Neutron spin echo study of the dynamics of micellar solutions of randomly sulphonated polystyrene

The dynamics of phase separated micellar solutions of randomly sulphonated polystyrene ionomers in toluene were examined with neutron spin echo spectroscopy (NSE). The correlation functions demonstrated single exponential decays with a constant background offset. The relaxation rate (Γ) of the ionomer micelles at small length scales in the q range 0.075-0.16 Å−1 was diffusive (Γ ∼ q2) as expected for the collective breathing mode of a cross-linked gel. At intermediate length scales in the q-range 0.025-0.075 Å−1 the relaxation rates were non-diffusive (Γ ∼ q0.36, q0.72), which is attributed to the hopping dynamics of the individual stickers inside the ionomer micelles (τsticker ∼ 10 ns). At large length scales the scattering due to the phase separated inhomogeneities of the micellar network did not relax on the time scales of the measurements (<20 ns), giving rise to a constant background on the correlation functions. This slow relaxation process may be due to the hopping dynamics of whole micelles previously observed in rheology experiments (τmicelle ∼ 0.05 s). The NSE results are in agreement with a model developed in previous small-angle neutron scattering and rheology experiments for concentrated solution of ionomeric micelles. The NSE results for the associating ionomers are markedly different from the Zimm dynamics (Γ ∼ q3) previously observed for semi-dilute and cross-linked polystyrene polymers in a good solvent. The ionomeric cross-links thus have a large impact on the polymer chain dynamics at the nanosecond time scale.