171 research outputs found
Dynamics of Droplets Impacting on Aerogel, Liquid Infused, and Liquid-Like Solid Surfaces
Droplets impacting superhydrophobic surfaces have been
extensively
studied due to their compelling scientific insights and important
industrial applications. In these cases, the commonly reported impact
regime was that of complete rebound. This impact regime strongly depends
on the nature of the superhydrophobic surface. Here, we report the
dynamics of droplets impacting three hydrophobic slippery surfaces,
which have fundamental differences in normal liquid adhesion and lateral
static and kinetic liquid friction. For an air cushion-like (super)hydrophobic
solid surface (Aerogel) with low adhesion and low static and low kinetic
friction, complete rebound can start at a very low Weber (We) number (∼1). For slippery liquid-infused porous
(SLIP) surfaces with high adhesion and low static and low kinetic
friction, complete rebound only occurs at a much higher We number (>5). For a slippery omniphobic covalently attached liquid-like
(SOCAL) solid surface, with high adhesion and low static friction
similar to SLIPS but higher kinetic friction, complete rebound was
not observed, even for a We as high as 200. Furthermore,
the droplet ejection volume after impacting the Aerogel surface is
100% across the whole range of We numbers tested
compared to other surfaces. In contrast, droplet ejection for SLIPs
was only observed consistently when the We was above
5–10. For SOCAL, 100% (or near 100%) ejection volume was not
observed even at the highest We number tested here
(∼200). This suggests that droplets impacting our (super)hydrophobic
Aerogel and SLIPS lose less kinetic energy. These insights into the
differences between normal adhesion and lateral friction properties
can be used to inform the selection of surface properties to achieve
the most desirable droplet impact characteristics to fulfill a wide
range of applications, such as deicing, inkjet printing, and microelectronics
Observation of interlayer phonon modes in van der Waals heterostructures
We have investigated the vibrational properties of van der Waals
heterostructures of monolayer transition metal dichalcogenides (TMDs),
specifically MoS2/WSe2 and MoSe2/MoS2 heterobilayers as well as twisted MoS2
bilayers, by means of ultralow-frequency Raman spectroscopy. We discovered
Raman features (at 30 ~ 40 cm-1) that arise from the layer-breathing mode (LBM)
vibrations between the two incommensurate TMD monolayers in these structures.
The LBM Raman intensity correlates strongly with the suppression of
photoluminescence that arises from interlayer charge transfer. The LBM is
generated only in bilayer areas with direct layer-layer contact and atomically
clean interface. Its frequency also evolves systematically with the relative
orientation between of the two layers. Our research demonstrates that LBM can
serve as a sensitive probe to the interface environment and interlayer
interactions in van der Waals materials
Achieving Strong Chemical Interface and Superior Energy-Saving Capability at the Crosslinks of Rubber Composites Containing Graphene Oxide Using Thiol-Vinyl Click Chemistry
Rapidly developments in international transportation inevitably lead to an increase in the consumption of energy and resources. Minimizing the rolling resistance of tires in this scenario is a pressing challenge. To lower the rolling resistance of tires, enhancing the interaction between fillers and rubber molecules while improving the dispersion of fillers are required to reduce the internal mutual friction and viscous loss of rubber composites. In this study, graphene oxide (GO) was modified using γ-mercaptopropyltrimethoxysilane (MPTMS) with thiol groups. A modified GO/natural rubber (MGO/NR) masterbatch with a fine dispersion of MGO was then introduced into solution-polymerized styrene butadiene rubber (SSBR) to create an MGO/SiO2/SSBR composite. During the crosslinking process at high temperatures, a strong chemical interface interaction between the MGO and rubber molecules was formed by the thiol-vinyl click reaction. The MGO sheets also act as crosslinks to enhance the crosslinking network. The results showed that the rolling resistance of the MGO SiO2/SSBR composite was superior by 19.4% and the energy loss was reduced by 15.7% compared with that of the base SiO2/SSBR composite. Strikingly, the wear performance and wet skid resistance improved by 19% and 17.3%, respectively. These results showed a strong interface that not only improved rolling resistance performance but also contributed to balancing the “magic triangle” (the combination of wear resistance, fuel efficiency, and traction) properties of tires
Coupling and stacking order of ReS2 atomic layers revealed by ultralow-frequency Raman spectroscopy
We investigate the ultralow-frequency Raman response of atomically thin ReS2,
a special type of two-dimensional (2D) semiconductors with unique distorted 1T
structure. Bilayer and few-layer ReS2 exhibit rich Raman spectra at frequencies
below 50 cm-1, where a panoply of interlayer shear and breathing modes are
observed. The emergence of these interlayer phonon modes indicate that the ReS2
layers are coupled and stacked orderly, in contrast to the general belief that
the ReS2 layers are decoupled from one another. While the interlayer breathing
modes can be described by a linear chain model as in other 2D layered crystals,
the shear modes exhibit distinctive behavior due to the in-plane lattice
distortion. In particular, the two shear modes in bilayer ReS2 are
non-degenerate and well separated in the Raman spectrum, in contrast to the
doubly degenerate shear modes in other 2D materials. By carrying out
comprehensive first-principles calculations, we can account for the frequency
and Raman intensity of the interlayer modes, and determine the stacking order
in bilayer ReS2
Stacking-Dependent Interlayer Phonons in 3R and 2H MoS
We have investigated the interlayer shear and breathing phonon modes in
MoS with pure 3R and 2H stacking order by using polarization-dependent
ultralow-frequency Raman spectroscopy. We observe up to three shear branches
and four breathing branches in MoS with thickness from 2 to 13 layers.
