Layer-by-layer Assembly Technique Research Articles

Reversible Sensing Technologies Using Upcycled TPEE: Crafting pH and Light Responsive Materials towards Sustainable Monitoring.

Multiresponsive materials with reversible and durable characteristics are indispensable because of their promising applications in environmental change detections. To fabricate multiresponsive materials in mass production, however, complex reactions and impractical situations are often involved. Herein, a dual responsive (light and pH) spiropyran-based smart sensor fabricated by a simple layer-by-layer (LbL) assembly process from upcycled thermoplastic polyester elastomer (TPEE) materials derived from recycled polyethylene terephthalate (r-PET) is proposed. Positively charged chitosan solutions and negatively charged merocyanine-COOH (MC-COOH) solutions are employed in the LbL assembly technique, forming the chitosan-spiropyran deposited TPEE (TPEE-CH-SP) film. Upon UV irradiation, the spiropyran-COOH (SP-COOH)molecules on the TPEE-CH-SP film undergo the ring-opening isomerization, along with an apparent color change from colorless to purple, to transform into the MC-COOH molecules. By further exposing the TPEE-CH-MC film to hydrogen chloride (HCl) and nitric acid (HNO3 ) vapors, the MC-COOH molecules can be transformed into protonated merocyanine-COOH (MCH-COOH) with the simultaneous color change from purple to yellow.

Layer-by-Layer Assembled Smart Antibacterial Coatings via Mussel-Inspired Polymerization and Dynamic Covalent Chemistry.

Bacterial colonization on the surface of medical implanted devices and bacterial infection-induced biofilm have been a lethal risk for patients of clinical treatment. While antibacterial coatings fabricated by layer-by-layer (LBL) assembly techniques have been well explored, the facile preparation of substrate-independent smart antibacterial coatings with on-demand antibiotics release profile and excellent antibacterial performance is still urgently needed. In this work, this goal is addressed by LBL assembly fabrication of robust antibacterial coatings using naturally occurring and commercially available building blocks (i.e., aminoglycosides, 5,6-dihydroxyindole, and formylphenylboronic acid) via the subsequentially performed mussel-inspired polymerization and dynamic covalent chemistries. The resulting antibacterial coatings on different substates all presente a dynamic feature (i.e., pH-responsive), on-demand antibiotics release properties, and highly effective antibacterial performance both in vitro and in vivo. It is envisioned that this work can expand the scope of LBL assembly technique toward the next generation of robust and universal antibacterial coating materials by using natural building blocks and readily available chemistries.

Designable functional polymer nanocomposites via layer-by-layer assembly for highly deformable power-boosted triboelectric nanogenerators

In this study, a designable functional polymer nanocomposite (FPN) layer has been employed to effectively boost the output performance of highly deformable triboelectric nanogenerators (TENGs) via a facile, simple, low-cost, reproducible, and eco-friendly layer-by-layer (LbL) process. The FPN interlayer with 2–16 bilayers between a negative tribomaterial and an electrode was designed by titanium dioxide (TiO2) nanoparticles (called as T-FPN). Owing to its high dielectric and surface charge maintaining characteristics, TENG with 12 bilayer T-FPN could exhibit a surface charge density of 120 μC/m2 and a surface potential of 649 mV. As a result, a maximum voltage of 568 V and a maximum current density of 86 mA/m2 were achieved at 4 Hz and 10 N, which were about 3.8- and 5.7-times greater than those without the T-FPN layer, respectively. More importantly, the T-FPN-based TENG exhibited highly deformable (i.e., bendable, foldable, and rollable) owing to the durable polymer nanocomposite and strongly incorporated interfaces prepared by the LbL assembly technique, which preserves the mechanical characteristics (i.e., no cracks and no delamination) of the original materials. Finally, the optimized T-FPN-based TENG lit up 117 green light-emitting diodes and powered the portable electronic calculator. The designable FPN via the LbL method can be a potential approach for the future development of sustainable energy sources for powering flexible portable electronic devices.

Layer-by-Layer Assembly of Reduced Graphene Oxide and MXene Nanosheets for Wire-Shaped Flexible Supercapacitors.

