The Quasi-Liquid Layer on ice observed with NEXAFS

<p><strong>The Quasi-Liquid Layer on ice observed with NEXAFS</strong></p><p><em>Gabathuler, Y. Manoharan, H. Yang, A. Boucly, A. Luca, M. Ammann, T. Bartels-Rausch</em></p><p>Paul Scherrer Institute, Villigen, Switzerland</p><p> </p><p> </p><p>As temperature approaches the melting point of ice from below, the hydrogen-bonding network at the air – ice interface evolves from a well-defined hexagonal structure towards more randomly spatialized interactions. The general agreement is that a Quasi-Liquid-Layer (QLL) exists at the surface of the ice, and reports on the thickness of this disordered interfacial layer range from 2 nm to 25 nm at 271 K, depending on the probing technique (atomic force microscopy (AFM), ellipsometry, optical reflectivity, sum-frequency generation (SFG)) [1]. These large differences partly arise from the fact that the different techniques are probing different properties of the interface, and the delicate calibration into the thickness of the QLL contributes greatly to the uncertainty.</p><p> </p><p>We investigate the QLL using Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy, as Bluhm and his group did in 2002 [2]. The technique probes Auger electrons emitted upon X-ray absorption, thus, NEXAFS becomes inherently sensitive to the upper few nm of the air-ice interfacial region. This work focuses on the probing depth associated with this method and proposes a comprehensive treatment of the data, to help resolve the discrepancy of current thickness data. The importance of the QLL’s thickness comes from its contribution to environmental science as a reservoir for chemical impurities and as a host of chemical reactions with an impact on atmospheric and cryospheric composition.</p><p> </p><p>We will present a first data set of NEXAFS from neat ice between – 40 °C and 0°C acquired at the ISS endstation at the Swiss Light Source of the Paul Scherrer Institute. Results including error bars will be compared to earlier studies. The preliminary analysis suggests that the interfacial disorder seems to be less pronounced than reported in many earlier studies, very much in agreement with recent SFG [3] and AFM data [4].</p><p> </p><p> </p><p> </p><p>Literature References:</p><p> </p><p> </p><p>Acknowledgment:</p><p>We thank A. Laso for technical help, SNF for funding (grant 178962)</p><p> </p>

The cooperative effect of the sorption of volatile molecules into metal–oxide frameworks as a function of the dielectric constant

Iso-polyoxomolybdates as molecular separation units: The formation of quasi-liquid layer as driven factor to govern the sorption of volatile molecules through the dielectric constant into the giant POMs.

Machine Learning Based Prediction of Nanoscale Ice Adhesion on Rough Surfaces

It is widely recognized that surface roughness plays an important role in ice adhesion strength, although the correlation between the two is far from understood. In this paper, two approaches, molecular dynamics (MD) simulations and machine learning (ML), were utilized to study the nanoscale intrinsic ice adhesion strength on rough surfaces. A systematic algorithm for making random rough surfaces was developed and the surfaces were tested for their ice adhesion strength, with varying interatomic potentials. Using MD simulations, the intrinsic ice adhesion strength was found to be significantly lower on rougher surfaces, which was attributed to the lubricating effect of a thin quasi-liquid layer. An increase in the substrate–ice interatomic potential increased the thickness of the quasi-liquid layer on rough surfaces. Two different ML algorithms, regression and classification, were trained using the results from the MD simulations, with support vector machines (SVM) emerging as the best for classifying. The ML approach showed an encouraging prediction accuracy, and for the first time shed light on using ML for anti-icing surface design. The findings provide a better understanding of the role of nanoscale roughness in intrinsic ice adhesion and suggest that ML can be a powerful tool in finding materials with a low ice adhesion strength.

Contact Melting of Metals Explained via the Theory of Quasi-Liquid Layer

It has been shown that the contact melting rate for metals is determined by the fact that at least one of them has a quasi-liquid layer on the surface. As a result, the diffusion of metal atoms occurs in the liquid phase, and not in the solid phase, which determines the characteristic contact melting time (seconds and minutes).

Plasmon-Enhanced Photothermal and Optomechanical Deformations of a Gold Nanoparticle

Plasmon-enhanced photothermal and optomechanical effects on deforming and reshaping a gold nanoparticle (NP) are studied theoretically. A previous paper (Wang and Ding, ACS Nano 13, 32–37, 2019) has shown that a spherical gold nanoparticle (NP) irradiated by a tightly focused laser beam can be deformed into an elongated nanorod (NR) and even chopped in half (a dimer). The mechanism is supposed to be caused by photothermal heating for softening NP associated with optical traction for follow-up deformation. In this paper, our study focuses on deformation induced by Maxwell’s stress provided by a linearly polarized Gaussian beam upon the surface of a thermal-softened NP/NR. We use an elastic model to numerically calculate deformation according to optical traction and a viscoelastic model to theoretically estimate the following creep (elongation) as temperature nears the melting point. Our results indicate that a stretching traction at the two ends of the NP/NR causes elongation and a pinching traction at the middle causes a dent. Hence, a bigger NP can be elongated and then cut into two pieces (a dimer) at the dent due to the optomechanical effect. As the continuous heating process induces premelting of NPs, a quasi-liquid layer is formed first and then an outer liquid layer is induced due to reduction of surface energy, which was predicted by previous works of molecular dynamics simulation. Subsequently, we use the Young–Laplace model to investigate the surface tension effect on the following deformation. This study may provide an insight into utilizing the photothermal effect associated with optomechanical manipulation to tailor gold nanostructures.

