FOAM FORMATIOX IS ORGANC LIQUIDS
141
REFERESCES
(1) CARYL, c. R.: Ind. Eng. Chein. 33, 731 (1911). (2) D A M E R E LT'. L , R . , ASD L~RBASIC, .I.:J. Phys. Cheni. 48, 125 (19441. (3) EWIETT, P. H., DEWITT.T.. ASD THoxks. J.: Ind. Eng. Chem., . h n l . Ed. 13, 23(1941). (4) H a R ~ r s sW., , ASD DAHLSTROJI, R . : Ind. Eng. Cheni. 22, S97 (1930). HARKISS, W.,ASD GASB.D . : ,J, Phys. Cheni. 36, 86 (19323. HARKINS, W.,Rr.is, L.. ASD G a s s , D . : Ind. Eng. Chem. 24, 12% [1!)32',. ( 5 ) REHBISDER, P.: Z . physik. C'heni. 146A, 63 (1930).
FOAM F O R M d T I O S I S O R G - i S I C LIQCIDS C G R i Y KISGZ Mellon Instztute o f Iridusti znl Reseaich, PLttsbitrgh, Penrul/lcnnicr
Recezted J a n u a r y 2 1 , 1944
The investigations reported in this paper n-ere conducted to determine ivhether foams comparable in volume and stability to aqueous foams could be produced in organic liquids. Sumerous questions presented t hem-elves concerning these subjects. Could such foams be formed, and, if so, \I hat conditions n-ere necessary? K h a t types of compounds n ould be surface active in organic liquids, and v hich of them could be used as foaming agents? Hoir did the many physical factors said to be in1olved in the formation of aqueous foams affect organic foams? Could any relationship betn-een foamer and d v e n t be discerned? The relevant ansn-ers qet forth here are preliminary and empirical in nature. These findings indicate, hon ever, the possibilities of this relatively untouched held. and it is hoped that more attention will be given to it in consequence. Surpiisingly little TI ork has been recorded in the literature on either the measurement of the surface tension of solutions in organic solvent- 01 the production of foams in organic liquids. -\dam (1) has pointed out that no great amount of positive adsorption can lie expected in organic liquids, because the field of force around the hydrocarbon paits of molecules j s less than that around most other groups, and that a negative adsorption at the air-liquid interface is perhap.; more probable. Gilbert (9) has shonn that long-chain fatty acids produce a slight cliniinution of the surface tension of heavy hydrocarbons. >\.lorerecently JIcRain and Peiry (12) hare demonstrated that lauryl qulfonic acid appreciably clecrea-e3 the surface tension of Sujol, a liquid petrolatum, and ot tetraisoliutylene and hydrogenated tetraisobutylene, 11hereas the same solute scarcely lon eis the surface tension of isooctane, xylene, benzene, and heptane Sumerous other suhstances of widely different character h a w little influence on the surface tension I'ieaeiiteci before the I>i\isioii of Colloid C h e n n s t r a t tlie 106th l l e e t i n g of the h e r i ( heinical Societ) Pittchuigli Perins) 1\ ania Septemhei 10 194.3 2 qeiiioi incumbent of tlie 3Iultiple Intlustiinl Fellon ship on C 01 h Technology suqtainecl a t t h c 3Irllon Institute b\ the iinistiong C'oih Compony. Lancastei, Pennsylvani,i 1
can
142
E. GRAY I i I S G
of the h~drc>carlion~. Tauhman (17) has indicated that adsorption in the interfaces cf organic liquids can he vertical or horizontal, advancing the t>hesisthat differences in the orientation of the adsorbed molecules are a result of variations in the degree oi structure symmetry of those niolecules rather than of differences in polarity. Se\-eml vorkers have measured the surface tensions of organic solutions i\4'). Research oil oipanic i(ia111s has been restricted almost entirely to hot oils and fats (11 I . Tickell (18) has prepared petroleuni-nat~ii.al gas foams. Siimerous references occm in the literature to difficulties with foams during organic preparations. but no efiort has been made to aasemble this information. JIost of the foams probably occurred on the gelation of the product' with the simultaneous evolution of a gas, or in complex systems containing large quantities of water. X o studie;: appear to have been made on polar compounds with the specific intention of correlating their surface activity u-it'h their propensity to form stable and voluminous foams in organic liquids. IIATERLILS . I S D PRELIJIINARY 'TESTY
