Surface Energy Effects Research Articles

Effects of polymer surface energy on morphology and properties of silver nanowire fabricated via nanoimprint and E-beam evaporation

In this paper, we demonstrate that use of different nanoimprint resins as a polymer pattern has a significant effect on the morphology of silver (Ag) nanowires deposited via an E-beam evaporator. RM-311 and Ormo-stamp resins are chosen as a polymer pattern to form a line with dimensions of width (100nm)×space (100nm)×height (120nm) by using nanoimprint lithography (NIL). Their contact angles are then measured to evaluate their surface energies. In order to compare the properties of the Ag nanowires deposited on the various polymer patterns with different surface energies, hydrophobic surface treatment of the polymer pattern surface is implemented using self-assembled monolayers. In addition, gold and aluminum nanowires are fabricated for comparison with the Ag nanowires, with the differences in the nanowire morphologies being determined by the different atomic properties. The monocrystalline and polycrystalline structures of the various Ag nanowire formations are observed using transmission electron microscopy. In addition, the melting temperatures and optical properties of four kinds of Ag nanowire morphologies deposited on various polymer patterns are evaluated using a hot plate and an ultraviolet-visible (UV–vis) spectrometer, respectively. The results indicate that the morphology of the Ag nanowire determines the melting temperature and the transmission. We believe that these findings will greatly aid the development of NIL, along with physical evaporation and chemical deposition techniques, and will be widely employed in optics, biology, and surface wettability applications.

Surface instability of curved films under surface van der Waals forces

Abstract We investigate the surface instability of a curved film interacting with a curved contactor through the action of van der Waals forces. Any one of the two curved boundaries of the film can be subjected to surface interactions while the other is bonded to a curved rigid substrate. In each case, the corresponding bifurcation is governed by the critical value of the relative film thickness. The effects of Poisson's ratio, surface energy and film thickness on the film's instability are discussed in detail leading to a complete picture of stability and bifurcation in the system.

Ion distribution and selectivity of ionic liquids in microporous electrodes.

The energy density of an electric double layer capacitor, also known as supercapacitor, depends on ion distributions in the micropores of its electrodes. Herein we study ion selectivity and partitioning of symmetric, asymmetric, and mixed ionic liquids among different pores using the classical density functional theory. We find that a charged micropore in contact with mixed ions of the same valence is always selective to the smaller ions, and the ion selectivity, which is strongest when the pore size is comparable to the ion diameters, drastically falls as the pore size increases. The partitioning behavior in ionic liquids is fundamentally different from those corresponding to ion distributions in aqueous systems whereby the ion selectivity is dominated by the surface energy and entropic effects insensitive to the degree of confinement.

A Bilayer Model for Incorporating the Coupled Effects of Surface Energy and Microstructure on the Electromechanical Stability of NEMS

Herein, the static and dynamic pull-in instabilities of nanotweezers and nanoswitches fabricated from conductive cylindrical nanowires are studied. A bilayer model based on the Gurtin–Murdoch surface elasticity and the consistent couple stress theory is developed to incorporate the coupled effects of surface energy and microstructure phenomenon. The differential quadrature method is employed to solve the nonlinear governing equation of the system. The effects of various parameters on the static and dynamic pull-in parameters and stability threshold of the nanostructures are demonstrated.

Effect of surface energy of solid surfaces on the micro- and macroscopic properties of adsorbed BSA and lysozyme

