Interface Topography Research Articles

Laser-patterning bacterial nanocellulose for cell-controlled interaction

The interfacial topography of biomaterials has been identified as a major biophysical regulator of cell behavior and function, a role played through the interplay with biochemical cues. In this work, we demonstrate the potential of laser as a versatile technology for the direct fine-tuning of the topography of Bacterial nanocellulose (BNC) with bioinspired topographies and micropatterns on a cell size scale. Two lasers were used, with different wavelengths—IR (CO2, 10600 nm) and UV (tripled Nd: YVO4, 355 nm) —attempting to reproduce the Pitcher-plant topography and to create cell-contact guidance patterns, respectively. Different topographies with parallel grooves featuring a 20–300 μm period were generated on the BNC surface with high fidelity and reliability of the generated microstructures, as demonstrated by 3D optical profilometry and scanning electron microscopy. Moreover, it was demonstrated by X-ray photoelectron spectroscopy that laser processing does not result in detectable chemical modification of BNC. The developed anisotropic microstructures can control cell behavior, particularly regarding morphology, alignment, and spatial distribution. Thus, this proof-of-concept study on the high-resolution laser patterning of BNC opens new perspectives for the development of cell-modulating laser-engineered BNC interfaces, scaffolds, and other advanced medical devices, which can potentially broaden the application of BNC in the biomedical field.

Topographic variation and fluid flow characteristics in rough contact interface

Understanding flow characteristics of fluid near rough contact is important for the design of fluid-based lubrication and basic of tribology physics. In this study, the spreading and seepage processes of anhydrous ethanol in the interface between glass and rough PDMS are observed by a homemade optical in-situ tester. Digital image processing technology and numerical simulation software are adapted to identify and extract the topological properties of interface and thin fluid flow characteristics. Particular attention is paid to the dynamic evolution of the contact interface morphology under different stresses, the distribution of microchannels in the interface, the spreading characteristics of the fluid in contact interface, as well as the mechanical driving mechanism. Original surface morphology and the contact stress have a significant impact on the interface topography and the distribution of interfacial microchannels, which shows that the feature lengths of the microchannels, the spreading area and the spreading rate of the fluid are inversely proportional to the load. And the flow path of the fluid in the interface is mainly divided into three stages: along the wall of the island, generating liquid bridges, and moving from the tip side to the root side in the wedge-shaped channel. The main mechanical mechanism of liquid flow in the interface is the equilibrium between the capillary force that drives the liquid spreading and viscous resistance of solid wall to liquid. In addition, the phenomenon of “trapped air” occurs during the flow process due to the irregular characteristics of the microchannel. This study lays a certain theoretical foundation for the research of microscopic flow behavior of the liquid in the rough contact interface, the friction and lubrication of the mechanical system, and the sealing mechanism.

Plane SV-waves scattering by seawater convex surface topography and underlying lined tunnel in a saturated half-space

Analytical solutions of boundary-valued problems for aboveground topography and underground buried structures, especially for sites with overlying seawater, have always been challenging. Based on the region decomposition technique (RDT) and Hankel integral transform method (HITM), SV-waves scattering by the convex circular topography with seawater and underlying tunnel in a saturated half-space is solved. The primary problem is tackling additional scattered waves introduced by the water–soil interface and convex topography, while ensuring boundary conditions are all met. To this end, scattering wave potential functions in cylindrical coordinates are first transformed into the Hankel integral form in Cartesian coordinates. This greatly facilitates the straightforward application of free boundary conditions at the soil–seawater flat interface, rather than making a large circular arc approximate assumption, which, in turn, avoids the resultant accumulating errors. Secondly, scattering problem to be solved is mathematically and analytically formulated as solving a 5 × 5 linear equation system comprised of wave functions inside the convex topography and lining tunnel while satisfying all physical continuous boundary conditions. This is the main innovation and resulting consequence from the theoretical derivation process. Finally, validation of numerical examples between this paper, existing studies and theoretical analysis further demonstrates the reliability and general adaptability of solutions. Parametric studies of the incident SV waves are conducted to investigate the spatially varying seismic response. The effects of SV-waves incident angles and frequencies, tunnel burial depth, tunnel lining thickness, saturated soil porosity, and seawater depth are investigated and analyzed in detail. This study provides a feasible scheme of investigating the dynamic response of complex submarine sites, which is of great significance for both theoretical value and engineering purposes.

