Fabrication Of Hierarchical Structures Research Articles

Bio-inspired slippery surfaces with a hierarchical groove structure for efficient fog collection at low temperature

Many biological surfaces with hierarchical microstructures have been demonstrated to have the ability of fog collection. However, most of the current fog collection is achieved through a single structure, and the fabrication of hierarchical structures is mostly achieved through stepwise preparation. Besides, it is inevitable for the fog collector to work at low temperature environment. In this contribution, we fabricated a series of hierarchical slippery groove surfaces inspired by the surface structure of Sarracenia trichomes for efficient fog collection at low temperature, and the sample showed slippery properties after fluorination and oil injection treatments. Moreover, we evaluated the fog collection abilities of the surfaces for the condition of low temperature (0 °C). The results showed that the hierarchical groove surface showed better fog collection ability than the flat surface, and the oil film can hinder the heat transfer between droplet and surface, so as to prevent the droplets from freezing on the surface. So the injection of oil was essential for water transport and fog collection capabilities at low temperature. The proposed research is pioneering work in the area of functional surface towards the realization of fog collection at low temperature, one significant step towards fog collector to work under extreme condition.

Pattern formation in thin polymeric films via electrohydrodynamic patterning.

The free surface of a thin polymeric film is often unstable and deforms into various micro-/nano-patterns under an externally applied electric field. This paper reviews a recent patterning technique, electrohydrodynamic patterning (EHDP), a straightforward, cost-effective and contactless bottom-up method. The theoretical and numerical studies of EHDP are shown. How the characteristic wavelength and the characteristic time depend on both the external conditions (such as voltage, film thickness, template-substrate spacing) and the initial polymer properties (such as rheological property, electrical property and surface tension) is theoretically and experimentally discussed. Various possible strategies for fabricating high-aspect-ratio or hierarchical patterns are theoretically and experimentally reviewed. Aligning and ordering of the anisotropic polymers by EHDP is emphasized. A perspective, including novelty and limitations of the methods, particularly in comparison to some conventional patterning techniques, and a possible future direction of research, is presented.

Fabrication of hierarchical structures on titanium alloy surfaces by nanosecond laser for wettability modification

Titanium alloy is widely used in aerospace industry due to its low density, high specific strength and high-temperature resistance. To broaden its application scope, superhydrophobicity of titanium alloy is required in certain situations, such as self-cleaning and anti-icing. In this study, direct nanosecond laser ablation was applied to fabricate distinct pits with hierarchical structures on titanium alloy substrates, followed with chemical treatment to modify the wettability of the surfaces. The effects of laser processing parameters on surface morphology and surface wettability were explored systematically. Results show that, increasing the number of scans improves the depth of the pits and the accumulation of the micro-nano structures around the craters. The scanning space mainly affects the overlap of the heat affected zones, and hence the distribution of the laser-induced hierarchical structures. The wettability of a laser processed surface is determined by both surface roughness and surface chemistry, and the solid fraction of the rough surface is regulated by the number of scans as well as the scanning space. Moreover, superhydrophobic surfaces are obtained on the laser processed titanium alloy after chemical treatment, which has great potential for the as-mentioned applications.

Fabrication of hierarchical structures on concrete surfaces with superhydrophobicity using replicated micro-nano dendritic structures

Concrete with superhydrophobicity can protect it from being eroded by water and reduce accumulation of dust. Herein, a green and efficient method was proposed for fabricating hierarchical structures on concrete surfaces with superhydrophobicity by directly replicating micro-nano dendritic structures from superhydrophobic copper mesh to fresh concrete. Microstructures, chemical compositions and wettability of the as-fabricated concrete were characterized. Superhydrophobicity of the as-fabricated concrete was studied. Effect of water jet on the as-fabricated concrete was investigated. Wetting durability of the as-fabricated concrete were studied. Self-cleaning property was confirmed. It was found that owing to the successful replication of micro-nano dendritic structures and low surface energy stearic acid, the as-fabricated concrete displayed good superhydrophobicity, wetting durability and self-cleaning property.

