Surface Energy Effects Research Articles

Coupled effects of surface energy and size dependency on the stability of nanotweezers using GDQ method

Surface energy and size phenomenon can highly affect the physical performance of ultra-small systems. Herein, the static and dynamic stability of nanotweezers fabricated from conductive cylindrical nanowires is studied under the presence of Casimir force. The Gurtin---Murdoch surface elasticity in combination with the consistent couple stress theory is employed to incorporate the coupled effects of surface energy and size phenomenon. Using Green---Lagrange strain, the higher order surface stress components are incorporated in the governing equation. The Dirichlet mode is considered and an asymptotic solution, based on the path integral approach, is applied to consider the effect of the Casimir attraction. Numerical generalized differential quadrature is employed to solve the nonlinear governing equation of system. The effects of various parameters on the static and dynamic pull-in parameters and stability threshold of the tweezers are demonstrated.

Dust production in debris discs: constraints on the smallest grains

The surface energy constraint puts a limit on the smallest fragment $s_{surf}$ that can be produced after a collision. Based on analytical considerations, this mechanism has been recently identified as been potentially able to prevent the production of small dust grains in debris discs and cut off their size distribution at sizes larger than the blow-out size. We numerically investigate the importance of this effect to find under which conditions it can leave a signature in the small-size end of a disc's particle size distribution (PSD). An important part of this work is to map out, in a disc at steady-state, what is the most likely collisional origin for micron-sized grains, in terms of the sizes of their collisional progenitors. We implement, for the first time, the surface energy constraint into a collisional evolution code. We consider a debris disc extending from 50 to 100AU and 2 different stellar types. We also consider two levels of stirring in the disc: dynamically "hot" (e=0.075) and "cold" (e=0.01). For all cases, we derive $s_{surf}$ maps as a function of target and projectile sizes, $s_t$ and $s_p$, and compare them to equivalent maps for the dust-production rate. We then compute disc-integrated PSDs and estimate the imprint of the surface energy constraint. We find that the ($s_p$,$s_t$) regions of high $s_{surf}$ values do not coincide with those of high dust production rate. As a consequence, the surface energy constraint has generally a weak effect on the system's PSD. The maximum $s_{surf}$-induced depletion of $\mu$m-sized grains is $\sim 30$% and is obtained for a sun-like star and a dynamically hot case. For the e=0.01 cases, the surface energy effect is negligible compared to the massive small grain depletion induced by another mechanism: the natural imbalance between dust production and destruction rates in low-stirring discs identified by Thebault&Wu(2008).

Mathematical models of polymer-dentin physicochemical interactions and their biological effects

Dental adhesion is the result of a physicochemical interaction between tooth structure and the adhesive polymeric restorative material. Adhesion involves molecular interactions at the interface between these constituents. Furthermore, mechanical interlocking is a common type of adhesion important in dental materials. This type of bonding involves the penetration of the adhesive into the dental surface and requires different energetic considerations for an optimal interface. An adequate infiltration of adhesive monomers into demineralized dentin depends on several factors that are determined by the atoms on the surface of the structures and the effects of surface energy on the thermodynamic work of adhesion. The polarity, solubility and viscosity of the adhesive system and the surface energy and moisture of dentin tissue are key factors that contribute to adhesion energy. The main goal of dental material adhesion is to produce an interface that is strong and durable. Thus, it is important to optimize the infiltration of adhesive monomers into exposed collagen fiber networks and dentinal tubules in order to increase the strength of the Resin-dentin bonds and produce adequate dentin sealing.

