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Pd/TiO <sub/>2</sub> -Photocatalyzed Self-Condensation of Primary Amines To Afford Secondary Amines at Ambient Temperature
摘要： Symmetric secondary amines were synthesized by the self-condensation of primary amines over a palladium-loaded titanium dioxide (Pd/TiO2) photocatalyst. The reactions a?orded a series of secondary amines in moderate to excellent isolated yields at ambient temperature (30 °C, in cyclopentyl methyl ether). Applicability for one-pot pharmaceutical synthesis was demonstrated by a photocatalytic reaction sequence of self-condensation of an amine followed by N-alkylation of the resulting secondary amine with an alcohol.
关键词： secondary amines,Pd/TiO2,self-condensation,primary amines,photocatalysis
更新于2025-09-23 15:21:21
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Dipolar Quantum Mixtures of Erbium and Dysprosium Atoms
摘要： We report on the first realization of heteronuclear dipolar quantum mixtures of highly magnetic erbium and dysprosium atoms. With a versatile experimental setup, we demonstrate binary Bose-Einstein condensation in five different Er-Dy isotope combinations, as well as one Er-Dy Bose-Fermi mixture. Finally, we present first studies of the interspecies interaction between the two species for one mixture.
关键词： erbium,dipolar quantum mixtures,Bose-Einstein condensation,interspecies interaction,dysprosium
更新于2025-09-23 15:21:21
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Wettability Control of Copper Surface Using Picosecond Laser for Enhancing Condensation Heat Transfer
摘要： One of the most important and widely visualized process taking place in nature is condensation. Superhydrophobic surfaces, which facilitates dropwise condensation has been the principal area of research in the last decade or so. Fabrication of superhydrophobic surface can be achieved by either surface modification using mechanical process, surface treatment like coating or by the combination of both. But, the major drawback of coating is its durability and vulnerability. So, in this work we have fabricated a robust surface by means of picosecond laser machining. Apart from being a simple process, this method has an advantage of cutting down the surface fabrication time by several hours as compared to other methods like one-step immersion, electro-deposition, top-down fabrication method, etc. In our work three different work specimens irradiated with different laser power were studied for its surface morphologies by scanning electron microscope (SEM) images and its wettability was measured using contact angle meter. It is found that the wettability of surface changes with different laser power and hence it is possible to control the wettability by adjusting the laser parameters. Condensation experiment was carried out on these different surfaces and its performance was compared with plain surface.
关键词： Wettability control,micro grooves,Condensation heat transfer,Contact angle,Picosecond laser
更新于2025-09-23 15:21:01
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Opportunities and challenges of interlayer exciton control and manipulation
摘要： Advances in van der Waals heterostructures allow the control of interlayer excitons by electrical and other means, promising exciting opportunities for high-temperature exciton condensation and valley–spin optoelectronics.
关键词： TMD bilayers,exciton condensation,van der Waals heterostructures,valley–spin optoelectronics,interlayer excitons
更新于2025-09-23 15:21:01
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Syntheses of Chalcone-Type Chlorophyll Derivatives Possessing a Bacteriochlorin, Chlorin, or Porphyrin <i>π</i> -System and Their Optical Properties
摘要： C3-(Trans-arylethenyl)carbonylated chlorophyll derivatives possessing a bacteriochlorin or chlorin π-system were synthesized by cross-aldol (Claisen-Schmidt) condensation of methyl pyrobacteriopheophorbide-a or 3-acetyl-3-devinyl-pyropheophorbide-a bearing the C3-acetyl group with p-(un)substituted benzaldehydes under basic conditions. The corresponding porphyrin-type chlorophyll derivatives were prepared by the oxidation (17,18-didehydrogenation) of the chlorin-type. Their Qy absorption and fluorescence emission maxima in dichloromethane correlated well with Hammett substituent constants of the p-substituents. Several electron-withdrawing p-substituents suppressed the emission due to photoinduced electron transfer quenching in a molecule. The substitution sensitivities for their maxima and fluorescence quantum yields decreased in the order of bacteriochlorin-, chlorin-, and porphyrin-type derivatives.
关键词： Chlorophyll derivatives,Optical properties,Bacteriochlorin,Cross-aldol condensation,Hammett substituent constants,Porphyrin,Chlorin
更新于2025-09-23 15:21:01
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A Facile Approach to the Synthesis of n-Type π-Conjugated Hyperbranched Polymers
摘要： A facile approach for the synthesis of an n-type π-conjugated hyperbranched polymer, namely hyperbranched polypyridinebenzene, is proposed based on the copolymerization of 1,3,5-tribromobenzene (BeBr3) and 2,5-dibromopyridine via chain-growth condensation polymerization catalyzed by Ni(dppp)Cl2. The use of BeBr3 as a branching unit simplifies the synthesis of n-type π-conjugated hyperbranched polymers, compared with a similar hyperbranched polymer prepared from 2,4,6-tribromopyridine (PyBr3) and 2,5-dibromopyridine requiring a lengthy synthetic route to give the starting material PyBr3. The results of UV-Vis spectroscopy and cyclic voltammetry suggest that our synthesized polymer retains its hyperbranched structure, which is beneficial in electrochemical doping.
