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We report a rationally designed stretchable conductive composite of low Ag percolation threshold concentration with the aid of boron nitride (BN) as a non-conductive auxiliary filler.

The growth of lithium (Li) dendrites reduces the lifespan of Li-metal batteries and causes safety issues. Herein, hierarchically porous aramid nanofiber separators capable of effectively suppressing the Li dendrite growth while maintaining highly stable cycle performances at high charge/discharge rates are reported. A two-step solvent exchange process combined with reprotonation-mediated self-assembly is utilized to control the bimodal porous structure of the separators. In particular, when ethanol and water are used sequentially, aramid nanofibers form hierarchical porous structures containing nanopores in macroporous polymer frameworks to yield a mechanically robust membrane with high porosity of 97% or more. The optimized samples exhibit high ionic conductivities of 1.87-4.04 mS cm

When various optically and/or electronically active materials, such as conjugated polymers, perovskites, metals, and metal oxides, are confined at the nanoscale, they can exhibit unique nano-confined behavior that significantly differs from the behavior observed at the macroscale. Although controlled nano-confinement of functional materials can allow modulation of their electronic properties without the aid of any synthetic methodologies or additional chemical treatments, limited assembly approaches for nano-confinement and insufficient analytical tools for electronic characterization remain critical challenges in the development of novel optoelectronic materials and the investigation of their modulated properties. This review describes how the nano-confined features of organic and inorganic materials are related to the control and improvement of their optoelectronic properties. In particular, we focus on various assembly approaches for effective nano-confinement as well as methods for nano-electronic characterization. Then, we briefly present challenges and perspectives on the direction of nano-confinement in terms of the preparation of optoelectronic materials with desired functionalities. Furthermore, we believe that this review can provide a basis for developing and designing next-generation optoelectronics through nano-confinement.

Highly conductive and porous current collectors that can provide favorable interfacial interaction with sulfur components play a critical role in the performance of lithium–sulfur (Li–S) batteries. Although three-dimensional (3D) porous textiles have emerged as promising current collector materials, most reported approaches have reached a limit in producing textiles with metal-like conductivity and do not effectively utilize the large surface area of textiles. Here, we introduce a Li–S copolymer cathode with high areal/specific capacity and good rate capability using a metallic cotton textile (CT)-based current collector that exhibits strong interfacial interaction with sulfur. To fabricate the metallic current collector, CT was first carbonized and subsequently electroplated with nickel (Ni). When a sulfur copolymer-based hybrid slurry and layer-by-layer-assembled conductive capping layer were deposited onto the Ni-electroplated CT, the resulting Li–S copolymer cathode displayed significantly enhanced areal capacity, specific capacity, and rate capability. These improvements were realized due to the full utilization of the large conductive surface area of Ni-electroplated CT as well as the effective chemical confinement of soluble lithium polysulfides by a conductive capping layer. The Li–S copolymer cathode prepared in this study outperforms previously reported sulfur copolymer-based cathodes and provides a basis for the development and design of future high-performance electrodes.

Biofuel cells, which can convert chemical energy into electricity have been considered as one of the most promising candidates for powering implantable and microscale biomedical devices. However, most biofuel cells generate a low power output, limiting their practical applications. Here, we introduce a high-performance biofuel cell based on gold nanoparticle-modified carbon nanotube hybrid fibers. These hybrid electrodes could be converted into anodes through additional enzyme deposition and used directly as cathodes, allowing notable oxygen reduction reaction activity as well as high electrical conductivity (∼6100 S cm−1). The formed hybrid biofuel cell, composed of an enzymatic anode and a gold nanoparticle-coated carbon fiber cathode, provides an outstanding stationary power output of 1.2 mW cm−2 under a fixed external resistance (cyclic voltammetry measurement ∼2.1 mW cm−2) at 300 mmol L−1 glucose. Furthermore, these one-dimensional hybrid electrodes with extremely high electrical conductivity can be widely applied in various wire-type electrochemical devices.

Electrical conductivity, mechanical flexibility, and large electroactive surface areas are the most important factors in determining the performance of various flexible electrodes in energy storage devices. Herein, a layer-by-layer (LbL) assembly-induced metal electrodeposition approach is introduced to prepare a variety of highly porous 3D-current collectors with high flexibility, metallic conductivity, and large surface area. In this study, a few metal nanoparticle (NP) layers are LbL-assembled onto insulating paper for the preparation of conductive paper. Subsequent Ni electroplating of the metal NP-coated substrates reduces the sheet resistance from ≈103 to

We introduce high-performance supercapacitor electrodes with ternary components prepared from consecutive amphiphilic ligand-exchange-based layer-by-layer (LbL) assembly among amine-functionalized multi-walled carbon nanotubes (NH2-MWCNTs) in alcohol, oleic acid-stabilized Fe3O4 nanoparticles (OA-Fe3O4 NPs) in toluene, and semiconducting polymers (PEDOT:PSS) in water. The periodic insertion of semiconducting polymers within the (OA-Fe3O4 NP/NH2-MWCNT)n multilayer-coated indium tin oxide (ITO) electrode enhanced the volumetric and areal capacitances up to 408 ± 4 F cm−3 and 8.79 ± 0.06 mF cm−2 at 5 mV s−1, respectively, allowing excellent cycling stability (98.8% of the initial capacitance after 5000 cycles) and good rate capability. These values were higher than those of the OA-Fe3O4 NP/NH2-MWCNT multilayered electrode without semiconducting polymer linkers (volumetric capacitance ∼241 ± 4 F cm−3 and areal capacitance ∼1.95 ± 0.03 mF cm−2) at the same scan rate. Furthermore, when the asymmetric supercapacitor cells (ASCs) were prepared using OA-Fe3O4 NP- and OA-MnO NP-based ternary component electrodes, they displayed high volumetric energy (0.36 mW h cm−3) and power densities (820 mW cm−3).