As the demand for wearable electronic devices increases, interest in small, light, and deformable energy storage devices follows suit. Among these devices, wire-shaped supercapacitors (WSCs) are considered key components of wearable technology due to their geometric similarity to woven fiber. One potential method for creating WSC devices is the layer-by-layer (LbL) assembly technique, which is a "bottom-up" method for electrode fabrication. WSCs require conformal and adhesive coatings of the functional material to the wire-shaped substrate, which is difficult to obtain with other processing techniques such as vacuum filtration or spray-coating. However, the LbL assembly technique produces conformal and robust coatings that can be deposited onto a variety of substrates and shapes, including wires. In this study, we report WSCs made using the LbL assembly of alternating layers of positively charged reduced graphene oxide functionalized with poly(diallyldimethylammonium chloride) and negatively charged Ti3C2Tx MXene nanosheets conformally deposited on activated carbon yarns. In this construct, the added LbL film enhances capacitance, energy density, and power density by 240, 227, and 109%, respectively, relative to the uncoated activated carbon yarn, yielding high specific and volumetric capacitances (237 F g-1, 2193 F cm-3). In addition, the WSC possesses good mechanical stability, retaining 90% of its initial capacity after 200 bending cycles. This study demonstrates that LbL coatings on carbon yarns are promising as linear energy storage devices for fibrous electronics.

High-mobility patternable MoS2 percolating nanofilms

Fabrication of large-area and uniform semiconducting thin films of two-dimensional (2D) materials is paramount for the full exploitation of their atomic thicknesses and smooth surfaces in integrated circuits. In addition to elaborate vapor-based synthesis techniques for the wafer-scale growth of 2D films, solution-based approaches for high-quality thin films from the liquid dispersions of 2D flakes, despite underdeveloped, are alternative cost-effective tactics. Here, we present layer-by-layer (LbL) assembly as an effective approach to obtaining scalable semiconducting films of molybdenum disulfide (MoS2) for field-effect transistors (FETs). LbL assembly is achieved by coordinating electrochemically exfoliated MoS2 with cationic poly (diallyldimethylammonium chloride) (PDDA) through electrostatic interactions. The PDDA/MoS2 percolating nanofilms show controlled and self-limited growth on a variety of substrates, and are easily patterned through lift-off processes. Ion gel gated FETs are fabricated on these MoS2 nanofilms, and they show mobilities of 9.8 cm2·V−1·s−1, on/off ratios of 2.1 × 105 with operating voltages less than 2 V. The annealing temperature in the fabrication process can be as low as 200 °C, thereby permitting the fabrication of flexible FETs on polyethylene terephthalate substrates. The LbL assembly technique holds great promise for the large-scale fabrication of flexible electronics based on solution-processed 2D semiconductors.

Layer-by-Layer Assembly of Electroactive Dye/LDHs Nanoplatelet Matrix Film for Advanced Dual Electro-optical Sensing Applications

It proved that the most destructive effects of the toxic Al3+ ion on the human nervous system and disease that are involved with this system, such as Alzheimer's. The development of solid-state electrodes is still in its infancy during the sensor-based detection methods for Al3+. Hence, in this study, a novel flexible ITO/PET-based electrochemical solid-state sensor was designed and constructed. Modification of the surface of electrode bedding was done by layer-by-layer (LbL) assembly of Mg–Al LDH. nanoplatelets along with alizarin red S (ARS) in an interconnected matrix film. In the molecular design of sensing base of the electrode, the electroactive organic units (ARS molecules) present in the ITO/PET-layered (ARS/LDHs)n matrix are involved in electrochemical reactions when exposed to the target molecule (Al3+ ion), so the electrochemical changes of the new formed Al-chelated system are detectable. This type of sensor is used for sensitive and selective detection of Al3+. The minimum sheet resistance, morphology and high electrocatalytic activity of the modified matrix film are obtained in the fifth cycle of LbL assembly technique. In this electrochemical sensor, both electrochemical and optical methods were detected with high sensitivity and selectivity of Al3+, so that in a cyclic voltammetry electrochemical method, the lower detection limit of 10.1 nM with a linear range of [0.2–120 μM] was obtained compared to the fluorescence-based optical method.

