Document gbgOrw5jvekX2MZ26y2QX9KJL

Marketin Prom Information Center Stractsre aid Properties of Sarfactaats Theoretical Background y O. M. OANTX Anton Cbamlcsls PMMon Oonorol Anlliiw A Rim Corporation* INTRODUCTION Soap is the oldest surfactant, perhaps 2,000 years old, and until very recently dominated the field. Synthetic detergents or turfacunts are more than 100 years old but they were insignificant until a shortage of soap in Germany during World War I sparked their development. After the war, a tremendous number of synthetic detergents were made and patented, particularly in Germany. The greatest application for these new- products occurred in the textile industry. By the end of World War II it is estimated that production and consumption of synthetic detergents in this country was 90-100 million pounds per year. This was still small compared to an annual soap production of three billion pounds. Suiting in 1915 a vety marked growth occurred in synthetics and by 1917 soap sales began to decline. This is shown in Figure 1. Built deter gents based on synthetic surfactants continued to displace soap powders until synthetics surpassed soap in 1953. Most evidence points to a con tinuation oi this trend. As might be expected, the marked growth of synthetic surfacunts since the war prompted more and more research and development by the chemical industry. An increasing number of new surfacunts is being patented and very large numbers of tradename products are offered for sale.1- * * li is becoming much more difficult, therefore, to classify and discuss surfacunts. OOfBtAL NATURK OF SURFACTANTS The theory of surfacunu has been studied and developed at an im portant part of the field of surface chemistry. The contributions of Adam, Alexander, Harkins, and McBain plus many other eminent colloid chem ists, have led to a much better undersunding of the physicochemical properties of surfacunts. Concurrently with the scientific studies of surfacunts by chemists, physicists, and biologists, a vast technology has developed related to the application of surfacunu in many different industries. This work in cludes studies of the effect of surfacunt structure on wetting, detergency. 1 emulsification, dispersion of pigments, and foaming. Unfortunately, a large cap exists between our scientific knowledge and our practical knowl edge. when one is confronted with a practical problem involving sur factants, it is quite often necessary to try a great many of the products available. Correlation of molecular structure with surface activity and performance in specific applications is a fruitful field and one may expect more work of this type. A surfactant may be defined as a material which will greatly reduce the surface energy of a solvent at a very low concentration. A good wet- for example, will reduce the surface tension of water from 72 to 30 dynes/cm, at a concentration of less than 0.01 %. In general, sur facunts can be defined also as molecules conuining a hydrophobic group and a hydrophilic group. Figure Z illustrates this hydrophobic-hydro philic balance in sodium laurate, a soap molecule. If the molecule of sodium laurate were severed between the llth and 12th carbon atom, one would obtain n-undecane and sodium formate. As Oficiet Dkht, June, 1936 bfiriti Digvt, June, 1936 419 mmm * v itHttiim* *? = - Fig nr# 2--Hydrophobic-hydrophitic bal ance of todhtm lauraU a straight chain hydrocarbon, n-undecane might be found in kerosene or mineral oil. It would be iiuolublc in water and highly polar solvents but quite soluble in oils. Sodium formate on the other hand it quite solu ble in water but oil inaolubte. Neither fragment of thit aoap molecule would have any surface active properties. The unique character of sur factants depends upon the presence of both an oil soluble and a water tollable group within the molecule. * f e (orces acting upon a tingle meleawB ffMmil i as waterr (a) when the molecule la in the body of the HMiid and fb)u the molecule it at liquid-air interface (Figure S). In toe body of the Uqusd, cohesive forces w.i.ll...u..n...i.f.o..r.m....ly attract' the mo`lecule on aalll ri"de*. "For a molecule at the surface, however, there will be aft attractive fare down into the liauid to that the surface acta as if it wnoadcr auoiumsinn If a tew molecules of soap are added to the liquid, they will tend to collect at the surface. Water molecules have .liule or no attraction for the hydrocarbon tail of the aoap molecule and they get squeezed out and line up at the surface as shown in Figure 3. At more and more aoap mole cules collect at the surface, the surface tension it reduced until the surface it completely