In this study, we introduce hydrophobic and hydrophilic graphene oxide nanosheet (GON) catalysts prepared by consecutive ligand replacement of hydrophobically stabilized magnetic and catalytic nanoparticles (NPs); it exhibits high catalytic activity, fast magnetic response, and good dispersion in both nonpolar and aqueous media, allowing high loading amount of magnetic and catalytic NPs onto GON sheets. More specifically, these GON catalysts showed a high product yield of 66–99% and notable recyclability (93% of the initial product yield after 10 reaction cycles) in a Suzuki–Miyaura reaction in nonpolar media, outperforming the performance of the conventional hydrophilic GON catalysts. Additional coating of a hydrophilic layer onto GON catalysts also showed the notable performance (product yield ∼99%) in catalytic reactions performed in aqueous media. Given that ligand-controlled catalytic NPs adsorbed onto 2D nanosheets can be used as hydrophobic and hydrophilic stabilizers as well as catalysts, our approach can provide a tool for developing and designing 2D-nanosheet catalysts with high performance in nonpolar and polar media.

Herein, we introduce a high-performance and highly flexible asymmetric supercapacitor that is prepared from metallic cotton threads coated with pseudocapacitive nanoparticles without the aid of carbon-based conductive materials. In this study, Au nanoparticles are layer-by-layer assembled on highly porous cotton threads using amine-functionalized molecular linkers in organic media for the preparation of metallic cotton threads that can store a large amount of pseudocapacitive nanoparticles. The highly porous metallic cotton threads exhibit exceptional electrical conductivity (∼2.1 × 104 S cm−1, resistance of ∼0.1 Ω cm−1) and yet maintain the intrinsic flexibility of cotton. Using the same assembly method, Fe3O4 and MnO nanoparticles are deposited onto the metallic cotton threads to prepare the anode and the cathode, respectively, of the asymmetric supercapacitors, and furthermore, Au nanoparticles are periodically inserted between the pseudocapacitive multilayers to facilitate charge transport. The assembled all solid-state asymmetric supercapacitors with a unique structural design deliver a notable areal energy density of 80.7 μW h cm−2 (at 172.5 μW cm−2) and a power density of 3450.1 μW cm−2 (at 53.7 μW h cm−2), exceeding the performance of conventional thread-type asymmetric supercapacitors. We also emphasize that this energy performance can be further enhanced by increasing the number of metal and/or pseudocapacitive nanoparticle layers deposited.

The effective implantation of conductive and charge storage materials into flexible frames has been strongly demanded for the development of flexible supercapacitors. Here, we introduce metallic cellulose paper-based supercapacitor electrodes with excellent energy storage performance by minimizing the contact resistance between neighboring metal and/or metal oxide nanoparticles using an assembly approach, called ligand-mediated layer-by-layer assembly. This approach can convert the insulating paper to the highly porous metallic paper with large surface areas that can function as current collectors and nanoparticle reservoirs for supercapacitor electrodes. Moreover, we demonstrate that the alternating structure design of the metal and pseudocapacitive nanoparticles on the metallic papers can remarkably increase the areal capacitance and rate capability with a notable decrease in the internal resistance. The maximum power and energy density of the metallic paper-based supercapacitors are estimated to be 15.1 mW cm−2 and 267.3 μWh cm−2, respectively, substantially outperforming the performance of conventional paper or textile-type supercapacitors., With ligand-mediated layer-by-layer assembly between metal nanoparticles and small organic molecules, the authors prepare metallic paper electrodes for supercapacitors with high power and energy densities. This approach could be extended to various electrodes for portable/wearable electronics.

We investigated properties involved in the enhancement in electrocatalytic carbon dioxide (CO2) reduction to carbon monoxide (CO) in electrochemically treated Ag surfaces with surface sensitive analysis methods such as Auger spectroscopy, atomic force microscopy (AFM) coupled with Kelvin probe force microscopy (KPFM) techniques, and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. The absence of Ag M4,5VV Auger signals for the electrochemically treated Ag indicate the presence of localized surface oxygen (O) which survives on the best performing Ag electrocatalysts even in the reductive environment of the CO2 reduction reaction. Higher work functions were located at the nanostructure boundaries observed by KPFM/AFM implying the higher surface O concentrations in these regions. Furthermore, NEXAFS measured the selective prominence of π * states over σ * in the active Ag surfaces which suggests stronger interaction with intermediates of CO2 reduction while minimizing the –OH interaction contributing to increase CO2 reduction activity and selectivity. These results provide direction in engineering surfaces for efficient electrochemical CO2 conversion.