Fabrication of Metal–Organic Framework Thin Films Using Programmed Layer‐by‐Layer Assembly Techniques

AbstractMetal–organic frameworks (MOFs) are a rather new class of crystalline, nanoporous solids that are self‐assembled from inorganic, metal or metal‐oxo nodes and organic linkers. Powder MOFs are originally developed for gas storage and catalyst applications, but more recently, more advanced applications have used well‐defined MOF thin films in electronic, photonic, and sensing devices. MOF thin films for targeted applications can be fabricated on appropriately functionalized substrates using a programmed layer‐by‐layer (LbL) assembly technique, which yields oriented, highly crystalline MOF thin films (surface‐mounted MOFs, SURMOFs). The LbL assembly technique as well as the huge potential of SURMOFs is presented herein. Emerging SURMOF properties related to their heteroepitaxy, postsynthetic modification/crosslinking, lithography, and photoswitching are highlighted.

Fabrication of PEI-Fc/SGO multilayer films modified electrode through LBL assembly technique for the detection of dopamine

In this work, a sensor for the detection of dopamine (DA) based on electroactive polymer (PEI-Fc)/sulfonic acid-functionalized graphene oxide (SGO) multilayer film-modified glassy carbon electrode (GCE) through layer-by-layer (LBL) method was fabricated. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy revealed the successful functionalization of GO into SGO with negatively charged sulfonic groups. The obtained PEI-Fc/SGO multilayer films were characterized using scanning electron microscopy (SEM) and ultravioletvisible spectrometer (UV-Vis). Cyclic voltammetric studies demonstrated that the modified electrode presented enhanced electrocatalytic performance towards DA in terms of peak currents compared with bare GCE. The choronoamperometric results indicated that the modified electrode exhibited a wide linear range from 1 to 695 μM with a low detection limit of 0.255 μM towards the detection of DA. Besides, the modified electrode exhibited good selectivity, excellent reproducibility, and high stability of at least 1 month.

Wire-Shaped Supercapacitors with Organic Electrolytes Fabricated via Layer-by-Layer Assembly.

A wire-shaped supercapacitor (WSS) has structural advantages of high flexibility and ease of incorporation into conventional textile substrates. In this work, we report a thin reproducible WSS fabricated via layer-by-layer (LbL) assembly of multiwalled carbon nanotubes (MWCNTs), combined with an organic electrolyte of propylene carbonate (PC)-acetonitrile (ACN)-lithium perchlorate (LiClO4)-poly(methyl methacrylate) (PMMA) that extends the voltage window to 1.6 V. The MWCNTs were uniformly deposited on a curved surface of a thin Au wire using an LbL assembly technique, resulting in linearly increased areal capacitance of the fabricated WSS. Vanadium oxide was coated on the LbL-assembled MWCNT electrode to induce pseudocapacitance, hence enhancing the overall capacitance of the fabricated WSS. Both the cyclic stability of the WSS and the viscosity of the electrolyte could be optimized by controlling the mixing ratio of PC to ACN. As a result, the fabricated WSS exhibits an areal capacitance of 5.23 mF cm-2 at 0.2 mA cm-2, an energy density of 1.86 μ W h cm-2, and a power density of 8.5 mW cm-2, in addition to a high cyclic stability with a 94% capacitance retention after 10 000 galvanostatic charge-discharge cycles. This work demonstrates a great potential of the fabricated scalable WSS in the application to high-performance textile electronics as an integrated energy storage device.

A facile strategy to prepare superhydrophilic polyvinylidene fluoride (PVDF) based membranes and the thermodynamic mechanisms underlying the improved performance

Abstract This study provided a first report on a facile strategy to fabricate superhydrophilic and low-fouling multilayer coatings on polyvinylidene fluoride (PVDF) membrane by layer-by-layer (LBL) assembly of Fe3+ and phytic acid (PA) alternately. Successful modification was verified by scanning electron microscope (SEM) observation and element analysis. It was found that, the resulted PA/Fe@PVDF-OH membrane with five bilayers’ (BLs’) modification performed the optimal antifouling properties under conditions in this study. As compared to the original PVDF-OH membrane, the coated membrane surface possessed super hydrophilicity (water contact angle was 11.34°) and improved negative charge density. Thermodynamic analysis showed that, the changes of interaction energy caused by both of the modified surface thermodynamic properties and morphology were responsible for the improved antifouling performance of the coated membrane. The facile coating strategy, together with the method assessing interaction energy in this study provided a potential solution to optimize LBL assembly technique and to quantitatively tune antifouling ability of membranes.

