Chemomechanical Coupling Research Articles

Electro-Chemo-Mechanical Challenges and Perspective in Lithium Metal Batteries

AbstractThe development of next-generation batteries, utilizing electrodes with high capacities and power densities requires a comprehensive understanding and precise control of material interfaces and architectures. Electro-chemo-mechanics plays an integral role in the morphological evolution and stability of such complex interfaces. Volume changes in electrode materials and the chemical interactions of electrode/electrolyte interfaces result in nonuniform stress fields and structurally different interphases, fundamentally affecting the underlying transport and reaction kinetics. The origin of this mechanistic coupling and its implications on degradation is uniquely dependent on the interface characteristics. In this review, the distinct nature of chemo–mechanical coupling and failure mechanisms at solid–liquid interfaces and solid–solid interfaces is analyzed. For lithium metal electrodes, the critical role of surface/microstructural heterogeneities on the solid electrolyte interphase (SEI) stability and dendrite growth in liquid electrolytes, and on the onset of contact loss and filament penetration with solid electrolytes is summarized. With respect to composite electrodes, key differences in the microstructure-coupled electro-chemo-mechanical attributes of intercalation- and conversion-based chemistries are delineated. Moving from liquid to solid electrolytes in such cathodes, we highlight the significant impact of solid–solid point contacts on transport/mechanical response, electrochemical performance, and failure modes such as particle cracking and delamination. Finally, we present our perspective on future research directions and opportunities to address the underlying electro-chemo-mechanical challenges for enabling next-generation lithium metal batteries.

Direct identification of the rotary angle of ATP cleavage in F1-ATPase from Bacillus PS3

F1-ATPase is the world’s smallest biological rotary motor driven by ATP hydrolysis at three catalytic β subunits. The 120° rotational step of the central shaft γ consists of 80° substep driven by ATP binding and a subsequent 40° substep. In order to correlate timing of ATP cleavage at a specific catalytic site with a rotary angle, we designed a new F1-ATPase (F1) from thermophilic Bacillus PS3 carrying β(E190D/F414E/F420E) mutations, which cause extremely slow rates of both ATP cleavage and ATP binding. We produced an F1 molecule that consists of one mutant β and two wild-type βs (hybrid F1). As a result, the new hybrid F1 showed two pausing angles that are separated by 200°. They are attributable to two slowed reaction steps in the mutated β, thus providing the direct evidence that ATP cleavage occurs at 200° rather than 80° subsequent to ATP binding at 0°. This scenario resolves the long-standing unclarified issue in the chemomechanical coupling scheme and gives insights into the mechanism of driving unidirectional rotation.

Single-Molecule Optical Tweezers As a Tool for Delineating the Mechanisms of Protein-Processing Mechanoenzymes.

Mechanoenzymes convert chemical energy from the hydrolysis of nucleotide triphosphates to mechanical energy for carrying out cellular functions ranging from DNA unwinding to protein degradation. Protein-processing mechanoenzymes either remodel the protein structures or translocate them across cellular compartments in an energy-dependent manner. Optical-tweezer-based single-molecule force spectroscopy assays have divulged information on details of chemo-mechanical coupling, directed motion, as well as mechanical forces these enzymes are capable of generating. In this review, we introduce the working principles of optical tweezers as a single-molecule force spectroscopy tool and assays developed to decipher the properties such as unfolding kinetics, translocation velocities, and step sizes by protein remodeling mechanoenzymes. We focus on molecular motors involved in protein degradation and disaggregation, i.e., ClpXP, ClpAP, and ClpB, and insights provided by single-molecule assays on kinetics and stepping dynamics during protein unfolding and translocation. Cellular activities such as protein synthesis, folding, and translocation across membranes are also energy dependent, and the recent single-molecule studies decoding the role of mechanical forces on these processes have been discussed.

Creep Effect on Chemo-Mechanical Coupling Oxidation of Thermal Barrier Coatings

In this paper, a chemo-mechanical coupling model considering the creep effect during high-temperature oxidation is developed based on the diffusion-reaction equation. A sinusoidal curve model is developed by the finite element method to simulate the thickness and stress distribution of thermally grown oxide (TGO). The thickness and stress distribution of the TGO in the thermal barrier coating was investigated by changing the coupling effect and creep effect conditions of the model. The results show that with the increase of the coupling coefficient, the thickness of TGO gradually becomes smaller. In the late stage of oxidation, this effect diminishes, and the compressive stress located in the BC/TGO layer groove keeps decreasing, while the tensile stress located in the TC layer groove is the opposite. As the creep rate increases, the maximum tensile/compressive stress in the Y-direction within the thermal insulation coating slowly decreases, and the oxidation rate of the oxide layer moderately decreases. This study is important to find the corresponding solutions and preventive measures for the failure of the thermal barrier coating.

