Dynamic layer‐by‐layer self‐assembly of organic–inorganic composite hollow fiber membranes

Multilayer membranes constructed layer‐by‐layer (LbL) is finding increasing importance in many separation applications. The efficient construction of LbL multilayer on to hollow fiber substrates may offer many new opportunities for industrial applications. An organic–inorganic composite hollow fiber membrane has been developed using a dynamic LbL self‐assembly. This poly(acrylic acid)/poly(ethyleneimine) multilayer was dynamically assembled onto the inner surfaces of ceramic hollow fiber porous substrates pretreated by Dynasylan Ameo silane coupling agents. The hollow fibers were subsequently heat crosslinked to obtain stable permselective membranes. The formation of multilayers on the hollow fibers was characterized with a SEM, EDX, an electrokinetic analyzer and IR spectra. The effects of layer number, feed temperature and water content in the feed on the pervaporation performance have been investigated. To the best of our knowledge, this is the first report of LbL assembly of polymer building blocks onto ceramic hollow fiber porous substrates. © 2011 American Institute of Chemical Engineers AIChE J, 58: 3176–3182, 2012     

Self‐assembly of novel architectural nanohybrid multilayers and their selective separation of solvent‐water mixtures

A new architectural nanohybrid multilayer has been explored and built on various substrates. The building blocks of positive and negative charged polyelectrolyte‐coated nanoparticles (NPs) could be obtained by tuning the electrical properties of the amphoteric oxide NPs in acid and basic environments. The nanohybrid films were, thereafter, formed by layer‐by‐layer (LbL) assembly of polycation‐ and polyanion‐coated NPs. It was demonstrated that this approach could incorporate single component NPs into both polycation and polyanion layers, and in turn improve the NP loading, maintain good dispersion of NPs within the film. For separation applications, a dynamic LbL assembly was attempted as a means of fabricating such nanohybrid multilayers on both 2‐D and 3‐D polymeric porous substrates. The nanohybrid multilayer membrane renders both much higher selectivity and flux in the separation of solvent‐water mixtures. Moreover, such assembly of nanohybrid multilayers allows us to efficiently simplify the procedures by reducing 30–40‐fold process cycles. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Rapid assembly of polyelectrolyte multilayer membranes using an automatic spray system

The layer‐by‐layer (LbL) assembly of polyelectrolyte multilayers on to a porous supporting membrane is able to create various new composite membranes. However, the low efficiency and long time required for such procedures limit practical applications. In this study, an automatic spray system has been constructed for the rapid assembly of polyelectrolyte multilayers on to nanoporous supporting membranes. The compounds polyacrylic acid and poly(ethyleneimine), used as a model polyelectrolyte pair, were alternately sprayed on to a polyacrylonitrile ultrafiltration membrane. Experiments proved that the composite membrane obtained in this way had a good pervaporation dehydration performance. In addition, the process times were dramatically decreased, by as much as 80 folds, when compared with classical dip‐LbL methods. Such an automated system can easily be converted to the assembly of various organic species. Therefore, it is a versatile and highly efficient system for manufacturing composite multilayer membranes for many separation applications. © 2012 American Institute of Chemical Engineers AIChE J, 59: 250–257, 2013     

Enhanced mechanical properties of multilayer nano‐coated electrospun nylon 6 fibers via a layer‐by‐layer self‐assembly

We reported the mechanical properties of the polyelectrolyte multilayer nano‐coated electrospun fiber mats with different number of layers. Multilayer nano‐coatings composed of layers of PSS and PAH were successfully deposited onto electrospun nylon 6 fibers via layer‐by‐layer self‐assembly. Compared with pure nylon 6 fibers, the morphology of polyelectrolyte multilayer coated nylon 6 fibers was uniform and smooth. The mechanical properties of polyelectrolyte multilayer coated random and aligned nylon 6 fibers were remarkably enhanced. Moreover, it was found that the higher degree of alignment resulted in higher tensile strength, suggesting the combined effects of the alignment, the surface nanocoating and the formation of internal networks of polyelectrolytes on nylone 6 fibers. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Application of poly(diphenolic acid‐phenyl phosphate)‐based layer by layer nanocoating in flame retardant ramie fabrics

