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

Abstract

The properties of bicontinuous microemulsions, consisting of water, oil and a surfactant, depend to alarge extent on the bending moduli of the surfactant containing oil–water interface. In systems withCiEj as surfactant these moduli can be modified by the addition of diblockcopolymers (boosting effect) and homopolymers (inverse boosting effect)or a combination of both. The influence of the addition of homopolymers(PEPX and PEOX, X = 5 or 10 kg/mol molecular weight) on the structure, bending modulus and dynamics of the surfactantlayer is studied with small angle neutron scattering (SANS) and neutron spin-echospectroscopy (NSE). Besides providing information on the microemulsion structure, neutronscattering is a microscopic probe that can be used to measure the local bending modulusκ. The polymer addition gives access to a homologous series of microemulsions with changingκ values. We relate the results obtained by analysis of SANS to those from NSEexperiments. Comparison of the bending moduli obtained sheds light on the differentrenormalization length scales for NSE and SANS. Comparison of SANS and NSE derivedκ values yields a consistent picture if renormalization properties are observed.Finally a ready to use method for converting NSE data into reliable values forκ is presented.