Fundamental Physicochemical Processes Research Articles

Oriented attachment of silver nanoparticles in DMSO by collapsing under thermal stress

Nowadays, understanding the behavior of nanoparticle agglomeration is crucial to gain insight into the fundamental physicochemical processes that govern particle interactions at the nanoscale. In this work, we are focused on the thermal collapse of silver nanoparticles (NPs) stabilized with sodium citrate in dimethyl sulfoxide (DMSO). Therefore, we investigated the parameters that influence the transition from nearly isolated particles to elongated Ag agglomerates using Dynamic Light Scattering (DLS) and Ultraviolet-Visible Spectroscopy (UV-Vis). In addition, we conducted an in-depth study of the near-particle-particle interaction within the agglomerate using High-Resolution Transmission Electron Microscopy (HRTEM) observations of the agglomerates. The HRTEM results suggest that in the elongation of the agglomerate, the oriented attachment within the initial cluster plays a crucial role in the alignment along the longitudinal axis. The aging colloid exhibits minimal agglomeration, suggesting that the driving force of the collapse phenomenon is predominantly thermodynamic rather than kinetic in nature, and that the surface chemical equilibria play a key role in the preferential orientation mechanism.

A water probe for direct pH measurement of individual particles via micro-Raman spectroscopy

The acidity of atmospheric aerosols influences fundamental physicochemical processes that affect climate and human health. We recently developed a novel and facile water-probe-based method for directly measuring of the pH for micrometer-size droplets, providing a promising technique to better understand aerosol acidity in the atmosphere. The complex chemical composition of fine particles in the ambient air, however, poses certain challenges to using a water-probe for pH measurement, including interference from interactions between compositions and the influence of similar compositions on water structure. To explore the universality of our method, it was employed to measure the pH of ammonium, nitrate, carbonate, sulfate, and chloride particles. The pH of particles covering a broad range (0–14) were accurately determined, thereby demonstrating that our method can be generally applied, even to alkaline particles. Furthermore, a standard spectral library was developed by integrating the standard spectra of common hydrated ions extracted through the water-probe. The library can be employed to identify particle composition and overcome the spectral overlap problem resulting from similar effects. Using the spectral library, all ions were identified and their concentrations were determined, in turn allowing successful pH measurement of multicomponent (ammonium-sulfate-nitrate-chloride) particles. Insights into the synergistic effect of Cl–, NO3–, and NH4+ depletion obtained with our approach revealed the interplay between pH and volatile partitioning. Given the ubiquity of component partitioning and pH variation in particles, the water probe may provide a new perspective on the underlying mechanisms of aerosol aging and aerosol–cloud interaction.

The ro-vibrational ν2 mode spectrum of methane investigated by ultrabroadband coherent Raman spectroscopy.

We present the first experimental application of coherent Raman spectroscopy (CRS) on the ro-vibrational ν2 mode spectrum of methane (CH4). Ultrabroadband femtosecond/picosecond (fs/ps) CRS is performed in the molecular fingerprint region from 1100 to 2000cm-1, employing fs laser-induced filamentation as the supercontinuum generation mechanism to provide the ultrabroadband excitation pulses. We introduce a time-domain model of the CH4 ν2 CRS spectrum, including all five ro-vibrational branches allowed by the selection rules Δv = 1, ΔJ = 0, ±1, ±2; the model includes collisional linewidths, computed according to a modified exponential gap scaling law and validated experimentally. The use of ultrabroadband CRS for in situ monitoring of the CH4 chemistry is demonstrated in a laboratory CH4/air diffusion flame: CRS measurements in the fingerprint region, performed across the laminar flame front, allow the simultaneous detection of molecular oxygen (O2), carbon dioxide (CO2), and molecular hydrogen (H2), along with CH4. Fundamental physicochemical processes, such as H2 production via CH4 pyrolysis, are observed through the Raman spectra of these chemical species. In addition, we demonstrate ro-vibrational CH4 v2 CRS thermometry, and we validate it against CO2 CRS measurements. The present technique offers an interesting diagnostics approach to in situ measurement of CH4-rich environments, e.g., in plasma reactors for CH4 pyrolysis and H2 production.

