Fouling is the deposition of retained particles, colloids, macromolecules, salts, etc., at the membrane surface or inside the pore at the pore wall. Fouling reduces the membrane flux either temporarily or permanently. While the initial flux can be restored by washing the membrane or by applying back-pressures to the temporarily fouled membrane, it cannot be restored when the membrane becomes permanently fouled. The main focus of this Review is on the permanent flux decline. The fouling is caused by the interaction between the membrane surface and the foulants, which include inorganic, organic, and biological substances in many different forms. The foulants not only physically interact with the membrane surface but also chemically degrade the membrane material. For example, colloidal particles, such as natural organic matter (NOM), are considered as the main reason for membrane fouling, which could be controlled by the permeation hindrance and electric double layer repulsion. The formation of biofilms with extra-cellular polymeric substances (EPSs) and microbial cells matrix is the example of biofouling.1 Biofilms are developed by the microbial cell adhesion and subsequent colonization on the membrane surfaces through EPS, which may account for 50-90% of total organic carbon. The biofouling could be minimized by periodical washing with chemicals such as sodium hypochlorite solution, but it will result in the simultaneous degradation of the membrane material’s lifetime. It is a severe problem for membranes used in pressure-driven processes such as reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF), and microfiltration (MF) and also for other membrane processes, seriously hampering the applications of membrane processes. Hence, membrane fouling as well as its reduction has been a subject of many academic studies and industrial research and development efforts since the early 1960s when industrial membrane separation processes emerged. Selection of an appropriate membrane, pretreatment of the process fluid, adjustment of operating design, and conditions are all known to control fouling to some extent. On the other hand, development of absolutely nonfouling membranes seems extremely difficult, if not totally impossible. This Review surveys the latest efforts in which the reduction of irreversible fouling is attempted by the modification of the membrane surface. The separation process by membrane is essentially a surface phenomenon. More specifically, the skin layer or top surface layer plays the vital role. Therefore, it is a natural consequence to modify membrane surface for reducing the fouling. It is generally accepted that an increase in hydrophilicity offers better fouling resistance because protein and many other foulants are hydrophobic in nature. Most nanofiltration membranes are electrically charged, which significantly reduces the scale-formation. During the past decade, the emergence of atomic force microscopy (AFM) enabled us to study the effect of the surface roughness in nanoscale on the membrane fouling. It is believed that the membrane fouling with particulate substance is enhanced by an increase in the surface roughness. It is shown in this Review that all of the above concepts, except for the membrane surface charge, are based on correlation of data, which are, at best, valid within a limited range of surface property parameters. * To whom correspondence should be addressed. Phone: (613) 562-5800, ext 6085. Fax: (613) 562-5172. E-mail: rana@eng.uottawa.ca. Dipak Rana is presently a Research Scientist in the Industrial Membrane Research Institute, Department of Chemical and Biological Engineering, University of Ottawa, Ottawa, Canada. Dr. Rana has been a member of various prestigious organizations, such as the Indian Chemical Society, Society for Polymer Science, India, Society of Plastics Engineers, USA, American Chemical Society, etc., for a long period. He was awarded a Ph.D. in Science from Jadavpur University, Calcutta (presently Kolkata), when he was working at the Indian Association for the Cultivation of Science, Calcutta, India. He received his Master in Chemistry with specialization in Physical Chemistry as well as his Bachelor with Honors in Chemistry from the University of Calcutta, India. Dr. Rana has published over 50 professional papers and book chapters. Chem. Rev. 2010, 110, 2448–2471 2448

Surface Modifications for Antifouling Membranes

High resolution XPS of organic polymers The Scienta ESCA300 Database

Grafting: a versatile means to modify polymers Techniques, factors and applications