covered with aoap molecules. Toe quantitative relationship between the dqnt at adsorptioo at the surface and the lowering of surface tension was developed by J. Wil lard Cibba by thermodynamic methods. For dilute solutions the Gibbs equation can be given as follows: C d e = -TT HC where e it the excess concentration in the surface layer,, a is the concen tration in solution. R is the gw constant, T is absolute ternpertture and da is the rate of change of surface tension with concentration. air A typical curve of surface tension versus concentration for a surfact ant is shown in Figure 4. The conoentreiion at which no further reduc tion of surface tension occurs is known at the "critical'' micelle concentre- \\W 1 \\/ L ^11 ^ Figure J-kfaltmlar fonts fat a 420 Ofidd \ J-*. 1956 Ofidd Dorr, Jane, 19)6 421 0 00 iMUir fUtlU Figure f--Schematic repmentation of surfactant micelles tion. When no additional concentration of surfactant at the surface takes place, it must remain in solution. However, turfactant molecules do not diffuse separately throughout the liquid but clump together in mirH Surfactant micelles are shown schematically in figure 5. They may be spherical, lamellar, or even rod shaped. Although the theory of micelle structure is still being developed, their existence is no longer questioned. Measurements of conductivity, osmottic pressure, as well as both X-ray and optical studies confirm the presence of surfactant micelle*. Tbeae micelles are believed to be important in detergency, emulsification, solubilization. CLASSIFICATION Of SURFACTANTS The majority of surfactants can be classified into (our main groups; anionic, cationic, nonionic, and amphoteric. A schematic representation of these types is shown in figure 6. Anionic molecules are so be cause they bear a negative charge and migrate toward the anode or posi tive pole in solution. Cationic molecules migrate toward the cathode therefore contain a positive charge. Nonionic surfactants do not contain an ioniiable group and have no electrical charge. The hydrophilic end of this type of surfactant is usually made up of several hydroxyl groups or ether linkages As indi cated in figure 6, the hydrophilic pan of a nonionic molecule is usually 422 Ofidat Drvt, June, 1956 larger than that of anionics or cationics and may even be much large? than the hydrophobic part ot the molecule. Amphoteric surfactants contain both a positive charge and a nega tive charge. These changes may neutralize each other so that at a given pH, the surfactant behaves a* if it were nontonic. These surfactants us ually exhibit cationic propenies in add solutions and anionic praoertkl in alkaline solutions. Although amphoteric surfactants have been xnosm for a long time they have become commercially important only recently. Many classification systems have been devisea to cover surfactants. Perhaps the most comprehensive system is that devised by Schwartz and Perry in their book on surfactants.* The classification shown in Table 1 is by no means comprehensive but an effort has been made to include structures which are commercially important It will be noted in Table I that anionic surfactants indude just three hydrophilic groups: carboxyl, sulfate ester, and sulfonic. Although ani onic surfactants containing a variety of other solubilizing groups have been made and patented, none are believed to be of commercial import ance except the phosphate esters. The phosphate esters are expected to become more important in the future. In addition to good emulsifying properties, they are particularly useful as antistatic agents for textiles ana plastics. A. Carboxylic Adds: The fatty acid soaps will not be considered in any detail. They are made by saponification of natural fat* and oils and the most useful products contain between 12 and II carbon i< A major drawback of the fatty acid soaps, of course, is their sensitivity to hard water. Rosin soap* and tall oil soaps are also sensitive to hard water E Ofdd Dmr, June, 1956 48 Iiiii thes arc quite cheap and are used in manv industrial operations iihete color and cxlor ate not irnjxjrtant. Naphthenic acids are used primartls as their heavy nietat salts Mte copjier salt is a fungicide while the lead, tohalt. rirtt, and manganese salts are used as driers in paints and varnishes I) Sulfuric At td F. sifts (figure") Sulfa led fates alt ohols were among ihe first svtuhetic surlartanis to Iwmiit commercially inijxjrtant. These prixlucts. known bt stith tradenames as "Gardinols," "l)u|>onols," and 'Orvus.' are uses) prirnarih as detergents in the textile industry, as fine fabric detergents or in shamjxxrs. fatty akohols required fur sulfating