Uncovering the Early Stages of Magnesium Silicate Hydrate Formation: A Nonclassical Multistep Pathway

Understanding the fundamental physicochemical processes that occur during the hydration of cementitious materials is essential for developing alternative binders that enable the partial substitution of Portland cement (PC), lowering the carbon footprint associated with the cement industry. Magnesium-silicate-hydrate (M-S-H) stands as a potential alternative binder; however, its inferior mechanical properties attributed to its nanostructure, and the high-water demand for curing, hinder the application of MgO-based cement as PC surrogate. A potential strategy to tackle these major drawbacks is based on controlling M-S-H formation from the early stages, building the properties and nanostructure of this binding phase from its basic building units. The present work provides insights into M-S-H nucleation and early growth gathered by combining titration experiments with electrospray ionization mass spectrometry, analytical ultracentrifugation, and transmission electron microscopy. We evidenced a nonclassical multistep pathway where a highly complex mixture of defined hydrated magnesium (sodium)-silicate oligomeric species exists in solution prior nucleation. Our results suggest that these entities aggregate, yielding an ill-defined M-S-H precursor phase (depleted in Mg compared to the final product) which later transforms into a denser M-S-H interconnected network (Mg:Si ratio ca. 1) with a more defined sheet-like structure that still retains its poorly crystalline character. The identification of oligomeric silicates species prior nucleation is of great importance for developing means to regulate M-S-H (and potentially other hydrous silicates) formation by using a bottom-up approach. This work reveals that, during the hydration process of cementitious materials, the stages prior to the formation of hydrated solids cannot be disregarded, as they could open new avenues for engineering the properties of the final materials.

Progress and Perspectives of Spectroscopic Studies on Carbon K-Edge Using Novel Soft X-ray Pulsed Sources

The development of novel coherent and brilliant sources, such as soft X-ray free electron laser (FEL) and high harmonic generation (HHG), enables new ultrafast analysis of the electronic and structural dynamics of a wide variety of materials. Soft X-ray FEL delivers high-brilliance beams with a short pulse duration, high spatial coherence and photon energy tunability. In comparison with FELs, HHG X-ray sources are characterized by a wide spectral bandwidth and few- to sub-femtosecond pulses. The approach will lead to the time-resolved reconstruction of molecular dynamics, shedding light on different photochemical pathways. The high peak brilliance of soft X-ray FELs facilitates investigations in a nonlinear regime, while the broader spectral bandwidth of the HHG sources may provide the simultaneous probing of multiple components. Significant technical breakthroughs in these novel sources are under way to improve brilliance, pulse duration, and to control spectral bandwidth, spot size, and energy resolution. Therefore, in the next few years, the new generation of soft X-ray sources combined with novel experimental techniques, new detectors, and computing capabilities will allow for the study of several extremely fast dynamics, such as vibronic dynamics. In the present review, we discuss recent developments in experiments, performed with soft X-ray FELs and HHG sources, operating near the carbon K-absorption edge, being a key atomic component in biosystems and soft materials. Different spectroscopy methods such as time-resolved pump-probe techniques, nonlinear spectroscopies and photoelectron spectroscopy studies have been addressed in an attempt to better understand fundamental physico-chemical processes.

A Comprehensive Review of High-Pressure Laser-Induced Materials Processing, Part I: Laser-Heated Diamond Anvil Cells

Laser-heated diamond anvil cell (LH-DAC) experimentation has emerged as a leading technique for materials processing at extreme pressures and temperatures. LH-DAC systems are often employed to better characterise the structure and properties of materials in applications ranging from condensed matter physics to geophysical research to planetary science. This article reviews LH-DAC and related laser-based characterisation, as the first part of a series within the broader context of all high-pressure laser-induced material processing. In part I of this review, a synopsis of laser-heated diamond anvil cell experimental methods, developmental history, fundamental physicochemical processes, and emerging research trends are provided. Important examples of minerals/materials modified during LH-DAC investigations (since their inception) are also tabulated, including key phase transformations, material syntheses, laser parameters, and process conditions—as a reference for the reader and as a guide for directing future research efforts. Note that laser-dynamic-compression within diamond anvil cells (LDC-DAC experimentation) and laser-induced reactive chemical synthesis within diamond anvil cells (LRS-DAC experimentation) are treated separately, as Parts II and III of this review.

