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"Wenzel"
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Metternich : strategist and visionary
This is a major biography of Clemens von Metternich (1773-1859), perhaps the most important European politician of the first half of the nineteenth century. Metternich held the highest civilian posts in the Austrian Empire without interruption from 1809 to 1848, helped determine the shape of post-Napoleonic Europe, and established the system of international congresses (the Metternich system) that dominated international relations up to 1918 and set a precedent for the League of Nations and the United Nations. His influence on international affairs in the first half of the century was so profound that the period is sometimes called the Age of Metternich. He is usually considered a stubborn conservative and an enemy of liberalism and nationalism, which then went hand in hand. For many, he represents everything that the revolutionaries of 1848 opposed. In this biography, Wolfram Siemann argues that the conventional view of Metternich is wrong. He writes that Metternich idealized Britain's liberal constitution and aimed to make as much room as possible for liberalism and nationalism as was consistent with his overarching aim: the preservation of peace in Europe, a commitment arising from his horror at the death and destruction of the Revolutionary and Napoleonic Wars. Drawing on previously unopened archives belonging to the Metternich family, Siemann also presents in full his subject's active personal and social life. Metternich had many mistresses, one of them Napoleon's sister, and counted almost everybody with power in Europe as a friend or enemy.-- Provided by publisher.
Book
Spontaneous recovery of superhydrophobicity on nanotextured surfaces
Rough or textured hydrophobic surfaces are dubbed “superhydrophobic” due to their numerous desirable properties, such as water repellency and interfacial slip. Superhydrophobicity stems from an aversion of water for the hydrophobic surface texture, so that a water droplet in the superhydrophobic “Cassie state” contacts only the tips of the rough surface. However, superhydrophobicity is remarkably fragile and can break down due to the wetting of the surface texture to yield the “Wenzel state” under various conditions, such as elevated pressures or droplet impact. Moreover, due to large energetic barriers that impede the reverse transition (dewetting), this breakdown in superhydrophobicity is widely believed to be irreversible. Using molecular simulations in conjunction with enhanced sampling techniques, here we show that on surfaces with nanoscale texture, water density fluctuations can lead to a reduction in the free energetic barriers to dewetting by circumventing the classical dewetting pathways. In particular, the fluctuation-mediated dewetting pathway involves a number of transitions between distinct dewetted morphologies, with each transition lowering the resistance to dewetting. Importantly, an understanding of the mechanistic pathways to dewetting and their dependence on pressure allows us to augment the surface texture design, so that the barriers to dewetting are eliminated altogether and the Wenzel state becomes unstable at ambient conditions. Such robust surfaces, which defy classical expectations and can spontaneously recover their superhydrophobicity, could have widespread importance, from underwater operation to phase-change heat transfer applications.
Journal Article
O silêncio das colmeias: uma história da apicultura no Brasil (1970-2021)
Este artigo trata do tema da mortandade das abelhas no Brasil. O recorte temporal tem como parâmetros inicial e final, a experiência apícola da família Wenzel e o avanço do agronegócio na região Nordeste, respectivamente. A narrativa, construída a partir de fontes diversas (jornais, revistas, websites, mídias sociais, entrevistas), acompanha a migração dos Wenzel de São Paulo ao Piauí e ao Ceará, desvelada enquanto um projeto de fuga em relação a escalada de uso de venenos na região Sudeste, desde a década de 1970. A criação de abelhas e a produção de méis para o mercado nacional e internacional pelos Wenzel é analisada à luz dos paradoxos da ampliação do capital no campo que, por um lado, intensifica a agricultura capitalista monocultora, e, por outro lado, cria mecanismos de valoração por precificação de determinados produtos, como o mel orgânico. Por fim, é apresentado um estudo de caso com 38 apicultores no município do Tabuleiro do Norte, Estado do Ceará, que desvela como o uso de agrotóxicos pode ser letal para as abelhas, dado o desastre ambiental que promoveu naquele território.
Journal Article
Wetting Transition from Wenzel to Cassie States: Thermodynamic Analysis
Superhydrophobicity is closely linked to the chemical composition and geometric characteristics of surface roughness. Building on our structural studies on water and air–water interfaces, this work aims to elucidate the mechanism underlying the wetting transition from the Wenzel to the Cassie state on a hydrophobic surface. In the Wenzel state, the grooves are filled with water, meaning that the surface roughness becomes embedded in the liquid. To evaluate the effects of surface roughness on water structure, a wetting parameter (WRoughness) is proposed, which is closely related to the geometric characteristics of roughness, such as pillar size, width, and height. During the wetting transition from Wenzel to Cassie states, the critical wetting parameter (WRoughness,c) may be expected, which corresponds to the critical pillar size (ac), width (wc), and height (hc). The Cassie state is expected when the WRoughness is less than WRoughness,c (ac), decreasing width (hc). Additionally, molecular dynamic (MD) simulations are conducted to demonstrate the effects of surface roughness on superhydrophobicity.
Journal Article
Coexistence and transition between Cassie and Wenzel state on pillared hydrophobic surface
Water droplets on rugged hydrophobic surfaces typically exhibit one of the following two states: (i) the Wenzel state [Wenzel RN (1936) Ind Eng Chem 28:988-994] in which water droplets are in full contact with the rugged surface (referred as the wetted contact) or (ii) the Cassie state [Cassie, ABD, Baxter S (1944) Trans Faraday Soc 40:546-551] in which water droplets are in contact with peaks of the rugged surface as well as the \"air pockets\" trapped between surface grooves (the composite contact). Here, we show large-scale molecular dynamics simulation of transition between Wenzel state and Cassie state of water droplets on a periodic nanopillared hydrophobic surface. Physical conditions that can strongly affect the transition include the height of nanopillars, the spacing between pillars, the intrinsic contact angle, and the impinging velocity of water nanodroplet (\"raining\" simulation). There exists a critical pillar height beyond which water droplets on the pillared surface can be either in the Wenzel state or in the Cassie state, depending on their initial location. The free-energy barrier separating the Wenzel and Cassie state was computed on the basis of a statistical-mechanics method and kinetic raining simulation. The barrier ranges from a few tenths of kBT₀ (where kB is the Boltzmann constant, and T₀ is the ambient temperature) for a rugged surface at the critical pillar height to [almost equal to]8 kBT₀ for the surface with pillar height greater than the length scale of water droplets. For a highly rugged surface, the barrier from the Wenzel-to-Cassie state is much higher than from Cassie-to-Wenzel state. Hence, once a droplet is trapped deeply inside the grooves, it would be much harder to relocate on top of high pillars.