are usualls obtained b\ catalytic hydrogenation or reduction with sodium of the corresjxmding (attv acids. Secondary alcohol sulfates can be made by sulfating olefins obtained from (tetroleutn. The secondary alcohol sullates marketed under the trade* name " rergitor are believed to lie made, however, by aldol condensa tion. dehydration, and rediicttcm. Some of the ntexiucts of this type are particularly good as ssciting agents in strong acid, alkali, or salt solutions. In general, litlfale esters are not stable in at id solutions. Oxo pros ess alcohols produced by the Kitcher-Tropsch oxidation of paraffins ate giosvmg in tommercial importance. These primary alcohol), pariiccdartv the Utdecyl product, can lie sulfated to give surfactants. Sulfated oils, usually referred to as suHonated oils, ate the oldest syn thetic surfa< tarns. As earls as IfiH it was discovered that treatment of olise oil with stdluric acid then neutralising with potassium hydroxide 42i Official Digest, June, 1956 produced an oily, water dispersible product very u llyeing calico* reds. These sulfated triglycerides from various oils became known as Turkey Red oils, Products of this type are still used in the textile industry as dyeing assistants, particularly sulfated castor oil, Sullateil oils and fats surh as tallow are used in the textile industry (or finishing yarns and fabrics. They provide surface lubrication and softness. Many valuable surfactants are produced by sulfating esters such as the methyl, propyl, butyl or amyl ofeates or ricinoleates. These produrts foam more, and are better wetting and rewriting agents than the sulfated triglycerides. Sulfation of (he hydroxyl group in a mono or di-glyceride or a glycol ntonoester produces surfactants useful in household detergents, shampoos, and cosmetics. In general, sulfation of any pofyhydric alcohol partially esterified with a fatty acid will yield a surfactant. A variety of surfactants can lie made by reacting fatty acids with ethanolamines and sulfating the resulting alkylolamides. These products are easily manufactured and hase been offered by a number of companies for various textile and industrial uses. Sulfated ethers represent a fairly recent dtselopment in the field of surfactants. Sulfation of the terminal Off group of an alkyl phenol or a fatty alcohol ethylene oxide condensate yields surlattanis wiin good wet ting, foaming, and detergent properties. These products are used exten sively in the formulation of liquid household dishwashing compounds. C. Suljomc /iads Petroleum sulfonates obtained from the rnanu- Z aIR75 iUiU ?r=>l c Dc tMt-tr. c nd fitad tLX f {*1 -V* O' rwkfitad iljccJ Miff =>!. t s*0. t. " N4 '------- 1 -- ;t>rtr3er)ocrfos-o'. IT 1' v 5 figure 7--Sulfate ester surfactants Official Digest, June, I95u a.'' Pi*-' Ol* "* ..tf Fig*** 8--Alkyl aryl atrfacUmts facture of white oih ate complex mixture* of alkyl sulfonates. These are produced in large tonnage* and are used to make soluble cutting oils, textile spinning lubricants, and detergents for motor oils. Alkyl sulfonates can be made also from refined petroleum oil* by the Reed-Horn process involving sulfur dioxide and chlorine. Many product* of this type were made in Germany during World War 11,* and du Pont ha* pioneered their development in this country. Properties of the alkyl sulfonate* are similar to the alkyl arvl sulfonates. The alkyl aryl sulfonates have attained the largest tonnage among surfactants as a result of their use in packaged household detergents. Alkyl betuene types are most important and vary from xylene sulfonates to trialkyl bentene types (Figure 8). These products are used in a great many applications because they are very low in cost, versatile, and chemically stable. The dodecyl betuene or keryl betuene sulfonate is the most effec tive type for detergency. Larger alkyl chains reduce solubility while smaller alkyl chains reduce detergency but increase wetting sction. Alkyl naphthalene sulfonates such as the dibutvl or diisopropyl prod ucts represent another important npe in this clan ot surfactants. They are mwl in a variety of applications for wetting, detergency, emulsification, and dispersing action. An interesting clan of surfactants is made by condensing naphthalene sulfonates or alkyl naphthalene sulfonates with formaldehyde. These low 426 Ofidd Dkot, Jane, 1956 molecular weight polymen are extremely useful as dispersing agents. They are used in the manufacture of water dispersible dyestuff* as well as in paints, plastics, and rubber manufacture. One of the most versatile surfactants is made by condensing fatty acids with n-methyl taurine to give a sulfonated amide.