Dynamics of bicontinuous microemulsion phases with and without amphiphilicblock-copolymers

Neutron Spin Echo and Dynamic Light Scattering techniques are used for an e xtensive investigation of the bicontinuous phase in water/decane microemuls ions. The dynamical behavior of different surfactant systems, decyl polygly col ether (C10E4), C10E4 mixed with polyethylenepropylene/polyethyleneoxide amphiphilic block-copolymers-(PEPx/PEOy), and sodium-bisethylhexylsulfosuc cinate (AOT) is investigated under comparable conditions. At scattering wav e numbers q large compared to the inverse of the structure length scale, q( 0)=2 pi /d, always stretched exponential relaxations proportional toe(q)(-( Gamma)t)(beta) with Gamma (q)proportional toq(3) are found, as predicted th eoretically. The relaxation rate increases almost linearly as function of t he bicontinuous structure correlation scale-xi similar or equal tod/2. The apparent bare bending modulus kappa determined by fitting theoretical predi ctions to the experimental high-q data yields values of about 1.3k(B)T-as i nferred from previous small angle neutron scattering (SANS) studies and fro m other methods. The effect of increasing rigidity of the surfactant layers by anchoring amphiphilic block-copolymers, predicted theoretically and rev ealed experimentally in structural investigations, could not be clearly res olved due to its small influence on the dynamics. At structural length scal es, the relaxation rate in water-oil contrast shows a minimum corresponding to the maximum of the static structure factor. At length scales much large r than the typical structure length the relaxation is single-exponential wi th a q(2) dependent rate. In this regime we find indications of the additio nal membrane interaction due to the presence of block-copolymers. (C) 2001 American Institute of Physics.