Effect of shear on an onion texture
MacDiarmid Institute for Advanced Materials and Nanotechnology, School of Chemical and Physical Sciences, Victoria University of Wellington, New Zealand
* e-mail: Paul.Callaghan@vuw.ac.nz
Accepted: 31 August 2007
Published online: 6 November 2007
Lamellar systems are self-assemblies of surfactant molecules forming planar bilayers separated by layers of solvent. At sufficiently high shear rates, they are known to form spherical objects often referred to as onions. In this paper, we are concerned with the effect of shear on those multi-lamellar vesicles. We measure solvent diffusion by nuclear magnetic resonance (NMR) using a method which is sensitive to the time dependence of mean-squared displacements. This method, combined with NMR velocimetry, allows us to infer onion structure as a function of shear rate, identifying different regimes in which local viscosity is related to the onion size. The role of slip is examined and the stress dependence of wall slip velocities is determined.
PACS: 47.45.Gx Slip flows and accommodation – / 47.50.-d Non-Newtonian fluid flows – / 47.80.Jk Flow visualization and imaging – / 66.10.-x Diffusion and ionic conduction in liquids –
© EDP Sciences, Società Italiana di Fisica and Springer-Verlag, 2007