Effect Of Surface Free Energy Research Articles

Exploring size-dependent optical property alterations in fine-tuning intermetallic PdCd nanocube sizes.

Tuning the size of intermetallic nanocrystals is challenging due to the conflicting effects of surface free energy and surface diffusion on the disorder-to-order phase transition during wet-chemistry growth. Herein, we synthesized intermetallic PdCd nanocubes with tunable sizes ranging from 8 to 15 nm by adjusting the Cd precursor concentrations using a wet-chemistry approach. This process shares a mechanism of size tuning similar to quantum dot synthesis, involving the regulation of monomer concentration determined by the precursor concentrations. The intermetallic PdCd nanocubes exhibit distinct size-dependent optical properties compared to platinum group metal nanocrystals of similar size ranges, with increased light-induced catalytic enhancement as size increases. The 15 nm-sized nanocubes exhibited the most significant light-induced catalytic enhancement, reaching 3.3 times, while the 8 nm-sized nanocubes showed only a 1.6-fold enhancement in 4-nitrophenol reduction. This study emphasizes the importance of tuning the size of intermetallic nanocrystals, providing valuable insights for future exploration of their size-dependent properties.

From Silver Nanoparticle to Thin Films Produced by Pulsed Laser Deposition: Effects of Ar Gas Pressure and Substrate Surface Free Energy

From Silver Nanoparticle to Thin Films Produced by Pulsed Laser Deposition: Effects of Ar Gas Pressure and Substrate Surface Free Energy

Engineering PVDF omniphobic membranes with flower-like micro-nano structures for robust membrane distillation

Conventional PVDF membranes are easily wetted and contaminated in membrane distillation (MD) process, especially when used in separating high-salinity water and oil-contained saline water. To address these issues, an omniphobic membrane was fabricated in this work. ZnO micro-flowers with a rough structure were successfully deposited onto the PVDF membrane with the assistance of polydopamine assistance. After undergoing a fluorination process, the omniphobic membranes were prepared by the synergistic effect of surface microstructure and free energy. The effects of varying Zn(NO3)2 concentrations and deposition times on morphology, pore size and separation efficiency were comprehensively examined. It was demonstrated that at a Zn(NO3)2 concentration of 50 mM and a deposition time of 0.5 h, the resulting PVDF composite membrane exhibited high liquid repellency towards all the test liquids, such as water, ethanol solution, paraffin oil, and etc. Furthermore, the membrane consistently exhibited impressive salt rejection behavior (99.99%) and maintained an average flux (15.54 kg·m−2·h−1) when exposed to high-salinity solution (up to 20 wt%-NaCl). Meanwhile, during treating an oil-contained saline water emulsion with the oil content of 200 ppm, the membrane also displayed high resistance to wetting and fouling during the continuously 24 h tests. The membrane displayed a rejection rate of 99.99 % with an average vapor flux of 18.60 kg·m−2·h−1. In summary, this omniphobic membranes demonstrated a great potential in MD for practical challenging wastewater treatment.

Enhancing photoelectrochemical performance through surface engineering of CdSe and Al-doped CdSe nanoparticles on ZnO/FTO photoanodes

This study presents a comprehensive investigation into the enhanced performance of photoelectrochemical (PEC) cells through the decoration of CdSe and Al-doped CdSe nanoparticles on ZnO rods. The capacitance-voltage study reveals that Al doping increases the donor concentration and improves minority carrier diffusion time while reducing dispersion at grain boundaries. Spectral response analysis demonstrates that CdSe/ZnO/FTO and Al: CdSe/ZnO/FTO photoanodes exhibit maximum short-circuit currents at a wavelength of 675 nm, corresponding to a bandgap of 1.84 eV. Al doping shifts the spectral response to longer wavelengths, indicating an estimated bandgap of 1.72 eV. Furthermore, the effect of surface free energy and polarity on the developed photoanode materials is investigated. CdSe and Al-doped CdSe nano particles on ZnO/FTO surfaces exhibit reduced water contact angles, indicating improved wettability. The surface free energy decreases with Al doping, potentially influencing electrolyte absorption and the interaction between photoanodes and electrolytes. The presence of polar hydroxyl (-OH) groups and Al+++ ions on the Al: CdSe nano particles contributes to their impact on surface free energy. These findings provide valuable insights for optimizing PEC cell performance by manipulating doping concentrations and surface characteristics.

