Micellar growth, network formation, and criticality in aqueous solutions of the nonionic surfactant C12E5

We used cryo-TEM and light scattering to study the micellar growth and subs equent network formation in aqueous solutions of the nonionic surfactant C1 2E5 Cryo-TEM shows the first direct evidence for the existence of connected topology in the vicinity of the critical point and the two-phase separatio n curve of the C12E5/water micellar system. The coexisting phases within th e two-phase region consist of one concentrated and one dilute network of in terconnected cylindrical micelles. These findings are consistent with the r ecent theoretical explanation of criticality and phase separation in certai n nonionic surfactant systems as resulting from entropic attraction between network junctions. Away from the two-phase separation curve, we have ident ified uniaxial micellar growth, with increasing temperature and concentrati on, into long threadlike micelles. From the power-law dependence of the rad ius of gyration, R-G,R-z, and the hydrodynamic diameter, DH, on the molecul ar weight (R-G,R-z, (D) over bar(H) similar to M-w(nu)), We find that these threadlike micelles have properties resembling those of flexible polymers in a good solvent (nu similar to 0.6). Static and dynamic light scattering show that the mean micelle contour length (L) over right arrow increases as c(0.5) (c is the surfactant concentration) in agreement with theory. Final ly, we show that the end-cap energy E-c increases linearly with temperature .