Revealing inherent factors of SAPO-34 zeolites etching towards the fabrication of hierarchical structure

Fabrication of hierarchical SAPO-34 zeolites by chemical etching is a facile, economic and efficient route to address their intrinsic diffusion limitation. Various leaching strategies have been developed to prepare hierarchical SAPO-34 zeolites. However, the effect of inherent factors of SAPO-34 crystals on the etching, such as crystal size and Si content, have not been systematically investigated. In the present work, a series of SAPO-34 zeolites with different Si contents and crystal sizes are prepared and leached in the mother liquor. The crystal morphology, textural properties, framework environments, and acidity of the synthesized SAPO-34 samples are comprehensively characterized through transmission electron microscope (TEM), nitrogen adsorption-desorption, solid-state MAS NMR, and NH3-TPD measurements. The formation of hierarchical porosity by etching is dependent on the Si contents and particle sizes of SAPO-34 samples. After etching in the mother liquor, the nanosized SAPO-34 zeolites with low Si content exhibit remarkably prolonged lifetime and higher selectivity to ethylene and propylene than other counterparts in methanol-to-olefin reactions, owing to the more accessible sites and improved mass transport. This work will inspire the more suitable and efficient preparation of hierarchical SAPO-34 catalysts via etching route.

Fabrication of hierarchical structures on steel mesh with good superhydrophobicity and anti-corrosion property

Superhydrophobic surface is an effective strategy to prevent corrosion and pollution of stainless steel. Nevertheless, toxic modifying agents are often used to fabricate superhydrophobic surface on stainless steel, which is a great threat to the environment. Here, an environmental- friendly strategy was used for fabricating water-repellent stainless steel mesh with dendritic hierarchical structures through vacuum vapor deposition technology and replacement reaction. The fabricated superhydrophobic surface exhibited water bounce performance and repellency for liquids. Moreover, the good self-cleaning and anti-stain properties against contaminates and impurities were also displayed. In addition, the electrochemical experiments indicated the superhydrophobic surface obtained better anti-corrosive property compared with pristine stainless steel mesh. The whole preparation process is eco-friendly and easy to control. It is found that the superhydrophobicity can be acquired through heat treatment, without the need of fluorine-containing modified materials, which can prevent environmental pollution. It is expected that the superhydrophobic surface obtained by this method will have a potential application in anti-corrosion and anti-stain fields.

Single-step plasma-induced hierarchical structures for tunable water adhesion

Smart surfaces in nature have been extensively studied to identify their hierarchical structures in micro-/nanoscale to elucidate their superhydrophobicity with varying water adhesion. However, mimicking hybrid features in multiscale requires complex, multi-step processes. Here, we proposed a one-step process for the fabrication of hierarchical structures composed in micro-/nanoscales for superhydrophobic surfaces with tunable water adhesion. Hierarchical patterns were fabricated using a plasma-based selective etching process assisted by a dual scale etching mask. As the metallic mesh is placed above the substrate, it serves the role of dual scale etching masks on the substrate: microscale masks to form the micro-wall network and nanoscale masks to form high-aspect-ratio nanostructures. The micro-walls and nanostructures can be selectively hybridized by adjusting the gap distance between the mesh and the target surface: single nanostructures on a large area for a larger gap distance and hybrid/hierarchical structures with nanostructures nested on micro-walls for a shorter gap distance. The hierarchically nanostructured surface shows superhydrophobicity with low water adhesion, while the hybrid structured surface becomes become superhydrophobic with high adhesion. These water adhesion tunable surfaces were explored for water transport and evaporation. Additionally, we demonstrated a robust superhydrophobic surface with anti-reflectance over a large area.

Layer-by-Layer Assembly: Recent Progress from Layered Assemblies to Layered Nanoarchitectonics.

As an emerging concept for the development of new materials with nanoscale features, nanoarchitectonics has received significant recent attention. Among the various approaches that have been developed in this area, the fixed-direction construction of functional materials, such as layered fabrication, offers a helpful starting point to demonstrate the huge potential of nanoarchitectonics. In particular, the combination of nanoarchitectonics with layer-by-layer (LbL) assembly and a large degree of freedom in component availability and technical applicability would offer significant benefits to the fabrication of functional materials. In this Minireview, recent progress in LbL assembly is briefly summarized. After introducing the basics of LbL assembly, recent advances in LbL research are discussed, categorized according to physical, chemical, and biological innovations, along with the fabrication of hierarchical structures. Examples of LbL assemblies with graphene oxide are also described to demonstrate the broad applicability of LbL assembly, even with a fixed material.