Of late, the most bountiful natural biopolymer chitin and chitosan have become cynosure of all party because of an unusual combination of biological activities plus mechanical and physical properties. However applications of chitin are limited due to its inherent insoluble and intractable nature. Chitosan, alkaline hydrolytic derivative of chitin has better solubility profile, less crystallinity and is amenable to chemical modifications due to presence of functional groups as hydroxyl, acetamido, and amine. The chemical modification of chitosan is of interest because the modification would not change the fundamental skeleton of chitosan, would keep the original physicochemical and biochemical properties and finally would bring new or improved properties. In view of rapidly growing interest in chitosan its chemical aspects and chemical modification studies is reviewed. The several chemical modifications such as oligomerization, alkylation, acylation, quternization, hydroxyalkylation, carboxyalkylation, thiolation, sulfation, phosphorylation, enzymatic modifications and graft copolymerization along with many assorted modifications have been carried out. The chemical modification affords a wide range of derivatives with modified properties for specific end use applications in diversified areas mainly of pharmaceutical, biomedical and biotechnological fields. Assorted modifications including chitosan hybrids with sugars, cyclodextrin, dendrimers, and crown ethers have also emerged as interesting multifunctional macromolecules. The versatility in possible modifications and applications of chitosan derivatives presents a great challenge to scientific community and to industry. The successful acceptance of this challenge will change the role of chitosan from being a molecule in waiting to a lead player.

Chitosan-modifications and applications: Opportunities galore

The generation of polymer brushes by surface-initiated controlled radical polymerization (SI-CRP) techniques has become a powerful approach to tailor the chemical and physical properties of interfaces and has given rise to great advances in surface and interface engineering. Polymer brushes are defined as thin polymer films in which the individual polymer chains are tethered by one chain end to a solid interface. Significant advances have been made over the past years in the field of polymer brushes. This includes novel developments in SI-CRP, as well as the emergence of novel applications such as catalysis, electronics, nanomaterial synthesis and biosensing. Additionally, polymer brushes prepared via SI-CRP have been utilized to modify the surface of novel substrates such as natural fibers, polymer nanofibers, mesoporous materials, graphene, viruses and protein nanoparticles. The last years have also seen exciting advances in the chemical and physical characterization of polymer brushes, as well as an ev...

Surface-Initiated Controlled Radical Polymerization: State-of-the-Art, Opportunities, and Challenges in Surface and Interface Engineering with Polymer Brushes

Grafting of Zwitterion from Cellulose Membranes via ATRP for Improving Blood Compatibility

Improvement of blood compatibility on cellulose membrane surface by grafting betaines

Platelet adhesive resistance of segmented polyurethane film surface-grafted with vinyl benzyl sulfo monomer of ammonium zwitterions.

Platelet adhesion and protein adsorption on silicone rubber surface by ozone-induced grafted polymerization with carboxybetaine monomer.

Silicone rubber has been used as a biomaterial for more than two decades and displays good mechanical and optical properties, but its chemical nature, poor antithrombogenicity, as well as its hydrophobicity, prevents its use in many demanding biomedical applications. In order to provide modified silicone with enhanced haemocompatibility, surface modification techniques were used. Ozonization was used to introduce active peroxide groups onto the silicone film surface and, subsequently, graft polymerization of N,N′-dimethyl-N-methacryloyloxyethyl-N-(3-sulfopropyl) ammonium (DMMSA), a zwitterionic sulfobetaine structure, onto the ozone activated silicone surface was conducted. Surface analysis was accomplished by means of attenuated total reflectance-Fourier-transform infrared (ATR-FTIR), and X-ray photoelectron spectra (XPS), and scanning electron microscopy (SEM) and contact angle measurement. ATR-FTIR and XPS investigation confirmed the graft polymerization. The grafted film possessed a relatively hydrophilic surface as indicated by contact angle measurement. The blood compatibility of the grafted films was evaluated by platelet adhesion in platelet-rich plasma (PRP) and protein adsorption in bovine fibrinogen using silicone film as the reference. No platelet adhesion was observed for the grafted films incubated in PRP for 120 min. The protein adsorption was reduced on the grafted films after incubated in bovine fibrinogen for 120 min. These results confirmed that the improved blood compatibility was obtained by grafting this new zwitterronic sulfobetaine structure onto silicone film. Copyright © 2003 Society of Chemical Industry

Grafting sulfobetaine monomer onto silicone surface to improve haemocompatibility

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