Polyamide Membrane Surface Research Articles

Preparation of high performance TFC RO membranes by surface grafting of small-molecule zwitterions

Zwitterions have been attracting great attention for researchers to tailor the separation membranes featuring enhanced water permeability and excellent antifouling property. Here we functionalized polyamide membrane surface with small-molecule zwitterions through sequential interfacial polymerization (SIP) technique to improve the performance of RO membranes. Zwitterionic molecules 3-(4-(2-((4-aminophenyl)amino)ethyl)morpholino-4-ium)propane-1-sulfonate (PPD-MEPS) and amino acid arginine were covalently bonded onto the PA surface via the amine groups of two zwitterions. Consequently, the surface hydrophilicity of both modified membranes were significantly improved with WCA decreased from ~60° to ~28°, and their surface negative charge also decreased to some extent at high pH values. The water permeability increased from 2.45 LMH/bar to 3.81–3.85 LMH/bar, increasing by about 57%, while maintained a NaCl rejection as high as 98.5%. In addition, the zwitterions-modified RO membranes exhibited much improved antibacterial attachment (E.coil) and fouling resistance to model foulants bovine serum albumin (BSA), lysozyme (LYZ) and humic acid (HA). Therefore, the facile zwitterions modified membranes possessing high water permeability and excellent antifouling performance, especially using amino acid Arg may find their potential promising application in water treatment.

Prevention of Bacterial Colonization Based on Self-Assembled Metal-Phenolic Nanocoating from Rare-Earth Ions and Catechin.

Clinically related infection is a critical risk for human health and is usually caused by biofilm formation on medical devices. Herein, typical polyphenols, catechin (Cat), and rare-earth ions (Re3+) were used for self-assembled Cat-Re nanoparticles that can be facilely coated on the surface of a polyamide (PA) membrane to synergistically prevent bacterial adhesion and subsequent biofilm formation. The antibacterial adhesion feature of the assembled Cat-Re nanoparticles coated on the PA membrane surface was assessed using Pseudomonas aeruginosa, one of the most common pathogenic bacteria, as probe bacteria under static and dynamic simulation flow conditions. The Cat-Re nanocoating showed excellent antibacterial and anti-adhesion activities against P. aeruginosa and successfully prevented biofilm formation on the material's surface. Regardless of the conditions, the Cat-Re nanocoating significantly suppressed the growth and attachment of P. aeruginosa and maintained >90% inhibition activity with favorable reusability and long-term stability. The results suggest that the self-assembled rare-earth-phenolic nanocoating has promising application potential in the prevention of medical device-related biofilm formation.

Salt-tuned fabrication of novel polyamide composite nanofiltration membranes with three-dimensional turing structures for effective desalination

High performance thin-film nanofibrous composite (TFNC) membranes with Turing structures were constructed by interfacial polymerization (IP) of trimesoyl chloride (TMC) and piperazine (PIP) tuned with high content salt (NaCl) in aqueous phase onto a polyacrylonitrile (PAN) nanofibrous mat for nanofiltration (NF). The concentration of salt in aqueous phase played a key role in the structural transition of polyamide (PA) membrane surfaces with two type Turing structures from the crossed ridge networks to crowed nodular arrays. The introduction of NaCl induced the uneven distribution of the IP reaction and could fine-tune the hydrophilicity and compactness of the formed ultrathin PA layer. The skillful manipulation of IP by regulating the NaCl content in aqueous phase enabled a great improvement in NF performance. Under 0.5 MPa, the flux of the optimized TFNC membrane (20.0 wt% NaCl in aqueous phase) reached 129.0 L m-2 h-1 (Na2SO4 rejection was 99.1%) which was approximately 2.5 times greater than that of the original membrane fabricated without salt addition. Moreover, the resultant membrane exhibited excellent stability and anti-fouling properties for long-term use. This approach is easy to be connected with commercialized IP technology to prepare high-performance NF membranes.

