Order−Disorder Transition of Nonionic Onions under Shear Flow

Abstract

We have investigated the shear-induced ordering of multilamellar vesicles (onions) in a nonionic surfactant (C(12)E(4)) system using a small-angle light scattering (shear-SALS) and a small-angle X-ray scattering (shear-SAXS) technique. In a narrow shear rate-temperature space, the onions form a two-dimensional (2D) hexagonally close-packed structure that shows characteristic hexagonal scattering patterns in both SALS and SAXS. In the dynamic phase diagram, the ordered onion phase is surrounded by disordered onion phase, indicating reentrant behavior against the temperature. The disorder-order transition is accompanied by a jump in onion size by a factor of 5-6. In the disordered onion phase, by applying a shear flow, the planar lamellar membranes transform to an intermediate structure, multilamellae cylinders or a coherent stripe buckling, and then the intermediate structure develops to the isotropic onions. On the other hand, in the ordered onion phase, the intermediate structure breaks to onions stretched in the shear velocity direction, and then the stretched onions aligned gradually to form the 2D hexagonal close packing.

Transient and Steady-State Shear Banding in a Lamellar Phase as Studied by Rheo-NMR

“…% surfactant [16,27,[29][30][31][32][33][34][35][36][37][37][38][39][40][41][42][43], although shear-induced MLVs can be found in all surfactants of the C n E m type studied so far [26,28,33,[44][45][46][47][48][49][50][51][52][53][54][55]. The shear diagram of C 10 E 3 /water (40 wt.…”

Multi-lamellar vesicle formation in a long-chain nonionic surfactant: C16E4/D2O system

“…An example is the stability of multi-lamellar vesicles (MLVs) upon shearing and temperature variations [11,12]. Knowledge about the MLV formation mechanism is important for various applications, which often depend on the viscosity and rely on the vesicle structures.…”

“…Shear-induced MLVs can be stable for a long time, but they do not correspond to the thermodynamic equilibrium structure of the lamellar system [15][16][17][18]. Combining different structural techniques such as X-ray, neutron and light scattering, and NMR (all of these rheo tools equipped), make it possible to investigate fluid structures under flow like MLVs [1][2][3] and to determine their characteristic dimensions [10][11][12]18,20,[22][23][24][25][26][27][28][29][30].…”

“…Within this phase region, a relatively limited area exists where MLVs can be formed by shear. Although a large literature on MLV formation in C n E m (with n = 10 or 12) water systems has been produced [9,11,12,15,[18][19][20][21][22][23]26], not so much attention has been given to the study of the long-chain systems (i.e. n = 16) [28,29].…”

Homogeneous length scale of shear-induced multilamellar vesicles studied by diffusion NMR

“…Generally, the vesicle radius decreases with the shear rate; it is often approximately proportional to the square root of the inverse rate [2,14]. Sometimes the polydispersity of the MLV size is so low that periodic structures are formed [13,[15][16][17][18]. However, the simple picture of densely packed spheres is misleading since there are no solvent-filled voids in the system; electron microscopy has shown that space is completely filled by the lamellar phase and that the onions have polyhedral shape [19].…”