Narrow Results

In this work, the effect of thin films on the orientational, thermotropic and optical properties and on the peculiarities of the nematic–isotropic liquid phase transition has been carried out.

The planar textures of MBBA+EBBA eutectic mixture on the surfaces coated with Al₂O₃ and ZrO₂ thin films have been obtained. The optical and thermodynamical parameters of the obtained, oriented textures have been determined. The effect of thin films on the temperature width of heterophase region and on the nematic–isotropic liquid phase transition temperatures has been investigated. The shift of the phase transition temperatures and the change of the temperature width of the heterophase region have been revealed.

For the analysis of peculiarities of the nematic–isotropic liquid phase transition and the heterophase regions of this transition, the mean field theory has been used.

In this work, effect of thickness of the liquid crystalline layer on the morphologic, thermotropic and thermodynamical properties of the nematic–isotropic liquid and isotropic liquid–nematic phase transitions in Shiff based liquid crystals has been investigated.

The shift of temperatures of the nematic–isotropic liquid and isotropic liquid–nematic phase transitions to the lower temperatures and the widening of linear and temperature widths of the heterophase regions of these phase transitions by the increase in the thickness of liquid crystalline layer have been found.

The effect of thickness of liquid crystalline layer on morphologic, thermotropic and thermodynamical properties of liquid crystals under investigations is connected with change of interaction energy between liquid crystalline molecules and reference surfaces.

In this paper, the conformal mapping from a regular 2$n$-polygon hole with two collinear asymmetric cracks into a circle is constructed. Based on the Gurtin–Murdoch surface/ interface model and complex potential theory, two collinear asymmetric nanocracks emanating from an electrically semi-permeable regular 2$n$-polygon nanohole embedded in an infinite one-dimensional hexagonal piezoelectric quasicrystals with surface effect are investigated. The size-dependent stress intensity factors of phonon field and phason field, electric displacement intensity factor at the nanocrack tip are derived for electrically semi-permeable boundary condition. Numerical examples are illustrated to show that the size of the hole, mechanical load, electric load, cracks relative size change with stress intensity factor of phonon field and electric displacement intensity factor. Also analyzed the change of the electric displacement intensity factor with different electric permeability at the nanocrack tip and the dimensionless intensity factor with $n$.

Based on Gurtin–Murdoch surface/interface model and complex potential theory, by constructing a new conformal mapping function, the fracture behavior on n nano-cracks emanating from a n-polygon nano-hole under far-field anti-plane mechanical load, inplane electrical load and magnetic load is studied. The analytical solutions of stress intensity factor, electric displacement intensity factor and magnetic induction intensity factor at the crack tip are given under the boundary conditions of magnetoelectrically semi-permeable. In addition, numerical examples show that when considering the surface effect, the stress field intensity factor, electric displacement intensity factor and magnetic induction intensity factor have obvious size-dependence. The results of this paper show that when the defect size increases to a certain extent, the influence of the surface effect begins to decrease, and finally tends to the results of classical elastic theory.

In this work, the effect of thin films on the thermotropic and thermo-optical properties and peculiarities of the phase transitions between the smectic A and isotropic liquid have been investigated. Peculiarities of the heterophase regions of the straight smectic A-isotropic liquid and reverse isotropic liquid-smectic A phase transitions have been studied.

Change of morphologic properties of the heterophase regions, shift of the phase transition temperatures and the change of temperature widths of these heterophase regions under thin film influence have been observed.

Current-carrying nanowires are expected to be building blocks of the upcoming micro-nano-electromechanical devices, however, little is known on their dynamic interactions in a bundle. As a pivotal step towards realizing such a crucial mechanism, this work is devoted to vibrations and instability of a double-nanowire-system as an electric current carrier. Using Biot–Savart law, the Lorentz interactional forces between doubly parallel current-carrying nanowires are evaluated. Accounting for the surface elastic energy, equations of motion pertinent to the in-plane and out-of-plane vibrations are established. Using analytical techniques, the explicit expressions of both static and purely dynamic parts of the nanowires’ displacements are obtained. For each component of the transverse displacement field, two major vibration modes are observed: in-phase and out-of-phase modes. The frequencies associated with these vibration modes are analytically calculated. Further, the condition corresponds to the dynamic instability of the system is discovered, and the roles of initial tensile force, electric current, and interwire distance on frequencies and stability of the system are addressed.

This paper studies transverse vibration of nanoscale cantilevered and bridged sensors carrying a nanoparticle. The nanoscale sensors are modelled as Euler–Bernoulli beams with surface effect and nanoparticle as a concentrated mass. Frequency equations of cantilevered and bridged beam-mass system are derived and exact resonance frequencies are calculated. An alternative Fredholm integral equation method is used to obtain an approximate explicit expression for the fundamental frequency for both cases. A comparison between the approximate and analytical results is made and the approximation accuracy is satisfactory. The influences of the residual surface stress, surface elasticity, and attached mass on the resonance frequencies and mode shapes are discussed. These results are useful to illustrate the surface phenomena and are helpful to design micro-/nano-mechanical sensors.

