Polyelectrolyte layer-by-layer self-assembly enhanced by electric field and their multilayer membranes for separating isopropanol–water mixtures

An electric field enhanced method is developed for fabricating layer-by-layer (LbL) self-assembly polyelectrolyte multilayer membranes. Three kinds of electric field enhanced polyelectrolyte multilayer membranes (EPEMs), poly(diallyl dimethylammonium chloride)/poly(styrenesulfonate sodium salt) (PDDA/PSS), poly(diallyldimethylammonium chloride)/poly(acrylic acid sodium salt) (PDDA/PAA) and polyethylenimine/poly(acrylic acid sodium salt) (PEI/PAA), were self-assembled on a reverse osmosis membrane (ROM). The pervaporation performances of EPEMs for separating isopropanol–water mixtures (90/10, w/w) are all superior to those of corresponding normal self-assembled polyelectrolytes membranes (PEMs), and the selectivity increases with PDDA/PSS, PDDA/PAA and PEI/PAA in order. For (PEI/PAA)₄PEI EPEM, the separation factor is 1075 and permeation flux is 4.05 kg m⁻² h⁻¹ at 70 °C. This novel method speeds up the LbL process, which makes it promising for the practical application of the LbL multilayer membrane.     

Layer-by-layer self-assembly of TiO<Subscript>2</Subscript> sol on wool to improve its anti-ultraviolet and anti-ageing properties

A new method for improving the anti-ultraviolet and anti-ageing abilities of wool fabric was reported in this paper. TiO₂ sols and poly (sodium 4-styrene-sulfonate) (PSS) were coated on the wool fibers via layer-by-layer (LBL) electrostatic self-assembly deposition. The morphologies and compositions of TiO₂ sol-coated wool fabrics were characterized using SEM, surface Zeta potential, apparent color depth (K/S), ultraviolet (UV) transmission and alkali solubility. The SEM pictures showed that there were quite a few deposits absorbed on the wool surface. The dyeing depth and Zeta potential presented obvious “layer–layer alternate vibration” along with the change of deposited materials, revealing the surface structure of the assembled wool fiber. The results of ultraviolet (UV) transmission and alkali solubility indicated that the modified wool fabrics obtained good anti-ultraviolet and anti-ageing properties. In addition, the sol-assembled wool fabrics had good washing fastness. The studies proved that the LBL electrostatic self-assembly deposition is a promising way to endow the textiles with surface functionality.     

Separation of aminophenol isomers in polyelectrolyte multilayers modified PDMS microchip

The separation of three kinds of aminophenol isomers were achieved within 1 min in polyelectrolytes multilayers modified PDMS microchips by layer-by-layer assembly with electrochemical detection (EC). Two polyelectrolytes, poly(dially dimethyl ammonium chloride) (PDDA) and poly(sodium-4-styrene-sulfonate) (PSS) were used to form polyelectrolyte multilayers (PEMs). The surface characteristic of the modified microchip was studied by XPS. The electroosmotic flow (EOF) on PEMs modified PDMS microchips was more stable than that of the native PDMS microchips and the adsorption of samples was greatly reduced on PEMs modified PDMS microchips during the electrophoretic process. The column efficiencies on PEMs modified microchip were increased by 100 times and the signals enhanced by 2 times compared with those of native microchips. The separation conditions such as running buffer pH, running buffer concentration and separation voltage were also optimized.     

聚电解质PDDA/PSS层层自组装膜的渗透汽化性能

采用聚电解质层层自组装(LbL)技术, 在不同盐浓度下制备了聚(二烯丙基二甲基氯化铵)/聚苯乙烯磺酸钠(PDDA/PSS) 多层自组装膜, 并用于渗透汽化性能的研究. 重点考察了组装溶液中NaCl的浓度、组装层数及操作温度对自组装膜的异丙醇脱水性能的影响. 同时, 用扫描电镜观测了不同条件下制备膜的表面形貌. 结果表明, 在高NaCl含量的聚电解质溶液中只需组装几个双层的LbL膜, 即能获得较高的分离因子和较大的通量, 并解释了该LbL膜呈现反“trade-off”现象的原因.     