Is water ice an efficient facilitator for dust coagulation?

ABSTRACT Beyond the snow line of protoplanetary discs and inside the dense core of molecular clouds, the temperature of gas is low enough for water vapour to condense into amorphous ices on the surface of pre-existing refractory dust particles. Recent numerical simulations and laboratory experiments suggest that condensation of the vapour promotes dust coagulation in such a cold region. However, in the numerical simulations, cohesion of refractory materials is often underestimated, while in the laboratory experiments, water vapour collides with surfaces at more frequent intervals compared to the real conditions. Therefore, to re-examine the role of water ice in dust coagulation, we carry out systematic investigation of available data on coagulation of water-ice particles by making full use of appropriate theories in contact mechanics and tribology. We find that the majority of experimental data are reasonably well explained by lubrication theories, owing to the presence of a quasi-liquid layer (QLL). Only exceptions are the results of dynamic collisions between particles at low temperatures, which are, instead, consistent with the JKR theory, because QLLs are too thin to dissipate their kinetic energies. By considering the vacuum conditions in protoplanetary discs and molecular clouds, the formation of amorphous water ice on the surface of refractory particles does not necessarily aid their collisional growth as currently expected. While crystallization of water ice around but outside the snow line eases coagulation of ice-coated particles, sublimation of water ice inside the snow line is deemed to facilitate coagulation of bare refractory particles.

Water and Ice Adhesion to Solid Surfaces: Common and Specific, the Impact of Temperature and Surface Wettability

Ice adhesion plays a crucial role in the performance of materials under outdoor conditions, where the mitigation of snow and ice accumulation or spontaneous shedding of solid water precipitations are highly desirable. In this brief review we compare the adhesion of water and ice to different surfaces and consider the mechanisms of ice adhesion to solids basing on the surface forces analysis. The role of a premelted or quasi-liquid layer (QLL) in the ice adhesion is discussed with the emphasis on superhydrophobic surfaces, and the temperature dependence of ice adhesion strength is considered with an account of QLL. We also very briefly mention some recent methods for the measurement of ice adhesion strength to the icephobic engineering materials outlining the problems which remain to be experimentally solved.

Solvation and Stabilization of Single Strand RNA at the Air/ice Interface Support a Primordial RNA World on Ice

<div>Outstanding questions about the RNA world hypothesis for the emergence of life</div><div>on Earth concern the stability and self-replication of prebiotic aqueous RNA.</div><div>Recent experimental work has suggested that solid substrates and low</div><div>temperatures could help resolve these issues. Here, we use classical molecular</div><div>dynamics simulations to explore the possibility that the substrate is ice itself. We</div><div>find that at -20 C, a quasi-liquid layer at the air/ice interface solvates a short (8-</div><div>nucleotide) RNA strand such that phosphate groups tend to anchor to specific</div><div>points of the underlying crystal lattice, lengthening the strand. Hydrophobic bases,</div><div>meanwhile, tend to migrate to the air/ice interface. Further, contacts between</div><div>solvent water and ribose 2-OH’ groups are found to occur less frequently for RNA</div><div>on ice than for aqueous RNA at the same temperature; this reduces the likelihood</div><div>of deprotonation of the 2-OH’ and its subsequent nucleophilic attack on the</div><div>phosphate diester. The implied enhanced resistance to hydrolysis, in turn, could</div><div>increase opportunities for polymerization and self-copying. These findings thus</div><div>offer the possibility of a role for an ancient RNA world on ice distinct from that</div><div>considered in extant elaborations of the RNA world hypothesis. This work is, to the</div><div>best of our knowledge, the first molecular dynamics study of RNA on ice</div>

Solvation and Stabilization of Single Strand RNA at the Air/ice Interface Support a Primordial RNA World on Ice

<div>Outstanding questions about the RNA world hypothesis for the emergence of life</div><div>on Earth concern the stability and self-replication of prebiotic aqueous RNA.</div><div>Recent experimental work has suggested that solid substrates and low</div><div>temperatures could help resolve these issues. Here, we use classical molecular</div><div>dynamics simulations to explore the possibility that the substrate is ice itself. We</div><div>find that at -20 C, a quasi-liquid layer at the air/ice interface solvates a short (8-</div><div>nucleotide) RNA strand such that phosphate groups tend to anchor to specific</div><div>points of the underlying crystal lattice, lengthening the strand. Hydrophobic bases,</div><div>meanwhile, tend to migrate to the air/ice interface. Further, contacts between</div><div>solvent water and ribose 2-OH’ groups are found to occur less frequently for RNA</div><div>on ice than for aqueous RNA at the same temperature; this reduces the likelihood</div><div>of deprotonation of the 2-OH’ and its subsequent nucleophilic attack on the</div><div>phosphate diester. The implied enhanced resistance to hydrolysis, in turn, could</div><div>increase opportunities for polymerization and self-copying. These findings thus</div><div>offer the possibility of a role for an ancient RNA world on ice distinct from that</div><div>considered in extant elaborations of the RNA world hypothesis. This work is, to the</div><div>best of our knowledge, the first molecular dynamics study of RNA on ice</div>