8 research outputs found
Manufacturable Conducting Rubber Ambers and Stretchable Conductors from Copper Nanowire Aerogel Monoliths
We report on a low-cost, simple yet efficient strategy to fabricate ultralightweight aerogel monoliths and conducting rubber ambers from copper nanowires (CuNWs). A trace amount of poly(vinyl alcohol) (PVA) substantially improved the mechanical robustness and elasticity of the CuNW aerogel while maintaining a high electrical conductivity. The resistivity was highly responsive to strains manifesting two distinct domains, and both followed a power law function consistent with pressure-controlled percolation theory. However, the values of the exponents were much less than the predicted value for 3D systems, which may be due to highly porous structures. Remarkably, the CuNW-PVA aerogels could be further embedded into PDMS resin, forming conducting rubber ambers. The ambers could be further manufactured simply by cutting into any arbitrary 1D, 2D, and 3D shapes, which were all intrinsically conductive without the need of external prewiring, a condition required in the previous aerogel-based conductors. The outstanding electrical conductivity in conjunction with high mechanical compliance enabled prototypes of the elastic piezoresistivity switches and stretchable conductors
Free-Standing Bilayered Nanoparticle Superlattice Nanosheets with Asymmetric Ionic Transport Behaviors
Natural cell membranes can directionally and selectively regulate the ion transport, which is critical for the functioning of living cells. Here, we report on the fabrication of an artificial membrane based on an asymmetric nanoparticle superlattice bilayered nanosheet, which exhibits similar ion transport characteristics. The superlattice nanosheets were fabricated <i>via</i> a drying-mediated self-assembly of polystyrene-capped gold nanoparticles at the liquidāair interface. By adopting a layer-by-layer assembly process, an asymmetric nanomembrane could be obtained consisting of two nanosheets with different nanoparticle size. The resulting nanomembranes exhibit an asymmetric ion transport behavior, and diode-like currentāvoltage curves were observed. The asymmetric ion transport is attributed to the cone-like nanochannels formed within the membranes, upon which a simulation map was established to illustrate the relationship between the channel structure and the ionic selectivity, in consistency with our experimental results. Our superlattice nanosheet-based design presents a promising strategy for the fabrication of next-generation smart nanomembranes for rationally and selectively regulating the ion transport even at a large ion flux, with potential applications in a wide range of fields, including biosensor devices, energy conversion, biophotonics, and bioelectronics
Two-Dimensional Bipyramid Plasmonic Nanoparticle Liquid Crystalline Superstructure with Four Distinct Orientational Packing Orders
Anisotropic plasmonic nanoparticles
have been successfully used
as constituent elements for growing ordered nanoparticle arrays. However,
orientational control over their spatial ordering remains challenging.
Here, we report on a self-assembled two-dimensional (2D) nanoparticle
liquid crystalline superstructure (NLCS) from bipyramid gold nanoparticles
(BNPs), which showed four distinct orientational packing orders, corresponding
to horizontal alignment (H-NLCS), circular arrangement (C-NLCS), slanted
alignment (S-NLCS), and vertical alignment (V-NLCS) of constituent
particle building elements. These packing orders are characteristic
of the unique shape of BNPs because all four packing modes were observed
for particles with various sizes. Nevertheless, only H-NLCS and V-NLCS
packing orders were observed for the free-standing ordered array nanosheets
formed from a drying-mediated self-assembly at the air/water interface
of a sessile droplet. This is due to strong surface tension and the
absence of particleāsubstrate interaction. In addition, we
found the collective plasmonic coupling properties mainly depend on
the packing type, and characteristic coupling peak locations depend
on particle sizes. Interestingly, surface-enhanced Raman scattering
(SERS) enhancements were heavily dependent on the orientational packing
ordering. In particular, V-NLCS showed the highest Raman enhancement
factor, which was about 77-fold greater than the H-NLCS and about
19-fold greater than C-NLCS. The results presented here reveal the
nature and significance of orientational ordering in controlling plasmonic
coupling and SERS enhancements of ordered plasmonic nanoparticle arrays
Shape Transformation of Constituent Building Blocks within Self-Assembled Nanosheets and Nano-origami
Self-assembly of
nanoparticles represents a simple yet efficient
route to synthesize designer materials with unusual properties. However,
the previous assembled structures whether by surfactants, polymer,
or DNA ligands are āstaticā or āfrozenā
building block structures. Here, we report the growth of transformable
self-assembled nanosheets which could enable reversible switching
between two types of nanosheets and even evolving into diverse third
generation nanosheet structures without losing pristine periodicity.
