title: Persistence of birefringence in sheared solutions of wormlike micelles.
abstract: When aqueous solutions containing wormlike micelles (worms) are sheared, the micellar chains tend to align with the flow, which in turn leads to flow-birefringence. When shear is stopped, the worms rapidly revert to an isotropic state in typical samples, and the birefringence disappears. In this study, we present a system of cationic worms that shows a different behavior: not only do the samples become intensely birefringent when sheared but the birefringence also persists for hours (and even days) after shear is stopped. These results suggest that shear-aligned worms in the sample are trapped in their aligned state for long periods of time, an aspect that is confirmed by cryo-transmission electron microscopy (cryo-TEM). We seek to determine the origin of this unusual behavior. Our results show that the persistent birefringence is observed for cationic worms induced by hydroxy-naphthoate but not salicylate counterions. These observations suggest that the micellar alignment is stabilized by intermicellar attractive interactions (such as pi-pi and cation-pi) that arise when large aromatic counterions are anchored within the micelles.
authors.affiliation: Department of Chemical & Biomolecular Engineering, University of Maryland, College Park, Maryland 20742-2111, USA.
authors.forename: Bradley D
authors.initials: BD
authors.lastname: Frounfelker
authors.forename: Gokul C
authors.initials: GC
authors.lastname: Kalur
authors.forename: Bani H
authors.initials: BH
authors.lastname: Cipriano
authors.forename: Dganit
authors.initials: D
authors.lastname: Danino
authors.forename: Srinivasa R
authors.initials: SR
authors.lastname: Raghavan
mesh_terms: D020285:Cryoelectron Microscopy; D008027:Light; D008823:Micelles; D046529:Microscopy, Electron, Transmission; D012212:Rheology; D012542:Scattering, Radiation; D012996:Solutions
chemical_list: D008823:Micelles; D012996:Solutions