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Research on the chiral magneto-optical properties of inorganic nanomaterials has enabled novel applications in advanced optical and electronic devices. However, the corresponding chiral magneto-optical responses have only been studied under strong magnetic fields of ≥1 T, which limits the wider application of these novel materials. In this paper, we report on the enhanced chiral magneto-optical activity of supra-assembled Fe3O4 magnetite nanoparticles in the visible range at weak magnetic fields of 1.5 mT. The spherical supra-assembled particles with a diameter of ∼90 nm prepared by solvothermal synthesis had single-crystal-like structures, which resulted from the oriented attachment of nanograins. They exhibited superparamagnetic behavior even with a relatively large supraparticle diameter that exceeded the size limit for superparamagnetism. This can be attributed to the small size of nanograins with a diameter of ∼12 nm that constitute the suprastructured particles. Magnetic circular dichroism (MCD) measurements at magnetic fields of 1.5 mT showed distinct chiral magneto-optical activity from charge transfer transitions of magnetite in the visible range. For the supraparticles with lower crystallinity, the MCD peaks in the 250-550 nm range assigned as the ligand-to-metal charge transfer (LMCT) and the inter-sublattice charge transfer (ISCT) show increased intensities in comparison to those with higher crystallinity samples. On the contrary, the higher crystallinity sample shows higher MCD intensities near 600-700 nm for the intervalence charge transfer (IVCT) transition. The differences in MCD responses can be attributed to the crystallinity determined by the reaction time, lattice distortion near grain boundaries of the constituent nanocrystals, and dipolar interactions in the supra-assembled structures.

Chiral-structured nanoscale materials exhibit chiroptical properties with preferential absorptions of circularly polarized light. The distinctive optical responses of chiral materials have great potential for advanced optical and biomedical applications. However, the fabrication of three-dimensional structures with mirrored nanoscale geometry is still challenging. This study introduces chiral plasmonic nanopatterns in wavy shapes based on the unidirectional alignment of block copolymer thin films and their tilted transfer, combined with buckling processes. The cylindrical nanodomains of polystyrene-iblock/i-poly(2-vinylpyridine) thin films were unidirectionally aligned over a large area by the shear-rolling process. The aligned block copolymer thin films were transferred onto uniaxially prestrained polydimethylsiloxane films at certain angles relative to the stretching directions. The strain was then released to induce buckling. The aligned nanopatterns across the axis of the formed microwrinkles were selectively infiltrated with gold ions. After reduction by plasma treatment, chiral plasmonic nanowave patterns were fabricated with the presence of mirror-reflected circular dichroism spectra. This fabrication method does not require any lithography processing or innately chiral biomaterials, which can be advantageous over other conventional fabrication methods for artificial nanoscale chiral materials.

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.

Here, we report that metal nanoparticle (NP)-based paper/textile electrodes with bulk metallic conductivity can be prepared via organic linker-modulated ligand exchange reaction and in situ room-temperature metallic fusion without additional chemical or thermal treatments. For this study, amine-functionalized molecule linkers instead of bulky polymer linkers were layer-by-layer (LbL)-assembled with tetraoctylammonium bromide (TOABr)-stabilized Au NPs to form Au NP multilayered films. By conversion of the amine groups of the organic molecule linkers from -NH3+ to the -NH2 groups, as well as by a decrease in the size of the organic linkers, the LbL-assembled Au NPs became highly interconnected and fused during LbL deposition, resulting in Au NP multilayers with adjustable conductivity and transport behavior. These phenomena were also predicted by a density functional theory investigation for the model system. Particularly, LbL-assembled films composed of TOABr-Au NPs and diethylenetriamine ( Mw: ∼104) exhibited a remarkable electrical conductivity of 2.2 × 105 S·cm-1, which was higher than the electrical conductivity of the metal NP-based electrodes as well as the carbon material-based electrodes reported to date. Furthermore, based on our approach, a variety of insulating flexible papers and textiles were successfully converted into real metal-like paper and textile electrodes with high flexibility preserving their highly porous structure. This approach can provide a basis for further improving and controlling the electrical properties of flexible electrodes through the control of organic linkers.

