Universal Nature-Inspired Coatings for Preparing Noncharging Surfaces

Static charge generated by contact electrification on surfaces can lead to many undesirable consequences such as a reduction in the efficiency of manufacturing processes, damage to equipment, and explosions. However, it is extremely challenging to avoid contact electrification because it is ubiquitous: almost all types of materials charge on contact. Here, we coated materials with naturally occurring polydopamine (PDA) and tannic acid (TA) for preparing noncharging surfaces. Importantly, these coatings are very versatile and can be coated on a wide range of materials, including metals, inorganic materials, semiconductors, and polymers. Once coated, the amount of charge generated was found to reduce dramatically at different humidities. The reduction in charge may be due to the radical-scavenging property of PDA and TA. This simple general approach is ideal for coating the vast variety of materials that need to resist charging by contact electrification

Polarization State of Light Scattered from Quantum Plasmonic Dimer Antennas

Plasmonic antennas are able to concentrate and re-emit light in a controllable manner through strong coupling between metallic nanostructures. Only recently has it found that quantum mechanical effects can drastically change the coupling strength as the feature size approaches atomic scales. Here, we present a comprehensive experimental and theoretical study of the evolution of the resonance peak and its polarization state as the dimer–antenna gap narrows to subnanometer scale. We clearly can identify the classical plasmonic regime, a crossover regime where nonlocal screening plays an important role, and the quantum regime where a charge transfer plasmon appears due to interparticle electron tunneling. Moreover, as the gap decreases from tens of to a few nanometers, the bonding dipole mode tends to emit photons with increasing polarizability. When the gap narrows to quantum regime, a significant depolarization of the mode emission is observed due to the reduction of the charge density of coupled quantum plasmons. These results would be beneficial for the understanding of quantum effects on emitting-polarization of nanoantennas and the development of quantum-based photonic nanodevices

Ion association in lithium metaborate solution: a Raman and <i>ab initio</i> insight

<p>Ion association and hydration clusters in aqueous lithium borate solution are extremely important to understand some extraordinary properties of lithium borates. In the present work, polyborate distribution in aqueous LiBO₂ solution was investigated through Raman and thermodynamics equilibrium analysis. Geometry and stability of hydrated clusters LiB(OH)₄(H₂O)<i>_n</i> up to <i>n</i> = 8 were calculated at the B3LYP/aug-cc-pVDZ level. Three different types of ion association, namely, contact ion pairs (CIP), solvent-shared ion pairs (SIP) and solvent separated ion pairs (SSIP) were obtained; characteristics of all of these stable configurations were determined, and the most stable hydrated clusters were chosen. Then the mechanisms of ion aggregation and crystal nuclei formation in the LiB(OH)₄ solution were proposed. The tight four-hydrated sphere of Li⁺ makes it difficult for the dehydrated form of its first hydration sphere to from a CIP, which is the passible reason that lithium borate always has a large super-saturation degree.</p

Global Establishment Risk of Economically Important Fruit Fly Species (Tephritidae)

<div><p>The global invasion of Tephritidae (fruit flies) attracts a great deal of attention in the field of plant quarantine and invasion biology because of their economic importance. Predicting which one in hundreds of potential invasive fruit fly species is most likely to establish in a region presents a significant challenge, but can be facilitated using a self organising map (SOM), which is able to analyse species associations to rank large numbers of species simultaneously with an index of establishment. A global presence/absence dataset including 180 economically significant fruit fly species in 118 countries was analysed using a SOM. We compare and contrast ranked lists from six countries selected from each continent, and also show that those countries geographically close were clustered together by the SOM analysis because they have similar fruit fly assemblages. These closely clustered countries therefore represent greater threats to each other as sources of invasive fruit fly species. Finally, we indicate how this SOM method could be utilized as an initial screen to support prioritizing fruit fly species for further research into their potential to invade a region.</p></div

Anomalous Charging Behavior of Inorganic Materials

Surface charge on materials is important due to its wide range of consequences and applications in many industries (e.g., semiconductor). One important parameter needed for the design of devices and selection of materials is the polarity of charge of solid surfaces after the surfaces are charged by contact electrification. Currently, it is only known that one surface charges positively, whereas the other surface charges negatively after contact (i.e., in accordance to the law of conservation of charge). This manuscript describes a previously unreported anomalous charging behavior of a general class of materials: the inorganic materials. Both contacting inorganic materials charged either both positively (e.g., mica and NaCl) or both negatively (e.g., quartz and CaF₂). A close monitoring of the charge in real time showed that charge was conserved immediately after contact; however, an active interaction of the separated surfaces and the surrounding atmosphere unexpectedly changed the polarity of one surface rapidly (e.g., 1 s), thus resulting in both positively or both negatively charged surfaces. This anomalous charging behavior fundamentally changes our understanding of the design of devices related to contact electrification of inorganic materials and the triboelectric series

Solution Structure of Energy Stored System I: Aqua-B(OH)₄^–: A DFT, Car–Parrinello Molecular Dynamics, and Raman Study

