18 research outputs found
Resonant optical trapping of Janus nanoparticles in plasmonic nanoaperture
Controlled trapping of light absorbing nanoparticles with low-power optical
tweezers is crucial for remote manipulation of small objects. This study takes
advantage of the synergetic effects of tightly confined local fields of
plasmonic nanoaperture, self-induced back-action of nanoparticles, and resonant
optical trapping method to demonstrate enhanced manipulation of Janus
nanoparticles in metallic nanohole aperture. We theoretically demonstrate that
displacement of Au-coated Janus nanoparticles toward plasmonic nanoaperture and
proper orientation of the metal coating give rise to enhanced near-field
intensity and pronounced optical force. We also explore the effect of resonant
optical trapping by employing dual laser system, where an on-resonant green
laser excites the metal-coated nanoparticle whereas an off-resonant
near-infrared laser plays trapping role. It is found that, at optimum
nanoparticle configuration, the resonant optical trapping technique can result
in three-fold enhancement of optical force, which is attributed to excitation
of surface plasmon resonance in Janus nanoparticles. The findings of this study
might pave the way for low power optical manipulation of light-absorbing
nanoparticles with possible applications in nanorobotics and drug delivery
Hybrid plasmonic modes for enhanced refractive index sensing
Compared to single nanoparticles, strongly coupled plasmonic nanoparticles
provide attractive advantages owing to their ability to exhibit multiple
resonances with unique spectral features and higher local field intensity.
These enhanced plasmonic properties of coupled metal nanoparticles have been
used for various applications including realization of strong light-matter
interaction, photocatalysis, and sensing applications. In this article, we
review the basic physics of hybrid plasmonic modes in coupled metallic
nanodimers and assess their potentials for refractive index sensing. In
particular, we overview various modes of hybrid plasmons including bonding and
antibonding modes in symmetric nanodimers, Fano resonances in asymmetric
nanodimers, charge transfer plasmons in linked nanoparticle dimers, hybrid
plasmon modes in nanoshells, and gap modes in particle-on-mirror
configurations. Beyond the dimeric nanosystems, we also showcase the potentials
of hybrid plasmonic modes in periodic nanoparticle arrays for sensing
applications. Finally, based on the critical assessment of the recent
researches on coupled plasmonic modes, the outlook on the future prospects of
hybrid plasmon based refractometric sensing are discussed We believe that,
given their tunable resonances and ultranarrow spectral signatures, coupled
metal nanoparticles are expected to play key roles in developing precise
plasmonic nanodevices with extreme sensitivity
Power Generation with Thermolytic Reverse Electrodialysis for Low-Grade Waste Heat Recovery
Closed-loop reverse electrodialysis (RED) systems that use a thermolytic solution for low-grade waste heat recovery have attracted significant attention. They have several cost benefits, e.g., the absence of repetitive pretreatment and removal of locational constraints, when compared with open-loop RED systems using seawater and river water. This study presents a model of RED that uses ammonium bicarbonate, and this is a promising solution for closed-loop systems. The modified Planck-Henderson equation is used to calculate the ion exchange membrane potential. The calculation is based on the conductivity measurements as ionization carbonate electrochemical information has not been reported before this study. The solution resistance is experimentally determined. The experimentally obtained permselectivity is implemented into the model to predict the membrane potential more accurately. The results of the improved model are well matched with experimental results under results under various operating conditions of the RED system. In addition, in the model of this study, the net power density was characterized with the consideration of the pumping loss. The improved model predicts a maximum net power density of 0.84Â W/m2 with an intermembrane distance of 0.1Â mm, a flow rate of 3Â mL/min, and a concentration ratio of 200 as optimum conditions. The results of the study are expected to improve our understanding of the ammonium bicarbonate-RED system and contribute to modeling studies using ammonium bicarbonate or certain other compounds for novel technologies of waste heat recovery
Nanoengineered condenser surfaces for enhancing transport in thermal desalination by air gap membrane distillation
Thermal desalination is a technique that uses heat or thermal energy to desalinate water, unlike reverse osmosis. Membrane distillation (MD) is a type of thermal desalination technology having various configurations. Air gap membrane distillation (AGMD) is one of the more energy efficient MD configurations, being especially advantageous over other configurations at high salinity. However, the large mass transfer resistance of the air gap dramatically reduces the permeate flux, impairing performance. Higher condensation performance can be achieved by using a smaller air gap size, but typical film-wise condensation flow patterns flood the air gap at the optimal gap size (\u3c1 mm). Experiments show that dropwise and jumping-droplet condensation regimes, achieved using hydrophobic and superhydrophobic condensing surfaces respectively, can improve droplet shedding, allowing for thinner gap sizes. A systemlevel numerical model is used to demonstrate that these surfaces could thereby enable improved energy efficiency (2.1× increase of gained output ratio) while avoiding flooding at gap sizes as small as 0.2 mm. Superhydrophobic surfaces with directional jumping of droplets, specifically in the direction of gravity, are also tested and compared to droplets that jump normal to the condensing surface. Novel condensing surfaces that include a combination of the superhydrophobic and superhydrophilic patterns create flow regimes having pathways for faster permeate removal. Other condensing surfaces, including SLIPS (slippery liquidinfused porous surfaces) and laser-ablated superhydrophobic patterned surfaces are tested to the check the extent to which they improve the permeate removal rate while exhibiting different condensation regimes that merit further exploration
Atmosphere-Mediated Superhydrophobicity of Rationally Designed Micro/Nanostructured Surfaces
Superhydrophobicity
has received significant attention over the
past three decades owing to its significant potential in self-cleaning,
anti-icing and drag reduction surfaces, energy-harvesting devices,
antibacterial coatings, and enhanced heat transfer applications. Superhydrophobicity
can be obtained via the roughening of an intrinsically hydrophobic
surface, the creation of a re-entrant geometry, or by the roughening
of a hydrophilic surface followed by a conformal coating of a hydrophobic
material. Intrinsically hydrophobic surfaces have poor thermophysical
properties, such as thermal conductivity, and thus are not suitable
for heat transfer applications. Re-entrant geometries, although versatile
in applications where droplets are deposited, break down during spatially
random nucleation and flood the surface. Chemical functionalization
of rough metallic substrates, although promising, is not utilized
because of the poor durability of conformal hydrophobic coatings.
