Miscibility study of poly(ethylene oxide)/ polyacrylates blends using thermal, morphology, melt rheological and conductivities properties of the blends with lithium perchlorate / Hairunnisa Ramli

Miscibility on binary blend system of the high molar mass of poly(ethylene oxide) (PEO) (M, = 300,000 g mol"1) with polyacrylates such as poly(methyl acrylate) (PMA) (M„ = 40,000 g mol"1) and poly(w-butyl methacrylate) (PnBMA) (Mw = 337, 000 g mol" !) were studied. The thin films of the samples were prepared via the solution casting method with various mass percent (m/m %) compositions ranging from 0/100 to 100/0. The investigation of the miscibility was by thermal characterization using differential scanning calorimeter (DSC). The miscibility of PEO/PMA blends is confirmed through the presence of single and composition-dependent glass transition temperature, Tg which follows the Fox equation and the reduced apparent melting temperature, Tm of PEO (from 66 °C to 53 °C) throughout the blend compositions. On the other hand, PEO and PnBMA are immiscible for entire blend compositions where the quantities Tg of PEO in the blends remain constant with Tg of neat PEO which is -53 °C while quantities change of heat capacity, ACP of PEO show increment with the increasing mass fraction of PEO, WVEO which marks the constancy of quantity ACP of PEO in the blends. Also, the insignificant variation of Tm of PEO (~ 66 °C) and the constancy of the crystallinity, X* of PEO in the blends imply that these blends are immiscible agreed with the results of Tg and ACP. The optical micrographs taken using an optical microscope at the molten state further corroborate the homogeneity of PEO and PMA phases with the Han plots from the melt rheological studied at T = 80 °C superimpose to one another and the slopes do not vary significantly. In contrast, the heterogeneity is confirmed where matrix-droplet and co-continuous structures can be observed. Meanwhile, the Han plots do not superimpose and the slopes vary dependently on the blends' compositions which implies the immiscibility between PEO and PnBMA. From the correlation of the thermal, morphology and melt-rheological behaviour of miscible PEO/PMA and immiscible PEO/PnBMA blends presented, we may conclude that the behaviour of the binary sy sterns of the polymers may vary depending especially on their molar mass and molecular structure. The entanglement of the polymers (especially for high molar mass) may affect the flow behaviour especially when the systems are in the molten state. These correlations follow a simple model like Flory-Huggins theory which offers new insight into the miscibility of polymer blends with high molar mass. This understanding is crucial for determining the optimal compositions prior to incorporating additional components, such as salt, in the preparation of solid polymer electrolytes (SPE) for various applications. Additionally, the selected blends of PEO/PnBMA (80/20, 60/40 and 10/90) blends compositions with the addition of lithium perchlorate, LiC104 (with salt concentration, Ws = 0.00099 to 0.107) were studied. The studies incorporated with salts were also compared with a few blend systems from the literatures. PEO/PnBMA blends studied exhibiting the liquid-liquid phase separation upon the addition of salt with the constancy of quantity Tg of neat polymers (at WVEO = 0). It can be concluded that upon the addition of salt, the immiscibility of the systems still could not improve. Impedance spectroscopy (IS) studies show that the ionic conductivities (ÖDC) of the polymer blends at room temperature slightly increase with increasing PEO with the order of magnitude of 10"11 - 10"10 S cm"1. However, the addition of salt into the PEO/PnBMA blends system does not improve the ÖDC.