Wetting and Spreading Properties of Aqueous Solutions Mixtures of Sodium Hydroxide with n-Caproic, n-Caprylic, n-Capric, Lauric, Myristic, and Palmitic Acids’ H. L. CUPPLES solution was a good indicator HE efficiency of sprays Bureau of Entomology and Plant Quarantine, of its dirt-suspending power that function as contact insecticides or fungicides u. s.&,partment of Agriculture, Washington, D, c. and efficiency as a detergent. I n other w o r d s , the foamis directly related to the ease producing power, dirt-suspendwith which they wet the surfaces to be covered (4, 6,7), and water-soluble “wetters” or ing power, and detergent properties were found to attain “spreaders” are now widely uesd as auxiliary agents to ina maximum value at a given pH, with lower values accomcrease their efficiency. The situation is different with panying higher or lower pH values. The present writer stomach poisons and protective fungicides, which function wishes to emphasize that this correlation may not apply to by means of the deposit that remains after evaporation of materials other than the usual fatty acid soaps. In previous papers (2) the author pointed out that the wetthe liquid medium. I n this case the aim is generally to obtain a maximum deposit, evenly distributed over the ting power of certain soap solutions may be substantially surfaces to be protected. Solutions with high wetting decreased by using a slight excess of caustic alkali. This decrease in wetting power is accompanied by a readily apparent power will generally produce excessive runoff , thus causing loss of spray material and a lessened deposit of the active decrease in foam-producing power. Excess of carbonate, however, did not produce a similar decrease in wetting power material. Maximum efficiency in a spray solution of this type may well be associated with relatively high surface and and foam-producing power, and the results as a whole have interfacial tensions against the surface being covered-i. e., led to the conclusion that the wetting power of soap solutions depends to a substantial degree upon their hydrogen-ion conwith a low wetting power (spreading coefficient). If the wetcentration. It thus appears that the wetting power of a soap ting power is too low, however, the spray solution will collect in droDs instead of evenly covering the surface, and thus leave solution, as measured by its spreading coefficient on mineral oil, is-closely related to its a spot‘ty deposit. O&g to foam-producing power, dirtuncontrollable variations in suspending power, and effithe surfaces to be protected, For aqueous mixtures of sodium hyciency as a detergent. it may be difficult to deterdroxide with a number of fatty acids, at a The present paper extends mine and to maintain the the previous work to mixtures particular degree of wetting concentration of 1 .O per cent of fatty acid, of sodium hydroxide with six power that will produce the it is found that the surface tension, intera d d i t i o n a l fatty acidsm a x i m u m effectiveness in facial tension against mineral oil, and namely, n-caproic, n-caprylic, sprays of this type. spreading coefficient, when plotted as n-capric, lauric, myristic, and Wetting power is also an functions of the alkali-fatty acid mole palmitic-at the concentrai m p o r t a n t factor in the tion of 1.0 gram of fatty acid detergent action of aqueous ratio, give curves which are similar in per 100 cc. Some of the solutions. The d e t e r g e n t form. The relative positions of the previously reported measureaction of such solutions is curves correspond approximately with the ments with oleic acid mixgenerally recognized as deorder of increasing molecular weight of tures are included for compending upon such factors as the fatty acids. parative p u r p o s e s . The w e t t i n g p o w e r , solvent measurements include surface action, deflocculating power, The wetting power of a soap solution, tension, interfacial tension, and emulsifying power, alas measured by its spreading coefficient and spreading coefficient on though under a particular set on mineral oil, is closely related to its mineral oil, with the alkaliof conditions one or more of foam-producing power, dirt-suspending fatty acid mole ratio varying these factors may be more power, and efficiency as a detergent. for each acid from 0.80 to 3.0. important than the others. Baker (1) found that with Others have shown that the wetting solutions of sodium stearate Experimental power of a contact spray is directly rethe abundance of foam deProcedure lated to its insecticidal efficiency. The pended on the hydrogen-ion influence of wetting power in sprays that The calculated quantities of concentration, and that the function as stomach poisons or protecstandard sodium hydroxide, foam-producing power of a fatty acid, and water were tive fungicides merits investigation. 1 For previoua articles in this measured into loosely stopseries. see literature citation 3.
