THE JOURNAL OF
PHYSICAL CHEMISTRY (Registered in U. 8. Patent Office)
VOLUME64
(0 Copyright, 1QG0,by the American Chemical Society)
JANUARY 20, 1960
NUMBER1
STUDIES ON MICELLAR GROWTH IN SURFACTAKT SOLUTIOSS, WITH AND WITHOUT ADDITIVES BYARUNK. BISWAS AND B. K. MUKHERJI Coniiributionfrom the Department of Applied Chemistry, University of Calcutta, Calcutta, India Recezued December 50,1958
A study has been made of micellar formation in ionic surfactant solutions in the presence of sodium chloride and a nonionic surfactant. Experiments on sodium monolaurin sulfate (SMLS), preparation and properties of which have not been so far reported, reveal that the electrolyte reduces the critical micellar concentration of the surfactant solution. The dyetitration method gives a value of c.m.c. lower than that found by the conductance method; with increased electrolyte concentration, the difference in the two values gradually decreases to a small order. Conductance-concentration curves of ionic detergents with and without non-ionic additive suggest that on addition of non-ionic additive, mixed micelles are formed, in which hydrogen bonds are the main binding factors. While conductance of an anionic detergent solution increases, that of a cationic detergent solution decreases on minute addition of non-ionic detergent; in both the cases, the characteristic bend in the conductance-concentration curve tends to disappear gradually, for which plausible explanations are offered.
Introduction Surfactant molecules or ions are known to associate to form micelles a t a particular concentration known as the critical micellar concentration, or c.m.c. Hartley,' McBain and his co-workers2 and Tartar, et ~ l . have , ~ shown that the presence of electrolytes lowers the c.m.c. It has been shown by Williams, et 1d14 that log (c.m.c.) bears a linear relation with log [e (c.m.c.)] where "c" denotes molarity of added salt and c.m.c. is expressed in moles/liter. Klevens5 has noted that the dyetitration method gives a lower value for c.m.c. than that obtained by other standard methods. Mukherji and Mysels6have shown that log (c.m.c.) us. log [e (c.m.c.)] plottings in the case of dyetitration and conductimetric experiments give two straight lines which meet and cross each other. The above findings need rechecking and clarification. Only few available literatures deal with the influence of non-ionic additives to micellar and con-
ductimetric properties of ionic surfactant solutions. Yoda and Meguro' showed with sodium dodecyl sulfate that the typical break in the conductance us. concentration curve, which denotes c.m.c., gradually disappears with additions of non-ionic detergents such as polyoxyethylene glycol (PEG) or polyoxyethylene glycoldodecyl alcohol ether (PED). Further work on the above aspects seemed desirable.
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Reagents Used. (i) Sodium Monolaurin Sulfate.Purified lauric acid (E. hlerck grade lauric acid purified by repeated cryst. from 25,y0 s o h in acetone a t -25"; purified product had m.p. 44.1 , sapon. value 279.1, iodine value less than 0.1) was esterified with an equimolar proportion of glycerol; the product obtained was subjected to liquidliquid extraction in petroleum ether (b.p. 60-8O0)-ethy1 alcohol system and subsequently crystallized from diethyl ether (m.p. monolaurin 61.9"). (Purity of monolaurin as represented by % a-monoglyceride, determined according to standard method: was 98.5%.) The monolaurin was then sulfated using C1S03H-NaC1 mixture. The sulfate was neutralized with alcoholic NaOH, alcohol was evaporated off and the product crystallized from acetone. (P.C. sulfate (-SO3) gp. as determined by standard methods was found to be 21.01.) (ii).-Lissapol C and LS, used in the experiments, are anionic surfactants manufactured by I.C.I. Ltd., the active ingredients in them being sodium salts of, respectively, cetyl oleyl alcohol sulfate and anisidine sulfate. The com-
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(1) G. S. Hartley, J'. Chem. Soc.. 1968 (1938). (2) J. W. McBain and A . P. Brady, J . Am. Chsm. SOC.,66, 2072 (1943); J. W, McBain and R. C. Merrill, I n d . Eng. Chem., 34 915 (1942). (3) K. .4. Wright, A . D. Abbott, V. Sivcrta and 11. V. Tartar, J. A m . Chem. Soe., 61, 549 (1939). (4) R . J. Williams, J. N. Phillips and K. J. Mysois, Tra7cs. Faraday Soc., 61,728 (1955). (5) I
