Effect Of Interfacial Energy Research Articles

Effect of interfacial energy on the viscosities of two-phase mixtures—A physical modeling approach

With a view to understanding the viscosities of metal emulsions in viscous slags, the present work was carried out to study the phenomena underlying the viscous flow in a two-phase mixture with widely differing viscosities. Experimental study was carried out to determine the effective viscosities of emulsions of silicone oils of known viscosities (345 and 1010 mPa · s at 293 K) with small amounts of water evenly distributed in the same. The viscosities of these emulsions were measured at a constant temperature by the rotating-cylinder method. The uniformity of the preparation of the emulsions was confirmed by the reproducibility of the results. The measured viscosities were generally found to be independent of the torque under the experimental conditions, so that the two-phase mixture could be considered as a Newtonian liquid. The variation of viscosities with temperature and the effect of the addition of a surface-active substance were also studied in this work. The viscosities were found to be higher than those of both pure water and silicone oil. The experimental results were used to examine the applicabilities of the theoretical models developed by Einstein, Taylor, and Oldroyd. It was found that interfacial energy would play an important role in the viscous flow of the two-liquid mixture.

Semifluorinated Polymeric Liquid Crystals as A Mechanistic Tool to Study The Effects of Interfacial Energies on The Orientation of Liquid Crystals

ABSTRACTObtaining spontaneous orientation and fast collective response of ultra thin liquid crystalline (LC) layers to external stimuli without memory effects, is one of the major challenges in achieving the next generation of LC devices. The relationship between interfacial energies, structure and dynamics of support layers and their effects on surface orientation of liquid crystals has been investigated. A model polymeric system, containing a mesognic group, α- methylstilbene as anchoring group, bridged by an energy controlling moiety, fluorocyclobutyl, has been used to obtain substrates with controlled surface energy and structure. Neutron reflectivity was used to study the surface structure of the polymer. The orientation of a well characterized liquid crystal, 8CB that exhibits both nematic and Smectic phases, was studied by optical microscopy and small angle X-ray scattering. Correlation between the surface structure of the polymeric layer and the orientation of the Smectic phase indicated direct correlation between the surface orientation and the concentration of fluorine at the interface.

Evaluation of composition region for peritectic coupled growth

The composition region for stable coupled peritectic growth is evaluated by means of extending Boettinger's analysis. Our present analysis demonstrates that there exists a critical composition between C α (composition of primary α at peritectic equilibrium) and C β (compostion of peritectic β at peritectic equilibrium), i.e. C crit, separating the peritectic plateau (between C α and C β) into two regions where coupled and banded growth regimes dominate between C crit and C β and between C α and C crit, respectively. The calculated critical composition, C crit, is consistent with the observation in Ni–Al, Ti–Al and Sn–Cd peritectic systems. Effects of interfacial energies of constituent phases and convection on the separation of these two growth regimes are also discussed.

Pattern selection induced by electroconvection in the electrodeposition of iron

The morphology of iron electrodeposit is shown to relate closely to the pH of the electrolyte solution. Macroscopically, depending on the strength of the interbranch convection, which is associated with the concentration of H3O+ in the electrolyte, the deposit morphology varies from treelike pattern to meshlike pattern and dense-branching morphology. Microscopically the deposit is ramified and dense-branching at lower concentration of H3O+, while it becomes relatively smooth and stringy at higher H3O+ concentration. The symmetry of the convective vortices on the two sides of the growing tip is observed to decide the growth behavior of the tip. We suggest that H3O+ influences the pattern formation and pattern selection in the electrodeposition of iron from FeSO4 solution by either initiating interbranch convection or changing the effective interfacial energy of the deposit and the electrolyte.

Structural evolution of water swollen perfluorosulfonated ionomers from dry membrane to solution

The structural evolution of perfluorosulfonated ionomer (PFSI) membranes from dry materials to highly swollen membranes and solutions was investigated using mainly small-angle scattering techniques. The small-angle scattering maximum (“ionomer peak”) is shown to be observable up to very large water content and shifts continuously toward small-angle as water content increases. A modification of the swelling process is observed for a water content larger than 50% by volume. This behavior is attributed to an inversion of the structure from a reverse micellar structure to a connected network of polymer rod-like particles. The swelling behavior of the membranes was determined in different solvents and was analyzed in terms of interfacial energy effects. The conductivity measurements indicate that the structure of the highly swollen membrane is close to the one observed for solutions.