Viral Small Terminase: A Divergent Structural Framework for a Conserved Biological Function.

The genome packaging motor of bacteriophages and herpesviruses is built by two terminase subunits, known as large (TerL) and small (TerS), both essential for viral genome packaging. TerL structure, composition, and assembly to an empty capsid, as well as the mechanisms of ATP-dependent DNA packaging, have been studied in depth, shedding light on the chemo-mechanical coupling between ATP hydrolysis and DNA translocation. Instead, significantly less is known about the small terminase subunit, TerS, which is dispensable or even inhibitory in vitro, but essential in vivo. By taking advantage of the recent revolution in cryo-electron microscopy (cryo-EM) and building upon a wealth of crystallographic structures of phage TerSs, in this review, we take an inventory of known TerSs studied to date. Our analysis suggests that TerS evolved and diversified into a flexible molecular framework that can conserve biological function with minimal sequence and quaternary structure conservation to fit different packaging strategies and environmental conditions.

Direct observation of chemo-mechanical coupling in DnaK by single-molecule force experiments

Protein allostery requires a communication channel for functional regulation between distal sites within a protein. In the molecular chaperone Hsp70, a two-domain enzyme, the ATP/ADP status of an N-terminal nucleotide-binding domain regulates the substrate affinity of a C-terminal substrate-binding domain. Recently available three-dimensional structures of Hsp70 in ATP/ADP states have provided deep insights into molecular pathways of allosteric signals. However, direct mechanical probing of long-range allosteric coupling between the ATP hydrolysis step and domain states is missing. Using laser optical tweezers, we examined the mechanical properties of a truncated two-domain DnaK(1–552ye) in apo/ADP/ATP- and peptide-bound states. We find that in the apo and ADP states, DnaK domains are mechanically stable and rigid. However, in the ATP state, substrate-binding domain (SBD)∗ye is mechanically destabilized as the result of interdomain docking followed by the unfolding of the α-helical lid. By observing the folding state of the SBD, we could observe the continuous ATP/ADP cycling of the enzyme in real time with a single molecule. The SBD lid closure is strictly coupled to the chemical steps of the ATP hydrolysis cycle even in the presence of peptide substrate.

Mechanism of AAA+ ATPase-mediated RuvAB–Holliday junction branch migration

The Holliday junction is a key intermediate formed during DNA recombination across all kingdoms of life1. In bacteria, the Holliday junction is processed by two homo-hexameric AAA+ ATPase RuvB motors, which assemble together with the RuvA–Holliday junction complex to energize the strand-exchange reaction2. Despite its importance for chromosome maintenance, the structure and mechanism by which this complex facilitates branch migration are unknown. Here, using time-resolved cryo-electron microscopy, we obtained structures of the ATP-hydrolysing RuvAB complex in seven distinct conformational states, captured during assembly and processing of a Holliday junction. Five structures together resolve the complete nucleotide cycle and reveal the spatiotemporal relationship between ATP hydrolysis, nucleotide exchange and context-specific conformational changes in RuvB. Coordinated motions in a converter formed by DNA-disengaged RuvB subunits stimulate hydrolysis and nucleotide exchange. Immobilization of the converter enables RuvB to convert the ATP-contained energy into a lever motion, which generates the pulling force driving the branch migration. We show that RuvB motors rotate together with the DNA substrate, which, together with a progressing nucleotide cycle, forms the mechanistic basis for DNA recombination by continuous branch migration. Together, our data decipher the molecular principles of homologous recombination by the RuvAB complex, elucidate discrete and sequential transition-state intermediates for chemo-mechanical coupling of hexameric AAA+ motors and provide a blueprint for the design of state-specific compounds targeting AAA+ motors.

Onsager reciprocal relations and chemo-mechanical coupling for chemically active colloids.

Similar to cells, bacteria, and other micro-organisms, synthetic chemically active colloids can harness the energy from their environment through a surface chemical reaction and use the energy to self-propel in fluidic environments. In this paper, we study the chemo-mechanical coupling that leads to the self-propulsion of chemically active colloids. The coupling between chemical reactions and momentum transport is a consequence of Onsager reciprocal relations. They state that the velocity and the surface reaction rate are related to mechanical and chemical affinities through a symmetric matrix. A consequence of Onsager reciprocal relations is that if a chemical reaction drives the motion of the colloid, then an external force generates a reaction rate. Here, we investigate Onsager reciprocal relations for a spherical active colloid that catalyzes a reversible surface chemical reaction between two species. We solve the relevant transport equations using a perturbation expansion and numerical simulations to demonstrate the validity of reciprocal relations around the equilibrium. Our results are consistent with previous studies and highlight the key role of solute advection in preserving the symmetry of the Onsager matrix. Finally, we show that Onsager reciprocal relations break down around a nonequilibrium steady state, which has implications for the thermal fluctuations of the active colloids used in experiments.

