Intermembrane spacing and velocity profiling of a lamellar lyotropic complex fluid under flow using x-ray diffraction

Abstract

We report on the use of x-ray diffraction as a means of extracting velocity profiles from a non-Newtonian complex fluid under laminar flow. In particular, we applied this technique to a concentrated undulating membrane system flowing through a cylindrical capillary tube. The intermembrane separation d was measured as a function of simple shear using a Couette flow cell. A logarithmic dependence of d as a function of the shear rate was observed, while there was a linear relationship between the fractional intermembrane spacing and the shear stress. Subsequent measurement of the system's intermembrane spacing as a function of position within the cylindrical flow pipe allowed for the calculation of a shear-rate profile within the capillary. Simple numerical integration then yielded an accurate velocity profile of the fluid flowing through the pipe. Both shear thickening and plug flow shear thinning profiles were observed.

Shear banding in a lyotropic lamellar phase. I. Time-averaged velocity profiles

“…This effect has been shown in a lot of lyotropic lamellar phases using neutron and x-ray diffraction [26,47]. In our system, as measured with neutron scattering, the smectic period changes sligthly over the range ofγ under study [26].…”

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

“…The minimum value of d is nearly equal to the thickness of the bilayers irrespective of the concentration, suggesting phase separation into concentrated lamellar and water-rich regions, although macroscopic phase separation could not be observed by the naked eye (the outer cylinder of the shear SANS cell is made of quartz). A reduction in the repeat distance by shear flow has been reported by several groups (Yamamoto & Tanaka, 1995;Idziak et al, 2001;Welch et al, 2002). In these experiments, however, the amount of reduction is only a few per cent of the initial repeat distance at rest.…”

Effects of shear flow on structures of lamellar phase in a nonionic surfactant/water system

“…This leads to a reduction in the ratio A s /A^and therefore in the repeat distance. In fact, the reduction of d by shear flow has been found experimentally [14,18,19]. In these studies, however, the ratio (d 0 -d)/d 0 (d 0 and d are the repeat distance at rest and under shear, respectively) is only a few %.…”

“…In the past 10 years, effects of shear flow on the structure of the surfactant lamellar phase have been studied extensively by using microscopy, NMR, and various kinds of scattering techniques. After the pioneering work of Roux and coworkers [2][3][4][5] who found the transformation from the lamellar phase to the multilamellar vesicles (onions), various types of shear effects have been reported: change in orientation of membranes [6][7][8], sponge-to-lamellar transformation [9,10], multilamellar-to-unilamellar vesicle transformation [11][12][13], reduction in the spacing [14][15][16][17][18][19], collapse of membranes [20], formation of multilamellar cylinders as intermediate structures between lamellar and onions [21][22][23][24], and formation of Ribbon phase [25]. These effects have been found for the shear rate of 1$5 · 10 3 s )1 .…”