Mica Nanosheets Research Articles

Origin of observed narrow bandgap of mica nanosheets

Mica nanosheets possess peculiar feature of narrowed bandgap with the decrease of thickness but a conclusive theoretical understanding of the narrowing mechanisms is still under development. In this report, first-principles calculations were carried out to investigate the electronic band structure of mica nanosheets with the deposition of K2CO3. Bulk mica shows an indirect bandgap of 4.90 eV. Mica nanosheets show similar electronic structures to bulk mica with a gradually increased bandgap of 4.44 eV, 4.52 eV and 4.67 eV for 1-layer, 2-layers and 3-layers nanosheets, respectively, which is attributed to the lattice relaxation. K2CO3 is found to have strong affinity towards mica nanosheets. The K2CO3 deposited mica nanosheets showed an increased bandgap with the increase of thickness, consistent with experimental observations. The calculated bandgap of K2CO3 deposited mica for 2-layers and 3-layers nanosheets are 2.60 eV and 2.75 eV, respectively, which are comparable with the corresponding experimental values of 2.5 eV and 3.0 eV. Our theoretical findings support the experimental evidence of surface contamination of mica by K2CO3, and provide new insight into the structure and properties of 2D mica.

Synergistic effect of barium titanate and insulating fillers on dielectric performance of sandwich-structured PLA composites

The polylactic acid (PLA) based sandwich-structured composites consisted of polydopamine (PDA) coated insulating fillers such as boron nitride (BN) and mica nanosheets dispersed in degradable PLA as the outer layer and PDA coated barium titanate (BT) dispersed in PLA as the middle layer. The sandwich-structure of PLA composites can enhance dielectric and energy storage performance. The energy density of PLA/40PDA@BT/8PDA@BN and PLA/40PDA@BT/8PDA@Mica composites are 2.23 and 1.72 J/cm3 respectively because the increase of energy density reflecting their high-field polarizable ability may be due to the interfacial polarization between fillers and PLA. The energy storage efficiency of PLA/40PDA@BT/8PDA@BN and PLA/40PDA@BT/8PDA@Mica are 40 and 83% respectively because PDA@Mica with the larger size of 3–4 μm as insulated barriers can effectively restrain the leakage currents compared with PDA@BN with the size of 0.8–1.3 μm.

Nanostructured and Advanced Designs from Biomass and Mineral Residues: Multifunctional Biopolymer Hydrogels and Hybrid Films Reinforced with Exfoliated Mica Nanosheets.

Transforming potential waste materials into high-value-added sustainable materials with advanced properties is one of the key targets of the emerging green circular economy. Natural mica (muscovite) is abundant in the mining industry, which is commonly regarded as a byproduct and gangue mineral flowing to waste rock and mine tailings. Similarly, chitin is the second-most abundant biomass resource on Earth after cellulose, extracted as a byproduct from the exoskeleton of crustaceans, fungal mycelia, and mushroom wastes. In this study, exfoliated mica nanosheets were individualized using a mechanochemical process and incorporated into regenerated chitin matrix through an alkali dissolution system (KOH/urea) to result in a multifunctional, hybrid hydrogel, and film design. The hydrogels displayed a hierarchical and open nanoporous structure comprising an enhanced, load-bearing double-cross-linked polymeric chitin network strengthened by mica nanosheets possessing high stiffness after high-temperature curing, while the hybrid films (HFs) exhibited favorable UV-shielding properties, optical transparency, and dielectric properties. These hybrid designs derived from industrial residues pave the way toward sustainable applications for many future purposes, such as wearable devices and tissue engineering/drug delivery.

Double-Layer Nacre-Inspired Polyimide-Mica Nanocomposite Films with Excellent Mechanical Stability for LEO Environmental Conditions.

Owing to their outstanding comprehensive performance, polyimide (PI) composite films are widely used on the external surfaces of spacecraft to protect them from the adverse conditions of low Earth orbit (LEO). However, current PI composite films have inadequate mechanical properties and atomic oxygen (AO) resistance. Herein, this work fabricates a new PI-based nanocomposite film with greatly enhanced mechanical properties and AO resistance by integrating mica nanosheets with PI into a unique double-layer nacre-inspired structure with a much higher density of mica nanosheets in the top layer. In addition, the unique microstructure and the intrinsic properties of mica also impart the nanocomposite film with favorable ultraviolet and high-temperature resistance. The comprehensive performance of this material is superior to those of pure PI, single-layer PI-mica, and previously reported PI-based composite films. Thus, the double-layer nanocomposite film displays great potential as an aerospace material for use in LEO.