Organic-ligand-based solution processes of metal and transition metal oxide (TMO) nanoparticles (NPs) have been widely studied for the preparation of electrode materials with desired electrical and electrochemical properties for various energy devices. However, the ligands adsorbed on NPs have a significant effect on the intrinsic properties of materials, thus influencing the performance of bulk electrodes assembled by NPs for energy devices. To resolve these critical drawbacks, numerous approaches have focused on developing unique surface chemistry that can exchange bulky ligands with small ligands or remove bulky ligands from NPs after NP deposition. In particular, recent studies have reported that the ligand-exchange-induced layer-by-layer (LE-LbL) assembly of NPs enables controlled assembly of NPs with the desired interparticle distance, and interfaces, dramatically improving the electrical/electrochemical performance of electrodes. This emerging approach also demonstrates that efficient surface ligand engineering can exploit the unique electrochemical properties of individual NPs and maximize the electrochemical performance of the resultant NP-assembled electrodes through improved charge transfer efficiency. This report focuses on how LE-LbL assembly can be effectively applied to NP-based energy storage/conversion electrodes. First, the basic principles of the LE-LbL approach are introduced and then recent progress on NP-based energy electrodes prepared via the LE-LbL approach is reviewed.

Nanocomposites with aligned nanofillers have received significant attention because of their excellent mechanical properties. However, because of the difficulty in identifying interfacial interactions in mechanical responses, the anisotropic dynamic mechanical properties of aligned nanocomposites, especially those with high reinforcement contents, are not fully understood. In this study, aligned aramid nanofiber/poly(vinyl alcohol) (ANF/PVA) nanocomposites with a nanofiller volume fraction of 48% are fabricated by using the swelling-assisted stretching method. This method enabled high degree of alignment of the ANF nanofibers with a sheath of PVA matrix. Enhancement of mechanical strength and stiffness is attributed to improvements of interfacial interactions between aligned ANFs and PVA via effective stress transfer. The damping properties are varied by activation of different dissipation modes, such as the stick–slip and reversible matrix-tearing at the interfaces, that are dependent to the loading angle relative to the nanofiber alignment direction. Resultant viscoelastic properties evaluated by the weight-adjusted viscoelastic figure of merits, the combination of stiffness and damping properties, exceed the conventional limit line up to three folds in magnitude. Deepening the understanding of anisotropic dynamic mechanical responses is required for designing aligned nanocomposite materials for mechanical and electronic applications.

We demonstrate a direct-write patternable water-based poly (3,4-ethylenedioxythiophene): poly (styrene sulfonate) (PEDOT:PSS) composite ink which is capable of providing highly stretchable and washing-resistant electrodes on a fabric substrate for electronic textile applications. An aqueous composite ink consisting of PEDOT:PSS, graphene oxide nanosheets and anionic polyurethane does readily not permeated into hygroscopic fabric, which facilitate direct drawing of fine PEDOT electrode on the fabric without undesired blur effect. This limited permeation of aqueous PEDOT composite ink on the hygroscopic fabric is mainly originated from the intermolecular interactions of anionic polyurethane including hydrogen bonding with water molecules, and charge balancing interactions with PEDOT chains. Furthermore, addition of the graphene oxide nanosheets contributes to enhance the electrical conductivity of the composite by improving crystallization of PEDOT molecules. The PEDOT composite film shows unique structure of the PEDOT nanofibril network embedded by the polyurethane matrix, which resulted in an enough electrical pathway for charge carriers even though only 2.9 wt% of PEDOT:PSS existed in the composite film. The PEDOT composite film exhibited electrical conductivity of 4.6 S/cm, extremely high stretchability of 375% rupture strain, and high durability for repeated washing process with strong bleaching agent. Light emitting diode incorporated on the stretchable spandex with interconnects of the PEDOT composite pattern showed that LED light intensity was almost maintained even with stretching of PEDOT interconnects to 290%.

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.

We introduce a layer-by-layer (LbL) assembly-induced triboelectric nanogenerator (TENG) with a high and stable electric output under a wide range of humidity conditions. In this study, highly porous (cationic poly(allylamine hydrochloride) (PAH)/anionic poly(acrylic acid) (PAA))n multilayer films were prepared via a pH-controlled electrostatic LbL assembly with a subsequent acid treatment and were used as a mold for the triboelectric poly(dimethylsiloxane) (PDMS) replica. The electrical output of the TENGs composed of a protuberant PDMS plate and Al electrodes significantly increased based on the evolution of the nano-/micro-structured PDMS bumps. Particularly, the protuberant PDMS film molded from the porous (1.5 mg mL−1 PAH/0.5 mg mL−1 PAA)20 multilayers displayed a high open-circuit voltage output of 242 V and a short-circuit current density of 16.2 μA cm−2 under a compressive force of 90 N in a relative humidity (RH) of 20%. When this hierarchical PDMS surface was additionally modified by fluorine self-assembled monolayer, the voltage output and current density of the resultant TENG at the same experimental conditions were increased up to approximately 288 V and 17 μA cm−2, respectively, exhibiting a remarkably high humidity-resistant electrical performance (16% loss of the initial voltage at 80% RH).