Pharmaceutical Product Development Exploiting 3D Printing Technology: Conventional to Novel Drug Delivery System

3D printed pharmaceutical products are revolutionizing the pharmaceutical industry as a prospective mean to achieve a personalized method of treatments acquired to the specially designed need of each patient. It will depend upon age, weight, concomitants, pharmacogenetics and pharmacokinetic profile of the patient and thus transforming the current pharmaceutical market as a potential alternative to conventional medicine. 3D printing technology is getting more consideration in new medicine formulation development as a modern and better alternative to control many challenges associated with conventional medicinal products. There are many advantages of 3D printed medicines which create tremendous opportunities for improving the acceptance, accuracy and effectiveness of these medicines. In 2015, United State Food and Drug Administration has approved the first 3D printed tablet (Spritam®) and had shown the emerging importance of this technology. This review article summarizes as how in-depth knowledge of drugs and their manufacturing processes can assist to manage different strategies for various 3D printing methods. The principal goal of this review is to provide a brief introduction about the present techniques employed in tech -medicine evolution from conventional to a novel drug delivery system. It is evidenced that through its unparalleled advantages of high-throughput, versatility, automation, precise spatial control and fabrication of hierarchical structures, the implementation of 3D printing for the expansion and delivery of controlled drugs acts as a pivotal role. 3D printing technology has an extraordinary ability to provide elasticity in the manufacturing and designing of composite products that can be utilized in programmable and personalized medicine. Personalized medicine helps in improving drug safety and minimizes side effects such as toxicity to individual human being which is associated with unsuitable drug dose.

Hierarchical 3D VO2/ZnV2O4 microspheres as an excellent visible light photocatalyst for CO2 reduction to solar fuels

The photocatalytic reduction of CO2 has a great potential to produce fuels and chemicals, as well as, it reduces CO2 emission and addresses the environmental issues. To date single metal based catalysts still suffer from lower efficiency, uncontrollable selectivity and instability. In this study, hierarchical microspheres (HMs) of ZnV2O4 with VO2 impurity were synthesized through the single step reduction process, to explore highly efficient photocatalyst towards visible light responsive photocatalytic CO2 reduction. HMs of ZnV2O4 were successfully synthesized with mesoporous structure, higher surface area and functional under visible light irradiations. The highest yield of CO and CH3OH of 378 and 202 µmole g-cat−1 h−1 were obtained over ZnV2O4 synthesized after 24 h of reaction time, respectively. The performance of optimized 3D HMs of ZnV2O4 for CO and CH3OH production was 2.30 folds and 10.7 folds higher than using ZnO/V2O5 composite sample, respectively. Other products detected with appreciable amounts were CH4 and C2H6. This reveals, HMs structure of ZnV2O4 not only allows the transfer of electrons towards CO2, but also provides short pathways for electron transfer and empty space in the microspheres will serve as the reservoirs to store the electrons, hence leading to enhanced photoactivity. In addition, VO2 presents in the sample further contribute to enhance performance of ZnV2O4 HMs due to enabling efficient charge carrier separation. The prolong stability of ZnV2O4 in the CO2 reduction system confirmed that 3D HMs structure provides controllable selectivity and stability. This brings to conclusions that fabrication of hierarchical structures will stimulate further development towards high performance photo-catalysts for the photocatalytic CO2 reduction to solar hydrocarbon fuels.

Hierarchical Polymer Structures Using Templates and the Modified Breath Figure Method.

Hierarchical structures are commonly observed in nature and possess unique properties. The fabrication of hierarchical structures with well-controlled sizes in different length scales, however, is still a great challenge. To further understand the morphologies and properties of the hierarchical structures, here we present a novel strategy to prepare hierarchical polymer structures by combining the modified breath figure method and the template method. Poly(methyl methacrylate) (PMMA) honeycomb films with regular micropores are first prepared using the modified breath figure method by dipping PMMA films into mixtures of chloroform and methanol. The polymer chains on the honeycomb films are then annealed and wetted into the nanopores of anodic aluminum oxide templates via capillary forces, resulting in the formation of hierarchical polymer structures. The morphologies of the polymer structures, which can be controlled by the molecular weights of the polymers and the concentrations of the polymer solutions, are characterized by scanning electron microscopy. The surface wettabilities of the polymer structures are also examined by water contact angle measurements, and the hierarchical structures are observed to be more hydrophobic than the flat films and honeycomb films. This work not only provides a feasible approach to fabricate hierarchical polymer structures with controlled sizes but also gives a better understanding of the relationship between surface morphologies and properties.

