Structural transitions induced by shear flow and temperature variation in a nonionic surfactant/water system

In this study, we investigate structural transitions of tetraethylene glycol monohexadecyl ether (C16E4) in D2O as a function of shear flow and temperature. Via a combination of rheology, rheo-small-angle neutron scattering and rheo-small-angle light scattering, we probe the structural evolution of the system with respect to shear and temperature.Multi-lamellar vesicles, planar lamellae, and a sponge phase were found to compete as a function of shear rate and temperature, with the sponge phase involving the formation of a new transient lamellar phase with a larger spacing, coexisting with the preceding lamellar phase within a narrow temperature–time range.The shear flow behavior of C16E4 is also found to deviate from other nonionic surfactants with shorter alkyl chains (C10E3 and C12E4), resembling to the C16E7 case, of longer chain.

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► Dynamic phase diagram of the 40 wt.% C16E4/D2O system.
► Rheo-SANS, rheo-SALS, and rheology elucidate the shear-induced transitions.
► Intermediate lamellar phase of larger d-spacing (Lα+) in coexistence with the initial short d-spacing (Lα).
► The bending modulus (bilayer bending rigidity) as a parameter that governs the lamellar-to-MLV transition.