The surface energy, a macroscopic property, depends on the chemical functionality and micro- and macroscopic roughness of the surface. The adsorption of two widely used proteins bovine serum albumin (BSA) and lysozyme on surfaces of four different chemical functionalities were done to find out the interrelation between macroscopic and microscopic properties. We have observed the secondary structure of protein after its adsorption. In addition, we observed the variation of surface energy of proteins due to variation in adsorption time, change in protein concentration and effect of a mixture of proteins.Surfaces of three different chemical functionalities namely, amine, hydroxyl and octyl were obtained through self-assembled monolayer on silica surfaces and were tested for responses towards adsorption of lysozyme and BSA. The adsorbed lysozyme has higher surface energy than the adsorbed BSA on amine and octyl surfaces. On hydroxyl functional surface, the surface energy due to the adsorbed lysozyme or BSA increases slowly with time.The surface energy of the adsorbed protein increases gradually with increasing protein concentration on hydrophobic surfaces. On hydrophilic surfaces, with increasing BSA concentration in bulk solution, the surface energy of the adsorbed protein on GPTMS and amine surfaces is maximum at 1μM concentration. During the adsorption from a mixture of BSA and lysozyme on octyl surface, first lysozyme adsorbs and subsequent BSA adsorption leads to a high surface energy.

Phase-field modeling of void anisotropic growth behavior in irradiated zirconium

A three-dimensional phase-field model was developed to study the effects of surface energy and diffusivity anisotropy on void growth behavior in irradiated Zr. The gamma surface energy function used in the phase-field model was developed with the surface energy anisotropy calculated from the molecular dynamics simulations. The model assumes that vacancies have larger mobility in the c-axis than in the a-axis and b-axis, whereas interstitials have larger mobility in the basal plane than in the c-axis. The equilibrium void morphology and the effect of defect concentrations and mobility anisotropy on void growth behavior were simulated using the developed model. The simulations demonstrated that (1) the developed phase-field model correctly reproduces the faceted void morphology predicted by the Wulff construction; (2) with isotropic diffusivity, the void prefers to grow on the basal plane; and (3) when the vacancy has large mobility along the c-axis and interstitial has a large mobility on the basal plane of hexagonal closed-packed Zr alloys, a platelet void grows in the c-direction and shrinks on the basal plane. These findings are in agreement with the observation of void morphology and growth behavior in irradiated Zr, and reveal that the strong mobility anisotropy of defects results in the anisotropic growth of voids in Zr.

Droplets in turbulence: a new perspective

Stirring olive oil and vinegar to make salad dressing creates an emulsion of vinegar droplets in oil. More vigorous stirring gives smaller droplets, while if left to sit the droplets will begin to coalesce and the two fluids will separate. In this vein, Dodd & Ferrante (J. Fluid Mech., vol. 806, 2016, pp. 356–412) present a new analysis of how homogeneous turbulence in a carrier fluid interacts with a suspension of droplets of an immiscible liquid. Based on a set of direct numerical simulations, the authors provide new insights on how turbulence affects the motion of the droplets, their shape and size; then in turn how the droplets alter the flow including effects of interfacial surface energy on the kinetic energy of the flow.

In-plane vibration and instability of nanorotors made from functionally graded materials accounting for surface energy effect

Nanorotors are nano-scaled rotating components of electromagnetic nanosystems in the electric nanomotors, alternators or nanopumps, however, their vibrations have not been investigated yet. Herein, in-plane vibration of functionally graded annular plate-like nanorotors is of concern. In the context of the Gurtin–Murdoch elasticity theory, the equations of motion of both bulk and the surface layers are constructed. By employing Hamilton’s principle, a meshless-based approach is developed to evaluate dynamic elastic fields of the rotating nanostructure with fixed-free and free–free boundary conditions. The influences of the steady angular velocity, frequency of the angular velocity, outermost radius, power-law index, initial excitation duration, and surface energy effect on the elasto-dynamic fields are addressed. The obtained results reveal that the surface effect on the resulting maximum elasto-dynamic fields becomes important by decreasing of the outermost radius, or increasing of the duration of initial excitation. However, variation of the steady angular velocity has a slight influence on the relative discrepancies between the results of the surface elasticity model and those of the classical continuum theory. Further, the effect of the power-law index on the size-dependency of elasto-dynamic fields strongly depends on the boundary conditions. The possible dynamic instability of the rotating nanostructure is also explained.