Nonlinear three-dimensional stability characteristics of geometrically imperfect nanoshells under axial compression and surface residual stress

Abstract Through reduction of thickness value in nanostructures, the features of surface elasticity become more prominent due to having a high surface-to-volume ratio. The main aim of this research work was to examine the surface residual stress effect on the three-dimensional nonlinear stability characteristics of geometrically perfect and imperfect cylindrical shells at nanoscale under axial compression. To do so, an unconventional three-dimensional shell model was established via combination of the three-dimensional shell formulations and the Gurtin–Murdoch theory of elasticity. The silicon material is selected as a case study, which is the most utilized material in the design of micro-electromechanically systems. Then, the moving Kriging meshfree approach was applied to take numerically into account the surface free energy effects and the initial geometrical imperfection in the three-dimensional nonlinear stability curves. Accordingly, the considered cylindrical shell domain was discretized via a set of nodes together using the quadratic polynomial type of basis shape functions and an appropriate correlation function. It was found that the surface stress effects lead to an increase the critical axial buckling load of a perfect silicon nanoshell about 82.4 % 82.4 \% for the shell thickness of 2 nm 2{\rm{nm}} , about 32.4 % 32.4 \% for the shell thickness of 5 nm 5{\rm{nm}} , about 15.8 % 15.8 \% for the shell thickness of 10 nm 10{\rm{nm}} , and about 7.5 % 7.5 \% for the shell thickness of 20 nm 20{\rm{nm}} . These enhancements in the value of the critical axial buckling load for a geometrically imperfect silicon nanoshell become about 92.9 % 92.9 \% for the shell thickness of 2 nm 2{\rm{nm}} , about 36.5 % 36.5 \% for the shell thickness of 5 nm 5{\rm{nm}} , about 17.7 % 17.7 \% for the shell thickness of 10 nm 10{\rm{nm}} , and about 8.8 % 8.8 \% for the shell thickness of 20 nm 20{\rm{nm}} .

Atomistic and continuum modeling of nanoparticles: Elastic fields, surface constants, and effective stiffness

The elastic fields, surface constants and effective elastic moduli of nanoparticles are studied by means of classical molecular dynamics and continuum mechanics. Two analytical models of isotropic nanoparticles are considered. The first model is a sphere coated with a thin surface layer, which simulates the effect of the free surface energy in the nanoparticle. In the second model, the surface effect is taken into account by applying the boundary conditions in accordance with the Gurtin–Murdoch theory of material surfaces. The effective elastic moduli of nanoparticles are evaluated using the general and consistent from the micromechanical viewpoint surface averaging scheme. The geometric and material parameters of the continuum models are found by fitting the MD data for nanoparticles of three monocrystalline solids with diverse atomic mass, lattice type, and elastic moduli. It is shown that the properly calibrated analytical models correctly predict the size effect of surface free energy on the lattice contraction, residual stress, surface constants, and the elastic stiffness of nanoparticles. Applicability of the developed continuum models to the faceted nanocrystals is discussed. Comparison of the atomistic and continuum models of nanoparticles yields a simple and robust method for evaluating the surface constants. The parametric and asymptotic study of these models is performed. The established analytical relationships between the parameters of the continuum models facilitate using the surface layer model in the numerical simulation of nanostructures.

Effect of surface free energy of organic underlayer on the dissolution kinetics of poly(4-hydroxystyrene) film in tetramethylammonium hydroxide aqueous developer

Abstract Understanding the interaction of resist materials with the underlayers is important for the development of highly resolving resist materials. In this study, the effect of the surface free energy of the organic underlayer on the dissolution kinetics of poly(4-hydroxystyrene) (PHS) film in a tetramethylammonium hydroxide (TMAH) aqueous developer was investigated by the quartz crystal microbalance (QCM) method. By using 0.95 wt% TMAH standard developer, we observed the correlation between the polar component of the surface free energy of the underlayer and the interaction area of the QCM chart (impedance) near the end of PHS dissolution. The interaction area was defined by the product of impedance change and time. The interaction of the hydroxyl groups of PHS with the underlayer increased with the polar component of the surface free energy of the underlayer. The analytical method developed in this study is useful for the investigation of the resist-underlayer interaction during development.