As 110 information was available concerning the nature of compounds which might be surface active in organic liquids, advantage was taken of that large class of readily obtainalde polar compounds known as detergents, emulsifiers, and wetting agents. While there was no reason to assiinie that t,hese colloidal electrolyte.< would show surface-active properties in organic liquids, seT.eral factors suggested their examination in preliminary experiments. These synthetic compounds include a large number of different Combinations of hydrophobic and hydrophilic groups, thtifi providing ample scope for observation of the effect of different structures. In a few instances families or series of cornpounds of similar structure h i t containing substituents of different chain length are procurable,-for example, the Alerosols. In addition, some of these substances are used for dispersing pigments in paint vehicles, n-hile others are proposed for \caterin-oil emnlsiona. Some of these proprietary compounds contain large quantities of inorganic salts. but this fact did not appear to be too ohjectionalsle, inasmuch as the inorganic fraction would in most cases be insoluble. Many of the compounds contain water, but the quantity is negligible considering the concentration in which the reagents \\-ere used. The grade of solvent employed throughout this 11-ork vas, for the most part, that usually supplied commercially by the nianufacturer. Forty-seven commercial surface-active agents were examined in the first qualitative tests. These wbstance.s represented most of the structural types of colloidal electrolyte? commercially arailable. indication of t'he structure of most of these products can be had by referring to several lists ( 5 , 6, 7 , 8, 10). To facilitate the discussion in this paper, however, the general chemical structures of seveid of these reagents, found to he the most interesting in connection v-ith this study, are given in figures 1 and 2. Initial tests \\-ere made to determine which of the substances showed tendencies to foam in three solvents of different chemical nature,--namely, methyl alcohol,
143
FO131 FOIZM.ITIOS IX 0 B G . i S I C LIQL-ID5
wetone, and lienzene. Preliminary experinients revealed that the foanis would, in the main, lie transient, and that the tendency t o ioani \\-as greater a t concentrations higher than those comnionly a.wimecl t o be required for foam formation. This finding may have resulted from the .qtabilizing action of the increased viscosity of the more concentrated solutions. The tests \\'ere first made a t a concenti~itionof 5 per cent; then the solutions \\-ere diluted to 0.2 per cent' for further examination. In the niajority of cases there \vas little or no activity a t the lower concentration. To determine the foaming tendency, 10 t o 15 cc. of the solution :\'a:: shaken in a glass-stoppered 100-nil. graduate. The ioanis produced were so transitory that the time of expiration of the foam produced on the surface of the
P,-co-s
/ \
C?H,-OH
C2Ha-OH C,H,-OH
R-CO--N
\
H/ C:H,--S
!\ I
CiHd
/T\1
C2Ha-OH
OH C?Ha-OH
OH
Si 11o 1s
(:I
I k y 101 ani i ne condensate) FIG. 1
0
'I
I CHI
R-
I
,-SOaSa
SaO-S-bH
!I
6
/\
\/
I C O O C H ~ C HCH? , CH, C H ~
Sncconol S R Saiitomerse D
Aerosol A T
FIG.2
solution \vas taken as i~ measure of its foaming capacity and stability. This observation was apparently unaffected by the volume of liquid or the violence of the agitation. In a few instances R substantial head of foam was obtained. The greatest tendency to foam \vas displayed hy the agents listed in table 1. The follo\ving substances shoiyed little or no foaming tendency in the three solvents investigated : -Uiates PO, calcium stearate, diethanolaniide of castor oil, Eniulphor EL, Flotation ;Ildol -1,JIaprimol, Maprofis, Mapromin, Saccolene F, Peregal 0, Sapaniine FL, Sapainine AIS, saponin, 2nd Triton W30. It appears from the reeults of these qualitative tests that \-oluniinous foams in volatile solvents are unlikely. Certain general tendencies, howerer, \\-ere
144
E. GRAY KING
evident. More compounds gave an indication of foam formation in methyl alcohol than in acetone or benzene. The greater activity in methyl alcohol might
Foamzng tendency at 5 per. SUBSTANCE
Atlas G 720 Emulphor Emulphor 0 Flotation Aldol B Glyceryl abietate Glyceryl oleate Glyceryl phthalate Igepon AP Igepon T Ivory soap
ThBLE 1 concentration as indicated b y t i m e of expzratioii ____
U E T H I L \LCOHOL
-
Aerosol ill’ Aerosol AI.% Aerosol OT .%quaresin Areskap 100 A reskelene 400 Aresket 300 .itlas G 759
ceiit
....
