High-flux nanofiltration membranes prepared by adsorption of multilayer polyelectrolyte membranes on polymeric supports

Layer-by-layer deposition of anionic and cationic polyelectrolytes readily converts polymeric ultrafiltration membranes into materials capable of nanofiltration. ATR-FTIR spectra confirm that layer-by-layer deposition occurs on the ultrafiltration substrates, and adsorption of as few as 2.5 bilayers of poly(styrenesulfonate) (PSS)/protonated poly(allylamine) (PAH) or 3.5 bilayers of PSS/poly(diallyldimethylammonium chloride) (PDADMAC) reduces the molecular weight cutoff of polyethersulfone ultrafiltration supports from 50 kDa to <500 Da. Deposition of multilayer polyelectrolyte films on 300 and 500 kDa membranes also decreases molecular weight cutoffs, but solute rejections are significantly lower when using these supports, suggesting that the polyelectrolyte films do not completely cover large (0.2-0.4 microm in diameter) pores. On the 50 kDa substrates, PSS/PDADMAC films containing 3.5 bilayers exhibit a 95% rejection of SO(4)(2-) and a chloride/sulfate selectivity of 27, whereas 4.5-bilayer PSS/PAH coatings show a glucose/raffinose selectivity of 100. Pure water flux for [PSS/PAH](3)PSS-coated membranes at 4.8 bar is 1.6 m(3)/(m(2)day), which is more than 2-fold higher than that through a commercial 500 Da membrane.     

Asymmetric layer-by-layer polyelectrolyte nanofiltration membranes with tunable retention

Nanofiltration (NF) membrane processes are attractive to remove multivalent ions. As ion retention in NF membranes is determined by both size and charge exclusion, negatively charged membranes are required to reject negatively charged ions. Layer-by-layer assembly of alternating polycation (PC) and polyanion layers on top of a support is a versatile method to produce membranes. Especially the polyelectrolyte (PE) couple polydiallyldimethylammoniumchloride and poly(sodium-4-styrenesulfonate) (PDADMAC/PSS) is extensively investigated. This PE couple cannot form highly negatively charged membrane surfaces, due to interdiffusion and charge overcompensation of PDADMAC into the PSS layers, which limits the operational window to tailor membrane properties. We propose the use of asymmetric layer formation and show how combining two charge densities of one PC can produce negatively charged NF membranes. Starting from hollow fiber ultrafiltration supports coated with base layers of PDADMAC/PSS, they are coated with PDADMAC/PSS or poly(acrylamide-co-diallyldimethylammoniumchloride), P(AM-co-DADMAC)/PSS layers. P(AM-co-DADMAC) has a charge density of only 32% compared to 100% for PDADMAC. The particular novel membranes coated with P(AM-co-DADMAC) have a highly negatively charged surface and high permeabilities (7–19 L/[m²hbar]), with high retentions for Na₂SO₄ of up to 95%. These values position the developed membranes in the top range compared to commercial and other layer-by-layer membranes.     

Multilayer polyelectrolyte films as nanofiltration membranes for separating monovalent and divalent cations

Alternating adsorption of polyanions and polycations on porous supports provides a convenient way to prepare ion-selective nanofiltration membranes. This work examines optimization of ultrathin, multilayer polyelectrolyte films for monovalent/divalent cation separations relevant to water softening. Membranes composed of five bilayers of poly(styrene sulfonate)/poly(allylamine hydrochloride) (PSS/PAH) on porous alumina supports allow a solution flux of 0.85 m³/(m² day) at 4.8 bar, and exhibit 95% rejection of MgCl₂ along with a Na⁺/Mg²⁺ selectivity of 22. Similar results were obtained in Na⁺/Ca²⁺ separations. PSS/poly(diallyl-dimethylammonium chloride) (PDADMAC) films permit higher fluxes than PSS/PAH systems due to the higher swelling of films containing PDADMAC, but the Mg²⁺ rejection by PSS/PDADMAC membranes is less than 45%. However, capping PSS/PDADMAC films with a bilayer of PSS/PAH yields Mg²⁺ rejections and Na⁺/Mg²⁺ selectivities that are typical of pure PSS/PAH membranes. Separation performance can be optimized through control over deposition conditions (pH and supporting electrolyte concentration) and the charge of the outer layer since Donnan exclusion is a major factor in monovalent/divalent cation selectivity. Streaming potential measurements demonstrate that the magnitude of positive surface charge increases with increasing concentrations of Mg²⁺ in solution or when the outer polycation layer is deposited from a solution of high ionic strength.     

