Number Of Polyelectrolyte Bilayers Research Articles

Enhanced monovalent over divalent cation selectivity with polyelectrolyte multilayers in membrane capacitive deionization via optimization of operational conditions

In this work, we tuned the ion selectivity of a polyelectrolyte multilayer (PEM)-coated, cation-exchange membrane (CMX) in a membrane capacitive deionization (MCDI) process by carefully studying different operational modes, namely constant voltage (CV) and constant current (CC). The monovalent cation selectivity and its time-dependent behavior were monitored at different voltage and current values. Upon optimizing the current density (10 A/m2) and the number of polyelectrolyte bilayers (5.5) on the CMX membranes, a time-independent and nearly full monovalent cation selectivity was obtained for various feed solutions, provided a polycation-terminated PEM was applied. Furthermore, the selectivity values of several commercially available cation-exchange membranes were tested under the optimized conditions and compared with CMX and PEM-CMX, yielding the best performance for PEM-CMX, regardless the composition of feed solution. Before this optimization, this MCDI system showed a time-dependent selectivity, with a maximum of ρMgNa ≈3. The results were rationalized by applying an MCDI model based on the dynamic potential profile, describing the potential drops across the membrane and demonstrating a threshold for the current density.

Conductive polyelectrolyte multilayers PANI membranes synthesis for tunable filtration ranges

Polyaniline membrane tends to swell and brittle when it undergoes excessive acid doping upon increasing its conductivity and hydrophilicity properties. Therefore, modification was done by introducing polyelectrolyte layers on polyaniline membrane surface with the aim to produce nanofiltration range membrane. Modification of PANI membrane with layer-by-layer polyelectrolyte is a new method for modifying PANI membrane; thus, the effect of doping time with number of polyelectrolyte bilayers with the membrane properties was investigated. From the results, the optimum doping time was 120 min to maximally increase the membrane’s hydrophilicity and conductivity. Next, introduction of polyelectrolyte layers on the membranes’ surface via layer-by-layer coating has found to decrease the porosity of the membranes top layer up to 10 times from ultrafiltration to nanofiltration ranges. Their surface hydrophilicity and negativity has also increased significantly while having a similar conductivity increment trend upon measured in wet condition (similar to water filtration condition). Furthermore, the permeability of the modified PANI membranes before and after back-flushing was performed for membranes cleaning process was seen to have no significant difference. Thus, it can be concluded that the presence of polyelectrolyte multilayers on the membrane surface has successfully formed a stable nano-range membrane with the same desired permeability even after back-flushing.

Development and Characterization of New Pervaporation PVA Membranes for the Dehydration Using Bulk and Surface Modifications.

In the present work, the novel dense and supported membranes based on polyvinyl alcohol (PVA) with improved transport properties were developed by bulk and surface modifications. Bulk modification included the blending of PVA with chitosan (CS) and the creation of a mixed-matrix membrane by introduction of fullerenol. This significantly altered the internal structure of PVA membrane, which led to an increase in permeability with high selectivity to water. Surface modification of the developed modified dense membranes, based on composites PVA-CS and PVA-fullerenol-CS, was performed through (i) making of a supported membrane with a thin selective composite layer and (ii) applying of the layer-by-layer assembly (LbL) method for coating of nano-sized polyelectrolyte (PEL) layers to increase the membrane productivity. The nature of polyelectrolyte type—(poly(allylamine hydrochloride) (PAH), poly(sodium 4-styrenesulfonate) (PSS), poly(acrylic acid) (PAA), CS), and number of PEL bilayers (2–10)—were studied. The structure of the composite membranes was investigated by FTIR, X-ray diffraction, and SEM. Transport properties were studied during the pervaporation separation of 80% isopropanol–20% water mixture. It was shown that supported membrane consisting of hybrid layer of PVA-fullerenol (5%)–chitosan (20%) with five polyelectrolyte bilayers (PSS, CS) deposited on it had the best transport properties.