Effect of surface free energy on water absorption of roller-compacted concrete pavement containing calcium stearate powder

The impact of surface free energy (SFE) on water absorption of roller compacted concrete pavement (RCCP) containing calcium stearate powder with different water to cement (w/c) ratios, was investigated. For this purpose, 60 cylindrical specimens were prepared with various percentages of calcium stearate powder. Water absorption, contact angle and air void tests were performed, and SFE values were calculated for various specimens. Accordingly, the addition of calcium stearate powder to RCCP reduced water absorption and SFE while increasing the contact angle. The air void content in RCCPs increased by adding hydrophobic powder. The computed tomography scans showed that the increase of voids was mainly due to the increase in number of pores with a diameter of less than 10 µm. Besides, a relationship between SFE and voids was proposed for RCCPs with different w/c ratios. This relationship indicated that with increasing the percentage of voids, the SFE decreases, which reduces capillary suction and water absorption.

Effects of chemical composition on the hydrophobicity and antifouling performance of epoxy-based self-stratifying nanocomposite coatings

Inspired by nature, the superhydrophobic surface has great potential for application in the field of antifouling due to its excellent fouling resistance. Nanocomposite coatings are an economical way to fabricate superhydrophobic surfaces by controlling the surface chemical composition and topography. However, the available open literature assessing the chemical composition effects on hydrophobicity and antifouling performance is rare. In this study, epoxy-based nanocomposite coatings with various wettability were fabricated by using the air-spray technique. The element distributions of the coatings at different depths were characterised by EDS and XPS. The results showed that the top coating surfaces of ER-F, ZnF40-1:5, and ZnF40-1:9 were enriched in F and Si elements, evidencing the self-stratifying. And by reducing the solid surface free energy, the hydrophobicity of ER-F, ZnF40-1:5, and ZnF40-1:9 was significantly improved. And the coating ZnF40-1:9 achieved super-hydrophobic. Based on the Young's equation and the “equation of state for the interfacial tensions”, it was found that the effect of solid surface free energy on CAH was greater than that on WCA due to the greater coefficient of the variable. The superhydrophobic coating ZnF40-1:9 shows great antifouling performance against marine diatom P. tricornutum and its antifouling rate is up to 94.1%. By reducing the surface free energy, the hydrophobicity of nanocomposite coatings can be improved significantly, consequently improving the antifouling performance effectively. These findings might provide insight into developing superhydrophobic nanocomposite coatings to inhibit biofouling.

Surface properties of chlorophyll-a sensitized TiO2 nanorods for dye-sensitized solar cells applications

Dye-sensitized solar cells (DSSCs) based on TiO2 nanorods have recently achieved improvement by tuning surface polarity with the help of chlorophyll-a dye. Additionally, we have successfully explored the effects of surface free energy, oxygen defect concentration, micro strain, surface morphology, chemical composition, photoluminescence, and surface properties of chlorophyll-a sensitized TiO2 nanorods. Sensitization on TiO2 nanorods has been tested with photoelectrochemical performance, and the resulting surface shows a superhydrophobicity with CA = 154 ± 30 while oxygen defect is reduced to 2.7228 × 1021 cm−3. The surface free energy has been successfully studied with the help of Owens-Wendt-Rabel-Kaelble (OWRK) and the wetting envelope model. A sensitized system of chlorophyll-a and TiO2 nanorods for the DSSC application presents a maximum of 3.69 times PEC improvement under 1000 W light illumination.

