Macroscopic Films Research Articles

Supramolecular-covalent hybrid polymers for light-activated mechanical actuation.

The development of synthetic structures that mimic mechanical actuation in living matter such as autonomous translation and shape changes remains a grand challenge for materials science. In living systems the integration of supramolecular structures and covalent polymers contributes to the responsive behaviour of membranes, muscles and tendons, among others. Here we describe hybrid light-responsive soft materials composed of peptide amphiphile supramolecular polymers chemically bonded to spiropyran-based networks that expel water in response to visible light. The supramolecular polymers form a reversibly deformable and water-draining skeleton that mechanically reinforces the hybrid and can also be aligned by printing methods. The noncovalent skeleton embedded in the network thus enables faster bending and flattening actuation of objects, as well as longer steps during the light-driven crawling motion of macroscopic films. Our work suggests that hybrid bonding polymers, which integrate supramolecular assemblies and covalent networks, offer strategies for the bottom-up design of soft matter that mimics living organisms.

Self-Assembly Anisotropic Magnetic Nanowire Films Induced by External Magnetic Field.

Self‐assembly generated materials induced by an external magnetic field have attracted considerable interest following the development of nanodevices. However, the fabrication of macroscopic and anisotropic magnetic films at the nanoscale remains a challenge. Here, anisotropic magnetic films are successfully prepared using a solution‐based nanowire assembly strategy under a magnetic field. The assembly process is manipulated by changing the thickness of silica shell coated on the surface of magnetic nanowires. The anisotropic magnetic films show highly anisotropic magnetization under different angles of magnetic field and better magnetization properties than that of disordered magnetic films. The well‐defined nanowire arrays enable magnetization anisotropic property which may be useful in the magnetic energy conversion technologies and biomedical sciences which lie far beyond those achievable with traditional magnetic materials.

COFs Meet Graphene Nanoribbons

2D covalent organic frameworks (COFs) have received considerable attention because of their crystallinity, permanent porosity, and tunability, yet they exhibit low in-plane conductivity. In this issue of Chem, Fischer and co-workers report an approach for growing 2D COF thin films featuring high in-plane conductivity for potential use in organic electronics.

Hybrid modes of a cavity photon coupled with multiple magnons in ferromagnetic nanostructures

By using a microscopic dipole-exchange theory within a Green's function formalism, we study the coupling regime of microwave cavity photons to magnons in nanostructures. The ferromagnetic nanostructures considered are single- and double-layer films, nanowires with rectangular cross-sections, and one-dimensional magnonic crystal arrays of nanowires. In contrast with previous studies of magnon-photon hybrid systems, where either bulklike magnetic samples or macroscopic spheres or films were utilized, a discrete lattice of effective spins is employed to establish a microscopic theory for describing the dependence of the magnon frequencies on the wave vector. We explore hybrid systems derived from the discrete magnons in nanostructures and a selected microwave cavity photon, where strong photon-magnon coupling is expected. This may extend the functionality of the existing hybrid systems or may introduce new functionality. The dependence of the hybridized frequency modes on applied magnetic field are calculated and it is shown that the results are significantly modified compared with those for magnetic bulk materials. In particular, a series of anticrossing phenomena of the cavity mode and multiple magnon modes of ferromagnetic nanostructures are reported. Our findings are important for future applications in integrated hybrid systems for quantum magnonics.

Two-Dimensional Superstructures of Silica Cages.

Despite extensive studies on mesoporous silica since the early 1990s, the synthesis of two-dimensional (2D) silica nanostructures remains challenging. Here, mesoporous silica is synthesized at an interface between two immiscible solvents under conditions leading to the formation of 2D superstructures of silica cages, the thinnest mesoporous silica films synthesized to date. Orientational correlations between cage units increase with increasing layer number controlled via pH, while swelling with oil and mixed surfactants increase micelle size dispersity, leading to complex clathrate type structures in multilayer superstructures. The results suggest that a three-dimensional (3D) crystallographic registry within cage-like superstructures emerges as a result of the concerted 3D co-assembly of the organic and inorganic components. Mesoporous 2D superstructures can be fabricated over macroscopic film dimensions and stacked on top of each other. The realization of previously inaccessible mesoporous silica heterostructures with separation or catalytic properties unachievable via conventional bulk syntheses is envisioned.