Force-Induced Self-Assembly of Supramolecular Modified Mica Nanosheets for Ductile and Heat-Resistant Mica Papers.

Mica is a naturally abundant layered silicate mineral that has higher strength than other layered silicate minerals, but its inherent brittleness limits its application in some fields. In this work, mica was ultrasonically exfoliated into a single-layered nanomaterial after thermal activation, acidification, sodium replacement, and cetyltrimethylammonium bromide (CTAB) intercalation and then modified with ureido-pyrimidinone (UPy)-based PEG chains. Vacuum-assisted self-assembly was used to construct supramolecularly modified single-layered mica into bulk materials, in which the mica nanosheets were stacked into mica paper. The reversible quadruple hydrogen-bonded UPy moieties provided a high binding constant and significantly improved the strength and toughness of the obtained mica paper. These force-induced assembled mica papers showed significantly improved tensile strength and toughness compared with pure mica paper and simultaneously maintained the heat resistance of the mica materials, which may be good candidates for the substrates of flexible sensors working at higher temperatures.

Effects of mica modification with ethylene‐vinyl acetate wax on the water vapor barrier and mechanical properties of poly‐(butylene adipate‐co‐terephthalate) nanocomposite films

AbstractPoly‐(butylene adipate‐co‐terephthalate) (PBAT) is one of the most popular raw materials for degradable plastic films because of its good biodegradability, ductility, and processability. However, the application of this material is limited by its unsatisfactory water vapor barrier property. This study aims to improve the water vapor barrier and mechanical properties of PBAT films by introducing mica modified by ethylene‐vinyl acetate copolymer waxes (EVA‐mica). The EVA‐mica nanosheets showed a more uniform dispersion in the PBAT films than the mica nanosheets. The PBAT/EVA‐mica films containing 2% EVA‐mica demonstrated outstanding crystallinity, water vapor barrier, and mechanical properties compared with the pure PBAT films. Results showed a 20.23% increase in crystallinity, an 80.09% reduction in water vapor permeability, a 26.82% increase in tensile strength, and a 9.10% increase in tear strength. The enhanced water vapor barrier and mechanical properties of the PBAT/EVA‐mica nanocomposite films are favorable for their future application as biodegradable films.

Epidermis microstructure inspired mica-based coatings for smart corrosion protection

Two-dimensional (2D) graphene-like nanomaterials have gained interest in anticorrosion coatings due to their enable to act as physical barriers to aggressive species, yet 2D coatings are not always effective or sustainable. Inspired by the epidermis microstructure, herein we designed a high-performance anticorrosion coating with rapid self-healing ability via integrating the excellent adhesion property of polydopamine (PDA) and superior barrier properties of natural mica nanosheets (MNSs) for the first time. Such the coating comprises a protective hard top layer with MNSs constituents (“sealing” agents) and a bottom hybrid soft polymer multilayer, forming a stratified epidermis microstructure, can realize a complete restoration of coating defects under water owing to their mutual benefit. These MNSs not only can enhance the barrier performance of the coating matrix to retard the diffusion of aggressive species and hamper polymer release into water, but also induce an anisotropic diffusion to promote the self-healing of the polymer chains. The microstructures of the bioinspired coatings were systemically investigated by scanning electron microscopy (SEM) and optical microscopy (OM) measurements. Electrochemical results confirmed the anticorrosion performance of the coatings were significantly improved. This work provides a new insight for the design and fabrication of 2D nanomaterials reinforced high-performance and smart anticorrosion coatings.

Layer etching of mica nanosheets using a focused electron beam

Mica, a cleavable layered material, is a single-crystalline phyllosilicate having unique electronic and mechanical properties such as a wide bandgap and tolerance to strong electric fields and high temperatures, and is applicable to flexible electronics. This paper describes the nanometer-level layer etching of mica nanosheets exfoliated from artificially synthesized phlogopite and affixed on substrates, using a focused electron beam for fine-pattern fabrication of the nanosheets. The dependence of the etching on the irradiation time, beam current, and beam energy is examined. The etching process was analyzed by in situ scanning Auger electron spectroscopy and microscopy. The layer etching of mica nanosheets leads to the micro- and nano-fabrication of mica-based two-dimensional heterodevices.

