Deposition Of Polyelectrolytes Research Articles

Organic micropollutant removal and phosphate recovery by polyelectrolyte multilayer membranes: Impact of buildup interactions

Polyelectrolyte multilayer (PEM) deposition conditions can favorably or adversely affect the membrane filtration performance of various pollutants. Although pH and ionic strength have been proven to alter the characteristics of PEM, their role in determining the buildup interactions that control filtration efficacy has not yet been conclusively proved. A PEM constructed using electrostatic or non-electrostatic interactions from controlled deposition of a weak polyelectrolyte could retain both charged and uncharged pollutants from water. The fundamental relationship between polyelectrolyte charge density, PEM buildup interaction, and filtration performance was explored using a weak-strong electrolyte pair consisting of branching poly (ethyleneimine) and poly (styrene sulfonate) (PSS) across pH ranges of 4–10 and NaCl concentrations of 0 M–0.5 M. PEI/PSS multilayers at acidic pH were dominated by electrostatic interactions, which favored the selective removal of a charged solute, phosphate over chloride, while at alkaline pH, non-electrostatic interactions dominated, which favored the removal of oxybenzone (OXY), a neutral hydrophobic solute. The key factor determining these interactions was the charge density of PEI, which is controlled by pH and ionic strength of the deposition solutions. These findings indicate that the control of buildup interactions can largely influence the physico-chemical and transport characteristics of PEM membranes.

Selective recovery of silver from copper impurities by electrodialysis: Tailoring monovalent selective cation exchange membranes by monomolecular layer deposition

Selective recovery of silver from secondary resources enriched with copper impurities is a well-known challenge but is urgently needed by the industry. This study addresses the challenge by developing a highly efficient monovalent selective cation exchange membrane (CEM) with a specifically tailored polyelectrolyte deposition, enabling efficient Ag+/Cu2+ separation in electrodialysis. Based on the Ag+/Cu2+ separation mechanism in electrodialysis, a selected polyelectrolyte, polyethyleneimine (PEI), was deposited on a standard CEM as a monomolecular layer with precisely controlled polymer chain stretch patterns and optimized morphologies. The effects of deposition conditions, such as solution pH and ionic strength, were studied to ensure the desired surface properties. The selectivity performance of the developed membranes was tested using an equimolar binary mixture; a high Ag+/Cu2+ selectivity of > 20 was documented, exhibiting superior selectivity performance compared to commercial monovalent selective CEMs.

Micro crystalline cellulose aided surface modification and deposition of green polyelectrolytes for the improved hydrophilicity and flame retardancy of polyamide 66 fabric

In this work, microcrystalline cellulose (MCC) treated polyamide 66 (PA66) textiles were coated with green and naturally abundant polysaccharides specifically, chitosan (CS) and sodium alginate (SA) together with phytic acid (PA) via layer by layer (LbL) deposition. The prime focus of such treatment was to intensify both the hydrophilic and flame retardant properties of PA66 fabric substrates. Subsequently, the prepared coatings were further subjected to cross-linking modification by dipping them into the barium (Ba) salt solution. Obtained results indicated that the MCC-modified PA66 exhibited a water contact angle (WCA) value of 00 and revealed a drop in peak heat release rate (pHRR) up to 31 % with complete suppression of melt-dripping. Meanwhile, the Ba-ion-induced cross-linking treatment further escalated this reduction up to 36 % by adding enhanced thermal stability, improved char quality along better wash durability of as prepared coatings. In addition, the combined modification of PA66 textiles with MCC and Ba-ion handed a superb enhancement of physical properties like tensile strength by ca. 50 % compared to the pure PA66. Thus, this MCC-assisted surface modification paves the way for a new kind of greener treatment of PA66 textiles in attaining superior hydrophilic and flame retardant properties of the same.

Modification Approaches of Polyphenylene Oxide Membranes to Enhance Nanofiltration Performance.