Additive Manufacturing as a Means of Gas Sensor Development for Battery Health Monitoring

Lithium-ion batteries (LIBs) still need continuous safety monitoring based on their intrinsic properties, as well as due to the increase in their sizes and device requirements. The main causes of fires and explosions in LIBs are heat leakage and the presence of highly inflammable components. Therefore, it is necessary to improve the safety of the batteries by preventing the generation of these gases and/or their early detection with sensors. The improvement of such safety sensors requires new approaches in their manufacturing. There is a growing role for research of nanostructured sensor’s durability in the field of ionizing radiation that also can induce structural changes in the LIB’s component materials, thus contributing to the elucidation of fundamental physicochemical processes; catalytic reactions or inhibitions of the chemical reactions on which the work of the sensors is based. A current method widely used in various fields, Direct Ink Writing (DIW), has been used to manufacture heterostructures of Al2O3/CuO and CuO:Fe2O3, followed by an additional ALD and thermal annealing step. The detection properties of these 3D-DIW printed heterostructures showed responses to 1,3-dioxolan (DOL), 1,2-dimethoxyethane (DME) vapors, as well as to typically used LIB electrolytes containing LiTFSI and LiNO3 salts in a mixture of DOL:DME, as well also to LiPF6 salts in a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) at operating temperatures of 200 °C–350 °C with relatively high responses. The combination of the possibility to detect electrolyte vapors used in LIBs and size control by the 3D-DIW printing method makes these heterostructures extremely attractive in controlling the safety of batteries.

Characterization of a kHz sinusoidal Argon plasma jet impinging on water using Thomson scattering and fast imaging

The electron dynamics in a stable and non-filamentary Argon plasma jet, generated using AC excitation at kHz frequencies and interacting with a liquid surface either at floating potential or electrically grounded were examined using laser Thomson scattering. In the case of a floating liquid, two discharge events were observed during each half-cycle of the applied sinusoidal voltage. In the grounded liquid case only one discharge event was observed, which occurred during the positive half period. Through spatio-temporal imaging of the discharge, its repetitive breakdown behavior was analyzed and divided into pre-, main-, and post-breakdown phases. The dynamics and presence of the various phases differed depending upon the grounding of the liquid. Thomson scattering measurements revealed maximum electron densities and temperatures of 6.0–6.3 × 1014 cm−3 and 3.1–3.3 eV for the floating liquid case and 1.1 × 1015 cm−3 and 4.3 eV in the grounded liquid case. Electron-driven reactions are the primary source of reactive chemical species in a plasma jet. Therefore, the electrical characteristics of the liquid sample can impact the fundamental physicochemical processes at play in the discharge, ultimately influencing its chemical composition.

FACTORS AFFECTING MAYONNAISE DESTABILIZATION DURING FREEZING

The destabilization or phase separation of oil-in-water (O/W) emulsions, such as mayonnaise, is common during freezing and after thawing. However, emulsions must remain physically and chemically stable throughout processing, freeze-storage, and thawing. Different factors associated with the destabilization of mayonnaise and other O/W food emulsions include emulsifier, salt, and sugar concentrations, microstructure, cooling temperature, and crystallization of the oil and water phases. Herein, the role of each factor is reviewed, with probable mechanisms discussed. Knowledge of the fundamental physicochemical processes responsible for the stability of mayonnaise-type emulsions will aid the design of quality storage attributes.

Intermediate‐Scale Experimental Study to Improve Fundamental Understanding of Attenuation Capacity for Leaking CO2 in Heterogeneous Shallow Aquifers

AbstractTo assess the risks of Geologic Carbon Sequestration (GCS), it is crucial to understand the fundamental physicochemical processes that may occur if and when stored CO2 leaks upward from a deep storage reservoir into the shallow subsurface. Intermediate‐scale experiments allow for improved understanding of the multiphase evolution processes that control CO2 migration behavior in the subsurface, because the boundary conditions, initial conditions, and porous media parameters can be better controlled and monitored in the laboratory than in field settings. For this study, a large experimental test bed was designed to mimic a cross section of a shallow aquifer with layered geologic heterogeneity. As water with aqueous CO2 was injected into the system to mimic a CO2‐charged water leakage scenario, the spatiotemporal evolution of the multiphase CO2 plume was monitored. Similar experiments were performed with two different sand combinations to assess the relative effects of different types of geologic facies transitions on the CO2 evolution processes. Significant CO2 attenuation was observed in both scenarios, but by fundamentally different mechanisms. When the porous media layers had very different permeabilities, attenuation was caused by local accumulation (structural trapping) and slow redissolution of gas phase CO2. When the permeability difference between the layers was relatively small, on the other hand, gas phase continually evolved over widespread areas near the leading edge of the aqueous plume, which also attenuated CO2 migration. This improved process understanding will aid in the development of models that could be used for effective risk assessment and monitoring programs for GCS projects.

