Phase Behavior, Microstructure, and Dynamics in a Nonionic Microemulsion on Addition of Hydrophobically End-Capped Poly(ethylene oxide)

Abstract

We report on the effects on the phase behavior, microstructure, and rheology in the water-rich part of the ternary nonionic surfactant system comprising pentaethylene glycol dodecyl ether (C12E5)−water−decane, on addition of poly(ethylene oxide) (PEO) and hydrophobically end-capped PEO (HM-PEO). The two polymers destabilize both the micellar and the lamellar phases. With PEO, a segregative phase separation is observed, while with HM-PEO, an associative phase separation is seen. The micellar phase containing HM-PEO was investigated by NMR relaxation and self-diffusion measurements and small-angle neutron scattering as well as low shear viscosity and oscillatory frequency sweep measurements. It was found that the polymer affected the intermicellar interaction, leading to an increased ordering of the micelles, while leaving the micellar size unchanged. Addition of HM-PEO (≤2 wt %) led to a drastic decrease of the micellar self-diffusion coefficient and additionally to an increase of the low shear viscosity by several orders of magnitude. The storage and loss moduli were successfully fitted to a single Maxwell element. Analysis of the fitted parameters and comparison with percolation theory yielded the fraction of polymers that interconnected the micelles (thus forming bridges) as well as the fraction of polymers that did not contribute to the connectivity of the network (resulting in loops).