The influence of contact material on lateral wet-etching of nickel thin films in lamellae structure

The characteristics of lateral Ni film etching by nitric-acid-based etchant are examined using samples with patterned lamellar layers consisting of SiO2/Ni/Al2O3/Ni/Al2O3 toward the fabrication of hierarchical structures. The lateral etching length increased with increasing etching time, despite the difficult penetration of the etchant through the nanoscale passages in the lamellar layers. However, a higher etching rate (2.1 nm s−1) was observed in the lower Ni film that is in contact with SiO2 and Al2O3 layers on the bottom and top, respectively, compared to that (1.6 nm s−1) of the upper Ni film that contacts with only Al2O3 on both bottom and top sides, due to stronger wetting of SiO2, inducing easier penetration of the etchant into the nanoscale passage between the surrounding layers. Moreover, the influence of Ni film thickness on the lateral etching characteristic was also investigated. The difference in the lateral etching length of the upper and lower Ni films decreases when the Ni film thickness is increased, because of the reduced proportion of the interface region with respect to the Ni-film volume. Despite different contact materials, similar lateral etching lengths were observed in the 150-nm-thick Ni films due to negligible effect of the contact materials in the lamellar structure.

Elaborately prepared hierarchical structure titanium dioxide for remarkable performance in lithium storage

Titanium dioxide (TiO2) has been considered to be a promisingly alternative anode material for lithium-ion batteries and thus attracted wide research interest. But, its practical application in lithium-ion batteries is seriously impeded by low capacity and poor rate capability. In the present work, the electrochemical performance of TiO2 is significantly improved by elaborately fabricating hierarchical structures. These as-prepared four hierarchical structure TiO2 assembled by different building blocks (TO2-2 h, TO2-6 h, TO2-18 h and TO2-24 h) all exhibit impressed performance. More importantly, the TO2-6 h constructed by curved nanosheets exhibits the best performance, delivering a capacity of 231.6 mAh g−1 at 0.2C after 200 cycles, and capacities of 187.1 and 129.3 mAh g−1 at 1 and 10C after even 1200 cycles, respectively. The results indicated that design and fabrication of hierarchical structure is an effective strategy for significantly improving the electrochemical performance of TiO2 electrodes, and the electrochemical performance of hierarchical structure TiO2 is heavily dependent on its building blocks. It is suggested that thus excellent electrochemical performance may make TiO2-6 h a promising anode material for advanced lithium-ion batteries with high capacity, good rate capability and long life.

Hierarchical ZnO Nanostructures with Blooming Flowers Driven by Screw Dislocations

Hierarchical ZnO nanostructures with a large yield were fabricated by a simple thermal evaporation method. For the first time, novel ZnO flowers were observed blooming at certain sites of a variety of spines, identified as Zn-terminated polar (0001) planes or tips. The spines for as-synthesized hierarchical structures can be nanowires, nanobelts, nanodendrites, nanobrushes, etc. This growth phenomenon determines the key role of polar sites in the fabrication of hierarchical structures. The spiral feature of ZnO flowers indicates an unusual screw dislocation driven growth mechanism, which is attributed to a high concentration of Zn vapor.

Fabrication of hierarchical structures with ZnO nanowires on micropillars by UV soft imprinting and hydrothermal growth for a controlled morphology and wettability

Hierarchical structures of ZnO nanowires (NWs) with different lengths on well-defined micropillars are fabricated by UV soft imprinting and hydrothermal growth. X-ray diffraction (XRD), scanning electron microscope (SEM) and X-ray photoelectron spectroscope (XPS) are employed to characterize the crystal structure, morphology and chemical composition of the hierarchical structures of ZnO nanowires on micropillars. By varying the growth time, ZnO NWs of different lengths and morphology were obtained, showing distinct wettability which can be further modified by surface coating with octadecyltrichlorosilane (OTS). Our results show that under optimal growth conditions, the water contact angle (CA) and contact angle hysteresis (CAH) of the fabricated hierarchical structures after OTS surface treatment can reach 159±1° and 6°, respectively.