* These products, developed and sold by GAF under the tradename "Igepon" have been used extensively in the textile industry for many yean and are perhaps more like soap than any other surfactant, yet they have none of the dis cedvantages of soap. The related esters made from fatty adds and hydToxyethanetulfonic add developed and told by GAF under the trademark "Igepon A" (Figure 9) are less stable in hot add or hot alkali solutions. In recent yean these sulfonated amides and esten have found many nontextile applications. Another important dais of anionic* it the sulfosucdnic esters devel oped and sold by American Cyanamid Co. under the tradename "Aerosol" and "Deceresot." These product* are made by esterifying maleic anhydride with an alcohol and treating the diester with sodium bisulfite. The sulfosucdnic esters are particularly effident wetting agents, as Caryl hat shown.T II -- CaHonte Surfactant* Cationic surfactant* are used for quite different purposes than the anionics. Perhaps their most unique property is affinity for various nirfaces. In textiles they react with many direct dyes (anionic) to improve water resistance, they are powerful softening agents presumably because they orient strongly on individual fiber surfaces. Other important textile uses for cationic* are as water repellents, moth proofers. bacteri cides, and antistatic agents. The major industrial uses are as germicides or tanititers, corrosion inhibitors, and emulsifiers. Typical structures of cationic agents are shown schematically in Figure 10. i--- ..... i-I-q- .. .w* 4 0 KlfoBai^d mdd* llgvpwi T) MlInM HUr (!* 1) i--cC-*. . .. iTT'TO-o c-e-s-o'.. .* Sit I-MIvUbwI ) adlMlaU Figure Sulfonated amidet and ttUn Oficid Dscsrr, June, 1956 427 <z>" l--nri A. Simple Amine Salts: Straight chain fatty amine* with 8 to IS carbon atom* are rather inioluble in water but their hydrochloride or acetate salt* have wetting, foaming and detergent properties Actually these amines are not often used as such but serve as starting materials for preparing more effective surfactants. Reaction of fatty amines with ethylene oxide yields products which are used as emulsifiers and deter* gents. B. Quaternary Ammonium Salts: Alkylation of fatty amines with methyl chloride, dimethyl sulfate, benzyl chloride, etc. gives quaternary ammonium salts. These are much more soluble than the amine salts and retain their cationic nature in alkaline solutions. Product* of this type are most widely used as germicides. However, a variety of products for special applications fall in this classification. Lauryl pyridium chloride is a spin bath additive in viscose rayon manufacture. Methyloh icearamide pyridium chloride is used as a water repellent. Quatemiied amine-ethylene oxide types are used as dye stripping agents. C. Amino Amides and Imidazolines: The majority of textile softeners are made by reacting fatty adds with various polyamines. These amino amides may then be alkylated to eliminate any primary amine group or fully alkylated to the quaternary. It is obvious that a variety of complex products can be made and a very large number of proprietary cationic softeners are ffered to the textile trade. By modifying reaction conditions, fatty acids and polyamines will 428 0filial Digest, June, 1956 substituted____ ____ the or st high limn the___ amino amides and have not beeeant wed as widely as tesxti!le Quatemised imidazolines also have this disadvantage. AOtyl are prepared by condensing fatty adds with amines like 2-aeth 13 pnrmopmannneidliinoll. VPrkoiudlniucitns eoeMf ethkilsd htynpWe tare am Solvents Corp. under the " ------`Afkatofe.' As noted earlier, amphoteric surfactants, also called ampholytes oa aapholytic surfactants, contain both a positively charged nd a Mgalively charged poop (ftfirnr It). The cartonk group Is wnally an amine salt or a quaternary nitrogen. The anionir group Is oauam .a carboxyl, a sulfate eater, or a suMonfc add. This damificatfoai eirhadas such products a* the fatty amine ethylene oxide modewtri which may be cationk or nonfonic and the allylolamidea which may be anionic or nonionic. The former sre considered cationk while the latter are classed si noniooic. A. Amine end Carboxyl: Rearttoo of an alkyl amine with chloro acetic add produces an alkyl gtydne with typical amphoteric properties. C====3^*-* l%t mtm RtUta Figttrt tl--s lifcjle* Ofieid Dkot, June, 19)6 429 ^Ufc*T reaction will produce a betaine which containi the <]uaier4h^fc Vpm>gen group. Aa might be expected the betaine* are more catiOT^^ in nature than the simple glycine*. A variety of other method* may be u*ed to make both betaine* and aUtyl glycine* from latty amine*. Reaction ol a fatty acid with a polyamine give* an amino amide which can be reacted with monochloroacetic add to produce an ampho- ' tcric product. Likewise the amino amide may lint be converted to an' iraidaioline and then used to make an ampholyte. A number of product* marketed under the "Miranor tradename are claimed to be of thi* type.