Polymer Nanocomposites as Solid Electrolytes: Evaluating Ion−Polymer and Polymer−Nanoparticle Interactions in PEG-PU/PAN Semi-IPNs and Titania Systems

High Resolution Image Download MS PowerPoint Slide This paper is an investigation on the physicochemical properties and Li ion conductivity behavior of a new class of polymer nanocomposites, which holds promise for its potential use as solid polymer electrolytes (SPE). A family of nanocomposite semi-interpenetrating polymer networks of titania (TiO 2 )/poly(ethylene glycol)−polyurethane (PEG-PU)/poly(acrylonitrile) (PAN) incorporated with LiClO 4 was synthesized. The effects of titania loading, nanoparticle surface functionalization, and ion−polymer and polymer−nanoparticle interactions were evaluated in detail using XRD, FT-IR, TEM, DSC, TG-DTA, and dc conductivity studies. At low degree of TiO 2 loading, reasonably good dispersion and encapsulation within the semi-IPN matrix was achieved. FT-IR studies strongly indicate that analogous to the ion−polymer interaction, a strong interaction coexists between the polymer matrix (C−O−C) and the surface of TiO 2 nanoparticles. Electron micrographs of the semi-IPN nanocomposite films reveal nanophase separation within the polymer matrix. The larger poly(acrylonitrile) domains (∼50−400 nm) along with interspersed titania nanoparticles (∼5−20 nm) are well distributed throughout the PEG-PU parent networks. The even dispersion and low nanoparticle agglomeration apparent from the micrographs also indicate a reasonable degree of polymer−nanoparticle interaction. Interestingly, no substantial change in the thermal properties of the polymer−nanocomposite matrices is observed even with increased amounts of TiO 2 loading (up to 5%) and the glass-transition temperature remained well below the ambient (∼−38 °C). The degradation onset temperature for the semi-IPNs and TiO 2 nanocomposites ( T 0 ∼ 250 °C) suggests good thermal stability of the matrix. An enhancement in ionic conductivity for all the semi-IPN/nanocomposite was observed. The presence of a very disordered polymer phase in the near vicinity of the nanoparticle surface, interfacial dynamics possibly creating smaller domains of PEG segments wherein the cations (Li + ) are more loosely cross-linked under the circumstances of competitive interactions, may help faster ionic transport contributing to the overall increase in the bulk conductivity. Overall, tailoring the polymer−nanocomposite matrices further holds promise toward addressing the practical challenges in the success of solid polymer electrolytes in Li + ion batteries/dye-sensitized solar cells.