The breathing modes show the same Raman activity behavior for both polytypes,
but the 2H breathing frequencies are consistently several wavenumbers higher
than the 3R breathing frequencies, signifying that 2H MoS has slightly
stronger interlayer lattice coupling than 3R MoS. In contrast, the
shear-mode Raman spectra are strikingly different for 2H and 3R MoS.
While the strongest shear mode corresponds to the highest-frequency branch in
the 2H structure, it corresponds to the lowest-frequency branch in the 3R
structure. Such distinct and complementary Raman spectra of the 3R and 2H
polytypes allow us to survey a broad range of shear modes in MoS, from
the highest to lowest branch. By combining the linear chain model, group
theory, effective bond polarizability model and first-principles calculations,
we can account for all the major observations in our experiment.Comment: 18 pages, 8 figures (supplemental material: 23 pages, 13 figures). 2D
Materials, Accepted Manuscript online 24 January 201
Slippery Liquid-Like Solid Surfaces with Promising Antibiofilm Performance in both Static and Flow Conditions
[Image: see text] Biofilms are central to some of the most urgent global challenges across diverse fields of application, from medicine to industries to the environment, and exert considerable economic and social impact. A fundamental assumption in anti-biofilms has been that the coating on a substrate surface is solid. The invention of slippery liquid-infused porous surfaces—a continuously wet lubricating coating retained on a solid surface by capillary forces—has led to this being challenged. However, in situations where flow occurs, shear stress may deplete the lubricant and affect the anti-biofilm performance. Here, we report on the use of slippery omniphobic covalently attached liquid (SOCAL) surfaces, which provide a surface coating with short (ca. 4 nm) non-cross-linked polydimethylsiloxane (PDMS) chains retaining liquid–surface properties, as an antibiofilm strategy stable under shear stress from flow. This surface reduced biofilm formation of the key biofilm-forming pathogens Staphylococcus epidermidis and Pseudomonas aeruginosa by three–four orders of magnitude compared to the widely used medical implant material PDMS after 7 days under static and dynamic culture conditions. Throughout the entire dynamic culture period of P. aeruginosa, SOCAL significantly outperformed a typical antibiofilm slippery surface [i.e., swollen PDMS in silicone oil (S-PDMS)]. We have revealed that significant oil loss occurred after 2–7 day flow for S-PDMS, which correlated to increased contact angle hysteresis (CAH), indicating a degradation of the slippery surface properties, and biofilm formation, while SOCAL has stable CAH and sustainable antibiofilm performance after 7 day flow. The significance of this correlation is to provide a useful easy-to-measure physical parameter as an indicator for long-term antibiofilm performance. This biofilm-resistant liquid-like solid surface offers a new antibiofilm strategy for applications in medical devices and other areas where biofilm development is problematic
Meat tenderness: advances in biology, biochemistry, molecular mechanisms and new technologies
Meat tenderness is an important quality trait critical to consumer acceptance, and determines satisfaction, repeat purchase and willingness-to-pay premium prices. Recent advances in tenderness research from a variety of perspectives are presented. Our understanding of molecular factors influencing tenderization are discussed in relation to glycolysis, calcium release, protease activation, apoptosis and heat shock proteins, the use of proteomic analysis for monitoring changes, proteomic biomarkers and oxidative/nitrosative stress. Each of these structural, metabolic and molecular determinants of meat tenderness are then discussed in greater detail in relation to animal variation, postmortem influences, and changes during cooking, with a focus on recent advances. Innovations in postmortem technologies and enzymes for meat tenderization are discussed including their potential commercial application. Continued success of the meat industry relies on ongoing advances in our understanding, and in industry innovation. The recent advances in fundamental and applied research on meat tenderness in relation to the various sectors of the supply chain will enable such innovation
Observation of Interlayer Phonon Modes in van der Waals Heterostructures
We have investigated the vibrational properties of van der Waals heterostructures of monolayer transition metal dichalcogenides (TMDs), specifically MoS2/WSe2 and MoSe2/MoS2 heterobilayers and twisted MoS2 bilayers, by means of ultralow-frequency Raman spectroscopy. We discovered Raman features (at 30–40 cm−1) that arise from the layer-breathing mode (LBM) vibration between the two incommensurate TMD monolayers in these structures. The LBM Raman intensity correlates strongly with the suppression of photoluminescence that arises from interlayer charge transfer. The LBM is generated only in bilayer areas with direct layer-layer contact and an atomically clean interface. Its frequency also evolves systematically with the relative orientation between the two layers. Our research demonstrates that the LBM can serve as a sensitive probe to the interface environment and interlayer interactions in van der Waals materials
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