* The amino amides or imidasolino may be alkylated before or after reaction with monochloroacetic add to give betaine*. Neu* ha* indicated that many rueful ampholyte* have a structure which may be N-alkyl poly (aminoethyl) glycines. B. Amino and Sulfuric Ester or Sulfonic Group*; Surfactant* con taining an amino group plus a double bond may be sulfated readily to give an ampholyte. Similarly amino compounas containing hydroxyl groups may be sulfated. The alkyl amine-ethylene oxide conoensates contain two terminal OH groups so that one or both might be sulfated. Amino-amides made with nydroxyethyl ethylene diamine or the conesponding imidazolines can be tulfated at the hydroxyl group. Amphoteric surfactant* containing an amino group and a sulfonic acid group can be made by using a halogenated alkyl sulfonic acid in filace of monochloroacetic acid. Although many other type* of ampho teric* containing a sulfonic grouj&ppear in the patent literature, it is not believed (hat any have become commercially important. Probably the outstanding feature of the amphoteric surfactants is the fact that they behave like cationic* without the disadvantage of being in compatible with anionic materials. They are substantive to protein and cellulosic fiber* and exhibit softening and lubricating propierties. They also have a bactericidal action. Amphoteric surfactants may never become as important as the anionics or nonionics but they should find many applications where cationic* would be useful and cannot be used because of incompatibility. IV -- Nowlonlc Surfactants The hydrophilic group in anionics and cationics bears an electrical charge and it is usually small relative to the hydrophobic group. The electrical charge must have a marked solubiliiing action because the hy drophilic group in nonionics must tie quite large it the surfactant is to be water soluble. An important method of making nonionics involves reaction of ethylene oxide with a hydrophobe group containing an active hydrogen. After one mole of ethylene oxide has reacted with the active hydrogens, further reaction takes place until any desired mole ratio is obtained. This is illustrated in Table 2.'* A. Alkyl, Alkylaryl Ethers and Thioethers: Nonionics made from alkyl phenols were first produced in this country before the war. Their output has continued to rise and their price has continued to drop. Since they are manufactured Irom phenol, nonene {or diisobutylene) and eth- 430 Official Digest, June, 1936 ylene oxide, they may be considered as petroleum base surfactants. It is interesting to note that at the present time sales of nonionics are increas ing faster on a percentage basis than the alkylarylsulfonates. A variety of products can be made by adding various amounts of ethylene oxide to an alkyl phenol. There are eight nonylphenol products of this type available under the "Igepal CO" trademark varying from a water insoluble f mole product to a highly water soluble 30 mole product. A similar series of octylphenol nonionics is available under the "Triton" trademark. As the hydrophobic-hydrophilic balance is shifted the surface activity changes. In the nonylphenol series, the most versatile surfactant is obtained with a mole ratio of 8-10. Surfactants prepared from ethvlene oxide are not single compounds but mixtures of compounds with different mole ratios of ethylene oxide. Mayhew and Hyatt11 showed that the composition of a nonylphenol nonionic follows the Poisson distribution formula (Figure 12). Thus the mole ratio for an ethylene oxide non ionic refers to an average value. Fatty alcohols tnay be used to prepare nonionics and many products * of this type have found specific applications such as stabilization of rub ber latices. The Oxo process alcohols may be used to prepare nonionic surfactants with good wetting action and detergency. Alkyl mercaptans such as dodecyl mercaptan react with ethylene oxide to give good surf actants. A new- type of nonionic has been developed recently by adding ethylene oxide to polypropylene glycol.11 A polypropylene glycol having a molecular weight of 900 or more is water insoluble and can serve as the hydrophobic base (or producing high molecular weight nonionict. Prod uct* of this type, marketed under the "Pluronic" tradename, can be pro duced in a solid form. Ofidd Digest, June, 1936 