Surface Energy Effects Research Articles

Substrate Induced Effect on Structural and Optical Properties of Aluminum Nanoparticles

In this study, we investigate the effect of growing Aluminum nanoparticles (Al NPs) by Electron-Beam Physical Vapor Deposition (e-beam PVD) followed by thermal annealing on both Silicon (Si) and Indium Tin Oxide (ITO) substrates. Surface morphology and optical properties of the as-deposited and the thermally annealed aluminum thin-films were studied using Atomic Force Microscopy (AFM) and UV-Spectrophotometer respectively. AFM topography images of annealed Aluminum films on Si-substrate clearly show a formation of Al nanoparticles with average diameter about 40 nm while this was different in the case of Aluminum films on ITO-substrate where non-uniform flakes-like Aluminum nanostructures were observed. Other structural parameters such as surface roughness, particles distributions, and size of Aluminum nanostructures were extracted and studied for both substrates. UV-Vis absorption spectrum for annealed Aluminum film on ITO has shown a shift of about 14 nm in the absorption peak around 388 nm wavelength compared to as-deposited film. Different nanostructures in both substrates resulted from the effect of surface energy of the used substrate. Further characterization techniques will be carried out for the Al nanoparticles to provide a deep understanding of the substrate role combined with optimized properties of NPs to assist improving the control over the formation of metallic nanoparticles.

On the mechanics of Kirchhoff and Mindlin plates incorporating surface energy

In this paper, size-dependent Kirchhoff and Mindlin plate models are developed to investigate the coupling effects of nonlocal stress, strain gradient and surface energy on the dynamic response of nanoplate. The nonlocal stress and strain gradient effects are captured by nonlocal strain gradient theory, while the surface energy effects are incorporated by surface elasticity theory. The governing equations of motion and related boundary conditions are derived from Hamilton's principle. Analytical solutions for the natural frequencies of simply supported nanoplate are obtained through the Navier approach. A good agreement between the results of the present models and those available in literatures are observed. Selected examples are presented to show the influences of nonlocal parameter, material length scale parameter, length-to-thickness ratio, aspect ratio, surface energy and shear deformation on the vibration behavior of nanoplate. It is found that for nanoplate with lower length-to-thickness ratio, the nonlocal stress, strain gradient and surface energy have remarkable influences on the vibration characteristic simultaneously. While surface effects play a dominant role in the vibration behavior for nanoplate with higher length-to-thickness ratio.

Damping Vibration Behavior of Viscoelastic Porous Nanocrystalline Nanobeams Incorporating Nonlocal–Couple Stress and Surface Energy Effects

Damping vibration analysis of multi-phase viscoelastic nanocrystalline nanobeams on viscoelastic medium is carried out accounting for nano-grains and nano-voids sizes. For the first time, a contribution of nonlocal, couple stress and surface energy effects is applied for vibration analysis of nanocrystalline nanobeams. In fact, couple stress theory considers grains microrotations, while nonlocal elasticity theory considers long-range interactions between the particles. Viscoelastic medium is described as infinite parallel springs as well as shear and viscous layers. Hamilton’s principle is employed to derive the governing equations and the related boundary conditions which are solved applying differential transform method. The frequencies are compared with those of nonlocal and couple stress-based beams. It is observed that damping frequencies of a nanocrystalline nanobeam are significantly influenced by the grain size, grain rotations, porosities, interface, damping coefficient, surface energy, nonlocality and structural damping.

Pressure effects on interfacial surface contacts and performance of organic solar cells

This paper explores the effects of pressure on the interfacial surface contacts and the performance of organic solar cells. A combination of experimental techniques and analytical/computational models is used to study the evolving surface contacts profiles that occur when compliant, semi-rigid and rigid particles are interlocked between adjacent layers in model solar cell structures. The effects of layer surface roughness and interlocked (trapped) particles are also considered along with the effects of surface energy, adhesion energy, and pressure. The results show that increased interfacial contact lengths and decreased void lengths are associated with the application of increased pressure. Increased pressure also results in significant improvements in power conversion efficiency. These improvements in power conversion efficiency are associated with the closure up of micro- and nano-voids due to the application of pressure to layers produced via spin coating and thermal evaporation. The results suggest that pressure-induced contacts can be used to enhance the performance of organic solar cells.