SnO2 Free-standing anodes are regarded as a potential negative electrode for high energy lithium ion batteries (LIBs). However, they suffer from poor rate capability and reversibility because of very low electric conductivity of SnO2. In this study, in order to endow electrical conductivity to the surface of SnO2 particles, a novel and facile method using a plasma are employed to dope nitrogen into the lattice of SnO2. The SnO2 free-standing anode was fabricated by carbonizing an electro-spun fiber sheet followed by depositing SnO2 particles on the surface of carbon nanofibers (CNF) comprising the sheet through a hydrothermal process. The best N-doped SnO2 anode obtained under an optimized condition exhibits a 23 times higher specific capacity of 767 mAh g−1 than that of a pristine SnO2 anode (

Resistive switching behavior-based memory devices are considered promising candidates for next-generation data storage because of their simple structure configuration, low power consumption, and rapid operating speed. Here, the resistive switching nonvolatile memory properties of Fe 2 O 3 nanocomposite (NC) films prepared from the thermal calcination of layer-by-layer (LbL) assembled ferritin multilayers were successfully investigated. For this study, negatively charged ferritin nanoparticles were alternately deposited onto the Pt-coated Si substrate with positively charged poly(allylamine hydrochloride) (PAH) by solution-based electrostatic LbL assembly, and the formed multilayers were thermally calcinated to obtain a homogeneous transition metal oxide NC film through the elimination of organic components, including the protein shell of ferritin. The formed memory device exhibits a stable ON/OFF current ratio of approximately 10 3 , with nanosecond switching times under an applied external bias. In addition, these reversible switching properties were kept stable during the repeated cycling tests of above 200 cycles and a test period of approximately 10 5 s under atmosphere. These solution-based approaches can provide a basis for large-area inorganic nanoparticle-based electric devices through the design of bio-nanomaterials at the molecular level.

We introduce high-performance ultrathin electrochemical electrodes based on multi-stacking of high-energy multiwall carbon nanotube (MWCNT) hybrids and conductive MWCNTs. The MWCNT hybrids coated with oleic acid-stabilized pseudocapacitive nanoparticles (i.e., OA-PC–MWCNTs) were assembled via a sequential covalent-bonded layer-by-layer (LbL) approach with amine-functionalized MWCNTs (NH2–MWCNT) in organic media, generating a highly porous structure and allowing for precise nanoscale control of the electrode thickness. The resultant NH2–MWCNT/OA-PC–MWCNT multilayer electrodes exhibited a high energy capacity and remarkable operational stability, considerably higher than the capacity and stability of conventional blended nanocomposite or electrostatic LbL-assembled electrodes. The volumetric capacitances of the (NH2–MWCNT/OA–Fe3O4–MWCNT)20 and (NH2–MWCNT/OA–MnO–MWCNT)20 were approximately 394 ± 10, and 674 ± 13 F cm−3 at 1 A cm−3, respectively. Additionally, these electrodes maintained their high volumetric capacitances without loss of initial capacitance even after 10 000 cycles; this cycling stability stemmed from the formation of chemically stable covalent bonds between the MWCNT hybrids and NH2–MWCNTs and between the PC NPs and NH2–MWCNTs. Given that a variety of PC NPs can be used to prepare MWCNT hybrids and that this approach can be further expanded to nanocomposite films including LbL-assembled multilayers, our approach may provide a promising platform for designing electrodes for use as thin film-type energy storage devices.

Electrical communication between an enzyme and an electrode is one of the most important factors in determining the performance of biofuel cells. Here, we introduce a glucose oxidase-coated metallic cotton fiber-based hybrid biofuel cell with efficient electrical communication between the anodic enzyme and the conductive support. Gold nanoparticles are layer-by-layer assembled with small organic linkers onto cotton fibers to form metallic cotton fibers with extremely high conductivity (>2.1×104 S cm−1), and are used as an enzyme-free cathode as well as a conductive support for the enzymatic anode. For preparation of the anode, the glucose oxidase is sequentially layer-by-layer-assembled with the same linkers onto the metallic cotton fibers. The resulting biofuel cells exhibit a remarkable power density of 3.7 mW cm−2, significantly outperforming conventional biofuel cells. Our strategy to promote charge transfer through electrodes can provide an important tool to improve the performance of biofuel cells., Biofuel cells offer biocompatibility and operation at mild conditions, but application is limited by relatively low output power. Here the authors use layer-by-layer assembly for glucose oxidase-coated metallic cotton fibers for use as electrodes in a hybrid biofuel cell to achieve high output power.

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. Refereed/Peer-reviewed

New highly birefringent reactive liquid crystal materials based on the 2-methylhydroquinone core were designed and synthesised. Rod-type liquid crystal compounds bearing photo-crosslinkable reactive group of acryloyl, methacryloyl, cinnamoyl, furylacryloyl group were synthesised by introducing acetylene groups via Sonogashira coupling to obtain high birefringence, and lateral groups such as fluoro and methyl to adjust the temperature of the liquid crystal phase. The synthesised compounds were characterised using nuclear magnetic resonance spectroscopy, mass spectrometry and elemental analysis. In addition, their thermal behaviour was investigated using differential scanning calorimetry and polarised optical microscopy. After aligning the synthesised compounds, liquid crystal films were prepared by photo-irradiation. Photo-elastic modulator results showed that the obtained liquid crystal films had high birefringence (Δn) values of 0.32–0.40.