A numerical study of thermal shrinkage influence on the impact dynamics of alumina droplets thermally sprayed on flat, grit-blasted and laser treated surfaces

Thermal spray splat morphology and its microstructure are of significance to the coating resulting properties. Depending on the material, the changes in density as the droplet solidifies during splat development and solidification could have a substantial role in the particle deformation dynamics, formation of porosity and subsequent adhesion to the flat or rough target surface.In the current study, the effect of shrinkage on the final splat shape is numerically investigated for collisions occurring under several high-speed impact conditions using the Volume-of-Fluid (VOF) method on real surface topography. This influence is also studied for the interaction of two successive impacting particles. The developed models study the splat impact, development and dynamics of heat transfer on flat, laser-patterned, grit-blasted surfaces and numerically designed features. The results of droplet material variable density cases are compared with those assuming constant density. Experimentally obtained single splat depositions are also used to validate the developed models and obtained numerical results.Findings show that micro substrate surface features lead to splat stretching, porosity and limited finger creation subsequent to improved solidification through interfacial contact area increase. Macro surface characteristics, however, lead to splashing and separation from the substrate surface driven by fluid instabilities. Irrespective of the interface topography, shrinkage processes reduce droplet spreading and accentuate splat feature discontinuities such as porosity.

Imaging interfacial topography with coherent x-ray reflectivity

Imaging interfacial topography with coherent x-ray reflectivity

Determination of the Thickness of Interfacial Water by Time-Resolved Sum-Frequency Generation Vibrational Spectroscopy.

The physics and chemistry of a charged interface are governed by the structure of the electrical double layer (EDL). Determination of the interfacial water thickness (diw) of the charged interface is crucial to quantitatively describe the EDL structure, but it can be utilized with very scarce experimental methods. Here, we propose and verify that the vibrational relaxation time (T1) of the OH stretching mode at 3200 cm-1, obtained by time-resolved sum frequency generation vibrational spectroscopy with ssp polarizations, provides an effective tool to determine diw. By investigating the T1 values at the SiO2/NaCl solution interface, we established a time-space (T1-diw) relationship. We find that water has a T1 lifetime of ≥0.5 ps for diw ≤ 3 Å, while it displays bulk-like dynamics with T1 ≤ 0.2 ps for diw ≥ 9 Å. T1 decreases as diw increases from ∼3 Å to 9 Å. The hydration water at the DPPG lipid bilayer and LK15β protein interfaces has a thickness of ≥9 Å and shows a bulk-like feature. The time-space relationship will provide a novel tool to pattern the interfacial topography and heterogeneity in Ångstrom-depth resolution by imaging the T1 values.

Connection stiffness modeling of rotating dovetailed blade with macro-micro interface topography

The connection stiffness between the dovetailed blade and disk indicates the boundary condition of the blade, directly influencing the dynamic response of the blade-disk assembly and even the structural safety of the whole aero-engine. Due to the limited manufacturing precision, the contact interface of dovetailed joint is rough with macroscopic geometrical deviation inside. However, few researches are reported about the effect of macro-micro interface topography on the connection stiffness. In this paper, a stiffness model of the rotating dovetailed blade with interface topography characteristic is proposed. First, a statistical contact model is established to describe the normal and tangential contact responses of the rough interface in dovetailed joint. Then, by introducing the displacement and angle infinitesimals, the explicit expressions of the connection stiffnesses in different directions are derived out. Finally, based on the presented connection stiffness model, rotational speed, working temperature, macroscopic geometrical deviation, and microscopic topography parameters are investigated in detail. The results show a great influence of interface topography and operating parameters on the connection stiffness. The work in this paper provides a novel way to reveal the inner mechanical relationship between the macro-micro topography and the connection stiffness of dovetailed blade under the work condition, which is meaningful for the actual manufacturing and performance analysis of the aero-engine.