A systematic study on the structure, stability, and Raman spectra of the metaborate anion hydrated clusters, B­(OH)₄^–(H₂O)_<i>n</i>, (<i>n</i> = 1–15) was carried out by DFT in both gaseous and aqueous phase at the B3LYP/aug-cc-pVDZ level; all of these stable configurations were described, and the most stable hydrated clusters were chosen. The hydrogen bonds in those hydrated clusters were described in three different items: symmetrical double hydrogen bonding (DHB), single hydrogen bonding (SHB), and interwater hydrogen bonding (WHB). The distance of SHB is shorter than that of DHB, and multiple SHBs are more stable than a single DHB. In small size clusters (<i>n</i> ≤ 5), a structure with more DHBs is more stable than other arrangements. With continued increase in size, more SHBs were found in the first hydration sphere: when <i>n</i> ≥ 9, only SHBs can be found, and when <i>n</i> ≥ 12, a full hydration structure is formed with 12 SHBs and a hydration number of 10–12. The Car–Parrinello molecular dynamics simulation shows that only the first hydration sphere can be found, and the hydration number of B­(OH)₄^– is 9.2 and the hydration distance is 3.68. The total symmetrical stretching vibration of B­(OH)₄^– in hydrated B­(OH)₄^–(H₂O)_<i>n</i> is blue shifted with increasing cluster size. After consideration of hydration, the calculated characteristic frequencies are in accord with the experiment characteristic frequency of B­(OH)₄^–

<i>Ab Initio</i> Investigation of the Microspecies and Energy in Hydrated Strontium Ion Clusters

<p>Quantum chemistry calculations were used to study the structure and energy of strontium (Sr) ion hydrated clusters [Sr(H₂O)₁₋₂₅]²⁺. The saturated hydration number of the first hydration layer of Sr²⁺ was 8, and the hydration distance was 2.58 Å. The second hydration layer had 1–9 hydration numbers, and the hydration distance was in the range of 4.4–4.6 Å. This work also developed the relationship between the thermodynamic data (average water binding energy <i>E_n</i> and successive water binding energy Δ<i>E_n,n</i>₋₁, etc.) of the aforementioned low-energy structure and the hydration structures. The first hydration layer was formed by the strong electrostatic interaction between Sr²⁺ and water molecules, and the decrease in Δ<i>E_n</i>_,<i>_n</i>₋₁ was relatively large. Hydrogen bonds were formed between water molecules of the second hydration layer and water molecules of the inner layer, and the decrease in Δ<i>E_n</i>_,<i>_n</i>₋₁ was relatively small. When one water molecule was added beyond the second hydration layer, Δ<i>E_n</i>_,<i>_n</i>₋₁ was close to the hydrogen bond energy 8.88 kcal/mol (37.1 kJ/mol) of dimer water molecule, indicating that there was very weak interaction between Sr²⁺ and the water molecules beyond the second hydration layer.</p

Microhydration of BH₄^–: Dihydrogen Bonds, Structure, Stability, and Raman Spectra

Hydridic-to-protonic interactions in unconventional dihydrogen bonding influence the structure, reactivity, and selectivity in solution and in the solid state. In this study, the structure, stability, and Raman spectra of BH₄^– hydrated clusters, [BH₄(H₂O)_<i>n</i>]⁻ (<i>n</i> = 1–8, 10, 12, 14, 16) are systematically investigated using density functional theory (DFT) at the wB97XD/6-311++g­(3df,3pd) basis set level. The successive microhydration process is described to illustrate in detail the changes in dihydrogen bonding with increasing hydration cluster size. The results of DFT calculations indicate that seven or eight water molecules hydrate BH₄^– with a total of 12 dihydrogen bonds in the tetrahedral edge or tetrahedral corner forms, and a maximum of six water molecules in the tetrahedral-edge form. Raman spectra of [BH₄(H₂O)_<i>n</i>]⁻ show a blue shift in the B–H stretching band due to hydration. Car–Parrinello molecular dynamics simulations verify strong BH₄^– water interactions. The hydration number of BH₄^– is 6.7, with a hydration B–O­(W) distance of 3.40 Å, and each hydrogen in BH₄^– bonds with 2.66 hydrogen atoms from water

Unique and Unusual Pattern Demonstrating the Crystal Growth through Bubble Formation

Crystal growth occurs in nature in the form of snow flakes, igneous rocks, stalactites, stalagmites, etc., which sometimes arrest the growth pattern. The crystal growth in the lab or industry during a deposition process is generally evaluated by in situ microscopy techniques or by arresting the reaction at various time intervals. However, capturing the total growth process from the formation of nuclei to macrostructure is not easy. Here, we show a spontaneous formation of an unusual patterned growth during galvanic displacement of both gold and silver on silicon, wherein systematic concentric rings of 50–100 μm in diameter were formed at discrete places. The most striking pattern arrested the complete growth process from nuclei that formed the innermost concentric circle, to the formation of various network structures and dendrites, each forming separate circular patterns. The pattern formation was attributed to the bubble growth during the galvanic displacement reaction. We also compared the growth pattern formed in the concentric rings to the actual crystal growth process during the galvanic displacement reaction by arresting the reaction at various time intervals and found that spontaneously formed concentric rings provided greater detailed crystal growth phenomena. Thus, we could say that by controlling the growth of the bubble, it is possible to visualize the complete crystal growth process in one step

Countries clustering based on fruit fly species assemblages.

<p>Map of world showing those countries that were allocated to the same neuron in a SOM analysis (same colour) and hence those countries that have the most similar fruit fly species assemblages.</p