Surface Internal Energy Research Articles

Surface free energy calculation of the solid–fluid interfaces from molecular simulation

In this work, I present a straightforward approach for computing surface free energy γF based on the assessment of surface internal energy (γU), avoiding the difficulty connected to the determination of the elastic contribution in the case of a solid surface. This methodology has thus been extended to the calculation of γF for the interface between the liquid–vapor phase of water, the solid–vapor interface of aluminum, the aluminum–water interface, rigid graphene–water solid–liquid interfaces, and the n-dodecane–water liquid–liquid interface.

Thermocapillary migration of a deformed droplet in the combined vertical temperature gradient and thermal radiation

Thermocapillary migration of a deformed droplet in the combined vertical temperature gradient and thermal radiations with uniform and non-uniform fluxes is first analyzed. The creeping flow solutions show that the deformed droplet has a slender or a cardioid shape, which depends on the form of the radiation flux. The deviation from a sphere depends not only on the viscosity and the conductivity ratios of two-phase fluids but also on capillary and thermal radiation numbers. Moreover, in the roles of interfacial rheology on thermocapillary migration of a deformed droplet, only the surface dilatational viscosity and the surface internal energy can reduce the steady migration velocity, but the surface shear viscosity has not any effects on the steady migration velocity. The surface shear and dilatational viscosities affect the deformation of the droplet by increasing the viscosity ratio of two-phase fluids. The surface internal energy directly reduces the deformation of the droplet. However, the deformed droplet still keeps its original shape without the influence of interfacial rheology. Furthermore, it is found that, based on the net force balance condition of the droplet, the normal stress balance at the interface can be used to determine the steady migration velocity, which is not affected by the surface deformation in the creeping flow. From the expressions of the normal/the tangential stress balance, it can be proved that the surface shear viscosity does not affect the steady migration velocity. The results could not only provide a valuable understanding of thermocapillary migration of a deformed droplet with/without the interfacial rheology in a vertical temperature gradient controlled by thermal radiation but also inspire its potential practical applications in microgravity and microfluidic fields.

Experimental Study on the Influence of Gravitational Tilt Angle on the Spatio-Temporal Evolution of Solutocapillary Convection

This paper investigated the influence of surface internal energy instability caused by the gravitational tilt angle on solutocapillary convection. The results showed that the spatio-temporal evolution of solutocapillary convection in a non-axisymmetric liquid bridge was divided into three stages under different gravitational tilt angles, “the initiating stage near the upper corner”, “development to the intermediate height”, and “shrinking toward the bottom corner”. The non-equilibrium of the left or right interface curvature caused by internal energy instability promotes the distortion of the cell flow structure. The concentration gradient on the far-earth side increases first, due to the gravitational tilt angle. With the increasing gravitational tilt angle, the lateral extension of the cell flow is inhibited. The transverse/longitudinal velocity components are suppressed; however, the velocity gradient near the boundary is increased, and the uniformity of the velocity distribution in the center of the liquid bridge is improved. The axial component of the Bond number decreases in a small range (Bo′ = 1→0.98) with the internal energy instability, however, which has a significant effect on surface flow. Therefore, in the initiation and development stages of solutocapillary convection, the decay rate of the Marangoni number respectively decreases and increases with the increasing Bond number. The axial component of the Bond number decreases in a small range with the internal energy instability, which has a significant effect on the solute Marangoni number (Mac). In the initiation stage of solutocapillary convection, the decay rate of the Mac decreases with the increasing Bond number. Its change law is the opposite in the development stage of solutocapillary convection.

Thermocapillary migration of a planar droplet at small and large Marangoni numbers: effects of interfacial rheology

In this paper, roles of interfacial rheology on thermocapillary migration of a planar droplet at small and large Marangoni numbers are analyzed. Under quasi-steady-state assumption, the time-independent momentum and energy equations of thermocapillary droplet migration with boundary conditions are determined. An exact solution of the steady thermocapillary migration of the deformed droplet at small Marangoni numbers is obtained. It is found that the deformed droplet has an oblate shape. The deviation from the circular section depends on the Weber number and the migration speed. The surface shear viscosity, the dilatational viscosity and the surface internal energy parameter affect the deformation of the droplet through reducing the migration speed. The validity of the steady thermocapillary droplet migration at small Marangoni numbers is confirmed by determining the conservative overall integral energy equations. At large Marangoni numbers, the non-conservative overall integral energy equations imply that thermocapillary droplet migration is always an unsteady process.

