The dynamics of individual ring polymers in a shear flow is studied by a hybrid mesoscale simulation approach. New insight into the dynamics of ring polymers is provided: ring polymers exhibit both tumbling and tank-treading motions. A novel angle autocorrelation function is proposed to analyze the tank-treading motion that usually coexists with tumbling and may be applied to other highly deformable soft objects such as vesicles. The shear dependence of the average gyration tensor, the orientation angle, the tumbling and the tank-treading frequencies is determined quantitatively. The simulations also reveal that the existence of the tank-treading motion apparently increases the intrinsic viscosity of ring polymers under shear flow.
SnO2 nanosheets
with abundant vacancies (designated
as SnO2–x
) have been successfully
prepared by annealing SnSe nanosheets in Argon. The transmission electron
microscopy results of the prepared SnO2 nanosheets indicated
that high-density SnO2–x
nanoplates
with the size of 5–10 nm were distributed on the surface of
amorphous carbon. After annealing, the acquired SnO2–x
/amorphous carbon retained the square morphology.
The stoichiometric ratio of Sn/O = 1:1.55 confirmed that oxygen vacancies
were abundant in SnO2 nanosheets. The prepared SnO2–x
exhibited excellent performance
of sensing NO2 at room temperature. The response of the
SnO2–x
-based sensor to 5 ppm NO2 was determined to be 16 with the response time and recovery
time of 331 and 1057 s, respectively, which is superior to those of
most reported room-temperature NO2 sensors based on SnO2 and other materials. When the humidity varied from 30 to
40%, ΔR/R was 0.025. The ultrafast
humidity response (52 ms) and recovery (140 ms) are competitive compared
with other state-of-art humidity sensors. According to the mechanistic
study, the excellent sensing performance of SnO2–x
is attributed to its special structure.
Long-wavelength infrared (LWIR) photodetection is important for heatseeking technologies, such as thermal imaging, all-weather surveillance, and missile guidance. Among various detection techniques, photothermoelectric (PTE) detectors are promising in that they can realize ultra-broadband photodetection at room temperature without an external power supply. However, their performance in terms of speed, responsivity, and noise level in the LWIR regime still needs further improvement. Here, we demonstrated a high-performance PTE photodetector based on low-symmetry palladium selenide (PdSe 2 ) with asymmetric van der Waals contacts. The temperature gradient induced by asymmetric van der Waals contacts even under global illumination drives carrier diffusion to produce a photovoltage via the PTE effect. A responsivity of over 13 V/W, a response time of ∼50 μs, and a noise equivalent power of less than 7 nW/Hz 1/2 are obtained in the 4.6−10.5 μm regime at room temperature. Furthermore, due to the anisotropic absorption of PdSe 2 , the detector exhibits a linear polarization angle sensitive response with an anisotropy ratio of 2.06 at 4.6 μm and 1.21 at 10.5 μm, respectively. Our proposed device architecture provides an alternative strategy to design high-performance photodetectors in the LWIR regime by utilizing van der Waals layered materials.
How polymers with
different architectures respond to shear stress
is a key issue to develop a fundamental understanding of their dynamical
behaviors. We investigate the conformation, orientation, dynamics,
and rheology of individual star polymers in a simple shear flow by
multiparticle collision dynamics integrated with molecular dynamics
simulations. Our studies reveal that star polymers present a linear
transformation from tumbling to tank-treading-like motions as the
number of arms increases. In the transformation region, the flow-induced
deformation, orientation, frequency of motions, and rheological properties
show universal scaling relationships against the reduced Weissenberg
number, independent of the number and the length of arms. Further,
we make a comprehensive comparison on the flow-induced behaviors between
linear, ring, and star polymers. The results indicate that distinct
from linear polymers, star and ring polymers present weaker deformation,
orientation change, and shear thinning, either contributed by a dense
center or without ends.
Individual semiflexible ring polymers
in a steady shear flow are
studied by the multiparticle collision dynamics method combined with
molecular dynamics simulations. We report the effects of chain stiffness
on the conformational, dynamical, and rheological properties of ring
polymers. When the Weissenberg numbers are smaller than unity, the
behavior of semiflexible ring polymers is consistent with that of
flexible ones. For larger Weissenberg numbers, the effects of chain
stiffness are observed. We find that the radius of gyration tensor
elements, the orientation resistance parameter, and the alignment
distribution functions show strong stiffness dependences. The scaling
behavior of tumbling motion corresponding to large conformational
changes is found independent of chain stiffness, while the scaling
behavior of tank-treading motion corresponding to the motion of monomers
moving along the contour of the chain exhibits a chain stiffness dependence
in the crossover regime from a flexible to a rigid ring polymer. Chain
rigidities are found to have negligible effects on the polymer shear
viscosity. The simulations reveal the similarities and differences
in the nonequilibrium behavior of flexible and semiflexible ring polymers.
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