Photochemically Induced Marangoni Patterning of Polymer Bilayers

Surface-tension gradients created along a polymer film by patterned photochemical reactions are a powerful tool for creating surface topography. Here, we use mathematical modeling to explore a strategy for patterning photochemically inactive polymers by coupling a light-sensitive and light-insensitive polymer to form a polymer bilayer. The light-sensitive polymer forms the top layer, and the most dominant surface-tension gradients are introduced at the interface between this layer and air. Lubrication theory is used to derive nonlinear partial differential equations describing the heights of each layer, and linear analysis and nonlinear simulations are performed to characterize interface dynamics. Patterns form at both the polymer-air and polymer-polymer interfaces at early thermal annealing times as a result of Marangoni stresses but decay on prolonged thermal annealing as a result of the dissipative mechanisms of capillary leveling and photoproduct diffusion, thus setting a limit to the maximum individual layer deformation. Simulations also show that the bottom-layer features can remain "trapped", i.e., exhibit no significant decay, even while the top layer topography has dissipated. We study the effects of two key parameters, the initial thickness ratio and the viscosity ratio of the two polymers, on the maximum deformation attained in the bottom layer and the time taken to attain this deformation. We identify regions of parameter space where the maximum bottom-layer deformation is enhanced and the attainment time is reduced. Overall, our study provides guidelines for designing processes to pattern photochemically inactive polymers and create interfacial topography in polymer bilayers.

Experimental study on the interface topography evolution and vibration monitoring in thrust ball bearings induced by particulate contamination

Rolling bearings operating in harsh environments are extremely exposed to the risk of exogenous dust or wear debris particles, so there is a strong need to investigate the effects of particulate contamination on bearing operation and to identify problems early. The lubricated oil containing silica particles of various sizes and concentrations are prepared and introduced into thrust ball bearings to replicate the severe operating conditions. Vibration and acoustic emission (AE) signals were measured by accelerometer and AE sensor in a thrust ball bearing test rig. The experimental bearing raceway was observed by scanning electron microscope (SEM) and confocal laser scanning microscopy, and the evolution of the surface topography was analyzed to probe the wear mechanism. The results show that the most severe wear areas occur at the bottom of the bearing raceway, and its degree of wear is significantly influenced by the size and concentration of the silica particles. As the experimental time increases, the raceway surface undergoes an accelerated wear process originating from slight dimples, which leads to bearing failure. Furthermore, the introduction of particles into the lubricant increases surface root mean square (RMS) roughness, vibration and acoustic emission for different experimental durations. The vibration and AE signals are affected by a combination of solid particles and surface wear. The measured monitoring results can provide valuable information about the damage morphologies and subsequently about the state of the bearing during operation.

Molecular Engineering of Silicon Phthalocyanine to Improve the Charge Transport and Ammonia Sensing Properties of Organic Heterojunction Gas Sensors

AbstractNovel organic heterostructures fabricated with a bilayer consisting of an axially substituted silicon phthalocyanine (R2‐SiPc) derivative and lutetium bis‐phthalocyanine (LuPc2) are investigated for their ammonia sensing properties. Surface and microstructure characterization of the heterostructure films reveal either compact or highly porous surface topography in (345F)2‐SiPc and Cl2‐SiPc‐based heterostructures, while electrical characterization reveals a strong influence of the axial substituent in R2‐SiPc on NH3 sensing capabilities. Electrical characterization further demonstrates an apparent energy barrier for interfacial charge transport, which is higher in the (345F)2‐SiPc/LuPc2 heterojunction device. In‐depth charge transport studies by impedance spectroscopy further reveal a resistive interface in (345F)2‐SiPc/LuPc2 and faster bulk and interfacial charge transport in Cl2‐SiPc/LuPc2 heterojunction devices. Different interfacial charge transport capabilities and surface topographies affect NH3 sensing properties of the two heterojunction devices, in which (345F)2‐SiPc/LuPc2 reveals a fast and non‐linear response with a limit of detection (LOD) of 310 ppb, while Cl2‐SiPc/LuPc2 exhibits a slow, and linear response to NH3 with LOD of 100 ppb. Finally, different metrological parameters of the two sensors are correlated to the respective gas‐material interactions, in which adsorption and diffusion regimes are modulated by the surface topography and hydrophobicity of the sensing layer.

