We characterize the effect of adsorbed hydrophobically modified polymers (hm-polymers) on the dynamics of surfactant bilayers by small-angle neutron scattering and neutron spin-echo spectroscopy. Two kinds of hm-polymers, (a) hydrophobically modified poly(acrylate) with tetradecyl (C14) sidegroups randomly grafted to the poly(acrylate) backbone and (b) poly(PEG6k-lysine-stearylamide) with equally spaced hydrophobes, are added to bilayers of penta(ethylene glycol) dodecyl ether (C12E5) and hexanol. Both bare and polymer-doped membranes exhibit a stretched exponential relaxation in the form of S(q→,t) ≅ S(q→) exp[-(γqt)2/3], where S(q) is the static structure factor and γq is the relaxation rate. The relaxation rate depends subtly on the surface coverage of polymer. At high surface coverage, polymer slows down the relaxation by 20%, whereas at low surface coverage, polymer enhances the rate relative to that of the bare membranes. Hindered flow of solvent through the adsorbed polymer layer at high coverage appears to explain the retardation. The faster dynamics at low polymer coverage may be due to stiffening of the membrane or lateral diffusion of the dilute adsorbed polymer chains.
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Condensed Matter Physics
- Surfaces and Interfaces