Presently, water pollution poses a serious threat to the environment; the removal of organic pollutants from resources, especially dyes, is very important. Nanofiltration (NF) is a promising membrane method to carry out this task. In the present work, advanced supported poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) membranes were developed for NF of anionic dyes using bulk (the introduction of graphene oxide (GO) into the polymer matrix) and surface (the deposition of polyelectrolyte (PEL) layers by layer-by-layer (LbL) technique) modifications. The effect of PEL combinations (polydiallyldimethylammonium chloride/polyacrylic acid (PAA), polyethyleneimine (PEI)/PAA, and polyallylamine hydrochloride/PAA) and the number of PEL bilayers deposited by LbL method on properties of PPO-based membranes were studied by scanning electron microscopy (SEM), atomic force microscopy (AFM), and contact angle measurements. Membranes were evaluated in NF of food dye solutions in ethanol (Sunset yellow (SY), Congo red (CR), and Alphazurine (AZ)). The supported PPO membrane, modified with 0.7 wt.% GO and three PEI/PAA bilayers, exhibited optimal transport characteristics: ethanol, SY, CR, and AZ solutions permeability of 0.58, 0.57, 0.50, and 0.44 kg/(m2h atm), respectively, with a high level of rejection coefficients-58% for SY, 63% for CR, and 58% for AZ. It was shown that the combined use of bulk and surface modifications significantly improved the characteristics of the PPO membrane in NF of dyes.

Reduced Graphene Oxide/Polyelectrolyte Multilayers for Fast Resistive Humidity Sensing.

Fast humidity sensors are of interest due to their potential application in new sensing technologies such as wearable personal healthcare and environment sensing devices. However, the realization of rapid response/recovery humidity sensors remains challenging primarily due to the sluggish adsorption/desorption of water molecules, which particularly impacts the response/recovery times. Moreover, another key factor for fast humidity sensing, namely the attainment of equal response and recovery times, has often been neglected. Herein, the layer-by-layer (LbL) assembly of a reduced graphene oxide (rGO)/polyelectrolyte is demonstrated for application in fast humidity sensors. The resulting sensors exhibit fast response and recovery times of 0.75 and 0.85 s (corresponding to times per RH range of 0.24 and 0.27 s RH-1, respectively), providing a difference of only 0.1 s (corresponding to 0.03 s RH-1). This performance exceeds that of the majority of previously reported graphene oxide (GO)- or rGO-based humidity sensors. In addition, the polyelectrolyte deposition time is shown to be key to controlling the humidity sensing kinetics. The as-developed rapid sensing system is expected to provide useful guidance for the tailorable design of fast humidity sensors.

Hierarchically Structured, All-Aqueous-Coated Hydrophobic Surfaces with pH-Selective Droplet Transfer Capability.

Often inspired by nature, techniques for precise droplet manipulation have found applications in microfluidics, microreactors, and water harvesting. However, a widely applicable strategy for surface modification combining simultaneous hydrophobicity and pH-sensitivity has not yet been achieved by employing environmentally friendly assembly conditions. The introduction of pH-responsive groups to an otherwise fluorinated polyphosphazene (PPZ) unlocks pH-selective droplet capture and transfer. Here, an all-aqueous layer-by-layer (LbL) deposition of polyelectrolytes is used to create unique hydrophobic coatings, endowing surfaces with the ability to sense environmental pH. The high hydrophobicity of these coatings (ultimately reaching a contact angle >120° on flat surfaces) is enabled by the formation of hydrophobic nanoscale domains and controllable by the degree of fluorination of PPZs, polyamine-binding partners, deposition pH, and coating thickness. Inspired by the hierarchical structure of rose petals, these versatile coatings reach a contact angle >150° when deposited on structured surfaces while introducing a tunable adhesivity that enables precise droplet manipulation. The films exhibited a strongly pronounced parahydrophobic rose petal behavior characterized through the contact angle hysteresis. Depositing as few as five bilayers (∼25 nm) on microstructured rather than smooth substrates resulted in superhydrophobicity with water contact angles >150° and the attenuation of the contact angle hysteresis, enabling highly controlled transfer of aqueous droplets. The pH-selective droplet transfer was achieved between surfaces with either the same microstructure and LbL film building blocks, which were assembled at different pH, or between surfaces with different microstructures coated with identical films. The demonstrated capability of these hydrophobic LbL films to endow surfaces with controlled hydrophobicity through adsorption from aqueous solutions and control the adhesion and transfer of water droplets between surfaces can be used in droplet-based microfluidics applications and water collection/harvesting.