Engineering the interface for promoting ionic/electronic transmission of organic flexible supercapacitors with high volumetric energy density

Supercapacitors based on commercialized metallic collectors (such as Cu and Al) possess an innate interface imperfection, causing long ion diffusion pathway and sluggish electron conduction, as well as inferior flexibility. Herein, we explore carbon nanotubes macroscopic films (CMF) as current collectors to build near-integrated electrodes via anchored combination between CMF and commercial active carbon (AC). In addition, our fabricated CMF presents outstanding electrolyte permeation, which shortens the ion diffusion pathway, increases the electron conduction and ameliorates the flexibility. As a result, the supercapacitor based on CMF exhibits prominent electrochemical performance of specific capacitance (48.5 F cm−3 at 0.5 A g−1), rate capability (82.5% from 0.5 to 16 A g−1) and volumetric energy density (104.9 Wh L−1), which higher than those of reported flexible supercapacitors. More importantly, the supercapacitor exhibits remarkable stability under different folding conditions, even in particular circumstances (such as low temperature and negative pressure). Further, the supercapacitors show good energy features in parallels and series. Therefore, it is believed that these supercapacitors based on CMF are promising in the future wearable energy storage devices in different operating environments.

Critical Role of Degree of Polymerization of Cellulose in Super-Strong Nanocellulose Films

Summary Translation of the outstanding mechanical performance of individual nanocellulose to macroscopic nanocellulose films can be achieved by various alignment techniques. However, attention has seldom been paid to the degree of polymerization (DP) of cellulose that plays a pivotal role in increasing the mechanical strength of nanocellulose films. In this work, nanocellulose film with superior tensile strength (1,014.7 ± 69.1 MPa) is presented by a cellulose DP protection strategy. An alkaline sulfite-anthraquinone-methanol pulping is applied to not only rapidly remove most of lignin and hemicellulose from wood blocks, which facilitates the formation of hydrogen bonds among neighboring fiber cell walls in subsequent mechanical pressing, but also to significantly suppress the decomposition of cellulose DP. Such strong nanocellulose film sheds light on unlocking the exceptional mechanical potential of cellulose and has the potential for use in advanced applications traditionally dominated by nonrenewable materials such as plastics, glass, and metals.

Utilization of discarded crop straw to produce cellulose nanofibrils and their assemblies

A tremendous amount of wheat straw (WS) has been generated by wheat crops every year, while only a small percentage is being used in applications, and most get burned on the field, causing a large amount of the exhaust gas that pollutes the environment. Herein, we report on the extraction of cellulose nanofibrils (CNF) from the alkali treated WS by a combination of 2,2,6,6-tetramethylpyperidine-1-oxyl (TEMPO)-oxidation and mechanical disintegration method. The crystalline structures, thermal properties, natural charge of the CNF were examined. The resultant nano-building blocks of the CNF was assembled into macroscopic cellulose materials, i.e., film, aerogel, and filament in this work. Furthermore, the morphologies and microstructues as well as other properties of these three kinds of the CNF assemblies were investigated. The obtained CNF and its assemblies showed a potential application in new materials areas. This work explored a new way to utilize the discarded WS instead of being burned.

The Synthesis of a 2D Ultra-Large Protein Supramolecular Nanofilm by Chemoselective Thiol-Disulfide Exchange and its Emergent Functions.

