Journal of Membrane Science 184 (2001) 97–106 Theoretical model of the porosity of copolymer membranes Simcha Srebnik ∗ Division of Environmental Sciences, School of Applied Sciences, The Hebrew University, Jerusalem 91904, Israel Received 6 June 2000; received in revised form 5 October 2000; accepted 6 October 2000 Abstract A theoretical model is developed to explore the porosity and chemical morphology of copolymer membranes. The size of the leaving group during polycondensation of the cross-links is found to have unexpected effects on the porosity, leading to a nonuniform pore-size distribution. The size and formation of microdomains with different chemistries and porosities can be predicted using this model. Such knowledge of a membrane’s physical and chemical morphology is useful in the development of fouling-resistant filtration membranes. Reverse osmosis and nanofiltration membranes commonly used today frequently undergo degradation due to fouling and thus experience a diminishing water flux. Additional control over the properties of the membrane can be achieved by combining two or more polymers to form a heteropolymer network. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Copolymer membranes; Nanofiltration (NF); Reverse osmosis (RO) 1. Introduction Increasing awareness of the need of clean water over the years has led to a worldwide tendency towards stricter regulations on water quality. In the US, for example, EPA regulations [1,2] are calling for more stringent regulations on the removal of colloidal par- ticles, bioorganisms, salts, and disinfection byprod- ucts, requiring the development of novel separation processes that can achieve a higher degree of solute rejection. In recent years, the adaptation of nanofiltra- tion (NF) and reverse osmosis (RO) membranes has been considered as a potential method for the removal of pollutants since it can potentially achieve better removal than conventional filtration methods such as enhanced coagulation. Indeed, today membranes are being used for a variety of applications, including ∗ Tel.: +972-2-658-6155; fax: +972-2-658-6260. E-mail address: simchas@cc.huji.ac.il (S. Srebnik). desalination, disinfection, removal of turbidity and organics, water softening, and to recycle water and enrich potable water. Membrane technology is partic- ularly attractive since initial cost estimates show that smaller plants are already competitive with conven- tional treatments [3,4]. A key variable influencing the operating and capital cost of membranes is permeate flux. One major obsta- cle with NF and RO membranes today is the formation of a cake or foulant layer on the membrane’s surface which requires frequent cleaning of the membrane and/or replacement if irreversible fouling occurs, and which leads to permeate flux decline [5,6]. Modified composite membranes are increasingly being studied as more versatile possibilities [6–9]. Very recently, experiments on nanofiltration membranes whose ac- tive surface layer is composed of copolymers of water permeable hydrophilic blocks and foulant-rejecting hydrophobic blocks have been pursued as a possible solution to overcome fouling by natural organic mat- 0376-7388/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved. PII:S0376-7388(00)00607-4