Intumescent flame retardant finishing of polyester fabrics via the layer-by-layer assembly technique

PurposeThe purpose of this paper is to investigate the potential use of the layer-by-layer (LbL) assembly as an intumescent flame retardant for polyester, cotton and their blended fabrics.Design/methodology/approachIn this study, polyester (PET), cotton and their blends were applied with the flame retardant coating via the LbL assembly technique. The flame retardancy, melt dripping, thermal properties and morphology of coated polyester fabrics were then examined.FindingsThe scanning electron micrograph of uncoated and coated fabrics revealed that the LbL assembly coating on the fabric surface was successful. The assessment of the flame retardancy and thermal properties of the coated fabrics showed that the after-flame time and melt dripping during the vertical burning test decreased. The char residue at temperatures ranging from 450 to 800°C during thermogravimetric analysis was enhanced as compared with the uncoated fabric. Furthermore, the morphology of the char residual of coated fabrics was rougher and bulkier than the uncoated fabrics, suggesting the typical behavior of intumescence.Social implicationsThe LbL technique generally uses much fewer chemicals, thus making this flame retardant finishing much more environmentally friendly. It is also expected that these fabrics will show better touch characteristics. These fabrics may be tested for their comfort compared to that of conventional coating to enable their use on an industrial scale.Originality/valueThis work demonstrated the ability to apply an effective intumescent coating on polyester, cotton and blend fabric. In order to maintain fabric handle property, the Lbl coating technique is also employed.

Layer-by-layer assembly of versatile nanoarchitectures with diverse dimensionality: a new perspective for rational construction of multilayer assemblies.

Over the past few decades, layer-by-layer (LbL) assembly of multilayer thin films has garnered considerable interest on account of its ability to modulate nanometer control over film thickness and its extensive choice of usable materials for coating planar and particulate substrates, thus allowing for the fabrication of responsive and functional thin films for their potential applications in a myriad of fields. Herein, we provide elaborate information on the current developments of LbL assembly techniques including different properties, molecular interactions, and assembly methods associated with this promising bottom-up strategy. In particular, we highlight the principle for rational design and fabrication of a large variety of multilayer thin film systems including multi-dimensional capsules or spatially hierarchical nanostructures based on the LbL assembly technique. Moreover, we discuss how to judiciously choose the building block pairs when exerting the LbL assembly buildup which enables the engineering of multilayer thin films with tailor-made physicochemical properties. Furthermore, versatile applications of the diverse LbL-assembled nanomaterials are itemized and elucidated in light of specific technological fields. Finally, we provide a brief perspective and potential future challenges of the LbL assembly technology. It is anticipated that our current review could provide a wealth of guided information on the LbL assembly technique and furnish firm grounds for rational design of LbL assembled multilayer assemblies toward tangible applications.

Synthesis of antireflective silica coatings through the synergy of polypeptide layer-by-layer assemblies and biomineralization.

We report a versatile approach to synthesize silica coatings with antireflective (AR) characteristics through the combination of a layer-by-layer (LbL) assembly technique and biomineralization. LbL assembled decanoyl-modified poly(l-lysine)/poly(l-glutamic acid) (PLL-g-Dec/PLGA) multilayer films were used as templates for silica mineralization, followed by calcination. The specific deposition of silica onto the LbL polypeptide assemblies through amine-catalyzed polycondensation resulted in silica coatings that exhibited the transcription of the nano-/microstructured polypeptide films and their film thickness and porosity can be tuned by varying the number of bilayers, degree of substitution, and PLL molecular weight. AR silica coatings exhibiting more than 6% increase in transmittance in the near UV/visible spectral range can be obtained at an optimized refractive index, thickness, and surface roughness. The abrasion test showed that the silica coatings exhibited sufficient structural durability due to continuous silica nanostructures and low surface roughness. This study demonstrated that nanostructured thin films can be synthesized for AR coatings using the synergy between the LbL assembly technique and biomineralization.

