19 research outputs found
Uni-, Bi-, and Tri-Directional Wetting Caused by Nanostructures with Anisotropic Surface Energies
Wetting is a pervasive phenomenon that governs many natural
and
artificial processes. Asymmetric wetting along a single axis, in particular,
has generated considerable interest but has thus far been achieved
only by the creation of structural anisotropy. In this paper, we report
that such directional wetting can also be achieved by anisotropically
coating nanostructure surfaces with materials that modify the nanostructure
surface energy, a phenomenon that has not been observed in natural
or artificial systems thus far. Moreover, by combining this newfound
chemical influence on wetting with topographic features, we are able
to restrict wetting in one, two and three directions. A model that
explains these findings in terms of anisotropy of the pinning forces
at the triple phase contact line is presented. Through the resulting
insights, a flexible method for precise control of wetting is created
Uni-, Bi-, and Tri-Directional Wetting Caused by Nanostructures with Anisotropic Surface Energies
Wetting is a pervasive phenomenon that governs many natural
and
artificial processes. Asymmetric wetting along a single axis, in particular,
has generated considerable interest but has thus far been achieved
only by the creation of structural anisotropy. In this paper, we report
that such directional wetting can also be achieved by anisotropically
coating nanostructure surfaces with materials that modify the nanostructure
surface energy, a phenomenon that has not been observed in natural
or artificial systems thus far. Moreover, by combining this newfound
chemical influence on wetting with topographic features, we are able
to restrict wetting in one, two and three directions. A model that
explains these findings in terms of anisotropy of the pinning forces
at the triple phase contact line is presented. Through the resulting
insights, a flexible method for precise control of wetting is created
Uni-, Bi-, and Tri-Directional Wetting Caused by Nanostructures with Anisotropic Surface Energies
Wetting is a pervasive phenomenon that governs many natural
and
artificial processes. Asymmetric wetting along a single axis, in particular,
has generated considerable interest but has thus far been achieved
only by the creation of structural anisotropy. In this paper, we report
that such directional wetting can also be achieved by anisotropically
coating nanostructure surfaces with materials that modify the nanostructure
surface energy, a phenomenon that has not been observed in natural
or artificial systems thus far. Moreover, by combining this newfound
chemical influence on wetting with topographic features, we are able
to restrict wetting in one, two and three directions. A model that
explains these findings in terms of anisotropy of the pinning forces
at the triple phase contact line is presented. Through the resulting
insights, a flexible method for precise control of wetting is created
Mechanics of Catalyst Motion during Metal Assisted Chemical Etching of Silicon
Metal
assisted chemical etching (MACE) of Si has been used to fabricate
both simple and complex Si nanostructures, through the relatively
straightforward process of noble metal deposition and patterning followed
by immersion in a suitable etching solution. Under appropriate conditions,
etching is catalyzed by the metal and occurs only at the metalāsilicon
interface. MACE therefore requires that a force be present that keeps
the metal and silicon in close proximity during etching. The geometrical
characteristics of the etched nanostructures therefore depend not
only on the solution chemistry, but also on the mechanical properties
and constraints of the noble metal catalysts. Here we report experimental
studies of etching with nanoscale Au catalyst strips that are mechanically
constrained at both ends. The mechanical constraint of these strips
leads to termination of etching when a mechanical force balance is
achieved. Through experimental characterization of the etching end-state
and through modeling, we determine the force between the catalyst
and the silicon during etching, and determine how this force depends
on the chemistry of the solution
Mechanisms of Morphological Evolution of Li<sub>2</sub>O<sub>2</sub> Particles during Electrochemical Growth
LiāO<sub>2</sub> batteries,
wherein solid Li<sub>2</sub>O<sub>2</sub> is formed at the porous
air cathode during discharge,
are candidates for high gravimetric energy (3212 Wh/kg<sub>Li<sub>2</sub>O<sub>2</sub></sub>) storage for electric vehicles. Understanding
and controlling the nucleation and morphological evolution of Li<sub>2</sub>O<sub>2</sub> particles upon discharge is key to achieving
high volumetric energy densities. Scanning and transmission electron
microscopy were used to characterize the discharge product formed
in LiāO<sub>2</sub> batteries on electrodes composed of carpets
of aligned carbon nanotubes. At low discharge rates, Li<sub>2</sub>O<sub>2</sub> particles form first as stacked thin plates, ā¼10
nm in thickness, which spontaneously splay so that secondary nucleation
of new plates eventually leads to the development of a particle with
a toroidal shape. Li<sub>2</sub>O<sub>2</sub> crystallites have large
(001) crystal faces consistent with the theoretical Wulff shape and
appear to grow by a layer-by-layer mechanism. In contrast, at high
discharge rates, copious nucleation of equiaxed Li<sub>2</sub>O<sub>2</sub> particles precedes growth of discs and toroids
Condensation on Superhydrophobic Surfaces: The Role of Local Energy Barriers and Structure Length Scale
Water condensation on surfaces is a ubiquitous phase-change
process
that plays a crucial role in nature and across a range of industrial
applications, including energy production, desalination, and environmental
control. Nanotechnology has created opportunities to manipulate this
process through the precise control of surface structure and chemistry,
thus enabling the biomimicry of natural surfaces, such as the leaves
of certain plant species, to realize superhydrophobic condensation.
