Terms Of Interfacial Energy Research Articles

Mesoscopic irreversible thermodynamics of aging kinetics of alpha polypeptides [DNA] under various constraints: Special reference to the simple spring mechanics

The mesoscopic irreversible thermodynamic treatment of α-polypeptides and the helical polynucleotides (DNA) furnishes two sets of analytical expressions, which allow us not only to analyze the reversible force–extension experiments performed by atomic force microscopy (AFM) but also to predict the irreversible “aging” kinetics of the single-stranded and double-stranded polynucleotides (ssDNA and dsDNA) helical conformations exposed to aqueous solutions and applied static stress systems under the various constraints. The present physicochemical cage model emphasizes the fact that the global Helmholtz free energy of the helical conformation acts not only under the stored “intrinsic” unusual torsional and bending elastic energies inherited by the unfolded helical structure of the amino-acid (peptides) or the nucleic-acid (nucleotide) backbone but also reveals the importance of the interfacial Helmholtz free energy density associated with the interaction of the side-wall branches within the surrounding aqueous solutions. The analytical expression obtained for the unfolding force vs extension (FE) shows a strong non-linear elasticity behavior under the twist angle constraint when the interfacial Helmholtz energy term is incorporating into the scenario. This behavior is in excellent quantitative agreement with the AFM test results obtained by Idiris et al. (2000) on the poly-L-glutamic acid [Glu(n)-Cys] exposed to aqueous solutions, which show that acidity increases the degrees of helicity.

Coarsening mechanism of T1 precipitation and calculation of T1/Al interface properties in 2198 Al–Cu–Li alloys: Experimental and DFT studies

This paper aims to reveal the thickening mechanism of multiple different types of T1 precipitation through experimental characterization by HAADF-STEM. Meanwhile, a detailed theoretical analysis of the properties of the T1(0001)/Al(111) interface has been carried out for the first time by applying the first-principles. The experimental results show that the crystal orientation relationships of the T1/Al interface are (0001)T1/{111}Al and [1010]T1/[110]Al. Firstly, two T1 phase thickening mechanisms are proposed. (i) The Cu-rich layer in the T1 phase is used as a substrate for the coarsening of the precipitation. (ii) The Al–Cu transition layer is used as a starting point for precipitation thickening. Secondly, the first-principles were applied to calculate the properties of the T1/Al interface in terms of adhesion work, interfacial energy and electronic structure. The results of the interfacial energy and adhesion work calculations demonstrate that the AlLi-terminated T1/Al interface is more stable. The analysis of the electronic characteristics of the interface shows that the AlLi-terminated interface is more stable and that strong Al–Al and weak Al–Li covalent bonds are formed at the T1/Al interface. Meantime, the electronic structure features are in complete agreement with the findings of the energy calculations.

Improved interfacial adhesion of AlTiN coating by micro-grooves using ultrasonic surface rolling processing

The micro-textures fabricated on the substrate surface of coating are a feasible method to improve the interfacial adhesion of the coating. This research proposes an ultrasonic rolling texturing method, and for the first time reveals how different ultrasonic rolling texturing process parameters (including air pressure, step distance, and feed speed) impact the bonding properties of AlTiN coating. The texture profile, surface morphology, hardness, elasticity modulus, and surface stress state are investigated. Then, the scratch tests are implemented to study the adhesion properties of these textured AlTiN coatings. Results showed that periodic micro-grooves were controllably fabricated, accompanied by high compressive stress and increased surface energy on AISI 5140 steel surface by ultrasonic rolling texturing. The surface morphologies and mechanical properties of the textured surface were strongly dependent on the texturing parameters. And the ultrasonic rolling textured substrate was conducive to the coatings in terms of interfacial contact area, wettability, surface energy, hardness, and residual stress, which could enhance the interfacial adhesion of the coating-substrate. The critical failure loading force of all textured coatings ( F N = 43–59.35 N) exhibited higher value in comparison with the polished coating ( F N = 37.91 N), demonstrating that ultrasonic rolling texturing presented a great potential in the fabrication of high precision micro-textures for enhancing the interfacial bonding properties of coatings. Furthermore, the enhancement mechanism for the ultrasonic rolling texturing on the AlTiN coating adhesion was discussed. The developed texturing method supports the application of hard coatings on mechanical parts such as molds, bearings, etc. • USRP texturing method was proposed and verified. • The coating interfacial adhesion can enhance by USRP texturing pre-treatment. • The USRP texturing parameters had an impact on the coating adhesion behavior. • The enhancement can be attributed to the synergy of hardening and micro-grooves.