Construction of a biointerface for glucose oxidase through diazonium chemistry and electrostatic self-assembly technique

In this study, a new procedure for the fabrication of biosensors was developed. The method is based on the covalent attachment of nitrophenyl groups to the electrode surface via diazonium salt reaction followed by their conversion to amine moieties through electrochemical reduction and electrostatic layer-by-layer (LbL) assembly technique. In this procedure, highly stable iron oxide (Fe3O4) nanoparticles (IONPs), chitosan (CHIt), GOx, and Nile blue (NB) were assembled on the surface of aminophenyl modified glassy carbon electrode (AP/GCE) by LbL assembly technique. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to characterize the interfaces. The surface coverage of the active GOx and Michaelis–Menten constant (K M) of the immobilized GOx were Γ = 3.38 × 10−11 mol cm−2 and 2.54 mM, respectively. The developed biosensor displayed a well-defined amperometric response for glucose determination with high sensitivity (8.07 μA mM−1) and low limit of detection (LOD) of 19.0 μM. The proposed approach allows simple biointerface regeneration by increasing pH which causes disruption of the ionic interactions and release of the electrostatic attached layers. The biosensor can then be reconstructed again using fresh enzyme. Simple preparation, good chemical and mechanical stabilities, and easy surface renewal are remarkable advantages of the proposed biosensor fabrication procedure.

Using a layer-by-layer assembly method to fabricate a uniform and conductive nitrogen-doped graphene anode for indium-tin oxide-free organic light-emitting diodes.

Highly conductive, uniform, and transparent nitrogen-doped graphene multilayer films were produced by a layer-by-layer (LbL) assembly method. Such a technique was realized by alternate deposition of graphene oxide modified with the cationic surfactant N,N,N-trimethyl-1-dodecanaminium bromide (CTAB) and the anionic surfactant sodium dodecylbenzenesulfonate. In this way, we can achieve a highly conductive (900 S/cm), uniform, and controllable graphene film in terms of thickness, transmittance, and sheet resistance after high-temperature reduction. The improved conductivity is attributed to better graphitization and nitrogen-doping introduced by CTAB. The organic light-emitting diode using such a multilayer graphene film fabricated by the LbL method as an anode obtains higher current density and luminance at low voltage compared to that with an indium-tin oxide (ITO) anode. Moreover, the current efficiency of graphene-based device is comparable to that of an ITO-based device. It is proved that such a nitrogen-doped multilayer graphene film developed by the LbL assembly technique is a promising candidate for a transparent electrode in organic electronics.

Layer-by-layer Nanoarchitectonics: Invention, Innovation, and Evolution

Abstract Materials fabrication with nanoscale structural precision based on bottom-up-type self-assembly has become more important in various current disciplines in chemistry including materials chemistry, organic chemistry, physical chemistry, analytical chemistry, biochemistry, colloid and surface chemistry, and supramolecular chemistry. Although the design of new materials based on nanoscale self-assembly is anticipated as a key concept, preparing complete three-dimensional structures at nanoscale precision remains a difficult target using current technologies. Rather, dimension-reduced approaches such as layering of two-dimensional nanostructures into precisely controlled lamellar nanomaterials are currently achievable. In particular, layer-by-layer (LbL) assembly is known as a highly versatile method for fabrication of controlled layered structures from various kinds of component materials using very simple, inexpensive, and rapid procedures. Therefore, fabrication of multilayer films through the LbL deposition process has attracted growing interest from various research communities. The high versatility and flexibility of LbL assembly is continuously creating new concepts, new materials, new procedures, and new applications. In this highlight review, we focus on nanoarchitectonics by LbL assembly. After an initial introduction on the invention and a brief history of the LbL assembly technique, innovations and the evolution of the technique are described based mainly on recent examples, which are categorized into two sections: (i) developments in methodology (technical, material, and phenomenological aspects with expansion of concept) and (ii) progress in applications (physical, chemical/biochemical, and biomedical applications).