Structure and electrical properties of pure and yttrium-doped HfO2 films by chemical solution deposition through layer by layer crystallization process

Pure and yttrium doped HfO2 thin films were fabricated on Si (100) substrates by chemical solution deposition through a layer by layer crystallization process. We systematically investigated the effects of thickness and Y doped concentration on structure and electrical properties of the HfO2 films. Results revealed that 4nm thick undoped HfO2 was crystallized into a t/c-phase due to the surface energy effect, and this higher symmetry phase could be retained up to a film thickness of 16nm through the layer by layer crystallization process. This layer by layer crystallization process also required less Y doping to stabilize t/c-HfO2 in thick films. The films showed a high dielectric constant about 42, low leakage current density of about 10−7A/cm2 (at 1MV/cm) and a breakdown field up to 5MV/cm. Considering the cost-effective deposition technique and good electrical properties, these films would be suitable for insulator applications in microelectronic devices.

Size-dependent behavior of viscoelastic nanoplates incorporating surface energy and microstructure effects

In this paper, the simultaneous effects of the microstructure rotation and surface energy on the behavior of nanoplates are investigated in the framework of viscoelasticity. Firstly, the modified couple stress elasticity and Gurtin-Murdoch surface elasticity theories are reconsidered and harnessed to incorporate respectively the viscoelastic microstructure local rotation and viscoelastic surface energy effects into the classical viscoelastic plate theory. The couple stress tensor is obtained incorporating measures for the elastic and the viscous behaviors of the plate. Surface stress tensor is derived depending on the surface elastic and viscous parameters. Afterwards, a variational approach on the basis of D’Alembert’s principle in conjunction with the Kirchhoff plate theory is utilized to establish the size-dependent integral-differential governing equations and the associated boundary conditions of viscoelastic nanoplate. The developed model accounts for the viscoelastic behavior of the linear non-aging materials using integral-type constitutive relations through the Boltzmann’s principle of superposition. Finally, an analytical solution is derived for the simple supported plates according to the aforementioned phenomena using the Navier method and Laplace transformation. In the context of the linear viscoelasticity, a comprehensive parametric study is developed to present the influences of the various material and geometrical parameters on the bending behavior of the viscoelastic nanoplate.

Dynamics of silicon nanobeams with axial motion subjected to transverse and longitudinal loads considering nonlocal and surface effects

A microstructure-dependent dynamic model for silicon nanobeams with axial motion is developed by considering the effects of nonlocal elasticity and surface energy. The nanobeam is considered to subject to both transverse and longitudinal loads arising from nanostructural surface effect and all positive directions of physical quantities are defined clearly prior to modeling so as to clarify the confusions of sign in governing equations of previous work. The nonlocal and surface effects are taken into consideration in the dynamic behaviors of silicon nanobeams with axial motion including circular natural frequency, vibration mode, transverse displacement and critical speed. Various supporting conditions are presented to investigate the circular frequencies by a numerical method and the effects of many variables such as nonlocal nanoscale, axial velocity and external loads on non-dimensional circular frequencies are addressed. It is found that both nonlocal and surface effects play remarkable roles on the dynamics of nanobeams with axial motion and cause the frequencies and critical speed to decrease compared with the classical continuum results. The comparisons of the non-dimensional calculation values by present and previous studies validate the correctness of the present work. Additionally, numerical examples for silicon nanobeams with axial motion are addressed to show the nonlocal and surface effects on circular frequencies intuitively. Results obtained in this paper are helpful for the design and optimization of nanobeam-like microstructures based sensors and oscillators at nanoscale with desired dynamic mechanical properties.

Nano-milling on monocrystalline copper: A molecular dynamics simulation

ABSTRACTNano-milling is a promising technique for making miniaturized ultraprecision components. However, its underlying material removal mechanism is unclear and the accurate prediction of its performance is lacking. This study performs a systematic molecular dynamics analysis to reveal the material removal in the nano-milling of monocrystalline copper. It was found that the grooves by nano-milling, regardless of the machining parameters used, have two common features: (i) the groove top edge distortion is due to the effects of surface energy and high strain rate and (ii) the groove profile at the outlet side of the tool rotation aligns more closely with the designed geometry as a result of the atom flow variation and residual stress distribution. A dimensional analysis showed that the cutting speed factor and groove dimension factor significantly influence the specific energy and material removal rate in nano-milling. The groove quality can be improved by increasing the groove dimension factor or by decreasing the cutting speed factor. Finally, a machinability chart was developed for quality nano-milling processes.

