Project description:Due to their unique functionality, superomniphobic surfaces that display extreme repellency toward virtually any liquid, have a wide range of potential applications. However, to date, the mechanical durability of superomniphobic surfaces remains a major obstacle that prevents their practical deployment. In this work, a two-layer design strategy was developed to fabricate superomniphobic surfaces with improved durability via synergistic effect of interconnected hierarchical porous texture and micro/nano-mechanical interlocking. The improved mechanical robustness of these surfaces was assessed through water shear test, ultrasonic washing test, blade scratching test, and Taber abrasion test.
Project description:Superomniphobic textures are at the frontier of surface design for vast arrays of applications. Despite recent substantial advances in fabrication methods for reentrant and doubly reentrant microstructures, design optimization remains a major challenge. We overcome this in two stages. First, we develop readily generalizable computational methods to systematically survey three key wetting properties: contact angle hysteresis, critical pressure, and minimum energy wetting barrier. For each, we uncover multiple competing mechanisms, leading to the development of quantitative models and correction of inaccurate assumptions in prevailing models. Second, we combine these analyses simultaneously, demonstrating the power of this strategy by optimizing structures that are designed to overcome challenges in two emerging applications: membrane distillation and digital microfluidics. As the wetting properties are antagonistically coupled, this multifaceted approach is essential for optimal design. When large surveys are impractical, we show that genetic algorithms enable efficient optimization, offering speedups of up to 10,000 times.
Project description:Natural and artificial super-repellent surfaces are frequently textured with pillar-based discrete structures rather than hole-based continuous ones because the former exhibits lower adhesion from the reduced length of the three-phase contact line. Counterintuitively, here, the unusual topographic effects are discovered on hot-water super-repellency where the continuous microcavity surface outperforms the discrete microneedle/micropillar surface. This anomaly arises from the different dependencies of liquid-repellency stability on the surface structure and water temperature in the two topographies. The unexpected wetting dynamics are interpreted by determining timescales for droplet evaporation, vapor condensation, and droplet bouncing. The associated heat transfer process is unique to the wetting states and remarkably distinct from each other in the two topographies. It is envisioned that hot-water super-repellent microcavity surfaces will be advantageous for a variety of applications, especially when both self-cleaning and thermal insulation are imperative, such as clothing for scald protection and digital microfluidics for exothermic reactions.
Project description:Bioinspired dry adhesives have an extraordinary impact in the field of robotic manipulation and locomotion. However, there is a considerable difference between artificial structures and biological ones regarding surface adaptability, especially for rough surfaces. This can be attributed to their distinct structural configuration and forming mechanism. Here, we propose a core–shell adhesive structure that is obtained through a growth strategy, i.e., an electrically responsive self-growing core–shell structure. This growth strategy results in a specific mushroom-shaped structure with a rigid core and a soft shell, which exhibits excellent adhesion on typical target surfaces with roughness ranging from the nanoscale to the microscale up to dozens of micrometers. The proposed adhesion strategy extends dry adhesives from smooth surfaces to rough ones, especially for rough surfaces with roughness up to dozens or hundreds of micrometers, opening an avenue for the development of dry adhesive-based devices and systems. The design of bioinspired dry adhesives mimicking closely the structure and surface adaptability of biological adhesives is challenging. Here, the authors propose an electrically responsive self-growing core–shell mushroom-shaped structure with a rigid core and a soft shell, which exhibits excellent adhesion on surfaces with roughness ranging from the nanoscale to the microscale.
Project description:When two liquid droplets coalesce on a superrepellent surface, the excess surface energy is partly converted to upward kinetic energy, and the coalesced droplet jumps away from the surface. However, the efficiency of this energy conversion is very low. In this work, we used a simple and passive technique consisting of superomniphobic surfaces with a macrotexture (comparable to the droplet size) to experimentally demonstrate coalescence-induced jumping with an energy conversion efficiency of 18.8% (i.e., about 570% increase compared to superomniphobic surfaces without a macrotexture). The higher energy conversion efficiency arises primarily from the effective redirection of in-plane velocity vectors to out-of-plane velocity vectors by the macrotexture. Using this higher energy conversion efficiency, we demonstrated coalescence-induced jumping of droplets with low surface tension (26.6 mN m-1) and very high viscosity (220 mPa·s). These results constitute the first-ever demonstration of coalescence-induced jumping of droplets at Ohnesorge number >1.
Project description:We developed a method to fabricate a superomniphobic gold electrode by synthesizing hierarchical gold clusters on a gold substrate and treating the surface with low surface energy materials. The reduction of gold ions was repeated several times, causing the gold microparticles to grow in random directions and form hierarchical gold clusters. Treatment of the gold structures with perfluorothiol resulted in a superhydrophobic surface that also exhibited superoleophobicity for oils and liquids with surface tensions as low as 25.6 mN. The resulting electrode was not contaminated by hydrophilic and hydrophobic liquids, and by analyzing the current-voltage characteristics of the electrode with a PEDOT:PSS solution droplet, the electrode was found to be waterproof.