Controlling the nanofiltration properties of multilayer polyelectrolyte membranes through variation of film composition

We report the use of a variety of polyelectrolyte multilayers (PEMs) as selective skins in composite membranes for nanofiltration (NF) and diffusion dialysis. Deposition of PEMs occurs through simple alternating adsorption of polycations and polyanions, and separations can be optimized by varying the constituent polyelectrolytes as well as deposition conditions. In general, the use of polycations and polyanions with lower charge densities allows separation of larger analytes. Depending on the polyelectrolytes employed, PEM membranes can remove salt from sugar solutions, separate proteins, or allow size-selective passage of specific sugars. Additionally, because of the minimal thickness of PEMs, NF pure water fluxes through these membranes typically range from 1.5 to 3 m3/(m2 day) at 4.8 bar. Specifically, to separate sugars, we employed poly(styrene sulfonate) (PSS)/poly(diallyldimethylammonium chloride) (PDADMAC) films, which allow 42% passage of glucose along with a 98% rejection of raffinose and a pure water flux of 2.4 m3/(m2 day). PSS/PDADMAC membranes are also capable of separating NaCl and sucrose (selectivity of approximately 10), while high-flux chitosan/hyaluronic acid membranes [pure water flux of 5 m3/(m2 day) at 4.8 bar] may prove useful in protein separations.     

Cyclic hexapeptide of D,L-alpha-aminoxy acids as a selective receptor for chloride ion

Cyclic hexapeptide 2, prepared from linear hexapeptide 1 of alternating d- and l-alpha-aminoxy acids, was found to adopt a C3 symmetric and bracelet-like conformation with consecutive eight-membered-ring hydrogen bonds (N-O turns) in nonpolar solvents, similar to that of valinomycin, a cyclodepsipeptide that binds cations selectively. However, 2 showed affinities for halide ions with selectivity following the order of Cl- > F- > Br-. The observed higher selectivity for Cl- (Ka = 11880 M-1) over F- (Ka = 30 M-1) in CD2Cl2 suggested that the selectivity of 2 for halide ions is mainly governed by the size complementarity rather than the hydrogen-bonding strength. Upon Cl- ion binding, the original bracelet-like conformation of 2 turned into a rather flat conformation with all six amide NHs pointing inward to form hydrogen bonds with Cl-.     

Rigid oligonaphthalenediimide rods as transmembrane anion-pi slides

We report the design, synthesis, and evaluation of rigid oligonaphthalenediimide (O-NDI) rods that are expected to act as transmembrane anion-pi slides. Studies in fluorogenic large unilamellar egg yolk phosphatidylcholine vesicles reveal that rigid O-NDI rods mediate anion-selective transport with a rare halide VI selectivity sequence (Cl- > F- > Br- > I-). This and decreasing activity, selectivity, and halide sequence with increasing positive charge of the rod termini support the occurrence of anion-pi interactions. A strong anomalous mole fraction effect in Cl-/I- mixtures is in agreement with the existence of multiple active sites along the anion-pi slide and multi-anion hopping as a mechanism of transport. The strong inverted NDI quadruple moment found by DFT calculations is in excellent agreement with these results.     

Modulating the structure and properties of poly(sodium 4-styrenesulfonate)/poly(diallyldimethylammonium chloride) multilayers with concentrated salt solutions

Poly(sodium 4-styrenesulfonate) (PSS)/poly(diallyldimethylammonium chloride) (PDADMAC) multilayers were treated with 1-5 M NaCl solutions, resulting in continuous changes in the physicochemical properties of the multilayers. Significant mass loss was observed when the salt concentration was higher than 2 M and reached as high as 72% in a 5 M NaCl solution. The disassembly occurred initially in the superficial layers and then developed in the bulk multilayers. For the multilayers with PDADMAC as the outmost layer, the molar ratio of PSS/PDADMAC was increased and the surface chemistry was changed from PDADMAC domination below 2 M NaCl to PSS domination above 3 M NaCl. Owing to the higher concentrations of uncompensated for polyelectrolytes at both lower and higher salt concentrations, the swelling ratio of the multilayers was decreased until reaching 3 M NaCl and then was increased significantly again. The salt-treated PSS/PDADMAC thin films are expected to show different behaviors in terms of the physical adsorption of various functional substances, cell adhesion and proliferation, and chemical reaction activity.     