Rough contact surface reconstruction based on A mechanical-thermal contact model

Direct observation and measurement of stress and temperature distributions at contact interface is a challenge due to the randomness and complexity of surfaces, as well as the interface is always opaque. In this paper, the random contact process is characterized based on the real contact volume, and then the mechanical-thermal contact theory is established, which reveals the interaction mechanism between contact force and thermal resistance. Then, a reconstruction method of interface topography, contact stress and temperature distribution is established based on this model combination with modified W-M fractal function, which provides a visual evaluation method for the concealed interface performance of complex engineering structures. The proposed indirect method of interface contact characteristics is expected to be applied in the detection and evaluation of complex engineering structures.

Isotropic 3D printing using material extrusion of thin shell and post-casting of reinforcement core

Material extrusion (ME) can be used to manufacture a range of three-dimensional shapes by stacking extruded polymer layers with a heated nozzle. While the process is suitable for customized production in small quantities, the use of ME-printed features is often limited with regard to mechanical purposes due to the intrinsic anisotropic strength shortcoming, as parts can easily failure against a load in the transverse direction. In addition, the production speed for multiple parts is another major drawback preventing real competition with other mass manufacturing technologies. In this paper, we introduce an additive manufacturing strategy of shell pre-printing and core post-casting (referring as shell-core printing) that effectively enhances the isotropic strength and the production speed. Shell-core printing involves 3D printing a thin shell of the three-dimensional shape using the conventional ME method, followed by the injection and curing of a reinforcement resin inside the core. We show that the transverse strength of the layered shell can be reinforced by the core and that the reinforcement can be more effective when the shell-core interface roughness is effectively removed. Using an additional surface-polishing step between the pre-printing and the post-casting, the degree of isotropy with regard to the strength can be enhanced significantly from 0.4 to nearly 1, while the overall production time can also be reduced by half that in the conventional ME process. We also investigate the tensile behavior of the shell-core printed specimen and experimentally verify that the characteristics in general follow the classical theory of the rule of mixtures. In addition, we find that many different fracture modes exist in shell-core printed parts depending on the adhesive strength at the shell-core interface. We provide a theoretical criterion for the interfacial bonding energy which determines the different fracture behaviors and experimentally validate this in a mode II fracture test. • We introduce a shell-core printing strategy, material extrusion of 3D shell and casting of reinforcement material in the core. • Shell-core printing can improve the degree of isotropy in strength from 0.4 to nearly 1. • Total production time of shell-core printing can also be reduced by half that in general material extrusion 3D printing. • Shell-core Interface topography and adhesive strength determine the fracture behavior of the printed shell-core products.

Stress Heterogeneity and the Onset of Faulting Along Geometrically Irregular Faults

AbstractWe present a two‐dimensional analytical solution for the static stress field around a rough interlocked interface under background stresses and its applications to faulting. The solution is derived using perturbation theory for the defined interface topography and background stresses. The failure‐ratio, which scales the likelihood to failure of the bulk material around the interface, is calculated adopting the Coulomb failure criterion. We compare model predictions with results of experiments performed on rough rock interfaces and find good agreement between the locations of off‐fault deformation zones and calculated high failure‐ratio values. We further study the effect of fault topography on stress distribution and failure around the San Andreas Fault and find a moderate correlation between Failure‐Ratio values and off‐fault seismic events. We conclude that our model is able to delineate off‐fault regions that are relatively prone to bulk failure due to local effects of fault topography.

