“…A coverage ≈ # chains volume blobs chain area blob In this study, a model proposed by Nallet et al 35 was used to obtain η, d, and δ, with the details addressed elsewhere. 7,36 The Caille ´constant η and the interlamellar distance d are extracted from the structure factor S(q), while form factor P(q) yields the membrane thickness δ. The fitted membrane thickness δ of 24 ( 2 Å remains unchanged for all the samples studied, which is consistent with our previous observation.…”
We study the effect of hydrophobically modified polymers (hm-polymers) on the phase behavior and membrane elastic properties of the lyotropic lamellar (LR) phase of the nonionic surfactant penta(ethylene glycol) dodecyl ether (C12E5). The hm-polymer is a model comb-graft polymer with monodisperse PEG blocks (loops) of 6, 12, or 35 kg/mol connecting C18 stearylamide hydrophobes. The polymer is of interest because both its loops and hydrophobes are biocompatible. The membrane properties are extracted from the small-angle neutron scattering data based on the model of Nallet et al. The monophasic LR region exists over a narrower membrane volume fraction range but to a higher polymer concentration for hmPEGs with larger PEG spacers. The rigidity of the membranes increases by 40% with decreasing PEG spacer size from 12 to 6 kg/mol or increasing polymer concentration. For hmPEG polymers with 2-3 loops, the effect of finite chain lengths plays a role on the phase behavior and membrane properties.
“…A coverage ≈ # chains volume blobs chain area blob In this study, a model proposed by Nallet et al 35 was used to obtain η, d, and δ, with the details addressed elsewhere. 7,36 The Caille ´constant η and the interlamellar distance d are extracted from the structure factor S(q), while form factor P(q) yields the membrane thickness δ. The fitted membrane thickness δ of 24 ( 2 Å remains unchanged for all the samples studied, which is consistent with our previous observation.…”
We study the effect of hydrophobically modified polymers (hm-polymers) on the phase behavior and membrane elastic properties of the lyotropic lamellar (LR) phase of the nonionic surfactant penta(ethylene glycol) dodecyl ether (C12E5). The hm-polymer is a model comb-graft polymer with monodisperse PEG blocks (loops) of 6, 12, or 35 kg/mol connecting C18 stearylamide hydrophobes. The polymer is of interest because both its loops and hydrophobes are biocompatible. The membrane properties are extracted from the small-angle neutron scattering data based on the model of Nallet et al. The monophasic LR region exists over a narrower membrane volume fraction range but to a higher polymer concentration for hmPEGs with larger PEG spacers. The rigidity of the membranes increases by 40% with decreasing PEG spacer size from 12 to 6 kg/mol or increasing polymer concentration. For hmPEG polymers with 2-3 loops, the effect of finite chain lengths plays a role on the phase behavior and membrane properties.
“…Plotting q 4 I(q) highlights the maximum in form factor (once the incoherent background scattering has been subtracted), from which we estimate a bilayer thickness δ ) 24 ( 2 Å that is independent of polymer molecular weight, polydispersity, and polymer concentration. 39 The compressibility of the membrane stack is reflected in the low q behavior of the structure factor S(q) obtained from the experimental scattering intensity I(q) from eq 6. The structure factor S(q), form factor P(q), and scattering intensity I(q) are shown in Figure 4.…”
Section: Neutron Scattering Studies Of Membrane Propertiesmentioning
We investigate the effect of polysoaps on the phase behavior and membrane elastic properties of the lyotropic lamellar (LR) 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 randomly grafted to a polyacrylate (PAA) backbone. The membrane properties are extracted from small-angle neutron scattering data based on a model developed by Nallet et al. and the excess area method developed by Roux et al. The phase behavior, membrane rigidity, compression modulus, and bilayer mean bending modulus are found to be independent of molecular weight, polydispersity, and hydrophobe length of hm-polymers. The rigidity and compression moduli of membranes increase with increasing polymer concentration and hydrophobe substitution level. A minimum hydrophobic interaction strength (combination of hydrophobe length and hydrophobe substitution level) is required to produce single phase polysoap/lamellar surfactant systems. A scaling model is proposed that defines the boundaries between homogeneous and biphasic solutions based on two criteria: (1) the surface coverage of chain segments between hydrophobes (i.e. blobs) must be less than the available membrane area and (2) the interlamellar spacing must be larger than the blob size. This simple model captures the essential features of the phase diagrams.
“…The permeability of the PAA layer can be estimated by D ∼ η L /(2.1 × 10 12 ω 3/2 ), with ω being the mass fraction of polymer in the brush layer . The Young's modulus E is related to the bending modulus κ by κ = E δ 3 /12(1 − ν m 2 ), where ν m is the Poisson ratio of the surfactant membrane, which is ∼0.5 assuming the membrane is incompressible. , For the hmPEG-doped membrane system at φ = 0.3 and C p = 2 wt %, the estimated hydrodynamic relaxation time τ hyd for solvent to flow through the polymer layer is ∼900 ns, assuming the bending modulus κ ∼ 1 k B T . ,, This time scale is again comparable to that of the relaxation of polymer-doped membranes, which supports the hypothesis of slowed dynamics due to viscous dissipation in the adsorbed polymer layer. 8 The measured values of d φ vs ln φ over the whole dilution range for (a) the hmPAA systems with different surface coverages and (b) the hmPEG system.…”
Section: Resultsmentioning
confidence: 97%
“…At this point, we propose the following physical model. There are two possibilities for the “speeding up”: (1) Polymers make the membrane stiffer, ,, and therefore the relaxations are faster (as predicted from the dispersion relation for membrane undulations, Γ q ∝ κ , ) (Figure a). (2) There is a coupling between lateral polymer diffusion on the membrane surface and the relaxation of undulations in the low surface coverage case.…”
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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