Cell contractile force measured using a deformable hollow capsule

Abstract There are several possible ways to measure the contraction of cells in vitro. Here, we report measurements of the contractile properties of 3T3-L1 cells grown to confluence on 3D hollow capsules. The capsules were fabricated using the layer-by-layer polyelectrolyte deposition technique on a polymer core. After the polyelectrolyte film was completed, the core was dissolved to leave the hollow capsule. The contractile force of the cells was determined from the deformation in the capsule size induced by interruption of the actin cytoskeleton of the cells that adhered to the outer surface of the hollow capsules, using prior measurements of the elastic modulus of the capsule. From the measurements of the compressive modulus for the capsules (of 6.52 μN), those capsule deformations indicate that the forskolin relaxed the layer of cells by 19.6 μN and the cytochalasin-D relaxed the layer of cells by 45.6 μN. The density of cells in the layer indicated that the force associated with the forskolin-induced relaxation of a single cell is 3.2 nN and the force associated with the cytochalasin-D-induced relaxation of a single cell is 7.5 nN. The mechanism of action of forskolin through second messenger pathways to disrupt the assembly of actin stress fibres also explains its reduced effect on cell contraction compared to that for cytochalasin-D, which is a compound that directly inhibits the polymerization of F-actin filaments.

PH-Controlled assembly of polyelectrolyte layers on silica nanoparticles in concentrated suspension

HypothesisPreparation of suspensions of nanoparticles (>1 wt%) coated with a polyelectrolyte multilayers is a challenging task because of the risk of flocculation when a polyelectrolyte is added to a suspension of oppositely charged nanoparticles. This situation can be avoided if the charge density of the polymers and particles is controlled during mixing so as to separate mixing and adsorption events. ExperimentsThe cationic polyethylenimine (PEI) and the anionic carboxymethylcellulose (CMC) were used as weak polyelectrolytes. Polyelectrolyte multilayers build-up was conducted by reducing the charge of one of the components during the addition of the next component. Charge density was controlled by tuning pH. Analysis of the suspension of coated nanoparticles was done by means of dynamic light scattering, electrophoresis and small angle x-ray scattering measurements, while quartz crystal microbalance was used to study the build-up process on flat silica surfaces. FindingsCharge density, controlled through pH, can be used as a tool to avoid flocculation during layer-by-layer deposition of polyelectrolytes on 20 nm silica particles at high concentration (∼40 wt%). When added to silica at pH 3, PEI did not induce flocculation. Adsorption was triggered by raising the pH to 11, pH at which CMC could be added. The pH was then lowered to 3. The process was repeated, and up to five polyelectrolyte layers were deposited on concentrated silica nanoparticles while inducing minimal aggregation.

Layer-by-layer self-assembly of hollow dextran sulfate/chitosan-coated zein nanoparticles loaded with crocin: Fabrication, structural characterization and potential biological fate