Evaluation of the discrete thickness of exfoliated artificially synthesized mica nanosheets on silicon substrates: Toward characterization of the tunneling current through the nanosheets

Insulating two-dimensional (2D) materials, as well as conductive materials, should be further exploited for fabrication of nanomaterial devices and extension of their functions. Structural and elemental analyses of 2D materials are fundamental for nanoscale electronic devices. Here, as a 2D insulator, nanosheets of single-crystal layered artificially synthesized pure phlogopite (KMg3AlSi3O10F2) were prepared by mechanical exfoliation from its bulk crystal and then affixed to Si substrates using a polyurethane hand roller. Phlogopite is a member of the cleavable mica family with a band gap energy of ~7 eV. The nanosheets were extended to a few tens of micrometer widths on the substrates. Their discrete thicknesses were determined from several layers to a single layer (1 nm) by atomic force microscopy (AFM), and their chemical components were analyzed by scanning Auger electron spectroscopy/microscopy (SAM). Because the elemental peak intensities from Auger electron spectroscopy of the nanosheets changed with increasing number of layers up to five layers, conventional methods based on SAM are proposed to evaluate their thickness. The current–voltage characteristics of metal–nanosheet–metal contacts with different nanosheet thicknesses were investigated by conductive AFM, and they exhibited strong thickness dependence because of electron tunneling through the nanosheets.

Superior to graphene: super-anticorrosive natural mica nanosheets.

Graphene has been generally considered to be the most ideal anticorrosive material based on its extraordinary impermeability, but tends in practical applications to promote metal corrosion because of its inherently high electrical conductivity. Mica nanosheets (MNSs), in contrast, display excellent electrical insulation properties, as well as excellent temperature stability and chemical durability, and show tremendous potential for protecting metals, and hence are a promising substitute for graphene. To date, however, there have been no reports about MNS-based anticorrosive coatings, since it is much more difficult to exfoliate high-quality MNSs than other layered materials. In this work, high-concentration (4.3 mg ml-1) ultrathin MNS (1-5 layers) dispersions were synthesized based on a facile and efficient hydrothermal exfoliation approach. Epoxy (EP) coatings were filled with the as-obtained MNSs to enhance the anticorrosion performance of the coatings, and their corrosion behaviors were studied systemically through a series of measurements. With the addition of only 0.4 wt% MNSs, the corrosion rate was observed to be reduced 6500 fold, and the coating impedance increased by four orders of magnitude compared with the blank EP coating. We believe that this method opens a novel avenue for developing high-performance anticorrosive coatings to replace graphene materials for metal protection.

Dissipative interaction due to Joule heat through displacement current on mica nanosheets examined by non-contact atomic force microscopy

Dissipative interaction due to Joule heat through displacement current on mica nanosheets examined by non-contact atomic force microscopy

2D Black Mica Nanosheets: Synthesis of Ultrathin Biotite Nanosheets as an Intelligent Theranostic Platform for Combination Cancer Therapy (Adv. Sci. 19/2019)

In article number 1901211, Wei Tao, Omid C. Farokhzad, Xiaobin Zeng, and co-workers provide a novel exfoliation approach combining calcination, n-butyllithium exchange and intercalation, and liquid exfoliating processes for the high-quality synthesis of ultrathin biotite nanosheets. The developed nanosheets can be engineered as an intelligent theranostic platform for cancer combination therapy with unique features. Cover image designed by Xiaoyuan Ji.

Laminated mica nanosheets supported ionic liquid membrane for CO2 separation

Mica has attracted great attention due to its excellent photoelectric property and it is mainly used in the optics and electronics area. High-quality mica nanosheets exfoliated from natural ground mica have been successfully achieved recently. It improves the application potential of mica as well as extending the application field to gas separation as a new two-dimensional (2D) material. Herein, we firstly constructed a mica membrane by regularly stacking mica nanosheets and then immobilized ionic liquid (IL) into its 2D channels to separate CO2 from H2, CH4 and N2. Gas diffusion is changed from Knudsen diffusion in the mica membrane to a solution–diffusion mechanism after inserting IL. The resultant membrane, the mica supported IL membrane (M-SILM), has about 80 GPU for CO2 permeance, and selectivity for CO2/H2, CO2/CH4 and CO2/N2 of 7.7, 28.6 and 87, respectively. It is the first time a mica nanosheet to construct a gas separation membrane has been used. As a cheap raw material with facile treating, mica shows promising potential for gas separation and competitiveness among 2D material supported IL membranes.