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.

Synthesis of various earth-abundant electroactive materials in gram-scale via simple methods with excellent efficiency can effectively reduce the cost. In this context, we have demonstrated a gram-scale synthesis of α-Fe2O3@rGO core@shell nanocubes via a direct solution route. By the concept of charge-charge interactions, we have successfully wrapped the reduced graphene oxide (rGO) over the surface of α-Fe2O3 nanocubes resulting in the formation of α-Fe2O3@rGO core@shell nanocubes in a gram-scale. The synthesized α-Fe2O3@rGO core@shell nanocubes were characterized by a group of analytical methods and finally explored as an effective anode material for sodium-ion batteries (SIBs). The α-Fe2O3@rGO-10 wt% core@shell nanocubes sample displays an exceptional specific capacity of 970.2 mAh g−1 at 0.1 C-rate with a better rate capability of 77.8 mAh g−1 at 5.0 C-rate. Moreover, the α-Fe2O3@rGO-10 wt% sample also demonstrates a better specific capacity of about 586.9 mAh g−1 after 100 cycles at 0.1 C-rate. The current approach can enable the synthesis of various electroactive materials on a gram-scale using a cost-effective strategy with better electrochemical performance for practical energy storage devices.

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.

We report the instantaneous pulsed-light cross-linking of polymer gate dielectrics on a flexible substrate by using intensely pulsed white light (IPWL) irradiation. Irradiation with IPWL for only 1.8 s of a poly(4-vinylphenol) (PVP) thin film with the cross-linking agent poly(melamine-co-formaldehyde) (PMF) deposited on a plastic substrate was found to yield fully cross-linked PVP films. It was confirmed that the IPWL-cross-linked PVP films have smooth pinhole-free surfaces and exhibit a low leakage current density, organic solvent resistance, and good compatibility with organic semiconductor, and that they can be used as replacements for typical PVP dielectrics that are cross-linked with time and energy intensive thermal heating processes. The synchronization of the IPWL irradiation with substrate transfer was found to enable the preparation of cross-linked PVP films on large area substrates with a highly uniform capacitance. Flexible OTFT based on IPWL-cross-linked PVP dielectrics were found to exhibit good electrical performance that is comparable to that of devices with thermally cross-linked PVP dielectric, as well as excellent deformation stability even at a bending radius of 3 mm.

One of the most critical issues in electrochromic (EC) films based on transition metal oxides such as tungsten oxides (WOx) is their poor charge transfer property, which is closely related to EC performance. Herein, high-performance EC films with enhanced charge transport are prepared using small-molecule linkers and transparent/conductive nanoparticles (NPs). In this work, oleylamine (OAm)-stabilized WO2.72 nanorods (NRs) and OAm-stabilized indium tin oxide (ITO) NPs are layer-by-layer (LbL)-assembled with small-molecule linkers (tris(2-aminoethyl)amine, TREN) using a ligand-exchange reaction between bulky/insulating OAm ligands and TREN molecules. In this case, there is only one TREN layer between neighboring inorganic components (WO2.72 NRs and/or ITO NPs), resulting in a dramatic decrease in the separation distance. This minimized separation distance as well as the periodic insertion of transparent/conductive ITO NPs can significantly reduce the charge transfer resistance within WO2.72 NR-based EC films, which remarkably improves their EC performance. Compared to EC films without ITO NPs, the formed EC films with ITO NPs exhibit faster switching responses (4.1 times in coloration time and 3.5 times in bleaching time) and a maximum optical modulation of approximately 55.8%. These results suggest that electrochemical performance, including EC performance, can be significantly improved through structural/interfacial designing of nanocomposites.