Project description:Cross-scale self-similar hierarchical micro-nano structures in living systems often provide unique features on surfaces and serve as inspiration sources for artificial materials or devices. For instance, a highly self-similar structure often has a higher fractal dimension and, consequently, a larger active surface area; hence, it would have a super surface performance compared to its peer. However, artificial self-similar surfaces with hierarchical micro-nano structures and their application development have not yet received enough attention. Here, by introducing solvent-assisted UV-lasering, we establish an elegant approach to fabricate self-similar hierarchical micro-nano structures on silicon. The self-similar structure exhibits a super hydrophilicity, a high light absorbance (>90%) in an ultra-broad spectrum (200-2500 nm), and an extraordinarily high efficiency in heat transfer. Through further combinations with other techniques, such surfaces can be used for capillary assembling soft electronics, surface self-cleaning, and so on. Furthermore, such an approach can be transferred to other materials with minor modifications. For instance, by doping carbon in polymer matrix, a silicone surface with hierarchical micro-nano structures can be obtained. By selectively patterning such hierarchical structures, we obtained an ultra-high sensitivity bending sensor. We believe that such a fabrication technique of self-similar hierarchical micro-nano structures may encourage researchers to deeply explore the unique features of functional surfaces with such structures and to further discover their potentials in various applications in diverse directions.
Project description:Cell sheet-based scaffold-free technology holds promise for tissue engineering applications and has been extensively explored during the past decades. However, efficient harvest and handling of cell sheets remain challenging, including insufficient extracellular matrix content and poor mechanical strength. Mechanical loading has been widely used to enhance extracellular matrix production in a variety of cell types. However, currently, there are no effective ways to apply mechanical loading to cell sheets. In this study, we prepared thermo-responsive elastomer substrates by grafting poly(N-isopropyl acrylamide) (PNIPAAm) to poly(dimethylsiloxane) (PDMS) surfaces. The effect of PNIPAAm grafting yields on cell behaviours was investigated to optimize surfaces suitable for cell sheet culturing and harvesting. Subsequently, MC3T3-E1 cells were cultured on the PDMS-g-PNIPAAm substrates under mechanical stimulation by cyclically stretching the substrates. Upon maturation, the cell sheets were harvested by lowering the temperature. We found that the extracellular matrix content and thickness of cell sheet were markedly elevated upon appropriate mechanical conditioning. Reverse transcription quantitative polymerase chain reaction and Western blot analyses further confirmed that the expression of osteogenic-specific genes and major matrix components were up-regulated. After implantation into the critical-sized calvarial defects of mice, the mechanically conditioned cell sheets significantly promoted new bone formation. Findings from this study reveal that thermo-responsive elastomer, together with mechanical conditioning, can potentially be applied to prepare high-quality cell sheets for bone tissue engineering.
Project description:This study focuses on applying microbial self-healing cement in repairing cracks in cement-based materials and enhancing its resistance to water penetration performance. Traditional cement is susceptible to environmental influences, leading to the formation of microcracks and a reduction in durability. This research used Bacillus pseudofirmus to prepare microcapsules through sodium alginate gelation technology. We mixed microcapsules into the cement. The results indicate that the microbial self-healing cement, with a 1% self-healing agent added, increased its resistance to water penetration ability by 29.2% after 28 days. This improvement rose to 39.3% after 84 days. Additionally, we used the embedded needle method to make mortar blocks through microcracks, mimicking the cracks found in real cement. The self-healing effect of the microcapsules was especially noticeable for cracks under 0.3 mm in diameter, compared to the commonly used commercial crystallization penetration technology. This is attributed to the crystalline bodies formed by the self-healing agent in the microcapsules blocking the cracks and preventing water penetration. This study provides an environmentally friendly solution for the repair of cracks in cement-based materials using microbial self-healing technology and lays the foundation for improving the repair efficiency and durability and exploring stability and reliability in the future. Practical Application: This study investigated the application of microbial self-healing cement in repairing cracks in cement-based materials and enhancing its resistance to water penetration properties. Cement, a material widely used in infrastructure, has low tensile strength and often forms microcracks. These microcracks reducing the durability of cement and posing risks to the economy and safety. Adding 1% self-healing agent to microbial self-healing cement significantly increases the resistance to water penetration pressure of the mortar blocks. Compared to the standard specimens, the resistance to water penetration ability increased by 29.2% at 28 days and further increased to 39.3% at 84 days. Microbial self-healing cement could effectively restore the resistance to water penetration performance of the mortar blocks after repairing cracks. The repairing results are significantly better than the methods of mixing or applying cement crystalline materials.
Project description:A versatile method for the creation of multitier hierarchical structured surfaces is reported, which optimizes both antiviral and hydrophobic (easy-clean) properties. The methodology exploits the availability of surface-active chemical groups while also manipulating both the surface micro- and nanostructure to control the way the surface coating interacts with virus particles within a liquid droplet. This methodology has significant advantages over single-tier structured surfaces, including the ability to overcome the droplet-pinning effect and in delivering surfaces with high static contact angles (>130°) and good antiviral efficacy (log kill >2). In addition, the methodology highlights a valuable approach for the creation of mechanically robust, nanostructured surfaces which can be prepared by spray application using nonspecialized equipment.