Layer-by-layer electrostatic self-assembly of single-wall carbon nanotube polyelectrolytes

We have used anionic and cationic single-wall carbon nanotube polyelectrolytes (SWNT-PEs), prepared by the noncovalent adsorption of ionic naphthalene or pyrene derivatives on nanotube sidewalls, for the layer-by-layer self-assembly to prepare multilayers from carbon nanotubes with polycations, such as poly(diallyldimethylammonium) or poly(allylamine hydrochloride) (PDADMA or PAH, respectively), and polyanions (poly(styrenesulfonate), PSS). This is a general and powerful technique for the fabrication of thin carbon nanotube films of arbitrary composition and architecture and allows also an easy preparation of all-SWNT (SWNT/SWNT) multilayers. The multilayers were characterized with vis-near-IR spectroscopy, X-ray photoelectron spectroscopy (XPS), surface plasmon resonance (SPR) measurements, atomic force microscopy (AFM), and imaging ellipsometry. The charge compensation in multilayers is mainly intrinsic, which shows the electrostatic nature of the self-assembly process. The multilayer growth is linear after the initial layers, and in SWNT/polyelectrolyte films it can be greatly accelerated by increasing the ionic strength in the SWNT solution. However, SWNT/SWNT multilayers are much more inert to the effect of added electrolyte. In SWNT/SWNT multilayers, the adsorption results in the deposition of 1-3 theoretical nanotube monolayers per adsorbed layer, whereas the nominal SWNT layer thickness is 2-3 times higher in SWNT/polyelectrolyte films prepared with added electrolyte. AFM images show that the multilayers contain a random network of nanotube bundles lying on the surface. Flexible polyelectrolytes (e.g., PDADMA, PSS) probably surround the nanotubes and bind them together. On macroscopic scale, the surface roughness of the multilayers depends on the components and increases with the film thickness.     

Identification of Skim Milk Electroacidification Fouling: A Microscopic Approach

The self-assembly film fabricated via the layer-by-layer technique was studied by the dynamic contact angle (DCA) method (wilhelmy plate method). The used polyelectrolytes are poly(diallyl-dimethylammonium chloride) (PDDA), poly(etheleneimine) (PEI), diphenylamine-4-diazonium-formaldehyde resin (DR), 2-nitro-N-methyl-4-diazonium-formaldehyde resin (NDR), and poly(sodium-p-styrenesulfonate) (PSS). For the self-assembly systems of PDDA/PSS, PEI/PSS, DR/PSS, and NDR/PSS, their individual contact angle fluctuates regularly with the fabrication of each layer, while the magnitude of different systems' contact angle depends on the participant polycation. The re-organization of components and the adjacent layer interpenetration are presented here to explain this phenomena. We also found that DR or NDR can adsorb itself via the layer-by-layer method to form multilayer film, and the hydrophobic interaction is put forward to effect this process. Moreover, the procedure of washing and drying after adsorption was studied and considered as a prerequisite for the successful fabrication, especially of the same charge carried components. Copyright 2001 Academic Press.     

Fabrication of free-standing multilayer films by using pH-responsive microgels as sacrificial layers

A facile way to prepare free-standing polyelectrolyte multilayer films of poly(sodium 4-styrenesulfonate)(PSS)/poly(diallyldimethylammonium)(PDDA) was developed by applying a new pH-dependent sacrificial system based on cross-linked poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) microgels. The tertiary amine groups of PDMAEMA microgels can be protonated in acidic environment, and the protonated microgels were deposited by layer-by-layer (LbL) technique with PSS. PSS/PDDA multilayer films were constructed on the top of the PSS/microgels sacrificial layers. The LbL assembly process was investigated by UV–vis spectroscopy. Further study shows that the free-standing PSS/PDDA multilayer films can be obtained within 3 min by treating the as-prepared films in alkali aqueous solution with a pH of 12.0. The pH-triggered exfoliation of PSS/PDDA multilayer films provides a simple and facile way to prepare LbL assembled free-standing multilayer films.     