关键词： Cross-coupling,Doping,Polypyridine,Chain-growth condensation
更新于2025-09-23 15:21:01
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Self-propelled water droplet movement on a laser-etched radial gradient copper surface
摘要： This paper reports the behavior of water droplets on a topography-based, radial gradient on a metallic surface. The radial gradient was designed to concentrate water in the center region through the spontaneous motion and coalescence of individual droplets on the gradient pattern. In this work, parallel microchannels having a fixed width (~25 μm) and depth (100 μm) but variable spacing were used to impart a net surface tension force to the droplet for actuation. The diameter of the radial gradient (i.e. circular test region) was approximately 18.9 mm (or, ~0.75 in.). The surfaces were fabricated using a 355 nm YVO4 laser system and then characterized using droplet injection (5–38 μL) and spray testing techniques. Injected droplets were observed to move spontaneously away from the hydrophobic outer ring region of the circle towards the hydrophilic center as designed by the gradient. Droplet travel distances as large as 4 mm were measured depending on the droplet volume and injection site location. In application, such a design could be useful for promoting droplet coalescence on a surface and subsequently removal by gravity through the formation of sufficiently large droplets from two or more otherwise small droplets.
关键词： Surface tension gradient,Microchannels,Condensation,Heat exchangers,Radial pattern,Laser etching,Water droplet
更新于2025-09-23 15:21:01
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Few trapped quantum dipoles: quantum versus classical structures
摘要： We analyze the ground state of a two-dimensional quantum system of a few strongly con?ned dipolar bosons. Dipoles arrange in different stable structures that depend on the tilting polarization angle and the anisotropy of the con?ning trap. To this end, we use the exact diffusion Monte Carlo method and the quantum results are compared with classical ones obtained by stochastic optimization using simulated annealing. We establish the stability domains for the different patterns and estimate the transition boundaries delimiting them. Our results show signi?cant differences between the classical and quantum regimes which are mainly due to the quantum kinetic energy.
关键词： dipolar systems,Bose–Einstein condensation,quantum Monte Carlo,few-body physics
更新于2025-09-23 15:21:01
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Gas-vapor Interplay in Plasmonic Bubble Shrinkage
摘要： The understanding of the shrinkage dynamics of plasmonic bubbles formed around metallic nanoparticles immersed in liquid and irradiated by a resonant light source is crucial for the usage of these bubbles in numerous applications. In this paper we experimentally show and theoretically explain that a plasmonic bubble during its shrinkage undergoes two different phases: first, a rapid partial bubble shrinkage governed by vapor condensation and, second, a slow diffusion-controlled bubble dissolution. The history of the bubble formation plays an important role in the shrinkage dynamics during the first phase, as it determines the gas-vapor ratio in the bubble composition. Higher laser powers lead to more vaporous bubbles, while longer pulses and higher dissolved air concentrations lead to more gaseous bubbles. The dynamics of the second phase barely depends on the history of bubble formation, i.e. laser power and pulse duration, but strongly on the dissolved air concentration, which defines the concentration gradient at the bubble interface. Finally, for the bubble dissolution in the second phase, with decreasing dissolved air concentration, we observe a gradual transition from a R(t) ∝ (t0 ? t)1/3 scaling law to a R(t) ∝ (t0 ? t)1/2 scaling law, where t0 is the lifetime of the bubble and theoretically explain this transition.
关键词： dissolved air concentration,laser power,pulse duration,plasmonic bubbles,vapor condensation,shrinkage dynamics,diffusion-controlled dissolution
更新于2025-09-23 15:19:57
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Transparent Metasurfaces Counteracting Fogging by Harnessing Sunlight
摘要： Surface fogging is a common phenomenon that can have significant and detrimental effects on surface transparency and visibility. It affects the performance in a wide range of applications including windows, windshields, electronic displays, cameras, mirrors, and eyewear. A host of ongoing research is aimed at combating this problem by understanding and developing stable and effective anti-fogging coatings that are capable of handling a wide range of environmental challenges 'passively' without consumption of electrical energy. Here we introduce an alternative approach employing sunlight to go beyond state-of-the-art techniques—such as superhydrophilic and superhydrophobic coatings— by rationally engineering solar absorbing metasurfaces that maintain transparency, while upon illumination, induce localized heating to significantly delay the onset of surface fogging or decrease defogging time. For the same environmental conditions, we demonstrate that our metasurfaces are able to reduce defogging time by up to four-fold and under supersaturated conditions inhibit the nucleation of condensate outperforming conventional state-of-the-art approaches in terms of visibility retention. Our research illustrates a durable and environmentally sustainable approach to passive anti-fogging and defogging for transparent surfaces. This work opens up the opportunity for large-scale manufacturing that can be applied to a range of materials, including polymers and other flexible substrates.
关键词： renewable energy,condensation,defogging,anti-fogging,metasurface
更新于2025-09-19 17:15:36