Crocin is a water-soluble carotenoid and has shown potential to improve the neurodegenerative disease such as Alzheimer's disease (AD). However, its application is limited due to the high instability and susceptibility to process conditions. Here, hollow dextran sulfate/chitosan (DS/CH)-coated zein nanoparticles (NPs) loaded with crocin using sodium carbonate as a sacrificing template were fabricated by a layer-by-layer (LbL) self-assembly technique. The mean particle size, polydispersity index (PDI), encapsulation efficiency, zeta potential, morphology (e.g. TEM and AFM), and FTIR observation revealed that the surface of crocin-loaded LbL hollow zein NPs was generated by the deposition of polyelectrolyte through electrostatic interactions, hydrogen bonding, and hydrophobic interactions. In vitro simulated gastrointestinal digestion and antioxidant activity assays indicated that the NPs exhibited better controlled release behavior and stronger antioxidant activity than that of uncoated crocin-loaded zein NPs dispersed in water. Moreover, the study of the potential effect of the NPs on AD cell model showed that the amyloid-β (Aβ1-42) concentration of differentiated SH-SY5Y cells decreased from 300 pg/mg to 170 pg/mg. These results reveal that LbL self-assembly of hollow DS/CH-coated zein NPs loaded with crocin can be developed as a promising delivery system for effective therapeutic approach of AD, and provide a new practical technique for delivering bioactive ingredients.

Facile Modification of NF Membrane by Multi-Layer Deposition of Polyelectrolytes for Enhanced Fouling Resistance.

Fouling not only deteriorates the membrane structure but also compromises the quality of the permeate and has deleterious consequences on the membrane operation. In the current study, a commercial thin film composite nanofiltration membrane (NF90) was modified by sequentially depositing oppositely charged polycation (poly(allylamine hydrochloride)) and polyanion (poly(acrylic acid)) polyelectrolytes using the layer-by-layer assembly method. The water contact angle was decreased by ~10° after the coating process, indicating increased hydrophilicity. The surface roughness of the prepared membranes decreased from 380 nm (M-0) to 306 nm (M-10) and 366 nm (M-20). M-10 membrane showed the highest permeate flux of 120 L m−2 h−1 with a salt rejection of >98% for MgSO4 and NaCl. The fabricated membranes M-20 and M-30 showed 15% improvement in fouling resistance and maintained the initial permeate flux longer than the pristine membrane.

Tethered electrolyte active-layer membranes

Polyelectrolyte multilayer membranes (PEMs) produced by the sequential, layer-by-layer deposition of polyelectrolytes on porous supports have been shown to significantly reject ions in dilute saline solutions. However, polyelectrolyte thin films are susceptible to swelling or detachment from the substrate in higher salinities and extreme pH conditions, such that their performance is highly dependent on feed water composition. In this study, we introduce tethered electrolyte active-layer membranes (TEAMs), whereby charged block copolymers are covalently grafted-from a porous support, in aim of reducing the stimuli response of layered polyelectrolyte membranes under variable solution conditions. Cellulose support layers were modified using surface-initiated atom transfer radical polymerization of neutral precursor polymers, which were then converted into charged blocks after polymerization. An ultrathin layer of a single negative or positive block with a degree of polymerization (DP) ≥ 770 exhibited ∼15–20 L m-2 h-1 bar-1 pure water permeability, 45–60% rejection of monovalent co-ions, and ∼75% rejection of divalent co-ions. In mixed feed solutions, selectivity of monovalent over divalent co-ions with single-block TEAMs fell within the range of 2–4. Single-block TEAMs slightly shrank under high salt concentration, contrary to the typical substantial swelling of PEMs. As such, this new form of polyelectrolyte membrane may provide greater stability than conventional PEMs and may have potential applications in water softening and salinity reduction of surface waters.

Wetting-Induced Polyelectrolyte Pore Bridging.

Active layers of ion separation membranes often consist of charged layers that retain ions based on electrostatic repulsion. Conventional fabrication of these layers, such as polyelectrolyte deposition, can in some cases lead to excess coating to prevent defects in the active layer. This excess deposition increases the overall membrane transport resistance. The study at hand presents a manufacturing procedure for controlled polyelectrolyte complexation in and on porous supports by support wetting control. Pre-wetting of the microfiltration membrane support, or even supports with larger pore sizes, leads to ternary phase boundaries of the support, the coating solution, and the pre-wetting agent. At these phase boundaries, polyelectrolytes can be complexated to form partially freestanding selective structures bridging the pores. This polyelectrolyte complex formation control allows the production of membranes with evenly distributed polyelectrolyte layers, providing (1) fewer coating steps needed for defect-free active layers, (2) larger support diameters that can be bridged, and (3) a precise position control of the formed polyelectrolyte multilayers. We further analyze the formed structures regarding their position, composition, and diffusion dialysis performance.

