Confinement of polysoaps in membrane lyotropic phases

We study the confinement of polysoaps in lyotropic smectic (L_α) and sponge (L₃) solutions of the nonionic surfactant pentaethylene glycol dodecyl ether (C₁₂EO₅). The polysoap is a hydrophobically modified polymer with n-tetradecyl sidegroups randomly grafted to a polyacrylate backbone. Without the hydrophobic side chains the backbone polymer cannot be embedded into the intermembrane space, but confinement is achieved for a polysoap with as low as 1% of grafted groups. We measure by small angle x-ray and neutron scattering an increase of the bending rigidity of the lamellar membranes as a function of polysoap concentration.