hydrophilic inter - penetrating network charge modified microporous membranes are provided as well as a method of preparing the membranes by casting a membrane matrix blend containing matrix polymer , a solvent system , a wetting polymer compatible with the matrix polymer , and a charge modified system which forms a cross - linked interpenetrating network structure within the microporous membrane substrate during the membrane fabrication process which network structure optionally can be locked in by heat curing . the membranes are useful for filtering ultrapure water with 18 megaohm - cm resistivity for the electronic industry , and they can also be used for the removal of a variety of contaminants from fluid media , such as very fine negatively charged particles , bacteria and endotoxins , with greatly enhanced filtration efficiency .