Effect of Single-Walled Carbon Nanotubes On the Transport Properties of Poly(styrene-isobutylene-styrene) Membranes

In this study, the transport properties of poly(styrene-isobutylene-styrene) (SIBS) were measured as a function of sulfonation level and single-walled carbon nanotube loading for gas sensors and fuel cell applications. Sulfonated SIBS were functionalized with single walled carbon nanotubes to create highly selective polymer nanocomposite membranes. The nanocomposite membranes were characterized using fourier transform infrared spectroscopy (FTIR) and elemental analysis (EA), to confirm and determine accurate sulfonation levels. Thermogravimetric analysis (TGA) was performed in order to evaluate the thermal stability, which increases with sulfonation level while nanocomposite membranes maintained the same degradation temperature. Absorption limitations and their effect on the membrane transport were investigated for sulfonated and nanocomposite membranes through water swelling and permeability experiments. Although proton conductivity and methanol permeability increase with sulfonation level until a maximum suggesting an optimum sulfonation, the effect single-walled carbon nanotubes influences the transport properties based on the changes in morphology and nanochannel size and configuration. To complement the studies, selectivity (i.e., proton conductivity/methanol permeability) of the nanocomposite membranes were determined and compared to Nafion® 117.