The surface of ice has been reported to be disordered at temperatures well below the bulk melting point. However, the precise nature of this disorder has been a topic of intense debate. Herein, we ...study the molecular properties of the surface of ice as a function of temperatures using heterodyne‐detected sum‐frequency generation spectroscopy. We observe that, down to 245 K, the spectral response of the surface of ice contains a component that is indistinguishable from supercooled liquid water.
Ice, ice, maybe: The molecular properties of the surface of ice have been studied in the temperature region 245–270 K using heterodyne‐detected sum‐frequency generation spectroscopy. Down to 245 K, the spectral response of the quasi‐liquid layer is indistinguishable from that of supercooled liquid water.
Abstract
Flexible low-pressure sensors ( <10 kPa) are required in areas as diverse as blood-pressure monitoring, human–computer interactions, robotics, and object detection. For applications, it is ...essential that these sensors combine flexibility, high sensitivity, robustness, and low production costs. Previous works involve surface micro-patterning, electronic amplification (OFET), and hydrogels. However, these solutions are limited as they involve complex processes, large bias voltages, large energy consumption, or are sensitive to evaporation. Here, we report a major advance to solve the challenge of scalable, efficient and robust e-skin. We present an unconventional capacitive sensor based on composite foam materials filled with conductive carbon black particles. Owing to the elastic buckling of the foam pores, the sensitivity exceeds 35 kPa
−1
for pressure <0.2 kPa. These performances are one order of magnitude higher than the ones previously reported. These materials are low-cost, easy to prepare, and display high capacitance values, which are easy to measure using low-cost electronics. These materials pave the road for the implementation of e-skin in commercialized applications.
Nanoscopic and microscopic water droplets and ice crystals embedded in liquid hydrophobic surroundings are key components of aerosols, rocks, oil fields and the human body. The chemical properties of ...such droplets critically depend on the interfacial structure of the water droplet. Here we report the surface structure of 200 nm-sized water droplets in mixtures of hydrophobic oils and surfactants as obtained from vibrational sum frequency scattering measurements. The interface of a water droplet shows significantly stronger hydrogen bonds than the air/water or hexane/water interface and previously reported planar liquid hydrophobic/water interfaces at room temperature. The observed spectral difference is similar to that of a planar air/water surface at a temperature that is ∼50 K lower. Supercooling the droplets to 263 K does not change the surface structure. Below the homogeneous ice nucleation temperature, a single vibrational mode is present with a similar mean hydrogen-bond strength as for a planar ice/air interface.
On the surface of water ice, a quasi-liquid layer (QLL) has been extensively reported at temperatures below its bulk melting point at 273 K. Approaching the bulk melting temperature from below, the ...thickness of the QLL is known to increase. To elucidate the precise temperature variation of the QLL, and its nature, we investigate the surface melting of hexagonal ice by combining noncontact, surface-specific vibrational sum frequency generation (SFG) spectroscopy and spectra calculated from molecular dynamics simulations. Using SFG, we probe the outermost water layers of distinct single crystalline ice faces at different temperatures. For the basal face, a stepwise, sudden weakening of the hydrogen-bonded structure of the outermost water layers occurs at 257 K. The spectral calculations from the molecular dynamics simulations reproduce the experimental findings; this allows us to interpret our experimental findings in terms of a stepwise change from one to two molten bilayers at the transition temperature.
Molecular Insight into the Slipperiness of Ice Weber, Bart; Nagata, Yuki; Ketzetzi, Stefania ...
The journal of physical chemistry letters,
06/2018, Letnik:
9, Številka:
11
Journal Article
Recenzirano
Odprti dostop
Measurements of the friction coefficient of steel-on-ice over a large temperature range reveal very high friction at low temperatures (−100 °C) and a steep decrease in the friction coefficient with ...increasing temperature. Very low friction is only found over the limited temperature range typical for ice skating. The strong decrease in the friction coefficient with increasing temperature exhibits Arrhenius behavior with an activation energy of E a ≈ 11.5 kJ mol–1. Remarkably, molecular dynamics simulations of the ice–air interface reveal a very similar activation energy for the mobility of surface molecules. Weakly hydrogen-bonded surface molecules diffuse over the surface in a rolling motion, their number and mobility increasing with increasing temperature. This correlation between macroscopic friction and microscopic molecular mobility indicates that slippery ice arises from the high mobility of its surface molecules, making the ice surface smooth and the shearing of the weakly bonded surface molecules easy.
The goal of this article is to discuss one of Paul Pintrich's more enduring legacies: the Motivated Strategies for Learning Questionnaire (MSLQ), an 81-item, self-report instrument consisting of 6 ...motivation subscales and 9 learning strategies scales. The MSLQ has proven to be a reliable and useful tool that can be adapted for a number of different purposes for researchers, instructors, and students. The MSLQ has been translated into multiple languages and has been used by hundreds of researchers and instructors throughout the world. This article reviews the history of the MSLQ and discusses how it has been used to (a) address the nature of motivation and use of learning strategies in different types of content areas and target populations; (b) help refine our theoretical understanding of motivational constructs, how they are distinct from one another, and what individual differences exist in self-regulated learning; and (c) evaluate the motivational and cognitive effects of different aspects of instruction.
We study the signatures of the OH stretch vibrations at the basal surface of ice using heterodyne-detected sum-frequency generation and molecular dynamics simulations. At 150 K, we observe seven ...distinct modes in the sum-frequency response, five of which have an analogue in the bulk, and two pure surface-specific modes at higher frequencies (∼3530 and ∼3700 cm–1). The band at ∼3530 cm–1 has not been reported previously. Using molecular dynamics simulations, we find that the ∼3530 cm–1 band contains contributions from OH stretch vibrations of both fully coordinated interfacial water molecules and water molecules with two donor and one acceptor hydrogen bond.
We study experimentally and theoretically the thickness of the coating obtained by pulling out a rod from a reservoir of yield-stress fluid. Opposite to Newtonian fluids, the coating thickness for a ...fluid of large enough yield stress is determined solely by the flow inside the reservoir and not by the flow inside the meniscus. The stress field inside the reservoir determines the thickness of the coating layer. The thickness is observed to increase nonlinearly with the sizes of the rod and of the reservoir. We develop a theoretical framework that describes this behavior and allows us to precisely predict the coating thickness.
We study the resonant interaction of the OH stretch vibrations of water molecules at the surfaces of liquid water and ice using heterodyne-detected sum-frequency generation (HD-SFG) spectroscopy. By ...studying different isotopic mixtures of H2O and D2O, we vary the strength of the interaction, and we monitor the resulting effect on the HD-SFG spectrum of the OH stretch vibrations. We observe that the near-resonant coupling effects are weaker at the surface than in the bulk, for both water and ice, indicating that for both phases of water the OH vibrations are less strongly delocalized at the surface than in the bulk.
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