Band gaps for elastic wave propagation in a periodic composite beam structure incorporating microstructure and surface energy effects

A new model for determining band gaps for elastic wave propagation in a periodic composite beam structure is developed using a non-classical Bernoulli–Euler beam model that incorporates the microstructure, surface energy and rotational inertia effects. The Bloch theorem and transfer matrix method for periodic structures are employed in the formulation. The new model reduces to the classical elasticity-based model when both the microstructure and surface energy effects are not considered. The band gaps predicted by the new model depend on the microstructure and surface elasticity of each constituent material, the unit cell size, the rotational inertia, and the volume fraction. To quantitatively illustrate the effects of these factors, a parametric study is conducted. The numerical results reveal that the band gap predicted by the current non-classical model is always larger than that predicted by the classical model when the beam thickness is very small, but the difference is diminishing as the thickness becomes large. Also, it is found that the first frequency for producing the band gap and the band gap size decrease with the increase of the unit cell length according to both the current and classical models. In addition, it is observed that the effect of the rotational inertia is larger when the exciting frequency is higher and the unit cell length is smaller. Furthermore, it is seen that the volume fraction has a significant effect on the band gap size, and large band gaps can be obtained by tailoring the volume fraction and material parameters.

Surface energy effect on free vibration of nano-sized piezoelectric double-shell structures

Combining Goldenveizer-Novozhilov shell theory, thin plate theory and electro-elastic surface theory, the size-dependent vibration of nano-sized piezoelectric double-shell structures under simply supported boundary condition is presented, and the surface energy effect on the natural frequencies is discussed. The displacement components of the cylindrical nano-shells and annular nano-plates are expanded as the superposition of standard Fourier series based on Hamilton's principle. The total stresses with consideration of surface energy effect are derived, and the total energy function is obtained by using Rayleigh-Ritz energy method. The free vibration equation is solved, and the natural frequency is analyzed. In numerical examples, it is found that the surface elastic constant, piezoelectric constant and surface residual stress show different effects on the natural frequencies. The effect of surface piezoelectric constant is the maximum. The effect of dimensions of the double-shell under different surface material properties is also examined.

Preparation and Antiscaling Performance of Superhydrophobic Poly(phenylene sulfide)/Polytetrafluoroethylene Composite Coating

In this paper, the superhydrophobic poly(phenylene sulfide) (PPS)/polytetrafluoroethylene (PTFE) composite coating was fabricated and applied to evaluate the antiscaling performance. Compared with the commercial hydrophobic epoxy–silicone resin coating, the superhydrophobic PPS/PTFE composite coating exhibited unique antiscaling performance. The deposition rate of CaCO3 scaling on the superhydrophobic PPS/PTFE coating was only 38.6% of that on the epoxy–silicone resin coating. The surface morphology, size, and crystal type of the scaling were analyzed. The results indicated that the formation and growth of CaCO3 scaling were significantly influenced by the cooperative effect of topography and low surface energy of the superhydrophobic PPS/PTFE composite coating. There were few nucleation sites at the surface of superhydrophobic coating owing to the relatively low surface energy and absorbed bubbles. Together with the space constraint of the topography, the nucleation and growth of CaCO3 scaling were inhib...

Au@void@AgAu Yolk–Shell Nanoparticles with Dominant Strain Effects: A Molecular Dynamics Simulation

Au@void@AgAu yolk-shell nanoparticles with different morphologies were studied by classical molecular dynamics simulation. The results indicated that all of simulated yolk-shell nanoclusters with ∼3.8 nm size and different morphologies are unstable at room temperature, and collapse of the shell atoms into the void space completely fills it and creates more stable Au@AgAu core-shell structures. Also, it was observed that thermodynamic stabilities of the created core-shell structures strongly depend on the morphology of nanocluster, for which competition between strain and surface energy effects plays the key role in this phenomenon. Within this competition, strain effect is dominant and helps the stability of the created core-shell structure. Herein, the icosahedral nanocluster with the lowest strain effect exhibits the highest thermodynamic stability. By comparing the simulation results with experimental data, it was concluded that the essential factor that controls the stability of these nanoparticles is their size.