Towards high efficient nanodielectrics from linear ferroelectric P(VDF-TrFE-CTFE)-g-PMMA matrix and exfoliated mica nanosheets

Poly(vinylidene fluoride) (PVDF) based polymer/ceramic nanocomposites for high energy density dielectrics have long been plagued by their low discharging efficiency (40–60%), which originates from the matrix with high bulk ferroelectric relaxation and the high-k ceramics with large conduction loss. In this work, a linear-like PVDF-based polymer dielectric is synthesized through grafting poly(methyl methacrylate) (PMMA) onto main chains of poly(vinyl fluoride-trifluoroethylene-chlorotrifluoroethylene) (P(VDF-TrFE-CTFE)) terpolymer via an atom transfer radical polymerization (ATRP) process. PMMA grafted terpolymer (P(VDF-TrFE-CTFE)-g-PMMA) shows linear-like dielectric characteristics accompanied with greatly enhanced discharging efficiency of ∼80% under 250 MV/m, which is over 100% higher than that of pristine terpolymer. To further improve its breakdown strength and discharging efficiency, the grafted terpolymer are then compounded with ultrasonic-exfoliated mica nanosheets (eMica) by solution-cast method. Thanks to the low hysteresis loss of linear-like dielectric matrix and the high insulating 2D mica nanosheets, the composite with the highest discharging efficiency of ∼78% under 250 MV/m is achieved. The maximum energy density of the optimized composite reaches 9.6 J/cm3, which is nearly 290% that of the pristine terpolymer. Besides, its discharging efficiency is about 74% under 450 MV/m, which is much more advantageous than the other PVDF-based polymer/ceramics composite dielectrics. This work suggests that utilizing polymer matrix with linear dielectric property and fillers with high insulating 2D structure might be a facile strategy to achieve composite dielectrics with simultaneously high energy density and high discharging efficiency.

Enhanced breakdown strength and energy storage of PVDF‐based dielectric composites by incorporating exfoliated mica nanosheets

The development of flexible and high‐performance dielectric materials is of critical importance in energy storage devices. Since energy density of a dielectric capacitor is determined by the dielectric constant and breakdown strength, in this work, a simple and effective way is provided to increase the energy storage density of polymer matrix dielectric film via adding exfoliated mica nanosheets. Few‐layered mica nanosheets were successfully exfoliated by a facile one‐step method and incorporated with Poly(vinylidene fluoride) (PVDF) matrix. The mica nanosheets could act as the insulating barriers, which help to increase the breakdown strength of the PVDF/mica composites. The maximum discharged energy density of the prepared composite film was 7.93 J cm−3 at 450 MV m−1 with only 5 vol% of mica nanosheets, which is about three times higher than pure PVDF. This study introduced an economic and effective approach to get flexible and high energy density polymer composite films and broadened the application of mica. POLYM. COMPOS., 2018. © 2018 Society of Plastics Engineers

Flexible memristive devices based on polyimide:mica nanosheet nanocomposites with an embedded PEDOT:PSS layer

Flexible memristive devices with a structure of Al/polyimide:mica/poly(3,4-ethylenedioxythiophene) polystyrene sulfonate/indium-tin-oxide/polyethylene glycol naphthalate showed electrical bistability characteristics. The maximum current margin of the devices with mica nanosheets was much larger than that of the devices without mica nanosheets. For these devices, the current vs. time curves showed nonvolatile characteristics with a retention time of more than 1 × 104 s, and the current vs. number-of-cycles curves demonstrated an endurance for high resistance state/low resistance state switchings of 1 × 102 cycles. As to the operation performance, the “reset” voltage was distributed between 2.5 and 3 V, and the “set” voltage was distributed between −0.7 and −0.5 V, indicative of high uniformity. The electrical characteristics of the devices after full bendings with various radii of curvature were similar to those before bending, which was indicative of devices having ultra-flexibility. The carrier transport and the operation mechanisms of the devices were explained based on the current vs. voltage curves and the energy band diagrams.