We introduce a general and versatile methodology that allows a facile incorporation of the functional components with completely different chemistry of hydrophilic/hydrophobic properties within nanocomposite films, and furthermore combine a number of the distinctive advantages of traditional electrostatic layer-by-layer (LbL) assembly in aqueous media and covalent LbL assembly in nonpolar media. Our approach, amphiphilic LbL assembly, is based on the high affinity between sulfonic (or phosphonic) acid-functionalized materials in aqueous media and hydrophobic metal oxide (or metal) NPs stabilized by oleic acid (OA) in nonpolar solvent. For demonstrating the effectiveness of our approach, we show that amphiphilic LbL assembly can be easily applied to the preparation of functional colloid materials allowing the reversible phase transfer between aqueous and nonpolar media, and supercapacitor electrodes with high volumetric capacitance (280 F·cm(-3) at 10 mV·s(-1)) using reduced graphene oxide with sulfonic acid moieties and well-defined OA-Fe3O4 NPs.

We introduce a unique and facile strategy for the preparation of solvent-free nanocomposite colloidal fluids that allows accurate control over the integration of functionalities as well as the composition and dimensions of the nanocomposite structure. For the preparation of colloidal fluids with highly integrated functionalities, oleic acid (OA)-stabilized magnetic nanoparticles (i.e., OA-Fe3O4 NPs) and CdSe@ZnS quantum dots (QDs) were first synthesized in nonpolar solvent. In this case, OA-QDs dispersed in toluene were successively phase transferred to thiol-functionalized imidazolium-type ionic liquid (IL-SH) media with rheological and ionic conduction properties. After the functional NPs were synthesized, amine-functionalized dendrimers and OA-Fe3O4 NPs were alternately deposited onto silica colloids (i.e., SiO2/(dendrimer/OA-Fe3O4)n) using a ligand-exchange-induced LbL-assembly in organic media. Electrostatic LbL-assembled (anionic polyelectrolyte (PE)/cationic IL-SH-QD)n multilayers were then sequent...

O rganic fi eld-effect transistor (OFET) memory devices made using highly stable iron-storage protein nanoparticle (NP) multilayers and pentacene semiconductor materials are introduced. These transistor memory devices have nonvolatile memory properties that cause reversible shifts in the threshold voltage ( V th ) as a result of charge trapping and detrapping in the protein NP ( i.e., the ferritin NP with a ferrihydrite phosphate core) gate dielectric layers rather than the metallic NP layers employed in conventional OFET memory devices. The protein NP-based OFET memory devices exhibit good programmable memory properties, namely, large memory window Δ V th (greater than 20 V), a fast switching speed (10 μ s), high ON/OFF current ratio (above 10 4 ), and good electrical reliability. The memory performance of the devices is signifi cantly enhanced by molecular-level manipulation of the protein NP layers, and various biomaterials with heme Fe III /Fe II redox couples similar to a ferrihydrite phosphate core are also employed as charge storage dielectrics. Furthermore, when these protein NP multilayers are deposited onto poly(ethylene naphthalate) substrates coated with an indium tin oxide gate electrode and a 50-nm-thick high-k Al 2 O 3 gate dielectric layer, the approach is effectively extended to flprotein transistor memory devices that have good electrical performance within a range of low operating voltages ( < 10 V) and reliable mechanical bending stability.

We report the successful multifunctional colloids that enable reversible phase transfer between organic and aqueous phases via layer-by-layer (LbL) assembly. These colloids exhibited a high level of dispersion stability in a variety of solvents ranging from nonpolar to aqueous media, based on the type of outermost layer adsorbed onto the colloids. Hydrophobic nanoparticles (NPs) synthesized using carboxylic acid or ammonium moiety-based ligands (i.e., oleic acid or tetraoctylammonium) in a nonpolar solvent (toluene, hexane, or chloroform) were directly deposited onto dendrimer-coated SiO2 colloids via ligand exchange between the hydrophobic ligands and the amine-functionalized dendrimers in the same organic solvent. Additionally, these hydrophobic NPs were adsorbed onto the colloids forming the densely packed layer structure that could not be easily achieved by conventional electrostatic LbL assembly. The subsequent adsorption of amine-functionalized dendrimers onto hydrophobic NP-coated colloids led to w...

We herein report on the nonvolatile memory properties of iron phthalocyanine multilayers prepared using an electrostatic layer-by-layer assembly method. Cationic poly(allylamine hydrochloride) (PAH) and anionic iron(III) phthalocyanine-4, 4,′ 4″, 4′″-tetrasulfonic acid (Fe-TsPc) were alternately deposited onto quartz glass, indium tin oxide (ITO), or platinum-coated silicon substrates via electrostatic interactions. The electrochemical response of the PAH/Fe-TsPc, which was obtained from cyclic voltammograms (CV) in solution, indicated that redox reactions occurred at the phthalocyanine unit and at the metallic center. It was found that these redox reactions of the PAH/Fe-TsPc multilayer films in solution could be extended to resistive switching nonvolatile memory based on a charge trap/release mechanism in air. The PAH/Fe-TsPc multilayers sandwiched between the bottom (platinum) and top (Ag or tungsten) electrodes exhibited the characteristics of a resistive switching memory at a relatively low operating...

