Mesoscopic Space Research Articles

Reactant enrichment in yolk-shell structured Pd/TiN nanoreactors for boosting electrocatalytic hydrodechlorination performance

Enhancing the enrichment behavior of low-concentration chlorinated organic pollutants remains a significant challenge in electrocatalytic hydrodechlorination (EHDC) technology. Metal-loaded hollow nanoarchitecture has emerged as a promising nanoreactor to improve reaction enrichment behavior because of its tailorable microenvironments and electronic properties. Herein, a structural engineering strategy is developed to synthesize yolk-shell structured TiN spheres supported Pd nanoreactors (Pd/YS-TiN) with confined mesoscopic spaces. Characterization by multiple techniques reveals that the yolk-shell structure of YS-TiN, with high specific surface area (139.0 m2/g) and appropriately mesoporosity (6.9 nm), exposes numerous Pd nanoparticles (∼4.0 nm) on outer/inner surface of the shell and yolk-core solid sphere, ensuring an efficient utilization of active sites for enhancing the 2,4-DCP detoxification. Consequently, the structurally optimized Pd/YS-TiN nanoreactor consistently displays maximum reaction kinetics, dechlorination degree, faradaic current density, H* utilization and product selectivity, surpassing hollow TiN-supported Pd and Pd/C catalysts. The super EHDC performance of 91.8 % 2,4-DCP conversion, a specific activity of 1.68 min−1 molPd−1, and a mass activity of 6.06 min−1 gPd−1 is obtained at −0.85 V and 180 min, outperforming most reported catalysts. Combining experimental and density functional theory results, the exceptional reaction enrichment behavior of Pd/YS-TiN originates from (1) alleviating the overstrong adsorption of product phenol through strong metal-support interactions and (2) enhancing mass transport efficiency facilitated by the local concentration gradient and mesoporous shell. This study elucidates how metal-support interactions and mass transport synergistically enhance reaction enrichment behavior, showcasing potential benefits in environmental remediation applications.

(Invited) Gravitational Level Effects on Electrochemical Interfacial Phenomena

Electrochemical copper refining technology invented in Niagara area made a great progress over more than 100 years through better understanding of natural convection phenomena. Ionic mass-transfer rate enhanced by natural convection developing along 1m high vertical electrode surfaces has been unconsciously utilized by trial-and-error method. As the local electrolyte composition is partly stratified in an electrolytic cell (roughly 5m long x 1.3m wide x 1.3m depth). The industrial electrolytic tank house is composed of about 1000 cells through which the electrolyte is continuously supplied. Thus, the electrolyte circulation is a key technology in industrial copper refining processes as well as appropriate selection of effective additive and stable sedimentation of anode slime containing precious metals on the electrolytic tank bottom.On the other hand, Cu nanowire arrays were electrodeposited potentiostatically with PC filter template in two kinds of electrolytic cell configurations: cathode over anode (C/A) and anode over cathode (A/C). The effect of gravitational level on the coupling phenomena between the morphological variation and the ionic mass transfer rate in nanosized pores(a mesoscopic scale of a fewμm high and 30nm in diameter) was also found. Hitherto, the coupling phenomena accompanied with the electrochemical interfacial reactions confined in such a mesoscopic space has not been studies in spite of the great technological interest for the production of micro- or meso-scale fabrication techniques encountered in microelectronics and energy conversion & storage technology field. The initial stage including nucleation and growth process during electrochemical phase transformation reactions must be at first focused to profoundly comprehend the present subject in order to reasonably design such an advanced device technology.Fundamental aspects in electrochemical processes in microgravity environments have not been frequently reported. However, Artemis projects may provide the large opportunities on the energy storage and power generation, as well as materials processing. The effects of gravitational level and magnetic field gradient on the electrochemical interfacial phenomena should be understood. The drop tower facility surely offers the appropriate & “unique” experimental opportunities to propose such research program in the future space engineering fields. Electrocrystallization of metals is selected as a good subject for starting direction of research. Its reaction mechanism is relatively simple, the deposition rate can be easily varied by changing the current density or potential, and a smooth copper film is deposited so long as it is not too thick.By the way, the damascene process has been introduced to copper wiring process in ULSI field by IBM almost 25 years ago. It is important to control the nucleation and crystal growth in the initial stages of electrodeposition process. For this purpose, many effects of additive have been intensively examined. However, few quantitative examinations have been reported on the coupling phenomena of ionic mass transfer and nucleation and crystal growth. In the present work, we introduce various gravitational levels as new parameters into the nonequilibrium electrochemical processing in order to create or tailor the unique physical properties in nano space field. It is fruitful in terms of physicochemical hydrodynamics that the experiments are done under various gravitational levels. In fact, it has been confirmed that the gravitational levels as well as the magnetic field introduce the intensified effects from that under 1 G normal environment. Here is a report to analyze the effect of gravitational level on the initial stages of Cu electrodeposition on TaN or TiN substrate.