Origin of hydrophobicity and enhanced water hydrogen bond strength near purely hydrophobic solutes

Hydrophobicity plays an important role in numerous physicochemical processes from the process of dissolution in water to protein folding, but its origin at the fundamental level is still unclear. The classical view of hydrophobic hydration is that, in the presence of a hydrophobic solute, water forms transient microscopic "icebergs" arising from strengthened water hydrogen bonding, but there is no experimental evidence for enhanced hydrogen bonding and/or icebergs in such solutions. Here, we have used the redshifts and line shapes of the isotopically decoupled IR oxygen-deuterium (O-D) stretching mode of HDO water near small purely hydrophobic solutes (methane, ethane, krypton, and xenon) to study hydrophobicity at the most fundamental level. We present unequivocal and model-free experimental proof for the presence of strengthened water hydrogen bonds near four hydrophobic solutes, matching those in ice and clathrates. The water molecules involved in the enhanced hydrogen bonds display extensive structural ordering resembling that in clathrates. The number of ice-like hydrogen bonds is 10-15 per methane molecule. Ab initio molecular dynamics simulations have confirmed that water molecules in the vicinity of methane form stronger, more numerous, and more tetrahedrally oriented hydrogen bonds than those in bulk water and that their mobility is restricted. We show the absence of intercalating water molecules that cause the electrostatic screening (shielding) of hydrogen bonds in bulk water as the critical element for the enhanced hydrogen bonding around a hydrophobic solute. Our results confirm the classical view of hydrophobic hydration.

Pore‐scale simulation of mixing‐induced calcium carbonate precipitation and dissolution in a microfluidic pore network

We develop a 2‐D pore scale model of coupled fluid flow, reactive transport, and calcium carbonate (CaCO3) precipitation and dissolution. The model is used to simulate transient experimental results of CaCO3 precipitation and dissolution under supersaturated conditions in a microfluidic pore network (i.e., micromodel) in order to improve understanding of coupled reactive transport systems perturbed by geological CO2 injection. In the micromodel, precipitation is induced by transverse mixing along the centerline in pore bodies. The reactive transport model includes the impact of pH upon carbonate speciation and a CaCO3 reaction rate constant, the effect of changing reactive surface area upon the reaction, and the impact of pore blockage from CaCO3 precipitation on diffusion and flow. Overall, the pore scale model qualitatively captured the precipitate morphology, precipitation rate, and maximum precipitation area using parameter values from the literature. In particular, we found that proper estimation of the effective diffusion coefficient (Deff) and the reactive surface area is necessary to adequately simulate precipitation and dissolution rates. In order to match the initial phase of fast precipitation, it was necessary to consider the top and bottom of the micromodel as additional reactive surfaces. In order to match a later phase when dissolution occurred, it was necessary to increase the dissolution rate compared to the precipitation rate, but the simulated precipitate area was still higher than the experimental results after ∼30 min, highlighting the need for future study. The model presented here allows us to simulate and mechanistically evaluate precipitation and dissolution of CaCO3 observed in a micromodel pore network. This study leads to improved understanding of the fundamental physicochemical processes of CaCO3precipitation and dissolution under far‐from‐equilibrium conditions.