Promising sub-100 nm tailor made hollow chitosan/poly(acrylic acid) nanocapsules for antibiotic therapy

Herein, we report on the preparation of ultra-low sized (<100 nm in diameter) biodegradable polymeric capsules for potential applications as nanocontainers in antibiotic therapy. Hollow nanospheres based on the chitosan/poly(acrylic acid) pair are elaborated via (i) the layer-by-layer technique using gold nanoparticles (20 and 60 nm in size) as sacrificial templates, (ii) loading with amoxicillin, a betalactam antibiotic, and (iii) removal of the gold core via cyanide-assisted hydrolysis. Size, dispersity and concentration of the resulting nanocapsules are easily tuned by the nanoparticle templates, while wall thickness is controlled by the number of polyelectrolyte bilayers. Electrostatic interactions between the protonated amine groups of chitosan and the carboxyl groups of poly(acrylic acid) act as the driving attraction force allowing easy and fast design of robust and well-ordered multilayer films. Successful hydrolysis of the gold core is evidenced by time-dependent monitoring of the gold spectroscopic signature (absorbance at 519 nm and 539 nm for the gold nanoparticles with 20 and 60 nm, respectively). Crosslinked capsules are also prepared through crosslinking of the chitosan chains with glutaraldehyde. Chitosan-based nanocapsules are finally evidenced to be promising drug delivery vehicles of amoxicillin trihydrate with tuneable properties such as entrapment efficiency in the range of 62–75% and 3.5–5.5% concerning the drug loading.

Biocatalytic and salt selective multilayer polyelectrolyte nanofiltration membrane

We used layer-by-layer (LbL) self-assembly to fabricate a polyelectrolyte (PE) nanofiltration membrane for salt rejection and to immobilize trypsin on the membrane outer layer for biocatalytic activity. Poly(ethylene imine) (PEI) and poly(diallyl dimethyl ammonium chloride) (PDADMAC) were used as cationic PE while poly(acrylic acid) (PAA) and poly(styrene sulfonate) (PSS) were used as anionic PE. The impact of PE type, number of PE bilayers, and PE concentration on the rejection of inorganic salts (NaCl, MgCl2, Na2SO4, and MgSO4) and protein (bovine serum albumin, BSA) was systematically investigated. A maximum rejection of 12.7%, 45.2%, 85.5%, 94.0%, and 100% of MgCl2, NaCl, MgSO4, Na2SO4, and BSA, respectively, was obtained by the PDADMAC-PSS membrane with four bilayers. Trypsin (TRY) was immobilized on the membrane surface by electrostatic attraction or covalent bonding to produce a biocatalytic membrane and to alleviate protein fouling. Important parameters for enzymatic activity, such as immobilization time, pH, temperature, salt concentration and type, as well as the reuse number and storage time were investigated to expound the mechanism of enzyme activity in the presence of salt and BSA. BSA was used as a model protein for organic fouling experiments, and flux decline rate of the membranes was determined. Our results show that LbL-modified membranes with covalent enzyme immobilization had the lowest protein fouling rate, which we attribute to the biocatalytic activity of the immobilized trypsin.

High fouling-resistance of polyamide desalination-membrane modified with PEI/PAH polyelectrolyte multilayers