Poly(diphenolic acid‐phenyl phosphate) [poly(DPA‐PDCP)], obtained from diphenolic acid (a well‐known biomass chemical), was used together with polyethylenimine (PEI) to construct a flame retardant surface coating for ramie fabric using layer‐by‐layer self‐assembly. Attenuated total reflection Fourier transform infrared spectroscopy (ATR‐FTIR) and scanning electron microscope (SEM) equipped with an energy dispersive X‐ray spectrometer (EDX) were used to confirm the successful formation of layer by layer assembly. Assessment of the thermal and flammability properties for poly(DPA‐PDCP)/PEI‐coated ramie fabrics showed that the thermal stability, flame retardancy, and residual char were enhanced as the concentration of poly(DPA‐PDCP) and the BL number in the LbL process increased as well as the treatment of KH550 was applied. SEM and EDX analysis of the char residue confirmed further the intumescent flame retardant mechanism. This work demonstrated the great potentials of poly(DPA‐PDCP)/PEI flame retardant nanocoating constructed by LbL assembly method in the application of ramie fabric. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44795.     

Controlled heparinase‐catalyzed degradation of polyelectrolyte multilayer capsules with heparin as responsive layer

This work describes the enzymatic degradation of combined hollow capsules via layer‐by‐layer (LbL) self‐assembly technique. They previously showed the build‐up and characterization of capsules composed of synthetic [Poly(sodium 4‐styrene‐sulfonate)/Poly(allylamine hydrochloride)] and biodegradable (Heparin/Chitosan) polyelectrolytes. Biocatalytic response of assembled multilayer capsules provides a more functional and oriented approach in controlled release of encapsulated molecules: in this case multilayer capsule was disassembled by heparinase. Morphological change of individual capsule was assessed with Atomic Force Microscopy and Confocal Laser Scanning Microscopy. The sustained release of encapsulated FITC‐Dextran model was realized under enzymatic degradation of the capsule shells by heparinase. The release profile of FITC‐Dextran indicated the successful control in a concentration‐dependent manner, which shows the applicability as smart drug delivery system. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44916.     

Inkjet Printing Based Layer‐by‐Layer Assembly Capable of Composite Patterning of Multilayered Nanofilms

Surface modification involves developing a versatile thin film by combining the physical, chemical, or biological characteristics of the functional materials and can facilitate controlling material for desirable aims. Layer‐by‐layer (LbL) assembly can be used to create materials with controlled thicknesses and morphologies, diverse functionalities, and unique structures on any surface. However, despite the advantages of the LbL fabrication technique, there are limits to its application because it is a time‐consuming process and has difficulty controlling the shape of nanofilms. In addition, controlling the lateral organization is difficult because the preparation methods are based on one‐pot self‐assembly. In this study, a multilayered fabrication system is developed for the high‐throughput LbL assembly of nanofilms through inkjet printing. With various types of materials from synthetic polymer to graphene oxide to natural polymer and protein, the approach can tune the preparation of nanoscale multilayers with desired structures and shapes for specific applications on various substrates, including a silicon wafer, quartz glass, and cellulose‐based paper.     

Electric‐field‐induced layer‐by‐layer fabrication of stable second‐order nonlinear optical films