From graphene oxide wrapped iron oxide particles with etching/reduction process, high-performance anode and cathode materials of lithium-ion hybrid supercapacitors are obtained in the same process with different etching conditions, which consist of partially etched crumpled graphene (CG) wrapped spiky iron oxide particles (CG@SF) for a battery-type anode, and fully etched CG for a capacitive-type cathode. The CG is formed along the shape of spikily etched particles, resulting in high specific surface area and electrical conductivity, thus the CG-based cathode exhibits remarkable capacitive performance of 210 F g-1 and excellent rate capabilities. The CG@SF can also be ideal anode materials owing to spiky and porous morphology of the particles and tightly attached crumpled graphene onto the spiky particles, which provides structural stability and low contact resistance during repetitive lithiation/delithiation processes. The CG@SF anode shows a particularly high capacitive performance of 1420 mAh g-1 after 270 cycles, continuously increases capacity beyond the 270th cycle, and also maintains a high capacity of 170 mAh g-1 at extremely high speeds of 100 C. The full-cell exhibits a higher energy density up to 121 Wh kg-1 and maintains high energy density of 60.1 Wh kg-1 at 18.0 kW kg-1 . This system could thus be a practical energy storage system to fill the gap between batteries and supercapacitors.

We introduce an innovative and robust method for the preparation of nanocomposite multilayers, which allows accurate control over the placement of functional groups as well as the composition and dimensions of individual layers/internal structure. By employing the photocross-linkable polystyrene (PS-N(3), M(n) = 28.0 kg/mol) with 10 wt % azide groups (-N(3)) for host polymer and/or the PS-N(3)-SH (M(n) = 6.5 kg/mol) with azide and thiol (-SH) groups for capping ligands of inorganic nanoparticles, nanocomposite multilayers were prepared by an efficient photocross-linking layer-by-layer process, without perturbing underlying layers and nanostructures. The thickness of individual layers could be controlled from a few to hundreds of nanometers producing highly ordered internal structure, and the resulting nanocomposite multilayers, consisting of polymer and inorganic nanoparticles (CdSe@ZnS, Au, and Pt), exhibit a variety of interesting physical properties. These include prolonged photoluminescent durability, facile color tuning, and the ability to prepare functional free-standing films that can have the one-dimensional photonic band gap and furthermore be patterned by photolithography. This robust and tailored method opens a new route for the design of functional film devices based on nanocomposite multilayers.

We demonstrate that the nanoscopic block copolymer patterns on GaN can enhance light extraction efficiency of GaN-based light emitting diodes. Nanoporous patterns were fabricated on a bare GaN substrate via self-assembly of poly(styrene-b-methyl methacrylate) block copolymers from which PMMA microdomains were selectively removed later on. A bare GaN surface was treated with a photo-crosslinkable thin layer of poly(styrene-r-methyl methacrylate) random copolymers to tune the cylindrical microdomain orientations. The nanoporous block copolymer thin film was controlled to be thicker than its typical repeat period in bulk by incorporating PMMA homopolymer into block copolymer. Consequently, the light extraction efficiency in photoluminescence spectra could be tuned with the thickness of nanopatterned thin film on GaN.

Two different kinds of organic polyelectrolyte (PE)/inorganic silicate nanolaminates carrying dissimilar interfacial adhesion between the organic and the inorganic layers were prepared using the layer-by-layer self-assembly. To investigate the mechanical behavior of the prepared hybrid films, apparent modulus (E′), hardness (H), and crack length were measured by depth-sensing nanoindentation as well as a microVickers experiment. The fracture toughness of the hybrid films was then calculated based on the measured mechanical values. In the case of forming strong interfacial adhesion between the organic and the inorganic layers (A series), the fracture toughness and the crack resistance of hybrid multilayer films were significantly improved as a result of the redistribution of stress concentration and the dissipation of fracture energy by the plasticity of organic PE layers. On the other hand, samples with relatively low interfacial adhesion between the organic and the inorganic layers (T series) had little ...

We examine the interactions between gold nanoparticles stabilized by the 4-(dimethylamino)pyridine (DMAP−AuNP) and various polyelectrolytes (PEs), both in solution and in layer-by-layer (LbL) assembled multilayer films. UV−vis spectrophotometry studies showed that the plasmon absorption band of the DMAP−AuNP in solution red-shifts and broadens in the presence of poly(sodium 4-styrenesulfonate) (PSS), poly(allylamine hydrochloride) (PAH), or poly(ethyleneimine) (PEI). This suggests that the polyanion PSS electrostatically associates with the nanoparticles, while PAH and PEI bond through the amine functionalities, despite having the same charge as the nanoparticles. In contrast, the addition of poly(diallyldimethylammonium chloride) (PDADMAC) to a DMAP−AuNP dispersion has no influence on either the peak position or shape of the absorption spectrum of the nanoparticles, indicating no interaction. PE/nanoparticle hybrid films were assembled by a single-step adsorption of the DMAP−AuNP into preassembled LbL PE...

