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

Abstract

The temperature dependent rheological and structural behavior of a long-chain C(16)E(4) (tetraethylene glycol monohexadecyl ether) surfactant in D(2)O has been studied within the regime of low shear range. In the absence of shear flow, the system forms a lamellar liquid crystalline phase at relatively high temperatures. The present paper reports on the shear-induced multi-lamellar vesicle (MLV) formation in C(16)E(4)/D(2)O at 40 wt.% of surfactant in the temperature range of 40-55 °C. The transition from planar lamellar structure to multi-lamellar vesicles has been investigated by time-resolved experiments combining rheology and nuclear magnetic resonance (rheo-NMR), rheo small-angle neutron scattering (rheo-SANS) and rheometry. The typical transient viscosity behavior of MLV formation has been discovered at low shear rate value of 0.5s(-1).

Rheochaos and flow instability phenomena in a nonionic lamellar phase

“…A viscous gel containing both MLVs and planar lamellae was obtained by pre-shearing the lamellar phase of the C 16 E 4 -D 2 O system at a constant shear rate of 1 s À1 for 1 hour. 26,38 Aer this pre-shear, an unstable temporal viscosity behaviour was observed applying a shear rate of 2 s À1 to the system. In Fig.…”

“…viscosity oscillations in time, and vorticity banding in a concentrated system of C 16 E 4 in D 2 O at 40 C. The oscillating viscosity is the "steady state" at the applied shear rates of 2, 5 and to a lesser degree 10 s À1 . Previously, partial MLV formation has been reported at a shear rate of 0.5 s À1 for C 16 E 4 , 26,38 where shear thickening behavior was observed. The transition leads to the formation of a viscous gel containing MLVs.…”

“…In these cases MLVs can be hexagonally packed into layers that slide relative to each other under shear ow and the corresponding small-angle neutron, X-ray and light scattering (SANS, SAXS, and SALS) patterns have hexagonal symmetries. [21][22][23][24][25][26][27][30][31][32][33][34][35][37][38][39] Experiments show sustained temporal oscillations in surfactant mesophases and solutions 17,18,42,43 and polymer solutions, 44 while erratic temporal responses have been found both in these and in related materials, e.g., wormlike micelles, [45][46][47] lamellar phases 42,43 and colloids. 48,49 There are some indications 4,8,9,18 that these erratic signals result from a deterministic chaotic dynamics.…”

Ferrihydrite nanoparticles entrapped in shear-induced multilamellar vesicles

“…CnEm surfactants are well known to form planar lamellar phase (Lα) morphology [13] even in mixed systems, [14] which under shear flow collapse into multilamellar vesicle (MLV) morphology; this is known as the Lα-to-MLV transition. [15][16][17][18][19] The d-spacing, i.e. layer spacing of the lamellae, for pure C12E4 at 40 wt.% in D2O is 6.8 nm.…”

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.…”