A selective detection of fluoride ions in DMSO by fluorescent and colorimetry competition assays based on 4-bromo-2,6-bis-(hydroxymethyl)phenol

A novel and very simple colorimetric and fluorometric method for selectively sensing F^- was proposed based on 4-bromo-2,6- bis（hydroxymethyl）phenol（BBHMP）,which is a simple and available phenolic receptor the absence of any special chromophoric function and with over wide range of anions（Cl^-,Br^-,I^-,AcO^-,HSO₄^-,NO₃^- and BzO^-） in DMSO media.The colorimetric method is described for naked-eye detection of F^- in the presence of the BBHMP.The BBHMP was found to show selective and sensitive fluorescence quenching response toward fluoride over than Cl^-,Br^-,I^-,AcO^-,HSO₄^-,NO₃^- and BzO^-.     

Stability of capillaries coated with highly charged polyelectrolyte monolayers and multilayers under various analytical conditions--application to protein analysis

The stability of capillaries coated with highly charged polyelectrolytes under various analytical conditions was studied, as well as their performance for the analysis of proteins by Capillary Electrophoreis (CE) over a wide range of pH (2.5-9.3). In this study, fused silica capillaries were modified either with a poly(diallyldimethylammonium) chloride (PDADMAC) monolayer or PDADMAC/poly(sodium 4-styrenesulfonate) (PSS) multilayer coatings, using optimal coating conditions previously determined. Results show that the coated capillaries are remarkably stable and efficient to limit protein adsorption under a variety of extreme electrophoretic conditions even in the absence of the coating agent in the background electrolyte which is exceptional for non-covalent coatings. Monolayer coated capillaries were demonstrated for the first time to be stable to acidic rinses and to organic solvents which proves that the stability of the capillaries is highly dependent on the coating procedure used. In addition, PDADMAC/PSS multilayer coatings were found to be stable to alkaline treatments. PDADMAC/PSS coated capillaries gave excellent performances for the analysis of proteins covering a large range of pI (4-11) and of molecular weight (14-65 kDa) over a wide pH range (i.e. 2.5-9.3). Even at high pH 9.3, protein analysis was possible with very good repeatabilities (RSD(tm)<1% and RSD(CPA)<2.6% (n ≥ 8)) and high peak efficiencies in the order of 700,000.     

Polyelectrolyte multilayers on wood fibers: influence of molecular weight on layer properties and mechanical properties of papers from treated fibers

This paper compares the influence of the molecular weight of polylelectrolytes forming polyelectrolyte multilayers (PEM) on wood fibers on adhesion and paper strength. Sheets were made from fibers treated with poly(allylamine hydrochloride) (PAH)/poly(acrylic acid) (PAA) of molecular mass 70,000 and 240,000, respectively, and of poly(dimethyldiallylammonium chloride) (PDADMAC)/poly(styrene sulfonate) (PSS) of molecular mass 30,000 and 80,000, respectively. The results were compared to what has recently been reported for PEM formation on fibers using a low-molecular-mass combination of PAH and PAA and a high-molecular-mass combination of PDADMAC/PSS. There was a less significant improvement in the case of the low-molecular-mass PDADMAC/PSS and the high-molecular-mass PAH/PAA. The adsorbed amounts of PAH and PDADMAC were also determined, showing a lower adsorbed amount of the low-molecular-mass PAH than of the high-molecular-mass PDADMAC. The amount of low-molecular-mass PDADMAC was similar to that found for high-molecular-mass PDADMAC/PSS. Individual fibers were partly treated and studied, showing a less significant decrease in wettability with low-molecular-mass PDADMAC/PSS than with the high-molecular-mass combination. The effect of the molecular weight on the adhesion was discussed in terms of the structure and wettability of the PEMs.     

Modeling Anion Adsorption on Kaolinite

Anion adsorption onto kaolinite was quantified using the triple layer surface complexation model. Fluoride adsorption data were described by both anion exchange and H-bonded complexation mechanisms. The outer-sphere complexation mechanism was used to describe the weak adsorption of Cl-, Br-, and I- on kaolinite. The F- adsorption in the presence of Br- or I- was decreased over a range of pH 4-5 whereas Cl- showed a negligible effect. Competition for binding sites appeared to be an important factor in determining the adsorptive behavior of F- in Br- or I- mediated systems. Copyright 1999 Academic Press.     