Self-consistent fractal geometry in polyampholyte hydrogels undergoing exchange and correlation charge-density

Polyampholyte (PA) hydrogels are incorporated of many internally charged polymer chains, which play an important role to influence the fractal networks and dynamic elasticity of the PA hydrogels owing to their different exchange and correlation charge-densities. Many properties of the PA hydrogels, such as mechanical strength and deformation, are significantly dependent on their fractal networks. However, working principles of chemo-mechanical coupling between the fractal networks and the elasticity of PA hydrogels have not been fully understood. In this study, a self-consistent fractal geometry model integrated with a complex function is proposed to understand the constitutive relationship between dynamic networks and tailorable mechanics in the PA hydrogels. The newly developed model is uniquely incorporated with the mechanochemistry, and describes the chemical polarization reactions of charged networks and their mechanical behaviors using complex fractal functions. Based on the rubber elasticity theory, constitutive stress–strain relationships of fractal networks have been described using their elastic, conformational, repulsive and polarization free-energy functions. Finally, effectiveness of the proposed model has been verified using both finite element analysis and experimental results of the PA hydrogels reported in literature.

Modifying Crystal Symmetry and B-O Charge Distribution to Tailor Chemical Expansion in Mixed Conducting Perovskites

The exchange of ions between a lattice and the gaseous phase makes mixed conducting oxides ideal for a range of electrochemical applications. Altering oxygen ion concentration is accompanied by a change to electronic species concentrations, and this influences electrical, chemical, kinetic, and mechanical properties. The stability of electrochemical devices like fuel cells and batteries can heavily rely on the mechanical response to changes in chemical defect concentrations. Under both dynamic and steady-state operation of these devices, large volume strains and strain mismatch at interfaces can result in fracture, warping, and delamination that can cause performance degradation and/or failure. Strains between different materials are compared using the coefficient of chemical expansion (CCE), which normalizes the isothermal chemical strain by the change in defect concentration. Here, we advance the understanding of chemo-mechanical coupling through the study of PrGa0.9Mg0.1O3-δ and BaPr0.9Y0.1O3-δ by demonstrating CCEs 2-5x lower than any previously reported perovskite oxide1.Isothermal CCEs were evaluated with in situ, high temperature, and variable atmosphere x-ray diffraction and dilatometry for chemical strains, and with thermogravimetric analysis for stoichiometry changes. The experimental results show chemical strains to be significantly lower than predictions from simple empirical models that assume pseudo-cubic structures and full charge localization on multivalent cations, like Pr. To evaluate actual charge distribution, in situ impedance spectroscopy and density functional theory calculations were performed. The collaboration of experimental and computational work combines accurate and reliable material characterization with insights into atomic and electronic structures that are difficult to probe experimentally.Our results for the studied compositions indicate 2 primary factors that can be used to modify CCEs: 1) Altering the crystal structure away from the isotropic, cubic phase encourages anistropic expansion and lower CCEs in polycrystalline materials, and 2) Varying the distribution of charge along B-O bonds is shown to dramatically alter the CCE. While the first factor provides rather clear guidance to tailor expansion, we elaborate on the second by suggesting band structure design principles for near-zero redox-strain perovskites, and the benefit of locating holes partially or fully on oxygen is highlighted. These new findings add to the growing collection of crystal-chemical design rules for the rational tailoring of chemo-mechanical coupling in perovskite oxides.(1) Anderson, L. O.; Yong, A. X. Bin; Ertekin, E.; Perry, N. H. Toward Zero-Strain Mixed Conductors: Anomalously Low Redox Coefficients of Chemical Expansion in Praseodymium-Oxide Perovskites. Chem. Mater. 2021, 33 (21), 8378–8393. https://doi.org/10.1021/ACS.CHEMMATER.1C02739.