Glass and Structural Transitions Measured at Polymer Surfaces on the Nanoscale

This paper reviews our recent progress in determining the surface glass transition temperature, Tg, of free and substrate confined amorphous polymer films. We will introduce novel instrumental approaches and discuss surface and bulk concepts of Tg. The Tg of surfaces will be compared to the bulk, and we will discuss the effect of interfacial interactions (confinements), surface energy, disentanglement, adhesion forces, viscosity and structural changes on the glass transition. Measurements have been conducted with scanning force microscopy in two different shear modes: dynamic friction force mode and locally static shear modulation mode. The applicability of these two nano-contact modes to Tg will be discussed.

The Effect of Interfacial Free Energies on the Stability of Microlaminates

ABSTRACTLaminated composites with polycrystalline layers typically break down at high temperatures through grain boundary grooving and the pinch-off of individual layers. Such materials, when exposed to high temperatures, develop grooves where grain boundaries meet the interfaces between layers. The depths of the grooves are controlled by the ratios of grain boundary and interfacial free energies, γgb/γint. Depending on the dimensions of the grains, these grooves can extend through the entire layer, causing pinch-off at the grain boundary. This pinch-off destroys the layering and eventually leads to a gross coarsening of the microstructure. Because microstructural stability is critical to performance for most applications, the ability to understand and predict the stability of microlaminates is a necessary tool. An existing model of this capillarity-driven breakdown requires the interfacial free energies, γgb and γint, as input parameters. Both biaxial and uniaxial zero creep tests have been used in conjunction with transmission electron microscopy to measure these interfacial energies in Ag/Ni and Nb/Nb5Si3 microlaminates.

Effect of interface energy on the impact strength of agglomerates

The mechanical strength of agglomerate materials under impact has been investigated by means of computer simulation using Distinct Element Analysis (DEA). The effects of impact velocity and surface energy are addressed. The agglomerates show increasing extent of breakage with increasing impact velocity, but eventually reach a limit above which the damage approaches an asymptotic value. Particles held together by larger adhesive forces yield stronger agglomerates. This is largely related to the effect of the surface energy on the mechanical properties of the agglomerate, such as Young's modulus and fracture surface energy. Observations of particle breakage show no clear planar crack propagation, but rather the disintegration of the agglomerate from the impact site, propagating to the rear of the agglomerate. It is considered that the structure of the agglomerate, as influenced by the method of preparation, does not store sufficient strain energy to allow crack propagation.

Effect of elastic interaction energy on coarsening of γ′ precipitates in a mechanically alloyed ODS Ni-base superalloy

The coarsening behavior of γ′ precipitates with a uniform size distribution and with a bimodal size distribution in a mechanically alloyed ODS Ni-base superalloy were investigated to clarify the effect of elastic interaction energy on the coarsening behavior of γ′ precipitates. The coarsening rate decreased with increasing size of γ′ precipitates with a uniform size distribution, contrary to the classical LSW theory, and the coarsening behavior of γ′ precipitates with a bimodal size distribution exhibited Ostwald ripening in which the larger precipitates grow at the expense of smaller precipitates. The driving force for coarsening of γ′ precipitates was analyzed based on the two-particle model, considering the effect of elastic interaction energy in addition to the effect of interfacial energy. The contribution of elastic interaction energy on the total energy was found to increase with increasing size of precipitates, and the decelerated coarsening of γ′ precipitates was attributed to the decrease in the driving force for coarsening with increasing size of precipitates.

Effect of Surface Diffusion on the Contact Formation and Adhesion of Atomically-Clean Surfaces of Lead, Tin and Pb-Sn Eutectic Alloy

The role of sintering on contact formation and adhesion of polycrystalline lead, tin and Pb-62%Sn alloy in the temperature range 0.4-0.6 T m has been investigated. Atomically-clean surfaces were obtained by the method of controllable internal rupture. Pronounced surface diffusion was observed on free surfaces for all metals investigated. However, contribution to the contact formation and adhesion strength from sintering was found to be essential for Pb-Sn alloy only.The effect of interface energy and grain boundary grooving on sintering is considered.

