A Study of the Adsorption at the Benzene–Sodium Oleate Solution Interface.

Abstract

Since Langmuir (11,12) and Harkins (4) first suggested that an oriented monomolecular layer of adsorbed material existed at the interface of emulsions, considerable experimental work has been done to test the validity of their suggestion. The results obtained are conflicting; some shorn adsorption equivalent to a monomolecular film, while others give evidence of films of greater thickness.Griffin ( 2 ) attempted to confirm the theory with a study of emulsions of kerosene with solutions of sodium oleate and stearate. He found approximately a monomolecular layer. Van der Meulen and Riemann (17, 18) reported similar results with toluene emulsified with solutions of sodium ricinoleate and sodium oleate. In the latter case phenol was added to the toluene used in preparing the emulsions. Undoubtedly phenol or sodium phenolate was adsorbed a t the interface in addition to the sodium oleate.Since the interfacial areas were calculated statistically by these workers from relatively small amounts of material the results are somewhat uncertain. Studies by McBain and his coworkers (13, 14) on the adsorption of such substances as p-toluidine, amyl alcohol, nonylic acid, phenol, etc., a t the interface between the aqueous solution and nitrogen gas have repeatedly shown the formation of films more than one molecule thick. With sodium oleate solutions and nitrogen bubbles, Laing, McBain, and Harrison (10) found sufficient adsorption for a dimolecular layer, Nonaka (20), using a Donnan pipet, studied the adsorption of sodium oleate and palmitate on droplets of toluene and found greater than monomolecular adsorption.Harkins and Beeman (3) made measurements on emulsions containing a much greater number of droplets than those of Griffin and of van der NIeulen and Riemann. Using emulsions of various oleates and octane they failed to find adsorption more than sufficient to form monomolecular films. Harkins and Fischer ( 5 ) , in examining sodium oleate-paraffin oil emulsions, measured the size of 1000 to 3000 droplets in each emulsion 1 DuPont Fellog. 1931Fellog. -1932