Here we develop a radically different approach to achieve stable superhydrophobicity.
By utilizing laser processing and thermal oxidation of copper (Cu)
to create a high surface energy hierarchical copper oxide (CuO), followed
by repeatable and passive atmospheric adsorption of hydrophobic volatile
organic compounds (VOCs), we show that stable superhydrophobicity
with apparent advancing contact angles ≈160° and contact
angle hysteresis as low as ≈20° can be achieved. We exploit
the structure length scale and structure geometry-dependent VOC adsorption
dynamics to rationally design CuO nanowires with enhanced superhydrophobicity.
To gain an understanding of the VOC adsorption physics, we utilized
X-ray photoelectron and ion mass spectroscopy to identify the chemical
species deposited on our surfaces in two distinct locations: Urbana,
IL, United States and Beijing, China. To test the stability of the
atmosphere-mediated superhydrophobic surfaces during heterogeneous
nucleation, we used high-speed optical microscopy to demonstrate the
occurrence of dropwise condensation and stable coalescence-induced
droplet jumping. Our work not only provides rational design guidelines
for developing passively durable superhydrophobic surfaces with excellent
flooding-resistance and self-healing capability but also sheds light
on the key role played by the atmosphere in governing wetting
Rapid Fabrication of Tungsten Oxide-Based Electrochromic Devices through Femtosecond Laser Processing
The sol-gel method is a widely adopted technique for the preparation of tungsten trioxide (WO3) materials, favored for its cost-effectiveness and straightforward production procedures. However, this method encounters challenges such as prolonged annealing periods and limited flexibility in fabricating patterned WO3 films. This study introduces a novel approach that integrates femtosecond laser processing with the sol-gel method to enhance the fabrication of WO3 films. By adjusting polyvinylpyrrolidone (PVP) concentrations during sol-gel synthesis, precise control over film thickness and optimized film properties were achieved. The innovative technique significantly reduced the annealing time required to achieve an 80% transmittance rate from 90 min to 40 min, marking a 56% decrease. Laser processing increased the surface roughness of the films from Sa = 0.032 to Sa = 0.119, facilitating enhanced volatilization of organics during heat treatment. Additionally, this method improved the transmittance modulation of the films by 22% at 550 nm compared to unprocessed counterparts. This approach not only simplifies the manufacturing process but also enhances the optical efficiency of electrochromic devices, potentially leading to broader applications and more effective energy conservation strategies
Resonant optical trapping of Janus nanoparticles in plasmonic nanoaperture
Controlled trapping of light absorbing nanoparticles with low-power optical tweezers is crucial for remote manipulation of small objects. This study takes advantage of the synergetic effects of tightly confined local fields of plasmonic nanoaperture, self-induced back-action of nanoparticles, and resonant optical trapping scheme to demonstrate enhanced manipulation of Janus nanoparticles in metallic nanohole aperture. We theoretically demonstrate that displacement of Au-coated Janus nanoparticles toward plasmonic nanoaperture and proper orientation of the metal coating give rise to enhanced near-field intensity and pronounced optical force. We also explore the effect of resonant optical trapping by employing two-laser system, where an on-resonant green laser excites the metal-coated nanoparticle whereas an off-resonant near-infrared laser plays trapping role. It is found that, at optimum nanoparticle configuration, the resonant optical trapping method can result in three-fold enhancement of optical force, which is attributed to excitation of surface plasmon resonance in Janus nanoparticles. These findings might have implications for efficient manipulation of light-absorbing nanoparticles of various compositions with low-power
Molecular Dynamics Simulation of the Effect of Angle Variation on Water Permeability through Hourglass-Shaped Nanopores
Water transport through aquaporin water channels occurs extensively in cell membranes. Hourglass-shaped (biconical) pores resemble the geometry of these aquaporin channels and therefore attract much research attention. We assumed that hourglass-shaped nanopores are capable of high water permeation like biological aquaporins. In order to prove the assumption, we investigated nanoscale water transport through a model hourglass-shaped pore using molecular dynamics simulations while varying the angle of the conical entrance and the total nanopore length. The results show that a minimal departure from optimized cone angle (e.g., 9° for 30 Å case) significantly increases the osmotic permeability and that there is a non-linear relationship between permeability and the cone angle. The analysis of hydrodynamic resistance proves that the conical entrance helps to reduce the hydrodynamic entrance hindrance. Our numerical and analytical results thus confirm our initial assumption and suggest that fast water transport can be achieved by adjusting the cone angle and length of an hourglass-shaped nanopore