Reactant enrichment in hollow void of Pt NPs@MnOx nanoreactors for boosting hydrogenation performance.

In confined mesoscopic spaces, the unraveling of a catalytic mechanism with complex mass transfer and adsorption processes such as reactant enrichment is a great challenge. In this study, a hollow nanoarchitecture of MnOx-encapsulated Pt nanoparticles was designed as a nanoreactor to investigate the reactant enrichment in a mesoscopic hollow void. By employing advanced characterization techniques, we found that the reactant-enrichment behavior is derived from directional diffusion of the reactant driven through the local concentration gradient and this increased the amount of reactant. Combining experimental results with density functional theory calculations, the superior cinnamyl alcohol (COL) selectivity originates from the selective adsorption of cinnamaldehyde (CAL) and the rapid formation and desorption of COL in the MnOx shell. The superb performance of 95% CAL conversion and 95% COL selectivity is obtained at only 0.5MPa H2 and 40min. Our findings showcase that a rationally designed nanoreactor could boost catalytic performance in chemoselective hydrogenation, which can be of great aid and potential in various application scenarios.

On the description of the microdomains within carbon fiber precursory mesophase pitch: a mesoscopic continuum approach

The present paper proposes a mesoscopic continuum approach in order to describe the behavior of microdomains within carbon fiber precursory mesophase pitch. The microdomains are assumed to have an orientation, which is determined by the average orientation of the particles that form it. On the mesoscopic space, balance equations for the microdomains are presented. Evolution equations for the density and for the orientation of the crystalline microdomains are proposed. In order to determine the temporal variation of the microdomain density, it was deduced a quite simple relation between mass production, critical density of microdomains and a mesoscopic operator acting on the orientation distribution function. As presented in the present work, the mass production can be determined by the crystallization kinetics theory via the steady-state nucleation rate. Specific forms for the mesoscopic operator are proposed in this work, although they may be extended to other models that describe oriented microstructures. There are not yet enough experimental data to test the mesoscopic model deduced here, but in turn, it is presented as a new tool for experimental studies, since it can estimate the time rate of microdomain property changes. Possible extensions of this model could be applied to describe mechanical and rheological properties of carbon fibers.

Reconstruction of mesostructural material twin models of engineering textiles based on Micro-CT Aided Geometric Modeling

Engineering textiles are used as fibrous reinforcements in high performance polymer composites. The mechanical properties of composite materials depend on their dual-scale porous structure: long and elongated microscopic open spaces (micropores) appear between the filaments of fiber tows, and up to two orders of magnitude larger mesoscopic spaces (mesopores) exist between yarns. Because of the complex structure of composites, it is difficult to establish a connection between fiber architecture and mechanical behavior. To achieve this goal, X-ray microtomography (Micro-CT) can be used to provide detailed information on the geometric mesostructure of continuous fiber composites. The objective of this paper is to present a new approach based on “Micro-CT Aided Geometric Modeling” (Micro-CT AGM) to construct detailed geometric models of engineering textiles from Micro-CT three-dimensional (3D) images. The obtained geometric models are called “material twins” because of three distinctive features: (1) they are representative of the material variability; (2) their accuracy can be evaluated; and (3) they can be used to carry out computer simulations of mechanical behavior. This new method is applied to two industrial reinforcements: a 2D plain woven fabric and a 3D orthogonal glass textile. By introducing a new multiple factor morphological accuracy criterion, the quality of the “material twin” reconstruction can be compared to models obtained by standard image processing techniques or textile modeling software.