The design and scalable synthesis of robust 2D biological ultrathin films with a tunable structure and function and the ability to be easily transferred to a range of substrates remain key challenges in chemistry and materials science. Herein, we report the use of the thiol-disulfide exchange reaction in the synthesis of a macroscopic 2D ultrathin proteinaceous film with the potential for large-scale fabrication and on-demand encapsulation/release of functional molecules. The reaction between the Cys6-Cys127 disulfide bond of lysozyme and cysteine is chemo- and site-selective. The partially unfolded lysozyme-cysteine monomers aggregate at the air/water or solid/liquid interface to form an ultra-large 2D nanofilm (900 cm2 ) with about 100 % optical transparency. This material adheres to a wide range of substrates and encapsulates and releases a range of molecules without significantly affecting activity.

The Synthesis of a 2D Ultra‐Large Protein Supramolecular Nanofilm by Chemoselective Thiol–Disulfide Exchange and its Emergent Functions

AbstractThe design and scalable synthesis of robust 2D biological ultrathin films with a tunable structure and function and the ability to be easily transferred to a range of substrates remain key challenges in chemistry and materials science. Herein, we report the use of the thiol–disulfide exchange reaction in the synthesis of a macroscopic 2D ultrathin proteinaceous film with the potential for large‐scale fabrication and on‐demand encapsulation/release of functional molecules. The reaction between the Cys6–Cys127 disulfide bond of lysozyme and cysteine is chemo‐ and site‐selective. The partially unfolded lysozyme–cysteine monomers aggregate at the air/water or solid/liquid interface to form an ultra‐large 2D nanofilm (900 cm2) with about 100 % optical transparency. This material adheres to a wide range of substrates and encapsulates and releases a range of molecules without significantly affecting activity.

Janus MXene nanosheets for macroscopic assemblies

Amphiphilic Janus MXene nanosheets are synthesized for the first time by a one-step transferring method, which can act as promising solid surfactants to stabilize emulsions, and assemble into macroscopic 2D ultrathin MXene films and 3D MXene aerogels.

Macroscopic two-dimensional monolayer films of gold nanoparticles: fabrication strategies, surface engineering and functional applications.

In the last few decades, two-dimensional monolayer films of gold nanoparticles (2D MFGS) have attracted increasing attention in various fields, due to their superior attributes of macroscopic size and accessible fabrication, controllable electromagnetic enhancement, distinctive optical harvesting and electron transport capabilities. This review will focus on the recent progress of 2D monolayer films of gold nanoparticles in construction approaches, surface engineering strategies and functional applications in the optical and electric fields. The research challenges and prospective directions of 2D MFGS are also discussed. This review would promote a better understanding of 2D MFGS and establish a necessary bridge among the multidisciplinary research fields.

Evolution of magnetic anisotropy in cobalt film on nanopatterned silicon substrate studied in situ using MOKE

Evolution of magnetization behaviour of cobalt film on nano patterned silicon (1 0 0) substrate, with film thickness, has been studied. In situ magneto-optical Kerr effect measurements during film deposition allowed us to study genuine thickness dependence of magnetization behaviour, all other parameters like surface topography, deposition conditions remaining invariant. The nanopatterned substrate had a 8 nm thick amorphous silicon nitride surface layer. Thus, induced magnetic anisotropy in the Co film is expected to be of purely topographical origin, excluding any effect of the single crystalline Si (1 0 0) surface on magnetic anisotropy film due to possible epitaxy or surface step-induced anisoropy. In conformity with earlier results, the film induces a uniaxial magnetic anisotropy in the film, with its magnitude decreasing with increasing thickness. A magnetically dead layer of 2.6 nm forms at the interface with the substrate. Analysis of the magnetic layer thickness dependence of anisotropy shows that it has contributions from both, i) exchange energy which is volume dependent and, ii) stray dipolar fields at the surface/interface. This suggests that local magnetization follows only partially the topography of the rippled surface. As expected from energy considerations, for small film thickness, the local magnetization closely follows the surface contour of the ripples making the volume term as the dominant contribution. With increasing film thickness, the local magnetization gradually deviates from the local slope and approaches towards a uniform magnetization along the macroscopic film plane making the surface term as the dominant contribution. Significant deviation of the observed stray dipolar field contribution from the anisotropy energy calculated on the basis of Schlomann’s theory is observed, which can be attributed to several factors like, deviation of surface topography from an ideal sinusoidal wave, breaks of continuity along the ripple direction, topological defects like, pattern dislocations, and small film thicknesses compared to the correlation length of surface corrugations.

