Dynamical Properties of Decorated Lamellar Microemulsions in the Brush Regime

Abstract

The elastic constants of bicontinuous microemulsions, consisting of water, oil (decane) and a surfactant, can be modified by the addition of diblock-copolymers (boosting effect). A similar decoration of the surfactant membrane is possible in the lamellar phase. At high diblock copolymer densities, in the brush regime, a change in the dependence of the bending rigidity on the molecular size and concentration of the diblock copolymer is predicted theoretically. In particular a very strong dependence of the bending rigidity on the radius of gyration of the diblock copolymer (κ ∝ R⁵) is predicted. We have studied the structure and dynamics of lamellar microemulsions by small angle neutron scattering (SANS) and neutron spin echo spectroscopy (NSE) in the brush regime, with high diblock copolymer density. Decyl polyglycol ether (C₁₀E₄) has been used as surfactant, the amphiphilic diblock-copolymers were polyethylenepropylene/polyethyleneoxide (PEP₅–PEO₅). The influence of the diblock copolymer concentration when entering the brush regime on the bending rigidity κ and the correlation length ξ will be discussed.