Surface Energy Theory Research Articles

Thermal Buckling and Postbuckling Behaviors of Couple Stress and Surface Energy-Enriched FG-CNTR Nanobeams

Small-sized structural elements such as beams, plates, and shells are usually used as nanomechanical resonators, nanoscale mass sensors, nanoelectromechanical actuators, and nanoenergy harvesters. At the nanoscale, the structures usually possess a high surface area-to-bulk volume ratio, leading to the free energy related to surface atoms becoming considerable compared to that of the bulk part. Earlier reports indicated several physical reasons for size-dependent phenomena, e.g., nonlocal stress, surface energy, and couple stress. To provide an in-depth insight into the mechanical behavior of small-scale structures, size-dependent continuum models including two or more physical factors have attracted the attention of the academic community. This research analyzes the thermal buckling and postbuckling characteristics of functionally graded carbon nanotube-reinforced (FG-CNTR) nanobeams with a tri-parameter, nonlinear elastic foundation and subjected to a uniform temperature rise. Chen-Yao’s surface energy theory and Yang’s symmetrical couple stress theory are combined to capture two types of size effects in nanobeams. The postbuckling model is formulated based on the Euler–Bernoulli deformation hypothesis and Euler–Lagrange equation. Using a two-step perturbation technique, the related postbuckling equilibrium path is determined. In numerical analysis, the impacts of surface energy, couple stress, elastic foundation, boundary conditions, geometric factor, layout type, and volume fraction of CNTs on the thermal buckling and postbuckling behaviors of nanobeams are revealed. It is indicated that considering couple stress or surface energy can lead to a significant increase in the postbuckling stability of nanobeams compared to the case in which it is not considered. In addition, there is a reverse competition between couple stress or surface energy effects on the thermal buckling responses of nanobeams. As the temperature rise will cause the material elastic moduli softening, the thermal buckling load–deflection curves of nanobeams with the temperature-independent case are much higher than those with the temperature-dependent cases.

Using a Traveling-Wave Piezoelectric Device to Generate a Liquid Wave for Efficient Lightweight Particle Transfer

In this study, the transfer process of extremely light and small-sized particles along a defined direction without flipping them over on the transportation surface is evaluated by using a traveling wave. For this, the use of a liquid, as the contact layer injected onto the top surface of a piezoelectric traveling-wave device, is proposed to transmit the wave into the particles. As a preload is unlikely to be assigned here, the adhesion force between the lightweight particle and the liquid is expected to dominate the delivery effect. A short-beam linear motor is chosen as an example of a piezoelectric device that can generate a traveling wave in association with several selected liquids such as water, saline water, oil, and glycerol. The influence on the traveling-wave amplitude transmitted to liquids with different viscosities and heights is studied by an analytical approach and the finite-element simulation. The surface energy theory is used to determine the adhesion force between the liquid and the lightweight particle. An experiment is conducted to measure the speed of particles with variable sizes that are transported by the liquid wave. The analytical and experimental results are in good agreement, verifying the influence of the above concerned factors on the particle transfer speed.

Surface Free Energy Theory for Evaluating Moisture Damage in Expandable Polyurethane Grouting Materials

The resistance properties of the interface between polyurethane(PU) grouting materials and rocks subjected to water erosion are the theoretical basis for evaluating the long‐term performance, which, however, is not clear yet. Herein, surface free energy (SFE) theory is used to analyze the mechanism of water damage at the interface between the polyurethane and rock. The surface energy parameters of various PU grouting materials with different densities, limestone, and granite rock materials are tested. The adhesion and peeling work indices are calculated by the SFE theory. The results show that water brings little influence on PU grouting materials. The lower the density of PU is, the better the hydrophobicity is. The increase in the density of PU promotes adhesion between the PU and rock with and without water. Moreover, density increases the difference between SFEs of PU–rock and water–rock, decreasing the detachment tendency of PU over the rocks. Lithology also affects the adhesion of PU and rocks. PU–granite composite exhibits the largest adhesion work and smallest peeling work, which indicates that it has stronger water damage resistance. Finally, the validity of the surface energy theory is proved by mechanical, bond tests and the application.