Double pattern improves the Schlieren methods for measuring liquid–air interface topography

Double pattern improves the Schlieren methods for measuring liquid–air interface topography

Qualified interlayer modifier for organic solar cells with optimized interfacial topography and boosted efficiency based on biomass-derived acid

The cathode interlayer modification is crucial for the performance of organic solar cells (OSCs), which ensures an efficient electron extraction. However, the research progress of the cathode interlayer is seriously lagging behind, compared with the emerging of OSCs. In this research, three different biomass-derived acid, oxalic acid, azelaic acid and tannic acid, are investigated as the modifiers for the PDIN cathode interlayer of the non-fullerene acceptor based OSCs. The best performance is obtained via the modification of oxalic acid, due to its small conjugated molecule structure. It improves the cathode interlayer quality without disrupting the intermolecular stacking of PDIN. After the modification of oxalic acid, the energy barrier between the active layer and the cathode interlayer is reduced and the carrier recombination is suppressed. It helps the formation of a good ohmic contact and enhances the electron collection. Therefore, the average power conversion efficiency increases from 17.61% of the control device to 18.28%, with a champion efficiency of 18.43%. This research first demonstrates the application of biomass-derived acid in the cathode interlayer modification. It offers a novel strategy to achieve high-efficient cathode interlayer for OSCs using biomaterials.

Non-Intrusive Single Camera Diagnostic For Measurement Of Interfacial Topography In Three-Dimensional Space And Time

Liquid-gas interfaces are complex boundaries that can be of great interest in various fields, from fundamental science to industrial applications. They usually span across multiple spatio-temporal scales and, they can be a key parameter in multiple complex physical processes such as bubble entrainment and interfacial transfer. These make their simulation and measurement challenging but at the same time essential. Although computational fluid dynamic (CFD) models had become very powerful through the years, they still include some degree of empiricism. Experimental high spatio-temporal data for the interfacial topography could not only provide more insights and evidence for the physical process at play but also valuable validation datasets for the CFD models. Non-intrusive interfacial reconstruction, especially in the threedimensional (3D) space is a challenging task and it usually forces to complex experimental configurations. Here, we present a new, non-intrusive, refraction-based diagnostic for reconstruction of liquid-gas interfaces in 3D with one single camera and laser plane. Concisely, a vertical, two-dimensional (2D), laser-induced fluorescent grid is written directly in the liquid phase and captured from the gas phase through a deformed liquid interface. A robust ray tracing algorithm relates the optical deformation of the grid to the interfacial topography. The orientation of the grid provides boundary conditions for the surface reconstruction and minimizes restrictions of existing schemes. These, enable not only to simplify the experimental setup but also to extend the applicability of the refraction-based techniques. The grid generation scheme employed here is Talbot-effect structured illumination (TESI); a flexible method to create a wide range of very fine laser patterns. This allows to easily adapt the technique in a broad range of scales and applications, as well as to combine it with velocimetry. Profilometry and velocimetry can share the same grid and therefore they can be deployed simultaneously enabling the measurement of quantities such as the interfacial shear stress. Finally, the algorithm can treat the data both as time independent and time resolved. Both approaches are elaborated below and preliminary data from a droplet impact are presented and discussed.

An estimation of water levels associated with a storm along the coast of Bangladesh using a non-central difference method of lines

In this paper, depth-averaged shallow water equations were solved using a non-central difference method of lines together with the classical RK(4,4) method to estimate water levels associated with a cyclone along the coast of Bangladesh. A 4-point backward finite difference method was adopted in discretizing spatial derivatives retaining time derivatives as continuous. Thus, the shallow water equations together with the boundary conditions were transformed into a system of initial value problems, which was solved using the RK(4,4) method. A nesting approach was employed to incorporate the land-sea interface and bottom topography effectively with economic cost. A stable tidal oscillation was generated in the domain applying the M2 tidal constituent along the southern boundary of the parent model and the surge model was then run to get water levels owing to dynamic tide-surge interaction. Numerical experiments were performed to simulate water levels due to tide, surge, and nonlinear tide-surge interactions associated with the cyclonic storm, AILA. The obtained results were in good agreement with those attained in some previous studies and observations and the WLs due to the nonlinear tide-surge interaction were in a reasonable agreement with respect to the root mean square error values and predictive skills.

