Important Interfacial Phenomena Research Articles

Void Evolution on the Li-Solid Electrolyte Interface in Solid-State Batteries: A Parametric Study Under Varied Mechanical and Electrochemical Conditions

Void growth during the plating and stripping process is an important interfacial phenomenon that hinders the development of Li-metal solid-state batteries (SSBs) because it can potentially result in inter-component delamination or growth of Li dendrites. Behind the void growth is the complex interaction between electrochemistry and mechanics. Voids usually grow from micro- or nanoscale initial imperfections on the Li-solid electrolyte (SE) interface. It is, therefore, important to analyze the stress concentration at the initial void tips, which largely determines the growth/shrinking of the void as well as the consequent changes in the internal resistance and overall battery efficiency. Recently, the development of in situ operando experimental technology has enabled the electro-chemo-mechanical characterization of the void growth phenomenon on the Li-SE interface. In this study, we explore how voids in SSBs evolve with a multi-physics model in COMSOL Multiphysics. Based on this model, we perform a systematic parametric study in the space of the mechanical stack pressure and the applied current density. The simulation results show different deformation patterns and potential failure mechanisms under different combination of stack pressure and current density. To better understand the phenomena, we develop an analytical solution to understand the void deformation induced by the inhomogeneous Li-ion concentration field under stack pressure. This analytical approach offers a complementary and intuitive perspective on the mechanical aspect of our simulation findings. By combining the simulation and analytical solutions, we depict a phase diagram, in which we identify the “safe zone” that will not result in void growth. The new insights of this research hold the promise of guiding the development of stabilized SSB interfaces.

Equation-of-state-based lattice Boltzmann model of multicomponent adsorption onto fluid–fluid interfaces

In diffuse interface models, such as the lattice Boltzmann method (LBM), interfacial physics plays an important role. An example of an important interfacial phenomenon is adsorption onto a fluid–fluid interface. In the context of LBM, adsorption studies have traditionally only focused on adsorption onto a solid surface. The studies on adsorption onto fluid–fluid interfaces have been qualitative in nature, suffer from restrictions on the number of components, or are based on simple thermodynamic models designed for fully immiscible phases. Our recently published fugacity-based LBM model introduces a platform for the accurate modeling of multiphase fluids unrestricted by the number of components, and governed through accurate equations of state (Soomro and Ayala, 2023). In this study, we utilize the fugacity-based LBM to capture interfacial adsorption. This paper begins by simulating adsorption in a binary system with a flat interface, and shows that the amount of adsorption, quantified by relative adsorption measures, is in exact agreement with Gibbs theory. Next, the analysis is continued for a ternary system with two species adsorbing onto the interface. The binary and ternary simulations are then repeated for the case of a droplet and finally a five component case is presented. The study shows that the fugacity-based LBM can capture adsorption in full agreement with Gibbs adsorption theory. This provides a path for a generalized LBM model for adsorption, based on robust thermodynamic models for the fluids and unrestricted by the number of components, marking a significant contribution to the LBM literature.

Improved photocatalytic performance of TiO2/carbon photocatalysts: Role of carbon additive

A series of TiO2 – based photocatalysts have been prepared by the incorporation of 10 wt% of various carbon-based nanomaterials as modifying agents to titania. More specifically, commercial TiO2 P25 was modified through a wet impregnation approach with methanol with four different carbon nanostructures: single-walled carbon nanotubes (SWCNTs), partially reduced graphene oxide (prGO), graphite (GI), and graphitic carbon nitride (gCN). Characterization results (XPS and Raman) anticipate the occurrence of important interfacial phenomena, preferentially for samples TiO2/SWCNT and TiO2/prGO, with a binding energy displacement in the Ti 2p contribution of 1.35 eV and 1.54 eV, respectively. These findings could be associated with an improved electron-hole mobility at the carbon/oxide interface. Importantly, these two samples constitute the most promising photocatalysts for Rhodamine B (RhB) photodegradation, with nearly 100% conversion in less than 2 h. These promising results must be associated with intrinsic physicochemical changes at the formed heterojunction structure and the potential dual-role of the composites able to adsorb and degrade RhB simultaneously. Cyclability tests confirm the improved performance of the composites (e.g., TiO2/SWCNT, 100% degradation in 1 h) due to the combined adsorption/degradation ability, although the regeneration after several cycles is not complete due to partial blocking of the inner cavities in the carbon nanotubes by non-reacted RhB. Under these reaction conditions, Rhodamine-B xanthene dye degrades via the de-ethylation route.

