Studies of Sulfonates. III. Solubilities, Micelle Formation and Hydrates of the Sodium Salts of the Higher Alkyl Sulfonates

Abstract

This and the papers which immediately follow are a continuation of former work in this Laboratory.2 The investigation reported herein is largely a study of the solubility of the sodium salts of straight chain alkyl sulfonates of 10, 12, 14, 16 and 18 carbon atoms. The work was undertaken to obtain information relating to micelle formation in these solutions.McBain and c o -~o r k e r s ,~ in their studies on the different soaps, have shown quite conclusively that the abnormal behavior of aqueous soap solutions is due to the presence of micelles. Although the existence of micelles has now become generally accepted, investigators are not in accord regarding their structure nor the concentration a t which their formation becomes significant.The equivalent conductance of sufficiently dilute aqueous solutions of long chain paraffin salts, such as soaps, sulfates and sulfonates4-' is quite normal, but with increasing concentration it diminishes extremely rapidly and may reach a minimum after which it actually increases slightly at higher concentration. McBain and his coworkers, using the earlier conductivity, freezing (1) point and vapor pressure data for solutions with concentrations not more dilute than 0.1 N , brought forth the view that the sudden drop in equivalent conductance was due to a rapid increase in the formation of undissociated molecules from ions, with the subsequent formation of neutral micelles and ionic micelles, the effect of the latter becoming predominant when the conductivity reaches a minimum.Hartley and co-workers,8 using conductivity and transference number data for dilute solutions and the modern theories of strong electrolytes, have simplified McBain's explanation by employing his ionic micelle concept only to account for the properties of solutions of these substances. Hartley offers some very plausible arguments in support of the hypothesis that the ionic micelle is formed directly from the paraffin chain ions a t dilutions much greater than those formerly associated with the ionic micelle, that its formation begins to take place a t a fairly definite concentration and that the sudden diminution in equivalent conductance is due largely to a decrease in the amount of ionization with the formation of gegenions. Applying the law of mass action, he shows that the formation of ionic micelles can explain this behavior quite satisfactorily. He also interprets, with less surety, the increase of equivalent conductance in the more concentrated solutions as being due to a loosening of the gegenions, a type of ('retr~grade'~ dissociation. (8) Hartley, "Aqueous Solutions of Paraffin-Chain Salts," Hermann et Cie., Pans, 1936. 539

Surface Chemistry of Froth Flotation

“…Solutions of surfactants possessing an alkyl group attached to a nonionic polyoxyethylene and polyoxypropylene group can also form micelles Laurate Myristate Preston (1948); (b) sodium alkyl sulfates, Tartar and Wright (1939); and (c) effect of chain length on the Krafft point for sodium alkyl sulfates, Raison (1957). in appropriate concentrations. However, micellar solutions of such nonionic surfactants become cloudy or turbid when heated above a certain temperature and often separate into two phases.…”

The Kinetics of Coagulation of an Emulsion

“…Preheating of latex without addition of acid had no effect on either the coagulation velocity or the particle size. I t might be noted that Maron et al (12) have also obscrved increased stabilization of latex with high temperature treatment in the presence of electrolytes, while critical phenomena of the type indicated above have been observed with soap solutions (17,18,20). Hence, it appears that coagulation of GR-S latex exhibits the same characteristics as coagulation of a monodisperse sol, to which the Sn~oluchowski equation is applicable.…”

Properties of aqueous solutions of several salts of α,ω‐alkanediol disulfates

“…The characteristic properties of surfactants with methylene groups of different length are conditioned by the sudden great increase of the solubility at the Krafft point (7,8). It is well recognized by many authors that micelles exist only at temperatures above the Krafft point.…”