Effect of Hydrophobically Modified Polymers on Shear-Induced Multilamellar Vesicles

Abstract

The effects of polymer concentration, polymer molecular weight, and hydrophobe substitution level of modified poly(acrylic acid) polymers on the formation, size, and viscoelastic properties of shear-induced multilamellar vesicles (onions) are studied by rheology and light diffraction. The onions are close-packed, space-filling vesicles formed by shearing aqueous lamellar phases of C12E5 surfactant to produce phases with sufficient order and size uniformity (O(1-3 microm)) to diffract light. The addition of hydrophobically modified polymers enhances the rate of formation, uniformity, and stability independent of hydrophobe substitution level. Onion size decreases with increasing shear rate as observed for pure surfactant onion systems, but the shear-rate dependence is changed by the polymer. The onion phase has a plateau modulus that increases with polymer concentration but is independent of hydrophobe substitution level or molecular weight. The model presented by Panizza et al. that relates the plateau modulus of the onion phase to membrane rigidity and the compression modulus is consistent with independent measurements of membrane properties from SANS.

Shear-induced onion formation of polymer-grafted lamellar phase

“…5. Weak shear effect on the onion radius was also observed for the hydrophobically modified polymer-grafted lamellar systems by Yang et al 26 As X P is increased, the four-leaf pattern eventually vanishes at X P ¼ 1.2%. The shear-thinning behavior at X P ¼ 1.2% in Fig.…”

“…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.…”

“…25 In such systems, additives obviously influence the shear-induced onion phase formation behavior. [26][27][28][29][30] Berghausen et al presented that the addition of hydrophobically modified polymers suppresses the shear-induced onion phase formation of ionic surfactant systems. 27 We have also previously observed the same behavior for a polymer-grafted lamellar phase composed of amphiphilic triblock copolymer, Pluronic P123, and nonionic surfactant C 10 E 3 .…”

“…31 On the contrary to these results, Yang et al showed that the shearinduced onion formation is accelerated for a hydrophobically modified polymer-grafted lamellar phase compared to the polymer-free lamellar phase. 26 Anomalously, it has also been reported that grafting amphiphilic polymer chains onto the membrane causes the onion structure even without shear. 25,32,33 Such puzzling behavior motivated us to study the effect of polymers grafted onto the membrane on the shear-induced onion formation behavior systematically.…”

Shear-Induced Structural Transition and Recovery in the Salt-Free Catanionic Surfactant Systems Containing Deoxycholic Acid

“…Shear flow has been well-known to have a strong influence on complex fluids, especially the self-assembled structures of surfactants − or polymers − in solutions, because the import of a mechanical force can alter the structure of aggregates. Thus it has attracted growing interest over decades from both theoretical and experimental viewpoints.…”