153 Nearly free Surface Silanols: from Silica Towards a new Paradigm for Particle Toxicity

Abstract Respirable crystalline silica (RCS) is the leading cause of occupational respiratory diseases worldwide. RCS is associated with inflammatory lung reactions, which can lead to silicosis, cancer, and autoimmune diseases. The extreme variability of silica specimens, including its amorphous forms, the surface heterogeneity, and variable toxicity effects, generated one of the most intriguing enigmas in particle toxicology, i.e., deciphering which physico-chemical features explain and predict the variable hazard of silica. Using a set of ad hoc prepared synthetic and natural quartz particles, we have identified a unique subfamily of surface silanols as a key initiator of the toxicity of silica particles. These moieties, namely the "nearly-free silanols" (NFS), appear on the surface of quartz when crystals are fractured, and their amount can be modulated by physico-chemical processes. The peculiar spatial arrangement of NFS was demonstrated as the most energetically favorable and selective for interacting zwitterionic phospholipids that make up cell membranes. The toxic activity of NFS was also confirmed with amorphous nanosilica synthesized at high temperatures, and our recent findings suggest that NFS could impart toxic properties to other silica polymorphs and hydroxylated surfaces, including aluminosilicates and engineered stones. Overall, NFS occurrence accounts for the origin and variability of the toxicity of silica, opening perspectives for controlling RCS hazard, and may contribute to understand other important interfacial phenomena of hydroxylated materials.

A Moving Front Kinetic Monte Carlo Algorithm for Moving Interface Systems.

This work presents the development of a new kinetic Monte Carlo algorithm, referred to as Moving Front kinetic Monte Carlo (MFkMC), for simulating processes subject to moving interfaces. This framework is designed to capture the movement of transiently varying interfaces in a kinetic-like manner so that its movement can be described using Monte Carlo sampling. The MFkMC algorithm accomplishes this task by evaluating the behavior of the interfacial molecules and assigning kinetic Monte Carlo-style rate equations that describe the transition probability that a molecule would advance into the neighboring phase, displacing an interfacial molecule from the opposing phase and thus changing the interface. Due to its kinetic Monte Carlo structure, the MFkMC algorithm can additionally account for other important interfacial phenomena, such as interfacial surface reactions. The proposed algorithm was tested via applications to three different simple interfacial case studies. These studies validate the MFkMC algorithm and demonstrate its capabilities to accurately and efficiently simulate a variety of different moving interface systems.

Ferrofluids and bio-ferrofluids: looking back and stepping forward.

Ferrofluids investigated along for about five decades are ultrastable colloidal suspensions of magnetic nanoparticles, which manifest simultaneously fluid and magnetic properties. Their magnetically controllable and tunable feature proved to be from the beginning an extremely fertile ground for a wide range of engineering applications. More recently, biocompatible ferrofluids attracted huge interest and produced a considerable increase of the applicative potential in nanomedicine, biotechnology and environmental protection. This paper offers a brief overview of the most relevant early results and a comprehensive description of recent achievements in ferrofluid synthesis, advanced characterization, as well as the governing equations of ferrohydrodynamics, the most important interfacial phenomena and the flow properties. Finally, it provides an overview of recent advances in tunable and adaptive multifunctional materials derived from ferrofluids and a detailed presentation of the recent progress of applications in the field of sensors and actuators, ferrofluid-driven assembly and manipulation, droplet technology, including droplet generation and control, mechanical actuation, liquid computing and robotics.

Photosensitization mechanisms at the air-water interface of aqueous aerosols.

