Effect of NaCl on Aggregation Number, Microviscosity, and Cmc ofN-Dodecanoyl Amino Acid Surfactant Micelles
✍ Scribed by Shigeyoshi Miyagishi; Wataru Akasohu; Takashi Hashimoto; Tsuyoshi Asakawa
- Publisher
- Elsevier Science
- Year
- 1996
- Tongue
- English
- Weight
- 127 KB
- Volume
- 184
- Category
- Article
- ISSN
- 0021-9797
No coin nor oath required. For personal study only.
✦ Synopsis
because the surfactant derived from a different amino acid Microviscosity, micellar aggregation number ( N ) , and critical has a different headgroup. For the amino acid surfactants, micelle concentration ( cmc ) were determined in solutions of the critical micelle concentrations (cmc) (1-6), formation sodium N-dodecanoyl-glycinate ( Lau-Gly ) , -valinate ( Lauof liquid crystals (7-12), melting points (13, 14), and the Val ) , -leucinate ( Lau-Leu ) , and -phenylalaninate ( Lau-Phe ) as states of the monolayer film at the air-water interface (15a function of NaCl using fluorescent probes ( auramine, pyrene ) .
22) are remarkably influenced by their headgroups. There-
The microviscosity increased with increasing concentration of fore, the microenvironment in the micelles, micelle aggrega-NaCl and reached a saturated value. In addition, two tion number, and micelle shape transition point are expected breakpoints were found on the curve of microviscosity vs NaCl to vary with the headgroup. Miyagishi et al. found that the concentration and by comparison with the data of N and solution viscosity. The first and second breakpoints were explained, microviscosity determined by fluorescent probe methods respectively, as the beginnings of micellar growth and intermichanged at the cmc, a transition point from small globular cellar interaction. The value of N increased steeply above the micelles to large micelles and an intermicellar entanglement first breakpoint and the solution viscosity began to increase at point, in sodium N-acylvalinate solutions (23, 24). In addithe second breakpoint. The NaCl concentrations at the first and tion, when the concentrations of both salt and surfactant second breakpoints increased in the order Lau-Phe õ Lau-Leu were high, the values of microviscosity were nearly the same õ Lau-Val Ç Lau-Gly. The absolute value of the slope of the regardless of their acyl groups. Using these data, the surfac-Corrin -Harkins plot of the cmc was smaller for Lau -Leu and tant solutions were divided into four regions. Region I is a -Phe than for Lau-Gly and -Val. Larger absolute values of the monomer surfactant solution, Region II is a solution conslope ( 1.2 Ç 2 ) , which suggested the contribution of a salting taining small micelles of spherical or ellipsoidal shape, and out effect on cmc, were observed at high NaCl concentration
Region III, where remarkable growth in micelle size occurs, for Lau-Gly and -Val. The micellar growth and intermicellar interaction occurred at lower NaCl concentration with increased is located between Regions II and IV. In Region IV, where size of the amino acid residue when the amino acid of the amino both surfactant and salt concentration are high, the micelles acid surfactant was larger than valine; that is, the hydrophoare entangled with each other. In the previous paper (24), bicity of the amino acid residue was the dominant factor rather we revealed that the position of each region strongly depends than steric hindrance.