Surface Elasticity Research Articles

Phospholipase-catalyzed degradation drives domain morphology and rheology transitions in model lung surfactant monolayers.

Lung surfactant is inactivated in acute respiratory distress syndrome (ARDS) by a mechanism that remains unclear. Phospholipase (PLA2) plays an essential role in the normal lipid recycling processes, but is present in elevated levels in ARDS, suggesting it plays a role in ARDS pathophysiology. PLA2 hydrolyzes lipids such as DPPC-the primary component of lung surfactant-into palmitic acid (PA) and lyso-PC (LPC). Because PA co-crystallizes with DPPC to form rigid, elastic domains, we hypothesize that PLA2-catalyzed degradation establishes a stiff, heterogeneous rheology in the monolayer, and suggests a potential mechanical role in disrupting lung surfactant function during ARDS. Here we study the morphological and rheological changes of DPPC monolayers as they are degraded by PLA2 using interfacial microbutton microrheometry coupled with fluorescence microscopy. While degrading, domain morphology passes through qualitatively distinct transitions: compactification, coarsening, solidification, aggregation, network percolation, network erosion, and nucleation of PLA2-rich domains. Initially, condensed domains relax to more compact shapes, and coarsen via Ostwald ripening and coalescence up until the domains solidify, marked by a distinct roughening of domain boundaries that does not relax. Domains aggregate and eventually form a percolated network, whose elements then erode and whose connections are broken as degradation continues. The relative enzymatic activity of PLA2, set by the age of the sample, impacts the order and the duration of morphology transitions. The fresher the PLA2, the faster the overall degradation, and the earlier the onset of domain solidification: domains solidify before aggregating with fresh PLA2 samples, but aggregate and percolate before solidification with aged PLA2. Irrespective of the activity of the PLA2, all measured linear viscoelastic surface shear moduli obey the same dependence on condensed phase area fraction (log|G*| ∝ ϕ) throughout monolayer degradation. Moreover, the onset of domain solidification coincides with the time when the relative surface elasticity begins to increase.

Spontaneous crumpling of active spherical shells.

The existence of a crumpled phase for self-avoiding elastic surfaces was postulated more than three decades ago using simple Flory-like scaling arguments. Despite much effort, its stability in a microscopic environment has been the subject of much debate. In this paper we show how a crumpled phase develops reliably and consistently upon subjecting a thin spherical shell to active fluctuations. We find a master curve describing how the relative volume of a shell changes with the strength of the active forces, that applies for every shell independent of size and elastic constants. Furthermore, we extract a general expression for the onset active force beyond which a shell begins to crumple. Finally, we calculate how the size exponent varies along the crumpling curve.

Определение диэлектрических свойств воды в тонком слое

A technique is proposed for determining the dielectric properties of water in a nanoscale layer at frequencies corresponding to orientation polarization. The method is based on the registration of the change in the velocity of elastic surface waves resulting from the interaction with a thin layer of a liquid. It was assumed that the dispersion of the dielectric permittivity of water in the thin layer is described by the Debye's equations of dielectric relaxation. In order to demonstrate the capabilities of the proposed method, the values of the real part of the dielectric permittivity of adsorbed water at various frequencies f (43.2; 64.8; 108; 129.6, 194.4, 302.4, 388.8 MHz) were experimentally determined at a fixed thickness of the adsorption layer h (2.2; 2.8; 3.7; 13 nm). The determination of the value of the imaginary part of the dielectric permittivity as well as the calculation of the time of dielectric relaxation, static, and high-frequency dielectric permittivities was enabled by the use of the experimental values and Debye's equations. A comparison was made between the dielectric properties of adsorbed water and those of water in the bulk liquid phase. The high-frequency dielectric permittivity of adsorbed water was found to be lower than that of water in the bulk liquid phase, while the static dielectric permittivity was significantly higher. The dielectric relaxation time of adsorbed water is dependent on the thickness of the adsorption layer and is significantly longer than that of water in the bulk liquid phase.

