. For example, instead of a conventional experiment on adsorption from solution one can substitute evaluation of adsorptive power of an activated and unactivated clay or charcoal, involving a judicious combination of literature recommendation and original experiment in choosing activation conditions, relative quantities of adsorbate and sorbent, analytical method, etc. Fmally, the laboratory work is very well adapted to developing skill in presentation of results and in the critical use of the literature. This can be effected by requiring that the results of experiments be presented in the form of a short article ready for publication, with adequate presentation of the purpose of the work, the technique employed, the results themselves, and their significance and correlation with published data and interpretations.
JANUARY. 1949
one to the graduate student, who is all too frequently bedeviled with an elaborate set of requirements to he met, and who 6nds that a laboritory course takes a disproportionately large amount of his time. Still it is scarcely possible to realize the desired value8 without
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putting forth this effort. Possibly this difficulty could be surmounted by less attention to formal requirements and greater emphasis on mastery of a subject field as a measure of the student's preparation for Ph.D. or Master's examinations.