A Non-Classical Model for Circular Mindlin Plates Incorporating Microstructure and Surface Energy Effects

A new non-classical model for circular Mindlin plates is developed using a modified couple stress theory, a surface elasticity theory and Hamilton's principle. The equations of motion and boundary conditions are simultaneously obtained through a variational formulation, and the microstructure and surface energy effects are treated in a unified manner. The new plate model contains a material length scale parameter to account for the microstructure effect and three surface elasticity constants to describe the surface energy effect. The current non-classical model includes the plate models considering the microstructure influence only and the surface energy effect alone as special cases, and it recovers the classical elasticity-based circular Mindlin plate model when both the microstructure and surface energy effects are suppressed. To illustrate the new model, the static bending problem of a clamped circular Mindlin plate under a uniform normal load is analytically solved by directly applying the general formulas derived.

Effects of surface energy on the nonlinear behaviors of laminated nanobeams

Using an improved multilayer-beams model, the surface effect caused by surface stress and surface elasticity on mechanical properties of laminated nanobeams in bending, bucking and vibration is incorporated into the nonlinear beam theory. Analytical solutions are obtained to study the influence of surface and interface effects for simply supported boundary conditions. Unlike the deduction of previous beam theory, the theoretical derivation in present work includes the effect of both surface and interface. Numerical cases of double layer and multilayer Nickel-silver laminated beams indicate that the interface effect observably change the elastic behaviour of laminated beams on the nanometer scale, especially for multilayer cases.

Sequential water molecule binding enthalpies for aqueous nanodrops containing a mono-, di- or trivalent ion and between 20 and 500 water molecules.

Sequential water molecule binding enthalpies, ΔHn,n-1, are important for a detailed understanding of competitive interactions between ions, water and solute molecules, and how these interactions affect physical properties of ion-containing nanodrops that are important in aerosol chemistry. Water molecule binding enthalpies have been measured for small clusters of many different ions, but these values for ion-containing nanodrops containing more than 20 water molecules are scarce. Here, ΔHn,n-1 values are deduced from high-precision ultraviolet photodissociation (UVPD) measurements as a function of ion identity, charge state and cluster size between 20-500 water molecules and for ions with +1, +2 and +3 charges. The ΔHn,n-1 values are obtained from the number of water molecules lost upon photoexcitation at a known wavelength, and modeling of the release of energy into the translational, rotational and vibrational motions of the products. The ΔHn,n-1 values range from 36.82 to 50.21 kJ mol-1. For clusters containing more than ∼250 water molecules, the binding enthalpies are between the bulk heat of vaporization (44.8 kJ mol-1) and the sublimation enthalpy of bulk ice (51.0 kJ mol-1). These values depend on ion charge state for clusters with fewer than 150 water molecules, but there is a negligible dependence at larger size. There is a minimum in the ΔHn,n-1 values that depends on the cluster size and ion charge state, which can be attributed to the competing effects of ion solvation and surface energy. The experimental ΔHn,n-1 values can be fit to the Thomson liquid drop model (TLDM) using bulk ice parameters. By optimizing the surface tension and temperature change of the logarithmic partial pressure for the TLDM, the experimental sequential water molecule binding enthalpies can be fit with an accuracy of ±3.3 kJ mol-1 over the entire range of cluster sizes.

Carbon steel corrosion: a review of key surface properties and characterization methods

The effects of surface morphology, defects, texture and energy on carbon steel corrosion are elucidated along with relevant characterization methods.