Such <i>in situ</i> transformation of nanoparticle building
blocks can even be achieved in a free-standing two-dimensional system
and three-dimensional origami. The success in such <i>in situ</i> nanocrystal transformation is attributed to robust āplant-cell-wall-likeā
ion-permeable reactor arrays from densely packed polymer ligands,
which spatially define and confine nanoscale nucleation/growth/etching
events. Our strategy enables efficient fabrication of nanocrystal
nanosheets with programmable building blocks for innovative applications
in adaptive tactile metamaterials, optoelectronic devices, and sensors
Omnidirectional Hydrogen Generation Based on a Flexible Black Gold Nanotube Array
Solar-driven hydrogen generation
is emerging as an economical
and
sustainable means of producing renewable energy. However, current
photocatalysts for hydrogen generation are mostly powder-based or
rigid-substrate-supported, which suffer from limitations, such as
difficulties in catalyst regeneration or poor omnidirectional light-harvesting.
Here, we report a two-dimensional (2D) flexible photocatalyst based
on elastomer-supported black gold nanotube (GNT) arrays with conformal
CdS coating and Pt decoration. The highly porous GNT arrays display
a strong light-trapping effect, leading to near-complete absorption
over almost the entire range of the solar spectrum. In addition, they
offer high surface-to-volume ratios promoting efficient photocatalytic
reactions. These structural features result in high H2 generation
efficiencies. Importantly, our elastomer-supported photocatalyst displays
comparable photocatalytic activity even when being mechanically deformed,
including bending, stretching, and twisting. We further designed a
three-dimensional (3D) tree-like flexible photocatalytic system to
mimic Natureās photosynthesis, which demonstrated omnidirectional
H2 generation. We believe our strategy represents a promising
route in designing next-generation solar-to-fuel systems that rival
natural plants
Unconventional Janus Properties of Enokitake-like Gold Nanowire Films
We
report on unconventional Janus material properties of vertically
aligned gold nanowire films that conduct electricity and interact
with light and water in drastically different ways on its two opposing
sides. These Janus-like properties originate from enokitake-like nanowire
structures, causing the nanoparticle side (āheadā) to
behave like bulk gold, yet the opposing nanowire side (ātailā)
behaves as discontinuous nanophases. Due to this Janus film structure,
its head side is hydrophilic but its tail side is hydrophobic; its
head side reflects light like bulk gold, yet its tail side is a broadband
superabsorber; its tail side is less conductive but with tunable resistance.
More importantly, the elastomer-bonded Janus film exhibits unusual
mechatronic properties when being stretched, bent, and pressed. The
tail-bonded elastomeric sheet can be stretched up to ā¼800%
strain while remaining conductive, which is about 10-fold that of
head-bonded film. In addition, it is also more sensitive to bending
forces and point loads than the corresponding tail-bonded film. We
further demonstrate the versatility of nanowire-based Janus films
for pressure sensors using bilayer structures in three different assembly
layouts
Unconventional Janus Properties of Enokitake-like Gold Nanowire Films
We
report on unconventional Janus material properties of vertically
aligned gold nanowire films that conduct electricity and interact
with light and water in drastically different ways on its two opposing
sides. These Janus-like properties originate from enokitake-like nanowire
structures, causing the nanoparticle side (āheadā) to
behave like bulk gold, yet the opposing nanowire side (ātailā)
behaves as discontinuous nanophases. Due to this Janus film structure,
its head side is hydrophilic but its tail side is hydrophobic; its
head side reflects light like bulk gold, yet its tail side is a broadband
superabsorber; its tail side is less conductive but with tunable resistance.
More importantly, the elastomer-bonded Janus film exhibits unusual
mechatronic properties when being stretched, bent, and pressed. The
tail-bonded elastomeric sheet can be stretched up to ā¼800%
strain while remaining conductive, which is about 10-fold that of
head-bonded film. In addition, it is also more sensitive to bending
forces and point loads than the corresponding tail-bonded film. We
further demonstrate the versatility of nanowire-based Janus films
for pressure sensors using bilayer structures in three different assembly
layouts
Large-Scale Self-Assembly and Stretch-Induced Plasmonic Properties of CoreāShell Metal Nanoparticle Superlattice Sheets
We report on a facile interfacial
self-assembly approach to fabricate large-scale metal nanoparticle
superlattice sheets from nonspherical coreāshell nanoparticles,
which exhibited reversible plasmonic responses to repeated mechanical
stretching. Monodisperse Au@Ag nanocubes (NCs) and Au@Ag nanocuboids
(NBs) could be induced to self-assembly at the hexane/water interface,
forming uniform superlattices up to at least ā¼13 cm<sup>2</sup> and giving rise to mirror-like reflection. Such large-area mirror-like
superlattice sheets exhibited reversible plasmonic responses to external
mechanical strains. Under stretching, the dominant plasmonic resonance
peak for both NB and NC superlattice sheets shifted to blue, following
a power-law function of the applied strain. Interestingly, the power-law
exponent (or the decay rate) showed a strong shape dependence, where
a faster rate was observed for NB superlattice sheets than that for
NC superlattice sheets