Design Of Functional Surfaces Research Articles

Composite scattering characteristics analysis of micro-ellipsoidal periodic structure optical surface and microdefects

In order to adjust and detect micro-nano periodic structure optical surface accurately and efficiently, the problem of composite scattering between micro-ellipsoidal periodic structure optical surface and pore defects is studied use the multi-resolution time domain (MRTD) approach. A calculation model is established for the intensity distribution of composite scattering, which is modulated by the micro-ellipsoidal periodic structure optical surface and microdefects. Results are in good agreement with those obtained using CST Microwave Studio software and the finite-different time-domain (FDTD) approach, which demonstrates the effectiveness of the calculation model and method. By combining the field distribution of the micro-ellipsoidal periodic structure optical surface containing microdefects with the optical response at different wavelengths, it is necessary to study the influence of various parameters of the micro-ellipsoidal structure and microdefects on the optical system of metamaterials. The effects of the parameters such as roughness, structure of micro-ellipsoidal unit, defect sizes and buried depths on the composite scattering characteristics are analyzed numerically. The results provide technical support for the fields of functional surface design, ultrasensitive detection, scattering peak orientation and frequency selection.

Comparative study of normal condyle and temporomandibular joint prosthesis movement during mouth opening by dynamic magnetic resonance imaging and computed tomography.

To analyze and compare the trajectory of condylar motion during mouth opening in normal volunteers and patients after total joint replacement (TJR) of the temporomandibular joint (TMJ). Condylar movement during mouth opening was recorded by dynamic magnetic resonance imaging (MRI) for volunteers with normal TMJs and dynamic computed tomography (CT) for patients after TMJ TJR. Trajectories of the points selected every 5 mm from the superior point of the condyle (P0) along its axis to the mandibular angle (P-25) were recorded. The arc length and curvature radius of average trajectories for each point were calculated and compared between the normal joints and TJRs, especially P-10 which is the corresponding point of the prosthesis apex without lateral pterygoid muscle (LPM) attachment at the normal joint with LPM attachment. The location of the point with the most similar trajectory was identified in the normal joints and compared with the condylar prosthesis. A total of 9 volunteers with 18 normal TMJs, and 5 patients with 6 prostheses were included in this study. For normal TMJs, the average condylar trajectories during mouth opening were a concave upward curve. Meanwhile, the trajectories of contralateral normal joints in patients with unilateral TJR and all condylar prostheses were significantly decreased. The arc length and curvature radius of average trajectories gradually decreased from P0. In the normal joints, P-20 had the most similar trajectories with the average arc lengths and a curvature radius of 13.0/4.2 mm. In P-10, the average arc lengths and curvature radius of the normal cases, natural TMJ of the unilateral replacement patients, prosthetic TMJ of the unilateral replacement patients, and prosthetic TMJ of the bilateral replacement patient, were 15.6/6.6 mm, 13.1/4.9 mm, 4.7/4.4 mm, and 6.4/5.8 mm, respectively. P-20 in the normal joint exhibited the most similar trajectory among individuals. The trajectory difference between the prosthesis apex without LPM attachment and the corresponding point at the normal joint with LPM attachment provides a reference for fossa prosthesis functional surface design.

Special Issue “Recent Developments on Functional Coatings for Industrial Applications, Volume II”

“Recent Developments on Functional Coatings for Industrial Applications, Volume II” addresses the provision of further insights into new and emerging research assets concerning the design, manufacturing, characterization and optimization of functional coatings for industrial applications. The aim of this Issue is to further contribute to the improvement of knowledge on functional coatings synthesis, characterization and tailoring, emphasizing its emerging industrial applicability in several industrial fields. The multidisciplinary nature of the theme represents a further stimulus aimed at enhancing the applicative importance and the technological versatility of the engineering design of functional surfaces. A multidisciplinary approach will act as a further stimulus in encouraging researchers to exploit suitably the applicative relevance and adaptability of functional coating and surface engineering design and tailoring.