-
Sone
i
3
9 9
5
15 11 15
Sone 11 11 Very slight 9
10 :it 10 per cent
10 a t 10 per cent
20 20-25 11 17 10 29 9
9 17 Sone
15
s 10
8 5 15 Sonc Sone Sone
1’2
Sone Plight Slight Slight Slight Sone Plight S o n e doLm t o 0.1 per cent 4 Yery slight 4
10 Sone 18 14
4 l-one 4 3
liaccoiiol S R Sekal A Sekal B S Kino1 313 S i n o l 400 S i n o l 466 S i n o l 555 base Ninol 700
Sone
Xino1 967 Prestahit oil T’ Santoinerse D
10 9
Sapamine IiW. Triton K 6 0 . . . . , . . . u1t raven I- to form films; agitator produced 350 per cent overrun Film formation less pronounced; air readily and stably dispersed, but overrun small Slight amount of foam; 90 per cent expired in 1 min.; expired completely in 2 min. S o tendency to foam Slight amount of foam; 90 per cent expired in 1 min.; expired conipletely in 2 min. Cloudy solution with no tendency tu fo:mi Slight foam which expired in 30 sec.
13.3 i
10.8
Slight foam which espired in 25 sec Slight foam which expired in 30-60 sec.
,
Slight foam which expired in 3&60 sec Effect of addition of 5 per cent .lerosol -11-
9.8
Ethylene glycol
47.5
Furfural
42 2
Sitrohenzene
1.3
Propylene glycol . . . 1.4-Dioxane. . . . . . . .
33.1 31.6
0.9 0.5
Ethylene tlichloride
30 , I?
2.0
' l _-.-
1
2.5 11.5
~
Only slight tendency to foam when agitated rapidly Foam voluine small; 15 cc. increased t o 25 c c . ; foam stable for more than 24 h r . \-oluminous foam; 15 cc. increased to 07 c c . ; eqriivalent to the best aqueous foams Air dispersed. but little tendency to fo3m Foam volume sniall; 15 c c . increased to 23 c c . ; 80 per cent espired in 30 sec.; remainder teiiacioris Considerable f o a m ; 15 c c . increased to 40 c c . , hut 95 per cent expired in 1 inin.; remainder stable severnl hour8
to forni bubbles or film-, measuring the volume of foam if it was appreciable, and observing the time of expiration if the foam was unstable.
143
E. GRAY K I S G
-1s expected, Eniulplior 0 gave the greate.qt tendency t o produce foam in hydroxylic sol\-ents. V-itli glycol mi overriin of se\-era1 hundred per cent \vas ohtaiiietl, and a hulihle 2 in. in diameter was h l o ~ ni l ( i i i i the solution. There i v z s decidedly l e tendency for thc clieth\-lenc glycd n i i t l methyl Carhitol solution.; tci ioam. -1marked cleci,ease in surfncc ten?ioii occurred on dissolving Emulphor 0 in the diethylene glycol, hut 110 tlecrense \vas olwrvetl in the ca;e of nieth!-l Carbit 01. I t is interwting that iiit~dmizene,fu1iui~:d. :ind 1 .4-dioxane, in spite oi their relatively high surface tenssionsand otliei- properties conducive to foam formation, tlid not tend t o foam with Emulphor O! and that the latter compound cau.setl ni.) appreciahle decrease in their surface tensions. -As\vas the case ivith the solyeiits of lou- surface tensioii listed in table I , ('ellosolve, h t y l acetate, hutyl alcohol, and diacetone alcohol showed little tendency to foam in conjunction with Emidphor 0, but they had a somen-hat greatel. tenclciicy to pi'opagate foam than tlid nieth?