Effects of temperature on the rheological behavior of worm-like micelles in a mixed nonionic surfactant system.
We examined the effects of temperature on the rheological behavior of worm-like micelles in a nonionic surfactant system consisting of polyoxyethylene (10) phytosterol (PhyEO(10))/glyceryl monocaprylate (GFA-C(8))/Water. First, the phase diagram of a PhyEO(10)/GFA-C(8)/Water system was examined when the weight ratio, R, of GFA-C(8) to the total surfactants was changed keeping the total concentration of the surfactants at 5 wt%. The formation of worm-like micelles was confirmed over a wide temperature range. Next, the effect of temperature on the rheological properties of the worm-like micelles was examined. From steady-flow viscosity measurements of the worm-like micelles, it was found that the zero-shear viscosity (eta(0)) gave a maximum value more than 1,000 times greater than the minimum value in the temperature range 20-50 degrees C. Further, the temperature at which the maximum eta(0) was observed decreased with increasing R value. These results indicate that there is an optimal temperature at which the entanglement of worm-like micelles is at its greatest. From dynamic viscoelasticity measurements, it was shown that the viscoelastic behavior observed for the worm-like micelles was consistent with the Maxwell model, which is the basic model for a viscoelastic body. In addition, the plateau modulus (G(0)), which reflects the volume fraction of entangled worm-like micelles, gradually increased with increasing temperature, while the relaxation time (tau), which reflects the disentanglement time of the worm-like micelles, rapidly decreased with increasing temperature. From these results, it was clarified that, for a nonionic worm-like micelle, tau influences the change in eta(0) more strongly than G(0).
College of Pharmacy, Nihon University, Funabashi, Chiba, Japan. hashizaki.kaname@nihon-u.ac.jp
Kaname
K
Hashizaki
Hiroyuki
H
Taguchi
Yoshihiro
Y
Saito
D002210:Caprylates / Q000737:chemistry*; D005989:Glycerides / Q000737:chemistry*; D008823:Micelles; D010840:Phytosterols / Q000737:chemistry*; D011092:Polyethylene Glycols / Q000737:chemistry*; D015203:Reproducibility of Results; D012212:Rheology; D013501:Surface-Active Agents / Q000737:chemistry*; D013696:Temperature; D014783:Viscosity; D014867:Water / Q000737:chemistry
D002210:Caprylates; D005989:Glycerides; D008823:Micelles; D010840:Phytosterols; D013501:Surface-Active Agents; D014867:Water; D011092:Polyethylene Glycols; C025343:monooctanoin