Gaseous "nanoprobes" for detecting gas-trapping environments in macroscopic films of vapor-deposited amorphous ice.

Vapor-deposited amorphous ice, traditionally called amorphous solid water (ASW), is one of the most abundant materials in the universe and a prototypical material for studying physical vapor-deposition processes. Its complex nature arises from a strong tendency to form porous structures combined with complicated glass transition, relaxation, and desorption behavior. To gain further insights into the various gas-trapping environments that exist in ASW and hence its morphology, films in the 25-100 μm thickness range were codeposited with small amounts of gaseous "nanoprobes" including argon, methane, helium, and carbon dioxide. Upon heating in the 95-185 K temperature range, three distinct desorption processes are observed which we attribute to the gas desorption out of open cracks above 100 K, from internal voids that collapse due to the glass transition at ∼125 K and finally from fully matrix-isolated gas induced by the irreversible crystallization to stacking disordered ice (ice Isd) at ∼155 K. Nanoscale films of ASW have only displayed the latter desorption process which means that the first two desorption processes arise from the macroscopic dimensions of our ASW films. Baffling the flow of water vapor toward the deposition plate greatly reduces the first desorption feature, and hence the formation of cracks, but it significantly increases the amount of matrix-isolated gas. The complex nature in which ASW can trap gaseous species is thought to be relevant for a range of cosmological processes.

Environmentally stable macroscopic graphene films with specific electrical conductivity exceeding metals

Air stable, lightweight, and electrically conductive carbon-based films are highly desired for flexible electronic devices and products. Graphene film, a macroscopic assembly of individual graphene sheets, holds great potential to replace conventional brittle pyrolytic carbon film due to the excellent electrical transport property and flexibility. However, the electrical conductivity of graphene film is still inferior to metallic conductors, usually unstable in air as doped. We chose metal chloride (MoCl5) as air stable dopant and fabricated doped graphene film with well-controlled intercalation structure. The MoCl5 modified graphene film shows record high electrical conductivity of 1.73 × 107 S m−1, record high mobility of 2190.47 cm2 V−1 s−1, remarkable specific electrical conductivity exceeding benchmark metals (e.g., Au, Ag, Cu), and ultralow temperature coefficient of resistance (1.4 × 10−4 K−1). Importantly, the electrical conductivity and overall structure of MoCl5 intercalated films are exceptional stable in atmospheric environment, enabling wide applications in electronic devices, electromagnetic interference, and energy storage.

Thermal properties of thin films made from MoS2 nanoflakes and probed via statistical optothermal Raman method

A deep understanding of the thermal properties of 2D materials is crucial to their implementation in electronic and optoelectronic devices. In this study, we investigated the macroscopic in-plane thermal conductivity (κ) and thermal interface conductance (g) of large-area (mm2) thin film made from MoS2 nanoflakes via liquid exfoliation and deposited on Si/SiO2 substrate. We found κ and g to be 1.5 W/mK and 0.23 MW/m2K, respectively. These values are much lower than those of single flakes. This difference shows the effects of interconnections between individual flakes on macroscopic thin film parameters. The properties of a Gaussian laser beam and statistical optothermal Raman mapping were used to obtain sample parameters and significantly improve measurement accuracy. This work demonstrates how to address crucial stability issues in light-sensitive materials and can be used to understand heat management in MoS2 and other 2D flake-based thin films.