Numerical study of bioconvection and Cattaneo-Christov heat flux model in MHD Maxwell nanofluid flow over a variable thickness elastic surface

Numerical study of bioconvection and Cattaneo-Christov heat flux model in MHD Maxwell nanofluid flow over a variable thickness elastic surface

Analysis of Properties of Polymer Composites with Various Types of Fillers

The processes of structure formation of composite building materials (KSM) on different polymer binders are presented. It is shown that one of the most significant components of KSM are fillers, which help to improve their structural and operational characteristics. This work is devoted to the analysis of the results of an experimental study of the properties of epoxy composites with fillers having various elastic-plastic and strength properties. The research was carried out in three stages: at the first stage, studies were conducted aimed at assessing the influence of the nature of the filler on the curing processes of KSM; at the second, the influence of the type of filler and its quantitative content on the strength of composites was established, at the third, compositions were optimized using fillers with different indicators of grain composition and elastic-plastic properties. Powders of glass, dolomite, thermolite, and diatomite were considered as fillers at the first and second stages of the research, and powders of glass, ceramics, and chalk were considered at the second stage. The research at the third stage was carried out using mathematical methods of experiment planning with the construction of a planning matrix for a complete factor experiment and the determination of the values of the response functions relative to the encoded factors. The physico-mechanical properties, degree of curing, and chemical resistance of filled epoxy CCM have been established. On the basis of artificial neural networks, the maximum properties of the studied composites with fillers were determined. An assessment of structural properties based on rank correlation is also proposed. The results of the research can be used to predict the properties of KSM, as well as to clarify the extreme parameters of the properties. The dependences of changes in the properties of polymer composites on the surface characteristics, the dispersion of fillers and the degree of filling were established; preferred fillers for epoxy composites were determined; fillers were determined to assess the effect of elastic surface properties of composites, allowing to improve the strength and deformability of polymer composites; regression models were obtained based on a complete factorial experiment; an assessment of the «structural stability» of the studied composites using Pearson, Kendall, Spearman rank correlation; On the basis of artificial neural networks, the extreme properties of the studied composites with fillers were determined, neural networks.

Surface–dislocation interaction by various models of surface elasticity

The effect of applying different surface elasticity models related to the Gurtin–Murdoch and Steigmann–Ogden theories to the problem on an interaction of a dislocation row with a flat surface of a semi-infinite three-dimensional body is analyzed in the paper. The boundary conditions in the case of an arbitrary shape of a cylindrical surface under the plane strain are derived within the framework of the Steigmann–Ogden model involving all simplified versions of the Gurtin–Murdoch model and the Gurtin–Murdoch model itself. The boundary condition used in the paper for the flat surface is a particular case of the general one. The analytical solution of the corresponding boundary value problem is obtained in the paper in a closed form for the elastic field. Based on this solution, some numerical examples of the stress distribution at the surface and the image force acting on each dislocation are presented. It is shown that incorporating the bending resistance of the surface in the Steigmann–Ogden model leads to the decrease of some stresses and increase the other ones at the surface and to the decrease of the image force, as compared with those obtained by the Gurtin–Murdoch membrane theory of the surface.

Simulation of Multi-Layered Ballistic-Resistant Armour with Enhanced Energy Absorption Properties

This research focuses on the simulation of ballistic impact on multi-layered ballistic resistant armour. The efficiency of spring-loaded backing plate armour was compared with armour that has solid end plate with a view to introducing a more elastic surface that enhances energy absorption properties. The design consists of three major layers of different materials: fibre cement as the first layer; Kevlar as the second; and a spring-loaded backing plate made of steel as the third layer. SolidWorks was used to model the multi-layered armour and ANSYS Workbench Explicit Dynamics and AUTODYN 3D solver were used to simulate the ballistic impact. The simulation involved testing different configurations of the multi-layered structure. Analysis of the effect of the spring wire diameter on the armour's energy-absorbing characteristics was carried out while keeping the overall weight within the acceptable range. The simulation results for the different configurations were compared and the ballistic-resistant armour designed with a spring-loaded backing plate of 0.40 mm spring wire diameter gave the least deformation. The research suggested an enhanced armour performance using embedded elastic material.

Investigation on enhancing classification of moist material by variable vibration intensity elastic screening

In mineral beneficiation, screening is critical for classifying materials. There are problems with low screening efficiency and adhesion and accumulation of material during the screening process of moist material. So, the process of enhancing the classification of moist material by an elastic screen surface with variable vibration intensity (ESSVVI) was investigated in this paper. The feeding speed of material was optimized during screening, and the synergistic effect of multi-parameters was further investigated by response surface methodology (RSM). The results showed that this screen surface could achieve elastic screening with variable vibration intensity, effectively overcome the moist material adhesion, and resolve the issue of material accumulation. The screening efficiency reached the maximum at 10.00 t·h−1·m−2 feeding speed. The impacts of screen body amplitude, frequency, and feeding speed on elastic screening performance with variable vibration intensity were found significant, and there were significant interactions among these parameters. This work can provide a reference to enhance the classification of moist material.