Non-Euclidean geometry model for chemo-mechanical coupling in self-assembled polymers towards dynamic elasticity

Self-assembly plays a fundamental role to determine thermodynamic properties of polymer systems, e.g., resulting in the formation of dynamically cross-linked networks with varied elasticity. However, the working principle of chemo-mechanical coupling between the self-assembly and elasticity of polymers is complex and has not been well understood. In this study, a non-Euclidean geometry model incorporating thermodynamics of microphase separation is proposed to understand the chemo-mechanical coupling in self-assembled triblock polymers. The thermodynamic separation of microphases, which is resulted from the self-assembly of polymeric molecules, is formulated using a non-Euclidean geometry equation, of which the geometrical parameters are applied to characterize the topologies of self-assembled and cross-linked networks. The non-Euclidean geometry model is further employed to describe chemo-mechanical coupling between the self-assembled network and dynamic elasticity of the triblock polymers, based on the rubber elasticity theory. Effectiveness of the proposed model is verified using both finite-element analysis and experimental results reported in literature. This study provides a new geometrical approach to understand the mechanochemistry and thermodynamics of self-assembled block polymers.

On oxide growth fracture analysis of thermal barrier coatings based on a three-dimensional chemo-mechanical model

The chemical mechanism is the main driven force of the thermally grown oxide (TGO) in thermal barrier coatings (TBCs), and the considerable derives of oxide growth damage are the locally additional perpetual swelling and shape deformation. A three-dimensional chemo-mechanical model is developed to explore the TGO growth based on the chemo-mechanical extended layerwise method (CM-XLWM), and the oxide growth analysis is also carried out for the TBCs with damage in this paper. The contributions of chemical reaction and ionic expansion are taken into account. The numerical simulations of the high-ambient temperature oxidation in TBCs are implemented to demonstrate the mechanism of this physical phenomenon. The chemo-mechanical coupling fracture analysis is established to delve into the principle of TGO growth and the stress states. The interface crack, transverse crack and their combination are considered, and the interactions between the TGO growth and TBC fracture are investigated as well.

Diselenide as a Dual Functional Mechanophore Capable of Stress Self-Reporting and Self-Strengthening in Polyurethane Elastomers

Diselenide as a Dual Functional Mechanophore Capable of Stress Self-Reporting and Self-Strengthening in Polyurethane Elastomers

How Does F1-ATPase Generate Torque?: Analysis From Cryo-Electron Microscopy and Rotational Catalysis of Thermophilic F1.

The F1-ATPase is a rotary motor fueled by ATP hydrolysis. Its rotational dynamics have been well characterized using single-molecule rotation assays. While F1-ATPases from various species have been studied using rotation assays, the standard model for single-molecule studies has been the F1-ATPase from thermophilic Bacillus sp. PS3, named TF1. Single-molecule studies of TF1 have revealed fundamental features of the F1-ATPase, such as the principal stoichiometry of chemo-mechanical coupling (hydrolysis of 3 ATP per turn), torque (approximately 40 pN·nm), and work per hydrolysis reaction (80 pN·nm = 48 kJ/mol), which is nearly equivalent to the free energy of ATP hydrolysis. Rotation assays have also revealed that TF1 exhibits two stable conformational states during turn: a binding dwell state and a catalytic dwell state. Although many structures of F1 have been reported, most of them represent the catalytic dwell state or its related states, and the structure of the binding dwell state remained unknown. A recent cryo-EM study on TF1 revealed the structure of the binding dwell state, providing insights into how F1 generates torque coupled to ATP hydrolysis. In this review, we discuss the torque generation mechanism of F1 based on the structure of the binding dwell state and single-molecule studies.

Generalized Theory for DISes in a Large Deformed Solid

Analysis of diffusion-induced stress in the electrode materials of metal-ion batteries, especially in silicon-anode lithium-ion battery with large deformation, involves an in-depth understanding of the interaction between atomic migration and matrix volume expansion. Under large migration velocity of solute atoms in a host matrix, such chemo-mechanical coupling can result in the damage or structural degradation of the matrix (electrode), leading to capacity fading. Incorporating the effects of concentration changing rate on strain energy in Helmholtz free energy and the finite deformation framework, a generalized theory has been established to solve stresses in an elasto-plastic electrode induced by lithiation. Numerical calculations of lithiation-induced stresses are performed in an amorphous nano-spherical silicon electrode by using the free-volume-based constitutive relation of amorphous materials and the generalized theory. We analyze the effects of the volumetric expansion coefficient associate with solute atoms and the volumetric expansion coefficient associate with the concentration changing rate of solute atoms on the stress evolution. The results reveal that the concentration changing rate of solute atoms likely accelerates surface cracking of electrode materials during lithiation.