Metallosupramolecular Chemistry in Two Dimensions

Ultrathin films of metallosupramolecular coordination polyelectrolytes (MEPEs) on planar solid substrates assembled by electrostatic layer-by-layer self-assembly (ELSA) are characterized with UV-vis spectroscopy, optical ellipsometry, and X-ray reflectometry. MEPEs based on different ditopic ligands and transition metal ions are employed and shown to form regular ELSA multilayers. A quantitative analysis is in agreement with a surface coverage of approximately two MEPE monolayers per deposition step. In addition, we demonstrate that multilayers of MEPEs with different transition metal ions can be assembled. Even with kinetically labile metal ions, there is no metal ion exchange in these multilayers. Absorption spectra of multilayers on silicon show a band inversion of the MLCT band, which is rationalized in terms of optical effects.     

PSS/PDDA自组装膜形成过程中的临界浓度效应

Decher等提出的阴阳聚电解质层层组装膜技术(LbL),方便快捷,结构有序,其纳米级可控,可用于生物传感器、杂多酸多层膜修饰电极及天然多糖类功能膜等领域．LbL膜的厚度直接影响其性能,而膜厚度与紫外吸光度(A)成正比．故A是通常用于评价膜厚度的一种简便方法．紫外吸光度与聚电解质溶液浓度(cp)往往呈递增关系,随着溶液中cp的增大,单位面积上吸附聚电解质的量也增加。     

预混合自组装辣根过氧化物酶生物活性膜及其催化活性研究

以阳离子化的辣根过氧化物酶 (HRP)和阴离子聚苯乙烯磺酸钠 (PSS)的预混合溶液 ,与阳离子聚电解质聚二甲基二烯丙基氯化铵 (PDDA)通过逐层组装 ,在阴离子化聚对苯二酸乙二酯 (PET)表面构建了多层生物活性膜 .用紫外 可见光谱仪 (UV Vis)和原子力显微镜 (AFM)研究了交替自组装膜的结构和表面形膜 ,并测定了自组装膜的生物催化活性 .结果表明 ,预混合溶液中的PSS与HRP一起沉积在PDDA膜层上组装成 (PSS+HRP)膜层 ,且每层中PSS和HRP的比例一致 ;(PSS +HRP)膜层呈条状分布 ,膜表面较为平整 ;多层膜中的HRP催化H2 O2 与 4 氨基安替比林的显色反应的表观米氏常数为 9 7× 10 - 5mol·L- 1 (相对于H2 O2 底物 ) ,较溶液中 (1 5 2× 10 - 4mol·L- 1 )的小 .     

Preparation of Polyelectrolyte Nanotubes by a Pressure filter-template Technique Using Microporous Anodic Aluminum Oxide (AAO) as the Template

Polyelectrolyte nanotubes of poly(sodium 4‐styrene‐sulfonate) (PSS) with cationic poly(diallyl dimethyl ammonium chloride) (PDDA) (PSS/PDDA) were fabricated by a pressure‐filter‐template technique using microporous anodic aluminum oxide (AAO) as the template. UV‐Vis spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X‐ray diffraction (XRD) and infrared spectroscopy (FT‐IR) were applied to characterize the obtained PSS/PDDA nanotubes. The results have shown that the PSS/PDDA nanotubes exhibit an amorphous structure and have the outer diameter of 200 nm and length of 25 µm respectively, which are in good agreement with the dimensions of the AAO template pores. The wall thickness of the nanotubes may be controlled by the number of the self‐assembled layers. Formation of the nanotubes follows a layer‐by‐layer (LbL) mechanism due to the electrostatic interactions, where the SO^?₃ groups of PSS are first adsorbed on the Lewis acid sites of AAO template pores.     

Self-assembly, optical behavior, and permeability of a novel capsule based on an azo dye and polyelectrolytes

A novel capsule composed of an azo dye, Congo red (CR), and different polymers, including poly(styrenesulfonate, sodium salt) (PSS), poly(allylamine hydrochloride) (PAH), and poly(diallyldimethylammonium chloride) (PDDA), have been successfully fabricated by the layer-by-layer self-assembly technique. The stepwise linear deposition process was monitored by means of UV-visible absorption measurements. The formation of hollow capsules was verified by confocal laser scanning microscopy (CLSM) and scanning force microscopy (SFM). The resulting hollow PSS/PAH/CR/PDDA capsules displayed a sensitive response to visible light. Optical changes of the hollow capsules prior to and after the photoreaction were investigated in detail by means of UV-visible spectroscopy, CLSM, and SFM. It was found that the photochemical reaction of the assembled hollow capsules depends strongly on the matrix. Qualitative results on the permeability of the hollow capsule walls with CR as one component indicate that the permeability of the walls can be easily photo-controlled at varying irradiation time intervals without addition of external chemicals.     

