Nanoclay compatibilization of phase separated polysulfone/polyimide films for oxygen barrier

Abstract

Polyimide (PI) and Polysulfone (PSF) films are used in many applications ranging from electronic film capacitors to membranes for gas separation and water purification, yet their phase separation issues limit many potential synergistic blend film applications. To this end, we examine the potential of nanoclays as non-traditional compatibilizers and re-enforcing agents in these technologically important polymer blend films. Herein, we quantify the effect of a nanoclay, Cloisite 30B on the phase separated blend film morphology compatibilization of PSF/PI and associated changes in its mechanical properties and film surface energy. Addition of as little as 1 mass% of organoclay strongly compatibilized the blend phases at all compositions, reducing the scale of blend phase separation by ~5–10 times, and interestingly, the net discreet surface phase separated domain area converged to that observed in 50% blend composition for other off-symmetric blend compositions. Clay compatibilization effects also induced a notable reduction of aspect ratio of surface phase separated domains in thin film blends, attributed to a high degree of exfoliation of the nanoclay by the PSF component so that the effective PSF domain interfacial tension with PI is reduced. Surface modification effects on topography leveling and surface energy changes are only qualitatively similar to our previous observations of block copolymer compatibilizer effect on polymer thin film blend phase separation. Thermal decomposition (TGA) measurements of PSF/PI films showed a decrease in thermal stability upon adding C30B due to its surfactant modification, while film mechanical tensile modulus properties improved slightly by adding low concentration of C30B (~1 mass%), but higher nanoclay loading decreased tensile strength and elongation at break. Finally we note that in terms of processing, the viscosities of the polymer solutions dramatically changed with addition 1 mass% and 3 mass% of C30B. We anticipate that more generally, nanoclays can act similarly to traditional polymeric compatibilizers in many aspects in suppressing polymer thin film blend phase separation that can have ramifications for many advanced technological applications such as sensors and membranes. To this end, we present preliminary oxygen barrier properties of adding Cloisite 30B on PSF/PI blend films.