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HIGH-SCHOOL CHEMISTItY
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Industrial Applications of Wetting Agents CLYDE A. SLUHAN American Cyanamid and Chemical Corporation, New York, New York
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INKING ducks startle us from headlines describing wettmg . agents. These immensely useful synthetics perform a growing number of tasks in industry less picturesque than these headline items but far more valuable and important to you and to me. Their functions are involved in what happens a t and in surfaces, and are based on changing and controlling surface forces. Oil and water, for example, do not mix because they are mutually insoluble. No parts of the molecules of either are soluble or similar to those of the other. However, if there be introduced into either a substance whose molecule is made up of two parts, one attracted to and soluble in each, the situation is entirely changed. Such a substance tends to collect a t the interface between the oil and the water, and its molecules orient themselves with their water soluble ends toward the water and their oil soluble ends toward the oil. If a sufficient quantity of such two-ended, amphibious molecules are present to form a continuous layer between the two, the character of the interface is completely changed and mixing, or rather emulsification, occurs quite readily. It is as if the surfaces of the two substances were provided with a zipper. What is true of oil and water applies quite as well to other pairs of substances. While mixing is not the thing desired in all cases, the effect of a wetting agent is so to alter the interfacial characteristics of two substances that contact between them is improved. Wetting agents, for example, increase spreading power and penetration of surface coatings; they aid penetration and improve leveling of colors produced by dye solutions; they aid contact, and hence better adhesion of cements and glues; they regulate the characteristics of precipitates; they accelerate reactions between two phases or two immiscible liquids. All of these actions result from the more intimate contact produced by wetting agents between two materials separated by an interface. The 'effectiveness of a wetting agent depends, as we have noted, upon the zipper effect of the dual nature of its molecules. The molecules of common soaps possess this dual nature, since their sodium ions are water seeking (hydrophilic) and the alkyl groups of the fatty acid is water repellent (hydrophobic) and oil soluble. Thus soaps are important and valuable wetting agents. But they are by no means universal in their application. One of the principal drawbacks to the use of soap for such purposes is its sensitivity to
acidity and to ions of metals other than sodium and potassium in the solution in which they are used. Calcium and magnesium, which commouly occur in natural waters, readily form precipitates with common soaps and thus remove them from action. Even sodium chloride dissolved in water reduces the solubility of common soaps to an extent that interferes with their action. Furthermore, since wetting agents are added substances (hence, impurities, even though useful ones) wherever they are used, the smaller the quantity required, the better. Many types of compounds possess value as wetting agents, but the most powerful series having the widest range of applications are the sodium salts of dialkyl esters of sulfosuccinic acid, marketed under the trademark "Aerosol." Of this family, the dioctyl ester is the most powerful wetting agent now marketed. Consideration of its molecular structure suggests reasons for its value. Here i t is:
This valuable compound possesses two strongly hydrophobic, oil-soluble groups in the two octyl radicals a t the top of the structural formula. The two octyl groups give the molecule a relatively large hydrophobic area and thus fewer molecules are required to cover any surface completely. The lower end of the molecule with its sulfonic acid radical is strongly hydrophilic. The forces involved in orienting these molecules a t interfaces are extremely strong and consequently the effect of their action is also great. The vital properties of wetting agents are their effects on interfacial and surface tensions of solutions containing them. Thus the behavior of wetting agents