The effect of surface free energy on the fracture behaviors of nanoparticle-reinforced composites

By considering the surface free energy effect, an analytical investigation on the fracture behaviors of nanoparticle-reinforced composites was performed in this study. The plastic zones ahead of the crack tips based on the Irwin model were introduced in our analysis, which has a significant influence on the fracture toughness of inelastic structures, especially for polymer and metal matrix composites. Take copper and aluminum nanoparticles as examples, comprehensive parametric studies were conducted to investigate the interaction between a Griffith crack and the nearby nanoparticle. It was found that for nanoparticles with the radius of less than 10 nm, apart from the mechanical property of the nanoparticle, the surface free energy effect plays a dominant role in determining the fracture behaviors of the nanoparticle-reinforced composites. Moreover, taking the surface free energy into account, a decrease in the plastic zone size is obtained, particularly for the crack tip nearer the nanoparticle.

Dependence of the Growth Mode in Epitaxial FePt Films on Surface Free Energy.

Epitaxial thin films of L10-ordered FePt alloys are one of the most important materials in magnetic recording and spintronics applications due to their large perpendicular magnetic anisotropy (PMA). The key to the production of these required superior properties lies in the control of the growth mode of the films. Further, it is necessary to distinguish between the effect of lattice mismatch and surface free energy on the growth mode because of their strong correlation. In this study, the effect of surface free energy on the growth mode of FePt epitaxial films was investigated using MgO, NiO, and MgON surfaces with almost the same lattice constant to exclude the effect of lattice mismatch. It was found that the growth mode can be tuned from a three-dimensional (3D) island mode on MgO to a more two-dimensional (2D)-like mode on MgON and NiO. Contact angle measurements revealed that MgON and NiO show larger surface free energy than MgO, indicating that the difference in the growth mode is due to their larger surface free energy. In addition, MgON was found to induce not only a flat surface as FePt grown on SrTiO3 (STO), which has a small lattice mismatch, but also a larger PMA than that of STO/FePt. As larger lattice mismatch is favored to induce a higher PMA into the FePt films, MgO substrates are exclusively used, but 3D island growth is indispensable. This work demonstrates that tuning the surface free energy enables us to achieve a large PMA and flat film surface in FePt epitaxial films on MgO. The results also indicate that modifying the surface free energy is pertinent for the flexible functional design of thin films.

A three-dimensional surface elastic model for vibration analysis of functionally graded arbitrary straight-sided quadrilateral nanoplates under thermal environment

AbstractIn this paper, a three-dimensional (3D) size-dependent formulation is developed for the free vibrations of functionally graded quadrilateral nanoplates subjected to thermal environment. The plate model is constructed within the frameworks of the Gurtin–Murdoch surface and the 3D elasticity theories. In this way, the effect of surface free energy and all the components of stress and strain tensors are considered without any initial assumption on them as there is no need to assume the variation of transverse normal stress inside the bulk material in advance. The variational differential quadrature approach and the mapping technique are applied to derive a discretized weak form of the governing equations. The present solution method bypasses the transformation and discretization of the higher order derivatives appearing in the equations of the strong form. The effects of surface stress, thermal environment, material gradient index and geometrical properties on the size-dependent vibrational behavior of quadrilateral nanoplates are investigated. It is observed that the thermal load intensifies the effect of surface free energy on the natural frequency of the nanoplates. The present model is exact in the extent of the continuum models and can be employed for structures with any thickness–span ratios.

Effects of Hydrophilicity, Adhesion Work, and Fluid Flow on Biofilm Formation of PDMS in Microfluidic Systems.

Polydimethylsiloxane (PDMS) has been the most widely used material in microfluidic systems, especially for cell biology applications. However, the antibacterial performance of PDMS in flow conditions has never been reported in the literature. In this paper, we analyzed the effects of contact angle (CA), adhesion force (work), and surface free energy on the antibacterial activities of PDMS by varying the ratio of curing agents (crosslinking degree) and surface modification with oxygen plasma. The results show that the Young's modulus has no particular effects on bacterial adhesion compared to the CAs of samples. For the first time, we analyzed the adhesion work (AW) effect on biofilm formation, and we found that biofilms tend to form on the surface with less AW. Furthermore, we analyzed the dual effect of hydrophilicity and shear force induced by fluid flow on the bacterial adhesion in PDMS microfluidic systems. We found that at low flow rates in microfluidic conditions, the adhesion of the bacteria on the PDMS surface is inhibited when the fluid flow exceeds a certain value. It required higher shear force to inhibit bacterial adhesion on the hydrophilic surface than on the hydrophobic surface. Therefore, hydrophilicity might be the dominant factor affecting bacterial adhesion.

