1. How ultrafiltration membranes work

It is the thin film that controls the selective passage of substances. It is generally accepted that the selectivity and permeability of ultrafiltration membranes are mainly due to the sieve effect of the pores . In practice, however, the identification of substances according to their geometric dimensions is only used in microfiltration and filtration: in these two techniques, it is actually possible to classify particles according to their apparent dimensions, as proposed by W. Ostwald (Nobel Prize 1909) a century ago. Thus, below 1 nm (10 ^–9 m), particles are classified as molecular dispersions, between 1 nm and 0.1 m as colloids,...