Physicochemical properties of [cnmim][thr] (n = 3, 5, 6) amino acid ionic liquids

A series of ionic liquids based on amino acid, threonine, [Cnmim][Thr] (n=3, 5, 6) (1-alkyl-3-methylimidazolium threonine salt), was designed and synthesized. The density, surface tension and refractive index were measured over the range of T=(288.15–328.15)K and the atmospheric pressure. The molar surface Gibbs energy, g, have been calculated. Using the molar surface Gibbs energy, a new Eötvös equation was obtained in which each parameter has a clear physical meaning. In terms of the thermodynamic relationship, the molar surface entropy, s, enthalpy, h, and the ratio of molar surface internal energy to molar internal energy of vaporization, Er were calculated and the molar entropy of vaporization of surface, ΔSvs was estimated. For [Cnmim][Thr] and other ILs, low values of s and high values for ΔSvs, and low values for Erψ were obtained and these data indicate the surface layer of the ILs is almost the same as that of the bulk liquid, except for a few neighbours in the direction of the gas phase. From the refractive index and the molar surface Gibbs energy, an equation to predict the surface tension of ILs was derived and the predicted values were highly correlated with the corresponding experimental ones.

The study on temperature dependence of viscosity and surface tension of several Phosphonium-based deep eutectic solvents

Deep eutectic solvents (DESs) are derived from two or more salts as the hydrogen bond acceptors (HBAs) and hydrogen bond donors (HBDs). In this work, six deep eutectic solvents (DESs) were prepared namely allyltriphenyl phosphonium bromide- diethylene glycol (ATPPB-DEG) and allyltriphenyl phosphonium bromide - triethylene glycol (ATPPB-TEG) using three molar ratios of 1:4, 1:10 and 1:16 salt to HBDs. The temperature range for experimental viscosity was from 293.15 to 343.15K and that of the experimental surface tension was between 298.15 and 343.15K. The results disclosed that hydrogen bonding in DESs has a great effect on the properties. Among all DESs with the same components, the DESs with the strong hydrogen bonding in their structures had the higher viscosity and surface tension. Besides, by increasing the temperature and quantity of HBDs in DESs, both of these properties experienced a decreasing trend in the amount. It was found that the molecular weight of DESs with the same component has an effect on the properties. The higher molecular weight caused the higher viscosity and surface tension. Further, ATPPB-TEG DESs had the higher viscosity and lower surface tension than ATPPB-DEG DESs because of the higher alkyl chain in their structures. Several models and a new empirical equation were used to correlate the experimental viscosity data. It was found that there is a well agreement between theoretical and experimental values especially when the new empirical equation is used. In addition, the activation parameters for all DESs were calculated using the experimental viscosity data and application of Eyring's absolute rate theory. The experimental surface tension was employed to predict the critical temperature, surface entropy and internal surface energy of DESs. Finally, two empirical equations were used for relating the experimental surface tension to the experimental viscosity of DESs.

Thermodynamic model of meat drying by infrarred thermography

Drying operation is one of the most important unit operations used to preserve meat products. Drying process involves a lot of mechanisms coupled together, and traditional kinetic theory of drying explains part of them, covering up the most important behaviors in the falling drying period. Therefore, it is necessary to determine the critical points of each transformation throughout the drying, and to analyse and quantify all of them. In this sense, an irreversible thermodynamic model has been developed, focusing on the falling drying period. In this work, infrared thermography has been used in order to obtain the evolution of meat surface temperature during drying operation. Infrared measurements were made with an Optris PI® 160 thermal imager (Optris GmbH, Berlin, Germany), with a spectral infrared range of wavelength from 7.5 to 13μm. Surface water activity, volume, mass and moisture were obtained at different drying times. Drying analysis shows five stages, the traditional induction and the constant kinetic drying period (wet temperature of 22°C) and three more stages in the falling drying period, shared out by the evolution of the surface internal energy and the vitreous transition.

Thermal effects of phase transformations: A review

All the stages of phase transformations in materials, nucleation, growth, and coarsening, are subject to thermal effects that stem from the redistribution of energy in the system, like release of latent heat, and heat conduction. The thermal effects change the rate and outcome of the transformation and may result in the appearance of unusual states or phases, in particular in nanosystems. This review will cover the attempts of researchers to build a comprehensive theory of thermal effects in different phase transformations. Although the dynamical Ginzburg–Landau (continuum) approach will be used for the analysis of the effects, they are robust and conceivably independent of the theoretical method employed. On general physical grounds a possibility of an oscillatory regime in nucleation is considered and evolution equations for the interfacial motion are derived. The equations show that there are two distinctly different sets of thermal effects of interface motion: one set originates from the existence of the Gibbs–Duhem thermodynamic force on the interface, which has opposite directions compared to the velocity of the interface in the cases of continuous and discontinuous transitions, resulting in a heat trapping effect for the latter and a drag effect for the former. The other set of thermal effects stems from the existence of the surface internal energy and the necessity to carry it over together with the moving interface. As a result, temperature double layers accompany moving domain boundaries after a continuous transition or the surface creation and dissipation effect appear after a discontinuous one. An unusual, novel phase that may appear in isolated nanosystems (adiabatic nanophase) is described. Several experiments are suggested for the verification of the thermal effects in different material systems.