Infrared Spectroscopy and Hydrogen-Bond Dynamics of Liquid Water from Centroid Molecular Dynamics with an Ab Initio-Based Force Field

A molecular-level description of the unique properties of hydrogen-bond networks is critical for understanding many fundamental physicochemical processes in aqueous environments. In this Article, a novel simulation approach, combining an ab initio-based force field for water with a quantum treatment of the nuclear motion, is applied to investigate hydrogen-bond dynamics in liquid water with a specific focus on the relationship of these dynamics to vibrational spectroscopy. Linear and nonlinear infrared (IR) spectra are calculated for liquid water, HOD in D(2)O and HOD in H(2)O, and discussed in the context of the results obtained using other approaches that have been employed in studies of water dynamics. A comparison between the calculated spectra and the available experimental data yields an overall good agreement, indicating the accuracy of the present simulation approach in describing the properties of liquid water under ambient conditions. Possible improvements on the representation of the underlying water interactions as well as the treatment of the molecular motion at the quantum-mechanical level are also discussed.

The Galactic Interstellar Medium: an Overview

It is given a bird's eye view of the galactic interstellar environment, its structure and composition. It is also given a short description of some fundamental physico-chemical processes, that are important for gravitational collapse and hence for the formation of stars, for the shaping galaxies, for regulating their dynamics and in a sense for allowing the Universe to be as we observe it today.

Charge-transfer reactions at liquid/liquid interfaces and their applications in bioassays

Charge (electron and ion)–transfer reactions at a liquid/ liquid (L/L) interface are one of the most fundamental physicochemical processes. The liquid/liquid interface is actually made up of two immiscible electrolyte solutions. For instance, one organic solvent with a supporting electrolyte usually contacts with an immiscible aqueous solution. The study of such soft molecular interfaces by various electrochemical techniques is called electrochemistry at liquid/liquid interfaces. Although Nernst et al. carried out experiments at a water/phenol interface in 1902, this field has only been developed fully in the last 30 years because it has relevance to mimicking biomembranes, studying drug release, chemical and biological sensing, and understanding the mechanism of phase-transfer catalysis etc. [1–5]. Unlike a solid/electrolyte interface in conventional electrochemistry, in which redox species are the main task and electron-transfer reactions and sometimes adsorption/desorption processes are involved, one of the characteristics of electrochemistry at liquid/liquid interfaces is the diversity of charge-transfer reactions (CTRs), which can be studied and applied [5]. These CTRs can be classified into three main categories: (1) ion-transfer (IT) reactions; (2) facilitated ion-transfer (FIT) reactions; and (3) electron-transfer (ET) reactions. Apparently, apart from electroactive species, many electro-inactive species can also be investigated electrochemically at a liquid/liquid interface, and this actually opens many potential analytical applications. Charge– transfer reactions at liquid/liquid interfaces

Photodecarbonylation of Dibenzyl Ketones and Trapping of Radical Intermediates by Copper(II) Chloride in Frozen Aqueous Solutions

This paper presents a quantitative and qualitative study of the Norrish type I reaction of dibenzyl ketone (DBK) and 4-methyldibenzyl ketone (MeDBK), producing the benzyl radicals and consequently recombination products, in frozen aqueous solutions over a broad temperature range (-80 to 20 degrees C). This work extends previous research on the cage effects in various constrained media to provide information about the dynamics and reactivity of the photochemically generated intermediates at the grain boundaries of ice matrix. As the temperature of aqueous solutions decreases, the solute concentrations become high at layers covering ice crystals, causing efficient molecular segregation. The cage effect experiments have shown that diffusion of the benzyl radicals within such reaction aggregates is still remarkably efficient at temperatures below -50 degrees C, independently of the initial ketone concentration in the range of 10(-6)-10(-4) mol L(-1). In addition, the study of trapping the benzyl radicals formed in situ by CuCl2 was used as a qualitative probe of heterogeneous bimolecular reactions in the frozen aqueous matrix and on its surface. Molecules of both solutes were found to be segregated from the ice phase to the same location and underwent chemical reactions within diffusion and intermediates lifetimes limits. Understanding the fundamental physicochemical processes in ice is unquestionably important in related environmental or cosmochemical investigations.

Weatherability of coated EPDM rubber compound by controlled UV irradiation

Polymeric composites for automotive window seal applications are generally exposed to complex service environment conditions. The fundamental physico-chemical processes that control the durability of such composite systems on a micro and macroscopic level were evaluated in the present case using thermal analysis (TA), elemental mapping and microscopy. Five different EPDM rubber compounds (control, three bulk modified and one surface modified), coated with polyurethane coating were exposed to controlled UV irradiation. The higher the adhesion, the less the extent of UV penetration through the interface. The photo-oxidation mainly takes place from the surface, as the energy gets consumed and the intensity of the UV decreases on its passage through the strongly adhered layers to the rubber compound. The coating layer being on the surface, is more affected and photodegraded by UV irradiation than the rubber compound. The sample P 1cc, being multiphasic in nature and with a strong interface, can scatter the UV strongly and hence shows best weatherability among all the systems.