Droplet impact on sparse hydrophobic pillar surface: Impact phenomena, spreading mode, and droplet breakup

Functional surfaces with controllable droplet spreading and breakup dynamics have received widespread attention in self-cleaning, spraying cooling, 3D printing, etc. The arrangement of a microstructure is of great value for the design of functional surfaces. Here, we numerically investigated the droplet impact dynamics on the sparse hydrophobic pillar surface with OpenFOAM. We investigated the effect of Weber number, impact locations, and pillar spacing. Outcomes are most strongly influenced by impact locations, pillar pitch, Weber number, and eight spreading patterns were registered, including circle, square, cross-shaped, Chinese knot, octopus, ellipse, dumbbell, and hexagram. Furthermore, a set of theoretical models were developed for the spreading pattern transition to predict the critical Weber number for different droplet spreading patterns. The breakup dynamics of droplets strongly depend on the spreading patterns and the impact location, which can emit secondary droplets in specific directions. The cross pattern significantly reduces the threshold for secondary droplet generation. The results obtained some essential characteristics for droplet impinging sparse hydrophobic pillar surface, which could provide valuable insights into functional surface design, fluidic-based systems and applications.

Numerical study on effects of large curved superhydrophobic surfaces on droplet post-impact dynamics

Droplet impact on curved solid surfaces is a widely observed phenomenon. Curved surfaces with large object-to-droplet ratios, termed size factor, are expected to impose influence on the droplet post-impact dynamics. In this work, droplet impact on curved surfaces with a range of size factors is simulated. The simulation results show that both the size factor and initial impact velocity can significantly affect the post-impact dynamics of the droplet. Three post-impact dynamics states, stick state, bounce state, and shatter state are identified and found to highly depend on the size factor and impact velocity. Besides, the spreading dynamics, contact time for bouncing droplets, and the detachment velocity also depend on the size factor and initial impact velocity to some degree. Splashing of droplet at higher impact velocity is also discussed. The current study could inspire the design of functional surfaces with water-resistant and anti-icing properties in relevant applications.

Rapid Forming of Nanowire Array on Polyvinylidene Fluoride Polymer Surfaces at Room Temperature by Ultrasonic Loading

Forming nanostructures on a substrate have been an effective approach to regulating surface properties without changing material chemical compositions. However, such nano‐forming processes are generally based on thermal plastic forming that needs to heat substrate material to its melting point, which is time‐consuming and induces a risk of oxidation, aging, or phase transition, especially when the material is a polymer. This research work develops a novel method to rapidly form nanowire arrays on polyvinylidene fluoride (PVDF) polymer at room temperature. Assisted by ultrasonic vibration, nanowires with a diameter of 200 nm are formed on PVDF surface within 0.7 s, while the highest forming temperature is 124 °C only, which is much lower than the melting point. In addition, the original β phase of PVDF can be retained after nano‐forming by adjusting ultrasonic loading time. The agglomeration mechanism of the formed nanowires on the surface was also proposed based on the transverse flow and residual stress release during ultrasonic forming process. The water contact angle measurement showed that nanowire arrays altered the surface wettability of PVDF from hydrophilic to hydrophobic. This ultrasonic‐assisted processing provides a new approach for functional surface design of PVDF and rapid nanostructure forming for various applications.

Competition between Mullins and curvature effects in the wrinkling of stretched soft shells

A highly stretched hyperelastic shell exhibits a coupling behavior of local wrinkling and global bending within the stability boundary, and curvature resists and can even suppress surface wrinkles beyond a critical threshold. Here, we report a novel phenomenon that smooth surface maintains upon stretching a soft shell, while wrinkles emerge upon unloading, which implies a nonlinear interplay between curvature and Mullins (stress softening and residual strain) effects in the entire loading–unloading cycle. To quantitatively account for such material damage (Mullins effect) and explore the underlying mechanism, we develop a finite-strain pseudo-elastic shell model that can predict the entire post-buckling morphology evolution. Results reveal three representative scenarios of morphology evolution of stretched soft shells. For shells within a certain range of aspect ratios and curvatures, no wrinkle appears upon loading while wrinkling occurs during the unloading process. For shells with smaller curvature, wrinkles exist during loading and unloading, while the shells with larger curvature remain constantly smooth in the loading–unloading process. The Mullins effect advances wrinkle formation, while curvature resists instability occurrence. Understanding such coupling effects between material and curvature on morphological evolution is critical for wrinkle-tunable design of functional surfaces.