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 (

Despite considerable interest in textile-based battery electrodes with large surface areas and mechanical flexibility, issues have restricted further advances in the energy performance of textile electrodes. These issues include the ineffective incorporation of conductive and/or active components into textile frameworks, the poor charge transfer between energy materials, and the formation of numerous unstable interfaces within textile electrodes. Herein, we introduce an aluminum textile-based lithium-ion battery cathode with remarkable areal capacity, high rate performance, and good cycling stability. Ligand exchange reaction-induced layer-by-layer (LbL) assembly of metal nanoparticles and small molecule linkers, with subsequent metal electroplating, perfectly converted polyester textiles to 3D-porous aluminum textiles that can be used as current collectors and high-energy reservoirs. The consecutive LbL assembly of high-energy LiFePO4 and conductive indium tin oxide nanoparticles onto the aluminum textiles using small organic linkers significantly increased the areal capacity and cycling stability (at least 580 cycles) of the resultant cathode, allowing facile charge transfer within the textile electrodes. Furthermore, the areal capacity of these textile electrodes increased from 1.07 to 3.28 mA h cm−2, with an increase in the folding number from 0 to 2.

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.

Current energy production habits deplete fossil fuels and accumulate atmospheric CO 2 , which contribute to the global climate change. Electrochemical fuel production via CO 2 reduction reaction is an idealistic yet an achievable process that mitigates CO 2 emissions and simultaneously satisfies energy demands. Here, the enhancement of CO 2 reduction activity and stability on size-controlled particulate Ag electrocatalysts derived from a simple, one-step cyclic voltammetry (CV) process by changing scan rates (1–200 mV/s) was demonstrated. Interestingly, larger nanoparticles prepared by slower scan rates (1–5 mV/s) have exhibited the most degree of enhancement for CO 2 reduction to CO product. Compared to untreated Ag foil, nanostructured Ag electrode has shown an anodic shift of approximately 200 mV in the onset potential of CO partial current density ( j CO ), 160 mV reduction of overpotential at j CO = 10 mA/cm 2 , and increased Faradaic efficiency (F.E.) for CO production especially at lower biased potentials (−0.89 to −1.19 V vs. RHE). Stability tests have demonstrated a drastic improvement in maintaining CO F.E. X-ray photoelectron spectroscopy suggests that the enhancement is associated with stable oxygen species incorporated on the nanoparticle Ag surfaces during the CV fabrication process.

We introduce high-performance ultrathin supercapacitor electrodes obtained through the direct covalent-bonding layer-by-layer (LbL) assembly (or ligand-exchange LbL assembly) of amine-functionalized multiwalled carbon nanotubes (CNTs) and transition metal oxide nanoparticles (TMO NPs). The main characteristic of our approach is that the internal interfacial resistance of the electrodes can be minimized through the direct covalent-bonding adsorption of densely packed, high-quality TMO NPs onto CNTs without the aid of nonactive binders or insulating NP ligands, and the resulting volumetric capacitance and cycling stability of the electrodes can be significantly enhanced. For this study, well-defined oleic acid-stabilized pseudocapacitive metal oxide nanoparticles (i.e., OA–Fe 3 O 4 and OA–MnO NPs) prepared in toluene were densely adsorbed onto the CNT layer due to the high affinity between the surface of the TMO NPs and the NH 2 moieties of the CNTs. The (CNT/OA–Fe 3 O 4 NP) 20 multilayer electrode exhibited a high volumetric capacitance of 248±15 F cm −3 (128±7 F g −1 ) at 5 mV s −1 despite the intrinsically low specific capacitance of the Fe 3 O 4 NPs. Additionally, these film electrodes exhibited high performance stability, maintaining 99.2% of their initial capacitance after 1000 cycles. Furthermore, upon the insertion of OA–MnO NPs with high crystallinity and a high theoretical pseudocapacitance value within multilayers instead of OA–Fe 3 O 4 NPs, the formed electrodes (i.e., (CNT/OA–MnO NP) 20 multilayers) exhibited a higher volumetric capacitance of 305±10 F cm −3 (183±5 F g −1 ) (at a scan rate of 5 mV s −1 ) than other conventional ultrathin supercapacitor electrodes, including manganese oxide or iron oxide NPs.

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.