-l alcohol or acetone. Sitrohenzene containing -1ero.d -11affortlecl a foam \\-liich \vas equi\-aleiit t o tlie average aqueous foam. The cleerease in .surface tension was 11.5 dyne;. Furfmal, on the other hand, although it has approximately tlie same siiri'acc teiision as nitrobenzene, shelved only :i slight tenclciicy to foam ivith Aierosol.I\-. \\-bile the surface-tension decrease \vas only 2.5 tlyiies in the lntter case. this fact does not explain entirely the lack of' foaming po\ver. The surface tension of ethylene glycol \vas decreased 9.8 dynes 1)y the addition of -4erosol AI-, that oi diethylene glycol 10.8 dynes hy Eniulphor 0. ant1 that of glycerol 31.1 dynes 11s Eiiiulphor 0, ivithout the development of the capacity to form voluminous foani,~. These observations lead to the inference t h t , together n-ith positive adsorption, a structural halance hetiveen the solvent and tlie foamer is needed to living ahout frothing. It has yet to he ascertained whether this balance increases the abruptness of the change from the body of tlie liquid t o the film, affects the solvation of the solute, or actually determines tlie degree of effective orientation in the film. In a further series of esperinients t o extend the information on types of coniurface active in organic liquid., six of the most promising foamers \\-ere chosen from table 1: namely, Sinol 555 hase, Santonierse D, herosol -IT, Saccono1 S R , Sekal RS, and Eniulphor 0. These compounds vary rather widely in cheniical structure (see figures 1 and 2). Their foaming tendency and surface activity were measured in glycol, dibutyl phthalate, tricresyl phosphate, and Halow\-axS o . 1000, liquids of relatively high surface tension and of J - a r i d chemical structures. The evaluation \vas made at 1 per cent concentration of tlie .siirface-active material, and the foaming tendency \vas noted at room teniperatui*e, as i n tlie previous experiments, and also a t 90°C'. In a fen- cases a >light separation of the solute occurred on standing. In connection with this series of experiments. it \vas also notecl that the foaming capacity of some of the surface-actii-e agent$>Sacconol S R and Santomerse D, for example, was considerahly diminished after tlie samples had been stored for. several years.
FOh3I FOR3I.iTIOS IS ORGAXIC LIQUIDS
149
Glycol A2s previously brought out, Emulphor 0 is a n effective foaming agent in glycol. The foaming capacity of the other compounds was very much less; their tendency t o foam at 90°C. was in the following order: Santomerse D 2. Sacconol S R 2 S e k a l BX 2 -4erosol .i\- > Sin01555 base The cold solutions were in niuch the same order.
Dibutyl phthalate S o very substantial foam.; were obtained in dibutyl phthalate, either a t 90°C. or a t room temperature. Santomer.;e D was largely insoluble, and the filtered solution had no tendency t o foam. although the unfiltered liquid had given about 0.5 in. of tenacious foam. -1ero.ol -11-caused about the same amount of foam. The other compounds s h o ~ \ little ~ d or no tendency t o produce foam..
Tricwsyl phosphate Both -Aerosol -41-and Santomer..;e D yielded about 0.5 in. of foam, stable for *evrral hourq. Santonier3e D \I a+ iiot qoluble t o the extent of 1 per cent, but the hltered solution retained its ahility to foam. Some of the -4erosol *\I-cry.;tallized from the 1 per cent solution after stancling several day-. The order of the tendency t o foam a t 90°C. I\ a.; a- follon-s: -1erowl -IT 2 Santonierqe D > Sekal BX > Sacconol S R ha-e > Emulphor 0
> Siiiol 555
The cold wlutions were vivous and their foaming tendencies were difficult to evaluate. but the order appeared to lie about identical. Sinol 555 baqe and Emulphor 0 exhibited practically no inclination to foam. . I q u n Res, Igepon .1P, :mcl -Itla- G 720 u-ere alao ineffective.