Polyelectrolyte (PE)/gold nanoparticle hybrid films that can be utilized as efficient electrochemical sensors were prepared by infiltrating 4-(dimethylamino)pyridine-stabilized gold nanoparticles (DMAP−AuNP) into PE multilayers preassembled on indium tin oxide (ITO) electrodes. Quartz crystal microgravimetry (QCM) and UV−vis spectroscopy showed that via this infiltration method, composite films with densely packed DMAP−AuNP were obtained. Electrochemical experiments revealed that the presence of gold nanoparticles in the PE multilayers could significantly improve the electron-transfer characteristics of the films, which showed high electrocatalytic activity to the oxidation of nitric oxide (NO). The sensitivity of the composite films for measuring NO could be further tailored by controlling the gold nanoparticle loading in the film.

A new method is introduced to build up organic/organic multilayer films composed of cationic poly(allylamine hydrochloride) (PAH) and negatively charged poly(sodium 4-styrenesulfonate) (PSS) by using the spinning process. The adsorption process is governed by both the viscous force induced by fast solvent elimination and the electrostatic interaction between oppositely charged species. On the other hand, the centrifugal and air shear forces applied by the spinning process significantly enhance the desorption of weakly bound polyelectrolyte chains and also induce the planarization of the adsorbed polyelectrolyte layer. The film thickness per bilayer adsorbed by the conventional dipping process and the spinning process was found to be about 4 a and 24 a, respectively. The surface of the multilayer films prepared with the spinning process is quite homogeneous and smooth. Electroluminescence (EL) devices composed of alternating poly(p-phenylene vinylene) (PPV) and polyanions films show higher quantum efficiency when prepared by the spin self-assembly (SA) method.

Organic field-effect transistor (OFET) memories have rapidly evolved from low-cost and flexible electronics with relatively low-memory capacities to memory devices that require high-capacity memory such as smart memory cards or solid-state hard drives. Here, we report the high-capacity OFET memories based on the multilayer stacking of densely packed hydrophobic metal NP layers in place of the traditional transistor memory systems based on a single charge trapping layer. We demonstrated that the memory performances of devices could be significantly enhanced by controlling the adsorption isotherm behavior, multilayer stacking structure and hydrophobicity of the metal NPs. For this study, tetraoctylammonium (TOA)-stabilized Au nanoparticles (TOA-Au(NPs)) were consecutively layer-by-layer (LbL) assembled with an amine-functionalized poly(amidoamine) dendrimer (PAD). The formed (PAD/TOA-Au(NP))(n) films were used as a multilayer stacked charge trapping layer at the interface between the tunneling dielectric layer and the SiO2 gate dielectric layer. For a single AuNP layer (i.e. PAD/TOA-Au(NP))1) with a number density of 1.82 × 10(12) cm(-2), the memory window of the OFET memory device was measured to be approximately 97 V. The multilayer stacked OFET memory devices prepared with four Au(NP) layers exhibited excellent programmable memory properties (i.e. a large memory window (ΔV(th)) exceeding 145 V, a fast switching speed (1 μs), a high program/erase (P/E) current ratio (greater than 10(6)) and good electrical reliability) during writing and erasing over a relatively short time scale under an operation voltage of 100 V applied at the gate.

Electrochemical properties of enzymes are of fundamental and practical importance in bio-electrochemical applications. These redox properties, which can cause the reversible changes in the current according to their redox reactions in solution, often depend on the chemical activity of transition metal ions as cofactors within the active sites of enzymes. Here, we demonstrate that the reversible resistance changes in enzyme-based multilayer films can be caused by the externally applied voltage as a result of charge trap/release of haem Feᴵᴵᴵ/Feᴵᴵ redox couples in dry form. It is also demonstrated that the electrically bistable switching properties of redox enzymes can be applied to nonvolatile memory devices requiring low power consumption. For this study, cationic poly(allylamine hydrochloride) (PAH) was alternately layer-by-layer assembled with anionic catalase enzyme onto Pt-coated substrates until the desired number of layers was deposited. A top electrode was deposited onto (PAH/catalase)ₙ multilayer films to complete device fabrication. When an external bias was applied to the devices, a switching phenomenon depending on the voltage polarity (i.e., bipolar switching) was observed at low operating voltages (RESET at 1.8 V and SET voltage at −1.5 V), fast switching speed at the nanosecond level, and an ON/OFF current ratio of ~10². In the case of inserting insulating layers of about 2 nm thickness between adjacent catalase (CAT) layers, these devices exhibited the higher memory performance (ON/OFF current ratio of ~10⁶) and the lower power consumption than those of (PAH/CAT)₁₅ multilayer devices. Refereed/Peer-reviewed

We introduce a novel and versatile approach for the preparation of multilayers, based on catalase-encapsulated gold nanoparticles (CAT-Au(NP)), allowing electrostatic charge reversal and structural transformation through pH adjustment. CAT-Au(NP), which are synthesized directly from CAT stabilizer, can be electrostatically assembled with anionic and cationic PEs as a result of the charge reversal of the catalase stabilizers through pH control. In particular, at pH 5.2, near the pI of catalase, dispersed CAT-Au(NP) are structurally transformed into colloidal or network CAT-Au(NP) nanocomposites. Furthermore, we demonstrate that the layer-by-layer assembled multilayers composed of PEs and CAT-Au(NP) induce an effective electron transfer between CAT and the electrode as well as a high loading of CAT and Au(NP), and resultantly exhibit a highly catalytic activity toward H(2)O(2).