Dynamic instability analysis of doubly clamped cylindrical nanowires in the presence of Casimir attraction and surface effects using modified couple stress theory

The dynamic instability of free-standing size-dependent nanowires by considering the Casimir force and surface effects is investigated in the following research work. The study is carried out for nanosystems with circular cross section and cylinder–plate geometry for which the governing equation of motion is derived based on the Gurtin–Murdoch model and modified couple stress theory. Two methods including the proximity force approximation for small separations and Dirichlet asymptotic approximation for large separations are utilized to formulate the Casimir attraction of a free-standing cylinder–plate geometry. To solve the complex nonlinear problem faced in this work, a stepwise numerical procedure is developed and the effects of length scale parameter, surface energy and vacuum fluctuations on the dynamic instability and adhesion time of nanowires are studied. Based on the obtained results, the phase portrait of Casimir-induced nanowires shows periodic and homoclinic orbits.

Effect of surface energy upon size-dependent yield strength of single-crystalline hollow micro- and nanopillars

The physical nature of the size-dependent yield strength of micro- and nanopillars is still an open issue, where the surface energy may be one factor that influences the size effect of these pillars, especially for hollow pillars. In this study, the influence of the surface energy and surface elasticity upon the size-dependent yield strength of single-crystalline hollow micro- and nanopillars is considered quantitatively. An analytical expression of the size-dependent yield strength is established that considers the surface energy and the inner defects by the principle of minimum potential energy. The predicted yield strength of our model as a function of the pillar size is more precise than that of the well-known single arm source model when comparing the predictions with the experimental results of pillars made of Al or Ni. According to the surface elasticity, the surface energy can be determined by the thickness of the hollow pillars, the surface modulus and the surface strain, where the latter two are related to the external damages.

Surface wettability and energy effects on the biological performance of poly-3-hydroxybutyrate films treated with RF plasma

The surface properties of poly-3-hydroxybutyrate (P3HB) membranes were modified using oxygen and an ammonia radio-frequency (RF, 13.56MHz) plasma. The plasma treatment procedures used in the study only affected the surface properties, including surface topography, without inducing any significant changes in the crystalline structure of the polymer, with the exception being a power level of 250W. The wettability of the modified P3HB surfaces was significantly increased after the plasma treatment, irrespective of the treatment procedure used. It was revealed that both surface chemistry and surface roughness changes caused by the plasma treatment affected surface wettability. A treatment-induced surface aging effect was observed and resulted in an increase in the water contact angle and a decrease in the surface free energy. However, the difference in the water contact angle between the polymers that had been treated for 4weeks and the untreated polymer surfaces was still significant. A dependence between cell adhesion and proliferation and the polar component of the surface energy was revealed. The increase in the polar component after the ammonia plasma modification significantly increased cell adhesion and proliferation on biodegradable polymer surfaces compared to the untreated P3HB and the P3HB modified using an oxygen plasma.

Size-dependent axial buckling and postbuckling characteristics of cylindrical nanoshells in different temperatures

One of the most important reasons that give rise to the extraordinary behaviors of nanostructures is the free surface energy. In the current investigation, a size-dependent shell model is introduced which has an excellent capability to take surface energy effects into account. To this end, Gurtin–Murdoch elasticity theory is implemented into the classical shell theory. Using virtual work׳s principle, the non-classical governing differential equations related to the cylindrical nanoshell subjected to axial compressive load are derived. Subsequently, a boundary layer theory is extended to solve the problem with considering the effects of surface free energy in addition to the nonlinear prebuckling deformations and the large postbuckling deflections. Finally, a solution methodology based on a two-stepped perturbation technique is put to use in order to obtain the size-dependent critical buckling loads and related postbuckling equilibrium paths corresponding to different surface properties and various sets of thermal environments. It is found that for all sets of thermal environment, the surface free energy has significant influence on the postbuckling strength of nanoshell. Also, it is seen that thermal environment causes to decrease the both critical buckling load and critical end-shortening, but it has a negligible influence on the value of minimum postbuckling load.