Based on the Gurtin–Murdoch surface/interface model and complex potential theory, by constructing a new conformal mapping, the anti-plane fracture problem of three nano-cracks emanating from a magnetoelectrically permeable triangle nano-hole in magnetoelectroelastic materials with surface effect is studied. The exact solutions of the stress intensity factor, the electric displacement intensity factor, the magnetic induction intensity factor, and the energy release rate are obtained under the boundary conditions of magnetoelectrically permeable and impermeable. The numerical examples show the influence of surface effect on the stress intensity factor, the electric displacement intensity factor, the magnetic induction intensity factor, and the energy release rate under two different boundary conditions. It can be seen that the surface effect leads to the coupling of stress, electric and magnetic field, and with the increase of cavity size, the influence of surface effect begins to decrease until it tends to classical elasticity theory.

Surface effect often plays a significant role in the pull-in performance of nano-electromechanical systems (NEMS) but limited works have been conducted for taking this effect into account. Herein, the influence of surface effect has been investigated on instability behavior of cantilever nano-actuator in the presence of van der Waals force (vdW). Three different methods, i.e. an analytical modified Adomian decomposition (MAD), Lumped parameter model (LPM) and numerical solution have been applied to solve the governing equation of the system. The results demonstrate that surface effect reduces the pull-in voltage of the system. Moreover, surface energy causes the cantilever nano-actuator with the assigned parameter to deflect as a softer structure. It is found that while surface effect becomes important for low values of the cantilever nano-actuator thickness, vdW attraction is significant for low initial gap values. Surprisingly, the increase in the initial gap, enhances the contribution of surface effect in pull-in instability of the system while reduces the contribution of vdW attraction. Furthermore, the minimum initial gap and the detachment length of the cantilever nano-actuator that does not stick to the substrate due to vdW force and surface effect has been approximated. A good agreement has been observed between the values of instability parameters predicted via these three methods. Whilst compared to the instability voltage predicted by numerical solution, the pull-in voltage obtained by MAD series and LPM method is overestimated and underestimated, respectively.

This paper is concerned with the surface effect on the buckling behavior of double nanobeam system using the nonlocal Timoshenko beam theory. The size effect is taken into consideration by using the Eringen’s nonlocal elasticity theory and the exact solution for buckling loads for simply supported boundary condition is presented. Influences of various parameters such as stiffness constant, nonlocal parameter, shear effect and buckling mode number are investigated. Also for the sake of validation, the present results are compared with those obtained from the Euler–Bernoulli model. It is shown that the proposed nonlocal model is able to produce results with high accuracy and it can be used as a benchmark in future studies on buckling of nano-sandwich structures.

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.

In this paper, the surface effect on the static bending behavior of functionally graded porous (FGP) nanobeams subjected to a concentrated transverse load is studied by using Reddy’s higher-order beam theory. Three types of porosity distributions are considered for the nanobeam, i.e. uniform porosity distribution, symmetric and asymmetric non-uniform porosity distributions. With the consideration of the surface effect, the nanobeams can be abstracted as a composite beam composed of a surface layer and a bulk volume. According to the generalized Young–Laplace equation, the normal stress discontinuity across a surface due to the effect of surface stress is taken into consideration. The analytical solutions of the static bending problem of FGP nanobeams are obtained for the beams with hinged-hinged, clamped-clamped and clamped-free boundary conditions. The effects of the residual surface stress, porosity distribution type, porosity coefficient and length-to-thickness ratio on the transverse displacement of the FGP beams are discussed.

Nanoporous materials and structures have attracted widespread attention due to their excellent mechanical properties. Based on the surface elasticity, the effective Young’s moduli are derived for four typical nanoporous structures with periodic unit cells. When the cross-sectional size reduces to nanoscale, the effective Young’s modulus is revealed to be strongly size-dependent. Both the effects of residual surface stress and effective-surface Young’s modulus are examined. The results indicate that negative effective Young’s modulus can be achieved when the residual surface stress is less than zero. The influences of the cross-sectional shape on the relationship between the overall deformation and applied loads are examined. The relative density also plays an important role to the mechanical characteristics not only at macroscales, but also at nanoscales.

Collecting electric power from the vibration of piezoelectric beams is practical and has been widely used for decades. This paper investigates a porous piezoelectric cantilever Timoshenko-beam energy harvester at nanoscale. The aim is to propose an optimized Timoshenko beam in order to gain more power with the same working conditions. For this purpose, the width of the beam is assumed to be exponentially changing and pores are also introduced into the beam to relieve the inherent brittleness of piezoelectric materials. Based on Timoshenko beam theory and porous piezoelectric elasticity, the uncoupled motion equations of the porous piezoelectric nanoTimoshenko beam are deduced. The analytical solutions to the output voltage and power density are obtained. According to the numerical calculation, it can be concluded that the electrical output can be improved by increasing the section parameter. Moreover, the surface effects and pore properties on the energy harvesting characteristics are discussed. In addition, when there is a concentrated mass at the free end of the beam, the displacements and output power are studied.