Perovskite nanoparticle-based nanocomposite thin films strictly tailored using unconventional layer-by-layer (LbL) assembly in organic media for piezoelectric nanogenerators (NGs) are demonstrated. By employing sub-20-nm BaTiO3 nanoparticles stabilized by oleic acid ligands (i.e., OA-BTONPs) and carboxylic acid (COOH)-functionalized polymers, such as poly(acrylic acid) (PAA), the resulting OA-BTONP/PAA nanocomposite multilayers are prepared by exploiting the high affinity between the COOH groups of PAA and the BTONPs. The ferroelectric and piezoelectric performance of the (PAA/OA-BTONP)n thin films can be precisely controlled by altering the bilayer number, inserted polymer type, and OA-BTONP size. It is found that the LbL assembly in nonpolar solvent media can effectively increase the quantity of adsorbed OA-BTONPs, resulting in the dramatic enhancement of electric power output from the piezoelectric NGs. Furthermore, very low leakage currents are detected from the (PAA/OA-BTONP)n thin films for obtaining highly reliable power-generating performance of piezoelectric NGs.

We introduce an adsorption mechanism for a layer-by-layer (LbL) assembly (i.e., a ligand addition-induced LbL assembly) and demonstrate that the (polymer/perovskite nanoparticle (NP))n nanocomposite films based on the ligand addition LbL exhibit ferroelectric and resistive switching properties. Oleic acid (OA)-stabilized BaTiO3 NPs (OA-BTO NPs) with a size of approximately 8 nm were LbL-assembled with amine-functionalized dendrimers (NH2-dendrimers) using the high affinity between NH2 moieties and Ti ions. The ferroelectric properties of the (NH2-dendrimer/OA-BTO NP)n multilayers were generated by the Ti disorder in the OA-BTO NP unit cell despite the use of sub-10 nm OA-BTO NPs (i.e., OA-BTO NPs), which are near the critical size for ferroelectric properties. Additionally, the (NH2-dendrimer/OA-BTO NP)n multilayers sandwiched between the bottom (platinum) and top (silver or tungsten) electrodes exhibited a resistive switching memory at a relatively low operating voltage below 2 V with a switching speed of approximately 100 ns and an ON/OFF current ratio of approximately 10(4). Furthermore, the ferroelectric and resistive switching properties could be further improved by controlling the bilayer number (n). We believe that our approach can provide a basis for designing and exploiting multifunctional memory electronics based on a variety of perovskite NPs with ferroelectric properties.

We present multifunctional dendrimer ligands that serve as the charge injection controlling layer as well as the adhesive layer at the interfaces between quantum dots (QDs) and the electron transport layer (ETL) in quantum dot light-emitting diodes (QLEDs). Specifically, we use primary amine-functionalized dendrimer ligands (e.g., a series of poly(amidoamine) dendrimers (PADs, also referred to PAMAM)) that bind to the surface of QDs by replacing the native ligands (oleic acids) and also to the surface of ZnO ETL. PAD ligands control the electron injection rate from ZnO ETL into QDs by altering the electronic energy levels of the surface of ZnO ETL and thereby improve the charge balance within QDs in devices, leading to the enhancement of the device efficiency. As an ultimate achievement, the device efficiency (peak external quantum efficiency) improves by a factor of 3 by replacing the native ligands (3.86%) with PAD ligands (11.36%). In addition, multibranched dendrimer ligands keep the QD emissive layer intact during subsequent solution processing, enabling us to accomplish solution-processed QLEDs. The approach and results in the present study emphasize the importance of controlling the ligands of QDs to enhance QLED performance and also offer simple yet effective chemical mean toward all-solution-processed QLEDs.

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.

There is rising demand for metal or metal oxide nanoparticle (NP)/polymer nanocomposite films with desired functionalities. However, it is difficult to directly combine well-defined NPs synthesized using organic fatty acids in nonpolar media with water-soluble polymers, except polyelectrolytes with specific functional moieties, because they differ in their hydrophobic/hydrophilic properties. We have developed a facile and universal hydrophilic/hydrophobic layer-by-layer (LbL) assembly method that enables perfect nanoblending between water-soluble polymers and hydrophobic NPs, maintaining their specific functionalities. Various hydrophobic NPs stabilized by using oleic acid (OA) (e.g., OA-TiO2, OA-Fe3O4, OA-Ag, and OA-Pt NPs) were directly LbL assembled with various water-soluble polymers (including biomaterials) containing carboxylic acid (–COOH), tertiary ammonium (N+), hydroxyl (–OH), and/or ether (–O–) groups. This adsorption behavior is based on the affinities between water-soluble polymers with multidentate binding sites and the surfaces of metal or metal oxide NPs stabilized by OA ligands. Our approach can be used to fabricate unipolar switching nonvolatile memory devices with ON/OFF current ratios greater than ∼1010 and good memory stability, despite the use of water-soluble polymers.