Asiatic acid-entrapped transfersomes for the treatment of hypertrophic scars: In vitro appraisal, bioactivity evaluation, and clinical study

Non-invasive treatment options for hypertrophic scars (HTS) are limited, and treating HTS remains challenging due to their unappealing appearance and associated social stigma. In this work, a novel transfersomal system named Asiatic acid-entrapped transfersomes (AATs) was prepared. AATs were evaluated for their skin permeability, anti-inflammatory activity, and other characteristic parameters to determine the most promising formulation. Asiatic acid-entrapped transfersomal gel (AATG), which was obtained by incorporating the lead AATs in a gel base, underwent testing in an 8-week, double-blind, placebo-controlled, split-skin clinical study. The net skin elasticity (R5), melanin index (MI), and skin surface hydration were analyzed employing Cutometer®, Mexameter®, and Corneometer®, respectively, in order to evaluate the effectiveness of the developed AATG. AATs exhibited vesicular sizes and zeta potential values within the range of (27.15 ± 0.95 to 63.54 ± 2.51 nm) and (-0.010 to −0.129 mV), respectively. TW80AAT gave the highest %EE (90.84 ± 2.99%), deformability index (101.70 ± 11.59 mgs−1), permeation flux at 8 h (0.146 ± 0.005 mg/cm2/h), and anti-inflammatory activity (71.65 ± 1.83%). The clinical study results of AATG indicated no adverse skin reactions. Furthermore, product efficacy tests demonstrated a significant reduction in MI and an increase in net skin elasticity at 2, 4, and 8 weeks. These pilot study outcomes support the effectiveness of the AATG.

Dynamic BEM analysis of elastic anisotropic nano‐sheet with surface imperfections and cavities

AbstractThe paper considers elastic anisotropic nano‐sheet with nanotopography and containing embedded nanocavities under time‐harmonic in‐plane wave motion. The mechanical model is based on the classical elastodynamic theory for the anisotropic bulk solid and the nonclassical boundary conditions along its boundary derived by Gurtin and Murdoch. A localized constitutive equation for the half‐plane boundary is considered in the frame of surface elasticity theory. The computational tool is an efficient direct displacement boundary element method (BEM) based on the frequency‐dependent elastodynamic fundamental solution for elastic generally anisotropic material. To show the versatility of the proposed methodology, wave propagation in an elastic anisotropic heterogeneous nano‐sheet with nanorelief presented by hill‐canyon nanotopography is studied. The simulations illustrate the dependence of the wave field on the material anisotropy, on the surface elasticity properties, on the nanorelief peculiarities, on the nanocavities existence and their dynamic interaction, and on the incident wave characteristics. The obtained results reveal the potential of the developed mechanical model based on the boundary integral equations in the frame of surface elasticity theory to produce highly accurate results by using strongly reduced discretization mesh in comparison with the domain‐based methods.

New Shear Horizontal (SH) Surface-Plasmon-Polariton-like Elastic Surface Waves for Sensing Applications.

The advent of elastic metamaterials at the beginning of the 21st century opened new venues and possibilities for the existence of new types of elastic (ultrasonic) surface waves, which were deemed previously impossible. In fact, it is not difficult to prove that shear horizontal (SH) elastic surface waves cannot exist on the elastic half-space or at the interface between two conventional elastic half-spaces. However, in this paper we will show that SH elastic surface waves can propagate at the interface between two elastic half-spaces, providing that one of them is a metamaterial with a negative elastic compliance s44(ω). If in addition, s44(ω) changes with frequency ω as the dielectric function ε(ω) in Drude's model of metals, then the proposed SH elastic surface waves can be considered as an elastic analogue of surface plasmon polariton (SPP) electromagnetic waves, propagating at a metal-dielectric interface. Due to inherent similarities between the proposed SH elastic surface waves and SPP electromagnetic waves, the new results developed in this paper can be readily transferred into the SPP domain and vice versa. The proposed new SH elastic surface waves are characterized by a strong subwavelength confinement of energy in the vicinity of the guiding interface; therefore, they can potentially be used in subwavelength ultrasonic imaging, superlensing, and/or acoustic (ultrasonic) sensors with extremely high mass sensitivity.