The usefulness of the neutron meter is limited for moisture measurement near the soil surface. In this present work, optimum dimension of a paraffin block has been calculated to correct the surface effect in order to use neutron probe near the soil surface by MCNP4C code and Particle Swarm Optimization (PSO) technique. PSO is chiefly a technique to find a global or quasi-minimum for a nonlinear and non-convex optimization problem, and there have been few studies into optimization problems with discrete decision variables. The results show a paraffin block 23.55 × 23.55 cm² square base with 4.84, 4.92, 5.10, 5.23, and 5.47 cm thickness which can correct the surface effect fairly for 0.10, 0.20, 0.30, 0.40, and 0.50 g/g moisture.

Surface effects often significantly alter the physical and mechanical properties of nanosized materials and devices. In the present paper, we investigate the influence of surface elasticity on the mixed-mode fracture by a new finite element method with surface effects being incorporated. It is found that when the curvature radius at the crack root shrinks to nanometers, surface elasticity considerably affects the local stress distributions in the vicinity of the crack tip. Using the fracture criterion of maximum hoop stress, the influences of surface elasticity on the critical stress intensity factor and the propagation direction are addressed.

Surface effects, including surface elasticity, surface piezoelectricity and residual surface stress, on the postbuckling of piezoelectric nanobeams due to an electric field are investigated using an energy method in this paper. The critical buckling voltage and amplitude are obtained analytically in terms of the bulk and surface material properties and geometric parameters. The results show that surface effects play a significant role in the postbuckling of piezoelectric nanobeams. It is found that the influences of surface piezoelectricity and residual surface stress are more prominent than the surface elasticity. These results might be helpful for designing piezoelectric nanobeam-based devices.

This paper is proposed to study the dynamic pull-in instability of nonlocal nanobridges incorporating the surface effect and intermolecular forces. The second-order frequency-amplitude relation is introduced via an asymptotic approach namely homotopy perturbation method (HPM). The effects of applied voltage and intermolecular parameters on pull-in instability as well as the natural frequency are investigated. Furthermore, the influence of nonlocal parameter and surface energy on the dynamic pull-in voltage is considered. It is shown that two terms in series expansions are sufficient to produce an acceptable solution of the mentioned nanostructure. The obtained results from numerical methods verify the strength of the analytical procedure. The qualitative analysis of the system dynamic shows that the equilibrium points of the autonomous system include center points with periodic trajectories and unstable saddle points with homoclinic orbits.

Curved structures are common shapes used in practical engineering. In this paper, the large deflection behavior of a curved elastic nanobeam with rectangular cross-section under static bending is investigated. Surface stresses in the curved nanobeam are considered as an external load and derived on the basis of the general Young-Laplace equation. The governing equations for the large deflection of the curved nanobeam with surface effect are established. By using the shooting method, the boundary value problem is solved numerically. Some numerical examples are given for cantilever, simply supported, and fixed–fixed nanobeams with positive and negative residual surface stresses. It is found that nanobeams in the presence of surface effect may be stiffer or more flexible, which is related to the residual surface stress, initial curvature of the nanobeam, the externally applied load, and boundary conditions. For nanobeams with smaller cross-sectional sizes, the height of the nanobeam can affect the deflection of the nanobeam considerably and the influence of the width of the nanobeam is negligible. The findings in the present investigation are helpful in understanding the mechanical behavior of curved nanobeams with surface effects.

As a basic element of the micro/nanodevices, nanobeams have remarkable physical properties and have attracted considerable attention in the previous studies. However, previous publications did not study the large deformation problem of nanobeams under follower loading when the surface effect becomes significant and especially for the influence of surface effect on mechanical behaviors of the nanobeams under follower loading remains unclear. In this paper, we investigated the large deformation behavior of nanobeams subjected to follower loads in consideration of the surface effects. The mechanical model of large deflection of extensible cantilever nanobeams under follower loading is presented in combination with the surface elasticity and residual surface stress, and then a MATLAB program of shooting method with a technique for determining the initial value was developed to solve the problems. The results indicate that the surface effects have an important influence on the large deflection of nanobeams under follower loading: when the surface residual stress is positive, the maximums of displacement in horizontal and vertical directions and the rotation angle of the free end become lager, but the corresponding follower force related to those maximums becomes smaller. When the residual surface stress is negative, the results are the opposite. In addition, the influence of the cross-sectional dimension of the nanobeams under follower loading on surface effects was discussed. This work is beneficial to understand the mechanism of large deformation of nanobeams with surface effects subjected to follower loads, and can also provide inspirations to design advanced nanomaterials and nanoscaled devices.