Rheology at the phase transition boundary: 2. Hexagonal phase of Triton X100 surfactant solution

The phase behavior of the Triton X100/water binary mixture is investigated using rheological, optical, and X-ray synchrotron techniques. In particular, the storage shear modulus G' response, Lis a function of temperature and strain amplitude, has been related to the structural transformation into the hexagonal phase of cylindrical micelles. Results demonstrate a characteristic critical behavior at the phase transition boundary T = T,. However, we also find that the rheological signature of the ordering phase transition crucially depends on the particular dynamical mode applied to the sample. Stress-strain variation reflects the shear-induced alignment of the principle column axis, which results in the two-dimensional melting of hexagonal order and the onset of creep flow above a threshold strain epsilon*.