431 9 Rflftfntf R t. Maybrw nd K. C Hrtit, Coml AbJHm ind file Gorp., JouiW of ih* Ammetn Chcmitml Socittf, Sep*. IHt, re. 9, p. S97-SC1. Figure 12--Mole ratio distribution of ethylene oxide in polyoxyethylaled surfactants H. Esters and Amides: Ethylene oxide reacts with fatty acids (or Cats and oils) to yield nonionic surfactants. These esters, however, in contrast to the ethers, are not stahle in strongly alkaline solutions. Nonionic ester surfactants may also be made by esterifying a fatty acid with a polyeth ylene glycol. These glycol esters can be made in rather simple equipment and a great many manufacturers offer nonionics of this type. The pre dominant use for the fatty ester nonionics is in emulsification and textile tarn lubrication. The tall oil ethylene oxide condensates should be noted because they are produced in lane quantities. A built tall oil nonionic is used in one of ire popular low foaming household detergents. Tall oil products are cheaper than the alkyl phenol products but they are less efficient in most applications. Fatty adds may be reacted with polybydric alcohols such as glycerol, sorbitol, pentaerythritol, and glucose. IneK esters are sparingly soluble in water but are used extensively as oil soluble emulsifiers. The polyhy dric alcohol partial esters may he reacted with ethylene oxide to give 452 Official Digest, June, 1956 water soluble nonionics. Combinations of the partial esters. ethos^fe sted esters such as those available under the tralemarfu "Spainn"" JF "Tween," can be used for a variety f emulsion problems. The reaction of ethylene oxide with fatty amines to yield cationk surfactant* has been mentioned. Ethylene oxide aljo reacts with fatty amides to yield nonionic surfactants. Such products available under the trademark "Ethomid" are used primarily for emulsification and dispers ing action. A class of compounds variously known as amine condensates, alka- nolamides, or Kritchevsky compounds and available under the trademark "Ninol" are produced by reacting one mole of a fatty acid with 2 molt of diethanolamine. The structure of these compounds has not been establisted definitely but they are usually considered at nonionic. A variety of products can be made by using various fatty acids and various hydroxy amines. These nonionics are used extensively in detergent formulations as foam ttabiliieri at well as in many textile and coametic applications STRUCTURI AND SURFACE ACTIVITY Although a vast amount of work has been done on correlating chem ical structure with surface activity, there is a lack of general test methods which permit prediction of performance in specific applications The lowering of surface tension by surfactants does not always correlate with wetting action. Lowering of interfadal tension does not always correlate with emulsification. Dispersing action for one pigment does not correlate with dispersing action tor other pigments In spite of these difficulties it is well to review the results that have been obtained and di aw some taAl generalizations. A. Solubility: Like other organic compounds, surfactants of higher molecular weight are less soluble than those of lower molecular weight. Solubility increases with temperature and any given surfactant will usu ally show a maximum efficiency at a certain temperature. Selection of a surfactant for use at a given temperature should be based on tests made at the same temperature. Nonionic surfactants exhibit a phenomenon known as a cloud point. As the temperature of a nonionic solution it raised, a point is reached where the solution becomes cloudy. This cloud point increases with ethylene oxide content (Figure 13). B. Surface Tension Lowering or Wetting: Probably the most exten lively studied feature of surfactants is their ability to lower the surface tension of water. A variety o( methods have been devised to measure this property and the du Noiiy ring method is most widely used. Many articles ran be found in the literature relating chemical structure of surfactants to their ability to lower the surface tension ol water. Surfactant manu lacturers often furnish such data in their technical bulletins. The nraves-Ctarkson test'* has been used extensively to indicate the wetting power of surfactant solutions. This test measures the time re quired for a cotton skein to wet out and sink in a dilute surfactant lolu uon. Although Grumfest, Hager, and Walker" have pointed out some shortcomings of the Draves test, it usually correlates quite well with sur face tension and contact angle measurements. The excellent work by Caryl* on the wetting power of sulfosucrinir official Digest, June, 1956 4)3 90 M* kUi *r RkflM* u