Ha1oica.r: S o . 1000 T701uniinous stable foam;: comparable with aqueous saponin foams u-ere obtained in this liquid with Santomerse D. Although the Santomerse was iiot soluble t o the extent of 1 per cent, the filtered solution foamed hot or cold. The bubble structure of this foam vas extremely fine. z4erosol-41-n-a:: only ahout 50 per cent as effectire as Santomerse D a t 90"C., and the bubbles in the foam were larger and less stable. The foam produced with Sacconol S R was only slightly less voluminous, but it was more stable than the -1erosol -41foam. Sekal R S gave a viscous stable foam of aliout the same volume as the -1erosol -41-foam. The foaming capacities of these solutions n-ere slightly less a t rooni temperature and in about' the same order. The Sekal B S foam \vas unwually stable. Sinol 555 base produced only 0.5 t o 0.75 in. of foam at 30"C., and it evinced little or no tendency t o foam in the hot solution. Emulphor 0 n-as ineffectil-e. Little further comment c m lie made regarding these results. They seem t o
150
E. GRAY KIKG
bear out the previous conception that there must be some chemical structiiral relationship betiveen the solvent and the solute for effective foam propagation. -4dditional liquids xi11 ]in\-e t o be examined before it can lie determined ivhetlier some liquids h a w a greater propensity for ioiming than others with coniparahle propertie:: such as 1-iscosity, surface tension, v21por p i w w r e , and dielectric const ant . Surface-tension nieasiirenieiits \\-ere made on the wlutions used in the pre\-ious series of esperinieiiti:. The decreases in suriare tension on the addition of 1 per cent solute are gil-en in table 4. -1s expected froni tlie previous observations, Sinol 555 base and Emulphor ( ) showed coiiniclernble surface activity in glycol and glycerol but little activity in tlie other solvent. can he produced in organic liquid-. I t appears that liquids \\ ith surface ten-ion- higher than those of the common volatile solvents are more susceptible to foam propagation. There are some indications that certain solrents have a greater tendency to support foam formation than other solvents of comparable surface tension. On the other hand. it is possible that diligent search will reveal for every solvent n chemical structure \vhich i- an efficient foaming agent. 2 . Foaming is u n a n l l ~accompanied ~ hy n decrease in qurface ten-ion, but the
F 0 . N F O l t l i . ~ T I O S IS OlZG-ISIC LIQUIDS
153
154
A. DE BRETTEVILLE, JR., AND F. V. RYER
(12) MCBAIS,31. E. I,., ASI) PERRY. I,. H . : J. .Im.Cheni. Soc. 62, 989-91 (1940). (13) MCBAIS,J. IT.. ASD SPESCER, W .V.: J. Am. Cheiu. Soc. 62, 243 (1940). (14) MACY,R . : J . Cheiii. Education 12, 573-6 (1935). (15) PRESTOS, IV. C . , ASD RI(*HAKDSOS, A. S.: J . Pliys. Chem. 33, 1142-50 (1929). (16) SLUHAS,C. -1.: P:iper Trade J. 111, S o . 8, 26-31 (1940). SSELL,FOSTER DEE: Ind. Eng. Chem. 35, 108 (1943). (17) TAUBMAP;, A. E . : Coiiipt. rend. w a d . s r i . I*.R.S.S. 29, 22-6, 103-7, 210-15 (19-10) (in English). (18) TICKELL, F. G.: Oil G:is J. 27, 1-22. 175 (1928s).
h METHOD OF GROWISG S I S G L E CRYSThLS OF SODIUM STEARATE A S D S O D I U N P,iLMITAiTE A.
DE
BRETTES'ILLE, JR.
64 Terrace Road, Sledford, Massachusetts ASD
F. V. RYER 11.4 Farxhani Street, Belnzont, .llassachusetls
Received February
4 , 1948
Although single crystals of sodium stearate have been grown for x-ray work (6) in a gel, the procedure described proved unsuitable for use by the authors. -inother technique of growing sodium stearate crystals is offered. In addition, the authors show for the first time how to gron- sodium palmitate crystals. An easier method of synthesizing the soap without the additional work involved in the method of Thiessen and Stauff (G) proved feasible. EXPERIMESTAL
The first samples of sodium stearate n-ere made by a method similar t o that of Thiessen and Stauff ( G ) . The ethyl ester was prepared from Eastman stearic acid ( S o . 402), and w a ~fractionated in a vacuum at 1-mm. pressure, the first fraction being rejected. The ester was then saponified \\-ith caustic, and the solution evaporated to dryness a t 105°C. Subsequently it was discovered that the above method was not necessary, since adequate crystals of sodium palmitate and sodium stearate could be gron-n by a shorter method by saponifying the acid material with caustic soda. The sodium stearate single crystals were prepared by adding 0.32 g. of anhydrous material to 100 cc. of 95 per cent alcohol (unneutralized). The material was then heated in a refluxing flask by a gentle gas flanie. -ifter the solution had cooled to room temperature it was poured into a 250-ml. round-bottomed flask. The flask was suspended in an oil bath at 25OC. by rubber bands, with a hole in the stopper to allow don- evaporation. The oil and rubber bands were used hecause they damp out vibration that inight adversely sffect the gron-th of the