Combining air recharging and membrane superhydrophobicity for fouling prevention in membrane distillation

In previous studies of the desalination technology membrane distillation (MD), superhydrophobicity of the membrane has been shown to dramatically decrease fouling in adverse conditions, but the mechanism for this is not well understood. Additionally, air layers present on submerged solid superhydrophobic surfaces have been shown to dramatically reduce biofouling, and air-bubbling has been used to reducing fouling and increase flux and efficiency in MD. The present work studies the effect of maintaining air layers on the membrane surface and superhydrophobicity as a new method for preventing fouling of MD membranes by salts, particulates, and organic particles. Superhydrophobic MD membranes were prepared using initiated chemical vapor deposition (iCVD) of perfluorodecyl acrylate (PFDA) on poly(vinyldene fluoride) PVDF membranes and used to study the effects of surface energy on fouling. A static MD setup with evaporation through an MD membrane but no condensing of permeate was used to examine the effect of air exposure on fouling, by measuring the increase in weight of the membrane caused by scale deposition. Theory was derived for the reduction of fouling on superhydrophobic surfaces, and a review of related theory was included. Air layers may displace fouling gels, reduce the area of feed in contact with the membrane, reduce foulant adhesion, and enhance superhydrophobicity in a Cassie–Baxter state. The study shows that the presence of air on the membrane surface significantly reduces biological fouling, but in some cases had mildly exacerbating effects by increasing crystal formation of salts, especially when the air was not saturated with water vapor. Air recharging combined with superhydrophobicity reduced fouling in several cases where hydrophobic membranes alone did little.

Effect of surface energy on the dynamic response and instability of fluid-conveying nanobeams

Abstract A modified continuum model of fluid-conveying nanobeams is presented by incorporating the surface elasticity in this paper. The classical beam theory is adopted to model the bulk, while Gurtin and Murdoch's theory of surface elasticity is applied to model the surfaces. Based on the Timoshenko beam theory, the equation of motion for transverse vibrations of fluid-conveying nanobeams is formulated and the differential quadrature method is applied to solve this complex problem. Beams made from aluminum (Al) and silicon (Si) are chosen as examples. The surface effects on the vibrational characteristics are discussed for simply supported and clamped nanobeams. The results show that, due to the different surface elastic properties between Al and Si, the surface energies will increase the frequency and critical flow velocity of Al nanobeams but decrease those of Si beams. In addition, the frequency and critical flow velocity of Al and Si nanobeams obtained from the Timoshenko beam model are generally smaller than those from the Euler–Bernoulli beam model due to the effects of shear deformation and rotary inertia. However, when the cross-sectional size of the Si nanobeams is relatively small, their Timoshenko beam results are found to be close to the Euler–Bernoulli beam results.

Fabrication and Characterization of Gecko-inspired Dry Adhesion, Superhydrophobicity and Wet Self-cleaning Surfaces

In this study, gecko-inspired polydimethylsiloxane (PDMS) microfiber surfaces were fabricated by combining Inductively Coupled Plasma (ICP) and micro-mold casting. The effect of roughness and surface energy of counterface on the adhesion of gecko-inspired microfiber surfaces and its superhydrophobicity and wet self-cleaning were studied. The adhesion of gecko-inspired microfiber surfaces depended on the roughness of the counterfaces due to the influences of contact area and interlocking mechanism. SEM images of interfaces between counterfaces with different roughness and gecko-inspired microfiber surfaces revealed the matched and dis-matched contact directly. The gecko-inspired microfiber surface got the larger adhesive force from the higher surface energy counterface, which is consisted with Johnson-Kendall-Roberts (JKR) theory. The smaller dimension and lower duty ratio of microfibers on PDMS resulted in the increasing of Water Contact Angle (WCA) and the decreasing of Sliding Angle (SA) compared to those of smooth PDMS. Particularly, sample P-8-28-20 had the biggest WCA (155°) and SA (7°), which displayed the superhydrophobicity and the best wet self-cleaning efficiency in all samples. The present studies showed that the roughness and surface energy of counterface both affected the adhesion of gecko-inspired microfiber surfaces. The smaller dimension and lower duty ratio of microfibers on PDMS endowed it with the superhydrophobicity and the wet self-cleaning abilities.

