Dynamics and Structure of Polyelectrolytes in Aggregates with Oppositely Charged Surfactants

Dynamics and Structure of Polyelectrolytes in Aggregates with Oppositely Charged Surfactants

I. Hoffmann

, B. Farago

and M. Gradzielski

1TU Berlin Institut für Chemie

Stranski-Laboratorium für Physikalische und Theoretische Chemie Straße des 17. Juni 124, Sekr. TC 7, D-10623 Berlin

2Institut Laue Langevin 6, rue Jules Horowitz F-38042 Grenoble Cedex 9 E-Mail: ingo.hoffmann@tu-berlin.de

Systems composed of oppositely charged polyelectrolytes and surfactants show rich self- aggregation behavior that varies over a large size range and have many applications e.g. in cosmetics, detergency and drug delivery. Mixtures of the cationic polyelectrolyte JR 400 with anionic surfactants (SDS, SDBS) in the semi-dilute regime with a slight excess of polymer charges form highly viscous network structures, with their viscosity increasing by 3-4 orders of magnitude as compared with the pure polymer solution, while mixtures with excess surfactant charges form solutions with viscosities even below those of the polymer solution[1,2]. In this study we investigated the structure of the polyelectrolyte chain in the aggregates with the aid of small-angle neutron scattering (SANS).

Furthermore, the dynamics of the polyelectrolyte has been studied with the help of Neutron Spin-Echo (NSE). Previous studies with Dynamic Light Scattering (DLS) have shown, that data can be described in terms of the mode-coupling theory. However, NSE allows to access significantly smaller size ranges, corresponding to the aggregates seen in SANS. Therefore the dynamics of local segments of individual chains and of the micellar aggregates are monitored rather than those of larger clusters as in DLS. Measurements show that the effect on the dynamics is much less pronounced in NSE as compared to DLS.

In summary, we studied the behaviour of polyelectrolytes in solutions of mixed aggregates of polyelectrolytes and oppositely charged surfactants with the help of neutron scattering, gaining an understanding of the role that the polyelectrolyte component plays in the formation of such aggregates and in particular with respect to its dynamic properties. This understanding can be valuable for the design of future formulations.

References

[1] I. Hoffmann, P. Heunemann, S. Prévost, R. Schweins, N.J. Wagner and M. Gradzielski, Langmuir 27, 4386–4396 (2011)

[2] I.Hoffmann, S. Prévost, M. Medebach, S. Rogers, N. J. Wagner, M. Gradzielski, Tenside, Surfactants, Deterg. 48, 488-494 (2011)