Membrane fouling is a persistent problem in reverse osmosis (RO) process which leads to higher operating pressure, quality deterioration, and frequent chemical cleaning of the membranes. The objective of this paper is to prepare a fouling-resistant RO desalination membrane while keeping high salt rejection and permeate flux. Polyamide (PA) membranes were prepared and modified using spin assisted Layer-by-Layer assembly of polyelectrolytes (PEI/PAH), characterized and tested in a cross-flow desalination setup. The effect of preparation conditions (number of coating layers, concentration and pH of the polyelectrolyte solutions) on the performance of the membrane was also investigated. SEM micrographs showed that the surface of the PA membrane is rough and has typical ridge and valley structure. However, images of the modified membranes showed smoother surfaces as the number of polyelectrolyte bilayers was increased which was verified using the AFM analysis. In addition, contact angle measurements suggested that the surfaces of the modified membranes became more hydrophilic due to the presence of hydrophilic hydroxyl and amine groups. Permeation results showed comparable salt rejection under saline feed water of 2000ppm. 50 bilayer modified membrane having 110mg/L of polyelectrolyte solution, possess permeability of 0.83L/m2hbar with 95% salt rejection. However, 27 bilayer modified membrane having 200mg/L of polyelectrolyte solution, possess greater permeability of 1.78L/m2hbar with 96% salt rejection. Fouling experiments showed that after three hours of filtration, functionalized membranes retained more than 88% of water flux compared to pristine polyamide membrane which suffered from more than 42% flux drop.

Stability and Performance Study of Polyethersulfone Membranes Modified Using Polyelectrolytes

In this research work, porous PES membranes were initially pre-heated for certain duration of time and then surface-modified to reject the MgSO4 salt solutions through self-adsorption of polyelectrolytes. From the experimental work, higher membrane salt rejection capability can be obtained when the number of polyelectrolyte bilayers is increased. The images of the cross-sectional morphology of modified and non-modified membranes were obtained using field emission scanning electron microscopy (FESEM). All modified membranes showed relatively lower contact angle values.

Stratified rod network model of electrical conductance in ultrathin polymer–carbon nanotube multilayers

The electronic conductance of polymer--carbon nanotube multilayered composite films assembled by the spin-spray layer-by-layer method is investigated. Our measurements show that the film conductance per bilayer ${\ensuremath{\sigma}}_{1}$ vanishes for film thickness below a critical value, and above this threshold it grows logarithmically with the number of polyelectrolyte bilayers ${k}_{\mathrm{l}}$. The results of our experiments are interpreted using a stratified quasi-two-dimensional conducting-network model, in which the junction resistance between nanotubes deposited in different bilayers is a function of the interlayer distance. Using scaling arguments and numerical simulations, we show that the linear dependence of the junction resistance on the layer separation leads to the logarithmic behavior ${\ensuremath{\sigma}}_{1}\ensuremath{\sim}\mathrm{log}{k}_{\mathrm{l}}$ for large ${k}_{\mathrm{l}}$, as observed in our experiments. Properties of our stratified-network model are investigated, and we show that with proper rescaling, different sets of experimental measurements can be collapsed onto a master curve. The overall shape of the master curve is determined by a single dimensionless parameter characterizing the slope of the junction-resistance function.

Fabrication of conductive polymer-coated sulfur composite cathode materials based on layer-by-layer assembly for rechargeable lithium–sulfur batteries

Lithium–sulfur battery is a promising energy storage system due to its high specific energy density, low cost and environmental friendliness. Layer-by-layer (LbL) assembly technique is introduced as a simple method to fabricate polymer-coated sulfur cathode materials for rechargeable lithium–sulfur batteries. Conductive polyaniline (PANI) were assembled on the outer shell of sulfur particles to provide an electron conducting paths for the charge and discharge of lithium–sulfur battery. The low permeability of sulfur shells was obtained by assembling the enough number of polyelectrolyte bilayers. A crosslinker and heat treatment were utilized to further reduce its permeability. The assembled polymer shells can be expected to be permeable for Li+ and slowly or hardly for sulfur and polysulfide during charge and discharge process. The obtained sulfur composite cathode materials were characterized by four-point probe instrument, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) patterns and Fourier transform infrared (FTIR) spectroscopy. The results demonstrated polymers have been coated on the surface of sulfur only by physical interaction and have no effect on sulfur. The conductive polymer-coated sulfur cathode also represents a well conductivity of 0.23Scm−1. Moreover, after coated by polymers, the crystal structure of sulfur still keeps its orthorhombic corresponding to cyclooctasulfur molecule (S8).