A phase field fracture model for ultra-thin micro-/nano-films with surface effects

Surface effects usually remarkably affect the mechanical response of ultra-thin micro-/nano-structures. However, the mechanisms of surface effects on the fracture characteristics of ultra-thin films are still not fully understood. To this end, this paper develops a modeling framework to investigate the fracture of ultra-thin films at microscales or below. Such a framework couples the Gurtin–Murdoch theory with a phase-field fracture model, in which the former is adopted to introduce the surface effects, i.e., the surface residual stress and surface elasticity of a thin film, and the latter is able to model crack evolution without requiring predefined crack paths or any criteria. Furthermore, a novel crack driving force is introduced, which encompasses the tensile components of both bulk elastic energy and surface elastic energy. Several numerical examples including the biaxial tension test as well as the single-edge notched tension/shear test are performed. The simulation results indicate that the surface strain energy plays a major role in the total elastic strain energy of an ultra-thin film when its thickness is at a micro level, thus demonstrating the significance of surface effects. Moreover, the mode-I fracture test shows that the surface elasticity and surface residual stress have a remarkable influence on the displacement at failure, while for the mode-II fracture test, the surface residual stress significantly influences the fracture characteristics such as the crack path and failure displacement. The developed model paves the way for revealing the fracture mechanisms of ultra-thin micro-/nano-films and conducting their safety assessment.

Robust surface light scattering spectroscopy for fluid interfaces

Surface Light Scattering Spectroscopy (SLSS) can characterize the dynamics of an interface between two immiscible fluids by measuring the frequency spectrum of coherent light scattered from thermophysical fluctuations—‘ripplons’. In principle, and for many interfaces, SLSS can simultaneously measure surface tension and viscosity, with the potential for higher-order properties, such as surface elasticity and bending moments. Previously, this has been challenging. We describe and present some measurements from an instrument with improvements in optical design, specimen access, vibrational stability, signal-to-noise ratio, electronics, and data processing. Quantitative improvements include total internal reflection at the interface to enhance the typically available signal by a factor of order 40 and optical improvements that minimize adverse effects of sloshing induced by external vibrations. Information retrieval is based on a comprehensive surface response function, an instrument function, which compensates for real geometrical and optical limitations, and processing of almost real-time data to report results and their likely accuracy. Detailed models may be fit to the power spectrum in real time. The raw one-dimensional digitized data stream is archived to allow post-experiment processing. This paper reports a system design and implementation that offers substantial improvements in accuracy, simplicity, ease of use, and cost. The presented data are for systems in regions of low viscosity where the ripplons are underdamped, but the hardware described is more widely applicable.

Environmentally Friendly Wood Adhesives Based on Dextrin/Arabic Gum Blends

Wood adhesives are widely used consisting of urea-formaldehyde resins. Most of the studies aim to find alternative natural materials to replace the carcinogenic chemical adhesives. A mixture of natural materials that are available in abundance, cheap in price and are resistant to water and heat, the failure of the interface between two solid dielectrics is a major source of insulation system failure, hence it is crucial to understand the principles regulating this breakdown occurrence. It is generally agreed that the tangential AC breakdown strength of solid-solid surfaces is primarily determined by the elastic modulus (elasticity), radial/tangential pressure, surface smoothness/roughness, and dielectric strength of the ambient environment. For this purpose, we made use of dextrin and Arabic gum. Physical parameters (Lap shear strength, pull off strength, hardness, roughness, electrical and thermal insulations) of the combination formed with varying amounts of each ingredient were investigated. The adhesive characteristics of D were enhanced by the incorporation of AG, with improved pull off adhesion and lap shear strength at increasing AG levels at 80%. D /AG 20/80 compositions had pull off adhesion values 189 times greater than pure D, and lap shear strength values 820 times higher. It is evident because of the dispersion of AG molecules in decreasing the surface roughness of D/AG films and increasing their hardness on the shore scale. There is a positive correlation between the amount of AG added and the blending matrix of D, therefore boosting A with AG increases A. The dielectric strength, and thermal insulation increases with the increase in the weight ratio of Arabic gum. The blend prepared as an adhesive for wood is a good electrical and thermal insulator at 8% AG/20% D.

A Note on Counting the Multiplicities of Elastic Surface Waves Using Weyl’s Law

A Note on Counting the Multiplicities of Elastic Surface Waves Using Weyl’s Law

Buckling of a nano‐rod with taken into account of surface effect

AbstractBuckling of a simple supported and cantilever nano‐rod and under action of self‐weight was modeled, taking into account the surface effect according to two models of surface elasticity – Gurtin–Murdoch and Steigmann–Ogden. The size effect under the buckling was studied by the Ritz method using two kinematic hypotheses, known as the rod theories of Euler–Bernoulli and Timoshenko. The simulation results were compared depending on the accepted surface elasticity model and the kinematic hypothesis.

