Chemical Relaxations in Aqueous Micellar Solutions by Ultrasonic Spectroscopy. I. Alkali Metal Hexyl and Octyl Sulfates

Abstract

Ultrasonic absorption studies have been performed in dilute micellar solutions of Li, Na, and K octylsulfates, Na methylhexylsulfate, and Na hexylsulfate at 40" by the pulse technique in the range 13-143 MHz. Chemical relaxations associated with micelle formation were found In each system. The single-valued relaxation frequencies were concentration independent in solutions as concentrated as twice the c r~t~c a l m~celle concentration. The relaxation data can be accounted for in terms of monomermicelle association-dissociation.--Des etudes d'absorption ultrasonique ont Cte effectukes sur des solutions micellaires diluees d'octylsulfates de Li, Na et K, de mtthylhexylsulfate de Na et d'hexylsulfate de Na, a 40" par la mCthode des pulsations, entre 13 et 143 MHz. Des relaxations chimiques associees a la formation de micelles ont etC trouvkes dans chaque systeme. Les frequences de relaxation de valeur unique sont independantes de la concentration dans des solutions aussi concentrtes que deux fois la concentration critique en micelles. Les donnees de relaxation peuvent i t r e interprCtCes en termes d'association-dissociation monomeremicelle.[Traduit par le journal]Can.

Effect of short-chained sodium alkylsulfate micelles on the kinetics of metal complex formation

“…The cmc values for SOS at 25OC as determined by four methods were 0.117 rnol dm-3 (PADA solubility), 0.114 rnol dmp3 (Ni-murexide), 0.11 to 0.12 rnol dm-3 (onset of micellar rate enhancement), and 0.115 rnol dm-3 (electrical conductivity). These agree well with cmc values of 0.118 and 0.1 15 rnol dm-3 from two different ultrasonic absorption studies (9,10). The nickel murexide experiment was particularly impressive (Fig.…”

Chemical relaxations in micellar solutions by ultrasonic spectroscopy. II. Sodium heptylsulfate and hexylammonium chloride solutions

“…from the high concentration side, we shall content ourselves with saying that in the dilute micellar range, the relaxation frequency remains constant within experimental error. This was the conclusion of our previous work with hexyl and octylsulfates (5).…”

“…from the c.m.c. (critical micelle concentration) to roughly twice the c.m.c., fc has been reported by other workers to remain approximately constant (5) or to decrease in linear fashion from the high concentration values to either a finite number (2) or to zero (3). A different model must be invoked in each case.…”

“…described previously (5). Impurities are now known to affect relaxation frequencies in the neighbourhood of the c.m.c.…”

“…The faster process, studied almost exclusively by the ultrasonic technique -s), is generally assumed to involve some exchange equilibrium between monomer and micelle (2)(3)(4)(5). Investigators, however, are not agreed on which model of micelle dissociation-association can best explain the observed facts, in particular the concentration dependence of the relaxation frequency fc.…”