Surface energy effect on buckling behavior of the functionally graded nano-shell covered with piezoelectric nano-layers under torque

In this paper, based on the electro-elastic surface/interface theory, the size-dependent effect on the torsional buckling behavior of functionally graded (FG) cylindrical nano-shell covered with piezoelectric nano-layers is studied. According to the classical shell theory together with von-Karman-Donnell type kinematics of nonlinearity, the primary formulations are given. The total energy of the nano-shell is derived by introducing the constitute relations for piezoelectric surfaces and interfaces. The principle of minimum potential energy is employed to establish the governing differential equations. An analytical solution is firstly presented, and then the generalized differential quadrature (GDQ) method is used to obtain the numerical results of nano-shells with different boundary conditions. Afterwards, the results without surface/interface effect are compared with the datum in the open literatures, and some numerical examples are presented to investigate the effect of surface/interface parameters and power-law index on the critical buckling load of the nano-shell.

Effects of the deposition rate on growth modes of Ag islands on the hydrogen-terminated Si(111)-(1 × 1) surface: The role of surface energy and quantum size effect

We have investigated the early stage of Ag island growth at 2 monolayer (ML) coverage on the hydrogen-terminated Si(111)–(1 × 1) surface using low-energy electron-diffraction (LEED) and scanning tunneling microscopy (STM) at room temperature. First, it is found that the Ag(10) LEED pattern varies from arc-like spots to three spots by changing the Ag deposition rate from 1.0×10−1 (a fast deposition rate) to 1.1×10−4 (a slow deposition rate) ML/s. Second, STM observation reveals that adsorbed Ag atoms grow into dome-like three dimensional (3D) clusters at the fast deposition rate and flat-top two dimensional (2D) islands at the slow deposition rate. Third, most abundant 2D islands show the 8 atomic layer height, which coincides with that obtained from the quantum size effect. The side structures of 2D islands agree well with those calculated from Wulff theory. We will discuss the exact nature of 3D clusters and 2D islands of Ag grown on the hydrogen-terminated Si(111)–(1 × 1) surface and these results indicate the possibility of using kinetic controlled growth to investigate the physics of crystal growth.

Instability Characteristics of Free-Standing Nanowires Based on the Strain Gradient Theory with the Consideration of Casimir Attraction and Surface Effects

AbstractSize-dependent dynamic instability of cylindrical nanowires incorporating the effects of Casimir attraction and surface energy is presented in this research work. To develop the attractive intermolecular force between the nanowire and its substrate, theproximity force approximation(PFA) for small separations, and the Dirichlet asymptotic approximation for large separations with a cylinder-plate geometry are employed. A nonlinear governing equation of motion for free-standing nanowires – based on the Gurtin-Murdoch model – and a strain gradient elasticity theory are derived. To overcome the complexity of the nonlinear problem in hand, a Garlerkin-based projection procedure for construction of a reduced-order model is implemented as a way of discretization of the governing differential equation. The effects of length-scale parameter, surface energy and vacuum fluctuations on the dynamic instability threshold and adhesion of nanowires are examined. It is demonstrated that in the absence of any actuation, a nanowire might behave unstably, due to the Casimir induction force.