BACKGROUND: Second‐order nonlinear optical (NLO) films have been made using electric field poling polymer and Langmuir–Blodgett techniques with non‐centrosymmetric structures that exhibit relatively high values of nonlinear susceptibility (χ²), but the shortcomings of insufficient temporal or mechanical stability have restricted their potential applications. In this study, electric‐field‐induced layer‐by‐layer assembly was investigated as an effective technique to prepare low molecular weight chromophoric (LMWC) molecules of high degree of self‐ordering and density in NLO films. RESULTS: A new and stable LMWC molecule, 2‐({4‐[4‐(2‐carboxy‐2‐cyanovinyl)‐Z‐phenylazo]‐phenyl}‐methylamino)‐ethyl acid (DRCB), was first designed and synthesized successfully. The chromophore possesses two negative groups, one at each end, and still retains molecular polarity after ionization. DRCB was successfully assembled with polycationic diazoresin using the electric‐field‐induced layer‐by‐layer assembly method to construct stable organic second‐order NLO multilayer films. Upon UV irradiation, the interaction between multilayers was converted from an electrostatic interaction to covalent bonds. CONCLUSION: Due to the DC electric field effect in the assembly process, in addition to introducing the stable chromophore molecule and the covalent crosslinking structure in the films, the second‐order NLO films fabricated using the method described have large second harmonic generation response, good thermal stability and excellent chemical stability, which offer potential advantages for device applications. Copyright © 2009 Society of Chemical Industry     

Fabrication and structural tuning of novel composite hollow fiber membranes for pervaporation

A series of polysiloxaneimide (PSI)/polyetherimide (PEI) composite hollow fibers were fabricated by coextrusion and phase inversion. The hydrophobic PSI outer layer was set as the selective layer which was supported by the PEI inner layer. The PSI was synthesized by polycondensation of 3,3′,4,4′‐Biphenyltetracarboxylic Dianhydride (BPDA) with amino siloxane X‐22‐161A and a chain extender, 1,3‐Bis (3‐aminopropyl) ?1,1,3,3‐tertramethyldisiloxane (BATS). It was found that the macroscopic uniformity of PSI layer was dependent on the dope formulation, coagulant composition and dope flow rate: (1) the higher similarity degree of the solvent(s) for different layers in terms of solubility parameters, (2) the utilization of surfactant as a component in the water coagulant, and (3) higher flow rates of the outer layer dopes, led to the formation of more uniform and smoother PSI outer layer. The maximum outer layer thickness was around 2 μm. The bulk of the PEI layers were porous with finger like macrovoids. The outer surface of the inner PEI layer for some batches of the hollow fibers was confirmed to be porous. The original dual‐layer hollow fibers showed poor pervaporation performance. Post treatment was applied to cure the hollow fiber, delivering composite membranes with performance dominated by the coating material of PDMS. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43324.     

Rapid and efficient sprayed multilayer films for controlled drug delivery

The speed and scalability of film fabrication can dictate the translation of technologies from the laboratory scale to industrial level mass production. Spray‐assisted layer‐by‐layer (LbL) film assembly enables the rapid coating of geometrically complex and porous substrates with functional polyelectrolyte multilayers. Unfortunately, the encapsulation efficiency can be as low as one percent, making this technique prohibitively costly with even modestly priced materials. Herein, we used containment chambers to separately capture the aerosolized solutions for each step in the spray‐LbL process and analyzed the effect of recycling on multilayer film assembly. With potential biomedical applications, we studied the controlled release films of (Poly 2/heparin/lysozyme/heparin)_n films and tracked the distribution of lysozyme after film assembly. In a “Conventional” Spray‐LbL protocol, only 6% of the aerosolized lysozyme is incorporated into the film. By collecting and returning the expended solutions to their respective reservoirs (Recycle Spray‐LbL), we increased this efficiency to 15%. We also tuned the final distribution of lysozyme by adjusting the spray times (Optimized Spray‐LbL), which minimized the amount of lysozyme lost to non‐specific adsorption and reduced the fraction of lysozyme lost to the wash step from 30% and 75% (Conventional and Recycle Spray‐LbL, respectively) to 13%. Despite the changes in film assembly parameters, each film demonstrated similar controlled release properties. With the inherent limitations of time and cost facing Dip and Conventional Spray‐LbL technologies, respectively, the implementation of recycling to the latter demonstrates improvements in efficiency and time that may make it more attractive for the manufacture of biomedical coatings. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43563.     

