X-Ray Diffraction (XRD) and Surface Morphology Studies of PVC complexes Modified with Doping Salt and Additives

Abstract

In this work, the proton-conducting polymer electrolytes were prepared using the solution casting technique. Poly (vinyl chloride) PVC is used as the polymer host, ammonium triflate (NH4CF3SO3) as the doping salt, and ethylene carbonate (EC) and butyltrimethyl ammonium bis trifluoromethyl sulfonyl imide (Bu3MeNTf2N) is used as the plasticizers. XRD and FESEM characterization techniques were used to study the properties of the PVC-based proton-conducting polymer electrolytes. XRD studies show that amorphous PVC becomes largely amorphous upon adding NH4CF3SO3. Largely amorphous is also obtained upon adding EC and Bu3MeNTf2N to PVC-NH4CF3SO3. XRD studies of the salted samples showed they are largely amorphous. However, XRD studies could not identify the most amorphous sample for sure. Identifying the most amorphous sample is imperative, as conduction in polymer electrolytes is known to occur in the amorphous region. The FESEM micrographs gave a qualitative idea of the amorphousity of the salted samples in that 30 wt. % NH4CF3SO3 (A4) had the greyest regions in its micrograph, giving a strong indication of it being the most amorphous sample. In the case of the EC plasticized system, the micrographs showed that the pore size increased with increasing concentration of EC, which in turn caused the amorphous regions (a grey area) to decrease. This means that 5 wt. % of EC (B1), which has the smallest pore size and the greyest area, is the most amorphous sample. In the micrographs of Bu3MeNTf2N plasticized samples, the sample 15 wt. % Bu3MeNTf2N (C3) is observed to be more homogeneous with whiter spherulites indicating the presence of more trapped ionic liquid. This indicates that 15 wt. % Bu3MeNTf2N (C3) is the most amorphous due to its homogeneity compared to the sample 5 wt. % Bu3MeNTf2N (C1). XRD results show that the salt and plasticizers have decreased the crystallinity of PVC and salted PVC-based polymer electrolytes. The surface morphology images give a qualitative idea of the degree of crystallinity of the complexes studied in this work.