Mechanistic understanding of the discrete morphology formed by multi-cycle assembly of tannic acid with Poloxamer 188 on silicon using QMC-D

Formation of discrete microdome-shaped features on planar silicon surfaces through multi-cycles of alternate adsorption of tannic acid (TA) and Poloxamer 188 of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (P188) has been reported recently. To further our understanding of the underlying fundamentals, we turned to quartz crystal microbalance with dissipation (QCM-D) for non-invasive monitoring of the process using SiO 2 -coated quartz crystals. Different concentrations of TA and P188 solutions were used for the step-by-step assembly, and the corresponding QCM-D responses were investigated. Additional TA-P188 assemblies were prepared on silicon substrates using the same concentration settings and subjected to surface morphology characterizations before and after drying. The results showed that increasing the concentration of P188 causes increased restructuring of the constructs during the assembling process, and leads to the formation of well-hydrated but less spherically shaped morphology with more continuity in coverage. In contrast, increasing TA concentration helps the assembled discrete features grow in size without inducing drastic change in morphology, and the large dissipation shift recorded is most likely related to water trapped in between the features. Furthermore, the study revealed that, besides the amphiphilic nature of P188 and the right solution concentration of TA, the surface of the underlying silicon substrate being hydrophilic is also instrumental in achieving discrete features of TA-P188 assembly. Collectively, findings reported herein allow for further tailored design of functional surfaces using TA and P188 as building blocks.

How to Achieve a Monostable Cassie State on a Micropillar-Arrayed Superhydrophobic Surface.

Superhydrophobic surfaces with a monostable Cassie state possess numerous interesting applications in many fields, such as microfluidics, oil-water separation, drag reduction, self-cleaning, heat dissipation, and so on. How to guarantee a monostable Cassie state of a superhydrophobic surface is still an interesting problem. In this paper, considering the influence of external interferences that may induce the possible wettability transition, the whole wetting process of a droplet on a trapezoidal micropillar-arrayed superhydrophobic surface is divided into six possible stages. Both the Gibbs-free energy in each stage and the energy barrier between adjacent stages are obtained and analyzed theoretically. It is interesting to find that the finally stable wettability of a trapezoidal micropillar-arrayed superhydrophobic surface significantly depends on the apparent contact angle of the lateral surface of a single micropillar, which can be divided into three regions from 0 to 180°, corresponding to the Wenzel state, metastable Cassie state, and monostable Cassie state. Furthermore, the size of each region is explicitly related to and can be well-tuned by the geometry of microstructures. Such a wettability classification is well verified by a number of existing experimental results and our numerical simulations. As a relatively general case, such a trapezoidal micropillar-arrayed superhydrophobic surface can also be conveniently degenerated to the triangular or rectangular micropillar-arrayed surface. All the results should be useful for the precise design of functional surfaces of different wettabilities.

Wetting‐Empowered Surface Functions for Engineering Applications

One of the main characteristics of a surface is its ability to be wetted by a liquid. Surfaces can be explicitly designed for full or poor wetting by different liquid types or for the easy sliding or sticking of droplets. The design of functional surfaces crosses multiple length-scales and includes surface chemical functionalization, micro/nano-engineered surface structures, chemical/physical gradients, elasticity, etc. These design features form the basis for even more complex functionalities. Recent approaches have involved increasingly complex surface architectures and techniques such as controlling droplet shape/motion on slippery liquid-infused porous surfaces (SLIPS), and reducing lateral adhesion by employing the Leidenfrost phenomenon (article number 202001249). The importance of this research is underpinned by its role in resolving global challenges, such as environmental crises, sustainable energy, food and water production and consumption. Established in 2013, the Smart Materials and Surfaces Laboratory (SMSL) in Northumbria University has achieved considerable progresses in the areas of bio-inspired surface/interface science, smart materials, microdevices and systems, leading to a well-recognized profile in scientific significance and academic impact worldwide. The origin of this special issue is based on discussions among Prof. Butt, Prof. Xu, Dr. Li, and Dr. Smith, starting at the Droplets 2019 conference, which was co-organised by the SMSL. At last, we hope this collection of papers provides an interesting benchmark for wetting-empowered technological developments toward the discovery of frontier engineering applications. We appreciate the support from the whole editorial team of Advanced Materials Interfaces and the reviewers. We would like to gratefully acknowledge the contributions from all authors and their co-authors to this special issue, at this unprecedent time. Ben B. Xu is a Professor of Materials and Mechanics and Director of Research and Knowledge Exchange in the Department of Mechanical and Construction Engineering at Northumbria University, UK. Ben obtained his Ph.D. in Mechanical Engineering (2011) at Heriot-Watt University in Edinburgh, then moved to the University of Massachusetts, Amherst (US), to work (2011–2013) with Prof. Ryan C. Hayward as a postdoc. Since joining Northumbria in 2013, Ben has established a multidisciplinary research profile with diverse interests in responsive materials/surface, soft matter, materials chemistry, mechanics, energy materials and technology, and micro-engineering. Yifan Li was appointed as a Senior Lecturer in the Department of Mechanical and Construction Engineering at Northumbria University (UK) in 2014, having been a Research Fellow at the School of Engineering, University of Edinburgh (UK) where he also gained Ph.D. degree in 2008. He studied Engineering with a B.Eng. degree obtained from the School of Electronics and Electrical Engineering at Shanghai Jiao Tong University, Shanghai, China in 2003. Yifan's research interests are droplet microfluidics, microsystems, flexible electronics and transducers. Hans-Jürgen Butt is a director at the Max Planck Institute for Polymer Research (MPIP), Mainz, Germany. He studied physics in Hamburg and Göttingen. He defended his Ph.D. thesis in 1989 at the Max Planck Institute for Biophysics (MPIBP). After one-year postdoc experience at the University of California, he moved back to MPIBP and habilitated in 1995. In 1996, he became an associate professor at the Johannes Gutenberg-University in Mainz. In 2000, he became a full professor at the University of Siegen for Physical Chemistry. In 2002, he joined MPIP as a director working on soft matter interfaces.