Kinetic studies of glucose oxidase in polyelectrolyte multilayer films by means of scanning electrochemical microscopy (SECM)

Multilayer films of glucose oxidase (GOx) and poly(dimethyl diallyl ammonium chloride) (PDDA) prepared by layer-by-layer deposition were studied using scanning electrochemical microscopy (SECM). Aminated glass slides were coated with five bilayers of poly(styrene sulfonate) (PSS) and PDDA and used as substrates onto which GOx/PDDA multilayers were deposited. UV-Vis experiments confirmed multilayer growth, scanning force microscopic images provided morphological information about the films. SECM current-distance curves enabled the determination of kinetic information about GOx in GOx/PDDA multilayers as a function of layer number, film termination, inert covering layers, and enzyme substrate concentration after fitting to numerical models. The results indicate that only the topmost layers contributed significantly to the conversion. An odd-even pattern was observed for PDDA-terminated films or GOx-terminated films that correlated with morphological changes.     

Activity and lifetime of urease immobilized using layer-by-layer nano self-assembly on silicon microchannels

Urease has been immobilized and layered onto the walls of manufactured silicon microchannels. Enzyme immobilization was performed using layer-by-layer nano self-assembly. Alternating layers of oppositely charged polyelectrolytes, with enzyme layers “encased” between them, were deposited onto the walls of the silicon microchannels. The polycations used were polyethylenimine (PEI), polydiallyldimethylammonium (PDDA), and polyallylamine (PAH). The polyanions used were polystyrenesulfonate (PSS) and polyvinylsulfate (PVS). The activity of the immobilized enzyme was tested by pumping a 1 g/L urea solution through the microchannels at various flow rates. Effluent concentration was measured using an ultraviolet/visible spectrometer by monitoring the absorbance of a pH sensitive dye. The architecture of PEI/PSS/PEI/urease/PEI with single and multiple layers of enzyme demonstrated superior performance over the PDDA and PAH architectures. The precursor layer of PEI/PSS demonstrably improved the performance of the reactor. Conversion rates of 70% were achieved at a residence time of 26 s, on d 1 of operation, and >50% at 51 s, on d 15 with a six-layer PEI/urease architecture.     

静电层层自组装制备聚苯乙烯微球(核)/MCM-41纳米粒子(壳)阶层结构复合微粒

采用聚苯乙烯磺酸钠(PSS)和聚二烯丙基二甲基氯化铵(PDDA)两种聚电解质, 通过静电层层自组装成功地将MCM-41介孔二氧化硅纳米粒子包覆到聚苯乙烯(PS)微球表面. 实验结果表明, 当以尺寸为1.4 μm的PS微球为核时, 包覆了两个聚电解质双层(PDDA/PSS)2的PS(PDDA/PSS)2(PDDA/MCM-41)复合结构微粒与包覆了一个聚电解质双层(PDDA/PSS)的PS(PDDA/PSS)(PDDA/MCM-41)复合结构微粒相比, 复合结构微粒之间的交联程度降低, 但是MCM-41纳米粒子在聚苯乙烯微球表面的包覆都比较松散, 且产物中存在大量杂质. 而当以尺寸为5 μm的聚苯乙烯微球为核时, MCM-41纳米粒子紧密地包覆在聚苯乙烯微球表面, 复合结构微粒之间只有少量桥连物, 且产物中杂质很少.     

