Spatially Resolved Concentration and Segmental Flow Alignment in a Shear-Banding Solution of Polymer-Like Micelles

Abstract

We measure the spatially resolved microstructure and concentration in the plane of flow for a viscoelastic solution of polymer-like micelles comprised of mass fraction 6.0% (volume fraction 6.6%) solution of 2:1 molar ratio cetylpyridinium chloride/sodium salicylate in 0.5 mol/L NaCl/D2O through the shear banding transition. Spatially resolved flow small-angle neutron scattering measurements in the velocity–velocity gradient (1–2) plane of flow establish the local microstructure, and scanning narrow-aperture flow ultrasmall-angle neutron scattering (SNAFUSANS) measurements indicate no flow-induced concentration gradients within measurement accuracy. These results show shear banding in this solution is not associated with an isotropic–nematic transition and are fundamentally important for validating models of shear-banding complex fluids. Improvements in the SNAFUSANS method are also documented.

Effect of the salt-induced micellar microstructure on the nonlinear shear flow behavior of ionic cetylpyridinium chloride surfactant solutions

“…In Fig. 6 Recent scanning narrow-aperture flow ultrasmall-angle neutron scattering experiments have demonstrated that the formation of shear bands is connected to the strong alignment of micelles at the rotating wall, where they align along the flow direction and form a high shear rate band, whereas the remaining region is composed of less ordered micelles, constituting the lower shear rate band [10,26,46]. This is exemplified by butterflylike patterns as observed earlier by Refs.…”

“…Macroscopically, this phenomenon consists in a transition from a homogeneous to an inhomogeneous state characterized by a shear rate independence of the shear stress on * danila.gaudino@unina.it the macroscopic shear rate [22,23]. Microscopically, shear banding is related to the coexistence of a paranematic band and a quasi-isotropic one, where micelles are aligned along the flow direction and entangled as in the quasi-quiescent state, respectively [19,[24][25][26]. It must be stressed that, although shear banding has been widely observed, a definitive physical explanation, in particular of the microscopic mechanisms leading to shear banding development, is still missing.…”

Rheology of branched wormlike micelles

“…This is shown for long, linear, entangled WLMs in Fig. 2, [25]. However, as the angular frequency approaches the inverse of the breaking time of the micelles, deviations from this simplistic behavior are observed.…”

“…Cole-Cole plot for a highly entangled solution of linear micelles of CPCL/NaSal showing the primary relaxation time and the breakage time[25].…”

The microstructure and rheology of a model, thixotropic nanoparticle gel under steady shear and large amplitude oscillatory shear (LAOS)

“…As the structure of this flowing microstructure cannot be deduced solely from interpreting scattering data in the 1-3 plane as demonstrated and noted in this prior literature, additional measurements in the plane of flow (the 1-2 plane) are made to understand the nature of the effects of shear on the local microstructure under flow. This is performed using a recently developed novel sample environment for SANS under flow ; Gurnon et al (2014b); Liberatore et al (2006); Gurnon et al (2014c)]. …”