Influence of Surface Energy Effects on Elastic Fields of a Layered Elastic Medium under Surface Loading

This paper presents the analysis of a layered elastic half space under the action of axisymmetric surface loading and the influence of the surface energy effects. The boundary value problems for the bulk and the surface are formulated based on classical linear elasticity and a complete Gurtin-Murdoch constitutive relation. An analytical technique using Love’s representation and the Hankel integral transform is employed to derive an integral-form solution for both displacement and stress fields. An efficient numerical quadrature is then applied to accurately evaluate all involved integrals. Selected numerical results are presented to portray the influence of various parameters on elastic fields. Numerical results indicate that the surface stress displays a significant influence on both displacement and stress fields. It is also found that the layered half space becomes stiffer with the presence of surface stresses. In addition, unlike the classical elasticity solution, size-dependent behavior of elastic fields is noted. The present analytical solutions provide fundamental understanding of the influence of surface energy on layered elastic materials. It can also be used as a benchmark solution for the development of numerical techniques such as FEM and BEM, for analysis of more complex problems involving a layered medium under the influence of surface energy effects.

Free torsional vibration of cracked nanobeams incorporating surface energy effects

This paper investigates surface energy effects, including the surface shear modulus, the surface stress, and the surface density, on the free torsional vibration of nanobeams with a circumferential crack and various boundary conditions. To formulate the problem, the surface elasticity theory is used. The cracked nanobeam is modeled by dividing it into two parts connected by a torsional linear spring in which its stiffness is related to the crack severity. Governing equations and corresponding boundary conditions are derived with the aid of Hamilton’s principle. Then, natural frequencies are obtained analytically, and the influence of the crack severity and position, the surface energy, the boundary conditions, the mode number, and the dimensions of nanobeam on the free torsional vibration of nanobeams is studied in detail. Results of the present study reveal that the surface energy has completely different effects on the free torsional vibration of cracked nanobeams compared with its effects on the free transverse vibration of cracked nanobeams.

Vibration analysis of viscoelastic inhomogeneous nanobeams incorporating surface and thermal effects

This article deals with the free vibration investigation of nonlocal strain gradient-based viscoelastic functionally graded (FG) nanobeams on viscoelastic medium considering surface stress effects. Nonlocal strain gradient theory possesses a nonlocal stress field parameter and a length scale parameter for more accurate prediction of mechanical behavior of nanostructures. Surface energy effect is incorporate to the nonlocal strain gradient theory employing Gurtin–Murdoch elasticity theory. Thermo-elastic material properties of nanobeam are graded in thickness direction using power-law distribution. Hamilton’s principal is utilized to obtain the governing equations of FG nanobeam embedded in viscoelastic medium. The effects of surface stress, length scale parameter, nonlocal parameter, viscoelastic medium, internal damping constant, thermal loading, power-law index and boundary conditions on vibration frequencies of viscoelastic FGM nanobeams are discussed in detail.

Linear and nonlinear vibrations of fractional viscoelastic Timoshenko nanobeams considering surface energy effects

In this paper, the linear and nonlinear vibrations of fractional viscoelastic Timoshenko nanobeams are studied based on the Gurtin–Murdoch surface stress theory. Firstly, the constitutive equations of fractional viscoelasticity theory are considered, and based on the Gurtin–Murdoch model, stress components on the surface of the nanobeam are incorporated into the axial stress tensor. Afterward, using Hamilton's principle, equations governing the two-dimensional vibrations of fractional viscoelastic nanobeams are derived. Finally, two solution procedures are utilized to describe the time responses of nanobeams. In the first method, which is fully numerical, the generalized differential quadrature and finite difference methods are used to discretize the linear part of the governing equations in spatial and time domains. In the second method, which is semi-analytical, the Galerkin approach is first used to discretize nonlinear partial differential governing equations in the spatial domain, and the obtained set of fractional-order ordinary differential equations are then solved by the predictor–corrector method. The accuracy of the results for the linear and nonlinear vibrations of fractional viscoelastic nanobeams with different boundary conditions is shown. Also, by comparing obtained results for different values of some parameters such as viscoelasticity coefficient, order of fractional derivative and parameters of surface stress model, their effects on the frequency and damping of vibrations of the fractional viscoelastic nanobeams are investigated.