以聚电解质多层膜为纳米反应器制备Au@Pt核壳纳米粒子

以聚二烯丙基二甲基氯化铵和聚苯乙烯磺酸钠为构筑单元,通过静电层层自组装制备了多层膜,利用薄膜中存在的抗衡阴离子,选择AuCl-4和PtCl2-6作为Au和Pt的前驱体,通过连续的阴离子交换/还原,原位制备了Au-Pt双金属纳米粒子。 紫外-可见分光光度法、透射电子显微镜和能量色散X射线能谱数据表明,在聚电解质多层薄膜中成功地制备了具有核壳结构的Au@Pt双金属纳米粒子。 这种纳米粒子在电化学催化、燃料电池方面具有潜在的应用价值。     

Layer-by-Layer Self-Assembly Immobilization of Catalases on Wool Fabrics

A new immobilization strategy of catalases on natural fibers was reported in this paper. Catalase (CAT) from Bacillus subtilis was assembled into multiple layers together with poly(diallyldimethylammonium chloride) (PDDA) on wool fabrics via layer-by-layer (LBL) electrostatic self-assembly deposition. The mechanism and structural evaluation of LBL electrostatic self-assembly were studied in terms of scanning electron microscopy (SEM), surface zeta potential, and apparent color depth (K/S). The SEM pictures showed obvious deposits absorbed on the wool surfaces after LBL self-assembly. The surface zeta potential and dyeing depth of CAT/PDDA-assembled wool fabrics presented a regular layer-by-layer alternating trend along with the change of deposited materials, revealing the multilayer structure of the wool fiber immobilized catalases. The V _max values were found to be 2,500?±?238 U/mg protein for the free catalase and 1,000?±?102 U/mg protein for the immobilized catalase. The K _m value of free catalase (11.25?±?2.3 mM) was found to be lower than that of the immobilized catalase (222.2?±?36.5 mM). The immobilized catalase remained high enzymatic activity and showed a measureable amount of reusability, which proved that LBL electrostatic self-assembly deposition is a promising approach to immobilize catalases.     

Fabrication of Layer-by-layer Films of Polyhedral Oligomeric Silsesquioxanes

Layer-by-layer(LBL)self-assembly method was used to fabricate siliceous ultrathin films by using polyhedral oligomeric silsesquioxanes as building blocks.Ammonium salt of kctasilsesquioxane acid (OSi8) and bply(diallyldimethylammonium chloride)(PDDA) were altermately assembled onto CaF2 slide to form nanocomposite multilqyers,Linear build-up of the LBL films was confirmed by UV-Vis spectroscopy.IR spectrum suggests existence of OSi8 and PDDA in the LBL films.Atomic force microscopic surface topography of the LBL films indicates the OSi8 covers the entire surface of the topmost layer and shows a granular morphology.     

Ion‐Specific Oil Repellency of Polyelectrolyte Multilayers in Water: Molecular Insights into the Hydrophilicity of Charged Surfaces

Surface wetting on polyelectrolyte multilayers (PEMs), prepared by alternating deposition of polydiallyldimethylammonium chloride (PDDA) and poly(styrene sulfonate) (PSS), was investigated mainly in water‐solid‐oil systems. The surface‐wetting behavior of as‐prepared PEMs was well correlated to the molecular structures of the uncompensated ionic groups on the PEMs as revealed by sum frequency generation vibrational and X‐ray photoelectron spectroscopies. The orientation change of the benzenesulfonate groups on the PSS‐capped surfaces causes poor water wetting in oil or air and negligible oil wetting in water, while the orientation change of the quaternized pyrrolidine rings on the PDDA‐capped surfaces hardly affects their wetting behavior. The underwater oil repellency of PSS‐capped PEMs was successfully harnessed to manufacture highly efficient filters for oil‐water separation at high flux.     

A polyelectrolyte bearing metal ion receptors and electrostatic functionality for layer-by-layer self-assembly

A polyelectrolyte (BiPE) containing bipyridine ligands as metal ion receptors and quaternary ammonium groups is described, which can be assembled via electrostatic interactions or metal ion coordination. Electrostatic layer-by-layer self-assembly of BiPE with sodium poly(styrene sulfonate) (PSS) as oppositely charged component results in striated multilayers. The BiPE/PSS multilayers can reversibly bind and release transition metal ions including Fe(II), Ni(II), and Zn(II). Formation of 2-D arrays of metallo-units is achieved by μ-contact stamping transition metal salts onto the BiPE/PSS interface. Also, multilayers of BiPE are readily assembled through metal ion coordination. Due to the reversible nature of metal ion coordination, exposure of the multilayers to EDTA causes instant disassembly of the layer, a property needed to implement stimulus triggered release functions. The importance of metal ion coordination for multilayer formation is demonstrated by force-distance curves measured with AFM.