Application of Solid Waste in Asphalt Pavement Based on Surface Energy Theory

Application of Solid Waste in Asphalt Pavement Based on Surface Energy Theory

Abatement of scale precipitation in oilfields using green scale inhibitors

Scale formation in upstream oil operations may cause lower production rate, higher operational costs and detrimental environmental impacts when hazardous chemical inhibitors should be used to combat scaling. Green scale inhibitors (SI) are also gaining increased attention but their utilization is still a matter of much debate with many open questions to be addressed. In this study, green SIs, i.e., folic acid and inulin were investigated from experimental and theoretical perspectives. In the experimental part, two brines were mixed incompatibly through standard high-temperature static tests i) to examine the performance of green SIs and also ii) to discern their optimum concentrations and pH. Furthermore, SEM (Scanning Electron Microscopy) and EDX (Energy Dispersive X-ray) analyses were carried out to identify mechanisms under which the mitigation of scale precipitation would take place. The results revealed that folic acid and inulin could optimally be applied with concentrations of 450 mg/L (pH = 4) and 600 mg/L (pH = 6), respectively. SEM analyses also showed that the dominant inhibition mechanism for folic acid was crystal modification whereas it was threshold inhibition for inulin. Moreover, based on the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, the work of cohesion was calculated which confirmed that folic acid and inulin retarded calcite from getting precipitated almost %65 and 54%, respectively. Finally, the performance of a commercial phosphonated SI was also investigated for the sake of comparison with the green SIs which confirmed their comparable efficacy. • Assessment of two green scale inhibitors for utilization at reservoir conditions. • Experimentally optimization of concentration and pH of green scale inhibitors. • Utilization of surface energy theory to calculate the inhibition efficiency. • Comparable efficacy of green scale inhibitors with respect that of commercial one.

Discussion of “Two-Step Mixing Process Elaboration of the Hot-Mix Asphalt Mixture Based on Surface Energy Theory” by Liping Liu, Mingchen Li, and Qingbing Lu

Discussion of “Two-Step Mixing Process Elaboration of the Hot-Mix Asphalt Mixture Based on Surface Energy Theory” by Liping Liu, Mingchen Li, and Qingbing Lu

Closure to “Two-Step Mixing Process Elaboration of the Hot-Mix Asphalt Mixture Based on Surface Energy Theory” by Liping Liu, Mingchen Li, and Qingbing Lu

Closure to “Two-Step Mixing Process Elaboration of the Hot-Mix Asphalt Mixture Based on Surface Energy Theory” by Liping Liu, Mingchen Li, and Qingbing Lu

Mechanism of texture formation in submicron Cu thin films

We successfully fabricated the submicron Cu thin films with different texture components and thicknesses by magnetron sputtering method, and investigated the underlying mechanism of texture formation. The X-ray diffraction, electron backscatter diffraction and transmission electron microscopy were employed to elucidate the {111}, {011}, {001} and random texture components formation mechanism. In addition, the orientation factors were calculated to clarify the influencing mechanism of grain preferential growth in the yielding submicron Cu thin films. The film sputtered at 100 W has a preponderance growth of {111} oriented grains, which is explained by the minimum of surface energy theory. With sputtering power increased to 200 W, the formation of random texture could be attributed to the presence of extensive twinning. Increase the sputtering power to 300 W and simultaneously keep the thickness to 200 nm, then the texture transforms to {001} texture component. Further increased the thickness to 1000 nm, the fraction of {011} texture component reveals preponderantly, which is controlled by the differences of orientation factors during yield process. The qualitative coincidence between the experimental results and theoretical analysis indicated that the underlying mechanism of preferential growth in the submicron Cu thin films was related to the competition of different driving forces. From adjusting the major driving force, different texture components could successfully be manipulated in submicron Cu thin films.

On bending, buckling and free vibration analysis of 2D-FG tapered Timoshenko nanobeams based on modified couple stress and surface energy theories

In this study, the static bending, buckling, and free vibration behaviors of two-dimensional functionally graded (2D-FG) tapered micro/nanobeams are modelled and analyzed. For the first time, the nonclassical equations of motion and corresponding boundary conditions of 2D-FG beam are simultaneously derived in the framework of the modified couple stress and Gurtin-Murdoch surface elasticity theories in conjunction with the Timoshenko beam theory. Here, all the material properties of the beam are graded along the thickness and length directions according to the power-law. Both thickness and width of the beam are considered to vary linearly along the length direction. Unlike existing Timoshenko beam models, the current formulation accounts for the axial and bending deformations, Poisson’s effect, and exact position of the physical neutral plane. Differential quadrature method is employed to estimate the variable coefficients of the derived equations. The bending deflection, critical buckling load, and free vibration frequency of simply supported 2D-FG Timoshenko nanobeam are obtained employing the Navier's method. A parametric study is accompanied to investigate the effects of the different material and geometrical parameters on the mechanics of 2D-FG micro/nanobeams. It is observed that these parameters are very important in investigating the static and dynamic responses of 2D-FG micro/nanobeam.

