Rheology of Concentrated Polymer/Ionic Liquid Solutions: An Anomalous Plasticizing Effect and a Universality in Nonlinear Shear Rheology

Abstract

An anomalous plasticizing effect was observed in polymer/ionic liquid (IL) solutions by applying broad range of rheological techniques. Poly(ethylene oxide)(PEO)/IL solutions exhibit stronger dynamic temperature dependence than pure PEO, which is in conflict with the knowledge that lower-Tg solvent increases the fractional free volume. For poly(methy methacrylate)(PMMA)/IL solutions, the subtle anomaly was detected from the fact that the effective glass transition temperature Tg,eff of PMMA in IL is higher than the prediction of the self-concentration model, while in conventional polymer solutions, Tg,eff follows the original Fox equation. Observations in both solutions reveal retarded segmental dynamics, consistent with a recent simulation result (Macromolecules, 2018, 51, 5336) that polymer chains wrap the IL cations by hydrogen bonding interactions and the segmental unwrapping delays their relaxation. Start-up shear and nonlinear stress relaxation tests of polymer/IL solutions follow a universal nonlinear rheological behavior as polymer melts and solutions, indicating that the segment-cation interaction is not strong enough to influence the nonlinear chain orientation and stretch. The present work may arouse the further theoretical, experimental, and simulation interests in interpreting the effect of complex polymer-IL interaction on the dynamics of polymer/IL solutions.

Ionic Liquid–Poly(lactic acid) Blends as Green Polymer Electrolyte Membranes

“…This could be explained by the retardment of the segmental dynamics of PLA in ILs when compared with conventional polymer solvents, mainly due to polymer segment−cation interactions according to the simulation data. 36 These results are in accordance with FTIR−ATR and XRD analyses and suggest that even though PLA and IL phase separate (Figure 3), an amount of ILs is dissolved in the PLArich phase, allowing interactions between those materials. 37 This behavior results in fairly low water absorption capability, which in the case of the pure PLA membranes prepared for this study leads to an increase in mass of less than 1 wt % under nearly saturated conditions (P/P 0 = 95%).…”

Glass Transitions in Hydrated Polyelectrolyte Complexes

“…C 1 and C 2 are both empirical constants that can be used to predict the mechanical properties of the specific material at different temperatures. With C 1 , the fractional free volume at the reference temperature f / B can be obtained − (Table )­ where B is a constant of order unity. The value of f / B measures the segmental dynamics as it correlates the monomeric friction coefficient ζ 0 by ζ 0 ≈ exp­( B / f ).…”

Influence of Nonstoichiometry on the Viscoelastic Properties of a Polyelectrolyte Complex

“…Using the fitting parameter C 1 , the fractional free volume at the reference temperature f (ϕ, T ref )/ B can be obtained where B is a constant of order unity, ϕ is the polymer volume fraction, and T ref is the reference temperature. The value of f (ϕ, T ref )/ B measures the segmental dynamics as it correlates the monomeric friction coefficient ζ 0 by ζ 0 ≈ exp­( B / f ) …”

“…The value of f(ϕ, T ref )/B measures the segmental dynamics as it correlates the monomeric friction coefficient ζ 0 by ζ 0 ≈ exp(B/f). 66 Using the water weight % in each sample and the densities of PDADMAC and PSSNa, the water volume fraction and polymer−salt volume fraction were calculated and are shown in Table 3. Compared to the polymer, the volume occupied by salt ions is negligible here.…”