Experimental studies on the novel compositions of gel polymer electrolytes, comprised of plastic crystal succinonitrile (SN) dispersed with pyrrolidinium and imidazolium-based ionic liquids (ILs) entrapped in a host polymer poly(vinylidine fluoride-co-hexafluoropropylene) (PVdF-HFP), are reported. The gel electrolytes are in the form of free-standing films with excellent mechanical, thermal, and electrochemical stability. The introduction of even a small content (~1 wt %) of ionic liquid (1-butyl-1-methylpyrrolidinium bis(trifluoromethyl-sulfonyl)imide (BMPTFSI) or 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMITf) in the PVdF-HFP/SN system (1:4 w/w) enhances the electrical conductivity by 4 orders of magnitude, that is, from ~10(-7) to ~10(-3) S cm(-1) at room temperature. The structural changes due to the entrapment of SN or SN/ILs mixtures and ion-SN-polymer interactions are examined by Fourier transform infrared (FTIR)/Raman spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), and differential scanning calorimmetry (DSC). Various physicochemical properties and fast ion conduction in the gel polymer membranes show their promising characteristics as electrolytes in different ionic devices including supercapacitors.
Di(2-ethylhexyl) phthalate (DEHP) is a commonly employed plasticizer for poly(vinyl chloride) (PVC). Diffusion of di(2-ethylhexyl) phthalate (DEHP) takes place when plasticized PVC is immersed in hexane. Rather than determining DEHP concentration in the immersion solvent, an IR window for PVC from 1500-1900 cm-1 enabled direct measurement of HADD (hexane assisted DEHP diffusion) using ATR-IR by monitoring the DEHP carbonyl absorption at 1715 cm-1. The present study employed PVC containing 45% plasticizer (PVC-45, tygon tubing). A fast diffusion process was observed for short times (< 30 s) while a slower diffusion process occurred at longer immersion times (30 s < t < 6 min). A synergistic increase in mesosurface T g toward that of PVC coupled with low solubility of hexane in PVC accounts for decreased DEHP diffusion rates (10-12-10-13 cm 2 sec-1) for immersion times > 30 sec. Analysis by XPS shows the outermost surface is PVC free of plasticizer after 6 min immersion. After an induction period, back diffusion coefficients D b were estimated from peak areas during a subsequent fast recovery period (10-14-10-15 cm 2 sec-1). A model is proposed for the induction period associated with re-plasticization that involves a change from a mesosurface glass to a gel like solid.
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