Grain size-dependent energy partition in phase transition of NiTi shape memory alloys studied by molecular dynamics simulation

Nanocrystalline NiTi shape memory alloys show fundamental changes in phase transition behavior when the grain size is reduced down to nano-scale (grain size <30 nm). However, due to the extreme difficulties of in-situ experimental observation, universally acknowledged physical mechanisms and detailed microstructures at atomic level are still not clear. In this paper, detailed microstructure images and quantified energy partition at atomic level during stress-induced phase transition are obtained by molecular dynamics simulation. Phase transition is gradually suppressed and incomplete phase transition occurs as grain size decreases. The potential energy landscape of the nanocrystalline system changes significantly from nonconvex to convex, which leads to corresponding changes in stress–strain response and microstructural evolution. With decreasing grain size, the interface (grain boundary and phase boundary) energy makes much more contributions in variation of the system potential energy than the crystallite (austenite and martensite) energy. The mechanism of energy dissipation changes from atomic interface friction in phase transition to plastic deformation caused by grain boundary sliding. It is the gradual dominance of interfacial energy terms in total potential energy that leads to the observed fundamental changes of phase transition behavior in nanocrystalline NiTi.

Morphological instability of iron-rich precipitates in Cu[sbnd]Fe[sbnd]Co alloys

The mechanical properties of metallic materials are determined by their microstructure, and in particular, the different morphologies of precipitates lead to distinct strengthening effects. Usually, the shape of precipitates changes during growth and coarsening regimes, leading to modification of the macroscopic properties of the materials. Thus, understanding of this phenomenon is key to tailoring the precipitate strengthening of industrial alloys. In this article, a general approach to explain the shape instability of iron-rich nanoparticles in CuFeCo alloys during casting and ageing processes is proposed. The evolution of particle shape from sphere to cuboid to petal and finally splitting into eight sub-nanoparticles is observed using transmission electron microscopy. Phase-field modelling and thermodynamic calculations are combined into a general model that describes and elucidates the morphological evolution of precipitates in alloys in terms of particle size, interfacial and elastic strain energy, and chemical driving force. These findings have the potential to promote new microstructural design approaches for a wide range of materials.

Interpreting slip transmission through mechanically induced interface energies: a Fe–3%Si case study

Nanoindentation experiments are performed at the vicinity of grain boundaries, in Fe–Si tricrystals, to illustrate the existence of a critical stress at which slip transmission occurs across grain boundaries. Such a critical stress can be considered as a grain boundary yield stress and can be quantified within the framework of conventional gradient plasticity theory, enhanced by introducing a new mechanically induced “interface energy” term. The present study takes a first step in trying to provide a physical interpretation for this “far from thermodynamic equilibrium” interface energy term by conducting nanoindentation tests in three Fe–3wt%Si tricrystals, each of which had three distinct types of grain boundary misorientations, namely 22.5°, 42.0° and 44.6°. By relating the experimentally measured grain boundary yield stress to the predictions of interfacial gradient plasticity, it is possible to determine the interface parameter ( $$ \xi $$ ), which provides a measure of the resistance to slip transmission for each grain boundary examined. In particular, microscopic arguments from standard dislocation theory reveal that $$ \xi $$ depends on both the grain interior properties and the grain boundary structure. The internal length is shown to depend on multiple characteristic lengths of the microstructure, while a new expression is deduced for relating the Hall-Petch slope to both the interface parameter and internal length.

