8 research outputs found
Bioinspired Polymeric Photonic Crystals for High Cycling pH-Sensing Performance
Artificial
photonic crystals (PCs) have been extensively studied to improve the
sensing performance of poly(acrylic acid) (PAAc), as it can transform
the PAAc volume change into optical signal which is easier to read.
Nevertheless, these PCs are limited by the monostructure. We herein
developed new photonic crystals (PCs) by coating acrylic acid and
acrylamide (AAm) via <i>in situ</i> copolymerization onto <i>Papilio paris</i> wings having hierarchical, lamellar structure.
Our PCs exhibited high performance of color tunability to environmental
pH, as detected by reflectance spectra and visual observation. The
introduction of AAm into the system created covalent bonding which
robustly bridged the polymer with the wings, leading to an accurate
yet broad variation of reflection wavelength to gauge environmental
pH. The reflection wavelength can be tailored by the refractive index
of the lamellar interspacing due to the swelling/deswelling of the
polymer. The mechanism is not only supported by experimenta but proved
by finite-difference time-domain simulation. Moreover, It is worth
noting that the covalent bonding has provided the PCs-based pH sensor
with high cycling performance, implying great potential in practical
applications. The simple fabrication process is applicable to the
development of a wide variety of stimuli-responsive PCs taking advantage
of other polymers
Near-Infrared Trigged Stimulus-Responsive Photonic Crystals with Hierarchical Structures
Stimuli-responsive
photonic crystals (PCs) trigged by light would provide a novel intuitive
and quantitative method for noninvasive detection. Inspired by the
flame-detecting aptitude of fire beetles and the hierarchical photonic
structures of butterfly wings, we herein developed near-infrared stimuli-responsive
PCs through coupling photothermal Fe<sub>3</sub>O<sub>4</sub> nanoparticles
with thermoresponsive poly(<i>N</i>-isopropylacrylamide)
(PNIPAM), with hierarchical photonic structured butterfly wing scales
as the template. The nanoparticles within 10 s transferred near-infrared
radiation into heat that triggered the phase transition of PNIPAM;
this almost immediately posed an anticipated effect on the PNIPAM
refractive index and resulted in a composite spectrum change of ∼26
nm, leading to the direct visual readout. It is noteworthy that the
whole process is durable and stable mainly owing to the chemical bonding
formed between PNIPAM and the biotemplate. We envision that this biologically
inspired approach could be utilized in a broad range of applications
and would have a great impact on various monitoring processes and
medical sensing
Coupled Chiral Structure in Graphene-Based Film for Ultrahigh Thermal Conductivity in Both In-Plane and Through-Plane Directions
The
development of high-performance thermal management materials to dissipate
excessive heat both in plane and through plane is of special interest
to maintain efficient operation and prolong the life of electronic
devices. Herein, we designed and constructed a graphene-based composite
film, which contains chiral liquid crystals (cellulose nanocrystals,
CNCs) inside graphene oxide (GO). The composite film was prepared
by annealing and compacting of self-assembled GO-CNC, which contains
chiral smectic liquid crystal structures. The helical arranged nanorods
of carbonized CNC act as in-plane connections, which bridge neighboring
graphene sheets. More interestingly, the chiral structures also act
as through-plane connections, which bridge the upper and lower graphene
layers. As a result, the graphene-based composite film shows extraordinary
thermal conductivity, in both in-plane (1820.4 W m<sup>–1</sup> K<sup>–1</sup>) and through-plane (4.596 W m<sup>–1</sup> K<sup>–1</sup>) directions. As a thermal management material,
the heat dissipation and transportation behaviors of the composite
film were investigated using a self-heating system and the results
showed that the real-time temperature of the heater covered with the
film was 44.5 °C lower than a naked heater. The prepared film
shows a much higher efficiency of heat transportation than the commonly
used thermal conductive Cu foil. Additionally, this graphene-based
composite film exhibits excellent mechanical strength of 31.6 MPa
and an electrical conductivity of 667.4 S cm<sup>–1</sup>.
The strategy reported here may open a new avenue to the development
of high-performance thermal management films
História Unisinos
A facile
bottom-up method is reported here for the fabrication of N-doped graphene
for oxygen reduction. It consists of a two-step calcination strategy
and uses α-hydroxy acids (AHAs) as carbon source and melamine
as nitrogen source. Three different AHAs, malic acid, tartaric acid,
and citric acid, were chosen as the carbon sources. The prepared N-doped
graphenes have a typical thin layered structure with a large specific
surface area. It was found that the N content in the obtained N-doped
graphenes varies from 4.12 to 8.11 at. % depending on the AHAs used.