Mesoscopic continuum thermodynamics for mixtures of particles with orientation

The aim of the present paper is a continuum theoretical framework for mixtures of different chemical components, including the possibility of chemical reactions. The molecules are assumed to have an orientational degree of freedom, i.e. they are needle-shaped or planar. In the first case the microscopic director is the orientation of the particle long axis, in the second case it is the unit vector normal to the disc. This orientation is introduced as an additional variable in the domain of the field quantities. On this enlarged domain, the mesoscopic space, balance equations are derived. Compared to usual continuum theory, additional fluxes in orientation space occur. These are constitutive functions, like internal energy, heat flux and stress tensor. The restrictions on constitutive functions imposed by the second law of thermodynamics are derived by the method of Liu. Therefore, this new approach is very promising, since microscopic features of the particles, discarded in traditional continuous thermodynamics, become now an important part in the understanding of chemical systems. In addition, the results presented here can be extended to the study of other complex materials such as alloys, ferrofluids, carbon fibers, etc.

New Phonon Dynamics in a Diamond Crystal during Post-Annealing

A new mesoscopic response in a crystal during post-annealing (PA) after ion implantation has been discovered. PA is an indispensable procedure for activating the implanted dopant center by retrieving the lost crystallinity of the host crystal, which usually elapses over periods longer than a few milliseconds. By using an empirical molecular-dynamics simulation, we examined what actually happened during extended PA for up to one nanosecond in case of sub-keV N2 beam implantation into bulk diamond at room temperature with annealing at 1000 K. While observing the changes in the long-range-order (LRO) parameter, a notable phase transition from the crystalline to the amorphous state (CA transition) occurred synergistically at approximately a few picoseconds (ps). After the CA transition, PA was initiated. A few tens of ps later, a sequence of restoration spikes was observed in LRO parameter with a regular time interval of 70–80 ps. Each sharp peak showed the spontaneous restoration of “amorphous -> crystal -> amorphous” transitions. This process may trigger a “critical state” that occurs during the slow and steady recovery of the lost crystallinity in the early stages of PA. It was found that annealing not only enhances the vibration amplitude of the individual atoms in the bulk but also causes phonon-assisted restoration in a mesoscopic space.

Emergence of the Coherent Structure of Liquid Water

We examine in some detail the interaction of water molecules with the radiative electromagnetic field and find the existence of phase transitions from the vapor phase to a condensed phase where all molecules oscillate in unison, in tune with a self-trapped electromagnetic field within extended mesoscopic space regions (Coherence Domains). The properties of such a condensed phase are examined and found to be compatible with the phenomenological properties of liquid water. In particular, the observed value of critical density is calculated with good accuracy.

Cavities in a visco‐plastic material: A mesoscopic concept

AbstractIn the present work we investigate the temporal development of arbitrarily distributed voids in a visco‐plastic material under different loading regimes. A mesoscopic continuum model is used in order to take the microstructure of the material into account. In particular, we introduce a mesoscopic space representing an extension of the space‐time domain of the continuum mechanical fields. This extended domain requires a reformulation of the classical balance equations as well as the consideration of additional constitutive quantities. Furthermore a mesoscopic distribution function can be introduced which follows an own balance. Assuming a special model of porous composites, the spherical shell model, all required steps are elaborated in order to describe load‐induced void‐growth in a metal‐like matrix. We conclude with some exemplary results which show astonishing similarities with co‐called LSW‐theories. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Sketch of the mesoscopic description of nematic liquid crystals