Superwettable PVDF/PVDF-g-PEGMA Ultrafiltration Membranes.

Poly(vinylidene fluoride) (PVDF) is a common and inexpensive polymeric material used for membrane fabrication, but the inherent hydrophobicity of this polymer induces severe membranes fouling, which limits its applications and further developments. Herein, we prepared superwettable PVDF membranes by selecting suitable polymer concentration and blending with PVDF-graft-poly(ethylene glycol) methyl ether methacrylate (PVDF-g-PEGMA). This fascinating interfacial phenomenon causes the contact angle of water droplets to drop from the initial value of over 70° to virtually 0° in 0.5 s for the best fabricated membrane. The wetting properties of the membranes were studied by calculating the surface free energy by surface thermodynamic analysis, by evaluating the peak height ratio from Raman spectra, and other surface characterization methods. The superwettability phenomenon is the result of the synergetic effects of high surface free energy, the Wenzel model of wetting, and the crystalline phase of PVDF. Besides superwettability, the PVDF/PVDF-g-PEGMA membranes show great improvements in flux performance, sodium alginate (SA) rejection, and flux recovery upon fouling.

Boundary layer modeling of surface residual tension in postbuckling behavior of axially loaded silicon panels at nanoscale embedded in elastic foundations

Here, nonlinear buckling and postbuckling properties of cylindrical silicon nanopanels of finite length resting on elastic foundation exposed to axial compression have been studied by taking into account surface free energy (SFE) effect. Size-dependent governing equations were constructed by integrating classical shell theory and Gurtin-Murdoch elasticity theory. Surrounding elastic media were considered as Pasternak foundations. Using shell buckling boundary layer theory, the influences of large deflections and SFE were extended to nonlinear instability analysis of nanopanels under axial loads. Finally, a perturbation-based solution procedure was applied to extract explicit equations for nanopanel postbuckling equilibrium paths at different surface elastic constants and geometric parameter values. It was revealed that surface effect related to positive surface elastic constant values shifted the minimum postbuckling domain point to lower maximum deflection while materials with negative surface values of elastic constant, SFE effect shifted the minimum point of postbuckling domain to higher maximum deflections.

A Surface Energy Density-Based Theory of Nanoelastic Dynamics and Its Application in the Scattering of P-Wave by a Cylindrical Nanocavity

AbstractThe scattering of elastic waves in nanoporous materials is inevitably influenced by the surface effect of nanopores. In order to investigate such a dynamic problem with surface effect of nanomaterials, a new theory of nanoelastic dynamics is proposed, in which both the effect of surface free energy and the effect of surface inertia force are included. With the new theory, a scattering of plane compressional waves (P-wave) by a cylindrical nanocavity is analyzed, and the corresponding dynamic stress concentration factor (DSCF) around the nanocavity is analytically solved. It is found that, when the size of cavity is at a nanoscale, the surface energy effect leads to a reduction of the maximum DSCF comparing with the classical counterpart without surface effect, while the surface inertial effect enlarges the maximum DSCF. The surface inertial effect gradually becomes dominant over the surface energy effect with an increasing incident wave frequency. Although both kinds of surface effects tend to vanish with an increasing cavity radius, the surface inertial effect can exist in a submicron-sized cavity if the wave frequency is sufficiently high. All these results should be of guiding value not only for an optimal design of porous structure possessing a better dynamic load bearing capacity but also for the non-destructive detection of nano-defects.

QCM-D Study of Time-Resolved Cell Adhesion and Detachment: Effect of Surface Free Energy on Eukaryotes and Prokaryotes.