All of the samples showed high performance in oxygen reduction reaction
(ORR). The N-doped graphene prepared from citric acid demonstrated
the highest electrocatalytic activity, which is comparable to the
commercial Pt/C and exhibited good durability, attributing to the
high pyridinic N content in the composite
Natural immunity and cell growth regulation
A carbon/SnO<sub>2</sub> composite (C-SnO<sub>2</sub>) with hierarchical photonic
structure was fabricated from the templates of butterfly wings. We
have investigated for the first time its application as the anode
material for lithium-ion batteries. It was demonstrated to have high
reversible capacities, good cycling stability, and excellent high-rate
discharge performance, as shown by a capacitance of ∼572 mAh
g<sup>–1</sup> after 100 cycles, 4.18 times that of commercial
SnO<sub>2</sub> powder (137 mAh g<sup>–1</sup>); a far better
recovery capability of 94.3% was observed after a step-increase and
sudden-recovery current. An obvious synergistic effect was found between
the porous, hierarchically photonic microstructure and the presence
of carbon; the synergy guarantees an effective flow of electrolyte
and a short diffusion length of lithium ions, provides considerable
buffering room, and prevents aggregation of SnO<sub>2</sub> particles
in the discharge/charge processes. This nature-inspired strategy points
out a new direction for the fabrication of alternative anode materials
Cellulose Nanocrystals/Polyacrylamide Composites of High Sensitivity and Cycling Performance To Gauge Humidity
Cellulose
nanocrystals (CNCs) have attracted much interest due to their unique
optical property, rich resource, environment friendliness, and templating
potentials. CNCs have been reported as novel photonic humidity sensors,
which are unfortunately limited by the dissolution and unideal moisture
absorption of CNCs. We, in this study, developed a high-performance
photonic humidity composite sensor that consisted of CNCs and polyacrylamide;
chemical bonding was induced between the two components by using glutaraldehyde
as a bridging agent. The composites inherited the chiral nematic structure
of CNCs and maintained it well through a cycling test. A distinct
color change was observed for these composites used as a humidity
indicator; the change was caused by polyacrylamide swelling with water
and thus enlarging the helical pitch of the chiral nematic structure.
The composites showed no degradation of the sensing performance through
cycling. The excellent cycling stability was attributed to the bonding
between polyacrylamide and CNCs. This composite strategy can extend
to the development of other photonic indicators
High-Performance Microsupercapacitors Based on Bioinspired Graphene Microfibers
The
miniaturization of portable electronic devices has fueled the development
of microsupercapacitors that hold great potential to complement or
even replace microbatteries and electrolytic capacitors. In spite
of recent developments taking advantage of printing and lithography,
it remains a great challenge to attain a high energy density without
sacrificing the power density. Herein, a new protocol mimicking the
spider’s spinning process is developed to create highly oriented
microfibers from graphene-based composites via a purpose-designed
microfluidic chip. The orientation provides the microfibers with an
electrical conductivity of ∼3 × 10<sup>4</sup> S m<sup>–1</sup>, which leads to a high power density; the energy
density is sustained by nanocarbons and high-purity metallic molybdenum
disulfide. The microfibers are patterned in-plane to fabricate asymmetric
microsupercapacitors for flexible and on-chip energy storage. The
on-chip microsupercapacitor with a high pattern resolution of 100
μm delivers energy density up to the order of 10<sup>–2</sup> W h cm<sup>–3</sup> and retains an ultrahigh power density
exceeding 100 W cm<sup>–3</sup> in an aqueous electrolyte.
This work provides new design of flexible and on-chip asymmetric microsupercapacitors
based on microfibers. The unique biomimetic microfluidic fabrication
of graphene microfibers for energy storage may also stimulate thinking
of the bionic design in many other fields
Bioinspired Fabrication of Hierarchically Structured, pH-Tunable Photonic Crystals with Unique Transition
We herein report a new class of photonic crystals with hierarchical structures, which are of color tunability over pH. The materials were fabricated through the deposition of polymethylacrylic acid (PMAA) onto a Morpho butterfly wing template by using a surface bonding and polymerization route. The amine groups of chitosan in Morpho butterfly wings provide reaction sites for the MAA monomer, resulting in hydrogen bonding between the template and MAA. Subsequent polymerization results in PMAA layers coating homogenously on the hierarchical photonic structures of the biotemplate. The pH-induced color change was detected by reflectance spectra as well as optical observation. A distinct U transition with pH was observed, demonstrating PMAA content-dependent properties. The appearance of the unique U transition results from electrostatic interaction between the −NH<sub>3</sub><sup>+</sup> of chitosan and the −COO<sup>–</sup> groups of PMAA formed, leading to a special blue-shifted point at the pH value of the U transition, and the ionization of the two functional groups in the alkali and acid environment separately, resulting in a red shift. This work sets up a strategy for the design and fabrication of tunable photonic crystals with hierarchical structures, which provides a route for combining functional polymers with biotemplates for wide potential use in many fields