Photosensitization reactions are believed to provide a key contribution to the overall oxidation chemistry of the Earth's atmosphere. Generally, these processes take place on the surface of aqueous aerosols, where organic surfactants accumulate and react, either directly or indirectly, with the activated photosensitizer. However, the mechanisms involved in these important interfacial phenomena are still poorly known. This work sheds light on the reaction mechanisms of the photosensitizer imidazole-2-carboxaldehyde through ab initio (QM/MM) molecular dynamics simulations and high-level ab initio calculations. The nature of the lowest excited states of the system (singlets and triplets) is described in detail for the first time in the gas phase, in bulk water, and at the air–water interface, and possible intersystem crossing mechanisms leading to the reactive triplet state are analyzed. Moreover, the reactive triplet state is shown to be unstable at the air–water surface in a pure water aerosol. The combination of this finding with the results obtained for simple surfactant-photosensitizer models, together with experimental data from the literature, suggests that photosensitization reactions assisted by imidazole-2-carboxaldehyde at the surface of aqueous droplets can only occur in the presence of surfactant species, such as fatty acids, that stabilize the photoactivated triplet at the interface. These findings should help the interpretation of field measurements and the design of new laboratory experiments to better understand atmospheric photosensitization processes.

Molecular-Level Insight into the Interfacial Reactivity and Ionic Conductivity of a Li-Argyrodite Li6PS5Cl Solid Electrolyte at Bare and Coated Li-Metal Anodes.

Sulfide glasses, with high room-temperature Li-ion conductivities, are a promising class of solid-state electrolytes for all-solid-state batteries. Yet, when in contact with Li metal, our current understanding of important interfacial phenomena such as electrolyte reduction and Li-ion transport is still quite limited, especially at the atomic scale. Here, using first-principles molecular dynamics simulations, we tackle these open questions head-on and examine key interfacial properties of Li-argyrodite Li6PS5Cl electrolyte at bare and coated Li-metal anodes. Specifically, we investigate the role of the interfacial composition and morphology in a number of Li-metal surfaces, including surfaces coated with thin films of Li2Sn5, MoS2, LiF, and Li3P. Our materials models are designed to gain insights into the early stages of interface formation and structural evolution. In addition, by employing a novel topological analysis of procrystal electron density distribution as applied to interfacial solid-state ionics, we thoroughly assess Li-ion conductivity through the investigated interfaces. Our results provide evidence of progressive breaking of P-S bonds in PS43- groups and eventual P-P recombination of intermediate species as the main reaction mechanisms of Li6PS5Cl reduction by Li metal. We also predict Li2Sn5 as the most suitable coating to partially prevent the electrolyte degradation while keeping a relatively low interfacial resistance. These findings shed light on the interface chemistry of sulfide-based electrolytes in contact with Li metal and pave the way for rationalizing further computational and experimental studies in the field.

Nonpolar Water Clusters: Proton Nuclear Magnetic Resonance Spectroscopic Evidence for Transformation from Polar Water to Nonpolar Water Clusters in Liquid State.

The hydrophilic/hydrophobic interactions of water are important in biological and chemical self-assembly phenomena. Water clusters in hydrophobic environments exhibit a unique morphology. Their process of formation and nonpolar properties have been extensively studied, but no direct experimental evidence has been available until now. This study provides spectroscopic evidence for the transformation of water to nonpolar configuration via clustering. Although individual water molecules form hydrogen bonds with the hydroxyl protons of n-hexanol when codissolved in a nonpolar solvent (toluene-d8), the water clusters are comprised solely of hydrogen bonds between water molecules and do not form hydrogen bonds with the hydroxyl protons of n-hexanol. This behavior indicates that the water clusters are nonpolar rather than polar. This study reports the first example of nonpolar water configuration produced via a liquid-state clustering. This property is a common and important interfacial phenomenon of water in chemistry, biology, materials science, geology, and meteorology.

Probing the Redox-Dependent Electronic and Interfacial Structures in Ferrocene-Terminated Self-Assembled Monolayers with Photoelectron Spectroscopy