Cell-material interactions are crucial for many biomedical applications, including medical implants, tissue engineering, and biosensors. For implants, while the adhesion of eukaryotic host cells is desirable, bacterial adhesion often leads to infections. Surface free energy (SFE) is an important parameter that controls short- and long-term eukaryotic and prokaryotic cell adhesion. Understanding its effect at a fundamental level is essential for designing materials that minimize bacterial adhesion. Most cell adhesion studies for implants have focused on correlating surface wettability with mammalian cell adhesion and are restricted to short-term time scales. In this work, we used quartz crystal microbalance with dissipation monitoring (QCM-D) and electrical impedance analysis to characterize the adhesion and detachment of S. cerevisiae and E. coli, serving as model eukaryotic and prokaryotic cells within extended time scales. Measurements were performed on surfaces displaying different surface energies (Au, SiO2, and silanized SiO2). Our results demonstrate that tuning the surface free energy of materials is a useful strategy for selectively promoting eukaryotic cell adhesion and preventing bacterial adhesion. Specifically, we show that under flow and steady-state conditions and within time scales up to ∼10 h, a high SFE, especially its polar component, enhances S. cerevisiae adhesion and hinders E. coli adhesion. In the long term, however, both cells tend to detach, but less detachment occurs on surfaces with a high dispersive SFE contribution. The conclusions on S. cerevisiae are also valid for a second eukaryotic cell type, being the human embryonic kidney (HEK) cells on which we performed the same analysis for comparison. Furthermore, each cell adhesion phase is associated with unique cytoskeletal viscoelastic states, which are cell-type-specific and surface free energy-dependent and provide insights into the underlying adhesion mechanisms.

Nonlinear secondary resonance of FG porous silicon nanobeams under periodic hard excitations based on surface elasticity theory

To impart desirable material properties, functionally graded (FG) porous silicon has been produced in which the porosity changes gradually across the material volume. The prime objective of this work is to predict the influence of the surface free energy on the nonlinear secondary resonance of FG porous silicon nanobeams under external hard excitations. On the basis of the closed-cell Gaussian-random field scheme, the mechanical properties of the FG porous material are achieved corresponding to the uniform and three different FG patterns of porosity dispersion. The Gurtin–Murdoch theory of elasticity is implemented into the classical beam theory to construct a surface elastic beam model. Thereafter, with the aid of the method of multiple time-scales together with the Galerkin technique, the size-dependent nonlinear differential equations of motion are solved corresponding to various immovable boundary conditions and porosity dispersion patterns. The frequency response and amplitude response associated with the both subharmonic and superharmonic hard excitations are obtained including multiple vibration modes and interactions between them. It is found that for the subharmonic excitation, the nanobeam is excited within a specific range of the excitation amplitude, and this range shifts to higher excitation amplitude by incorporating the surface free energy effects. For the superharmonic excitation, by taking surface stress effect into account, the excitation amplitude associated with the peak of the vibration amplitude enhances. Moreover, in the subharmonic case, it is demonstrated that by increasing the porosity coefficient, the value of the excitation frequency at the joint point of the two branches of the frequency-response curve reduces. In the superharmonic case, it is revealed that an increment in the value of porosity coefficient leads to decrease the peak of the oscillation amplitude and the associated excitation frequency.

Nonlinear primary resonance analysis of nanoshells including vibrational mode interactions based on the surface elasticity theory

The deviation from the classical elastic characteristics induced by the free surface energy can be considerable for nanostructures due to the high surface to volume ratio. Consequently, this type of size dependency should be accounted for in the mechanical behaviors of nanoscale structures. In the current investigation, the influence of free surface energy on the nonlinear primary resonance of silicon nanoshells under soft harmonic external excitation is studied. In order to obtain more accurate results, the interaction between the first, third, and fifth symmetric vibration modes with the main oscillation mode is taken into consideration. Through the implementation of the Gurtin-Murdoch theory of elasticity into the classical shell theory, a size-dependent shell model is developed incorporating the effect of surface free energy. With the aid of the variational approach, the governing differential equations of motion including both of the cubic and quadratic nonlinearities are derived. Thereafter, the multi-time-scale method is used to achieve an analytical solution for the nonlinear size-dependent problem. The frequency-response and amplitude-response of the soft harmonic excited nanoshells are presented corresponding to different values of shell thickness and surface elastic constants as well as various vibration mode interactions. It is depicted that through consideration of the interaction between the higher symmetric vibration modes and the main oscillation mode, the hardening response of nanoshell changes to the softening one. This pattern is observed corresponding to both of the positive and negative values of the surface elastic constants and the surface residual stress.