Liquid crystals are considered in the framework of the mesoscopic description. This mesoscopic approach introduces a more detailed description of the microstructure into a macroscopic theory. Especially in liquid crystal theory the macroscopic director, which represents an averaged orientation in a volume element about a given point in a liquid crystal, is replaced by a microscopic director, describing the orientation of a single uniaxial molecule. Therefore, in the mesoscopic theory the macroscopic director is a derived quantity in contrast to the usual director theories. The orientation of all microscopic directors in a given volume element is described by an orientation distribution function (ODF). This distribution function makes it possible to derive a family of alignment tensors. The macroscopic field of the alignment tensor of second order now replaces the macroscopic director, thus resulting in a more detailed description of the orientation. This first approximation by the alignment tensor of second order can be improved by taking into account alignment tensors of higher order. The case of total alignment of all molecules in a volume element corresponds to the Ericksen–Leslie theory of liquid crystals. In this special case, the macroscopic director is identical to the microscopic one. In the general case, beyond liquid crystal theory, a mesoscopic theory introduces additional mesoscopic variables forming a configuration space, called the mesoscopic space, on which the fields appearing in the balances of the theory are now defined. The orientation distribution function is now replaced by the mesoscopic distribution function, which describes the distribution of the mesoscopic variables at each time and position.

Mesoscopic theory of liquid crystals

Liquid crystals of uniaxial and biaxial molecules are considered in the framework of the mesoscopic description which is a general tool of continuum theory. A mesoscopic theory introduces the fields beyond hydrodynamics as additional variables of a configuration space, called mesoscopic space, on which the fields appearing in balances are defined. Besides the mesoscopic space, a mesoscopic distribution function is introduced which describes the distribution of the additional variables at each time and position. It is demonstrated, how the mesoscopic theory can be applied to liquid crystals, and how the Ericksen-Leslie theory and the alignment tensor theory of liquid crystals fit into the mesoscopic framework.

Dynamic studies of proton diffusion in mesoscopic heterogeneous matrix: II. The interbilayer space between phospholipid membranes

The thin water layer, as found in chloroplast or mitochondria, is confined between low dielectric amphypathic surfaces a few nm apart.The physical properties of this mesoscopic space, and how its dimensions affect the rate of chemical reactions proceeding in it, is the subject for this study.The method selected for this purpose is time resolved fluorometry which can monitor the reversible dissociation of a proton from excited molecule of pyranine (8 hydroxy pyrene 1,3,6 tri sulfonate) trapped in thin water layers of a multilamellar vesicle made of neutral or slightly charged phospholipids.The results were analyzed by a computer program of N. Agmon (Pines, E., D. Huppert, and N. Agmon. 1988. J. Am. Chem. Soc. 88:5620-5630) that simulates the diffusion of a proton, subjected to electrostatic attraction, in a thin water layer enclosed between low affinity, proton binding surfaces. The analysis determines the diffusion coefficient of the proton, the effective dielectric constant of the water and the water accessibility of the phosphomoieties of the lipids.These parameters were measured for various lipids [egg-phosphatidylcholine (egg PC), dipalmitoyl phosphatidylcholine (DPPC), cholesterol + DPPC (1:1) and egg PC plus phosphatidyl serine (9:1)] and under varying osmotic pressure which reduces the width of the water layer down to approximately 10 approximately across.WE FOUND THAT: (a) The effective dielectric constant of the aqueous layer, depending on the lipid composition, is approximately 40. (b) The diffusion coefficient of the proton in the thin layer (30-10 approximately across) is that measured in bulk water D = 9.3 10(-5) cm(2)/s, indicating that the water retains its normal liquid state even on contact with the membrane. (c) The reactivity of the phosphomoiety, quantitated by rate of its reaction with proton, diminishes under lateral pressure which reduces the surface area per lipid.We find no evidence for abnormal dynamics of proton transfer at the lipid water interface which, by any mechanism, accelerates its diffusion.