Micelle structures in aqueous solutions of glucose-based surfactants having an isoprenoid-type hydrophobic chain

Abstract

Surfactant self-diffusion coefficients have been measured on a binary system of 1- O- β-3,7-dimethyloctyl- d-maltopyranoside ( β-Mal 2(Ger))/water and a mixed surfactant system of β-Mal 2(Ger)/1- O- β-3,7-dimethyloctyl- d-glucopyranoside ( β-Glc(Ger))/water at 25 °C. For comparison, measurements have also been made on 1- O- β-decyl- d-maltopyranoside ( β-Mal 2C 10)/water and β-Mal 2C 10/1- O- β-decyl- d-glucopyranoside ( β-GlcC 10)/water. The hydrodynamic radius of β-Mal 2(Ger) micelles obtained from the micellar diffusion coefficient is around 3 nm and nearly equal to that of β-GlcC 10 micelles within experimental error. In the mixed surfactant systems, the hydrodynamic radii for both systems increase with increasing X G (the mole fraction of β-Glc(Ger) or β-GlcC 10 in the total mixed solute) above X G ≅ 0.4 when the total surfactant concentration is kept constant at 2 wt%. The R H of β-Glc(Ger)/Mal 2(Ger) micelles increases more rapidly than β-GlcC 10/ β-Mal 2C 10 micelles, and then phase separation occurs at X G ≅ 0.65 . On the other hand, the R H of β-GlcC 10/ β-Mal 2C 10 micelles continues to increase until the phase separation occurs at X G ≅ 0.92 . Measurements have also been performed as a function of total surfactant concentration at constant X G (=0.6). The CMC of the β-Glc(Ger)/Mal 2(Ger) system is larger than that of the β-GlcC 10/ β-Mal 2C 10 system as expected from the results of the pure surfactant systems published previously. The R H increases with increasing total surfactant concentration for both systems. At higher concentrations, the R H of β-Glc(Ger)/Mal 2(Ger) micelles increases more rapidly than β-GlcC 10/ β-Mal 2C 10 micelles. These results can be explained by the fact that the geranyl and decyl chains have the same volume but different chain lengths.