A methodology for calibration of DEM input parameters in simulation of segregation of powder mixtures, a special focus on adhesion

Conducting a numerical simulation for cohesive granular mixtures that is well comparable with experiments has always been a challenge. In this study, a systematic methodology is proposed for increasing the fidelity of Discrete Element Method (DEM) simulations of cohesive powder mixtures. Segregation of granules during heap formation of a ternary powder mixture is simulated as a proof of concept. The mixture contains three model particles, one of which is an enzyme placebo granule (EP), in order to simulate the segregation of the actual enzyme granules used in detergent formulations. These granules are at a low content level (~2 wt%) and are highly prone to segregation. In this study, the segregation tendency of the EP granules is mitigated by coating them with Polyethylene Glycol 400 (PEG 400). The resulting adhesion is expressed in terms of equivalent interfacial energy for the DEM numerical simulations and is tuned by careful calibration using the concept of the angle of repose. The Cohesion number is used to scale material stiffness or changing the particle size for faster simulation. The particles shapes in DEM are modelled as clumped spheres based on the X-ray tomograms of the real particles. The rest of the DEM input parameters are also selected and tuned based on the particles physical and mechanical properties. Considerable reduction in segregation tendency of the low-level ingredient granules is observed as a result of coating its surfaces by PEG400. Following the proposed calibration strategy, the DEM simulations have predicted the experimental trends closely and a reasonable agreement is achieved. It is observed that using the Cohesion number for scaling the interfacial energy can significantly reduce the number of calibration trials.

Magnetic skyrmion size and stability in ultrathin nanodots accounting Dzyaloshinskii-Moriya exchange interaction

The stability of the skyrmion magnetization configurations in ultrathin circular magnetic nanodots is calculated analytically and simulated micromagnetically considering realistic magnetic and geometrical dot parameters taken from recent experiments. The chiral Dzyaloshinskii-Moriya exchange interaction (DMI) is taken into account as an interfacial energy term. The diagram of single Néel skyrmion stability/metastability, skyrmion sizes and magnetization profiles are found as a function of the magnetic and geometrical dot parameters. It is shown that most of skyrmions are unstable or metastable and the stability region where the Néel skyrmion is the ground state is small. The Dzyaloshinskii criterion for the instability of ferromagnetic state in bulk ferromagnets with respect to the increasing DMI strength should be essentially modified to describe the stability of magnetic skyrmions in 2D systems like ultrathin ferromagnetic films and nanodots.

Interfacial free energy and stiffness of aluminum during rapid solidification

Using molecular dynamics simulations and the capillary fluctuation method, we have calculated the anisotropic crystal-melt interfacial free energy and stiffness of aluminum in a rapid solidification system where a temperature gradient is applied to enforce thermal non-equilibrium. To calculate these material properties, the standard capillary fluctuation method typically used for systems in equilibrium has been modified to incorporate a second-order Taylor expansion of the interfacial free energy term. The result is a robust method for calculating interfacial energy, stiffness and anisotropy as a function of temperature gradient using the fluctuations in the defined interface height. This work includes the calculation of interface characteristics for temperature gradients ranging from 11 to 34 K/nm. The captured results are compared to a thermal equilibrium case using the same model and simulation technique with a zero gradient definition. We define the temperature gradient as the change in temperature over height perpendicular to the crystal-melt interface. The gradients are applied in MD simulations using defined thermostat regions on a stable solid-liquid interface initially in thermal equilibrium. The results of this work show that the interfacial stiffness and free energy for aluminum are dependent on the magnitude of the temperature gradient, however the anisotropic parameters remain independent of the non-equilibrium conditions applied in this analysis. The relationships of the interfacial free energy/stiffness are determined to be linearly related to the thermal gradient, and can be interpolated to find material characteristics at additional temperature gradients.

