title: On the mesoscopic origins of high viscosities in some polyelectrolyte-surfactant mixtures.
abstract: Oppositely charged polyelectrolyte (PE) surfactant mixtures allow the control of rheological parameters of a solution even at fairly low concentrations. For example, addition of 0.3 wt. % of anionic surfactant to a 1 wt. % solution of the polycation JR 400 increases the viscosity by 4 orders of magnitude. Recently, we could show that this increase is related to the formation of mixed, rod-like PE/surfactant aggregates which interconnect several polyelectrolyte chains [Hoffmann et al., Europhys. Lett. 104, 28001 (2013)]. In this paper, we refine our structural model of the aggregates to obtain a more consistent picture of their internal structure for different anionic surfactants. Combining small angle neutron scattering (SANS) and neutron spin-echo (NSE) allows us to determine the size of the aggregates. By comparing different contrasts, the internal structure of the aggregates can be elucidated and it is seen that the PE in the aggregates retains a relatively high freedom of movement. We proceeded to investigate the influence of the surfactant concentration and the surfactant type on structure and dynamics of the mixed aggregates. It is seen that the structural parameters of the aggregates depend very little on the surfactant concentration and headgroup. However, it is crucial to incorporate a sufficient amount of PE in the aggregates to increase the viscosity of the aggregates. By comparing viscous samples at 1 wt. % PE concentration with samples at a PE concentration of 0.3 wt. %, where no significant increase in viscosity is observed, we find that similar aggregates are formed already at this lower PE concentrations. However, the amount of PE incorporated in them is insufficient to interconnect several PE chains and therefore, they do not increase viscosity. So, our detailed investigation combining contrast variation SANS and NSE does not only allow to explain the viscosity behavior but also to deduced detailed information regarding the structures and the dynamics especially of the polyelectrolyte within the complexes.
authors: Stranski-Laboratorium für Physikalische und Theoretische Chemie, Institut für Chemie, Technische Universität Berlin, Straße des 17. Juni 124, Sekr. TC 7, D-10623 Berlin, Germany.
authors: Ingo
authors: I
authors: Hoffmann
authors: Institut Max von Laue-Paul Langevin (ILL), F-38042 Grenoble Cedex 9, France.
authors: Bela
authors: B
authors: Farago
authors: Institut Max von Laue-Paul Langevin (ILL), F-38042 Grenoble Cedex 9, France.
authors: Ralf
authors: R
authors: Schweins
authors: Institut Max von Laue-Paul Langevin (ILL), F-38042 Grenoble Cedex 9, France.
authors: Peter
authors: P
authors: Falus
authors: Institut Max von Laue-Paul Langevin (ILL), F-38042 Grenoble Cedex 9, France.
authors: Melissa
authors: M
authors: Sharp
authors: Stranski-Laboratorium für Physikalische und Theoretische Chemie, Institut für Chemie, Technische Universität Berlin, Straße des 17. Juni 124, Sekr. TC 7, D-10623 Berlin, Germany.
authors: Sylvain
authors: S
authors: Prévost
authors: Stranski-Laboratorium für Physikalische und Theoretische Chemie, Institut für Chemie, Technische Universität Berlin, Straße des 17. Juni 124, Sekr. TC 7, D-10623 Berlin, Germany.
authors: Michael
authors: M
authors: Gradzielski