in media of various kinds is the important consideration. Their activity and potency must not be materially diminished by acids, alkalies, or salts present in the medium. Their solubilities must be unaffected (within the limits of concentration required) by any of the substances likely to be present. They must also be soluble in both organic solvents (non-polar liquids) and aqueous media. All of these essential criteria are fully met by Aerosol OT and by other members of the Aerosol family to an only slightly lesser degree. The number and variety of applications of wetting agents are constantly increasing as new uses are explored. In almost every industry operations are made easier, faster, or more complete by the intervention of a wetting agent. Many of these are quite obvious, like the leveling of the dyeing of a fabric by the addition of a wetting agent to the dye bath, and many different types of compounds can be successfullyemployed for these purposes. However, many other less obvious services of wetting agents can be performed by only the most potent members of the class. Some of these are covered by various patents and this fact must be considered in relation to what follows. Various operations in the rubber industry are significantly affected by Aerosol OT in relatively tiny amounts. Solutions of crude rubber in mineral spirits are more quickly formed and the quantity of rubber dissolved is increased by the addition of one-half to one per cent of this wetting agent to the mixture, the quantity being calculated on the weight of the rubber. Additions of similar amounts to chlorinated rubber solutious, used as protective coatings, reduces viscosity and makes the product easier to apply. The modem technic of compounding rubber in the f o m of liquid latex is improved if the dispersion of the various powdered ingredients (sulfur, pigments, accelerators, and the like) is assisted by the wetting agent. Furthermore, varnishing of rubber footwear is improved by adding wetting agent to the varnish to prevent condensation of moisture in water spots on the film on humid days. In each of these applications, the important point is that more intimate contact between materials of different characteristics is secured. Industries based on manufacture and use of paper find Aerosol OT extremely valuable in diverse applications. Cleaning and conditioning paper-making felts, pasting and gluing operations, the wetting-out and disintegration of "broke" in the reuse of waste paper, the dyeing of paper, increasing the absorbency of paper towels, and the manufacture of transparent papers--each of these important operations is facilitated by added wetting agent. In metal working industries many valuable applications of wetting agents speed production. Pickling and electroplating baths are more efficient if tiny amounts (one- or two-tenths of a per cent) of Aerosol OT are added. Here conditions of acidity and dissolved salts require that only a wetting agent unaffected by either be used. Cleaning of finished
metal parts with either aqueous or organic liquids is similarly improved. Even in the preparation of molds and cores for foundry use, wetting agents are useful in assisting the binding of sand and clay into the desired shapes. Characteristics of pigments can often be modified favorably by adding Aerosol OT to the precipitating bath, and the ease of dispersion of pigment in ink or paint vehicles is increased similarly. One effect of importance is a reduction in tendency of the pigmentvehicle mixture to stiffen on standing. In such applications the wetting agent must have no effect on the subsequent properties of the product, drying, water resistance, etc. Lubricating oils and greases, particularly those having emulsifying properties, are also improved by added wetting agent. Effectiveness of dry-cleaning solvents, glass cleaners, and leather finishes and dressings can be materially heightened by wetting agents. Flameprooiing and mothproofing treatments are similarly improved and fire extinguishers are made more effective by the addition of Aerosol OT to their fluid content. Such diverse operations as flotation of minerals in
Glass stoppers are easily removed from bottles when a few drops of Aerosol are released from a buret around the edaes of the stopper. The Aerosol quickly penetrates between &&per and neck of bottle, and breaks the friction that causes sticking. Care should be taken to remove the Aerosol from the stonner. to This is one of the many novel applications of the unusually effective Aerosol Wetting Agents.
ore dressing and the cleaning of fruit and vegetables to remove soil and spray residues prior to canning profit by the increased contact obtained with Aerosol OT and its related compounds. Obviously this list of applications could be extended far beyond the scope of this paper. Many of the
subjects that could be covered are of the greatest practical importance, all based on control and modification of surface forces between two substances of d i e r ing characteristics. Clearly wetting agents are among the most broadly useful developments of chemical industry.
