Implication of Size-Controlled Graphite Nanosheets as Building Blocks for Thermal Conductive Three-Dimensional Framework Architecture of Nanocarbons

<p>Preparation of three-dimensional (3D) networks has received significant attention as an effective approach for applications involving transport phenomena, such as thermal management materials, and several nanomaterials have been examined as potential building blocks of 3D networks for the improvement of heat conduction in polymer nanocomposites. For that purpose, nanocarbons such as graphene and graphite nanoplatelets have been spotlighted as suitable filler materials because of their excellent thermal conductivities (ca. 10²–10³ W·(m·K)⁻¹ along their lateral axes) and morphological merits. However, the implications of morphological features such as the lateral length and thickness of graphene or graphene-like materials have not yet been identified. In this study, a controlled dissociation of bulk graphite to graphite nanosheets (GNSs) using a low-cost, ecofriendly bead mill process was extensively examined and, when configured in a 3D framework architecture formation, the size-controlled GNSs demonstrated that the thermal conductivities of a 3D interconnected framework of GNSs and the corresponding polymer nanocomposite were intimately correlated with the size of the GNSs, thus demonstrating the successful preparation of an efficient thermal management material without highly sophisticated efforts. The capability of controlling the lateral size and thickness of the GNSs as well as the use of a 3D interconnected framework architecture should greatly assist the commercialization of high-quality graphene-based thermal management materials in a scalable production process.</p

Effective Propagation of Surface Plasmon Polaritons on Graphene-Protected Single-Crystalline Silver Films

Silver (Ag) is a promising material for manipulation of surface plasmon polaritons (SPPs), due to its optical and electrical properties; however, the intrinsic properties are easily degraded by surface corrosion under atmospheric conditions, restricting its applications in plasmonics. Here, we address this issue via single-crystalline Ag films protected with graphene layers and demonstrate effective propagation of SPPs on the graphene-protected Ag films. Single-crystalline Ag films with atomically flat surfaces are prepared by epitaxial growth; graphene layers are then transferred onto the Ag films. The propagation lengths of SPPs on the graphene-protected Ag films are measured, and their variations under corrosive conditions are investigated. The initial SPP propagation lengths for the bare Ag films are very long (about 50 μm in the wavelength range 550–700 nm). However, the values decrease significantly (11–13 μm) under corrosive conditions. On the contrary, the double-layer-graphene-protected Ag films exhibit SPP propagation lengths of about 23 μm and retain over 90% (21–23 μm) of the propagation lengths even after exposure to corrosive conditions, guaranteeing the reliability of Ag plasmonic devices. This approach can encourage extending the application of the graphene–metal hybrid structure and thus developing Ag plasmonic devices

Highly Ordered Nanoconfinement Effect from Evaporation-Induced Self-Assembly of Block Copolymers on In Situ Polymerized PEDOT:Tos

Organic thermoelectric materials based on conducting polymers have focused on increasing electrical conductivity and optimizing thermoelectric properties via dedoping processes. To control the crystallinity and crystal alignment for enhanced electrical conductivity, a confinement geometry in nanostructures with grapho-epitaxial growth of conducting polymers during in situ polymerization could be a promising approach. We obtained highly ordered lamellar, cylindrical and disordered nanostructures from PEO-<i>b</i>-PPO-<i>b</i>-PEO block copolymer (BCP) and iron­(III) tosylate (Fe­(Tos)₃) oxidant blended films and solvent evaporation-induced self-assembly (EISA) processes. Then, in situ vapor phase polymerization of poly­(3,4-ethylenedioxythiophene) (PEDOT):Tos on differently ordered oxidant/BCP films was performed. The effect of BCP nanostructures on the crystallinity, crystal orientation and electrical conductivity of the PEDOTs was confirmed by nanostructural and crystallographic analyses using grazing incidence small and wide-angle X-ray scattering (GISAXS and GIWAXS, respectively) experiments before and after polymerization and after a washing process. Different washing solvents also affected the electrical conductance and crystal structure. We achieved thermoelectric thermopowers up to 70 μW·m^–1·K^–2 by using an immersion dedoping process to reduce the carrier concentration and enhance the Seebeck coefficient, with little change of crystal structure

Reversibly Stretchable, Optically Transparent Radio-Frequency Antennas Based on Wavy Ag Nanowire Networks

