Microscopic structures in phase inversion membranes: the use of polymer blends for membrane formation by immersion precipitation

Membrane formation by immersion precipitation has been investigated for two different polymer blends: poly(ether sulfone) / poly(vinyl pyrrolidone), a common blend for obtaining high performance UF or MF membranes, and poly(ether sulfone) / poly(styrene). The latter blend contains a polymer as additive that is not soluble in the precipitant used. It yields structures that confirm the fundamental basis of a model describing the formation of membranes from polymer blends. It appears that the membrane formation is dominated by the diffusional behaviour of the polymers relative to each other.

A general classification of membrane structures from a polymer blend is presented; it is established that spinodal decomposition may well be responsible for the open porous structures usually found when using a polymer blend such as poly(ether sulfone) and poly(vinyl pyrrolidone).