Shear-induced structural transition in a lyotropic lamellar phase studied using small angle neutron and light scattering

Abstract

We study the effects of shear flow on structures of the lamellar phase formed in a nonionic surfactant C 16 E 7 (hepta(oxyethylene glycol)-n-hexadecylether)/D 2 O system by using small angle neutron scattering (SANS) and small angle light scattering (SALS) in the range of shear rate 10 −3-30 s −1. As the shear rate increases from 0.3 to 1 s −1 , the lamellar repeat distance for the 48 wt% sample is decreased significantly and discontinuously. With further increase in the shear rate, d increases through a sharp minimum at 1 s −1. The minimum value does not depend on the surfactant concentration very much and is nearly equal to the thickness of the bilayers. At this shear rate (1 s −1), the intensity of the polarized SALS is strongly enhanced in the small angle region in the vorticity direction. These results suggest that water layers are excluded by shear flow and that large concentration fluctuations on the µm scale are induced, which corresponds to local segregation into two regions; one of these has concentrated lamellar structures and the other is a water-rich region. As the shear rate increases further (to 3 s −1), a broad diffraction peak appears in the vorticity direction in the polarized SALS whereas a four-lobe pattern is observed in the depolarized SALS. There results, together with the two-dimensional SANS pattern, suggest the formation of close-packed onions elongated along the flow direction at 3 s −1. Comparison is made with the study of Nettesheim et al (2003 Langmuir 19 3618) who report the formation of multilamellar cylinders as intermediate structures, between lamellae and spherical onions.

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

“…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].…”

Shear-induced structural transition in the lamellar phase of the C16E7/D2O system. Time evolution of small-angle neutron scattering at a constant shear rate

“…In the previous study (Kato et al, 2004(Kato et al, , 2005, we measured SANS and SALS on the lamellar phase of a nonionic surfactant C 16 E 7 [a surfactant having a chemical formula C n H 2n+1 (OC 2 H 4 ) m OH is abbreviated as C n E m ] in D 2 O at 40, 48 and 55 wt% at 340 K in the range of shear rate 10 À3 -10 s À1 , which is lower than in other published studies. We have found a significant decrease in the lamellar repeat distance (d) at shear rates of 0.3-1 s À1 .…”