Surface energy effect on nonlinear free vibration behavior of orthotropic piezoelectric cylindrical nano-shells

Abstract In this paper, the electro-elastic surface/interface model is introduced to investigate the surface energy effect on the nonlinear free vibration behavior of orthotropic piezoelectric cylindrical nano-shells. On the basis of classical shell theory and von-Karman-Donnell-type geometric nonlinearity, the fundamental equations for vibration are given. By considering the constitute relations for surfaces, the total energy of the orthotropic piezoelectric cylindrical nano-shell is obtained. The governing equations of motion are derived from Hamilton's principle and solved by using the homotopy perturbation method (HPM). Afterwards, the results without surface effect are compared and validated with the datum available in the literature, and the influences of surface parameters and geometric characteristics on the nonlinear free vibration of the orthotropic piezoelectric cylindrical nano-shell are examined.

Effects of graphene surface energy on the structure and mechanical properties of phenolic foams

Abstract Graphene nanoplates (GNPs) and graphene oxide (GO) were used to investigate the effects of surface free energy (SFE) of nanoparticles on the cellular structure and mechanical properties of phenolic nanocomposite foams. The results showed that the SFE of nanoparticles is a key parameter in determining the interfacial action between fillers and matrix before foaming, which in turn determines the energy barrier of bubble nucleation during foaming process. It indicated that the higher interfacial energy of GO brought out the lower Gibbs free energy and smaller driving force for heterogeneous nucleation, leading to smaller cell size with more uniform distribution. According to the effect of SFE in foaming process, different mass fractions of GNPs and GO were used in phenolic foams to investigate the effects of heterogeneous nucleating agent on cell nucleation. As a result, phenolic foam with 0.6 wt% graphene oxide (GO-0.6/PF) exhibited the optimized mechanical properties and cell microstructure.

Nonlinear analysis of functionally graded nanoscale beams incorporating the surface energy and microstructure effects

A nonclassical size–dependent beam model is developed to study the geometrically nonlinear response of functionally graded (FG) nanoscale beams including the combined effect of surface elasticity, surface residual stress, microstructure and size-dependency. To this, the Gurtin–Murdoch surface elasticity theory in combination with the modified couple stress theory is employed to capture the simultaneous effects of surface energy and microstructure size phenomenon. Euler–Bernoulli and Timoshenko beam models considering the von Kármán geometric nonlinearity are adopted. The material properties of the bulk and surface of the FG beam are assumed to be changed continuously through the thickness according to a power law scheme and Mori–Tanaka homogenization technique. The geometrically nonlinear size–dependent governing equations and corresponding nonclassical boundary conditions are exactly obtained through Hamilton's principle. The generalized differential quadrature method (GDQM) is employed to discretize the nonlinear nonclassical governing differential equations and the nonclassical boundary conditions for various end supports. A good agreement between the results of the present model and those available in the literature is obtained. Selected numerical results show explicitly that the material length scale parameter, surface elastic modulus, surface residual stress, gradient index and material distribution have a significant influence on the geometrically nonlinear bending response of FG nanobeams.

Thermo-mechanical vibration, buckling, and bending of orthotropic graphene sheets based on nonlocal two-variable refined plate theory using finite difference method considering surface energy effects

In this article, the influence of temperature change on the vibration, buckling, and bending of orthotropic graphene sheets embedded in elastic media including surface energy and small-scale effects is investigated. To take into account the small-scale and surface energy effects, the nonlocal constitutive relations of Eringen and surface elasticity theory of Gurtin and Murdoch are used, respectively. Using Hamilton’s principle, the governing equations for bulk and surface of orthotropic nanoplate are derived using two-variable refined plate theory. Finite difference method is used to solve governing equations. The obtained results are verified with Navier’s method and validated results reported in the literature. The results demonstrated that for both isotropic and orthotropic material properties, by increasing the temperature changes, the degree of surface effects on the buckling and vibration of nanoplates could enhance at higher temperatures, while it would diminish at lower temperatures. In addition, the effects of surface and temperature changes on the buckling and vibration for isotropic material property are more noticeable than those of orthotropic. On the contrary, these results are totally reverse for bending problem.