Diverse morphologies of self-aggregates from dodecyl chain grafted poly(2-hydroxyethyl aspartamide) in aqueous solution

A series of amphiphilic graft copolymers, poly(2-hydroxyethyl aspartamide) grafted with dodecyl chains with different degree of substitution (DS), were synthesized and their self-aggregates showing various morphologies in aqueous media were prepared by direct dissolution method. Spherical micelles, wormlike micelles, tubular networks, and vesicles observed by TEM were found to be a function of DS of the hydrophobic dodecyl chain, and those self-assembled nanostructures can be explained in terms of interfacial energy and packing parameter. To our knowledge, this is the first report of diverse morphologies for a comb-like amphiphilic graft copolymer system. Our system suggests very attractive advantages for biomedical applications and for mass production of aggregates by direct dissolution into water without an organic solvent. Open image in new window

A. baumannii histone acetyl transferase Hpa2: optimization of homology modeling, analysis of protein–protein interaction and virtual screening

In the current scenario, widespread multidrug resistivity in ESKAPE pathogens demands identification of novel drug targets to keep their infections at bay. For this purpose, we have identified a novel target Hpa2 of A. baumannii, a member of GNAT superfamily of HATs. But due to sequence identity of equal or less than 35%, the correct sequence alignment and construction of 3D monomeric and dimeric models of Hpa2 having optimal structural parameters is a troublesome task. To circumvent these problems, we have designed an easy and optimized protocol for Hpa2 monomer modeling, and for generation of dimeric Hpa2 model using data-driven protein–protein docking experiment. Improvement in the structural features of generated model is an onerous process and generally achieved by paying time and computational cost. Herein, it is achieved by reconciliation of FoldX commands which takes less time in execution. Evaluations performed to validate structural parameters and stability of monomeric and dimeric Hpa2 attests to its quality. Analysis of interfacial residues, energy terms and RMSD values indicated a clear correlation between experimental and theoretical interface properties of the dimers, corroborating to the regime used for Hpa2 dimer generation. Structural information from the refined models was used for virtual screening of substrate-derived library and polyamines to achieve a new platform for developing A. baumannii inhibitory molecules. Molecules showing preferential binding at the dimer interface could be used as allosteric inhibitors. Binding of polyamines with model illustrated the same binding pattern as described experimentally in case of yeast Hpa2.

Hybrid level set phase field method for topology optimization of contact problems

The paper deals with the analysis and the numerical solution of the topology optimization of system governed by variational inequalities using the combined level set and phase field rather than the standard level set approach. The standard level set method allows to evolve a given sharp interface but is not able to generate holes unless the topological derivative is used. The phase field method indicates the position of the interface in a blurry way but is flexible in the holes generation. In the paper a two-phase topology optimization problem is formulated in terms of the modified level set function and regularized using the Cahn-Hilliard based interfacial energy term rather than the standard perimeter term. The derivative formulae of the cost functional with respect to the level set function is calculated. Modified reaction-diffusion equation updating the level set function is derived. The necessary optimality condition for this optimization problem is formulated. The finite element and finite difference methods are used to discretize the state and adjoint systems. Numerical examples are provided and discussed.

Deformation-induced dissolution and growth of precipitates in an Al–Mg–Er alloy during high-cycle fatigue

The dissolution and growth of Al3(Er,Zr) precipitates during tensile fatigue experiments were investigated by quasi-in situ and post-mortem scanning transmission electron microscopy with Z contrast imaging and X-ray energy dispersive spectroscopy. Al3(Er,Zr) particles were observed with both non-core–shell and core–shell structures, which were formed during multiple-stage precipitations, in an Al–Mg–Er alloy. After fatigue deformations, the average size of the non-core–shell structured precipitates increased significantly. By tracing the same precipitate particles before and after a high-cycle fatigue test, quasi-in situ electron microscopy revealed that the increase of average particle size is associated with the substantial dissolution of small non-core–shell structured Al3(Er,Zr) particles, whose diameters are generally less than 15nm, and a consequent growth of larger non-core–shell Al3(Er,Zr) precipitates. On the contrary, the core–shell structured Al3(Er,Zr) precipitates remain stable during high-cycle fatigue tests. Possible mechanisms for the dissolution and growth of non-core–shell structured Al3(Er,Zr) precipitates are discussed in terms of particle size, interfacial energy and lattice mismatch, in comparison to the stable core–shell structured precipitates.