We report a facile approach for producing reversibly stretchable, optically transparent radio-frequency antennas based on wavy Ag nanowire (NW) networks. The wavy configuration of Ag NWs is obtained by floating the NW networks on the surface of water, followed by compression. Stretchable antennas are prepared by transferring the compressed NW networks onto elastomeric substrates. The resulting antennas show excellent performance under mechanical deformation due to the wavy configuration, which allows the release of stress applied to the NWs and an increase in the contact area between NWs. The antennas formed from the wavy NW networks exhibit a smaller return loss and a higher radiation efficiency when strained than the antennas formed from the straight NW networks, as well as an improved stability in cyclic deformation tests. Moreover, the wavy NW antennas require a relatively small quantity of NWs, which leads to low production costs and provides an optical transparency. These results demonstrate the potential of these wavy Ag NW antennas in applications of wireless communications for wearable systems

Biaxial Stretchability and Transparency of Ag Nanowire 2D Mass-Spring Networks Prepared by Floating Compression

Networks of silver nanowires (Ag NWs) have been considered as promising materials for stretchable and transparent conductors. Despite various improvements of their optoelectronic and electromechanical properties over the past few years, Ag NW networks with a sufficient stretchability in multiple directions that is essential for the accommodation of the multidirectional strains of human movement have seldom been reported. For this paper, biaxially stretchable, transparent conductors were developed based on 2D mass-spring networks of wavy Ag NWs. Inspired by the traditional papermaking process, the 2D wavy networks were produced by floating Ag NW networks on the surface of water and subsequently applying biaxial compression to them. It was demonstrated that this floating-compression process can reduce the friction between the Ag NW–water interfaces, providing a uniform and isotropic in-plane waviness for the networks without buckling or cracking. The resulting Ag NW networks that were transferred onto elastomeric substrates successfully acted as conductors with an excellent transparency, conductivity, and electromechanical stability under a biaxial strain of 30%. The strain sensors that are based on the prepared conductors demonstrated a great potential for the enhanced performances of future wearable devices

Reliable Multistate Data Storage with Low Power Consumption by Selective Oxidation of Pyramid-Structured Resistive Memory

Multilevel data storage using resistive random access memory (RRAM) has attracted significant attention for addressing the challenges associated with the rapid advances in information technologies. However, it is still difficult to secure reliable multilevel resistive switching of RRAM due to the stochastic and multiple formation of conductive filaments (CFs). Herein, we demonstrate that a single CF, derived from selective oxidation by a structured Cu active electrode, can solve the reliability issue. High-quality pyramidal Cu electrodes with a sharp tip are prepared via the template-stripping method. Morphology-dependent surface energy facilitates the oxidation of Cu atoms at the tip rather than in other regions, and the tip-enhanced electric fields can accelerate the transport of the generated Cu ions. As a result, CF growth occurs mainly at the tip of the pyramidal electrode, which is confirmed by high-resolution electron microscopy and elemental analysis. The RRAM exhibits highly uniform and low forming voltages (the average forming voltage and its standard deviation for 20 pyramid-based RRAMs are 0.645 and 0.072 V, respectively). Moreover, all multilevel resistance states for the RRAMs are clearly distinguished and show narrow distributions within 1 order of magnitude, leading to reliable cell-to-cell performance for MLC operation

Thin Films of Highly Planar Semiconductor Polymers Exhibiting Band-like Transport at Room Temperature

We report the observation of band-like transport from printed polymer thin films at room temperature. This was achieved from donor-acceptor type thiophene-thiazole copolymer that was carefully designed to enhance the planarity of the backbone and the resulting transfer integral between the macromolecules. Due to the strong molecular interaction, the printed polymer film exhibited extremely low trap density comparable to that of molecular single crystals. Moreover, the energy barrier height for charge transport could be readily reduced with the aid of electric field, which led formation of extended electron states for band-like charge transport at room temperature

Expression of lubricin by human articular cartilage explants of different OA stages from total hip replacement operations.

<p>Immunostaining of lubricin represented decreased expression of lubricin in early (B), and advanced OA cartilage (C) than normal cartilage (A); Magnification x20; scale bars 100 µm.</p

Typical AFM images of human cartilage surfaces with OA and line profile analyses measured in PBS, showing severe wear on the cartilage surface with an advanced stage OA.

<p>(A) normal cartilage, (B) early OA cartilage, and (C) advanced OA cartilage. (D) Surface roughness (Rq) of human articular cartilage of normal, early and advanced OA in PBS solution, represents significant increase in Rq value with increasing OA stages. (**P<0.0001). The values of Rq were from 16 different locations on two cartilage samples of each OA score from a single femoral head. Vertical bars represent 95% of confidence interval (no of observation = 16).</p

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