Transforming ground mica into high-performance biomimetic polymeric mica film

Biomimetic assembly of high-quality nanosheets into nacre-like structures can produce macroscopic films with favorable mechanical and optical performances due to the intrinsic properties and high level of ordering of the nanoscale building blocks. Natural ground mica is abundant and exhibits great application potential. However, large size and low aspect ratio greatly limit its biomimetic assembly. Moreover, exfoliation of ground mica into high-quality nanosheets remains a significant challenge. Here, we report that large-scale exfoliation of ground mica into mono- or few-layered mica nanosheets with a production rate of ~1.0 g h−1 can be successfully achieved. The mica nanosheets are then assembled into strong biomimetic polymeric mica film that inherits the high electric insulation, excellent visible transmittance, and unique ultraviolet-shielding properties of natural mica. Its overall performance is superior to that of natural sheet mica and other biomimetic films, making the polymeric mica film a suitable substrate for flexible and transparent devices.

Ni nanoparticles supported on mica for efficient decomposition of ammonia to COx-free hydrogen

A wet impregnation method is used to synthesize Ni nanocatalysts supported on naturally abundant mica nanosheets for decomposition of ammonia to COx-free hydrogen. The prepared catalysts are characterized by XRD, SEM, TEM, N2 sorption, TG, XPS, H2-TPR and NH3/H2-TPD techniques. The catalytic tests exhibit that the Ni/mica catalysts are highly active for ammonia decomposition. The two-dimensional structure of mica favors mass transportation, which can remarkably promote the catalytic process. The NH3/H2-TPD curves of Ni/mica show no desorption signals of NH3 and H2, indicating the presence of weak desorption energy barrier. The content of Ni in the catalysts is related to the crystallite size of Ni species, affecting their catalytic properties. As demonstrated in this study, the Ni/mica catalyst with 15% Ni loading amount exhibits the highest catalytic activity and long-term stability. At a high space velocity of 30000 cm3 gcat−1 h−1, 97.2% ammonia conversion is achieved over the 15%Ni/mica catalyst at 650 °C, indicating the Ni/mica is a promising catalyst for ammonia decomposition.

Two-dimensional mica nanosheets supported Fe nanoparticles for NH3 decomposition to hydrogen

Two-dimensional mica nanosheets (MS) are employed as support for preparation of Fe/MS catalysts by three different methods namely homogeneous precipitation (HP), impregnation (IM), and deposition precipitation (DP) methods. Their catalytic performances for ammonia decomposition are tested, and their physicochemical properties are characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, hydrogen temperature-programmed reduction, X-ray photoelectron spectroscopy, ammonia/hydrogen temperature-programmed desorption, and N2 sorption techniques. The catalytic results show that the preparation methods would remarkably affect the catalytic performance of Fe/MS catalysts, and the Fe/MS catalysts prepared by HP method exhibit the highest catalytic activity. It is revealed that the coexistence of three types of Fe species including Fe3+, Fe2+ and Fe0 in the reduced Fe/MS catalysts are responsible for the ammonia decomposition. The excellent catalytic performance of Fe/MS-HP catalyst is attributed to the highly dispersed Fe species, layered structure of mica, and strong metal-support interactions between Fe and mica. Stability testing shows that the 5%Fe/MS-HP catalyst exhibits high catalytic stability, suggesting a very promising catalyst in ammonia decomposition.

Immobilization of silver nanoparticles on exfoliated mica nanosheets to form highly conductive nanohybrid films

Highly electrically conductive films were prepared by coating organic/inorganic nanohybrid solutions with a polymeric dispersant and exfoliated mica nanosheets (Mica) on which silver nanoparticles (AgNPs) had been dispersed in various components. Transmission electronic microscopy showed that the synthesized AgNPs had a narrow size distribution and a diameter of approximately 20 nm. Furthermore, a 60 μm thick film with a sheet resistance as low as 4.5 × 10−2 Ω/sq could be prepared by controlling the heating temperature and by using AgNPs/POE-imide/Mica in a weight ratio of 20:20:1. During the heating process, the surface color of the hybrid film changed from dark golden to white, suggesting the accumulation of the AgNPs through surface migration and their melting to form an interconnected network. These nanohybrid films have potential for use in various electrically conductive devices.