Interfacial polymerization of polyaniline and its layer‐by‐layer assembly into polyelectrolytes multilayer thin‐films

The layer‐by‐layer (LbL) self assembly deposition technique was used to prepare multilayer thin films of anionic polyaniline‐blend‐poly(sodium 4‐styrenesulfonate) (PANI‐PSS) and cationic poly(diallydimethylammonium chloride) (PDADMAC). Anionic polyaniline was prepared by the interfacial polymerization of aniline monomer in the presence of PSS which acted as template to provide water solubility. The PSS to PANI concentration ratios used in the synthesis step was found to have a major effect on the final PANI‐PSS synthesis, its self assembly and the electrical properties of the prepared films. The optical and electrical properties of the films were measured by ultraviolet‐visible spectroscopy (UV‐Vis) and a 4‐point probe setup, respectively while the thickness of the films was measured by atomic force microscopy (AFM). Results showed that the optimum condition for the film growth and optimal conductivity were obtained with different synthesis conditions. These results suggest that the PSS concentration used for interfacial synthesis of PANI must be finely tuned depending on the type of application aimed by the user. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Multilayer assembly of ionic starches on old corrugated container recycled cellulosic fibers

In this study, old corrugated container recycled fibers were treated with polyelectrolyte multilayers consisting of biopolymer cationic starch with two degrees of substitution (DS) each in combination with one anionic starch. Pulp zeta potential, paper strength and the thin layer ellipsometry technique were applied to examine the influence of cationic starch DS on the formation of polyelectrolyte multilayers. The results indicated a significant interaction between the DS of cationic starch and the number of ionic starch layers formed. When low‐DS cationic starch was used, the pulp zeta potential and the paper strength increased significantly in assembling the first cationic layer. However, in depositing high‐DS cationic starch a greater zeta potential and a stronger influence on the paper strength were observed with a larger number of starch layers. This was confirmed by thin layer ellipsometry when a greater thickness of multilayers was achieved by employing high‐DS cationic starch to form a higher number of layers. © 2017 Society of Chemical Industry     

Hollow PUA/PSS/Au microcapsules with interdependent near‐infrared/pH/temperature multiresponsiveness

In this work, smart hollow microcapsules made of thermal‐/pH‐dual sensitive aliphatic poly(urethane‐amine) (PUA), sodium poly(styrenesulfonate) (PSS), and Au nanoparticles (AuNPs) for interdependent multi‐responsive drug delivery have been constructed by layer‐by‐layer (LbL) technique. The electrostatic interactions among PUA, PSS, and AuNPs contribute to the successful self‐assembly of hollow multilayer microcapsules. Thanks to the shrinkage of PUA above its lower critical solution temperature (LCST) and the interaction variation between PUA and PSS at different pH conditions, hollow microcapsules exhibit distinct pH‐ and thermal‐sensitive properties. Moreover, AuNPs aggregates can effectively convert light to heat upon irradiation with near‐infrared (NIR) laser and endow the hollow microcapsules with distinct NIR‐responsiveness. More importantly, the NIR‐responsive study also demonstrates that the microcapsule morphology and the corresponding NIR‐responsive drug release are strongly dependent on the pH value and temperature of the media. The results indicate that the prepared hollow PUA/PSS/Au microcapsules have the great potential to be used as a novel smart drug carrier for the remotely controllable drug delivery. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43008.     

Fabrication of amorphous calcium carbonate composite particles‐polymer multilayer films by a layer‐by‐layer method

Organic–inorganic hybrid multilayer films were prepared on a precoated cationic glass substrate by using a layer‐by‐layer (LbL) electrostatic self‐assembly technique with poly(diallyldimethylammonium chloride) as a polycation and submicron‐sized stable amorphous calcium carbonate (ACC) composite particles. The ACC composite particles (ACP) stabilized with poly(acrylic acid) were obtained by a carbonate controlled‐addition method. The average particles size of ACP was (1.8 ± 0.4) × 10² nm. An ethanolic dispersion of ACP was used for the LbL electrostatic self‐assembly technique on the precoated substrate due to instability of ACP in water. The deposition of the particles was confirmed by SEM analysis. The film thickness of the multilayer assembly increased from 230 to 710 nm with increasing the deposition layers. The FTIR spectra of scratched multilayer samples showed characteristic broaden peaks of ACC. The amorphous phase was stable after the LbL assembly process as well as after 2 months in a dry film state. POLYM. COMPOS., 36:330–335, 2015. © 2014 Society of Plastics Engineers     