A novel nanofiltration membrane with [MimAP][Tf2N] ionic liquid for utilization of lithium from brines with high Mg2+/Li+ ratio

In order to utilize lithium from brines with high Mg2+/Li+ ratio, a positively charged nanofiltration (NF) membrane was prepared by grafting amine-functionalized ionic liquid 1-(3-aminopropyl)-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([MimAP][Tf2N]) onto the surface of polyamide (PA) membrane. The effects of [MimAP][Tf2N] contents on the chemical composition, surface morphology, surface charges and separation properties of the modified PA membranes were discussed. The results of chemical composition analyses indicated reaction of the amine group of [MimAP][Tf2N] with the residual acyl chloride groups, which was existed on the surface of the nascent PA membrane. The surfaces of all the modified PA membranes were positively charged at pH = 6.4 due to the quaternary ammonium group of [MimAP][Tf2N]. In the separation process, the resulting membrane presented high water permeance (37.8 L/(m2⋅h)) and mono-/divalent cation selectivity (Li+ and Mg2+) with much higher MgCl2 rejection (83.8%) than LiCl rejection (24.4%). For a simulative brine with a Mg2+/Li+ ratio of 20, the rejections to Mg2+ and Li+ by the optimized membrane (NF-IL-2.0%) were around 81.9% and −45.2%, respectively, where the permeate with the Mg2+/Li+ ratio of 3.5 was obtained and the selectivity (SLi,Mg) was 8.12. Additionally, the optimized membrane exhibited a stable performance for Mg2+/Li+ separation. Therefore, there is a very possibility for utilization of lithium from brine with high Mg2+/Li+ ratio by using the optimized NF membrane.

Chemical grafting N-GOQD of polyamide reverse osmosis membrane with improved chlorine resistance, water flux and NaCl rejection

Poor chlorine resistance shortens service life of polyamide (PA) reverse osmosis membrane. Here, nitrogen-doped graphene oxide quantum dots (N-GOQDs) were firstly applied to graft on PA membrane surface. Most grafting experiments are often accompanied by a decrease in water flux. In this study, the flux of the grafted membrane can be increased compared with commercial pristine membranes. Also, all modified membranes show better chlorine resistance than pristine ones. Specifically, N-GOQDs are integrated onto polyamide membranes through grafting method. Comprehensive regulation of chlorine resistance and desalination performance can be achieved by changing grafting conditions. For example, under the conditions of 12 h grafting time and 0.002 mg/mL of N-GOQD solution, water flux, NaCl rejection, and chlorine resistance of the modified membrane are improved by 11.1%, 2.3% and 32.8% after 280 h chlorine soaking respectively. FTIR analyses show that hydrogen bonded CO groups can be observed in the N-GOQD grafted membrane after chlorine tests, but they are destroyed and weakened in pristine membranes, which indicates that the modified membrane has better resistance to reactive chlorine.

The surface modification of polyamide membranes using graphene oxide

This paper presents the results of the surface modification of polyamide membranes using graphene oxide (GO) for reducing bacterial contamination. Prior to GO deposition on the surface of the membrane plasma treatment was used with a mixture of argon and oxygen (Ar-O2) to activate the surface of the flat sheet membranes. As a result, the process conditions for plasma activation were selected, which allow GO to be attached to the surface of polyamide membranes. In the study, the effect of a deposition of GO aqueous dispersion on filtration, antibacterial properties and morphology of produced materials was investigated. The elaborated conditions allowed to obtain membranes with antibacterial properties and high water permeability.

In-situ covalently bonded supramolecular-based protective layer for improving chlorine resistance of thin-film composite nanofiltration membranes

To improve the chlorine resistance of the polyamide-based NF membranes, ferric ion and tannic (FeIII-TA) networks were grafted onto the polyamide membrane surface via an in-situ modification strategy. The separation performance tests by a cross-flow NF system showed that the grafted membrane (TFC-n) possesses an obviously improved rejection for the selected salts, dyes, and micropollutants with only ~10.0% decrease in water permeability. The chlorination experiments under various pH values demonstrated that the TFC-n membrane presents much superior chlorine resistance than that of the control membrane. Importantly, the grafting layer was also applied to a commercial NF 270 membrane, and the FeIII-TA grafted NF 270 membrane exhibited much higher chlorine resistance than that of the bare NF 270 and polyvinyl alcohol (PVA) coated NF 270 membranes. The greatly enhanced chlorine resistance can be ascribed to the combined effects of enhanced size exclusion, additional protection, and sufficient radical scavenging originated from the grafted FeIII-TA networks. The high-performance of the grafted membrane highlight the feasibility of FeIII-TA networks as a promising material for the construction of chlorine resistant interfaces for environmental nanocomposites.

