Water sorption behavior in polyimide thin films controlled by inorganic additives

We investigated the decreased water diffusivity depending on the content and size of carbon black (CB) added to polyimide (PI) in order to synthesize composite films (PI-CB). CBs with different diameters were used: N110 (CB1, 11-19 nm), N326 (CB2, 26-30 nm) and N660 (CB3, 49-60 nm). The water diffusion coefficient of PI-CB decreased with increasing CB content from 2.67·10^-9 for pure PI films to 0.22·10^-9 cm²/s for PI-CB films containing 40 wt% CB1. Moreover, the decrease in water diffusivity with increasing CB content exhibited a linear relationship. The water diffusivity of PI-CB increased with the increasing size of CB at the same CB content. The water uptake of PI-CB had a linear relationship depending on the CB content, similar to water diffusivity; the water uptake of composite films decreased by 73% (from 3.67% to 0.98%) for PI-CB1 (40 wt%) films as compared to PI films. In addition, the water uptake varied not only with the CB content, but also by the size of the CB surface area. [Figure not available: see fulltext.]