Anisotropic rock permeability evolution model based on wing crack propagation after dynamic load testing

The permeability evolution of rock is essential in geotechnical engineering, which is related to seepage. A permeability evolution model, which is based on the wing crack propagation model and Darcy’s law, is created for rock after dynamic load testing with confining pressures. It is assumed that permeability has two types: isotropic initial permeability and anisotropic microcrack-induced permeability. In this model, the wing crack length is associated with the absorption energy per unit volume of the rock specimen under dynamic loads, in accordance with the surface energy theory. Assuming that the initial crack families are evenly distributed, the contribution of each crack family to permeability in different directions is investigated. In this study, an expression of permeability, which is related to axial stress, confining pressure, and absorbed energy per unit volume, is obtained. Two groups of dynamic load testing with confining pressures of sandstone are conducted using a modified split Hopkinson pressure bar technique. In group A, the incident energy is a variable, whereas in group B, the confining pressure is a variable. After the dynamic load testing, the permeability of the sandstone specimens is measured using the pulse decay method on MTS 815. Owing to the limitations on the test equipment, only the permeability in the direction of the dynamic load is measured. The permeability obtained from the dynamic load testing is in good agreement with the permeability calculated by the model. In this model, the anisotropy of rock permeability is theoretically studied. The minimum microcrack-induced permeability in all directions is about 0.65 of the maximum permeability value. In summary, the model discussed here enables the prediction of the permeability of the rocks under dynamic impact and establishes the relationship between macro-mechanical parameters and micro-mechanical parameters. In addition, it provides a new idea for the research on the anisotropy of rock permeability.

Green Preparation of Aqueous Graphene Dispersion and Study on Its Dispersion Stability.

The large-scale preparation of stable graphene aqueous dispersion has been a challenge in the theoretical research and industrial applications of graphene. This study determined the suitable exfoliation agent for overcoming the van der Waals force between the layers of expanded graphite sheets using the liquid-phase exfoliation method on the basis of surface energy theory to prepare a single layer of graphene. To evenly and stably disperse graphene in pure water, the dispersants were selected based on Hansen solubility parameters, namely, hydrophilicity, heterocyclic structure and easy combinative features. The graphene exfoliation grade and the dispersion stability, number of layers and defect density in the dispersion were analysed under Tyndall phenomenon using volume sedimentation method, zeta potential analysis, scanning electron microscopy, Raman spectroscopy and atomic force microscopy characterization. Subsequently, the long-chain quaternary ammonium salt cationic surfactant octadecyltrimethylammonium chloride (0.3 wt.%) was electrolyzed in pure water to form ammonium ions, which promoted hydrogen bonding in the remaining oxygen-containing groups on the surface of the stripped graphene. Forming the electrostatic steric hindrance effect to achieve the stable dispersion of graphene in water can exfoliate a minimum of eight layers of graphene nanosheets; the average number of layers was less than 14. The 0.1 wt.% (sodium dodecylbenzene sulfonate: melamine = 1:1) mixed system forms π–π interaction and hydrogen bonding with graphene in pure water, which allow the stable dispersion of graphene for 22 days without sedimentation. The findings can be beneficial for the large-scale preparation of waterborne graphene in industrial applications.

Quantitative Analysis Investigation of the Water Stability of Asphalt Mixtures with Crushed Gravel Based on the Theory of Surface Free Energy