T
924
AUGUST, 1937
INDUSTRIAL AND ENGINEERING CHEMISTRY
pered Erlenmeyer flasks.. Each mixture was heated to the boiling point, shaken well, and allowed to stand at least 1 hour before being tested. The fatty acids were reagent chemicals with alkali equivalents that agreed closely with the theoretical values. The recorded alkali-fatty acid ratios are based on the experimentally determined neutralizing values of the fatty acids. The surface tension and int,erfacial tension were measured with a du Nouy interfacial tensiometer, using ring correction factors as determined by Harkins and Jordan (3). The oil was a highly refined (medicinal) petroleum oil with surface tensions of 30.5, 28.5, and 27.5 dynes per cm. at 25", 50", and 65' C., respectively. To avoid errors due to curvature of the surfaoe or interface, it was desirable to have the diameter of the free surface as large as practicable; for these measurements the containing vessel had an internal diameter of 53 mm. Interfacial tensions were measured 10 minutes after formation of the interface. I n measuring both interfacial tension and surface tension, the pull on the platinum ring was increased very gradually to the point of rupture or maximum pull. Myristic and palmitic acids were tested at higher temperatures to avoid the formation of gels, and in the case of palmitic acid only a restricted range could be covered even then. The result6 are presented in Table I and Figure 1. TABLE I. VARIATION IN WETTING PROPERTIES WITH SODIUM HYDROXIDE-FATTY ACIDRATIO,FOR MIXTURES CONTAINING 1.00 GRAMOF FATTY ACIDPER 100 Cc. Interfacial Spreading NaOHSurFatt face Tension CoeffiAaii Ten- against cient Oil on Oil Ratio sion Moles ,-Dynes per cenlimet-n-Caproic Acid, 25' C.43.6 27.8 -40.9 0.80 47.1 31.1 -47.7 0.90 47.5 34.1 -51.1 1.00 52.5 31.0 -53.0 1.10 50.4 29.4 -49.3 1.25 49.8 29.4 -48.7 1.50 51.4 29.4 -50.3 2.00 --Caprylic Acid, 25O C.24.3 16.8 -11.6 0.80 24.3 16.6 -10.4 0.90 41.5 32.1 -41.3 1.00 -43.3 45.2 28.6 1.10 46.6 28.5 -44.6 1.25 -42.4 45.0 27.9 1.50 -39.7 43.8 26.4 2.00 3.00 46.4 24.4 -40.3 -n-Capric Acid, 25" C. 0.80 21.8 13.8 5.1 0.90 21.9 13.8 5.2 1.00 22.5 14.1 6.1 1.10 36.8 17.0 -23.3 1.25 36.6 17.4 -23.5 1.50 35.2 15.7 -20.4 2.00 34.5 15.1 -19.1 3.00 32.2 13.3 -15.0
-
InterNaOH- Surfacial Spreading Fatty face Tension CoeffiAcid Tenagainst cient Ratio sion Oil on Oil Moles -Dynes per cerclimeter-Lauric Acid, 25' C,4- 6.5 4- 6.4 - 3.4 -15.1 -15.2 -14.5 -13.9 -13.7 -12.1 -Myristic Aoid, 50° C.4- 4.8 5.9 1.0 9.6 -11.5 9.7 8.7 8.6 7.3 -Palmitic Acid. 65O C.0.80 21.0 0.8 5.7 0.90 20.1 1.2 4- 6.2 1.00 23.1 3.9 0.5 1.10 26.3 4.1 2.9 1.25 28.1 5.2 5.8 1.50 29.0 4.4 5.9 1.75 28.5 4.0 5.0
+ +-
+
+--
Discussion The curves show that the surface tension decreases with increase in molecular weight of the fatty acid. The curves for the palmitate, myristate, oleate, laurate, and n-caprate are close together and form a rather distinct group from the ~ u r v e sfor the FIGUREI. VARIATION IN SURra-caprylate and n-caproFACE TENSION, IN INTERFACIAL TENSION AGAINST MINERALOIL, ate, w h i c h a r e m o r e U D IN SPREADING COEFFICIENT widely separated from ON MINERALOIL, WITH SODIUM e a C h 0 t h e r and from HYDROXIDE-FATTY ACID RATIO those of the acids of higher molecular weight.
925
INDUSTRIAL AND ENGINEERING CHEMISTRY
926
TABLE 11. SURFACE TENSIONS OF FATTY ACIDS --Surface Tension? Ring Literature method valuesa c. Dynes per cm. 25 27.2 %-Caproic 27.1 25 a-Caprylic 27.9 28.2 35 n-Capric 27.5 28.4 55 Lauric 27.8 27.8 55 Myristic 28.8 28.5 65 Palmitic 28.6 28.2 Oleic 25 32.1 32.1 a Value for oleic acid from International Critical Tables obtained by drop-weight method; other values from Landolt-Bornstein: obtained by capillary-rise method. Minor interpolations made t o adjust temperatures. Fatty Acid
Temp.