Although the present volume has a title very similar t o that of the first book, i t very definitely is not a mere revision. I t is entirely new in arrangement of the material, illustrations, and much of content. An outstandine difference is the inclusion -~ the ~~~-~~~~~~ of quantitntive proccdurc. in ndditiuu to the qunlirntive. F u r thermore, many of thr newrr technics clevelopcd by the author and his co-worker, arc presented for thc first rtme in a complete form. While a comparison of this book with its predecessor is perhaps not warranted, i t should be observed that the present volume undoubtedly r d e c t s the author's experiences in using the former as a text in his courses. The book is divided into three main Darts. The first descrihes the aooaratns emoloved. . . . how to make it and how to use it. Thc author has w d y kft n discussion of the optics of the microscopr. to texts on the sullject, nnd limited himself to a bricf description of the rssrntial parts of thc instnxment, and thkir functioning. Experiments are interspersed to illustrate the use of the various pieces of equipment. Since there is often a choice of methods available for a certain operation, it is advisable for the beginner in microanalysis to familiarize himself with all, so that he may select the proper one for his particular purpose when he has a practical problem. These experiments are designed to illustrate basic technics using this equipment. The second part of the book consists of a desniption of the various technics of qualitative analysis, such as spot tests, slide tests, fiber tests, bead tests, etc., as well as methods for working with slides, capillaries, and centrifuge cones. Experiments illustrate each technic, and such manipulations as evaporation. extraction, etc. Although the accompanying experiments are based on the qualitative analysis of the metals, no complete scheme of analysis or separation is included. An outline of such a scheme is given far the copper and arsenic groups hut, as the author suggests, "any tried macro scheme may be applied t o the analysis of small samples once the basic technic has been learned." For greater flexibility in the application of the methods, this ~
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part of the book is divided into sections on centigram, milligram, and gamma procedures. The latter are the new methods using a micromanipulator, which approach spectroscopic analysis in sensitivitv. The thtrd part of the text dcscrihcs the quantitari\%prowdures using both the microchemicnl halancc of the Kuhlrnnnn type, and the urdmnry analyriral bala:lce and for both rentiyram and milligram samples. Gamma procedures are given rather brief consideration in this section. This part also describes the micromethods of titrimetric analysis. The appendix lists not only the reagents for bath qualitative and quantitative experiments, and the apparatus used in both types of work, hut also includes a bibliography and $ brief outline of a basic course in micro-technic. The book is written with the wealth of detail and attention to proper sequence of manipulations so necessary for the correct carrying out of the methods. The author has apparently made thecomfortable decision to describe only those methods which he found to be practicable and best suited for the particular purpose, rather than to make the hook a compendium of all puhlished methods. I n the opinion of the reviewer, a book on such a relatively new subject as this should give the reader the benefit of the author's experiences rather than present an overwhelming list of all known procedures, leaving the reader (who is probably a novice in this field) to decide which one to use. A welcome innovation is the listing of the required apparatus a t the beginning of each experiment. A statement by the author that even "experienced chemists should resist the temptation to limit their study to a few experiments which seem to be an immediate preparation for the contemplated practical use" is heartily endorsed by the reviewer. Too often micromethodo have been condemned as inadequate by persons who have not had sufficient experience with them. I t is certain that the publication of this book will give a great impetus to the adoption of micromethods in analytical laboratories, both academic and industrial.
URANIUM AND ATOMIC POWER. JackDe Mmt, Research Chemist, The Mineralogist Laboratories; and H. C. Dake, Editor, The Mineralogist Magazine. Chemical Publishing Co., Inc.. Brooklyn, New York, 1941. viii 335 pp. 16 figs. 13.6 X 21.7 cm. $5.00. This hook is a synthesis of the material in the literature to date on uranium and related compounds. I t is supplied with Lengthy bibliographies to its seven chapters which deal with: Atomic Power, The Uranium Minerals, The Physics of Uranium, Chemistry of Uranium, and two chapters on Specific Methods in Uranometry; plus six appendixes, which are full of carefully compiled data. The chapter dealing with the use of fluorescent indicators in urauometry is especially interesting in view of the authors' earlier book, "Fluorescent Light and its Applications." The study was made, in great part, with a view t o the future possibilities of uranium as a source of energy. The authors have summed this up: "We believe that we are treating some of the fundamentals of a new science which includes, hut which does not entirely consist of, the rapidly vanishing borderline between chemistry and physics. We also believe that we have described what may be the groundwork of a future industry, the possihilities of whichare fantastic to many, but not too highly improbable t o those with a mind t o progress."
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CHEMISTRY IN RELATION TO BIOLOGY AND MEDICINE WITA ESPECIAL REFERENCE TO INSULIN AND OTHERHORMONES.5. 1. Abel. Willisms and Wilkins Company, Baltimore. Maryland. 1939. 79 pp. 16 X 24.5 cm. This is the Willard Gihhs lecture by the late Dr. Ahel. The TO DUCKS WHOTRY TO SWIM IN WATER THISIS WHATHAPPEN* TO WHICHA WETTINGAGENTHAS BEEN ADDED (See pegc 38.) edition is limited and privately distributed. ,'
