Crystallinity and Stability of Poly(vinyl alcohol)‐Fumed Silica Mixed Matrix Membranes

Mixed matrix membranes (MMMs) containing poly(vinyl alcohol) (PVA) and 10–30% fumed silica (FS) were prepared using a solvent casting method. The FS particles were distributed evenly in the MMMs as revealed in the scanning electron microscopy/energy dispersive X‐ray spectroscopy (SEM/EDX) micrographs. The surface roughness increased with higher FS content. The thermogravimetric analysis (TGA) results showed that the MMM decomposition temperature was slightly improved with increasing FS content. The MMM crystallinity was determined using Fourier‐transform infrared spectroscopy (FT‐IR), X‐ray diffraction (XRD), and differential scanning calorimetry (DSC). All results indicated that the crystallinity was decreased with FS content. This was attributed to the fact that the FS particles restricted the polymer chain mobility during membrane formation. The confined chain mobility also slowed or inhibited crystal unfolding and, therefore, suppressed the membrane dissolution in water. The lower crystallinity drop of the swollen membranes with FS addition confirmed this finding. The incorporation of FS improved the thermal stability and resistance to water dissolution. These MMMs exhibit potential for use in alkaline direct methanol fuel cell applications.

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