Journal Article
On a Norm Inequality for Three 2 × 2 Matrices with One Normal Factor
In this paper, we continue to investigate the norm inequality for three real matrices that was recently conjectured by L. László. We establish the validity of the conjecture for the case where n=2 and one of the matrices is normal.
Journal Article
The influence of Nusselt number on dropwise condensation heat transfer for a single droplet on inclined and grooved surfaces
Dropwise condensation (DWC) is a widely studied vapor–liquid phase-change process that has attracted significant research attention due to its exceptional energy transfer efficiency. Therefore, it is highly important to predict the heat transfer rate during DWC and the factors that affect it. This study presents a computational fluid dynamics (CFD) investigation on DWC heat transfer under diverse circumstances for a single droplet on inclined and rough surfaces with Wenzel structure. Drop’s shape simulation was done utilizing the Surface Evolver (SE) software and the governing equations were solved based on the finite volume method. Moreover, for different Nusselt numbers (
), the average heat flux was calculated by considering the effect of different inclination angles, contact angles, and saturation temperatures. Validation was performed by comparing the outcomes with the available data in the literature, and a satisfactory agreement was achieved. The study revealed that the average heat flux for a water droplet with the saturation temperature
= 313 K on an inclined surface with an inclination angle of
β
= 90° increases by 151.79% when the Nu is increased from 510 to 740. Similarly, for a droplet on a rough surface with a roughness index of
= 0.6, the increase in heat flux is 152%. Moreover, an increase in saturation temperature results in a higher heat flux for both inclined and rough surfaces. The augmentation follows a specific trend for each of the surfaces.
Journal Article
Dependency of Contact Angles on Three-Phase Contact Line: A Review
The wetted area of a sessile droplet on a practical substrate is limited by the three-phase contact line and characterized by contact angle, contact radius and drop height. Although, contact angles of droplets have been studied for more than two hundred years, there are still some unanswered questions. In the last two decades, it was experimentally proven that the advancing and receding contact angles, and the contact angle hysteresis of rough and chemically heterogeneous surfaces, are determined by interactions of the liquid and the solid at the three-phase contact line alone, and the interfacial area within the contact perimeter is irrelevant. However, confusion and misunderstanding still exist in this field regarding the relationship between contact angle and surface roughness and chemical heterogeneity. An extensive review was published on the debate for the dependence of apparent contact angles on drop contact area or the three-phase contact line in 2014. Following this old review, several new articles were published on the same subject. This article presents a review of the novel articles (mostly published after 2014 to present) on the dependency of contact angles on the three-phase contact line, after a short summary is given for this long-lasting debate. Recently, some improvements have been made; for example, a relationship of the apparent contact angle with the properties of the three-phase line was obtained by replacing the solid–vapor interfacial tension term, γSV, with a string tension term containing the edge energy, γSLV, and curvature of the triple contact line, km, terms. In addition, a novel Gibbsian thermodynamics composite system was developed for a liquid drop resting on a heterogeneous multiphase and also on a homogeneous rough solid substrate at equilibrium conditions, and this approach led to the same conclusions given above. Moreover, some publications on the line energy concept along the three-phase contact line, and on the “modified” Cassie equations were also examined in this review.
Journal Article
Dependence of Wenzel–Cassie Transition on Droplet Size: The Critical Water Droplet
In this work, molecular dynamics (MD) simulations are applied to investigate the dependence of the Wenzel–Cassie transition on water droplet size. During the Wenzel–Cassie transition, the critical water droplet and corresponding critical roughness may be expected, which are respectively described as the critical radius (RDroplet,c) and wetting parameter (WRoughness,c). From the work, RDroplet,c may be termed as the smallest droplet size at which the Cassie state is expected for the corresponding WRoughness,c. In combination with the structural study of water, it is due to the structural competition between interfacial and bulk water. Additionally, RDroplet,c may be dependent on the WRoughness,c. It is found that the RDroplet,c is influenced by the distribution and geometric characteristics of surface roughness. A denser distribution of roughness is expected to result in a lower RDroplet,c. Consequently, superhydrophobicity may be influenced by the characteristics of surface roughness and the size of the water droplet. The Cassie state is achieved when the wetting parameter of roughness is less than the WRoughness,c and the water droplet is larger than the RDroplet,c.
Journal Article
Molecular Simulation Study on the Wettability of a Surface Texturized with Hierarchical Pillars
By using molecular dynamics simulation, we investigate the wettability of a surface texturized with a periodic array of hierarchical pillars. By varying the height and spacing of the minor pillars on top of major pillars, we investigate the wetting transition from the Cassie–Baxter (CB) to Wenzel (WZ) states. We uncover the molecular structures and free energies of the transition and meta-stable states existing between the CB and WZ states. The relatively tall and dense minor pillars greatly enhance the hydrophobicity of a pillared surface, in that, the CB-to-WZ transition requires an increased activation energy and the contact angle of a water droplet on such a surface is significantly larger.
Journal Article