Hydrogen gas barrier property of polyelectrolyte/GO layer‐by‐layer films

Different types of ultrathin multilayer composite membranes adsorbed on polyethylene terephthalate (PET) substrates are fabricated by the layer‐by‐layer (LBL) self‐assembly technique. The hydrogen gas barrier performances of these membranes are measured using a pressure permeation instrument. Polyethylenimines/graphene oxide (PEI/GO) are chosen as the optimal system; the multilayer film reduces the hydrogen transmission rate of the uncoated PET film from 1357 to 24 cm³/(m² 24 h 0.1 MPa). The membrane assembly process for the PEI/GO system is analyzed with UV–Visible spectroscopy, and the flat morphology of the ultrathin film is observed by scanning electron and atomic force microscopies. Moreover, in order to fully characterize the PEI/GO multilayer film system, we investigate the effects of multiple variables on the hydrogen resistance performance. These include the molecular weight of PEI, concentrations of PEI and GO, number of bilayers, soaking time, and drying methods. The film thickness is found to increase linearly during the LBL assembly process. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41973.     

Self-Assembly of Nanostructures on Surfaces Using Metal–Organic Coordination

Layer-by-layer (LbL) assembly of multilayers is an established method for the construction of layered nanostructures on surfaces, affording control of the thickness, composition, and organization in the vertical direction. Binding between layers is accomplished using various types of interactions, including electrostatic binding, hydrogen bonding, covalent bonding, metal–organic coordination, host–guest interactions, biospecific interactions, and others. Here we focus on LbL assembly using metal–organic coordination, and specifically on layered nanostructures based on bishydroxamate–M⁴⁺ binding. The coordination approach offers attractive features, such as a simple reaction, a defined geometry, and reversibility under certain conditions. The basic scheme includes self-assembly of a ligand (anchor) monolayer on the surface, followed by alternate binding of metal ions and multi-functional ligand layers, to form a coordination multilayer. This approach is demonstrated by the construction of a variety of coordinated nanostructures, including bilayers, multilayers, dendrimers, and nanoparticle assemblies, prepared on gold and oxide substrates.     

Covalent crosslinked assembly of tubular ceramic‐based multilayer nanofiltration membranes for dye desalination

A tubular ceramic‐based multilayer composite nanofiltration membrane has been developed for dye desalination. Poly(acrylic acid)(PAA)/poly(vinyl alcohol)(PVA)/glutaraldehyde(GA) was dynamically assembled on to the inner surfaces of tubular ceramic microporous substrates which had been pretreated using dynasylan ameo silane coupling agents. Subsequently, the composite membranes were thermally crosslinked to form covalent ester bonds. Experimental results proved that the composite membrane had good nanofiltration performance for dye desalination. The (GA/PVA/PAA)₃/ceramic multilayer membrane shows over 96% retention of Congo red and less than 3% NaCl retention using a permeate flux of about 25 L/(m²·h). An investigation of membrane performance as a function of operating conditions suggested that the covalent crosslinking multilayer membrane possessed much higher stability compared to other, electrostatically assembled, multilayer membranes. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3834–3842, 2013     

