6 research outputs found
Highly Stretchable and Wearable Graphene Strain Sensors with Controllable Sensitivity for Human Motion Monitoring
Because
of their outstanding electrical and mechanical properties,
graphene strain sensors have attracted extensive attention for electronic
applications in virtual reality, robotics, medical diagnostics, and
healthcare. Although several strain sensors based on graphene have
been reported, the stretchability and sensitivity of these sensors
remain limited, and also there is a pressing need to develop a practical
fabrication process. This paper reports the fabrication and characterization
of new types of graphene strain sensors based on stretchable yarns.
Highly stretchable, sensitive, and wearable sensors are realized by
a layer-by-layer assembly method that is simple, low-cost, scalable,
and solution-processable. Because of the yarn structures, these sensors
exhibit high stretchability (up to 150%) and versatility, and can
detect both large- and small-scale human motions. For this study,
wearable electronics are fabricated with implanted sensors that can
monitor diverse human motions, including joint movement, phonation,
swallowing, and breathing
Highly Stretchable and Wearable Graphene Strain Sensors with Controllable Sensitivity for Human Motion Monitoring
Because
of their outstanding electrical and mechanical properties,
graphene strain sensors have attracted extensive attention for electronic
applications in virtual reality, robotics, medical diagnostics, and
healthcare. Although several strain sensors based on graphene have
been reported, the stretchability and sensitivity of these sensors
remain limited, and also there is a pressing need to develop a practical
fabrication process. This paper reports the fabrication and characterization
of new types of graphene strain sensors based on stretchable yarns.
Highly stretchable, sensitive, and wearable sensors are realized by
a layer-by-layer assembly method that is simple, low-cost, scalable,
and solution-processable. Because of the yarn structures, these sensors
exhibit high stretchability (up to 150%) and versatility, and can
detect both large- and small-scale human motions. For this study,
wearable electronics are fabricated with implanted sensors that can
monitor diverse human motions, including joint movement, phonation,
swallowing, and breathing
AFM Probing of Polymer/Nanofiller Interfacial Adhesion and Its Correlation with Bulk Mechanical Properties in a Poly(ethylene terephthalate) Nanocomposite
The interfacial adhesion between
polymer and nanofiller plays an
important role in affecting the properties of nanocomposites. The
detailed relationship between interfacial adhesion and bulk properties,
however, is unclear. In this work, we developed an atomic force microscopy
(AFM)-based abrasive scanning methodology, as applied to model laminate
systems, to probe the strength of interfacial adhesion relevant to
poly(ethylene terephthalate) (PET)/graphene or clay nanocomposites.
Graphite and mica substrates covered with ∼2 nm thick PET films
were abrasively sheared by an AFM tip as a model measurement of interfacial
strength between matrix PET and dispersed graphene and clay, respectively.
During several abrasive raster-scan cycles, PET was shear-displaced
from the scanned region. At temperatures below the PET glass transition,
PET on graphite exhibited abrupt delamination (i.e., full adhesive
failure), whereas PET on mica did not; rather, it exhibited a degree
of cohesive failure within the shear-displaced layer. Moreover, 100-fold
higher force scanning procedures were required to abrade through an
ultimate “precursor” layer of PET only ∼0.2−0.5
nm thick, which must be largely disentangled from the matrix polymer.
Thus, the adhesive interface of relevance to the strength of clay–filler
nanocomposites is between matrix polymer and strongly bound polymer.
At 90 °C, above the bulk PET glass transition temperature, the
PET film exhibited cohesive failure on both graphite and mica. Our
results suggest that there is little difference in the strength of
the relevant interfacial adhesion in the two nanocomposites within
the rubbery dynamic regime. Further, the bulk mechanical properties
of melt mixed PET/graphene and PET/clay nanocomposites were evaluated
by dynamic mechanical analysis. The glassy dynamic storage modulus
of the PET/clay nanocomposite was higher than that of PET/graphene,
correlating with the differences in interfacial adhesion probed by
AFM
Polyol-Assisted Vermiculite Dispersion in Polyurethane Nanocomposites
The largest use of polyurethane (PU)
is as closed cell rigid foams for thermal insulation. One problem
is loss of blowing gases, which leads to slow increase in thermal
conductivity. PU composites with plate-like nanofillers create a diffusion
barrier, reducing gas transport and slowing insulation aging. In this
research, a new in situ intercalative polymerization is described
to disperse vermiculite (VMT) in PU. When VMT was modified by cation
exchange with long-chain quaternary ammonium, the dispersion in methylene
diphenyl diisocyanate (MDI) was significantly improved. Dispersion
of clay in MDI was further improved by combining high intensity dispersive
mixing with a polyol-clay preblend (master-batch). The VMT dispersibility
was characterized using rheology, microscopy, and X-ray scattering/diffraction.
With the method of polyol-assisted VMT dispersion, electron microscopy
revealed extensive intercalation and exfoliation of clay particles.
In contrast, simple mixing of organoclay in MDI resulted in macroscopic
localization and poor distribution of clay particles in PU. The final
nanocomposites prepared by the master-batch method showed enhancement
of mechanical properties (85% increase in elastic modulus) and reduction
in permeability to CO<sub>2</sub>, as much as 40%, at a low clay concentration
of 3.3 wt %
Plasmonic–Photonic Interference Coupling in Submicrometer Amorphous TiO<sub>2</sub>–Ag Nanoarchitectures
In this study, we report the crystallinity
effects of submicrometer
titanium dioxide (TiO<sub>2</sub>) nanotube (TNT) incorporated with
silver (Ag) nanoparticles (NPs) on surface-enhanced Raman scattering
(SERS) sensitivity. Furthermore, we demonstrate the SERS behaviors
dependent on the plasmonic–photonic interference coupling (P-PIC)
in the TNT-AgNP nanoarchitectures. Amorphous TNTs (A-TNTs) are synthesized
through a two-step anodization on titanium (Ti) substrate, and crystalline
TNTs (C-TNTs) are then prepared by using thermal annealing process
at 500 °C in air. After thermally evaporating 20 nm thick Ag
on TNTs, we investigate SERS signals according to the crystallinity
and P-PIC on our TNT-AgNP nanostructures. (A-TNTs)-AgNP substrates
show dramatically enhanced SERS performance as compared to (C-TNTs)-AgNP
substrates. We attribute the high enhancement on (A-TNTs)-AgNP substrates
with electron confinement at the interface between A-TNTs and AgNPs
as due to the high interfacial barrier resistance caused by band edge
positions. Moreover, the TNT length variation in (A-TNTs)-AgNP nanostructures
results in different constructive or destructive interference patterns,
which in turn affects the P-PIC. Finally, we could understand the
significant dependency of SERS intensity on P-PIC in (A-TNTs)-AgNP
nanostructures. Our results thus might provide a suitable design for
a myriad of applications of enhanced EM on plasmonic-integrated devices