Exploiting interface patterning for adhesion control

Surface force-mediated adhesion, e.g. via van der Waals forces, is critical for direct bonding of bulk solids in the absence of chemical bonding or an adhesive layer. However, no two surfaces are ideally flat or perfectly conformal due to surface roughness or intentional patterning. When adhered, non-zero surface tractions arise wherever the local separation of the interface differs from its intrinsic equilibrium separation, inducing regions of tensile and compressive stresses. A fundamental understanding of such imperfect adhesion is important and unlocks opportunities to control interfacial strength and toughness in various applications including MEMS/NEMS, micro-transfer printing, and processes to manufacture advanced 3D integrated-circuits. This paper investigates the fundamentals of direct adhesion of non-conformal surfaces by examining the interplay of the (i) intrinsic traction-separation relation (TSR), (ii) interface topography, and (iii) elastic properties of the adhered bodies. The TSR adopted accounts for strong repulsion when the interface separation is less than the equilibrium separation, and only the normal surface tractions are considered. The effective TSR properties, including the overall adhesion strength and work of separation, are determined from numerical calculations. Simple closed-form solutions are obtained for rigid bulk solids. A finite element model utilizing cohesive elements in a periodic cell is constructed to study cases with non-uniform deformation in the elastic solids.

Ionic polymer metal composite compression sensors with 3D-structured interfaces

In this paper, we report the development of tailored 3D-structured (engineered) polymer-metal interfaces to create enhanced ‘engineered ionic polymer metal composite’ (eIPMC) sensors towards soft, self-powered, high sensitivity strain sensor applications. We introduce a novel advanced additive manufacturing approach to tailor the morphology of the polymer-electrode interfaces via inkjet-printed polymer microscale features. We hypothesize that these features can promote inhomogeneous strain within the material upon the application of external pressure, responsible for improved compression sensing performance. We formalize a minimal physics-based chemoelectromechanical model to predict the linear sensor behavior of eIPMCs in both open-circuit and short-circuit sensing conditions. The model accounts for polymer-electrode interfacial topography to define the inhomogeneous mechanical response driving electrochemical transport in the eIPMC. Electrochemical experiments demonstrate improved electrochemical properties of the inkjet-printed eIPMCs as compared to the standard IPMC sensors fabricated from Nafion polymer sheets. Similarly, compression sensing results show a significant increase in sensing performance of inkjet-printed eIPMC. We also introduce two alternative methods of eIPMC fabrication for sub-millimeter features, namely filament-based fused-deposition manufacturing and stencil printing, and experimentally demonstrate their improved sensing performance. Our results demonstrate increasing voltage output associated to increasing applied mechanical pressure and enhanced performance of the proposed eIPMC sensors against traditional IPMC based compression sensors.

Three-dimensional characterization of bonding features for asphalt pavement interface using a novel interlayer isolation film

Pavement interface bonding largely depends on the interface topography characteristics. This study presents a procedure to characterize the interface bonding features between different types of asphalt concrete layers and reveals the difference of the “interaction effect” between layers. The top and bottom layers of asphalt mixtures were non-destructively separated by a novel interlayer isolation film. An ultra-high-resolution three-dimensional (3D) laser scanner was used to acquire 3D interface data of interlayer. Analysis of variance (ANOVA) was performed to examine the relationship between the damage rate of the interlayer isolation film and its corresponding bonding characteristics. The binary analysis results showed that the damage rate of the isolation film was different due to the asphalt mixture with different gradations in the top and bottom layers. The arithmetic mean curvature (Spc), height distribution skewness (Ssk), and root mean square deviation (Sq) have the most significant effects on the isolation film damage rate at the 99.9 % confidence interval. These characteristics can be used to describe pavement interlayer bonding states. This study provides theoretical support for optimizing the bonding characterization of pavement interfaces.