仿生制备有机-无机复合微囊固定化葡萄糖氧化酶

将层层自组装技术与仿生矿化技术相结合,由聚苯乙烯磺酸钠、聚二甲基二烯丙基氯化铵和二氧化硅成功制备(聚苯乙烯磺酸钠-聚二甲基二烯丙基氯化铵)₂-二氧化硅复合微囊.采用扫描电子显微镜、红外光谱和热重对微囊的形貌和化学结构进行了表征.以该复合微囊作为理想载体固定化葡萄糖氧化酶.结果表明,固定于复合微囊中的葡萄糖氧化酶的热稳定性、pH稳定性、操作稳定性得到了提高;在最适条件下,复合微囊固定化葡萄糖氧化酶的酶活回收率为72.85%,米氏常数是游离葡萄糖氧化酶的2.21倍.复合微囊在化学/生物催化、药物/基因传递系统和生物传感器应用方面具有一定的潜能.     

Controlled Stripping of Polyelectrolyte Multilayers by Quaternary Ammonium Surfactants

The quartz crystal microbalance with dissipation technique (QCM‐D) and atomic force microscopy (AFM) have been employed to study the interaction of N‐tetradecyl trimethyl ammonium bromide (TdTmAB) with polyelectrolyte multilayers containing poly(sodium 4‐styrene sulfonate) (PSS) as the polyanion and either poly(allylamine hydrochloride) (PAH) or poly(diallyl dimethyl ammonium chloride) (PDADMAC) as the polycations. The multilayers were exposed to aqueous solutions of TdTmAB. This resulted in a selective removal of PDADMAC PSS layers while layers with PAH as polycation remained stable. It is suggested that PDADMAC/PSS multilayers can be employed as strippable protecting layers.

     

Potentiometric response mechanism of a poly(acrylamide)-phthalocyaninato tin(II) film coated platinum electrode in acetonitrile and N,N-dimethylacetamide.

A new sensor constructed by a platinum electrode coated with a non-plasticized poly(acrylamide) polymer (PAA) film coupled with phthalocyaninato tin(II) ([Sn(II)(pc)]) was developed. The potentiometric response behavior of this PAA-[Sn(II)(pc)] electrode for such anions as CN-, F-, Cl-, and Br- in dimethylacetamide and acetonitrile were investigated. The electrode showed a Nernstian response to CN- and F- and a quite poor response to Cl- and Br-. The mechanism of the peculiar selective response was studied by cyclic voltammetric and spectrophotometric methods. The voltammetric investigation suggested that the charge of the host compound in the sensor membrane had no effect on the potential response of the electrode. It was also found by a spectrophotometric investigation that the complexing of [Sn(II)(pc)] with CN- and F- lead to the selective response of the electrode. The motive force of the complexing was considered to be a ligand exchange of CN- or F- with molecules at the axial site of [Sn(II)(pc)] due to solvent effects to the interest anions.     

间苯二甲醛缩双芳氨基硫脲的合成及阴离子识别研究

设计合成了5种间苯二甲醛缩双芳氨基硫脲受体分子, 利用紫外-可见吸收光谱及1H NMR, 考察了其与F-, Cl-, Br-, I-, CH3COO-, HSO-4, NO-3和H2PO-4等8种阴离子的作用. 当在受体分子S0, S1, S2, S3和S4的DMSO溶液中加入F-和CH3COO-四丁基铵盐的DMSO溶液时, 吸收光谱发生显著红移, 溶液颜色由无色变为深黄色, 而加入其它阴离子则无显著变化, 可以实现对这两种阴离子的裸眼检测及光谱分析. 计算结果表明, 随着苯环上取代基的变化, 此5种受体分子对F-和CH3COO-的识别作用呈现规律性变化. 1H NMR 及质子溶剂效应进一步证明了受体分子与阴离子之间以氢键作用方式相结合. Job工作曲线表明, 该类受体分子与阴离子形成1∶1的氢键配合物.     