The decrease in surface tension corresponds with the fact that, although the n-caproate solutions have substantially no foaming properties, the n-caprylate solutions foam a little better and the others are distinctly soapy. All the curves are similar in form, showing a minimum surface tension below a mole ratio of 1.0, a sharp rise in the vicinity of the ratio 1.0, and a gradual decrease beyond this point. The n-caprylate curve shows an especially large increase in surface tension near the point of equivalence, from 24.3 to 45.2 dynes per cm., between the mole ratios 0.90 and 1.10. Between approximately the same two mole ratios the oleate curve increases only from 25.4 to 30.6 dynes per cm. The increase between the mole ratios 0.90 and 1.10 may be taken as a sough measure of the rate of increase of surface tension with increase of the alkali-fatty acid mole ratio in the vicinity of the point of equivalence. These values are, in order of magnitude, oleate 5.2, n-caproate 5.4, palmitate 6.2, myristate 9.5, laurate 13.0, n-caprate 14.9, n-caprylate 20.9. Excluding the n-caproate the sequence parallels that of decreasing molecular weight. The form of the curves might lead one to suspect that the surface tensions in those mixtures containing excess fatty acid are the surface tensions of the respective fatty acids. Table I1 gives the surface tensions of the fatty acids used in these experiments. It is apparent that-the surface tensions of the fatty acids are higher than those of the corresponding aqueous soap solutions containing excess of fatty acid. This accords
VOL. 29, N O . 8
with the hypothesis, suggested by. the writer and by others ( 5 ) )that the lowest surface tensions of the aqueous solutions are due to the presence of an “acid soap” which has a high surface pressure. The curves representing the interfacial tensions of the same solutions against mineral oil (Figure 1) are similar to the surface tension curves. Minimum interfacial tensions are obtained with an alkali-fatty acid ratio less than 1.0. I n the vicinity of the ratio 1.0 a sharp rise occurs, and above this point there is a gradual decrease. In their effectiveness in lowering the interfacial tension the fatty acids follow the same order as their molecular weights, and this relation is more nearly uniform than in the case of surface tension. Whereas the oleate has the lowest interfacial tension curve, its surface tension curve is higher than several of the others. The ncaprate curve for interfacial tensions deviates from the curvee for the acids of higher molecular weight more widely than does the n-caprate curve for surface tension. As the spreading coefficient is obtained by subtracting the sum of the surface tension plus the interfacial tension from the surface tension of the reference mineral oil, which is a constant value a t a given temperature, it is to be expected that the spreading coefficient curves (Figure 1) should show relationships which are similar, but inverse, to those shown by the other two sets of curves. The magnitudes of the spreading coefficients, a t least in the range of alkali-fatty acid ratios above 1.0, are in the same order as the corresponding molecular weights.
Literature Cited (1) Baker, C. L., IXD.ENG.CHEM.,23, 1025 (1931). (2) Cupples, H. L., Ibid., 27,1219 (1935) ; 28,60,434 (1936). (3) Harkins, W. D., and Jordan, H. F., J. Am. Chem. SOC.,52, 17.5172 (1930). (4) Moore, W., J. Econ. Entomol., 11, 443 (1918). (5) N,ickerson, R. F., J. Phys. Chem., 40, 277 (1936). (6) 0 Kane, W. C . , et al., N. H. Agr. E x p t . Sta., Tech. Bull. 39, (1930); 46 (1931); 48 (1932); 51 (1932). (7) Wilcoxon, F., and Hartzell, A., Contrib. Boyce Thompson Inst., 3, 1-12 (1931). RECEIVED April 12, 1937.
CLOSE-UP VIEW O F T H E TWO GIANTTURBINE GENERATORS IN THE MOST POWERFUL STEAM-ELECTRIC POWER PLANT IN TEE WORLD THE HUDSONAVENUEGENERATING STATION OF THE BROOKLYN EDraoN COMPANY. THESET W O MACHINESARE O F 160,OOd-KILOWATT CAPACITY EACH,AND THEIRINSTALLATION IN 1932 BROUQHT THE CAPACITY OF THlD STATION UP TO 770,000 KILOWATTS. OR MORP.THAN 1,000,000 HORSEPOWER.Courtesy, New Y o r k Edmson Company.
