Nonuniversal Critical Behavior of Micellar Solutions

The critical behavior of two nonionic-amphiphile solutions showing a lower consolution point is investigated by laser-light scattering. The critical exponents $\gamma$ and $\nu$ take the values $\gamma =1.15\mathrm{}$ and $\nu =0.57\mathrm{}$ for the system ${\mathrm{H}}_2$O-${\mathrm{C}}_8$ ${\mathrm{Et}}_4$, and $\gamma =0.90\mathrm{}$ and $\nu =0.44\mathrm{}$ for ${\mathrm{H}}_2$O-${\mathrm{C}}_{12}$ ${\mathrm{Et}}_8$. Both sets of values are different from those previously found with the system ${\mathrm{H}}_2$O-${\mathrm{C}}_{12}$ ${\mathrm{Et}}_6$. The description of the observed nonuniversality of critical micellar solutions may require three-dimensional models which exhibit continuously varying critical exponents.