Dynamics of bicontinuous microemulsion phases with and without amphiphilic block-copolymers.

Neutron Spin Echo and Dynamic Light Scattering techniques are used for an extensive investigation of the bicontinuous phase in water/decane microemulsions. The dynamical behavior of different surfactant systems, decyl polyglycol ether (C[sub 10]E[sub 4]), C[sub 10]E[sub 4] mixed with polyethylenepropylene/polyethyleneoxide amphiphilic block-copolymers-(PEP[sub x]/PEO[sub y]), and sodium-bisethylhexylsulfosuccinate (AOT) is investigated under comparable conditions. At scattering wave numbers q large compared to the inverse of the structure length scale, q[sub 0]=2π/d, always stretched exponential relaxations ∝e[sup -(Γ[sub q]t)[sup β]] with Γ[sub q]∝q[sup 3] are found, as predicted theoretically. The relaxation rate increases almost linearly as function of the bicontinuous structure correlation scale—ξ=d/2. The apparent bare bending modulus κ determined by fitting theoretical predictions to the experimental high-q data yields values of about 1.3k[sub B]T—as inferred from previous small angle neutron scattering (SANS) studies and from other methods. The effect of increasing rigidity of the surfactant layers by anchoring amphiphilic block-copolymers, predicted theoretically and revealed experimentally in structural investigations, could not be clearly resolved due to its small influence on the dynamics. At structural length scales, the relaxation rate in water–oil contrast shows a minimum corresponding to the maximum of the static structure factor. At length scales much larger than the typical structure length the relaxation is single-exponential with a q[sup 2] dependent rate. In this regime we find indications of the additional membrane interaction due to the presence of block-copolymers. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]