3 research outputs found
Sponge-Templated Macroporous Graphene Network for Piezoelectric ZnO Nanogenerator
We
report a simple approach to fabricate zinc oxide (ZnO) nanowire
based electricity generators on three-dimensional (3D) graphene networks
by utilizing a commercial polyurethane (PU) sponge as a structural
template. Here, a 3D network of graphene oxide is deposited from solution
on the template and then is chemically reduced. Following steps of
ZnO nanowire growth, polydimethylsiloxane (PDMS) backfilling and electrode
lamination completes the fabrication processes. When compared to conventional
generators with 2D planar geometry, the sponge template provides a
3D structure that has a potential to increase power density per unit
area. The modified one-pot ZnO synthesis method allows the whole process
to be inexpensive and environmentally benign. The nanogenerator yields
an open circuit voltage of ∼0.5 V and short circuit current
density of ∼2 μA/cm<sup>2</sup>, while the output was
found to be consistent after ∼3000 cycles. Finite element analysis
of stress distribution showed that external stress is concentrated
to deform ZnO nanowires by orders of magnitude compared to surrounding
PU and PDMS, in agreement with our experiment. It is shown that the
backfilled PDMS plays a crucial role for the stress concentration,
which leads to an efficient electricity generation
Highly Flexible, Multipixelated Thermosensitive Smart Windows Made of Tough Hydrogels
In
a cold night, a clear window that will become opaque while retaining
the indoor heat is highly desirable for both privacy and energy efficiency.
A thermally responsive material that controls both the transmittance
of solar radiance (predominantly in the visible and near-infrared
wavelengths) and blackbody radiation (mainly in the mid-infrared)
can realize such windows with minimal energy consumption. Here, we
report a smart coating made from polyampholyte hydrogel (PAH) that
transforms from a transparency state to opacity to visible radiation
and strengthens opacity to mid-infrared when lowering the temperature
as a result of phase separation between the water-rich and polymer-rich
phases. To match a typical temperature fluctuation during the day,
we fine-tune the phase transition temperature between 25 and 55 °C
by introducing a small amount of relatively hydrophobic monomers (0.1
to 0.5 wt % to PAH). To further demonstrate an actively controlled,
highly flexible, and high-contrast smart window, we build in an array
of electric heaters made of printed elastomeric composite. The multipixelated
window offers rapid switching, ∼70 s per cycle, whereas the
device can withstand high strain (up to 80%) during operations
Highly Flexible, Multipixelated Thermosensitive Smart Windows Made of Tough Hydrogels
In
a cold night, a clear window that will become opaque while retaining
the indoor heat is highly desirable for both privacy and energy efficiency.
A thermally responsive material that controls both the transmittance
of solar radiance (predominantly in the visible and near-infrared
wavelengths) and blackbody radiation (mainly in the mid-infrared)
can realize such windows with minimal energy consumption. Here, we
report a smart coating made from polyampholyte hydrogel (PAH) that
transforms from a transparency state to opacity to visible radiation
and strengthens opacity to mid-infrared when lowering the temperature
as a result of phase separation between the water-rich and polymer-rich
phases. To match a typical temperature fluctuation during the day,
we fine-tune the phase transition temperature between 25 and 55 °C
by introducing a small amount of relatively hydrophobic monomers (0.1
to 0.5 wt % to PAH). To further demonstrate an actively controlled,
highly flexible, and high-contrast smart window, we build in an array
of electric heaters made of printed elastomeric composite. The multipixelated
window offers rapid switching, ∼70 s per cycle, whereas the
device can withstand high strain (up to 80%) during operations