Interaction of hydrophobically modified polymers and surfactant lamellar phase

We investigate the effect of polysoaps on the phase behavior and membrane e lastic properties of the lyotropic lamellar (L-alpha) phase of the nonionic surfactant penta(ethylene glycol) dodecyl ether (C12E5). The polysoap is a hydrophobically modified polymer (hm-polymer) with n-alkyl side groups ran domly grafted to a polyacrylate (PAA) backbone. The membrane properties are extracted from small-angle neutron scattering data based on a model develo ped by Nallet et al. and the excess area method developed by Roux et al. Th e phase behavior, membrane rigidity, compression modulus, and bilayer mean bending modulus are found to be independent of molecular weight, polydisper sity, and hydrophobe length of hm-polymers. The rigidity and compression mo duli of membranes increase with increasing polymer concentration and hydrop hobe substitution level. A minimum hydrophobic interaction strength (combin ation of hydrophobe length and hydrophobe substitution level) is required t o produce single phase polysoap/lamellar surfactant systems. A scaling mode l is proposed that defines the boundaries between homogeneous and biphasic solutions based on two criteria: (1) the surface coverage of chain segments between hydrophobus (i.e. blobs) must be less than the available membrane area and (2) the interlamellar spacing must be larger than the blob size. T his simple model captures the essential features of the phase diagrams.