Obtaining a full range of surface energies on single wall carbon nanotube samples through photo-initiated chemical vapor deposition

Event Abstract Back to Event Obtaining a full range of surface energies on single wall carbon nanotube samples through photo-initiated chemical vapor deposition Seyedehsan Hosseininasab1, Nathalie Faucheux2, Gervais Soucy2 and Jason R. Tavares1 1 Polytechnique Montreal, Chemical engineering, Canada 2 Université de Sherbrooke, Chemical and Biotechnological Engineering, Canada Introduction: Despite all the distinctive properties of carbon nanotubes (CNTs), their commercial use in biomedical applications is limited by their cytotoxicity [1]. Several factors can explain the CNT cytotoxicity including their dimension, surface hydrophobicity and degree of agglomeration [1],[2]. However, the effect of surface energy on the cytotoxicity of single wall carbon nanotubes (SWCNTs) has to be investigated further. For this purpose, well-characterized SWCNTs bearing similar functionalities with properties ranging from super-hydrophobic to super-hydrophilic must be prepared. In this study, photo-initiated chemical vapor deposition (PICVD) using a syngas precursor [3] was applied to SWCNTs and is presented as a viable technique to fulfill this goal. Materials and Methods: Raw-SWCNTs (R-SWCNTs) were first purified by a multi-step protocol as previously described [4]. Efficiency of purification was assessed by transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). These purified SWCNTs (P-SWCNT) were then dispersed in ethanol via sonication and immediately filtered under vacuum upon a polycarbonate membrane. The resulting “buckypaper” was placed in a vacuum oven to ensure complete ethanol evaporation. The surface of SWCNTs was then treated according to a method developed by Dorval Dion et al (2014) [3]. Briefly, P-SWCNTs were placed inside a UVC-illuminated quartz micro-reactor. After inert gas purging, the syngas precursor (CO and H2) was introduced at various ratios along with H2O2 as a radical photo-initiator (PI). To obtain the desired surface functionality, the process could be implemented under pressure (+15 kPag) or slight vacuum (-15 kPag). Hydrophilic surfaces were typically obtained under slight vacuum, while hydrophobic surfaces were achieved under pressure [3]. The surface energy of the treated P-SWCNTs was determined by applying the Owens-Wendt model [5]. Results and Discussion: TEM was used to both confirm the efficiency of the purification protocol and assess the morphology of P-SWCNTs after treatment. As shown Fig. 1A, the impurities in R-SWCNTs included amorphous and graphitic carbon, as well as catalytic metal nanoparticles, while these impurities in P-SWCNTs were decreased (Fig. 1B) (from 29% to 14% based on TGA results). Surface wetting of SWCNT samples was assessed through sessile drop contact angle measurements. The average contact angle of P-SWCNT samples was 79±2°, while it varied from 0+3° to 165±3° for treated nanotubes (T-SWCNTs) as a function of the molar ratio of H2/CO (Fig. 2). Conclusion: Using PICVD with a syngas precursor, we successfully functionalized P-SWCNTs bearing various oxygen-containing groups with properties ranging from superhydrophilic to superhydrophobic. This PICVD method will be helpful to better determine the effect of surface energy on the cytotoxicity of SWCNTs bearing similar functionalities. Fig. 1. TEM images of A) R-SWCNTs, B) P-SWCNTs. Fig. 2. Blue lozenge) Contact angle measurements of T-SWCNTs obtained by tensiometry in terms of molar ratio of H2/CO, Red Square) Surface energy measurements that have been plotted in terms of molar ratio. This project is supported by FRQNT Foundation

Slip of polymer melts over micro/nano-patterned metallic surfaces.