Functional brain imaging in neuropsychiatric disorders of childhood.

This review article presents a summary of the current state-of-the-art of functional brain imaging, with a primary focus on childhood neuropsychiatric disorders. Coverage is emphasized for developments that appear to be of current or potential future importance for the child neurologist and related pediatric specialist, and also from the perspective of the developmental neuroscientist. Emphasis is placed on the modalities of single photon emission computed tomography (SPECT), positron emission tomography (PET), and both "conventional" and "functional" magnetic resonance imaging, (MRI) including reference to the major new radiopharmaceutical and magnetic resonance-based imaging agents and techniques. The fundamental physicochemical processes underlying such studies are outlined, with citation of sources of more detailed information for the interested reader. A variety of imaging studies are reviewed for selected groups of childhood neuropsychiatric disorders, designed to illustrate the achievements and future promise of these imaging modalities. Areas of concentration are suggested for future imaging research in the field of childhood behavioral disorders, where these methods seem critical to improved understanding of pathogenetic mechanisms, as well as development of more effective treatment strategies.

Sol-gel silicon dioxide films

(Received November 5, 1990; revised July 1, 1991; accepted September 4, 1991 ) Abstract The influence of various preparations conditions such as sol composition, application and heat treatment conditions on the properties of sol gel silicon dioxide thin films has been studied. !. Introduction The preparation of silicon dioxide thin films from metal alkoxides as precursors has been known for more than 50 years. The first experiments concerning the prepara- tion of optical coatings by this method were carried out in Germany [1] and also in the U.S.S.R. [2, 3]. During the last decade this method has become a part of a new intensively advancing sol-gel technology [4]. This tech- nology is based on conversion to gels after chemical reactions of hydrolysis and polycondensation of sols, which are usually the solutions of metal alkoxides. Various types of materials and structures can be obtained as final products of this technology: gels, powders, ceramics, glasses, films etc. Recent investigations in this field allowed new information to be obtained on the fundamental physicochemical processes which are the basis of sol-gel technology and the determination of the main advantages and limitations of this method [5]. In microelectronics sol-gel films were used mainly as a diffusion source [6, 7]. During the last few years some new problems in microelectronics as well as the develop- ment of sol-gel technology gave a strong push to this method of thin film fabrication. Thus sol-gel silicon dioxide films (spin-on glass) are used as follows: for planarization of interlevel dielectrics in the multilevel metallization in very-large-scale integration [8, 9], for the taper etching of thermal oxide layers [10, 11], for the processes of device fabrication on AraB v materials [12, 13], for bonding silicon wafers [14, 15], for fabrica- tion of various types of sensors [16, 17] etc. The microstructure as well as the physical properties of silica films are significantly governed by the precursor polymer structure before deposition and the relative rates of condensation and evaporation during spinning. Owing to the brief time span of the film deposition process, the structures of the resulting films and bulk gels, prepared from the same precursors, may have significant distinc- tions [ 18]. The lack of systematic studies of the effect of the processing parameters on the properties of sol-gel films causes difficulty in designing optimum processes for broad industrial exploitation of this technology in mi- croelectronics and other fields. This paper is concerned with the study of some conditions that can influence the properties of sol-gel silicon dioxide thin films. 2. Experimental details Silica precursor solutions were prepared by mixing alkoxide with absolute alcohol, water and HC1. After stirring, all solutions were kept for 24 h at 60 'C. Application of films was performed by spinning in specially made equipment in a closed chamber in which gas with a fixed moisture content was supplied. We used mainly nitrogen in the course of the application and heat treatment processes. In order to obtain films with the necessary thickness, multiple applications with annealing of each layer for 20 min were used. Silicon wafers with a diameter of 60-100 mm purified by a standard mi- croelectronics cleaning process were used as substrates. The films' thickness and the refractive index were measured by multiangle ellipsometry at 632.8 nm [19]. The percent change in thickness of the films on drying and heat treatment