Preparation and characterization of polyacrylonitrile membranes modified with polyelectrolyte deposition for separating similar sized proteins

One of the challenges faced by ultrafiltration membranes is to separate proteins with a small difference in their molecular weights. Recently, some researchers tried to overcome this problem by using charged membranes. This study examined the use of layer by layer deposition of polyelectrolytes on the chemically-modified polyacyronitrile membrane to increase the selectivity of the ultrafiltration. The membranes were prepared by wet-phase inversion technique and polyethylenimine (PEI) and alginate (ALG) were chosen as cationic and anionic polyelectrolytes for the modification of the surfaces. Sieving coefficient data were obtained with myoglobin and lysozyme as model proteins. The influences of solution pH, ionic strengths of the protein and polyelectrolyte solution and the number of polyelectrolyte bilayers on both selectivity and throughput were investigated. The highest selectivity and throughput were achieved with the 1-bilayer PEI-ALG coated polyacrylonitrile (PAN) membrane. Increasing the number of coating bilayers or the ionic strength of the protein solution or adding salt into the polyelectrolyte coating solution decreased both the maximum selectivity and throughput of the modified membranes. ▸ Polyacyronitrile membranes were modified with polyelectrolyte deposition. ▸ Polyethylenimine and alginate were used as polyelectrolytes. ▸ The membranes were tested for the separation of myoglobin and lysozyme. ▸ The highest selectivity and throughput were achieved with the 1-bilayer coating.

Controlled Conductive Polymer Coating on Wood Microfibers via Layer-by-layer Nanoassembly

AbstractThis paper reports on layer-by-layer (LbL) self-assembly of poly (3, 4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT-PSS) conducting polymer on lignocellulose wood microfibers to make conducting paper. Polycation such as poly(allylamine hydrochloride) (PAH) was used with polyanionic PEDOT-PSS to construct the multilayers. The physical characterization of the microfiber was done using roughness step tester (RST) and surface profilometer (TENCOR). Thickness of the coated film was estimated using a quartz crystal micro-balance. Current – Voltage characterization was performed using a Keithley measurement system after each self-assembly of PEDOT-PSS to study the electrical properties of the coated film. It was observed that the conductivity of the microfiber was proportional to the number of polyelectrolyte bilayers deposited. The measured conductivities ranged from (1 to 5) × 10-3 Scm-1 to 1 to 10 Scm-1 for different bilayers of PEDOT-PSS on wood microfibers. It was also observed that the conductivity of the nano-coated fibers is dependent upon the salt concentration used in PAH polycations to from the multilayer. In this work we are developing scale integration from nano, to micro and macro (nanocoating-microfibers-macropaper). The results obtained show great promise for the development of smart paper technology and its contribution to the economic development of the nation.

Study of transport phenomena of FITC labeled dextran through nano self assembled microshells

The transport characteristics of hollow shells formed via self assembly of polyelectrolytes was the focus of this study. The shells were formed by layering on 5μm diameter sacrificial cores that were subsequently dissolved in an acidic media. The effect of two polyanions was compared: polyvinyl sulfonate (PVS) and polystyrene sulfonate (PSS) along with two polycations: polyallylamine hydrochloride (PAH), and polydimethyldiallyl ammonium (PDDA). The number of polyelectrolyte bilayers was varied from 2, 4, and 6. The diffusion of fluorescein-isothiocyanate (FITC) labeled dextran was monitored over a period of days after loading times of 12, 36, or 60h. Loading was also characterized using confocal laser scanning microscopy (CLSM). Two molecular weights of FITC labeled dextran, 4000 and 77,000, were utilized in this study. The choice in polycation results in the largest changes in wall permeability for the neutral pH tested. PDDA architectures produce a higher permeability than PAH structures. Loading of 77,000 MW FITC-dextran was observed in both the PVS/PDDA and PSS/PDDA structures.