fckiijmiii Figure i$--Clovdpoints of nonytphenol ethylene oxide products add filers may be died to illustrate the conclusion that maximum wet ting occurs for molecules with a branched chain structure. Thus the 2- ethyl hexyl diester gives a 25 second wetting time at only 0.20 grams/liter while the normal octyl diester requires 0.52 grams/liter. ' C. Dispersion: The fact that well dispersed solid particles remain suspended in a liquid is of great importance in paints, varnishes and printing inks. It is first necessary to wet out the solid particles in the liquid medium and then to coat the surface of each panicle so that ag glomeration does not occur. It is rather difficult to differentiate between surfactants and protective colloids as to the pan they play in preventing agglomeration. Protective colloids may contain ionizing groups, for example car- boxymethyl cellulose, or they may be nonionic such as methyl cellulose. One can visualize that protective colloids function by coating finely di vided solid panicles with a film. This film effectively reduces attracJfiKj forces between the solid panicles and they remain dispersed. ' Anionic or cationic surfactants may be adsorbed on solid particles 454 Official Digest, June, 1936 and provide them with charged surfaces. Repulsion between like charged particles prevents agglomeration. In the case of sulfonic acid surfactants, dispersing action in aqueous systems increases from alkyl to alkyl beiuene to alkyl naphthalene and is greatest for the naphthalene sulfonate con densates. From this and other evidence, it may be concluded that in creased aromaticity of the surfactant structure increases the adsorption on solid surfaces. Nonionic surfactants are quite effective dispenanu also, particularly the alkyl phenol ethylene oxide condensates. In this case the hydrophobic groups are adsorbed on the solid surfaces and the polyglycol chains form a film around the panicles more or less like protective colloids. Although these simple concepts are useful for explaining the rote of surfactants as dispersing agents, the actual mechanism is believed to be quite complex. D. Emulsification: Many of the concepts about surfactants as dis persing agents apply equally well to their use as emulsifiers. Hydrophobic groups dissolve in the surface of oil droplets with hydrophilic groups oriented outward into the water phase (conversely for water-in-oil emul sions). The most important concept in emulsions is that of an interfacial film between the water phase and oil phase. A strong film presents coales cence of the dispersed droplets. Charged droplets, like charged solid par ticles, are stabilized by virtue of repulsion between charged bodies of the same sign. Nonionic surfactants as a class are quite often superior to anionics or cationics for emulsification. Their ability to form tough interfacial films must be more important than the electrical repulsion (actor pro vided by ionic surfactants. Perhaps the most important structure factor in emulsification is hydrophobic-hydrophilic balance. The ease with which this balance can be altered in nomonici is one reason for their ex tensive use as emulsifiers. The technique of making an oil emulsion with triethanolamine oleate by dissolving the oleic acid in oil and the triethanolamine in water can be used with synthetic surfactants. A combination of an oil soluble nonionic and a water soluble nonionic, such as the sorbitol esters and ethylene oxide adducts mentioned earlier, often surpasses a single surfact ant. Anionie-nonionic combinations are very effective in many applica tions. Protective colloids ate used for stabilizing emulsion systems. E. Foam and Detergency: The ability of surfactants to foam has im portant uses such as ore flotation and firefighting and is quite important in detergent formulation. Although foaming has been studied scientific ally as well as in practical applications, no completely satisfacion explan ation of foaming has been developed and little or no correlation with surfactant structure is possible. Detergency is one of the most important properties of surfactants from a practical standpoint and it is an extremelv complex subject. Cer tainly wetting, dispersing action, and emulsification are ail involved in detergency. It is not difficult to measure the relative scouring power of a homologous series of surfactants for soiled cotton and wool (Figure I i). but it is generally recognized that laboratory testing methods do mu show Official Digest, June, 1956 453 --i--i--a--n--ft "~a--a--a--a--a--o--y 1 Ma tatla W Mfle &u> to Figure J4--Colton mod wool detergency of tumylphmol ethylene oxide