Effects of projectile orientation and surface impact site on the efficiency of projectile excitation in surface-induced dissociation: Protonated diglycine collisions with diamond {1 1 1}

Classical trajectory simulations are performed for collisions between protonated diglycine (gly 2-H +) and a diamond {1 1 1} surface at incident angles θ i of 0° and 45°, with respect to the surface normal, and initial translational energies E i of 35 and 70 eV. The trajectories are analyzed to determine how the orientation angle of the peptide ion and the surface impact site affect the collisional energy transfer. There are two distinct impact points on the surface on which the peptide ion can collide, hydrogen and carbon atoms, denoted as H- and C-sites. While the impact point plays little to no role in determining energy transfer, for θ i = 0° the orientation angle of the peptide has a significant effect on energy transfer. When the peptide ion collides with its backbone vertical to the surface plane and, thus, with a C- or N-terminus approach, the internal energy change is a maximum and the final translational energy and surface internal energy change are at a minimum. When the peptide ion collides horizontally, the opposite occurs. In addition, for vertical collisions more energy is transferred to the peptide ion if the C-terminus first strikes the surface instead of the N-terminus. For non-perpendicular collisions, with θ i = 45°, the energy transfer efficiency is less sensitive to the peptide orientation. Peptide orientation becomes more important as E i is increased.

The chemical potential in surface segregation calculations: AgPd alloys

We put forward a technique for calculating the surface segregation profile in substitutional disordered alloys. The surface internal energy and the effective bulk and surface chemical potentials are calculated using the full charge density exact muffin-tin orbitals method, combined with the coherent potential approximation. The application of our approach is demonstrated to the close-packed surface of Ag c Pd 1− c random alloys with 0 < c < 1. The surface concentration profile, surface energy and segregation energy are investigated as functions of bulk composition. The present results are compared with former theoretical and experimental data. It is found that at low temperature, Ag segregates to the surface layer for the entire bulk composition range. At 0 K, the subsurface layer contains 100% Pd for c ≲ 0.4, and somewhat more than (2 c − 1) Ag in alloys with c > 0.5. The temperature dependence of the segregation profile is significant for Pd rich alloys and for alloys with intermediate concentrations. At temperatures ≳600 K, the subsurface layer is obtained to be almost bulk like.

Moisture Induced Degradation of Porous Low-k Materials

AbstractInteraction of moisture with porous low-k films is evaluated by using in situ ellipsometry setup. The adsorbed water amount is calculated from change of refractive index measured during the adsorption. Pristine low-k films reversibly adsorb 2 - 5% of water that reflects presence of constitutive hydrophilic centrums. Plasma and thermal treatments increase the number of hydrophilic centrums. Once the amount of these centrums has reached a certain critical value sufficient to form a continuous water film, bulk water condensation is observed. Change of properties during the water adsorption in the damaged films is not fully reversible. Each additional adsorption cycle increases the dielectric function of the film because of decreasing porosity, increasing skeleton density and shrinkage. The pressure corresponding to the bulk condensation allows us to calculate internal contact angle (internal surface energy) of low-k materials. The water molecules adsorbed on separate OH groups play the role of a catalyst that hydrolyses the siloxane bridges initially present on hydrophobic surface.

Thermochemistry of guest-free melanophlogite

Melanophlogite is a naturally occurring clathrasil possessing a framework of linked silicate tetrahedra surrounding small, isolated cages, which can host small molecules. The energetics of a guest-free natural sample was determined by oxide-melt solution calorimetry. Melanophlogite is energetically metastable with respect to α-quartz by 9.5 ± 0.5 kJ/mol, a value similar to that for amorphous silica and for synthetic small-pore zeolitic silicas (Petrovic et al. 1993, Piccione et al. 2001). Thus, its occurrence in nature, for example in environments where it can occlude volcanic gases, is reasonable on energetic grounds. Molecular modeling of the internal pore volume of melanophlogite confirms that this enthalpy follows the trend previously established for a variety of silica zeolites, which defines an internal surface energy of 0.093 ± 0.010 J/m2, similar to that of the external surface energy of amorphous silica. Thus melanophlogite, despite its unique topology and isolated cages, behaves energetically as predicted from the enthalpies of more-open zeolitic frameworks.