The dispersion mechanism of TiB2 ceramic phase in molten aluminium and its alloys

Titanium diboride (TiB2) ceramic particulates are dispersed in molten aluminium and its alloys for grain refining and for making cast metal–matrix composites. For producing cast MMC, the dispersion of the ceramic phase via in-situ aluminothermic reduction of K2TiF6 and KBF4 flux mixture with molten aluminium and, via the addition of exogenously formed TiB2 with the fluoride flux has been studied at 900°C. In this article, the aspects of interfacial energy that govern the dispersion and agglomeration of TiB2 particulates are examined. The Gibbs-adsorption interface equation is particularly employed to define and to quantify the change in the surface energy as a function of the alloying element concentration and, consequently the effect of interfacial energy on the nucleation rate of TiB2 formed via metallothermic reduction reaction and the size of the ceramic phase is also explained.

Explanation of the melting behaviour of embedded particles; equilibrium melting point elevation and superheating

The observed melting temperature of embedded particles can be either lower or higher than the bulk equilibrium melting point. Explanations for the observed melting-temperature elevation are still controversial and have been attributed either to an elevation caused by a strain energy effect and/or an interfacial energy effect, or to metastable superheating. Furthermore, there seems to be some confusion regarding the relationship between equilibrium melting-point elevation and the superheating effect. We suggest that the observed increase in melting temperature for embedded particles is caused by both an equilibrium melting-point elevation and a metastable superheating effect, and the two effects tend to be concurrent. An attempt has been made to clarify the two effects in the melting process of indium particles embedded in an aluminium matrix.

Equilibrium thermodynamics of pseudoelasticity and quasiplasticity

Motivated by recent experimental results by Glasauer [1], a thermodynamic theory of shape memory alloys is proposed, which includes not only the high temperature – pseudoelastic – behavior but also the low temperature range of quasiplasticity. Due to the occurance of three different phases – austenite and two martensitic variants – several cases of two-phase equilibria and a three-phase equilibrium have to be taken into account. Their relevance is determined by minimization of the total free energy and subsequently illustrated by the construction of phase charts. A special point of interest is the influence of interfacial energy effects on these phase charts, resulting in phenomena like, for example, the apparent violation of Gibbs' phase rule. Furthermore, the role of interfacial energies in the hysteretic load-displacement behavior is discussed in the light of the additional quasiplastic case.

Theoretic calculation of ferrite growth in supersaturated austenite in FeC alloy

A theoretical model for growth of a ferrite plate into a supersaurated austenite for the FeC system is presented in detail. In the model, the effects of interfacial energy, diffusion in austenite, solute drag, coherency stresses, relaxation by interface dislocations and the finite mobility of the phase interface are taken into account simultaneously and consistently. Various calculations are made in an attempt to present a unified and self-consistent picture of ferrite plate growth.

Computer simulation of strain energy effects vs surface and interface energy effects on grain growth in thin films

A computer simulation of grain growth in two dimensions has been used to model microstructural evolution in Ag (001)Ni thin films. Two orientation dependent driving forces have been included in the simulation: surface and interface energy and strain energy. Surface and interface energy and strain energy do not favor the growth of the same orientations and compete to determine the orientation and microstructure of the film. Growth of grains with (001) texture is favored in highly strained, relatively thick films, while growth of grains with (111) texture is favored by surface and interface energy minimization, especially in very thin films. When a film is constituted of only (001) and (111) grains, (001) texture can develop only if the yield stress of the (111) grains is sufficiently high to prevent yielding at early times. Experimental results confirm that (001) texture can develop in Ag (001)Ni films depending on the state of strain and film thickness.