product! (93% demergers*) which surfactants or formulations are best for all around performance as household detergents.11 IDENTIFICATION OF SURFACTANTS Accurate identification of surfactants is extremely difficult and re quires a variety of analytical tools. It is often possible, however, to obtain a genera] idea about surfactant structures from simple laboratory tests. As a first step, the manufacturer'rtechnical literature should, be studied. The practice of revealing exact structures is growing, at least among the laiger manufacturers. Specifications on individual surfactants can be ob tained from the manufacturer in many cases and they may furnish analy tical procedures upon request. A due to the type of structure is often given by a product's price or iu recommended uses. Products recommended as germicides or corrosion inhibitors are usually cationic A detergent would be anionic or nonionic An edible product would be nonionic. A powerful wetting agent is probably anionic wbereas a substantive textile softener would be cationic. Several compilations are available which list surfactants by trade name1*4 For example McCutcheon lists over 1600 products by tradename and in most cases gives the ionic type, activity, and type of struc ture. It is interesting to note that about half this group are anionic one third are nonionic, ll% are cationic and less than 1% are amphoteric. Preliminary examination of an unknown surfactant would indude physical form, color, odor, ash, density, per cent volatile by oven drying, water content by xylene, and solubility in water and common solvents. Portions of a 1 % aqueous solution of the unknown should be tested by adding an equal amount of a 1 % anionic and also a cationic surfactant. 4)6 Oficiel Digest, June, 1956 Precipitation immediately or after 24 hours, wilt indicate the ionic nature f the surfactant whereas no precipitation suggests a nonionic The fol lowing generalities may be used at a guide: (1) Nooionics are usually oily liquids or low melting waxy solids and would show only a trace of ash. A 1% aqueous solution of a non ionic may exhibit a cloud point at some definite temperature upon heat ing. If a nonionic is suspected and shows no. doud point, repeal the test in a 3% sodium sulfate solution. (2) Products in powder form are most apt to be anionic. Products giving very high foam are probably anionic. Anionics are frequently cut with sodium sulfate and will not be soluble in alcohol, xylene, or carbon tetrachloride. (3) Cationics are often sold as waxy pastes containing water or isopropanol or both. They are substantive to cellulose and will impart a soft, slippery feel to cotton cloth soaked in a dilute aqueous solution. A qualitative test for nitrogen, sulfur, and chlorine by sodium fusion can be nelpful. Most anionics are sulfates or sulfonates and would show positive for sulfur. Most cationics contain nitrogen but nonionict usually contain neither sulfur or nitrogen. Mott cationics are chlorides but ace tates, sulfates, phosphates, .ind bromides may be encountered. Surfactants differ in stability to acid, alkali and salt solutions. Soaps are predpitated by calcium solutions and separate as an oily layer upon acidification. Sulfate esters are usually hydrolyzed by acid solutions but are stable to alkali. Carboxylic esters are saponified in alkaline solutions. Nonionic ethers are stable in both acids and alkalis but are often insol uble in strong solutions of acids, alkalis or salts. REFBIB4CES (1) McCulcheon. J. W., Soap b Ch-m. Specttllirt. July Ocl . (2) Technical Manual and Year Boot. AATCC, Yol. XXXI, Hown Publi-hing C . New York (1955). (5) Siller. I. P. and Wood. P J , "Encyclopedia ot Surface-Actice Agenta," Chemical Publishing Co . New York (1952). (4) Schwaru, A. M. and Petry, J. W., "Surface Active Agetiu." Immcimce TuMithen, Inc, New York (1942). (5) Hoyt. P. B. 5868, Office ot Technical Sen ice, L\ S. Department of Commerce, Washington, D. C (6) Katteru, M. L. and Ato J J . Ind. Eng. Chem., 42 1626 (1950). (7) Caryl. C R . Ind. Eng. Chem , }), 7)1 (1941). (8) U. S. Patent No. 2_52*J7I. (9) Nett, R., Manufacturing Chemur, January, 1994. (10) Jellnek. C. F. and Mayhew, R. L, Tratife Ret. Journal, 24, 765 (1954). (11) Mayhew. R. L and Hyatt. R. C.. ]. Am. Oil Chem. Soc., 29 915 (1952). (12) Vaughn, T. H,, Jackaon. D. R., LundUed, L. G,, J. Am. Oil Chem. Soc.. 29 240 (19S2). (II) Dram. C 1, and Clarkaon, R. C.. Am. Dyestuff Reporter, 20, 201 {1991} alao 21,421 (1999). (14) Gramteat. I.. Hager. O. B., and Walker, H. B.. Am. Dyestuff Reporter, H, 223 (1947). ^ (15) Lambert, J. M. and Sanders. H. L, Ind. Eng. Chem, 12, ISM (1990). Oficiel Digest, June, 1956 437