This study simulated the performance of Cu-cored solder joints in microelectronic components subjected to the extreme thermal cycling conditions often encountered in the automobile industry by comparing the thermal cycling behavior of Cu-cored solder joints containing two different coating layers of Sn–3.0Ag and Sn–1.0In with that of a baseline Sn–3.0Ag–0.5Cu solder joint under a severe temperature cycling range of −55 to +150 °C. Both Cu-cored solder joints can be considered a potential solution to interconnects in microelectronic semiconductor packages used under harsh thermal conditions on account of their greater resistance to thermal stress caused by the severe temperature cycling than the baseline Sn–3.0Ag–0.5Cu solder joint.

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...

We introduce a novel and efficient strategy for producing free-standing functional films via photo-crosslinking and electrostatic layer-by-layer (LbL) assembly, which can allow the buildup of hydrophilic multilayers onto hydrophobic surfaces. Hydrophobic multilayers were deposited on ionic substrates by a photo-crosslinking LbL process using photo-crosslinkable polymers. The photo-crosslinked surface was converted to an anionic surface by excess UV light irradiation. This treatment allowed also the stable adhesion between metal electrode or cationic polyelectrolyte and hydrophobic multilayers. After dissolving the ionic substrates in water, the formed free-standing films exhibited unique functionalities of inserted components within hydrophobic and/or hydrophilic multilayers.

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.

In this work, we fabricated the nanocomposite reverse osmosis (RO) membranes based on the layer-by-layer (LbL) assembly of functionalized multi-walled carbon nanotubes (MWCNTs) and polyelectrolytes (PEs). The CNTs were incorporated to enhance the mechanical strength and the chlorine resistance of multilayered RO membranes. To fabricate the MWCNT-based nanocomposite multilayers, poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) were used as positively and negatively charged PEs, respectively, and the surface of MWCNTs was modified with carboxylic group. During the LbL assembly process, 1 wt % of carboxylated MWCNTs relative to PAA were used and (MWCNT-PAA/PAH)n multilayers membranes with 10, 15, and 20 bilayers were prepared. The existence of MWCNTs in multilayers was confirmed by thermogravimetric analysis (TGA), and we observed the improvement in thermal stability of multilayers after incorporation of MWCNTs. The salt rejection and permeate flux of these membranes were measured by a homem...

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 describe a versatile approach for preparing flash memory devices composed of polyelectrolyte/gold nanoparticle multilayer films. Anionic gold nanoparticles were used as the charge storage elements, and poly(allylamine)/poly(styrenesulfonate) multilayers deposited onto hafnium oxide (HfO2)-coated silicon substrates formed the insulating layers. The top contact was formed by depositing HfO2 and platinum. In this study, we investigated the effect of increasing the number of polyelectrolyte and gold nanoparticle layers on memory performance, including the size of the memory window (the critical voltage difference between the 'programmed' and 'erased' states of the devices) and programming speed. We observed a maximum memory window of about 1.8 V, with a stored electron density of 4.2 x 1012 cm-2 in the gold nanoparticle layers, when the devices consist of three polyelectrolyte/gold nanoparticle layers. The reported approach offers new opportunities to prepare nanostructured polyelectrolyte/gold nanoparticle-based memory devices with tailored performance.

Despite a large number of developments of noble metal (or metal oxide) NP-based catalysts, it has been a great challenge to prepare high-performance recyclable catalysts with integrated functionalities that can be used in various solvent media. Here, we report on layer-by-layer (LbL) assembled multicatalysts with high catalytic performance, showing high dispersion and recycling stability in organic and aqueous media. The remarkable advantages of our approach are as follows. (i) Various metal or metal oxide NPs with desired catalytic performance can be easily incorporated into multilayered shells, forming densely packed arrays that allow one colloid to be used as a multicatalyst with highly integrated and controllable catalytic properties. (ii) Additionally, the dispersion stability of catalytic colloids in a desired solvent can be determined by the type of ultrathin outermost layer coating each colloid. (iii) Lastly, the covalent bonding between inorganic NPs and dendrimers within multilayer shells enhances the recycling stability of multicatalytic colloids. The resulting core-shell colloids including OA-Fe3O4 NPs, TOABr-Pd NPs, and OA-TiO2 NPs exhibited excellent performance in the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) and photocatalysis in aqueous media and in the Sonogashira coupling reaction (99% yield) in organic media. Given that the catalytic properties of recyclable colloids reported to date have entirely depended on the functionality of a single catalytic NP layer deposited onto colloids in selective solvent media, our approach provides a basis for the design and exploitation of high-performance recyclable colloids with integrated multicatalytic properties and high dispersion stability in a variety of solvents.