Composition-driven transition from amorphous to crystalline films enables bottom-up design of functional surfaces

Composition-driven transition to the crystalline state is characteristic of amorphous metal alloys and is widely observed in thin film. However, the transition zone (compositional range between single-phase amorphous and crystalline films) remains unexplored. Here, we demonstrate that this transition offers an excellent scenario for the fabrication of hybrid crystalline-amorphous architectures. The peculiar morphology of these nano(micro)-structured films provides a simple bottom-up route, applicable to a broad range of alloys, for obtaining adjustable multifunctional surfaces. In particular, we prove the feasibility of this approach as a one-step process for a precise control of specular and diffuse reflectance over the visible spectrum. Further, the growth kinetics of the formed two-phase nanostructures is demonstrated equivalent to a 2-dimensional amorphous-to-crystalline phase transformation. Using Zr-W alloys as a model system, fundamental parameters of the growth process and the corresponding metastable thickness-composition phase diagram are extracted. It evidences that the two-phase nanostructures, despite occurring in a wide range of compositions, can be easily hidden experimentally by growth kinetics and nucleation delay. These results open a new avenue on the surface morphology and related functional properties control in thin films.

Droplet Growth Model for Dropwise Condensation on Concave Hydrophobic Surfaces.

In this paper, mathematical models for predicting the droplet growth and droplet distribution of dropwise condensation on hydrophobic concave surface are developed and a theoretical analysis of the results of the model simulation is made. Under the assumptions of the Cassie–Baxter wetting mode and the consideration of noncondensable gases, the droplet growth model is not only established by heat transfer through a single droplet but also considered the thermal conductive resistance of the surface promoting layer. In addition, a droplet distribution model has been built based on the population balance theory. According to the calculation, the main thermal resistance in the droplet growth process is the conductive resistance inside the droplet. With the increase of contact angle, the above-mentioned thermal resistance increases; thus, the higher the hydrophobicity is, the slower the droplet growth and the less the droplet density are. Besides, the lower the temperature of the condensing surface is, the faster the droplets grow and the less the droplet density is. The models provide a mathematical tool for predicting the droplet radius at the initial stage of dewing on the concave surface and contribute to the design of functional surfaces in the field of water harvesting.

Directional Sliding Behavior of a Water Droplet on a Wedge-Shape Patterned Functional Surface.

Wedge-shape patterned functional surfaces have attracted considerable interests, due to the application of directional water droplet transport. It has been found that the directional sliding or rolling of water droplets rather than water film spreading on a functional surface is more popular in many applications due to its efficiency. In order to realize the directional sliding of water droplets, a patterned functional surface is well fabricated in the present study, which consists of a hydrophobic wedge-shaped region and a superhydrophobic region. The directional sliding behavior and its influencing factors of water droplet transport on the functional surface are studied experimentally and theoretically. It is found that the three-phase contact line of the water droplet presents three different shapes in the whole sliding process, which are mainly affected by the instant contact angle at the front and rear edges of the water droplet. The sliding velocity of the water droplet is significantly affected by the wedge angle, while the maximum transport displacement depends not only on the wedge angle but also on the static contact angle of the wedge-shape patterned surface and the volume of the water droplet itself. Further comparison shows that the transport displacement of a sliding water droplet is much larger than that of a spreading one. The results should be helpful for the design of functional surfaces with highly efficient water droplet transport, which are needed in the fields of heat transfer, water collection, and drug delivery.

