17 research outputs found
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. 10<sup>2</sup>–10<sup>3</sup> W·(m·K)<sup>−1</sup> 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 ironÂ(III) tosylate (FeÂ(Tos)<sub>3</sub>) oxidant blended
films and solvent evaporation-induced self-assembly (EISA) processes.
Then, in situ vapor phase polymerization of polyÂ(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<sup>–1</sup>·K<sup>–2</sup> 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