Anchoring vs bridging: new findings on polymer additives in bicontinuous microemulsions.

We show for the first time the effect of telechelic polymers as additives in bicontinuous microemulsions. We combined macroscopic observations of the phase behavior with microscopic measurements of the structure by small-angle neutron scattering (SANS) to recover the two elastic moduli, kappa and (kappa) over bar, namely the bending rigidity and saddle-splay modulus. On the basis of these results, we could classify the effect of telechelic polymers along with confinement, expressed as the ratio of the polymer end-to-end distance R-ee and the oil-water domain size d. Their unique property to anchor at two points in the membrane (bridging) acts like a switch from antibooster to booster of the surfactant efficiency (between low and ultralow confinement). In the region of medium confinement, all telechelic polymers are in the bridging configuration and we have a maximum of the boosting effect, while at high confinement, the reversed behavior is found where anchoring and/or bridging do not play any role anymore.