Droplet Self‐Propelling Control on Bioinspired Fiber in Low Temperature and High Humidity Environment

AbstractIn low temperature and high humidity environment, the self‐propelling of droplet on normal wettable gradient surface is often out of control. Here, inspired by surface features of wetted spider silk and cactus, a kind of multilevel‐structure bioinspired fiber (BSF) with multigradients is fabricated via a novel gas‐bubble template‐assisted electrodeposition. The multilevel structures are used to control the state of the condensed droplets and make multigradients still work in low temperature and high humidity environment, while the multigradients provide multiple driving forces to overcome resistance. More importantly, one of driving forces, i.e., the coalescence driving force, can be controlled via the temperature. Therefore, the BSF can not only realize the desired self‐propelling of deposited droplet in low temperature and high humidity environment similar to wetted spider silk and cactus, but also present the controllability of movement. The results may assist in the design of functional surfaces required for cold environment or high humidity, e.g., low temperature microreactors, chemical analytics under specific conditions, and sensors.

Spatial Surface Charge Engineering for Electrochemical Electrodes

We introduce a novel concept for the design of functional surfaces of materials: Spatial surface charge engineering. We exploit the concept for an all-solid-state, epitaxial InN/InGaN-on-Si reference electrode to replace the inconvenient liquid-filled reference electrodes, such as Ag/AgCl. Reference electrodes are universal components of electrochemical sensors, ubiquitous in electrochemistry to set a constant potential. For subtle interrelation of structure design, surface morphology and the unique surface charge properties of InGaN, the reference electrode has less than 10 mV/decade sensitivity over a wide concentration range, evaluated for KCl aqueous solutions and less than 2 mV/hour long-time drift over 12 hours. Key is a nanoscale charge balanced surface for the right InGaN composition, InN amount and InGaN surface morphology, depending on growth conditions and layer thickness, which is underpinned by the surface potential measured by Kelvin probe force microscopy. When paired with the InN/InGaN quantum dot sensing electrode with super-Nernstian sensitivity, where only structure design and surface morphology are changed, this completes an all-InGaN-based electrochemical sensor with unprecedented performance.

Directional Transport Behavior of Droplets on Wedge-Shaped Functional Surfaces

Functional surfaces attract considerable research interest because of many practical applications. A wedge-shaped functional surface is a typical example, which can be designed to achieve self-cleaning, water collection, heat dissipation, or separation of mixed droplets, depending on the wettability of wedge-shaped areas inset in a hydrophobic substrate surface. In this work, a simple technology is proposed to achieve a wedge-shaped functional surface, which could realize directional transport of droplets. It is found that the transport behavior of droplets depends significantly on the wedge angle, the static contact angle of the wedge-shaped hydrophilic region, and the droplet volume. An approximate theoretical model is established, which can predict the most important parameter, that is, the transport displacement. The theoretical prediction can be verified experimentally. Furthermore, an interesting phenomenon of multistep acceleration is also observed in the transport process. With the aid of the present simple technology, several functional surfaces for the directional transport of droplets can be well-designed, including root-like patterned surfaces and nonlinear spiral- or curve-patterned surfaces. All the results should be helpful for the flexible design of functional surfaces for droplet transport in microfluidics or lab-on-a-chip applications.

Material Characterization, Thermal Analysis, and Mechanical Performance of a Laser-Polished Ti Alloy Prepared by Selective Laser Melting

The laser polishing technique offers an adaptable, accurate, and environmentally friendly solution to enhance the surface quality of additive manufactured metallic components. Recent work has shown that the surface roughness of laser additive manufactured metallic alloys can be significantly reduced via the laser polishing method. This paper examines the mechanical performances of a laser polished surface fabricated by selective laser melting (SLM). Compared with the original SLM surface, systematic measurements revealed that the surface roughness of the laser polished surface can be effectively reduced from 6.53 μm to 0.32 μm, while the microhardness and wear resistance increased by 25% and 39%, respectively. Through a thermal history analysis of the laser polishing process using the finite element model, new martensitic phase formation in the laser polished layer is carefully explained, which reveals significant effects on residual stress, strength, and fatigue. These findings establish foundational data to predict the mechanical performance of laser polished metallic components fabricated by additive manufacturing methods, and pave the way for functional surface design with practical application via the laser process.

Triple-Bioinspired Burying/Crosslinking Interfacial Coassembly Strategy for Layer-by-Layer Construction of Robust Functional Bioceramic Self-Coatings for Osteointegration Applications.