A numerical framework for simulating fluid-structure interaction phenomena

In this paper, a numerical tool able to solve fluid-structure interaction problems is proposed. The lattice Boltzmann method is used to compute fluid dynamics, while the corotational finite element formulation together with the Time Discontinuous Galerkin method are adopted to predict structure dynamics. The Immersed Boundary method is used to account for the presence of an immersed solid in the lattice fluid background and to handle fluid-structure interface conditions, while a Volume-of-Fluid-based method is adopted to take trace of the evolution of the free surface. These ingredients are combined through a partitioned staggered explicit strategy, according to an efficient and accurate algorithm recently developed by the authors. The effectiveness of the proposed methodology is tested against two different cases. The former investigates the dam break phenomenon, involving the modeling of the free surface. The latter involves the vibration regime experienced by two highly deformable flapping flags obstructing a flow. A wide numerical campaign is carried out by computing the error in terms of interface energy artificially introduced at the fluid-solid interface. Moreover, the structure behavior is dissected by simulating scenarios characterized by different values of the Reynolds number. Present findings are compared to literature results, showing a very close agreement.

Spinel coatings on metallic interconnects: Effect of reduction heat treatment on performance

Typical manganese cobalt spinel oxide (MCO) coating processes involve both a reduction and an oxidation heat treatment to produce dense and well adherent coatings on metallic interconnects for solid oxide fuel cells (SOFCs). In a high volume production, to achieve the required cycle-time and capacity throughput, it is necessary to perform the reduction heat treatment in a continuous manner rather than batch firing. However, the continuous reduction heat treatment in furnaces requires large capital investments and also incurs high operating costs. Therefore, it is the reduction heat treatment that contributes to a significant portion of overall coating costs. For reduced cost and increased throughput, it would be preferable to eliminate the reduction heat treatment and oxidize the green coatings directly. However, it is anticipated that coatings without the reduction heat treatment would have poor adherence and density which would result in reduced functionality. In the present paper, the performances of MCO coatings processed with and without the reduction heat treatments are evaluated in terms of interfacial fracture energy from mechanical bend tests and area specific resistance (ASR) from electrical tests. Quantifying these mechanical and electrical properties allows for assessment of the benefits of the reduction firing.

Effects of grain size on phase transition behavior of nanocrystalline shape memory alloys

We report recent advances in the experimental and theoretical study of grain size (GS) effects on the thermal and mechanical properties of nanostructured NiTi polycrystalline shape memory alloy (SMA). It is shown that when GS < 60 nm, the superelastic stress-strain hysteresis loop area (H) of the polycrystal decreases rapidly with GS and tends to vanish as GS approaches 10 nanometers. At the same time, the temperature dependence of the transition stress also decreases with GS and eventually approaches zero, leading to a wide superelastic temperature window and breakdown of the Clausius-Claperyon relationship. Rate dependence of the stress-strain responses is significantly reduced and the cyclic stability of the material is improved by the nanocrystallization. It is proposed that the emergence of such significant changes in the behavior of the material with GS reduction originate from the large increase in the area-to-volume ratios of the nanometer-thick interfaces (grain boundary and Austenite-Martensite (A-M) interface) in the polycrystal. In particular, with GS reduction, interfacial energy terms will gradually become dominant over the bulk energy of the crystallite, eventually bring fundamental changes in the phase transition responses of the material. Modelling strategy leading to the establishment of quantitative relationships among GS, grain boundary, A-M interfaces and the macroscopic responses of the material are outlined. grain size effects, phase transition behavior, grain boundary and austenite-martensite (A-M) interface, nanocrystalline NiTi shape memory alloys