Anisotropic mechanical properties of β-Ga2O3 single-crystal measured via angle-dependent nanoindentation using a Berkovich indenter

Load-dependent and angle-dependent nanoindentation tests were performed on a (2¯01)-oriented single-crystal β-Ga2O3 substrate to study the mechanical properties of the material. The anisotropy of the mechanical properties was examined, especially with regard to the dependence of the elastic modulus (E), hardness (H), and form of plastic deformation on the rotation angle of a Berkovich indenter with respect to the monoclinic structure. E reached a maximum value and H a minimum value when the sample was rotated to such an angle that one of the three facets of the Berkovich indenter was parallel to the [010] direction. To compare our experimental results with the theoretical calculation based on the monoclinic structure, the elastic surface of β-Ga2O3 was calculated using fourth-rank stiffness and compliance tensors and visualized in three-dimensional space. Two-dimensional sectional maps of the elastic surface were obtained for a range of crystal planes, and good agreement was obtained between the experimental observations and calculations. Plastic deformation at the indenter impressions was evaluated using scanning and transmission electron microscopy, and dislocations, cleavage, and cracks were observed. Their structure and density depended on the rotation angle. Our results clearly show a strong anisotropy of the mechanical properties of β-Ga2O3, which is very different from what is found in other compound semiconductors for power-device applications, such as GaN and 4H-SiC. This emphasizes the importance of customizing the machining process for β-Ga2O3, rather than simply using “machining recipes” for other materials.

Large Deflection and Post-Buckling Analysis of Cantilever Nanorods Including Effects of Couple and Surface Stresses by Intrinsic Coordinate Finite Elements

This paper presents a novel approach to the analysis of large deflection and post-buckling behavior of cantilever nanorods under different load conditions. The proposed approach utilizes a variational method, incorporating the Gurtin–Murdoch surface elasticity theory and the consistent couple stress theory to account for size-dependency effects. By accounting for the strain energy contributions of the bulk material, surface layer, and load conditions, this approach expresses the behavior of the nanorods in terms of their intrinsic coordinates. A finite element method was used to solve this numerical problem, generating a system of non-linear equations that were iteratively solved using the Newton–Raphson method. The results obtained from the finite element method were confirmed by those from the shooting method. Also, it highlights the effectiveness of the variational model in predicting the large deflection and post-buckling behavior of cantilever nanorods while considering both surface stress and couple stress effects. Furthermore, the study investigated the influence of surface stress and couple stress on the response of the nanorods to point and uniform loads. The results showed that incorporating both effects enhanced the stiffness of the nanorods compared to scenarios in which these effects were neglected. In addition, the couple stress effect was found to have a greater influence on the stiffening of nanorods for the same value of unitless parameters compared to surface stress effects. These findings offer valuable insights into the large deflection and post-buckling behavior of cantilever nanorods and highlight the importance of surface stress and couple stress effects. The model proposed in this study has potential applications in advanced technological device designs by providing a comprehensive understanding of the mechanical response of nanorods, allowing for more accurate predictions and enhanced device performance.

Free vibration analysis of functionally graded nanobeams based on surface stress-driven nonlocal model

A surface stress-driven nonlocal model is employed in this manuscript to study the coupled effects of the long-range interaction and surface energy on the free vibrations of nano-beams made of metal-ceramic functionally graded material. The nanobeam theory is formulated based on the Bernoulli-Euler kinematics and surface effects include surface elasticity, surface residual stresses, surface density and rotary inertia. Hamilton’s principle is applied to derive the size-dependent governing equation. The main results of a parametric investigation, carried out considering four different kinematic boundary conditions, i.e. Cantilever, Simply-Supported, Clamped-Pinned and Doubly-Clamped, are also presented and discussed, varying the nonlocal parameter and the material gradient index. The results show how the proposed model is able to capture surface energy effects on the overall dynamic behavior of functionally graded Bernoulli-Euler nanobeams and provides a cost-effective method for the design and the optimization of nano-scaled structures.

Analytical solution for unsteady Walters-B fluid flow by a deforming surface with acceleration using OHAM based package BVPh2.0

Current study aims at simulating fluid flow due to a deformable heated surface in an otherwise static viscoelastic fluid obeying Walters-B model. Velocity of the surface is supposed to grow as time from its initiation of motion progress. Simulations in this work are based on the assumption of quadratic surface temperature distribution. Temperature rise attributed to the frictional heating effect is accounted for in the analysis. By choosing appropriate base functions, homotopy solutions are developed for reasonably large values of material fluid parameter. Reliability of the analytical results is established by computing averaged squared residual of the system. The contributions of the surface acceleration and elasticity on the boundary layer formation are enlightened through the plots of velocity components and temperature. Skin friction measuring the stress experienced by the surface is evaluated and examined under different controlling parameters. The paper also presents a numerical solution using NDSolve of MATHEMATICA in a special case of steady flow, and such solution agrees very well with the corresponding homotopy solution.