Experimental determination of bending rigidity and saddle splay modulus in bicontinuous microemulsions

Elastic properties of surfactant membranes can be described in terms of the bending rigidity [small kappa] and the saddle splay modulus [small kappa, Greek, macron]. Phase diagram measurements and neutron scattering experiments allowed the determination of these parameters. Recent simulations showed that the bending rigidity, which is deduced from the characteristic length scales in the microemulsion, is a mixture of [small kappa, Greek, macron] and [small kappa]. By combining neutron spin echo (NSE) spectroscopy, small angle neutron scattering (SANS) and phase diagram measurements, we show that also experimentally the different contributions can be separated. For supercritical CO2 microemulsions and bicontinuous microemulsions with additives, the prefactors of the [small kappa, Greek, macron] and [small kappa] contributions are determined and compared to those from simulations.