MICROSTRUCTURAL STUDY OF AQUEOUS-SOLUTIONS OF OCTADECYLAMIDE OLIGO(OXYETHYLENE)ETHER

The nonionic surfactant octadecylamide oligo(oxyethylene)ether is solu ble with water, giving rise to an isotropic solution phase over the en tire concentration range at 298 K. Solution properties of surfactants have been investigated by applying several experimental techniques. Th e existence of nonspherical micelles is indicated by a large broadenin g of the H-1 NMR linewidths, The surfactant self-diffusion coefficient determined by the pulse gradient spin echo NMR method identifies the presence of two types of micellar aggregates-small spherical micelles in coexistence with large nonspherical micelles, The radii of spherica l micelles (20-30 Angstrom) are almost independent of surfactant conce ntration. The nonspherical micelles formed at a very high dilute solut ion grow dramatically in size with surfactant concentration until a ma ximum (approximate to 20% surfactant) is reached, after which there is a slow decrease in micellar size. Direct imaging by the cryo-TEM tech nique also identifies a mixture of spheroidal- and thread-like micelle s in dilute solutions, The solution exhibits high viscosity which incr eases rapidly with concentration, (maximum at approximate to 20%) and then decreases again. Stress vs strain flow curves show the characteri stics non-Newtonian flow of the pseudoplastic type, High viscosity mea sured at low strain decreases to a concentration-independent constant low value at high shear strain. (C) 1996 Academic Press, Inc.