Highly permeable and fouling-resistant hollow fiber membranes for reverse osmosis

This paper reports a fast, cost-effective and environmental-friendly method to engineer the membrane structure, and simultaneously enhance the permeance and fouling resistance in reverse osmosis (RO). By free radical polymerization in water, copolymers containing fouling-resistant zwitterionic and hydroxyl-based anchoring groups are synthesized and quickly bonded to the polyamide membrane surface. The copolymer also functions as the molecular engine to reduce the thickness of the polyamide layer and drill nanopores, thereby re-shaping its 3D structure for higher permeability. It is revealed that by design of the size and functionality of the copolymer, the water permeability and salt rejection may be simultaneously increased. Our membrane demonstrates a pure water permeability of 10.5 L m−2 h−1 bar−1, NaCl rejection of 98.1%, and superior fouling resistance towards various foulants and realistic feed. This paper provides a new perspective for the development of highly permeable, fouling-resistance membranes not only for RO, but also nanofiltration.

Armor polyamide reverse osmosis membrane with POSS ‘armors’ through two-step interfacial polymerization for high anti-chlorine and anti-bacteria performance

Improvement of anti-chlorine and anti-bacterial properties of membranes has been a major challenge in desalinating process. In this paper, zero-dimension cage-like structure polyhedral oligomeric silsesquioxane (POSS) was in situ armored on the surface of polyamide (PA) membrane and acted as ‘armors’ to prevent active chlorine corrosion and bacterial fouling. PA/POSS hybrid membranes could be easily achieved through a simple two-step interfacial polymerization. Anti-chlorine and anti-bacterial properties of PA/POSS hybrid membranes significantly improved during desalination by tuning the content of POSS ‘armors’. Salt rejection reached approximately 98% after immersing PA/POSS hybrid membranes in the active chlorine solution for 24 h, which showed excellent anti-chlorine property. In addition, the anti-bacterial property of PA reverse osmosis (RO) membranes extremely enhanced after armoring with POSS nanoparticles. This finding demonstrated that the structure and chemical inert nature of POSS enabled PA/POSS membranes to block active chlorine and bacteria. PA/POSS membranes provided a promising approach to improve membrane desalination.

Supramolecular-Based Regenerable Coating Layer of a Thin-Film Composite Nanofiltration Membrane for Simultaneously Enhanced Desalination and Antifouling Properties.

A high-performance nanofiltration (NF) membrane with simultaneously improved desalination and antifouling properties while maintaining regeneration ability is highly desirable in water treatment. Surface modification is an effective approach to enhance the performance of NF membranes. In the present study, a multifunctional thin-film composite NF membrane (Fe-TFC) was fabricated via coating a regenerable ferric ion-tannic acid (FeIII-TA) layer on the nascent polyamide membrane surface. The Fe-TFC membrane exhibited enhanced hydrophilicity, smaller pore size, and lower negative charge compared with the control membrane. The salt rejections and selectivity of divalent to monovalent ions were greatly improved with only a slight decrease in water permeability due to the presence of the coating layer. Meanwhile, dynamic fouling tests with humic acid demonstrated that the Fe-TFC membrane possessed an enhanced antifouling property and excellent flux recovery rate. After coating, the normalized water flux and flux recovery of the Fe-TFC membrane increased from 0.02 to 0.26 and 32.1 to 76.4% at the end of five cycles of fouling tests, respectively. In addition, the resultant membrane exhibited excellent durability and stability under harsh conditions for ∼10 days. Interestingly, the fouled coating layer can be easily removed by HCl cleaning and regenerated through an in situ strategy. Consequently, the regenerated membranes presented stable antifouling properties and desalination performance after several times of regeneration. It was demonstrated that the unique feature of FeIII-TA networks enables the coating layer to act as a protective layer for the underlying polyamide membrane, leading to the high performance of the composite membrane. This study provides a new insight for surface functionalization and easy regeneration of the TFC nanofiltration membrane in water treatment technology.