The slip behavior of high-density polyethylenes (HDPEs) is studied over surfaces of different topology and surface energy. Laser ablation has been used to micro/nano-pattern the surface of dies in order to examine the effect of surface roughness on slip. In addition, fluoroalkyl silane-based coatings on smooth and patterned substrates were used to understand the effect of surface energy on slip. Surface roughness and surface energy effects were incorporated into the double reptation slip model (Ebrahimi et al., J. Rheol., 2015, 59, 885-901) in order to predict the slip velocity of studied polymers on different substrates. It was found that for dies with rough surfaces, polymer melt penetrates into the cavities of the substrate (depending on the depth and the distance between the asperities), thus decreasing wall slip. On the other hand, silanization of the surface increases the slip velocity of polymers in the case of smooth die, although it has a negligible effect on rough dies. Interestingly, the slip velocity of the studied polymers on various substrates of different degrees of roughness and surface energy, were brought into a mastercurve by modifying the double reptation slip velocity model.

An electrokinetic-combined electrochemical study of the glucose electro-oxidation reaction: effect of gold surface energy

Electrokinetic analysis demonstrates the effect of glucose adsorption on gold surfaces in the glucose electro-oxidation mechanism.

Free dynamic analysis of functionally graded tapered nanorods via a newly developed nonlocal surface energy-based integro-differential model

The nonlocality effect based on appropriate kernel functions plays an important role in mechanical analysis of nanostructures. This phenomenon is not limited to the bulk, but also includes the surface layer. However, these important issues have not been properly paid attention to in the previously developed continuum-based models. Using a novel nonlocal integro-differential model accounting for the surface energy effect, free longitudinal vibration of functionally graded tapered nanorods embedded in an elastic matrix is investigated. The material properties of both the bulk and the surface layer vary along the nanorod’s length based on a power-law relation. By considering the nonlocal integro-differential constitutive relations for the bulk as well as the surface layer, the equations of motion of the elastically supported nanostructure are obtained and analyzed via reproducing kernel particle method (RKPM). In particular cases, modal analysis is also implemented and the obtained results by the RKPM are successfully verified with those of the modal analysis approach. The roles of the surface energy, small-scale parameter, stiffness of the matrix and that of the supports, nanorod’s diameter, power-law index, and the nonlocal kernel function on the natural frequencies are explained in some detail.

Finite difference method for sixth-order derivatives of differential equations in buckling of nanoplates due to coupled surface energy and non-local elasticity theories

ABS TRACT: In this article, finite difference method (FDM) is used to solve sixth-order derivatives of differential equations in buckling analysis of nanoplates due to coupled surface energy and non-local elasticity theories. The uniform temperature change is used to study thermal effect. The small scale and surface energy effects are added into the governing equations using Eringen’s non-local elasticity and Gurtin-Murdoch’s theories, respectively. Two different boundary conditions including simply-supported and clamped boundary conditions are investigated. The numerical results are presented to demonstrate the difference between buckling obtained by considering the surface energy effects and that obtained without the consideration of surface properties. The results show that the finite difference method can be used as a powerful method to determine the mechanical behavior of nanoplates. In addition, this method can be used to solve higher-order derivatives of differential equations with different types of boundary condition with little computational effort. Moreover, it is observed that the effects of surface properties tend to increase in thinner and larger nanoplates; and vice versa.

Thermo-mechanical analysis of functionally graded plate-like nanorotors: A surface elasticity model

Nanorotors could have many applications in nanotechnology, however, their thermo-elasto-static responses due to rotary motion as well as externally applied loads have not been examined yet. This paper deals with thermo-elastic fields of rotating functionally graded nanoscale plate-like rotors using the surface elasticity theory of Gurtin and Murdoch. By dividing the nanoplate into adequate number of annular rings, the analytical expressions of elastic fields within these rings are appropriately derived. Due to the symmetry of both thermal loading and the exerted centrifugal force, the elastic field is symmetric and each ring has only two unknown parameters. To determine these parameters, appropriate boundary conditions at the interfaces of the rings as well as the non-classical conditions at the innermost and outermost surfaces of the nanoplate are defined and enforced. In a particular case, the obtained results are checked with those of another work and a good agreement is achieved. The roles of the environment׳s temperature, angular velocity, power-law index, and surface energy effect on the resulted thermo-elastic fields are carefully studied. This work can be regarded as a crucial step in nanomechanical assessing of advanced composite nanorotors.