It is demonstrated that notable resistive switching memory properties depending on voltage polarity (i.e. bipolar switching properties) can be obtained from the layer-by-layer (LbL) assembled multilayers based on transition metal oxides and metal nanoparticles. Cationic poly(allylamine hydrochloride) and anionic titania precursor layers were deposited alternately onto Pt-coated Si substrates using an electrostatic LbL assembly process. Anionic Pt nanoparticles (Pt(NP)) with about 5.8 nm diameter size were also inserted within the multilayers using the same interactions mentioned above. These multilayers were converted to Pt(NP)-embedded TiO(2) films by thermal annealing and the films were then coated with a top electrode. When external bias was applied to the devices, bipolar switching properties were observed at low operating voltages showing the high ON/OFF ratio (10(4)) and the stable device performance. These phenomena were caused by the presence of Pt(NP) inserted within TMO films.

Highly stable photoluminescent (PL) nanocomposite multilayers including quantum dots (see picture) were prepared using a nucleophilic substitution reaction. The assembly of functional nanoparticles in a nonpolar solvent can allow selective deposition and induce a hydrophobic surface with a water contact angle above 115°, which significantly enhances the PL durability of nanocomposite films.

Polymer hydrogels are used in diverse biomedical applications including drug delivery and tissue engineering. Among different chemical linkages, the natural and reversible thiol-disulfide interconversion is extensively explored to stabilize hydrogels. The creation of macro-, micro-, and nanoscale disulfide-stabilized hydrogels commonly relies on the use of oxidizing agents that may have a detrimental effect on encapsulated cargo. Herein an oxidization-free approach to create disulfide-stabilized polymer hydrogels via a thiol-disulfide exchange reaction is reported. In particular, thiolated poly(methacrylic acid) is used and the conditions of polymer crosslinking in solution and on colloidal porous and solid microparticles are established. In the latter case, removal of the core particles yields stable, hollow, disulfide-crosslinked hydrogel capsules. Further, a procedure is developed to achieve efficient disulfide crosslinking of multilayered polymer films to obtain stable, liposome-loaded polymer-hydrogel capsules that contain functional enzymatic cargo within the liposomal subcompartments. This approach is envisaged to facilitate the development of biomedical applications of hydrogels, specifically those including fragile cargo.

We introduce a novel and versatile approach for preparing self-assembled nanoporous multilayered films with tunable optical properties. Protonated polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) and anionic polystyrene-block-poly(acrylic acid) (PS-b-PAA) block copolymer micelles (BCM) were used as building blocks for the layer-by-layer assembly of BCM multilayer films. BCM film growth is governed by electrostatic and hydrogen-bonding interactions between the opposite BCMs. Both film porosity and film thickness are dependent upon the charge density of the micelles, with the porosity of the film controlled by the solution pH and the molecular weight (M(w)) of the constituents. PS(7K)-b-P4VP(28K)/PS(2K)-b-PAA(8K) films prepared at pH 4 (for PS(7K)-b-P4VP(28K)) and pH 6 (for PS(2K)-b-PAA(8K)) are highly nanoporous and antireflective. In contrast, PS(7K)-b-P4VP(28K)/PS(2K)-b-PAA(8K) films assembled at pH 4/4 show a relatively dense surface morphology due to the decreased charge density of PS(2K)-b-PAA(8K). Films formed from BCMs with increased PS block and decreased hydrophilic block (P4VP or PAA) size (e.g., PS(36K)-b-P4VP(12K)/PS(16K)-b-PAA(4K) at pH 4/4) were also nanoporous. This is attributed to a decrease in interdigitation between the adjacent corona shells of the low M(w) BCMs, thus creating more void space between the micelles. Multilayer films with antireflective and photochromic properties were obtained by incorporating a water-insoluble photochromic dye (spiropyran) into the hydrophobic PS core of the BCMs assembled in the films. The optical properties of these films can be modulated by UV irradiation to selectively and reversibly control the transmission of light. Light transmission of higher than 99% was observed with accompanying photochromism in the (PS(7K)-b-P4VP(28K)/PS(2K)-b-PAA(8K)) multilayer films assembled at pH 4/6. Our approach highlights the potential to incorporate a range of materials, ranging from conventional hydrophilic materials with specific interactions to hydrophobic compounds, into the assembled BCMs to yield multifunctional nanoporous films.

Polyelectrolyte multilayer thin films were prepared via the alternate deposition of poly(allylamine hydrochloride) (PAH) and a blend of poly(acrylic acid) (PAA) and poly(styrenesulfonate) (PSS). When the pH of the blend solution was 3.5, the presence of PAA in this solution significantly increased the total film thickness. With only 10 wt % PAA in the blend adsorption solution, a large increase in film thickness was observed (92 nm cf. 18 nm). It was also demonstrated that the total amount of PSS adsorbed was enhanced by the presence of PAA in the blend solution, showing that the blend solution composition influenced that of the multilayer films. Thin films prepared with nanoblended layers also showed improved pH stability, because they exhibited reduced film rearrangement upon exposure to acidic conditions (pH = 2.5).