Central to electrochemistry is the electric double layer (EDL) at the electrode-electrolyte interface where important interfacial phenomena including adsorption and charge transfer occur.1 Understanding the nature of the electric double layer regarding the electronic and structural characteristics has implications relating to bio(chemical) sensors, micro-mechanical actuators and energy storage/conversion devices. Amongst model systems, ferrocene-terminated alkanethiol self-assembled monolayers (Fc SAM) on Au are an attractive model electrochemical interface due to their practical applicability and versatility with structural modifications.2 Within the Fc SAM, a change in the ferrocene/ferrocenium (Fc/Fc+) redox state leads to notable changes to the interfacial structure with respect to the EDL, interactions with the electrolyte, and work function. While existing studies exist on probing the redox-induced Fc SAM structural changes using techniques such as surface plasmon resonance (SPR), Raman, IR and quartz crystal microbalance (EQCM),2 experimental efforts aimed at probing the changes in electronic structure are still limited. Here, we employ X-ray and ultraviolet photoelectron spectroscopy combined with an electrochemical cell (EC-XPS/UPS) which allows us to electrochemically control the Fc SAM redox state and spectroscopically probe the redox-induced electronic and structural changes.3 To perform our experiments, electrochemical (EC) measurements are performed in a separate EC chamber in Ar atmosphere followed by evacuation and then transfer to the XPS/UPS analysis chamber.4 The EC chamber contains a retractable PTFE (polytetrafluorethylene) cell where electrochemical measurements are performed under Ar atmosphere. The cell utilizes a hanging meniscus setup connected via PFA (perfluoroalkoxy alkane) tubing to a syringe containing the electrolyte. This controlled setup permits us to reliably probe the oxidized Fc+ moieties and prevent its decomposition upon exposure to the ambient. Using this approach, following EC and electrode immersion, we can probe changes to the ferrocene/ferrocenium (Fc/Fc+) redox center (Fe oxidation state), deduce the occurrence of ion-pairing, changes in molecular orientation and monolayer thickness (Figure 1). Oxidation to Fc+ is corroborated by UPS, which shows that a shift of the highest occupied molecular orbital (HOMO) towards higher binding energy along with an increase in work function. The reversibility of our observations is confirmed by reproducibly switching between the Fc/Fc+ states. More broadly, our approach is potentially applicable to a variety of electrochemically active systems to assist in the elucidation of redox-related structure-function relationships. Specific details will be provided during the presentation. Figure 1. (a) Schematic and photographs of hanging meniscus inside the EC chamber during EC measurements and following removal from the electrolyte. (b) Molecular structure of Fc SAM used in study and cyclic voltammagram performed in 0.1 M NaClO4. (c) Corresponding XPS Fe 2p, Cl 2p and O 1s spectra of the pristine, oxidized Fc+ and neutral Fc states. Kolb, D. M. Angew. Chem. Int. Ed. 2001, 40, 1162.K. Uosaki, Electrochemistry 1999, 12, 1105.R. A. Wong, Y. Yokota, M. Wakisaka, J. Inukai, Y. Kim, J. Am. Chem Soc. 2018, 140, 13672.M. Wakisaka, S. Mitsui, Y. Hirose, K. Kawashima, H. Uchida, M. Watanabe, J. Phys. Chem. B 2006 , 46, 23489. Figure 1

Van der Waals Correction to the Physisorption of Graphene on Metal Surfaces

Adsorption is a scientifically and technologically important interfacial phenomenon, which however presents challenges to conventional density functional theory (DFT) due to the long-range van der Waals (vdW) interactions. We have developed a model of long-range vdW correction for physisorption of graphene (G) on metals with the Lifshitz–Zaremba–Kohn second-order perturbation theory, by incorporating dipole- and quadrupole-surface interactions and screening effects. The physisorption energies calculated by the model between graphene and eight metal surfaces (Al, Ni, Co, Pd, Pt, Cu, Ag, and Au), and the adsorption energies for the same G/metal structures from self-consistent DFT PBE (Perdew–Burke–Ernzerhof) calculations, are obtained in a range of distances between G and the metal surfaces. The sum of these two parts is the total adsorption energy as a function of the distance, from which the equilibrium distance and the binding energy are determined simultaneously. The results show high accuracy, with the...

Molecular Modeling of Reaction and Diffusion Processes at Electrochemical Interfaces in Lithium Ion Batteries