Rapid roll-to-roll production of graphene films using intensive Joule heating

The development of rapid and scalable techniques for thermally conductive film is useful for the improved function and efficiency of electronic devices. The commercially available carbon film that made from polyimide film by sequential carbonization and graphitization in electrical furnace is usually produced in an intermittent way, which inevitably decreases the manufacturing efficiency and increases energy consumption and production cost. Macroscopic graphene film is considered to be an ideal alternative of traditional carbon film due to its combined merits of high thermal conductivity and flexibility. Here, we report a rapid approach to continuously fabricate graphene film by Joule heating of chemically reduced graphene oxide film integrated with a high-throughput roll-to-roll process. The achieved graphene film holds excellent electrical of 4.2 × 105 S/m and thermal conductivity of 1285 ± 20 W/mK. Moreover, the intensive Joule heating in a roll-to-roll manner is more time-saving, energy-efficient, and cost-effective than traditional heating method by electrical furnace. Such facial processing strategy offers new opportunities for the scaled-up manufacturing of large area graphene film with potential applications in the fields of thermal management, flexible electronics, and wearable devices.

Scanning Electrochemical Cell Microscopy Investigation of Single ZIF-Derived Nanocomposite Particles as Electrocatalysts for Oxygen Evolution in Alkaline Media.

“Single entity” measurements are central for an improved understanding of the function of nanoparticle‐based electrocatalysts without interference arising from mass transfer limitations and local changes of educt concentration or the pH value. We report a scanning electrochemical cell microscopy (SECCM) investigation of zeolitic imidazolate framework (ZIF‐67)‐derived Co−N‐doped C composite particles with respect to the oxygen evolution reaction (OER). Surmounting the surface wetting issues as well as the potential drift through the use of a non‐interfering Os complex as free‐diffusing internal redox potential standard, SECCM could be successfully applied in alkaline media. SECCM mapping reveals activity differences relative to the number of particles in the wetted area of the droplet landing zone. The turnover frequency (TOF) is 0.25 to 1.5 s−1 at potentials between 1.7 and 1.8 V vs. RHE, respectively, based on the number of Co atoms in each particle. Consistent values at locations with varying number of particles demonstrates OER performance devoid of macroscopic film effects.

Nanocomposite Elastomers Composed of Silica Nanoparticles Grafted with a Comb-Shaped Copolymer Brush

Nanocomposites composed of monodisperse silica nanoparticles (SiNPs) modified with an elastic comb-shaped block copolymer brush were produced for the first time. Comb-shaped polymer brushes consisting of glassy poly(methyl methacrylate) branches and a rubbery poly(butyl acrylate) backbone were grafted from 100 nm diameter SiNPs by surface-initiated atom transfer radical polymerization. The comb-shaped polymer brush-grafted SiNPs produced self-standing films with a face-centered cubic ordered lattice structure via solvent-casting. The composite films showed rubber elasticity because of the interparticle rubbery polymer brush boundary phase. The ordered lattice exhibited significant alignment and distortion in response to the macroscopic film strain, and then reproduced the initial ordered lattice after unloading.

Macroscopically Aligned Carbon Nanotubes as a Refractory Platform for Hyperbolic Thermal Emitters

Refractory nanophotonics, or nanophotonics at high temperatures, can revolutionize many applications, including data storage and waste heat recovery. In particular, nanophotonic devices made from hyperbolic materials are promising due to their nearly infinite photonic density of states (PDOS). However, it is challenging to achieve a prominent PDOS in existing refractory hyperbolic materials, especially in a broad spectral range. Here, we demonstrate that macroscopic films and architectures of aligned carbon nanotubes work as excellent refractory hyperbolic materials. We found that aligned carbon nanotubes are thermally stable up to $1600^{\circ}$C and exhibit extreme anisotropy - metallic in one direction and insulating in the other two directions. Such extreme anisotropy makes this system a hyperbolic material with an exceptionally large PDOS over a broadband spectrum range (longer than $4.3\mu$m) in the midinfrared, exhibiting strong resonances in deeply sub-wavelength-sized cavities. We observed polarized, spectrally selective thermal emission from aligned carbon nanotube films as well as indefinite cavities of aligned carbon nanotubes with volume as small as $\sim\lambda^3/700$ operating at $700^{\circ}$C . These experiments suggest that aligned carbon nanotubes possess naturally large PDOS that leads to thermal photon densities enhanced by over two orders of magnitude, making them a promising refractory nanophotonics platform.