Dynamical fluctuation of the mesoscopic structure in ternary C12E5-water-n-octane amphiphile system - art. no. 041402

Dynamical fluctuations of the bicontinuous microemulsion and lamellar struc tures in ternary C12E5-water-n-octane amphiphilic system are studied by mea ns of neutron spin echo (NSE) spectrometry. The decay rates of the time cor relation of the concentration were analyzed in terms of three theories: (1) A. G. Zilman and R. Granek. Phys. Rev. Lett. 77, 4788 (1996), (2) M. Nonom ura and T. Ohta, J. Chem. Phys. 110, 7516 (1999), and (3) R. Granek and M. E. Cates, Phys. Rev. A 46, 3319 (1992), in the first of which a Langevin eq uation for membrane plaquettes and in the latter two of which time-dependen t Ginzburg-Landau equations for the order parameters are considered. The re sult shows that the intermediate correlation functions I(q,t) for the range s of 0<t<15 ns and 0<q<0.2 Angstrom (-1) are well fitted to a stretched exp onential function in time, I(q,t) = exp[-(Gammat)(2/3)], for the bicontinuo us microemulsion and the lamellar phases of the same systems with the relax ation rate Gamma increasing as q(3) in agreement with theory (1) from which the bending modulus of the membrane kappa was estimated. For more restrict ed ranges of 0<t<5 ns and 0.05<q<0.15 Angstrom (-1) the NSE result can be e xpressed by an exponential function in time in agreement with theory (2) de termined exclusively by hydrodynamic interactions and for extended range of 0<t<10 ns and 0.03<q<0.15 Angstrom (-1) by a nonexponential function in ag reement with theory (3), from both of which the effective viscosities eta ( 0) and eta (eff) of the system were estimated. The effective viscosity from the nonexponential eta (eff) is five times greater than that from the simp le exponential eta (0) that is almost the same as the literature value. The implication of this result is discussed in terms of the effective viscosit y eta (eff) that takes into account the renormalization of the bending modu lus of the membrane.