Lithium batteries are well-known as a critical technology, but they are also a fundamentally interesting chemical system do to the presence of complex phenomena such as chemical and electrochemical reactions, phase changes, and ion transport across interfaces, to name a few. Such complexity, however, provides opportunity for computational approaches which are able to resolve size- and time-scales unreachable through experimental methods. Many of the practical hurdles moving forward in battery technologies lie at the interfaces between the electrolyte and the electrodes, making study of these interfaces an important application of computational tools. However, no single computational approach is robust enough to encapsulate the entirety of the interface while also providing the appropriate resolution to study charge transfer and chemical bond breaking/formation. For this reason, it is critical that a multi-scale approach is taken in order to incorporate both accurate models and accurate methods into the characterization of important interfacial phenomena. Our work focuses on the formation of the so-called solid electrolyte interphase (SEI) by the reductive decomposition of ethylene carbonate (EC) at a graphite electrode surface prior to the initial lithiation during its first charge cycle. The SEI is a solid film consisting of decomposed electrolyte which permits the conduction of Li+ ions to and from the electrode, while passivating further electron transfer. Thusly, its formation process consists of electrochemical reduction, subsequent chemical reactions, reactant/intermediate/product transport, and solid precipitation onto the electrode surface. In order to encapsulate all of these phenomena, multiple simulation tools must be used. In particular, we utilize molecular dynamics (both classical force field and ab initio), enhanced sampling techniques, and mixed MD/Monte-Carlo methods to model reaction, transport, and phase transformation phenomena which contribute to the formation of the SEI. In this talk, we will present some of our recent findings from our investigation of the SEI and the methods we use to study it. In particular, we will discuss our framework for modeling reactions and diffusion processes near the electrode and the importance of explicit consideration of the electrolyte in predicting kinetics. Interfaces are critical to electrochemical systems from lithium ion batteries, to electrocatalysts, to sensors and computational methods possess great potential in shaping our understanding of them.

Temporal and spatial evolution of the thin film near triple line during droplet evaporation

The evaporation process of the thin film region near the triple line for a liquid suspended with nanoparticles involves important interfacial phenomena such as contact line movement, deposition, and evaporation. In this paper, droplets that are seeded with fluorescent nanoparticles of different diameters and of the same particle numbers were investigated for their evaporation rates, deposition patterns, and in-plane average velocities within the field-of-view. The results present different modes of deposition patterns for the fluorescent nanoparticles, and stronger evaporation can be obtained using nanoparticles of small diameter. The temporal and spatial evolution of velocities and thicknesses in the thin films near the triple lines during the droplet evaporation were obtained by using a proposed sub-region method, which is developed from an evanescent wave based nanoparticle image velocimetry technique. It shows that, depending on the nanoparticle size, the spatial variation of the local thin film thickness can be linear or nonlinear. The fluorescent nanoparticles can affect the evaporation modes, the internal flow, and the temporal and spatial evolution of the thin film during the droplet evaporation through the interaction between the particles and the interface near the contact line and their influence on the change of the microscopic contact angle during the pinning process of the contact line. This work can help capture insights on how nanosized particles affect the droplet evaporation near the triple line.

Multiscale Modeling of the HKUST-1/Poly(vinyl alcohol) Interface: From an Atomistic to a Coarse Graining Approach

We present a computational multiscale study of a metal–organic framework (MOF)/polymer composite combining micro- and mesoscopic resolution, by coupling atomistic and coarse grained (CG) force field-based molecular dynamics simulations. As a proof of concept, we describe the copper paddlewheel-based HKUST-1 MOF/poly(vinyl alcohol) composite. Our newly developed CG model reproduces the salient features of the interface in excellent agreement with the atomistic model and allows the investigation of substantially larger systems. The polymer penetrates into the open pores of the MOF as a result of the interactions between its OH groups and the O and Cu atoms in the pores, suggesting an excellent MOF/polymer compatibility. Polymer structure is affected by the MOF surface up to a distance of ∼2.4 times its radius of gyration. This study paves the way toward understanding important interfacial phenomena such as aggregation and phase separation in these mixed matrix systems.

Computational Studies of Interfacial Reactions at Anode Materials: Initial Stages of the Solid-Electrolyte-Interphase Layer Formation

Understanding interfacial phenomena such as ion and electron transport at dynamic interfaces is crucial for revolutionizing the development of materials and devices for energy-related applications. Moreover, advances in this field would enhance the progress of related electrochemical interfacial problems in biology, medicine, electronics, and photonics, among others. Although significant progress is taking place through in situ experimentation, modeling has emerged as the ideal complement to investigate details at the electronic and atomistic levels, which are more difficult or impossible to be captured with current experimental techniques. Among the most important interfacial phenomena, side reactions occurring at the surface of the negative electrodes of Li-ion batteries, due to the electrochemical instability of the electrolyte, result in the formation of a solid-electrolyte interphase layer (SEI). In this work, we briefly review the main mechanisms associated with SEI reduction reactions of aprotic organic solvents studied by quantum mechanical methods. We then report the results of a Kinetic Monte Carlo method to understand the initial stages of SEI growth.

