polyvinylidene fluoride/polyvinylpyrrolidone (pvdf/pvp) hollow fiber membranes were fabricated by dry-jet wet-spinning process. the correlated effects of the air gap length and pvp concentration ((1) the air gap length effect at the low and high pvp concentration in the dope solutions, as well as (2) the effect of the pvp concentration at the same air gap length) on the cross-section structure ...