We demonstrated the memory effect of redox proteins in organic field-effect transistor (OFET) flash memory devices. Redox proteins include a heme structure, which has reversible redox reactions. These properties of the proteins could be successfully applied to the flash memory devices, which show a considerable memory window (~11 V) and relatively good endurance properties (~over 100 cycles).

Here we demonstrate the successful preparation of solvent-free inorganic nanoparticle (NP) fluids with high functionalities that allow mass production. The inorganic NPs (Ag, Au, and quantum dots [QDs]) used in this study were directly synthesized using hydrophobic stabilizers such as palmitic acid, oleic acid, or tetraoctylammonium bromide in a nonpolar solvent (chloroform or toluene), and these NPs were directly phase-transferred to solvent-free low molecular weight liquid media (i.e., thiol-containing imidazolium-type ionic liquid). The NP fluids formed at room temperature showed excellent functionalities (i.e., long-term dispersion stability, high electrical conductivity, strong optical energy transfer, and high photoluminescent intensity) without requiring any additional process such as anion exchange or thermal processing. Furthermore, layer-by-layer deposition of QDs stabilized by the ionic liquid induced highly fluorescent properties compared to those of layer-by-layer QD multilayers prepared using conventional ligands such as mercaptoacetic acid or cysteamine, which mainly originated from the high packing density and the relatively high quantum efficiency of ionic liquid-stabilized QDs.

Porous hybrid multilayer films composed of cationic poly(allylamine hydrochloride) (PAH)- and anionic poly(acrylic acid) (PAA)-stabilized gold nanoparticles (AuNPs) (i.e., PAH-AuNPs and PAA-AuNPs) were prepared on indium tin oxide (ITO) electrodes using pH-controlled layer-by-layer (LbL) assembly method with subsequent acid treatment. The exponential growth of AuNP deposition layers was caused by the “in-and-out” diffusion of PAH and PAA chains not bound to AuNPs. Immersion of the films in an acidic solution (pH 2.4) converted the nonporous films to porous films via the disruption of ionic bonds and the rearrangement of free PE chains. In this case, the pH-induced porous films showed high electrochemical activity. Nonporous/dense films were found to prevent direct contact between probe molecules in solution and the catalytic components immobilized on an electrode. Electrodes coated with porous films, however, exhibited higher electrocatalytic activity toward nitric oxide oxidation compared with electrodes coated with nonporous films, despite the same levels of AuNP loading. This work demonstrates that structural transformations via a facile pH treatment can significantly improve electrode sensitivity without the aid of porous supports or additional catalytic components.

We introduce a novel and facile approach to improve the desalination performance of pressure-driven layer-by-layer (LbL) assembled membranes. Electrostatic LbL multilayers composed of weak polyelectrolytes (PEs), e.g., cationic poly(allylamine hydrochloride) (PAH) and anionic poly(acrylic acid) (PAA), were prepared on commercial polysulfone substrates. In order to measure the ion rejection and permeate flux of these membranes, the ionic concentration of the feed solution and operating pressure were fixed at 2000 ppm NaCl and 20 bar, respectively. It was observed that the crosslinked (PAH pH 7.5/PAA pH 3.5)n=10,20 multilayers, which were assembled at the pH conditions allowing a low charge density of the respective PEs, show relatively high ion rejection compared to other multilayers. This result suggests that the optimal structures for desalination membranes should contain a large amount of freely charged groups with densely-packed structures via crosslinking. Finally, the recycling process was employed to further improve the desalination performance. In this case the (PAH pH 7.5/PAA pH 3.5)n=10,20 multilayers exhibited the ion rejection up to 99.8%. This pH-controlled and thermal crosslinking method suggests a new route for the design of well-defined desalination reverse osmosis membranes based on LbL multilayers.

Multilayer thin films of anionic gold nanoparticles (AuNPs) and cationic phosphorus dendrimers were deposited on 3-(diethoxymethyl-silyl)propylamine (3-APDMES)-coated substrates using layer-by-layer (LbL) assembly driven by electrostatic interactions. The growth of Au/dendrimer multilayers composed of AuNPs with diameters of ∼3 nm and ∼16 nm and dendrimer with ∼2 nm diameter was monitored by UV-vis spectroscopy. The relative amounts of AuNPs and dendrimers in the multilayer films were calculated using a quartz crystal microbalance. The Au-containing multilayers have two surface plasmon bands at ∼530 nm and ∼600 nm, where the latter exhibits a red shift upon increasing the areal density of AuNPs as well as increasing the layer number. The localized surface plasmon resonance (LSPR) band of the hybrid films can be tuned by adding NaCl to the dendrimer solution or by removing the organic matrix. These results demonstrate that the near-field coupling between the LSPR bands of neighboring Au layers is responsible for the controlled absorption behavior. Au mesoporous films after removing dendrimers show LSPR sensing properties for alcohols with different refractive indices in the range 1.33–1.41. A linear relationship was obtained between the LSPR peak wavelength and the refractive index of the surrounding medium.