To quantitatively analyze and study the water stability of crushed gravel asphalt mixture by using surface energy theory, the surface energy parameters of crushed gravel samples at 20℃ are tested by using the gas sorption method, and the surface energy parameters of four anti-stripping agent asphalts with different dosages (0%, 0.2%, 0.4%, 0.6%) at 20℃ are tested by using the Wilhelmy plate method. Then, the binding energy of crushed gravel and anti-stripping agent asphalts with different dosages and the surface energy evaluation index of water stability are calculated. On this basis, quantitative analysis and sequencing of water stability of crushed gravel asphalt mixture were carried out. The microscopic mechanism of the anti-stripping agent's improvement on adhesion between crushed gravel and asphalt was analyzed from the angle of surface energy. Marshall test (immersion Marshall test, vacuum saturation Marshall test, freeze-thaw splitting test) with anti-stripping agent contents of 0%, 0.2%, 0.4%, and 0.6% was conducted through strict control of crushed gravel material, gradation, and oil-stone ratio. Results show that (1) the surface energy parameters of crushed gravel are dominated by polar alkali component; (2) the addition of anti-stripping agent will reduce the surface energy of asphalt, thus increasing the wettability of asphalt to aggregate; (3) the improvement of the adhesion between crushed gravel and asphalt by adding anti-stripping agent is mainly reflected in two aspects: reducing the cohesive energy of asphalt itself to increase its wettability to aggregate and increasing the surface energy acid component of asphalt to increase its adhesion binding energy to aggregate; and (4) the order of microscopic surface energy evaluation index of water stability of crushed gravel asphalt mixture is the same as that of macroscopic performance test index, thus demonstrating the accuracy of the surface energy system for quantitative analysis of the water stability of the crushed gravel asphalt mixture.

Two-Step Mixing Process Elaboration of the Hot-Mix Asphalt Mixture Based on Surface Energy Theory

AbstractHot-mix asphalt (HMA) is a multicomponent mixture composed of asphalt, coarse and fine aggregates, fillers, and other necessary additives. The bitumen–aggregate adhesion and performance of ...

Adhesion of Bituminous Crack Sealants to Aggregates Using Surface Energy Theory

AbstractIn the system formed by bituminous crack sealant and the crack wall, the contact area of aggregate and sealant is maximum, and types and properties of aggregate have an obvious influence on...

Adhesion property of bituminous crack sealants to different asphalt mixtures based on surface energy theory

In order to quantitatively evaluate the adhesion property of bituminous crack sealants to the crack walls formed by different types of asphalt mixtures, the surface energy components of raw materials were determined by the sessile drop method. Then the adhesion work of sealants and pavement materials was calculated respectively. The correlation between indexes of adhesion work was verified by quantitative boiling method and scanning electron microscope (SEM) test. Finally, four kinds of mixture specimens were formed, and the geometrical information of cross-section of mixture was extracted based on the digital image processing (DIP) technique. The weighted average adhesion work of the cross-section was calculated and verified by the shear tests. The test results show that the surface energy of basalt is obviously higher than that of the SBS modified asphalt and sealant. Among the components of surface energy of three materials, the dispersion component is dominant. The adhesion work of sealant and aggregate is higher than that of SBS modified asphalt. Test results of quantitative boiling method show that there is a good linear relationship between the mass loss rate of the sealant and the index of the adhesion work. The determination coefficient is as high as 0.96, indicating that the index of adhesion work can accurately characterize the adhesion performance of sealant and aggregate. DIP test results show that the aggregate of four mixtures accounts for the largest area, which exceeds 71% of total area. The relationship between the weighted average adhesion work of four mixtures and sealant A is AC-13 > AC-25 > SMA-13 > AC-20, which is consistent with results of the shear tests. The determination coefficient of linear correlation is 0.8672, which indicates that the proposed weighted average adhesion work can accurately characterize the actual adhesion state of interface.

A nano-scale frictional contact problem incorporating the size dependency and the surface effects

In this paper, the nano-scale sliding contact problem of an isotropic semi-infinite medium is considered. The small scale effects are taken into account by means of the couple stresses and the surface energy theories. Employing the Fourier integral method, the plane elasticity problem is formulated in terms of the integral equations. The numerical results are provided for the plane strain state. The parametric study reveals that the surface material constants remarkably alter the surface stresses and the contact length. The results indicate that the stress singularity substantially decreases due to size effect compared with the classical theory predictions. For example, the in-plane stress tensile peak decreases by a %80 with respect to the Hertzian contact.

Exact Size-Dependent Elasticity Solution for Free Radial Vibration of Nano-Sphere

An exact size-dependent elasticity solution based on surface energy theory is used to investigate the free radial vibration behavior of a nanoscale sphere. The Gurtin-Murdoch surface elasticity model is employed to incorporate surface stress terms into pertinent boundary conditions. This leads to frequency equations involving spherical Bessel functions. Extensive numerical calculations have been carried out to illustrate the size effect of the nano-sphere on the first and second dimensionless breathing natural frequencies. The numerical results describe the imperative influence of surface energy and radii ratio on the vibrational characteristic frequency of the nano-sphere. In particular, the surface energy is much more important when the inner radius is smaller than 50 nm.

