Creation Of Superhydrophobic Surfaces Research Articles

Fabrication of robust superhydrophobic copper surface via highly efficient nanosecond laser-based surface functionalization

Creation of superhydrophobic surface via laser-based surface texturing has received considerable attention during the past decades. However, processing efficiency of the fabrication technique and robustness of the fabricated surface have been the major barriers that limit their wider applications. In this work, a laser-based surface functionalization technique was developed for fabrication of robust superhydrophobic surface with a highly efficient processing manner. Laser surface texturing was firstly employed to generate hierarchical surface structures, and silicone oil dripping and heat treatment were further utilized to modify the surface chemistry which ensures the realization of superhydrophobicity. The laser-based functionalized superhydrophobic surface also exhibits remarkable stability and durability subject to long-time storage in air and tape peeling test. More importantly, the developed technique only requires a total post-process treatment duration of ∼5–10 min, which takes significantly less time than the conventional chemical modification methods such as prolonged aging in air, deposition of chemical coating and low-temperature annealing. The high processing efficiency and surface robustness of the laser-based surface functionalization technique could potentially enable more practical applications in diverse areas.

Dynamic wetting characteristics of submicron‐structured injection molded parts

AbstractThe generation of submicron structures on plastic part surfaces can be used to modify their wetting properties allowing the creation of superhydrophobic surfaces. The modified wetting behavior can allow functionalities such as fluid collection or transport, which are critical for microfluidics. Consistent manufacturing is achieved through surface replication and process characterization. In this work, submicron structures were generated on steel mold inserts using ultrafast femtosecond laser and then replicated by micro injection molding on polypropylene and polylactic acid. Samples with Laser‐Induced Periodic Surface Structures (LIPSS) were fabricated using a femtosecond laser and characterized to investigate the effects of mold temperature, texture orientation, and material selection on the dynamic contact angle. The dynamic wetting functionality of the surfaces was investigated by analysis of the advancing and receding contact angles. The hysteresis obtained from the dynamic measurements provides information about the fluid/texture interaction dynamics. The experimental results show that the effects of mold temperature and drop orientation are only significant for the advancing contact angles. The large contact angle hysteresis suggests a parahydrophobic wetting behavior for the manufactured plastic parts.

Fabrication of superhydrophobic surfaces by laser surface texturing and autoxidation

The creation of superhydrophobic surfaces (SHS) has received exceptional thought from the entire research community due to its notable application in varied fields such as anti-icing, self-cleaning, drag reduction, anti-bacterial, and oil-water separation. The super­hy­drophobic (SH) conditions for a surface can be attained through the consolidation of a low surface energy surface with appropriate micro/nano-surface roughness through texturing. Motivated by the SH nature of lotus leaf and petal effect, microstructures have been prepared in this work on a metal surface by a fiber laser marking machine at 35 W. The textured surfaces with a different pitch to diameter (p/d) ratio (2.0-0.70) have been turned into hydrophobic and finally SH, after storing in an ambient environment for a few days due to oxide layer deposition on the textured surface. In this study, the maximum contact angle achieved by textured geometry after 30 days of auto-oxidation was 158.6 o. Further, test results showed that the fabricated surfaces have a high potential to maintain their SH nature even after the harsh condition of applications.

Superhydrophobicity of composite surfaces created from polymer blends

HypothesisWhen they are used alone, some polymers, such as polypropylene, Carnauba wax or polycarbonate allow the creation of superhydrophobic surfaces by spin coating or casting. On the other hand, some other polymers, such as polystyrene, polyvinylacetate or polychloroprene, are unable to render a superhydrophobic surface by these techniques. Using binary mixtures of these two types of polymers in a single common solvent, superhydrophobic composite surfaces can be created. We aim to show that superhydrophobicity is depending on the ratio between the two polymers in the initial blend and their intrinsic wettability. ExperimentsThe transition towards superhydrophobicity is studied on composite surfaces made of various polymers. Surfaces are created with simple coating methods, such as casting or spin-coating, of polymer solutions and letting the solvent evaporate at ambient conditions. FindingsTransitions are sharp and the amount of polypropylene in the blend to achieve superhydrophobicity decreases with the hydrophobicity of the second polymer. Topographic and wettability measurements are performed that show that both effects, topographical and chemical, interplay in the property of superhydrophobicity.

New Approach to Creating Superhydrophobic Surfaces

A new approach to the creation of superhydrophobic surfaces is proposed. The principle of the method is based on the phase separation in a composite, one of the components of which “pushes” another component onto the surface during melting, wherein the latter component remains in the solid state and has a particle shape that ensures the appropriate surface roughness. A composite of polytetrafluoroethylene (meltable component) with few-layer graphene nanoplatelets has been taken as an example.