A fracture mechanics-based approach for quantifying delamination of spray-applied fire-resistive insulation from steel moment-resisting frame subjected to seismic loading

This article presents a numerical approach based on fracture mechanics theory for evaluating crack initiation, propagation, and delamination of fire insulation at the interface of spray-applied fire insulation and steel surface of a moment resisting frame under the action of earthquake loading. Progression of delamination at the fire insulation-steel interface during cyclic loading is simulated through contact interaction analysis in which Cohesive Zone Model is adopted to model the interface damage and softening. The developed 3D finite element model is validated by comparing predictions from the model, namely crack initiation, crack propagation pattern and the extent of delamination of insulation, against test data generated both at material and structural levels. The validated model is applied to quantify the effect of cyclic damage accumulation at SFRM-steel interface through a parametric study in terms of interfacial critical fracture energy. The influence of local buckling occurring in flange on the extent of delamination is considered in the analysis. Results from the parametric studies indicate that critical fracture energy at steel-insulation interface has significant influence on the extent of damage accumulation over the plastic hinge zone. Further, flange local buckling can substantially enhance the development of tensile stresses at the crack tip leading to delamination over a larger surface area.

Generalized transport model for phase transition with memory

Article history: A general model for phenomenological transport in phase transition is derived, which extends Jackle and Frisch model of phase transition with memory and the Cahn-Hilliard model. In addition to including interfacial energy to account for the presence of interfaces, we introduce viscosity and relaxation contributions, which result from incorporating memory effect into the driving potential. Our simulation results show that even without interfacial energy term, the viscous term can lead to transient diffuse interfaces. From the phase transition induced hysteresis, we discover different energy dissipation mechanism for the interfacial energy and the viscosity effect. In addition, by combining viscosity and interfacial energy, we find that if the former dominates, then the concentration difference across the phase boundary is reduced; conversely, if the interfacial energy is greater then this difference is enlarged. © 2013 Elsevier B.V. All rights reserved.

Amorphization in Nanoparticles

Nanoparticles have more propensities for amorphization than their bulk counterparts, opening the opportunity to achieve the amorphous states in well-known poor glass-former compounds. Classical size effects are often invoked to explain such phenomenon. However, this argument is not sufficient to cover all experimental results such as functionalization effect. In this work, Y2O3 nanoparticles of 7 nm diameter are investigated under pressure. Special care is taken on the surface state of the particles by comparing the pressure-induced transformation of nanoparticles stored under different conditions (atmospheric vs argon environment). A clear difference is reported as one batch shows a transformation to an amorphous state, whereas the second undergoes a crystal-to-crystal transition. These results are discussed in terms of interface energy taking into account not only the usual surface energy but also the surface state contribution. The link between different types of amorphization (pressure-, mechanical-, and radiation-induced amorphization) in nanoparticles is underlined as a critical defect density is required to achieve the crystal-to-amorphous transformation. Defect creation may arise from multiple sources: irradiation, functionalization, and reconstructive transition.

The influence of one block polydispersity on phase separation of diblock copolymers: The molecular mechanism for domain spacing expansion

Comprehensive dissipative particle dynamics simulations are performed to investigate the effect of A-block polydispersity on the phase behavior of AB-diblock copolymers. The experimental results of Lynd and Hillmyer on polydispersity induced domain spacing expansion at different segregations (Macromolecules 2005, 38, 8803) are well reproduced and explained in terms of interfacial free energy and molecular stretching in domain center. Short block copolymers in polydisperse system are found to preferably accumulate at A/B interface as compatibilizers causing a reduction in interfacial free energy. At the same time, domain centers are found mainly occupied by long blocks which in turn determining the spacing of the corresponding domain. More importantly, increase in polydispersity will introduce more long blocks into system and therefore will enhance the molecular packing and stretching in the domain center. Such chain stretching in domain center and reduction in interfacial free energy are found to be more severe at stronger segregation, which will lead to more severe domain spacing expansion with increasing polydispersity.