Novel non-trimesoyl chloride based polyamide membrane with significantly reduced Ca2+ surface deposition density

Polyamide membranes based on trimesoyl chloride (TMC) have captured the majority of the market share for desalination in water treatment. The TMC based membrane is prone to form calcium bridges with the organic foulants due to the relatively strong deprotonation ability of the benzoic acid generated from the incomplete reaction of the acyl chloride monomers. The foulants are thus rapidly deposited on the surface of the TMC based membrane, which results in the deterioration of water production and decrease of membrane lifespan. Herein, we have fabricated a polyamide membrane based on novel trimesoyl-[4,4-dimethyl-5(4H)-azlactone] (TMDMA) monomer instead of TMC monomer. Since the carboxylic groups of the prepared TMDMA polyamide nanofilm are not directly connected to the phenyl ring, the acidity coefficient (pKa) value is higher and, consequently, deprotonation ability is expected to be weaker. To confirm this theory, we have conducted the fouling experiment on TMDMA based membrane using alginate as a model foulant and compared that with TMC based polyamide membranes. A lower flux decline (33%) and higher cleaning efficiency (90.72%) are observed for the TMDMA polyamide membrane, while the flux decline and cleaning efficiency for the TMC based polyamide membrane are 52% and 49.52% respectively. Furthermore, the average Ca2+ density of the TMDMA polyamide membrane surface before and after cleaning are 81.52 mg m−2 and 21.61 mg m−2 respectively, which are lower than that of the TMC based polyamide membrane surface. Thus, it is clearly showing that the surface of the TMDMA polyamide membrane is not prone to form calcium bridges with foulants due to the weaker complexation between Ca2+ and the carboxylic acid groups.

Preparation of high performance polyamide membrane by surface modification method for desalination

This work provides a new and simple method to improve the performance of polyamide reverse osmosis membrane, including selectivity properties and antifouling ability. Herein, quaternary ammonium groups have been immobilized on polyamide membrane surface by grafting and self-polymerization reaction of epoxy group in 2,3-epoxypropyl trimethyl ammonium chloride with tris(dimethylaminomethyl)phenol as curing catalyst. The surface properties of the modified membrane, such as surface charge, hydrophilicity and roughness have been characterized in detail and compared with virgin PA membrane. This novel modification method mainly achieves three advances in terms of membrane performance and fabricating technique. On one hand, the positively charged quaternary ammonium group immobilized on membrane surface can prevent cationic surfactant absorbing to improve fouling-resistance, due to the electric repulsion effect. On the other hand, self-polymerization reaction based on epoxy group occurred on polyamide surface can fill up the aggregate pore or reduce the pore size in polyamide, resulting in the increase of salt rejection. More importantly, the membrane modification process is very simple and efficient, which adapts to fabricate RO membrane with high performance on industrial production line completely.

Forward osmosis membrane performance during simulated wastewater reclamation: Fouling mechanisms and fouling layer properties

A thin-film composite (TFC) FO membrane was used to study the fouling characteristics of effluent organic matter (EfOM) fractions in treated wastewater effluent represented by alginate, bovine serum albumin, humic acid and octanoic acid. These model foulants were chosen to represent carbohydrates, proteins, humic substances and fatty acids. Inter foulant interactions and their influence on membrane flux loss was established by running series of fouling tests with feed solutions containing mixtures of model foulants. The obtained results demonstrated that under our experimental conditions humic acid (HA) and octanoic acid (OA) had no significant role on permeate flux loss during wastewater treatment over short periods. However, alginate and bovine serum albumin (BSA) and their mixtures caused significant total flux loss, through alginate-calcium complexation that led to the formation of a resistant gel layer on the membrane surface. Protein fouling was mainly attributed to multiple layer adsorption onto the polyamide membrane surface. Mixing alginate with BSA saw a further decline in permeate flux, worse than that caused individually by either of the foulants, and gives an indication of the synergistic effect between the two foulants. There were favourable inter-foulant interactions between the carbohydrates and the proteins that promoted the formation of hybrid aggregates that were deposited on the membrane surface and enhanced flux loss. The additional presence of humic acid to the mixture of BSA and alginate further aggravated membrane fouling. Polysaccharides and proteins were found to be the most dominant foulants during wastewater reclamation. The extent of interactions between the organic foulants had an effect on the fouling layer structure and its role in permeate flux loss.