Delayed Flammability for Natural Fabrics by Deposition of Silica Core-Amine Shell Microspheres through Dip-Coating Process

In this study, we synthesized a SiO2-APTES core-shell microsphere (Si-NH2-MS) flame retarding material (FRM) as a heat shielding layer on natural fabrics, such as jute, cotton, and flax(cellulose) fibers. This integration was made to improve the flame retardancy property of pure jute, pure cotton, and pure flax fibers by dip-coating deposition of charged anionic and cationic polyelectrolytes to create thin multilayer coatings on the surface of the fabrics via electrostatic interactions. Additionally, through interionic interactions, a strong gluing mechanism occurs between the fabric surface and Si-NH2-MS. Pure jute, pure cotton, and pure flax burned completely within 14, 12, and 10 s, respectively, whereas 2 wt% Si-NH2-MS treated jute, cotton, and flax fibers showed delayed burning times of 21, 18, and 15 s, respectively. Furthermore, 5 wt% Si-NH2-MS treated jute, cotton, and flax fibers showed delayed burning times of 48, 41, and 23 s, respectively, due to the thermal insulation layers developed by the proposed Si-NH2-MS, which were coated uniformly on the surface of the fibers with the help of covalent bonds. Moreover, ignition resistance and self-extinguishing competencies have been observed on fabrics coated with 5 wt% of Si-NH2-MS, which could be a great advantage for indoor fire quenching applications.

New method for the protection and restoration of calcareous cultural heritage stones by polyelectrolytes and hydroxyapatite nanocrystals

We have investigated the feasibility of a new two-step protocol for the restoration of marbles. The process employs a polyelectrolyte multilayer film that enhances the chemical affinity between the treated stone and restorative material (hydroxyapatite nanocrystals), through functionalization, while at the same time it attributes an acid resistant property to the resulting system. Surface functionalization and material deposition is achieved through spraying; a simple and versatile application method suitable for objects of various sizes and geometries. Polyelectrolyte (polyethylenimine and polyacrylic acid) deposition was examined through Attenuated Total Reflection Fourier-Transform Infrared Spectroscopy (ATR-FTIR) and Atomic Force Microscopy (AFM), and tested through contact angle, water absorption and dissolution experiments. The hydroxyapatite nanocrystals were studied by ATR-FTIR, z-potential, AFM and Scanning Electron Microscopy (SEM), and characterized via contact angle and color alteration measurements. Our results show that the polyelectrolyte multilayer was stable in an aqueous environment with increased acid resistance (up to 46% decrease in mass weight loss when compared with untreated samples) and decreased water absorption (up to 39%). Color measurements of the outer hydroxyapatite layer showed a minimal color alteration for one type of the tested substrates showing low color difference values (ΔΕ* < 5). The results suggest that the proposed method holds great potential for marble restoration as it attributes multi-functionality and is easy to apply.

