Relaxation modes in a smart system: weakly charged microemulsion and polyelectrolyte

ABSTRACT

The dynamic light scattering technique is used to probe the relaxation modes of a smart system composed of weakly charged microemulsion and a polyelectrolyte. The complex is formed by oil in water microemulsion comprising Triton X-100 (TX₁₀₀) as surfactant, cosurfactant (octanol), oil (decane) and Polyacrylic acid (PAA) which is a pH dependent polyelectrolyte. All the dynamic studies of the solutions were carried out in a basic medium at pH = 12. In the bare microemulsion (without PAA added), the analysis of the autocorrelation functions exhibits one relaxation mode, reflecting the Brownian motion of the particles. However, the dynamic light scattering (DLS) autocorrelation function shows the existence of two relaxation modes, fast and slow modes, in charged microemulsion mixed with PAA. The fast relaxation mode is diffusive and is associated to the collective diffusion of the charged particles. The slow mode is also diffusive but the mechanism at the origin is the subject of controversy. It is very likely that it arises from the entanglement of the network formed by the droplets of the microemulsion and the polyelectrolyte.

KEYWORDS:

• Collective and self diffusions
• dynamic light scattering
• microemulsion
• polyacrylic acid
• smart system

Acknowledgements

This work was achieved in collaboration with the Laboratory of Montpellier (Charles Coulomb). We are much indebted to Professor Luca Cipelletti, for his assistance and his support during the realization of this work.

Disclosure statement

No potential conflict of interest was reported by the author(s).