Coupling effect of surface energy and dispersion forces on nonlinear size-dependent pull-in instability of functionally graded micro-/nanoswitches

In this paper, an integrated nonclassical multi-physics model is developed to study the coupling effect of surface energy and local microstructure on the nonlinear size-dependent pull-in instability of electrostatically actuated functionally graded material (FGM) micro-/nanoswitches. The developed model incorporates the influences of fringing field, dispersion Casimir or van der Waals force in addition to residual axial stress and mid-plane stretching. For more accurate analysis of the FGM switches, a nonclassical beam model is developed based on the Euler–Bernoulli beam theory in conjunction with the modified couple stress theory and Gurtin–Murdoch surface elasticity theory to account for the size dependency and surface energy effects, respectively. Material properties of both bulk and surface layers of the FGM switch are assumed to vary according to a power law distribution through thickness. To this end, the Hamilton principle is employed to derive the nonlinear size-dependent governing integral–differential equations and the associated nonclassical boundary conditions, without neglecting any terms raised by surface energy. The size-dependent relations are derived in general form, which can be reduced to those based on different elasticity theories, including surface energy theory, modified couple stress and classical theories. The resulting nonlinear integral–differential equations are solved utilizing the generalized differential/integral quadrature method, in which the nonclassical boundary conditions are exactly implemented for different immovable ends. The obtained results are compared with the results available in the literature to valid the efficiency of the present solution method. A numerical analysis reveals that the nonlinear pull-in voltage of FGM micro-/nanoswitches is significantly influenced by the FGM’s gradient index, length scale parameter, surface energy, residual axial stress, initial gap, slenderness ratio, and dispersion forces for different immovable boundary conditions.

RELATIONSHIP BETWEEN FOAMING BEHAVIOR AND SURFACE ENERGY OF ASPHALT BINDER

To solve the problem of insufficiency in microscopic performance of foamed asphalt binder, surface energy theory was utilized to analyze the foaming behavior and wettability of asphalt binder. Based on the surface energy theory, the Wilhelmy plate method and universal sorption device method were employed to measure the surface energy components of asphalt binders and aggregates, respectively. Combined with the traditional evaluation indictor for foamed asphalt, the relationship between the foaming property and surface energy of asphalt binder was analyzed. According to the surface energy components, the wettability of asphalt binder to aggregate was calculated to verify the performance of foamed asphalt mixture. Results indicate that the foaming behavior of asphalt will be influenced by surface energy, which will increase with the decline of surface energy. In addition, the surface energy of asphalt binder significantly influences the wettability of asphalt binder to aggregates. Meanwhile, there is an inversely proportional relationship between surface energy of asphalt binder and wettability. Therefore, it can be demonstrated that surface energy is a good indictor which can be used to evaluate the foaming behavior of the asphalt binder. And it is suggested to choose the asphalt binder with lower surface energy in the process of design of foamed asphalt mixture.

FURTHER EVIDENCE OF FILLER–FILLER MECHANICAL ENGAGEMENT IN RUBBER COMPOUNDS FILLED WITH SILICA TREATED BY LONG-CHAIN SILANE

ABSTRACT The present study discusses that filler–filler mechanical engagement resulting from the grafted long-chain silanes on the silica surface is indeed a reinforcing mechanism in rubber composites, as already speculated by nonlinear viscoelastic properties in our previous study. The existence and severity of such a phenomenon are assessed purely by isolating the energetic contribution of reinforcement from interfering with filler mechanical engagement in the silica network formation and breakdown processes. In a novel approach, the driving force of fillers to flocculate energetically at elevated temperatures was defined using surface energy theories, and it was adjusted to be similar in two composites having silica treated by short- and long-chain silanes. Filler–filler mechanical engagement was monitored by tracking network formation (filler flocculation) in a matrix of styrene–butadiene rubber and also by conducting various dynamic viscoelastic experiments on liquid paraffin suspensions having short- and long-chain silica of similar surface energy. Results consistently confirmed the existence of mechanical engagement between silica particles having the long-chain silane in both rubber compounds and paraffin suspensions. The results may find applications in the rolling resistance of tires, for example, where stabilization of the filler network by displacing the peak energy dissipation of the network breakdown from applied service strains to larger values would be of technical importance.