Triclosan-immobilized polyamide thin film composite membranes with enhanced biofouling resistance

We report on a strategy to improve biofouling resistance of a polyamide (PA) thin-film composite (TFC) reverse osmosis (RO) membrane via chemically immobilizing triclosan (TC), known as a common organic biocide, on its surface. To facilitate covalent attachment of TC on the membrane surface, TC was functionalized with amine moiety to prepare aminopropyl TC. Then, the TC-immobilized TFC (TFC-TC) membranes were fabricated through a one-step amide formation reaction between amine groups of aminopropyl TC and acyl chloride groups present on the PA membrane surface, which was confirmed by high-resolution XPS. Strong stability of the immobilized TC was also confirmed by a hydraulic washing test. Although the TFC-TC membrane showed slightly reduced separation performance compared to the pristine control, it still maintained a satisfactory RO performance level. Importantly, the TFC-TC membrane exhibited excellent antibacterial activity against both gram negative (E. coli and P. aeruginosa) and gram positive (S. aureus) bacteria along with greatly enhanced resistance to biofilm formation. Our immobilization approach offers a robust and relatively benign strategy to control biofouling of functional surfaces, films and membranes.

Comparison of organic fouling resistance of thin-film composite membranes modified by hydrophilic silica nanoparticles and zwitterionic polymer brushes

We conducted a comparative study to investigate the efficacies of two different types of highly hydrophilic materials (i.e., silica nanoparticles (SiNPs) and zwitterionic polymers) for antifouling surface modification of polyamide thin-film composite (TFC) membranes. Dense layers of SiNPs and zwitterionic polymer brushes were grafted on the membrane surfaces via dip-coating with aminosilane-functionalized SiNPs (i.e., SiNP-TFC membrane) and surface-initiated atom-transfer radical-polymerization of sulfobetaine methacrylate (i.e., PSBMA-TFC membrane), respectively. With the same degree of enhancement of surface hydrophilicity and identical surface roughness, the PSBMA-TFC membrane exhibited significantly higher fouling resistance than the SiNP-TFC membrane in adsorption tests of proteins and bacteria as well as in forward osmosis (FO) dynamic fouling experiments using alginate as a model organic foulant. Chemical force microscopy measurements revealed that membrane-foulant electrostatic attraction aggravates organic fouling of the SiNP-TFC membrane to a certain degree, but the primary fouling mechanism is the complexation of organic foulants with carboxylic groups on the polyamide membrane surface. We attribute the lower fouling resistance of the SiNP-TFC membrane to the high density of surface carboxylic groups that may still be accessible to foulants as well as to membrane-foulant electrostatic interaction. On the contrary, the zwitterionic polymer brushes effectively shield the surface carboxylic groups and provide steric hindrance against foulant adsorption due to significant hydration of the zwitterionic brushes.

Bomb swab: Can trace explosive particle sampling and detection be improved?

The marked increase in international terror in recent years requires the development of highly efficient methods to detect trace amounts of explosives at airports, border crossings and check points. The preferred analytical method worldwide is the ion mobility spectrometry (IMS) that is capable of detecting most explosives at the nano-gram level. Sample collection for the IMS analysis is based on swabbing of a passenger's belongings to collect possible explosive residues. The present study examines a wide range of issues related to swab-based particle collection and analysis, in the hope of gaining deeper understanding into this technique that will serve to improve the detection process. The adhesion of explosive particles to three typical materials, plastic, metal and glass, were measured using atomic force microscopy (AFM). We found that a strong contribution of capillary forces to adhesion on glass and metal surfaces renders these substrates more promising materials upon which to find and collect explosive residues. The adhesion of explosives to different swipe materials was also examined. Here we found that Muslin, Nomex® and polyamide membrane surfaces are the most promising materials for use as swipes. Subsequently, the efficiency of multiple swipe use – for collecting explosive residues from a glass surface using Muslin, Nomex® and Teflon™ swipes – was examined. The study suggests that swipes used in about 5–10 “sampling and analysis cycles” have higher efficiency as compared to new unused swipes. The reason for this behavior was found to be related to the increased roughness of the swipe surface following a few swab measurements. Lastly, GC-MS analysis was employed to examine the nature of contaminants collected by the three types of swipe. The relative amounts of different contaminants are reported. The existence and interference of these contaminants have to be considered in relation to the detection efficiency of the various explosives by the IMS.