Application of Multivariate and Spectroscopic Techniques for Investigation of the Interactions between Polyelectrolyte Layers in Layer‐by‐Layer Assembled pH‐Sensitive Nanocapsules

AbstractHere, ultraviolet–visible (UV‐Vis) spectroscopy, zeta potential, and chemometrics approaches are used to study the interactions between alginate (Alg) and bovine serum albumin (BSA), respectively as polyanion and polycation. The optimum conditions are obtained at Alg/BSA mixing ratio of 1:4 and pH 4 due to the appropriate complexation between Alg and BSA polyelectrolytes. The layer‐by‐layer (LBL) assembled (Alg/BSA)7@SiO2 nanocapsules are prepared by repeated deposition of Alg and BSA polyelectrolytes on the surface of SiO2‐NH2 nanoparticles. The dried (Alg/BSA)7@SiO2 nanocapsules are dispersed in NH4F/HF buffer solution to remove the silica core and (Alg/BSA)7 hollow capsules are achieved. (Alg/BSA)7 hollow capsules are characterized by Fourier‐transform infrared (FT‐IR), scanning electron microscopy (SEM) with energy dispersive x‐ray analysis (EDX), thermal gravimetric analysis (TGA), and zeta potential analyses. The sensitivity of the hollow capsules to pH is investigated utilizing UV‐Vis spectroscopy. Evaluation of cytotoxicity analysis for (Alg/BSA)7@SiO2 nanocapsules using the MTT assays on Michigan Cancer Foundation‐7 (MCF‐7) cells shows no toxicity effect. The (Alg/BSA)7 hollow capsules have suitable potential as carriers for drug delivery due to their biocompatibility and bioavailability. Betamethasone disodium phosphate (BSP) is loaded on the (Alg/BSA)7 hollow capsules due to biocompatibility and shows a controlled releases profile at pH 7.4.

Peeling back the layers: Investigating the effects of polyelectrolyte layering on surface structure and stability of oil-in-water nanoemulsions

HypothesisLayer-by-layer deposition of polyelectrolytes is a useful technique for modifying surface functionalities. For drug delivery systems, alternating layers of biopolymers coat nanoemulsions, which house and protect the cargo until the time and destination of delivery. Here, we investigate molecular factors contributing to the stability and interfacial properties of nanoemulsions prepared by a co-adsorption of polymers poly(styrene sulfonate) and polyethylenimine (PEI), and surfactant dodecyltrimethylammonium bromide. We hypothesize the interplay between electrosteric and hydrophobic effects upon multi-polymer co-adsorption contributes to both macroscopic and molecular-level interfacial properties of nanoemulsions. ExperimentsTo probe interfacial layering properties, we use vibrational sum frequency scattering spectroscopy with ζ-potential measurements to determine the adsorptive behavior and molecular conformational arrangement of the polymer layers. Complementing these interfacial studies are dynamic light scattering experiments measuring the nanoemulsion size distribution and polydispersity index over a 30-day period. FindingsOur light scattering, ζ-potential, and spectroscopic results of the nanoemulsion surface show that the duration of droplet stability and the degree of molecular orientation of adsorbed polymers can be tuned by surfactant concentration, PEI concentration, and pH. These results illustrate how molecular surface properties of multi-polymer coated nanoemulsions contribute to synergistic effects and droplet stability, enabling advancements in applications surrounding biopharmaceuticals, cosmetics, and food sciences.

Reversible Supra‐Folding of User‐Programmed Functional DNA Nanostructures on Fuzzy Cationic Substrates

AbstractWe report that user‐defined DNA nanostructures, such as two‐dimensional (2D) origamis and nanogrids, undergo a rapid higher‐order folding transition, referred to as supra‐folding, into three‐dimensional (3D) compact structures (origamis) or well‐defined μm‐long ribbons (nanogrids), when they adsorb on a soft cationic substrate prepared by layer‐by‐layer deposition of polyelectrolytes. Once supra‐folded, origamis can be switched back on the surface into their 2D original shape through addition of heparin, a highly charged anionic polyelectrolyte known as an efficient competitor of DNA‐polyelectrolyte complexation. Orthogonal to DNA base‐pairing principles, this reversible structural reconfiguration is also versatile; we show in particular that 1) it is compatible with various origami shapes, 2) it perfectly preserves fine structural details as well as site‐specific functionality, and 3) it can be applied to dynamically address the spatial distribution of origami‐tethered proteins.