Growth dynamics of solid electrolyte interphase layer on SnO2 nanotubes realized by graphene liquid cell electron microscopy

Formation of stable solid electrolyte interphase (SEI) layer is critical to outstanding performance of energy storage devices, because it acts as a passive layer that allows facile transport of ions but forbids electron transport between the electrolyte and electrode. Although much study has been devoted to investigate the morphology and structure of SEI layer using a myriad of analytical devices on past decades, the direct observation of SEI layer on a real time scale has remained as a formidable challenge. In addition, it has been difficult to observe both the decomposition of electrolytes and formation process of stable SEI layer at nanometer scale. Here we utilize in situ transmission electron microscopy (TEM) using graphene liquid cell (GLC) to realize the observation of stable SEI layer formation in a sequential time scale. Upon e− beam irradiation, Li salts in the electrolytes react with reduced electrolytes and form gel-like agglomerates, which are deposited on the surface of the active material as a passivation layer and later stabilized to become more uniform in overall thickness. Additionally, growth dynamics of stable SEI layer were suggested, where the deposition of decomposed electrolytes eventually result in relatively uniform SEI layer. This paper demonstrates that it is possible to observe not only the formation of non-crystalline SEI layer but also the movement of decomposed electrolytes onto the surface of active materials which account for broader understanding of SEI layer, and has the potential to detect important interfacial phenomena in electrochemical devices that were overlooked so far.

Modeling of laser keyhole welding: Part I. mathematical modeling, numerical methodology, role of recoil pressure, multiple reflections, and free surface evolution

A three-dimensional laser-keyhole welding model is developed, featuring the self-consistent evolution of the liquid/vapor (L/V) interface together with full simulation of fluid flow and heat transfer. Important interfacial phenomena, such as free surface evolution, evaporation, kinetic Knudsen layer, homogeneous boiling, and multiple reflections, are considered and applied to the model. The level set approach is adopted to incorporate the L/V interface boundary conditions in the Navier-Stokes equation and energy equation. Both thermocapillary force and recoil pressure, which are the major driving forces for the melt flow, are incorporated in the formulation. For melting and solidification processes at the solid/liquid (S/L) interface, the mixture continuum model has been employed. The article consists of two parts. This article (Part I) presents the model formulation and discusses the effects of evaporation, free surface evolution, and multiple reflections on a steady molten pool to demonstrate the relevance of these interfacial phenomena. The results of the full keyhole simulation and the experimental verification will be provided in the companion article (Part II).

A graphical technique for calculating adsorption/desorption isotherms for different solid/liquid ratios

Adsorption of surfactants on solids from aqueous suspensions is an important interfacial phenomenon, with many industrial applications. Adsorption isotherms are often used to monitor surface properties of solids in suspensions. Many of these applications, however, involve suspensions of varying solid/liquid ratios, and sometimes mixing, causing dilution with possible desorption as well. Experiments to estimate the adsorbed amount from the final concentrations at every different solid/liquid ratio are unnecessarily tedious. An alternative graphical technique is presented here to accomplish the same from experiments conducted at only a few solid/liquid ratios. The results from the graphical method agree well with experimental values.

Surface films of lithium: an overview of electrochemical studies

There is considerable ambiguity in the literature about the importance of lithium surface film on the electrochemical reaction at the lithium/electrolyte interface. Some studies attribute the measured interfacial properties to the surface film on lithium alone and other studies consider the measured properties due entirely to electron-transfer reaction; while a few studies provide due recognition to both the surface film as well as the charge-transfer reaction. Literature on DC polarization and AC impedance spectroscopic studies of Li/non-aqueous liquid and solid polymer electrolyte interface is reviewed. Our electrochemical impedance spectroscopic studies of lithium/solid polymer electrolyte interface are analyzed using simple equivalent circuit models. The models include both the surface film properties as well as the electron-transfer reaction. The experimental results and reviewed literature support that both the surface film on lithium and the electron-transfer reaction are equally important interfacial phenomena, and should be considered simultaneously during an investigation.