In this paper, we present a convenient approach to prepare hierarchical structured superhydrophobic coatings with tunable adhesion force, composed of micro-size glass beads, nano-size SiO2 particles and epoxy resin. Surfaces of two types with different roughness were fabricated, one type is only with single-scale roughness demonstrating lotus effect with low sliding angle, the other type is hierarchically micro-nano-structured roughness exhibiting petal effect with high adhesion force. The surface roughness is pivotal for controlling the wetting behavior and regulating the contact angle including the contact angle hysteresis. Varying the density of micro-size glass beads could adjust the roughness of the surface, which means the adhesion force of the prepared surface could be easily controlled based on the proposed method. Through variation of glass beads’ amount, the surface could be designed to pin the water droplet with different adhesion force when the surface turned upside down. The surface wettability, surface morphology, adhesion force of the prepared samples are investigated and mechanism of the Cassie-to-Wenzel state transition are discussed in detail. Furthermore, the convenient method provides a possibility for controlling surface morphology, composition and corresponding surface adhesion which could be applied to various substrates such as tile, wood, steel and fabric. 相似文献
Cellulose fibers were surface modified with polypropylene–maleic anhydride copolymer. The physical properties of such fibers were characterized by contact angle measurements, and the chemical structure was identified with ESCA and FTIR. ESCA showed that the modifying agent was localized at the surface of the fibers. The modified fibers were compounded with polypropylene, and composites with various amount of fibers were manufactured by injection molding. All mechanical properties were improved when treated fibers were used. SEM showed improved dispersion, wetting of fibers, and adhesion. The nature of adhesion was studied using FTIR. It was found that the surface modifying agent is covalently bonded to the fibers through esterification. The degree of esterification is enhanced by activating the modifying agent before fiber treatment. This study has shown the effects of treatment conditions on activation of reactive species and chemical reaction between fiber and modifying agent. Moreover, a better understanding has been achieved of the nature of adhesion for the system. 相似文献
Inspired by liquid super-repellent skin of springtail, air pockets with tiny openings are fabricated on the surface of polydimethylsiloxane (PDMS) to achieve a stable existence of gas between liquid and micro-nanostructure. After further low-energy grafting, the PDMS with air pocket microstructures shows a well hydrophobic and oleophobic property. When the liquid droplet fell on the fabricated surface, the positive pressure generated by the air pocket promotes the wetting state to be much fitting with the Cassie–Baxter model. Based on the super-repellent microstructures, the flexible material shows properties of anti-icing and anti-fog. Additionally, the positive pressure of the air pocket to liquid droplet changed to be negative when stretching stress is applied to the PDMS elastomer. Based on the changed pressure, wetting state of the liquid droplet reversed from super-low adhesion to high adhesion. The stimulus-responsive material with reversible wettability has great potential in the applications of microfluidic chip and controlled releasing liquid micro-droplets. 相似文献
Collection of clean water from humid air has attracted immense attention in recent years due to the lack of access to pure drinking water among large section of population in several parts of the world. Hence, there is a persistent demand for the fabrication of robust, scalable membranes for efficient harvesting of pure water, especially in fog‐laden areas. Herein, three different membranes based on neat nanofibers, nanofibers with microparticles, and nanofibers with hierarchical structures (nanopillars) are successfully fabricated using poly(vinylidene fluoride‐co‐hexafluoropropylene) and fluorinated polyhedral oligomeric silsesquioxane composite mixture. Neat nanofibers and nanofibers with microparticles are fabricated by employing direct electrospinning and electrospinning combined with electrospraying process, respectively. Hierarchical structured fibers are fabricated by growing nanopillars on the surface of the fibers using electrospinning combined with template‐wetting method. The wettability properties including water contact angle and hysteresis of these membranes are investigated. Due to the increased surface roughness and low surface energy, the hierarchical fibers exhibit higher contact angle (153°) and lower hysteresis (3°) compared to the neat nanofibers and nanofibers with microparticles. Furthermore, the results demonstrate that the presence of nanopillars on the surface of the nanofibers improves the membrane's water collection efficiency when exposed to humid air.
Continuous anodic oxidation was employed to alter the surface chemical properties of carbon fibers. As expected, the wetting behavior by water improved and that of non-polar liquid diiodomethane deteriorated. The calculated surface tensions mirror the changes in the physicochemical surface properties. The zeta (ζ)-potential measurements performed also reflect changes in the surface chemistry of the investigated carbon fibers. A correlation between the measured ζ-potentials and the wetting behavior of water on anodically oxidized carbon fibers was found. The influence of anodic carbon fiber oxidation on the epoxy composite properties was studied by a modified axial tensile test, which allows additionally the measurement of the so-called 'notching force' as a measure of the interfacial composite properties. Common model-composite samples were used to check the reliability of this test. The determined 'notching force' as a measure of adhesion correlates with the increased polar component of the fiber surface tension. 相似文献
The tensile and dynamic mechanical properties of polystyrene and a poly(styrene-co-buty1 acrylate-co-cyclohexy1 methacrylate) statistical terpolymer (terpolymer) reinforced by randomly oriented, discontinuous ultra-high molecular weight polyethylene (UHMWPE) fibers are presented in terms of the fiber/matrix interfacial properties. Using a thermomechanical block model based on the parallel rule of mixtures, the adhesion characteristics of poly(butyl acrylate) (PBA) and poly(cyclohexyl methacrylate) (PCHM) grafted, plasma treated, and untreated fibers were determined. The model successfully predicts the tan δ response of the composites including peak height variations and the development of additional loss dispersions associated with the interphase. Moreover, the model yields a fiber reinforcement efficiency factor, K, which gives a quantitative measure of adhesion. The contact angle of PBA and PCHM grafted high density polyethylene (HDPE) films are also included and are compared to the contact angle of plasma treated fibers. The results indicate that PBA and PCHM grafts enhance adhesion through polymer graft/matrix interactions, not simply by improved wetting. 相似文献
Gel-spun ultra-high molecular weight polyethylene (UHMWPE) fibers have superior properties but their use in composite material applications is limited by their poor adhesion to polymer matrices. Previous studies have shown that etching improves the adhesion of epoxy to the fibers, but leads to a reduction in mechanical properties. The purpose of this research was to use uniaxially drawn gel-cast UHMWPE films as a model system since both films and fibers have a highly oriented fibrillar structural hierarchy. Etching has detrimental effects on the mechanical properties and crystallinity of these very thin films. The small amount of carbonyl and carboxyl groups added to the surface through etching raises the film's surface tension and enhances wetting by epoxy. Even though the unmodified film cannot be bonded with epoxy, the interlaminar shear strength between epoxy and the etched films approaches the cohesive strength of the epoxy. A combination of interfacial and UHMWPE cohesive failures is observed. The increase in adhesion is attributed to the slight increase in surface oxygen. 相似文献