Effect of Thiolated Ligands in Au Nanowire Synthesis.

Thiolated ligands are seldom used as morphology-directing reagent in the synthesis of Au nanostructures due to their low selectivity toward the different facets. Recently, we developed a thiolated ligands-induced synthesis of nanowires where the selective Au deposition only occurs at the ligand-deficient Au-substrate interface. Herein, the structural effect of thiolated ligands in this active surface growth is systematically investigated. It is revealed that their ability of rendering surface is closely related to the molecular structure. Ligands with aromatic backbones are capable of inducing nanowire formation, whereas those with aliphatic backbones cannot, likely because the former can pack better at short time scale of the rapid growth. The substituents of the ligands are critical for the colloidal stability of the final structure. It is further demonstrated that aromatic and aliphatic ligands could be mixed to turn on the continual lateral growth, leading to nanowires with tapered ends. The ligand generality in this growth mode also allows the creation of superhydrophobic surface, with the nanowire forest providing the nanoscale surface roughness and the hydrophobic ligand offering the surface property. These applications of the thiolated ligands in the nanosynthesis open a new approach for controlled synthesis of Au-based nanostructures with various morphologies and properties.

Fabrication of superhydrophobic, antibacterial, and ultraviolet-blocking cotton fabric

Inspired by the superhydrophobic behavior of lotus leaf, a simple coating method was developed which could facilitate bionic creation of superhydrophobic surfaces on cotton textiles with a new functional properties. Silver nanoparticles (AgNPs) with a high deposition density were formed on the surface of cotton fabric through an alkali pre-activation followed by in situ reduction of silver nitrate. The Ag-coated fabric was then reacted with octyltriethoxysilane (OTES) to form a low surface energy layer on the fiber surface. The fabrics were characterized by ultraviolet-visible reflectance spectrophotometry, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy, and X-ray diffractometry. Hydrophobicity properties were assessed by contact angle (CA) goniometry and shedding angle (SHA) technique. Antibacterial activity was measured against Staphylococcus aureus and Escherichia coli bacteria, and UV-blocking ability was measured using the AATCC method. SEM images showed the formation of AgNPs which were distributed uniformly on the fibers’ surface with a high coating density. Superhydrophobicity property of the treated fabric was confirmed with the CA of 156° and SHA of 8°. High antibacterial activity was observed without the reduction of inhibition size after coating with the OTES. The fabric also showed excellent UV-blocking with the ultraviolet protection factor of 266.01.

Micro/nanotextured polymer coatings fabricated by UV curing-induced phase separation: creation of superhydrophobic surfaces

Inspired by naturally occurring superhydrophobic surfaces, a number of approaches have been attempted to create specific surfaces having both micro- and nanoscale textures. To bring the artificial superhydrophobic surfaces closer to practical applications, a widely usable and simpler method that is systematically derived is required. Here, we describe a unique UV light-triggered micro/nanofabrication system for creating superhydrophobic surfaces, where the basic idea underlying this method comes from polymerization-induced phase separation (PIPS) phenomena. The operation consists of a three-step sequence and can be quickly performed within several minutes under an open-air condition: (1) coating of a precursor mixture for PIPS on a substrate, (2) UV curing to induce phase separation between the growing polymers and solvents, and (3) ethanol flushing to remove solvents to leave a specific texture at the surface. By selecting appropriate components of the PIPS mixture (cross-linkable monomers, solvents, and soluble polymer additives), phase separation rapidly and effectively occurred even in the film UV-polymerization format through the increasing thermodynamic instability; thereby specialized surfaces having micro- and nanoscale textures could be logically constructed. On the basis of the systematic investigation, this method was thus proved to be versatile and applicable for rational design of creating both transparent superhydrophobic films and water repellent fabric textiles.

One-step fabrication process of superhydrophobic green coatings

In general, creation of superhydrophobic surfaces is composed of two steps: (i) creation of a rough surface and (ii) passivation of the surface with the low surface energy molecules or coatings. Superhydrophobic properties cannot be achieved on a surface without these two essential factors fulfilled. In the present work we have demonstrated that superhydrophobic silver films on copper (Cu) substrates can be created in just a one-step process via galvanic reactions by immersing the Cu substrates in silver nitrate solution containing benzoic acid, simplifying the complexity of two different steps involved in the former method. Silver films were also fabricated using similar process without benzoic acid for comparative studies. The X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) confirmed the formation of benzoic acid incorporated silver films. Scanning electron microscopy (SEM) images showed micro-nano structured leaf-like and flower-like morphological features in the films prepared without and with benzoic acid, respectively. Benzoic acid incorporated flower-like silver films demonstrated water repellency as the water drops rolled off those surfaces whereas complete absorption of water drops were encountered on the leaf-like silver surfaces prepared without benzoic acid.