Large amplitude free vibration of electrically actuated nanobeams with surface energy and thermal effects

In this paper, large amplitude free vibration of electrically actuated nanobeams with consideration of surface energy, temperature change and Casimir force is studied. Results show that neglecting of surface energy and intermolecular Casimir force will result in a lower prediction and a higher prediction of fundamental frequency, respectively. Thermal effect may change the relationship between fundamental frequency and applied voltage. In addition, the effect of geometric nonlinear deformation on the fundamental frequency is more significant for large applied voltage. The influence of surface energy and geometric nonlinear deformation on the fundamental frequency depends on the length and height of the nanobeams.

Characterization of the surface properties of cellulosic fibers in fibrous and ground forms by IGC and contact angle measurements

Surface properties of fibrous and ground cotton and linen were investigated by inverse gas chromatography (IGC) and the contact angle with different liquids was also measured on fabrics composed of both fibers. Results proved that dispersion component of surface tension (γ s d ) determined by IGC depends not only on the surface energy, but also on several factors influencing the adsorbability of probe molecules on the cellulosic substrates. For cotton samples, the trapping of n-alkanes among waxy molecules in the outer layer of fibers can be presumed. This effect results in larger γ s d for cotton fibers than for linen in spite of the higher wettability of the linen fabrics. Besides the surface energy and trapping effects, the grinding also influences the γ s d values. Specific enthalpy of adsorption (ΔH ) of polar probes could be determined on all linen samples, but only on the ground cotton sample. Lewis acid-base character calculated for linen and ground cotton samples depends on the same effects as the γ s d does. The similar ΔH A ab values of chloroform (acidic) and THF (basic) measured on each of the samples support the conclusion that the surface character is amphoteric, which is also proved by the high ΔH values of the amphoteric ethyl acetate and acetone probes.

Postbuckling scrutiny of highly deformable nanobeams: A novel exact nonlocal-surface energy-based model

This paper deals with analytical postbuckling analysis of elastic slender beam-like nanostructures by considering both surface energy and nonlocality effects. Using Euler-Bernoulli beam theory, the continuum-based governing equation is established for axially compressed nanobeams with large displacements. To capture the postbuckling behavior of the nanostructure more accurately, an exact solution is proposed on the basis of elastica approach. The explicit expressions of postbuckling load and maximum displacements are obtained for nanobeams with various ends. The predicted results are successfully checked with those of a Galerkin-modal-based approach. The postbuckled shapes of nanobeams are then presented based on the classical elasticity theory and the newly developed size-dependent models to show the roles of the nonlocality and surface energy. The effects of both nanobeam's length and diameter on the nonlinear trends of load-displacement are displayed. The present work can be regarded as a benchmark for further numerical/analytical studies on postbuckling of nonlocal-surface energetic ensembles of vertically aligned nanostructures.

Effect of crystal orientation on corrosion behavior of directionally solidified Mg-4 wt% Zn alloy

Microstructure and crystallographic orientation of directionally solidified Mg-4wt% Zn alloy were characterized by X-ray computed tomography (XCT) and electron backscatter diffraction (EBSD) in this study. Results reveal that Mg-4wt% Zn alloy with dendritic microstructure exhibits typical {0002} basal texture along growth direction. Based on this, the effect of grain orientation on corrosion behavior of directionally solidified Mg-4wt% Zn alloy in 0.9wt% NaCl solution was investigated. Result shows that {0002} oriented planes have better corrosion resistance than {112¯0} and {101¯0} ones, which is attributed to a synergistic effect of surface energy, atomic packing density and the stability of oxidation film.

Large deformation of nonlinear elastic nanofilms with surface energy

The influence of nonlinear elasticity on the bending of nanofilms under transverse load has been studied. The effects of second order elasticity, surface energy and large deformation are incorporated in the present model. The general governing equation for the nonlinear bending of a rectangle shaped nano-film is derived. The general method for solving the general governing equation is illustrated. The results indicated that the existence of nonlinear elastic effects makes it easier for the nano-film to deform, the nonlinear effect is amplified in pace with the increase of the transverse load. Moreover, the effect of nonlinear elasticity on the nonlinear bending of the nanofilms is more significant for the nanofilms with negative surface energy and a large aspect ratio and large length-thickness ratio.