Facile assembly of Fe3O4@Au nanocomposite particles for dual mode magnetic resonance and computed tomography imaging applications

We report a facile approach for fabrication of Fe3O4@Au nanocomposite particles (NCPs) as a dual mode contrast agent for both magnetic resonance (MR) and computed tomography (CT) imaging applications. In this study, Fe3O4 nanoparticles (NPs) prepared by a controlled coprecipitation approach were used as core particles for subsequent electrostatic layer-by-layer (LbL) assembly of poly(γ-glutamic acid) (PGA) and poly(L-lysine) (PLL) to form PGA/PLL/PGA multilayers, followed by assembly with dendrimer-entrapped gold NPs (Au DENPs) formed using amine-terminated generation 5 poly(amidoamine) dendrimers as templates. After crosslinking the multilayered shell of PGA/PLL/PGA/Au DENPs via EDC chemistry, the remaining amine groups of the outermost layer of Au DENPs were acetylated to neutralize the surface charge of the particles. The formed Fe3O4@Au NCPs were well characterized via different techniques. We show that the formed Fe3O4@Au NCPs are colloidally stable, hemocompatible, and biocompatible in the given concentration range (0–100 μg mL−1). The relatively high r2 relaxivity (71.55 mM−1 s−1) and enhanced X-ray attenuation property when compared with either the uncoated Fe3O4 NPs or the Au DENPs afford the developed Fe3O4@Au NCPs with a capacity not only for dual mode CT and MR imaging of cells in vitro, but also for MR imaging of liver and CT imaging of subcutaneous tissue in vivo. With the facile integration of both Fe3O4 NPs and Au DENPs within one particle system via the LbL assembly technique and dendrimer chemistry, it is expected that the fabricated Fe3O4@Au NCPs may be further modified with multifunctionalities for multi-mode imaging of various biological systems.

Inkjet deposition of layer-by-layer assembled films.

Layer-by-layer assembly (LBL) can create advanced composites with exceptional properties unavailable by other means, but the laborious deposition process and multiple dipping cycles hamper their utilization in microtechnologies and electronics. Multiple rinse steps provide both structural control and thermodynamic stability to LBL multilayers, but they significantly limit their practical applications and contribute significantly to the processing time and waste. Here we demonstrate that by employing inkjet technology one can deliver the necessary quantities of LBL components required for film buildup without excess, eliminating the need for repetitive rinsing steps. This feature differentiates this approach from all other recognized LBL modalities. Using a model system of negatively charged gold nanoparticles and positively charged poly(diallyldimethylammonium) chloride, the material stability, nanoscale control over thickness, and particle coverage offered by the inkjet LBL technique are shown to be equal or better than the case of multilayers made with traditional dipping cycles. The opportunity for fast deposition of complex metallic patterns using a simple inkjet printer is also shown. The additive nature of LBL deposition based on the formation of insoluble nanoparticle-polyelectrolyte complexes of various compositions provides an excellent opportunity for versatile, multicomponent, and noncontact patterning for the simple production of stratified patterns that are much needed in advanced devices.

Effect of enzyme location on activity and stability of trypsin and urease immobilized on porous membranes by using layer-by-layer self-assembly of polyelectrolyte

The layer-by-layer (LbL) self-assembly of polyelectrolyte is one of the simplest ways to immobilize enzyme on membrane. In this paper, the immobilization of trypsin (TRY) and urease (URE) on polyacrylonitrile based membranes using the LbL assembly technique was presented. The studied systems consisted in bilayered assemblies with the enzyme layer as the outer layer and trilayered assemblies with the enzyme layer as the inner sandwiched layer. The membrane pore size was chosen so that the smaller enzyme TRY was mainly immobilized within the membrane and confined in the porous membrane structure while URE immobilization mainly took place at the membrane surface. No dramatic difference on reactivity was evidenced between these two enzyme locations. The catalytic activity of immobilized enzymes was found to be lower than the free ones in solution but their stability was dramatically enhanced. The higher activity was observed when the enzyme is deposited as the outer layer of the LbL assembly. On the other hand, the more stable catalytic membranes were obtained when the outer layer consists of a polyelectrolyte covering the enzyme layer.

Layer-By-Layer assembled thin films of inorganic nanomaterials: fabrication and photo-electrochemical properties

The sequential Layer-By-Layer (LBL) self-assembly technique is one of the most promising methods for thin film fabrication. Initially demonstrated by multilayer assemblies using polyelectrolytes, this elegant concept of precisely controlling composition, thickness and architecture of the thin films has been rapidly extended to a diverse array of functional materials including low-dimensional inorganic nanomaterials. This review first introduces some fundamental aspects of the LBL assembly technique; followed by representative examples of the LBL assembled multilayer thin films containing nanostructured materials as building blocks. The photochemical and electrochemical properties of such fabricated thin films were briefly reviewed in the second part.