Fabrication of Hierarchical Structures by Direct Laser Writing and Multi-Beam-Interference

We present a new method for the creation of hierarchical structures by two subsequent steps of laser ablation. To create certain functionalization of surfaces hierarchical structures are often required. These structures can be considered as a microstructure with a superposed nanostructure. Therefore the approach presented in this paper divides the patterning process into two parts: The microstructures are accomplished by direct laser writing with feature sizes down to a few microns whereas the nanostructure is subsequently added by Multi-beam-interference (MBI). Multi-beaminterference is a promising tool for the generation of nanostructures on 3D surfaces. Within this work the feasibility and limitations of this method are investigated.

Durable, superhydrophobic, superoleophobic and corrosion resistant coating on the stainless steel surface using a scalable method

In this study, superamphiphobic coating was produced using low surface energy materials and fabrication of hierarchical structures on stainless steel surface. Hierarchical structure was fabricated by silica multilayer coatings and adequate control of particles size in each layer. The surface energy was decreased by fluoropolymer compounds. The maximum static contact angle of DI water, ethylene glycol and fuel oil droplets on the prepared surface increased from 64° to 166°, from 33° to 157° and from 0° to 116°, respectively. Also, the minimum sliding angles of DI water, ethylene glycol and fuel oil droplets on the prepared surface were less than 2°, 5° and 12°, respectively. These results confirmed the superhydrophobicity and superoleophobicity of coated surfaces. These films maintained their superamphiphobicity after 16 days of immersion in water. In electrochemical corrosion evaluation, the highest protection efficiency of fabricated films reached as high as 97.33%. These satisfied results confirmed that this simple method can be used to fabricate large scale samples.

Fabrication of hierarchical structures by unconventional two-step imprinting

We present a simple sequential imprinting lithography method to fabricate micro/nanoscale hierarchical structures. This method involves hot embossing and capillary force lithography with two stamps of different microscales, which avoids using nanoscale stamps. By varying the experimental conditions in the capillary force lithography process, the morphology of the resulting structures can be controlled. This method may provide a facile and low-cost route for fabricating large area patterns of hierarchical structures.

Fabrication of hierarchical structures on alumina plate and its nonwetting property

We have fabricated a micro- and nano-hierarchical structure on an alumina plate by a simple hydrothermal method. Hexafluorophosphate octahedrons with nanoparticles on each of the eight plane surfaces were obtained. After self-assembling of a film of perfluorooctanoic acid, the Al plate with a high contact angle of 160 ± 2°, exhibited a nonwetting property.

Assembly of large-area, highly ordered, crack-free inverse opal films

Whereas considerable interest exists in self-assembly of well-ordered, porous "inverse opal" structures for optical, electronic, and (bio)chemical applications, uncontrolled defect formation has limited the scale-up and practicality of such approaches. Here we demonstrate a new method for assembling highly ordered, crack-free inverse opal films over a centimeter scale. Multilayered composite colloidal crystal films have been generated via evaporative deposition of polymeric colloidal spheres suspended within a hydrolyzed silicate sol-gel precursor solution. The coassembly of a sacrificial colloidal template with a matrix material avoids the need for liquid infiltration into the preassembled colloidal crystal and minimizes the associated cracking and inhomogeneities of the resulting inverse opal films. We discuss the underlying mechanisms that may account for the formation of large-area defect-free films, their unique preferential growth along the 110 direction and unusual fracture behavior. We demonstrate that this coassembly approach allows the fabrication of hierarchical structures not achievable by conventional methods, such as multilayered films and deposition onto patterned or curved surfaces. These robust SiO(2) inverse opals can be transformed into various materials that retain the morphology and order of the original films, as exemplified by the reactive conversion into Si or TiO(2) replicas. We show that colloidal coassembly is available for a range of organometallic sol-gel and polymer matrix precursors, and represents a simple, low-cost, scalable method for generating high-quality, chemically tailorable inverse opal films for a variety of applications.