Neutron Spin−Echo Study of Dynamics of Hydrophobically Modified Polymer-Doped Surfactant Bilayers

Abstract

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 b,t) = S(q b) 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.

Shear-induced onion formation of polymer-grafted lamellar phase

“…Influence of the grafted polymers on the elastic properties has been carefully investigated by some researchers. [25][26][27]30,34,41,42,[46][47][48][49] It is known that grafting polymers enhances the bending modulus and the repulsive interaction between membranes. Castro-Roman et al explained the enhancement of the repulsive Helfrich interaction by renormalizing the thickness of polymer layer into an effective thickness of membranes.…”

Dynamics of small unilamellar vesicles

“…A particularly interesting parameter for the understanding of the bilayer elasticity is its thickness, and there are some studies investigating its influence [27][28][29][30][31] on the membrane rigidity. A study on bilayer vesicles assembled from amphiphilic diblock copolymers showed that the mean bending rigidity κ for large polymersomes scales with the hydrophobic membrane thickness to the power two.…”

Bending elastic properties of a block copolymer-rich lamellar phase doped by a surfactant: a neutron spin-echo study

“…hydrophobically modied polymers like PAA or PEG; 4,[11][12][13][14] amphiphilic poly(ethylene propylene)-poly(ethylene oxide) added to bicontinuous microemulsions; 10,15,16 and a triblock-peptide added to a lamellar phase.…”

“…Especially in the case of microemulsions neutron spin-echo (NSE) spectroscopy was found to be a useful tool to study the elastic moduli of such interfacial lms. 1,2 In this context layered structures formed by amphiphilic block copolymers and surfactants also received much attention in recent years [3][4][5] as polymer-lipid interactions play a key role in biological membranes and as mixtures of amphiphilic polymers and surfactants are found in a growing number of technical products. 6 The dynamic properties of these membranes are of particular interest and can be studied by NSE.…”

“…[7][8][9] In the past such studies were concentrated on the inuence of polymers on surfactant-rich membranes. 10 Three types of polymers have been considered: hydrophobically modied polymers like PAA or PEG; 4,[11][12][13][14] amphiphilic poly(ethylene propylene)-poly(ethylene oxide) added to bicontinuous microemulsions; 10,15,16 and a triblock-peptide added to a lamellar phase. 17 An important conclusion of these studies has been that the bending elastic modulus k, 18 which is of the order of k B T in such systems, increases with the amount of added block copolymer.…”