Heterogeneous nucleation of σ′ on dislocations in a dilute aluminum-lithium alloy

The nucleation of S on dislocations with small undercooling in binary aluminum-lithium alloys has been examined. The study of related microstructures was performed using transmission electron microscopy (TEM), which demonstrates that σ′ preferentially nucleates on dislocations with a strong edge character and locates at the side where the stress field is compressive without destroying the dislocation core structure. This qualitatively justifies the theoretical prediction by Larche on coherent heterogeneous nucleation on edge dislocations. Following the evaluation of the volume free energy change for the binary system by the ideal solution model and the mean-field model by Khachaturyan, the nucleation barrier and the nucleation rate were calculated and compared with experimentally determined data based on Larche's model. Specifically, the back-calculated interfacial energies from the experimentally determined nucleation rate data are in good agreement with the interfacial energy temperature dependence predicted by the related interfacial energy model. The effects of misfit strain, volume diffusion, interfacial energy, and nucleation sites are discussed.

Effect of interfacial energy and viscosity on percolation time of carbon black-filled poly(methyl methacrylate)

The dispersion state of carbon black (CB) particles in a polymeric matrix was found to be affected by such factors as interfacial energy of the CB-polymer interface and the melt viscosity of matrix polymers. At a given CB volume fraction, the electrical conductivity of CB-filled poly(methyl methacrylate) (PMMA) was measured as a function of time at a temperature higher than the glass transition temperature (Tg ). At a characteristic time, as a result of the aggregation of CB, networks facilitating electrical conduction were formed and a percolation-like transition was observed. We defined this characteristic time as the percolation time (t p) and estimated the dispersion state of particles by the tp . The effects of interfacial energy of the CB-polymer interface and melt viscosity of the matrix were estimated quantitatively by changing the surface energy of CB and the temperature. The experimental values of tp were compared to the calculated values using a simple model. The percolation time decreased with increase of interfacial energy and CB content, and increased with the matrix viscosity. The model well explains the dependency as long as the volume fraction of CB is not large and matrix viscosity is neither very small nor very large.

Determination of potentially homogeneous-nucleation-based crystallization ino-terphenyl and an interpretation of the nucleation-enhancement mechanism

A homogeneous-nucleation-based crystallization was found in o-terphenyl in the glass-transition temperature region with an adiabatic calorimeter, and the crystallization process was investigated by direct microscopic observation. The crystallization showed its maximum rate at 248 and ceased at 250 K, while the ordinary crystal-growth process was observed to proceed only above 255 K. The two crystals formed at 248 and 297 K showed the same x-ray-diffraction patterns, indicating that they were in the same crystalline phase. The nucleation-based crystallization was observed in the temperature range of 225 to 250 K as advance of the crystal front into the liquid phase under the microscope, and the crystalline phase exhibited the appearance of the aggregation of fine crystallites which was consistent with the presence of residual entropy and the premelting property. From these results, the crystallization process was interpreted to proceed through the coalescence of crystal embryos into the crystalline phase on the liquid-crystal interface. It was concluded that the decrease in the effective interfacial energy of the embryo due to the coalescence produced an enhancement of the crystal nucleation, and that the enhancement mechanism must have played an essential role for the macroscopically observable crystallization below 250 K.

Effect of interface energy on erosion of A IIIB V substrates during liquid phase heteroepitaxy

Erosive damage to the solid phase surface is the frequently observed effect of the exposure of the multicomponent liquid solution of A III B V compounds to A IIIB V binary substrates. This erosion particularly affects heterocompositions with a high lattice parameter mismatch. The mechanisms leading to such a phenomenon were analyzed for the case of the Ga–In–P–As/InP and Ga–In–P–As/GaAs heteropairs. Based on the model of interatomic interactions at the interface, it was found that the erosion instability of the interface depends mainly on the excessive energy of the lattice in this region.

Glass Transition Temperature Of Ultrathin Polymer Films On Silicon

AbstractThe glass transition temperature, Tg, of polystyrene (PS) thin films on silicon wafers with different surface preparations was determined in order to explore the effect of interfacial interaction energy on local chain dynamics. To enhance interface behavior, the film thickness included in this work was as low as 50 Å. PS with monodisperse molecular weights was chosen as a model polymer. Two different silicon surfaces were prepared: sulfuric acid-clean and hydrogen passivated. Tg of thin films was determined by monitoring the film thickness as a function of temperature. Tgwas identified as the temperature where the thermal expansion coefficient underwent an abrupt change. X-ray reflectivity was used to determine film thickness with a precision of a few angstroms. Tg of PS was found to depend strongly on the initial film thickness, as well as the substrate surface.