Bending moduli of microemulsions; comparison of results from small angle neutron scattering and neutron spin-echo spectroscopy

The properties of bicontinuous microemulsions, consisting of water, oil and a surfactant, depend to a large extent on the bending moduli of the surfactant containing oil-water interface. In systems with C(i)E(j) as surfactant these moduli can be modified by the addition of diblock copolymers (boosting effect) and homopolymers (inverse boosting effect) or a combination of both. The influence of the addition of homopolymers (PEP(X) and PEO(X), X = 5 or 10 kg/mol molecular weight) on the structure, bending modulus and dynamics of the surfactant layer is studied with small angle neutron scattering (SANS) and neutron spin-echo spectroscopy (NSE). Besides providing information on the microemulsion structure, neutron scattering is a microscopic probe that can be used to measure the local bending modulus K. The polymer addition gives access to a homologous series of microemulsions with changing K values. We relate the results obtained by analysis of SANS to those from NSE experiments. Comparison of the bending moduli obtained sheds light on the different renormalization length scales for NSE and SANS. Comparison of SANS and NSE derived K values yields a consistent picture if renormalization properties are observed. Finally a ready to use method for converting NSE data into reliable values for K is presented.