Reversible Supra-Folding of User-Programmed Functional DNA Nanostructures on Fuzzy Cationic Substrates.

We report that user-defined DNA nanostructures, such as two-dimensional (2D) origamis and nanogrids, undergo a rapid higher-order folding transition, referred to as supra-folding, into three-dimensional (3D) compact structures (origamis) or well-defined μm-long ribbons (nanogrids), when they adsorb on a soft cationic substrate prepared by layer-by-layer deposition of polyelectrolytes. Once supra-folded, origamis can be switched back on the surface into their 2D original shape through addition of heparin, a highly charged anionic polyelectrolyte known as an efficient competitor of DNA-polyelectrolyte complexation. Orthogonal to DNA base-pairing principles, this reversible structural reconfiguration is also versatile; we show in particular that 1) it is compatible with various origami shapes, 2) it perfectly preserves fine structural details as well as site-specific functionality, and 3) it can be applied to dynamically address the spatial distribution of origami-tethered proteins.

Modification Approaches to Enhance Dehydration Properties of Sodium Alginate-Based Pervaporation Membranes.

Transport characteristics of sodium alginate (SA) membranes cross-linked with CaCl2 and modified with fullerenol and fullerene derivative with L-arginine for pervaporation dehydration were improved applying various approaches, including the selection of a porous substrate for the creation of a thin selective SA-based layer, and the deposition of nano-sized polyelectrolyte (PEL) layers through the use of a layer-by-layer (Lbl) method. The impacts of commercial porous substrates made of polyacrylonitrile (PAN), regenerated cellulose, and aromatic polysulfone amide were investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM), standard porosimetry method, and water filtration. The effects of PEL combinations (such as poly(sodium 4-styrene sulfonate) (PSS)/SA, PSS/chitosan, PSS/polyacrylic acid, PSS/poly(allylamine hydrochloride)) and the number of PEL bilayers deposited with the Lbl technique on the properties of the SA and SA/fullerene derivative membranes were studied by SEM, AFM, and contact angle measurements. The best characteristics were exhibited by a cross-linked PAN-supported SA/fullerenol (5%) membrane with five PSS/SA bilayers: permeation flux of 0.68–1.38 kg/(m2h), 0.18–1.55 kg/(m2h), and 0.50–1.15 kg/(m2h), and over 99.7, 99.0, and 89.0 wt.% water in the permeate for the pervaporation dehydration of isopropanol (12–70 wt.% water), ethanol (4–70 wt.% water), and tetrahydrofuran (5.7–70 wt.% water), respectively. It was demonstrated that the mutual application of bulk and surface modifications essentially improved the membrane’s characteristics in pervaporation dehydration.

A surface charge governed nanofluidic diode based on a single polydimethylsiloxane (PDMS) nanochannel

HypothesisNanofluidic diodes have attracted intense attention recently. Commonly used materials to design these devices are membrane-based short nanopores and aligned Carbon nanotube bundles. It is highly desirable and very challenging to develop a nanofluidic diode based on a single PDMS nanochannel which is easier to be introduced into an integrated electronic system on a chip. Layer-by-layer (LBL) deposition of charged polyelectrolytes can change the size and surface properties of PDMS nanochannels that provides new possibilities to develop high-performance nanofluidic based on PDMS nanochannels. ExperimentsA novel design of nanofluidic diode is presented by controlling the surface charges and sizes of single PDMS nanochannels by surface modification using polyelectrolytes. Polybrene (PB) and Dextran sulfate (DS) are used to reduce the PDMS nanochannel size to meet the requirement of ion gating by LBL method and generate opposite surface charges at the ends of nanochannels. The parameters of such a nanofluidic diode are investigated systematically. FindingsThis nanofluidic diode developed in this work has high effective current rectification performance. The rectification ratio can be as high as 218 which is the best ever reported in PB/DS modified nanochannels. This rectification ratio reduces with high voltage frequency and ionic concentration whereas increases in shorter nanochannels.