Metal‐chelated polyamide hollow fibers for human serum albumin separation

We modified microporous polyamide hollow fibers by acid hydrolysis to amplify the reactive groups and subsequent binding of Cibacron Blue F3GA. Then, we loaded the Cibacron Blue F3GA‐attached hollow fibers with different metal ions (Cu²⁺, Ni²⁺, and Co²⁺) to form the metal chelates. We characterized the hollow fibers by scanning electron microscopy. The effect of pH and initial concentration of human serum albumin (HSA) on the adsorption of HSA to the metal‐chelated hollow fibers were examined in a batch system. Dye‐ and metal‐chelated hollow fibers had a higher HSA adsorption capacity and showed less nonspecific protein adsorption. The nonspecific adsorption of HSA onto the polyamide hollow fibers was 6.0 mg/g. Cibacron Blue F3GA immobilization onto the hollow fibers increased HSA adsorption up to 147 mg/g. Metal‐chelated hollow fibers showed further increases in the adsorption capacity. The maximum adsorption capacities of Co²⁺‐, Cu²⁺‐, and Ni²⁺‐chelated hollow fibers were 195, 226, and 289 mg/g, respectively. The recognition range of metal ions for HSA from human serum followed the order: Ni(II) > Cu(II) > Co(II). A higher HSA adsorption was observed from human serum (324 mg/g). A significant amount of the adsorbed HSA (up to 99%) was eluted for 1 h in the elution medium containing 1.0M sodium thiocyanide (NaSCN) at pH 8.0 and 25 mM ethylenediaminetetraacetic acid at pH 4.9. Repeated adsorption–desorption processes showed that these metal‐chelated polyamide hollow fibers were suitable for HSA adsorption. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3346–3354, 2002     

Construction of multilayer coatings for flame retardancy of ramie fabric using layer‐by‐layer assembly

Complex multilayer coatings composed of α‐zirconium phosphate (ZrP), polyethylenimine (PEI), and ammonium polyphosphate (APP) were constructed via layer‐by‐layer assembly method for flame retardant ramie fabric. Bicomponent PEI/ZrP layers served as insulating barrier coating, and bicomponent PEI/APP layers served as intumescent coating. The flame retardancy of the coated ramie fabric was strongly dependent on the nature of the coatings and the layer‐by‐layer assembly patterns. The coated ramie fabric with inside PEI/ZrP layers and outside PEI/APP layers possessed the most uniform and consistent coating surface morphology, as well as the highest content of N and P elements, resulting in an excellent improvement in flame retardancy of ramie fabrics. When this kind of coated ramie fabric was heated, the inner PEI/ZrP layer effectively prevent oxygen and heat from penetrating into the substrate, and the outer PEI/APP layer exposed to air with good expansion during combustion. The synergistic effect was formed during the combustion process and could impart ramie fabrics with high flame retardancy. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45556.     

Role of clays in fouling-resistant clay-embedded polyelectrolyte multilayer membranes for wastewater effluent treatment

This study aimed to investigate the effects of cation exchange capacity (CEC) and location of clay nanoplatelets on the structure and performance of clay-embedded polyelectrolyte multilayer (c-PEM) membranes for wastewater effluent treatment. Two kinds of clay nanoplatelets, montmorillonite and kaolin, were deposited on the ultrafiltration membrane by employing layer-by-layer (LbL) assembly with poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA). Negatively charged clay platelets or PAA interacted with positively charged PAH to form a bilayer in the c-PEM membrane. The filtration effect of clay platelets was successively distinguished from PEM by reducing the number of (PAH/PAA) bilayers from four to one, while keeping the clay layer at the outermost layer of assembly. When the clay platelets were deposited only as the outermost layer of the LbL multilayers, the c-PEM membrane with one clay layer and one bilayer assembly showed significant flux barrier and fouling resistance. Clay platelets as the outermost layer physically increased the flow path length and decreased the number of pores, as well as effectively blocked the organic contaminants in the wastewater. Meanwhile, when the clay layer was embedded in the middle of the PEM, the synergistic effect of clay platelets and PEM for wastewater treatment was difficult to obtain because the presence of clay platelets defected the buildup of fully interdigitated c-PEM and the adsorption of clay platelets was decreased. For the clays having low CEC, a higher number of LbL multilayers were required to deposit the clay platelets and to improve the performance of membrane. The high CEC clays (montmorillonite) turned out to be better than the low CEC clays (kaolin) in the structure and performance of the c-PEM membrane for wastewater effluent treatment.