Effect of surface energy and seed layer annealing temperature on ZnO seed layer formation and ZnO nanowire growth

We discuss the effects of surface energy and seed layer annealing temperature (Tannealing) on seed layer growth and hydrothermally-grown zinc oxide (ZnO) nanowires (NWs). In this work, by varying the ultraviolet ozone (UVO) treatment times on a silicon surface, the surface energy conditions for the seed layer formation changed and the seed layer was annealed under different Tannealing conditions. Under a lower surface energy condition of the substrate, with increasing Tannealing, the coverage density and the average thickness of the seed layer increased, but island-like growth was observed. This case was inevitably accompanied by an increase in surface roughness, which resulted in agglomerated low density growth of ZnO NWs. After sufficient UVO treatment, hydroxyl groups on the silicon surface activated the ZnO seed layer formation in the chemical reaction and increased the bonding energy between the active nucleation sites of the seed layer and the substrate surface. This ensured higher coverage density of the seed layer with lower surface roughness under the same Tannealing condition, thereby providing the ZnO NW growth with an enhanced density and aspect ratio as well as good crystallinity.

Modeling the effect of surface energy on stressed grain growth in cubic polycrystalline bodies

A recently-developed constitutive theory of stressed grain growth is augmented to include the effect of excess surface energy via a surface effect state variable. The new constitutive theory is implemented into a coupled finite-element and phase-field computational framework. Through three-dimensional simulations, the new constitutive model is shown to be capable of predicting the experimental data of the annealing-induced texture transition in polycrystalline copper thin films of different thicknesses attached to a polyimide substrate. Our simulations show that the grain growth driving force arising from the through-film thickness grain boundary curvature plays a prominent role in such a transitional behavior.

The role of surface energy reducing agent in the formation of self-induced nanoscale surface features and wetting behavior of polyurethane coatings

Abstract The effect of surface energy reducing agent (SERA) on the surface chemistry and physics of the polyurethane (PU) coatings containing 0–10 mol% of SERA was studied. The coatings were carefully analyzed by differential scanning calorimeter, infrared spectroscope, field-emission scanning electron microscope, atomic force microscope and contact angle measurement system. Results indicated that at different concentrations of additive, the SERA segments took different strategies to minimize their interface area with other segments which affected their population on the coating surface. The concentration gradient of SERA segments on the surface of PU led to the creation of a local lateral pressure. The local lateral pressure along with the relative content of solvent showed a synergic effect on the formation of self-induced nanoscale surface features. Contact angle measurements revealed that the role of SERA segments in enhancing the hydrophobicity of PU coatings through creation of specific physical features was more pronounced than through chemical modification of the surface.

Modeling and analysis of nanobeams based on nonlocal-couple stress elasticity and surface energy theories

This paper aims to develop a new non-classical Bernoulli–Euler model, taking into account the effects of a set of size dependent factors which ignored by the classical continuum mechanics. Among those factors are the microstructure local rotation, long-range interactions between a particle and the other particles of the continuum and the surface energy effects. The model used the modified couple-stress theory to study the effect of the local rotational degree of freedom of a specific particle. Furthermore, the surface elasticity model developed by Gurtin and Murdoch has been used to determine the surface energy effects on the behavior of the particle. The effects of the local rotation and surface energy are investigated in the framework of nonlocal elasticity theory, which is employed to study the nonlocal and long-range interactions between the particles. In addition, Poisson׳s effect incorporated in the newly developed beam model. The equations of equilibrium and complete boundary conditions of the new beam are derived using the principle of virtual work.The developed model is validated, by comparing the obtained results with benchmark results. To illustrate the new model, analytical solutions for the static bending and critical buckling load are obtained. Numerical results reveal the significant effects of the nonlocal, microstructure, surface energy, length-to-height ratio and Poisson on the static bending and critical buckling load of nanobeams.