Here we report the first demonstration for centro-apical self-organization of organic semiconductors in a line-printed organic semiconductor: polymer blend. Key feature of this work is that organic semiconductor molecules were vertically segregated on top of the polymer phase and simultaneously crystallized at the center of the printed line pattern after solvent evaporation without an additive process. The thickness and width of the centro-apically segregated organic semiconductor crystalline stripe in the printed blend pattern were controlled by varying the relative content of the organic semiconductors, printing speed and solution concentrations. The centro-apical self-organization of organic semiconductor molecules in a printed polymer blend may be attributed to the combination of an energetically favorable vertical phase-separation and hydrodynamic fluids inside the droplet during solvent evaporation. Finally, a centro-apically phase-separated bilayer structure of organic semiconductor: polymer blend was successfully demonstrated as a facile method to form the semiconductor and dielectric layer for OFETs in one- step.

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...

Multilayer thin films were constructed on polystyrene colloidal particles by depositing alternating layers of poly(allylamine hydrochloride) (PAH) at pH 7.5 and varying composition blends of poly(acrylic acid) (PAA) and poly(styrenesulfonate) (PSS) at pH 3.5. Following the deposition of each layer, microelectrophoresis experiments showed alternating zeta-potentials, suggesting the formation of multilayered films on the particles. Scanning and transmission electron microscopy were used to examine the surface morphology of the colloidal particles, with homogeneous surface coatings apparent for films deposited from PAA/PSS blend solutions containing up to 90 wt % PAA. The colloidal stability of these particles is greater than those coated with individual PAH and PAA layers. In the case of the blend PAA/PSS = 25:75 wt %, up to 20 layers were assembled without compromising the colloidal stability of the dispersion. The results demonstrate that the deposition of layers from PE blend solutions containing a strong and weak PE can be used as a facile method for controlling the surface properties and hence the colloidal stability of core-shell particles, as well as the thickness and morphology of the coatings. Control of these parameters is important for subsequent processing and application of these particles in controlled delivery, photonics, catalytic, and separation applications.

We investigated the correlation between surface wettability and internal structure of polyelectrolyte (PE)/PE and PE/inorganic multilayer films prepared by the spin self-assembly (SA) method. Spin self-assembled poly(allylamine hydrochloride) (PAH)/poly(sodium 4-styrenesulfonate) (PSS) multilayer films deposited from PE solutions of 10 mM show the distinct oscillation in contact angles with variation of the outermost PE layer, representing the saturated values in contact angles of individual PAH and PSS layers. These contact angles are also well consistent with the angles measured from respective PE layers (i.e., PAH and PSS) of the spin SA (PAH/CdS-COO-) and (CdS-NH3+/PSS) films carrying the flat interface between PE and inorganic CdS nanoparticle layers as confirmed by X-ray reflectivity. Furthermore, based on the contact angle of CdS-NH3+ layer in the ordered (CdS-NH3+/PSS) films, the change in surface wettability of CdS-NH3+ layers of two different spin SA (CdS-NH3+/poly(methacrylic acid) (PMAA)) multilayer films with ordered and disordered internal structure is also investigated. The films with ordered and disordered internal structure were fabricated by the pH adjustment of PMAA. The CdS-NH3+ layer in both CdS-NH3+/PSS and CdS-NH3+/PMAA multilayer films with the ordered internal structure has the contact angle of about 25 +/- 2 degrees irrespective of the PSS or PMAA sublayer. As a result, the same surface wettability of PE or inorganic layers, despite different sublayers, strongly indicates that the spin SA method in optimum condition allows the top surface to be completely covered with a low level ofinterdigitation with a sublayer at each deposition step, and this leads to the conclusion that physical and chemical characteristics of the sublayers have no significant influence on those of the outermost layer.