However, this ābottom-upā wetting process is inadequately
described using typical global thermodynamic analyses and remains
poorly understood. In this work, we elucidate, through imaging experiments
on surfaces with structure length scales ranging from 100 nm to 10
Ī¼m and wetting physics, how local energy barriers are essential
to understand non-equilibrium condensed droplet morphologies and demonstrate
that overcoming these barriers via nucleation-mediated dropletādroplet
interactions leads to the emergence of wetting states not predicted
by scale-invariant global thermodynamic analysis. This mechanistic
understanding offers insight into the role of surface-structure length
scale, provides a quantitative basis for designing surfaces optimized
for condensation in engineered systems, and promises insight into
ice formation on surfaces that initiates with the condensation of
subcooled water
Condensation on Superhydrophobic Surfaces: The Role of Local Energy Barriers and Structure Length Scale
Water condensation on surfaces is a ubiquitous phase-change
process
that plays a crucial role in nature and across a range of industrial
applications, including energy production, desalination, and environmental
control. Nanotechnology has created opportunities to manipulate this
process through the precise control of surface structure and chemistry,
thus enabling the biomimicry of natural surfaces, such as the leaves
of certain plant species, to realize superhydrophobic condensation.
However, this ābottom-upā wetting process is inadequately
described using typical global thermodynamic analyses and remains
poorly understood. In this work, we elucidate, through imaging experiments
on surfaces with structure length scales ranging from 100 nm to 10
Ī¼m and wetting physics, how local energy barriers are essential
to understand non-equilibrium condensed droplet morphologies and demonstrate
that overcoming these barriers via nucleation-mediated dropletādroplet
interactions leads to the emergence of wetting states not predicted
by scale-invariant global thermodynamic analysis. This mechanistic
understanding offers insight into the role of surface-structure length
scale, provides a quantitative basis for designing surfaces optimized
for condensation in engineered systems, and promises insight into
ice formation on surfaces that initiates with the condensation of
subcooled water
Condensation on Superhydrophobic Surfaces: The Role of Local Energy Barriers and Structure Length Scale
Water condensation on surfaces is a ubiquitous phase-change
process
that plays a crucial role in nature and across a range of industrial
applications, including energy production, desalination, and environmental
control. Nanotechnology has created opportunities to manipulate this
process through the precise control of surface structure and chemistry,
thus enabling the biomimicry of natural surfaces, such as the leaves
of certain plant species, to realize superhydrophobic condensation.
However, this ābottom-upā wetting process is inadequately
described using typical global thermodynamic analyses and remains
poorly understood. In this work, we elucidate, through imaging experiments
on surfaces with structure length scales ranging from 100 nm to 10
Ī¼m and wetting physics, how local energy barriers are essential
to understand non-equilibrium condensed droplet morphologies and demonstrate
that overcoming these barriers via nucleation-mediated dropletādroplet
interactions leads to the emergence of wetting states not predicted
by scale-invariant global thermodynamic analysis. This mechanistic
understanding offers insight into the role of surface-structure length
scale, provides a quantitative basis for designing surfaces optimized
for condensation in engineered systems, and promises insight into
ice formation on surfaces that initiates with the condensation of
subcooled water
Condensation on Superhydrophobic Surfaces: The Role of Local Energy Barriers and Structure Length Scale
Water condensation on surfaces is a ubiquitous phase-change
process
that plays a crucial role in nature and across a range of industrial
applications, including energy production, desalination, and environmental
control. Nanotechnology has created opportunities to manipulate this
process through the precise control of surface structure and chemistry,
thus enabling the biomimicry of natural surfaces, such as the leaves
of certain plant species, to realize superhydrophobic condensation.
However, this ābottom-upā wetting process is inadequately
described using typical global thermodynamic analyses and remains
poorly understood. In this work, we elucidate, through imaging experiments
on surfaces with structure length scales ranging from 100 nm to 10
Ī¼m and wetting physics, how local energy barriers are essential
to understand non-equilibrium condensed droplet morphologies and demonstrate
that overcoming these barriers via nucleation-mediated dropletādroplet
interactions leads to the emergence of wetting states not predicted
by scale-invariant global thermodynamic analysis. This mechanistic
understanding offers insight into the role of surface-structure length
scale, provides a quantitative basis for designing surfaces optimized
for condensation in engineered systems, and promises insight into
ice formation on surfaces that initiates with the condensation of
subcooled water
Condensation on Superhydrophobic Surfaces: The Role of Local Energy Barriers and Structure Length Scale
Water condensation on surfaces is a ubiquitous phase-change
process
that plays a crucial role in nature and across a range of industrial
applications, including energy production, desalination, and environmental
control. Nanotechnology has created opportunities to manipulate this
process through the precise control of surface structure and chemistry,
thus enabling the biomimicry of natural surfaces, such as the leaves
of certain plant species, to realize superhydrophobic condensation.
However, this ābottom-upā wetting process is inadequately
described using typical global thermodynamic analyses and remains
poorly understood. In this work, we elucidate, through imaging experiments
on surfaces with structure length scales ranging from 100 nm to 10
Ī¼m and wetting physics, how local energy barriers are essential
to understand non-equilibrium condensed droplet morphologies and demonstrate
that overcoming these barriers via nucleation-mediated dropletādroplet
interactions leads to the emergence of wetting states not predicted
by scale-invariant global thermodynamic analysis. This mechanistic
understanding offers insight into the role of surface-structure length
scale, provides a quantitative basis for designing surfaces optimized
for condensation in engineered systems, and promises insight into
ice formation on surfaces that initiates with the condensation of
subcooled water