Coating bioceramics of inherent bioactivity onto biometallic implants is a straightforward yet promising solution to address poor osteointegration of the latter. One step further, it would be a nontrivial accomplishment to develop a mild, cheap, and universal route to firmly stabilizing, in principle, any ceramics onto any implant substrate, while imparting expectedly versatile biofunctional performances. Herein, we describe a triple-bioinspired burying/cross-linking interfacial coassembly strategy for enabling such ceramic coatings, which ingeniously fuses bioinspiration from sea rocks (burying assisted particle immobilization), marine mussels (universal adhesion and versatile chemical reactivity), and reef-building oysters (cross-linking rendered cohesion). Specifically, surface functionalized, aqueous dispersed ceramic particles were buried within an substrate-anchored organic matrix of polyelectrolyte multilayers (i.e., (poly(ether imide) (PEI)/poly(sodium-p-styrenesulfonate) (PSS)) n), through a new inorganic-organic hybrid layer-by-layer (LBL) coassembly scheme wherein mussel (oyster) inspired adhesive (cohesive) chemistries were exquisitely orchestrated. As a conceptual demonstration, bioactive baghdadite (Ca3ZrSi2O9) was synthesized as model ceramics, with which we constructed on medical titanium robust, biomimetic, and cross-linkable LBL self-assemblies harnessing the said strategy. Intimate substrate contacts and well-defined buried inorganic-organic interfaces were evidently seen, together with good structural and chemical stabilities, especially after cross-linking. Sustained bioactive ion releasing and appreciable biomineralization activity were confirmed in vitro. Subsequently, biological performances of the assemblies were systematically investigated with respect to surface hydrophilicity, protein adsorption, and osteoblast functions. Additionally, nanosilver deposition, which imparted the surfaces with added antibacterial potencies, was used to exemplify the strategy's versatility in allowing multifunctionality. What's more, the flexibility of our approach was testified through modifying clinically relevant complicated 3D porous scaffolds. Overall, our strategy basically met the design expectations, boding well for future medical adoption. This study offers the promise of an alternative broadly useful avenue to bioactive and functional surface design of bone implants. It may also provide insights into other multiple-bioinspired materials/interfaces for biological and other applications.

Moving Behavior of Nanodroplets on Wedge-Shaped Functional Surfaces

Surface functionalization has important application prospects in many aspects, for example, anti-drag, anti-pollution, anti-icing, self-cleaning, reversible adhesion, water collection, and so forth. Recently, a new technique of functional surface was proposed, in which a droplet can be activated to move from the narrow end of a wedge-shaped hydrophilic region imbedded in a hydrophobic surface to the wide end. Systematic molecular dynamics (MD) simulations and theoretical analysis are carried out in this paper in order to understand the motion mechanism, and more systematic designs for advanced functional surfaces are further proposed. It is found that the potential energy of the droplet decreases continuously as a function of distance when the droplet moves from the narrow end of the wedge-shaped track to the wide end and the corresponding potential energy achieves the minimum when the droplet completely enters the hydrophilic region. Effects of the wedge angle of hydrophilic area and the size of the droplet on the moving behavior are systematically investigated. It is interesting to find that both factors would show significant influence on the moving behavior of droplets, which is well consistent with the experimental observations. Theoretical analysis is further carried out, where driving force of droplet transport is well achieved. All the MD simulation results and experimental observations can be well explained by the nonlinearly changed driving force. Finally, several new designs of functional surfaces for controlling droplet transport, including droplet turning, pinning, accelerating, gathering, and moving path selection, are suggested, the feasibilities of which are further verified and discussed. The results in this paper would be helpful for the design of advanced functional surfaces to manipulate droplets in real applications.

Intelligent tribological surfaces: from concept to realization using additive manufacturing

In this paper, we provide a detailed account of our efforts in the design, development and prototyping of a novel intelligent surface by adapting initially curved diaphragms. Unlike the shortcomings that characterize current designs of functional surfaces, our adaptive surface design is characterised by simplicity, multifunctionality, adaptability, high flexibility and robustness as well as controlled autonomy. Four aspects of the work are accordingly examined. The first is concerned with the conceptual design of the new functional surface. The second with the development of functional prototypes of intelligent surfaces, showing its characteristics and ease of manufacturing using 3D additive manufacturing. The third with demonstrating the multi-frictional ability of the newly designed surface. Our friction test results show wide range friction control ability from the friction coefficient value 0.3 (same value of material itself) to 3 times higher value 1.1. Finally, we address the challenges that are faced in our new design and the efforts that are currently being adopted to overcome them.