Phase separation kinetics and rheological behavior of Poly(ethylene oxide)/ionic liquid mixtures with large dynamic asymmetry

Abstract

Phase separation kinetics of dynamically asymmetric mixtures poly(ethylene oxide)/ionic liquid (PEO/[EMIM][BF4]) was investigated through optical microscopy and rheological measurements. The distinct phase-separating morphologies including network structure at lower PEO concentrations of 10∼30 wt % (P10, P30) driven by viscoelastic phase separation (VPS), co-continuous structure at the moderate concentrations (P40, P50) governed by spinodal decomposition (SD) and droplets-matrix at higher concentrations (P60, P70) driven by either SD or nucleation and growth (NG) are observed under different temperatures. Evident deviation of the storage modulus G′ and gel-like behavior on loss tangent tanδ at low frequencies can be seen upon entering into the two-phase region dependent on different morphologies. During time sweeps, the initial increase of G′ can be ascribed to the growth of concentration fluctuation, and the subsequent decrease possibly due to the phase domain coarsening, breaking up or coalescence. The interfacial tension σ at the late stage of phase separation with droplet-matrix morphologies is estimated by using the Gramespacher-Meissner (G-M) model and Palierne model.