Opposite effect of salt on branched wormlike surfactant micelles with and without embedded polymer

Abstract

Linear rheology and small-angle neutron scattering were used to perform a comparative study of the influence of inorganic salt KCl on two types of branched wormlike micelles (WLMs) of anionic surfactant potassium oleate: with and without embedded polymer poly(4-vinylpyridine). In polymer-free system, enhanced screening of the repulsion of similarly charged headgroups of WLMs by salt induced the acceleration of the relaxation and the decline of the zero-shear viscosity as a result of the increase of the number of branching points. An opposite effect of salt was observed in polymer-containing WLMs, where it caused an increase of the zero-shear viscosity and the relaxation time. It may be due to the linking of different micelles by polymer molecules which is facilitated by enhanced screening of repulsion between WLMs by added salt. The data obtained demonstrate the benefits of application of the solutions containing WLMs with embedded polymer rather than polymer-free WLMs as thickening agents at high salt content.