Global existence of classical solutions for a reactive polymeric fluid near equilibrium

In this paper, we study a new micro-macro model for a reactive polymeric fluid, which is derived recently in [Y. Wang, T.-F. Zhang, and C. Liu, \emph{J. Non-Newton. Fluid Mech.} 293 (2021), 104559, 13 pp], by using the energetic variational approach. The model couples the breaking/reforming reaction scheme of the microscopic polymers with other mechanical effects in usual viscoelastic complex fluids. We establish the global existence of classical solutions near the global equilibrium, in which the treatment on the chemo-mechanical coupling effect is the most crucial part. In particular, a weighted Poincar\'e inequality with a mean value is employed to overcome the difficulty that arises from the non-conservative number density distribution of each species.

Transient Continuum Mechanics and Chemomechanics

Abstract A transient chemomechanical coupling formulation for solid continuum is presented. The second-order rate and the characterized time are introduced to include the transient effect through Taylor expansion. The transient Reynold’s transport theorem is derived with the new products or material elimination considered. Based on conservation laws and the second law of thermodynamic, we state a consistent Helmholtz-energy-based framework. The transient field equations take mechanical and chemical contributions and microscopic time into account. Either microscopic time or chemical reactions leads to the unsymmetry of the stress tensor. The relationship of Helmholtz energy and constitutive properties, the evolution equations, and the entropy are consistent with the classical continuum thermodynamics and the constitutive theory in continuum mechanics. Further, the transient equations of thermal conduction and diffusion with finite velocity are naturally derived rather than postulated, and a comparison with the existing theories is discussed.

Strain-modulated initial oxidation of Al(1-x)Nix alloy surface

Despite of extensive studies about surface oxidation of metals and alloys, the impact of external loadings on nanoscale initial oxidation remains relatively unclear. Here, we demonstrate that surface prestrains and dynamic loadings can effectively modulate the initial oxidation of Al(1-x)Nix alloys. We find that prestrains can not only suppress or promote outward and inward ionic diffusions, but change the oxygen Ehrlich-Schwöbel (ES) barrier across oxide islands. The former affects the oxidation kinetics while the latter leads to a oxide growth mode transtion, which comprehensively determines the evolution of oxide nanostructure. In addition, we propose a theoretical chemo-mechanical coupling model to predict the internal stress evolution and the stress relaxation in Al0.7Ni0.3 oxidation. Finally, the study of Al and Al0.7Ni0.3 oxidations under dynamic strains shows that alloying nickel in aluminum effectively enhances the oxidation resistance under cyclic loadings by intensifying the chemo-mechanical coupling effect. Findings in this work may shed the light on the modulation of surface oxidation through applying mechanical loadings, and is helpful to the materials design and protection.

Chemo-Mechanical Couplings at Granular Contact: The Effect of Mineral Dissolution and Precipitation across the Scales

Strong interactions between mechanical deformation and chemical reactions may play a critical role in the response of geomaterials or geological systems to evolving environmental circumstances that may occur in both natural and engineered processes. The present study focuses on mineral dissolution and precipitation at the intergranular contact whose consequences are often manifested at the macro-scale where the mechanical and transport properties of the geomaterial may be altered. Discrete element modeling is employed to explore two applications involving such mineral transformations. The first example is primarily focused on the chemo-mechanical coupling mechanisms of intergranular contact in the natural process of pressure solution and secondary compression. The effect of the mineral dissolution on the mechanical response at the grain contact is incorporated into the contact model. Discrete element simulations are performed to examine the overall mechanical response of particle assembles subject to mineral dissolution and the results demonstrate the important role of the kinetic rate characteristics of the dissolution process. The second part of the present study revolves around the effect of mineral precipitation in an engineered process known as microbially induced calcite precipitation for potential soil improvement. The kinetics of involved bio-chemical process is incorporated into on the contact model and the simulation results indicate considerable strengthening effect. Overall, the present study demonstrates the feasibility of discrete element approach as a numerical tool to model coupled chemo-mechanical phenomena across the scales.

A Markov model for rotary catalysis of F1-ATPase

Understanding how F1Fo-ATP synthase (F-ATP synthase) synthesizes ATP from ADP and phosphate is essential for understanding how life on the earth converts and utilizes energy. Studies on isolated F1-ATPase, the soluble sector of F-ATP synthase, which catalyzes ATP hydrolysis in aqueous solution, provide promising insights about the mechanism of F-ATP synthase. A paradigm named rotary catalysis, or binding-change mechanism, has been established to explain ATP hydrolysis mechanism of F1-ATPase, where rotation of the γ-subunit, conformational transition of the β-subunits and nucleotide exchange at catalytic sites are delicately coordinated to maintain a high chemo-mechanical coupling efficiency.