Bénard-Marangoni Instability of a Two-Layer System with Allowance for Variations in the Interfacial Internal Energy

The effect of variations of the internal surface energy due to local increments in the interfacial area on the conditions of onset of thermocapillary Marangoni instability in a two-layer system of reduced-viscosity fluids is studied. It is shown that in the linear approximation the effect considered leads to stabilization of the development of the monotonic instability mode.

Thermal Effects of Interfacial Dynamics

Dynamical Ginzburg-Landau theory is applied to the study of thermal effects of motion of interfaces that appear after different phase transitions. These effects stem from the existence of the surface internal energy, entropy and temperature gradients in the interfacial transition region. Evolution equations for the interfacial motion are derived. For the experimental verification of the thermal effects the expression is derived for the amplitude of temperature waves during continuous ordering.

Curvature correction model of droplet profiles

Using recent generalizations of the Laplace equation based on the curvature expansion for surface internal energy, the lowest-order surface curvature correction to the standard macroscopic energy minimization model of liquid droplet profiles is explained. Including this correction, the nonlinear differential equation governing cylindrical profile shape is derived and its numerical solutions under suitable boundary conditions are presented. The results show qualitative agreement with recent experiments in the production of melted microlenses. The standard spherical solution is recovered as the special case of global constant curvature.

Possible effect of variation in the internal energy of the free surface of a thin liquid layer on its wavy flow

A formally possible mechanism is considered for the development of longwave perturbations of flow of a thin layer of a heat-conducting viscous liquid with a free boundary, whose characteristic feature is that the Marangoni stresses occurring at the boundary are induced by variations in the internal energy of the interface. The effect of surface internal energy fluctuations on the layer flow in the approximation considered is of a dispersive character, and, in particular, it can facilitate regularization of wave regimes.

Efficient production of silicon-on-insulator films by co-implantation of He+ with H+

We have investigated the process of thin film separation by gas ion implantation and wafer bonding, as well as the more basic phenomenon of blistering, on which the technique is based. We show that when H and He gas implants are combined they produce a synergistic effect which enables thin-film separation at a much lower total implantation dose than that required for either H or He alone. By varying the H and He implantation doses we have been able to isolate the physical and chemical contributions of the gases to the blistering processes. We find that the essential role of H is to interact chemically with the implantation damage and create H-stabilized platelet-like defects, or microvoids. The efficiency of H in this action is linked to its effective lowering of the silicon internal surface energy. The second key component of the process is physical; it consists of diffusion of gas into the microvoids and gas expansion during annealing, which drives growth and the eventual intersection of the microvoids to form two continuous separable surfaces. He is more efficient than H for this process since He does not become chemically trapped at broken bonds and thus segregates into microvoids more readily. In particular, we have demonstrated that a 1×1016 cm−2 He dose in combination with a 7.5×1015 cm−2 H dose are sufficient to shear and transfer a thin silicon film onto a handle wafer after bonding the two wafers together.

Generalized curvature expansion for the surface internal energy

In this paper a generalized Taylor series expansion of the surface internal energy about zero mean and Gaussian curvature is presented. The static equilibrium of an isolated system is studied, substituting this expanded version of the surface internal energy. From the set of necessary conditions that follows from the equilibrium analysis, a sequence of subsequent approximations to the normal and tangetial components of the jump momentum balance at the interface is extracted. The first four members of this sequence are presented, and the result obtained by Boruvka and Neumann [J. Chem. Phys. 66 (1977) 5464] for the normal component of the jump momentum balance, are shown to be a special case of the third order approximation for this balance. The results are also compared with the expansions used by Blokhuis and Bedeaux [J. Chem. Phys. 95 (1991) 6986; Physica A 184 (1992) 42; HCR Adv.-Education Rev. 1 (1994) 55].

The interaction of dislocations and planar faults in solids

Abstract The equilibrium configurations of an array of straight parallel dislocations and planar defects bounded by dislocations in a solid are considered. On the basis of dimensional arguments and using Euler's theorem for homogeneous functions, it can be shown that the total internal surface energy of the planar defects is constant for all possible unrestrained equilibrium configurations of the array and is equal to the sum of all pre-logarithmic interaction energy factors.

Surface statistical thermodynamics for nonspecular boundary reflection in a quantizing magnetic field.

In this work we consider a model boundary condition representing nonspecular electron wave-function reflection at a surface, having a parameter characterizing the measure of diffuseness of reflection. We carry out an analysis of the surface statistical thermodynamic functions to determine their dependence on the diffuseness parameter. In this, we examine the surface density and state density, surface partition function, surface grand potential and Helmholtz free energy, surface internal energy, and surface magnetization and specific heat. We incorporate the role of a quantizing magnetic field, and treat both nondegenerate and degenerate statistical regimes, including de Haas--van Alphen oscillatory phenomena as well as the quantum strong-field limit.