Simple method for preparing thin film composite polyamide nanofiltration membrane based on hydrophobic polyvinylidene fluoride support membrane

This study attempts to prepare thin film composite (TFC) polyamide (PA) membrane using polyvinylidene fluoride (PVDF) as support membrane. PVDF has superior physical characteristics but is difficult to be used as TFC PA support membrane because of its strong hydrophobicity. However, in this study TFC PA membrane was prepared using a simple method of flowing trimesoyl chloride (TMC) organic solution at a specific velocity after putting specific quantity of m-phenylenediamine (MPD) aqueous solution on hydrophobic PVDF support membrane. The presence of polyamide formed by the interfacial polymerization of MPD and TMC were verified with X-ray photoelectron spectroscopy and attenuated total reflectance-fourier transform infra-red spectrophotometer, and field emission scanning electron microscopy and atomic force microscopy were used to observe the TFC PA membrane's surface and structural characteristics. The prepared TFC PA membrane showed maximum performance at TMC organic solution flow velocity of 1.21m/s and TMC concentration of 0.3% (w/v). The TFC PA membrane prepared under these optimal conditions showed rejection rates of 68.14, 88.80, and 96.06% against NaCl, CaCl2 Na2SO4 5000ppm, respectively. This proved that the TFC PA membrane prepared in this study had nanofiltration performance.

Polyamide membrane surface and bulk modification using humid environment as a new heat curing medium

Heat curing was devised in temperature-controlled steam and water environments to synthesize reverse osmosis (RO) polyamide (PA) membrane. The effect of new curing media on the physicochemical properties and RO performance of the synthesized polyamides was fully investigated using X-ray photoelectron spectroscopy (XPS), attenuated total reflection infrared (ATR-IR), scanning electron microscopy (SEM), atomic force microscopy (AFM), and water drop contact angle. The results show a reduction in amide linkage content on the surface of the steam-cured polyamide and surface and bulk of the water-cured polyamide. Additionally, it was revealed that heat curing in the humidity-controlled environment can be considered as a chemical modification process with the ability to change the cross-linking degree in adjustable depth and intensity. Heat curing in steam provided the membrane with great surface hydrophilicity, permeate flux, and salt rejection, which are required for treating dilute solutions. Moreover, the water-cured membrane exhibited extra high surface hydrophilicity and salt rejection that are necessary for treating solutions with high inorganic fouling tendency and high osmotic pressure.

Innovative hydrophobic coating of perfluoropolyether (PFPE) on commercial hydrophilic membranes for DCMD application

Innovative hydrophobic coated membranes have been prepared and characterised in Direct Contact Membrane Distillation (DCMD) for potential water treatment applications. A UV-curable perfluoropolyether (PFPE) hydrophobic compound (Fluorolink® AD 1700) was used as coating material to tailor the surface of commercial microfiltration hydrophilic polyamide (PA) membranes with different pore sizes.The coated membranes consisted of a top thin hydrophobic porous layer overlying the hydrophilic commercial membrane support. Produced membranes were fully characterised in terms of surface and cross-section morphology, water contact angle, porosity, pore size and liquid entry pressure. The innovative coated hydrophobic membranes were tested in DCMD configuration, using deionized water and salty solution 0.6M (NaCl) as feed. In particular, the effect of the coating concentration on the permeate fluxes was investigated for different hydrophilic pore size commercial membranes (0.1–0.22–0.45μm). The measured permeate fluxes ranged between 4.56–22.81kg/m2h at different feed temperatures (40–50–60°C) keeping constant the permeate temperature at 14°C, for deionized water, whereas an average value of 11kg/m2h, at 50°C was found in case of the salty solution.

Molecular Dynamics Simulations of a Poly(ethylene glycol)-Grafted Polyamide Membrane and Its Interaction with a Calcium Alginate Gel.

Molecular dynamics simulations are carried out to investigate the antifouling property of a polyethylene glycol (PEG)-grafted polyamide (PA) membrane. Our specific interest is the computational study of the interaction between a grafted PEG coating and an alginate gel foulant by a steered molecular dynamics approach. Simulation results show that the PEG coating can hold a tightly bound hydration water layer. When the alginate gel is dragged to approach the PEG coating surface, a strong repulsive hydration force is observed due to the compression of this hydration layer. Detailed calculations of the potential of mean force (PMF) show that the repulsive interaction between the alginate gel and the hydration water layer around the PEG coating has a dominant contribution to the total repulsive PMF. We have also studied the effect of the PEG coverage on the membrane-foulant interactions. We find that the alginate gel has a strong tendency to drift to the uncovered PA membrane surfaces (namely, the PEG hollows). However, direct attachment of the gel to the PA membrane surface can be avoided if the gel size is slightly larger than the PEG hollow site.