Influence of a Triblock Copolymer on Phase Behavior and Shear-Induced Topologies of a Surfactant Lamellar Phase

Abstract

The influence of a triblock copolymer, poly(ethylene oxide)20-b-poly(propylene oxide)70-b-poly(ethylene oxide)20 (Pluronic P123) on the phase behavior and on the shear-induced multilamellar vesicle (MLV, also called Onion) formation in the lyotropic lamellar phase of the nonionic surfactant C10E3 was investigated by means of rheology, small-angle neutron scattering (SANS), and microscopy. Added triblock copolymer shifted the Lalpha-L3 phase transition to lower temperatures. In the presence of triblock copolymer, MLV structure was not stable and easily transformed back into the lamellar phase with increasing polymer concentration and temperature. In the study of the shear-induced MLV formation, we found an increase of the critical shear rate for the onset of the shear-thickening, which also indicates the instability of MLV in the presence of the triblock copolymer. No MLV formation was observed at high polymer concentration. Suppression of the shear-induced MLV formation might be attributed to the enhancement of the effective surface tension originating from the excluded volume effect between polymers adsorbed onto the membranes.

Structural rheology of composite onion phase

“…In fig. 2, transient viscosity at different γ are summarized as a function of the applied shear strain γ = γ t. Transient viscosity increases with double steps as already reported [9,19,31,33]. The double step behavior gradually softens and disappears as γ is increased.…”

“…As the shear rate is increased, shear-thickening behavior appears at γ = 3s -1 . It is known that appearance of the shear-thickening is a sign of the onion phase formation [8,9,[17][18][19][20][21]. In the microscope image at γ = 3s -1 , one can see a tile-like pattern consisted of maltese cross which is a characteristic of the densely packed onion phase [1,20,31].…”

“…In their model, the shear-thickening behavior would be attributed to the buckling of membranes due to the effective lateral pressure. On the basis of their theory, the shear-induced onion phase formation has been studied from the viewpoint of structural development by the use of scattering and rheological methods [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. Richtering et al found intermediate structure, which can be either coherently buckled lamellar membranes, or multilamellar cylinder structure [9,11].…”

Shear-induced Onion Formation of Triblock Copolymer-embedded Surfactant Lamellar Phase

“…5,10,12) The oily streak is composed of focal conic domains (FCDs) which have negative Gaussian curvature, while the onion has a spherical form with positive Gaussian curvature. 6) As mentioned in Fig.…”

“…7,9) In this study, we use nonionic surfactant C 10 E 3 / Pluronic / H 2 O ternary lamellar systems as has been performed in our previous work. 5,10) We will control the concentration X P and degree of polymerization of hydrophobic PO part N PO of amphiphilic triblock copolymer with fixed degree of polymerization of hydrophilic EO part N EO~4 . Since the hydrophilic EO chain length N EO~4 is similar to that in C 10 E 3 , the effect from hydrophilic EO part can be negligible and hydrophobic PO part embedded into the bilayer influences.…”