一类缩双芳氨基硫脲受体的合成及阴离子识别

缩双芳氨基硫脲;合成;阴离子识别;氢键作用     

Thermal transitions in and structures of dried polyelectrolytes and polyelectrolyte complexes

Dynamic mechanical analysis (DMA) was used to explore the thermomechanical properties of dried polyelectrolytes and polyelectrolyte complexes (PECs) with different thermal and humidity histories. Although differences in the amount of water remaining in polyelectrolytes and PECs were small for ambient versus dessicator storage, the properties of polyelectrolyte‐based materials were drastically different for different humidity histories. Glass transition temperatures (T_gs) of poly(diallyldimethylammonium chloride) (PDADMAC) were shown to vary by 100 °C, depending on humidity and thermal histories. These parameters also change glassy storage modulus values by 100%. Furthermore, we observe that dried PDADMAC is highly lossy. DMA of dried poly(styrene sulfonate) (PSS) was more complex and did not exhibit a glass transition in the tested range. DMA of a PEC of PDADMAC and PSS revealed a humidity history‐dependent water melt in the first heating cycle, as well as storage modulus values of dried and annealed PECs that only varied by 17–26% over a 275 °C temperature range. Based on these results, we report for the first time humidity history as controlling structure and properties of polyelectrolyte‐based materials. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 684–691     

Preparation and characterization of polyelectrolyte-coated gold nanoparticles

Gold nanoparticles of 5 nm diameter, stabilized by 4-(dimethylamino)pyridine (DMAP), were coated with poly(sodium 4-styrene sulfonate) (PSS) via electrostatic self-assembly. The suspension stability, monitored by the gold surface plasmon band (SPB), was studied by varying the pH, the PSS chain length, and PSS concentration. Enhanced stability is obtained at pH 10 (above the pKa of DMAP) when the polymer chain length matches or exceeds the particle circumference. Solid state 13C NMR was used to determine the presence of DMAP and polymers after subsequent deposition of weak and strong polycations: poly(allylamine hydrochloride) (PAH) and poly(diallyldimethylammonium chloride) (PDADMAC). At pH 10, DMAP remains associated with the nanoparticle after the first PSS layer has been formed. When PAH or PDADMAC are subsequently added at pH 4.5, DMAP is expelled, the suspensions remain stable, and zeta potential values indicate complete charge reversal. In the case of PDADMAC, however, the first layer of PSS is not fully retained. When PDADMAC is added at pH 10, DMAP and the first PSS layer are retained but lower zeta potentials and a higher SPB shift indicate a degraded stability. For PAH addition at pH 9.5, both DMAP and PSS are expelled and the suspension becomes unstable. These differences in stability of the multilayer components and the nanoparticle suspension are rationalized in terms of chain flexibility, polymer charge density, and the ability of the polymer functional groups to directly interact with the gold surface.     

Swelling and shrinking of polyelectrolyte microcapsules in response to changes in temperature and ionic strength

Swelling and shrinking of polyelectrolyte microcapsules consisting of poly(styrene sulfonate, sodium salt) (PSS) and poly(diallyldimethyl ammonium) chloride (PDADMAC) multilayers have been observed in response to temperature and electrolyte exposure, respectively. Heat-induced capsule swelling and capsule wall volume reduction were observed by confocal laser scanning microscopy (CLSM) and scanning force microscopy (SFM). On the other hand, pronounced shrinking in diameter induced by exposure to an electrolyte was observed in parallel to increases in the thickness of the capsule wall. The estimated wall volume was reduced to two thirds of the control for the salt-exposed capsules and one half for the salt-exposed and simultaneously annealed capsules. This reduction in volume was supposedly mainly caused by the compression of the capsule wall due to the ionic screening from the electrolyte. The highly porous microstructure of the multilayers and loosely bound PSS/PDADMAC complex are thought to be responsible for the structure of the PSS/PDADMAC capsules being easily modulated upon annealing and salt-exposure.     

X@(HAINH)_(12)和X(HAINH)_(12)(X=F~-,Cl~-,Br~-,O~(2-),S~(2-),Se~(2-))复合物的结构和稳定性

用DFT的B3LYP方法在6-31G(d)基组的水平上,对闭式多面体簇合物(HA1NH)12及其内含式X@(HA1NH)12外接式X(HA1NH)12(X=F-,Cl-,Br-,O2-,S2-,Se2-)复合物的结构进行了构型优化和能量计算,并讨论了几何构型、自然键轨道(NBO)、振动频率、能量参数及NMR数据与结构的关系,最后得到复合物结构的稳定性信息,具有Th对称性的X@(HA1NH)12(X=F-,Cl-,Br-,S2-,Se2-)复合物和具有C3对称性的O2-@(HA1NH)12复合物为内含式的基态结构,从能量角度分析,内含式复合物比外接式复合物的结构稳定.