Recent Advances in TiO2 -Based Nanostructured Surfaces with Controllable Wettability and Adhesion

UV-Resistant and Thermally Stable Superhydrophobic CeO2 Nanotubes with High Water Adhesion

A novel type of sticky superhydrophobic cerium dioxide (CeO₂ ) nanotube material is prepared by hydrothermal treatment without any chemical modification. A water droplet on the material surface shows a static water contact angle of about 157° but the water droplet is pinned on the material surface even when the material surface is turned upside down. Interestingly, the as-prepared CeO₂ nanotube material displays durable superhydrophobicity and enhanced adhesion to water under ultraviolet (UV) light irradiation. Importantly, this change in water adhesion can be reversed by heat treatment to restore the original adhesive value of 20 µL. Further, the maximum volume of the water droplet adhered on the material surface of CeO₂ nanotubes can be regulated without loss of superhydrophobicity during the heating treatment/UV-irradiation cycling. Meanwhile, the superhydrophobic CeO₂ nanotube material shows remarkable thermal stability even at temperatures as high as 450 °C, long-term durability in chemical environment, and air-storage and good resistance to oily contaminant. Finally, the potential application in no-loss water transportation of this sticky superhydrophobic CeO₂ material is demonstrated.

Environmentally durable superhydrophobic surfaces with robust photocatalytic self-cleaning and self-healing properties prepared via versatile film deposition methods

Superhydrophobic (SH) surfaces with self-cleaning photocatalytic properties have become an important research focus in recent years. In this work, we fabricated multifunctional and environmentally durable SH surfaces via a facile one-step reaction of octadecyl isocyanate (ODI) with TiO₂ particles. The resulting films possess SH properties, facilitated by a combination of hydrophobic long alkyl chains and the hierarchical crystalline structure. Films can be prepared via spray or blade coating on a variety of hard and soft substrates, and function well when exposed to either air or oil. The coating retains its SH properties for at least 6 months in ambient conditions, and after organic pollution it can recover its SH properties using UV or sun light illumination. After water impalement, the SH properties can self-heal via the self-assembly of long alkyl chains to their original state within several hours at ambient conditions, or within minutes on a heating stage. The covalent bonds between alkyl chains and TiO₂, together with hydrogen bonds between adjacent alkyl chains, greatly increased the surface durability of the SH films. This multifunctional SH coating is a very promising material for commercial and industrial coating applications.

Tunable Microscale Porous Systems with Dynamic Liquid Interfaces

Solid microscale porous material systems have attracted more attention in recent years due to their various potential applications, such as energy source transportations, biomedical devices, wastewater treatments, phase separations, etc. However, such systems are still plagued with many issues including fouling, mechanical fragility, inability to self-heal, and low recyclability that restrict them for further industrial applications. Dynamic liquid-based microscale porous material systems, especially porous surfaces and membranes, provide a new opportunity for resolving these issues and possess many benefits, such as antifouling, slippery, transparent, recovery, self-healing, and recycling properties. This Concept is mainly concerned with how to obtain tunable microscale porous systems with dynamic liquid interfaces, and their applications from the surfaces to membranes. The authors hope this concept will attract interest of scientists in areas related to the rapid development and application of various liquid-based porous systems.

Rational design of materials interface at nanoscale towards intelligent oil-water separation

Oil-water separation is critical for the water treatment of oily wastewater or oil-spill accidents. The oil contamination in water not only induces severe water pollution but also threatens human beings' health and all living species in the ecological system. To address this challenge, different nanoscale fabrication methods have been applied for endowing biomimetic porous materials, which provide a promising solution for oily-water remediation. In this review, we present the state-of-the-art developments in the rational design of materials interface with special wettability for the intelligent separation of immiscible/emulsified oil-water mixtures. A mechanistic understanding of oil-water separation is firstly described, followed by a summary of separation solutions for traditional oil-water mixtures and special oil-water emulsions enabled by self-amplified wettability due to nanostructures. Guided by the basic theory, the rational design of interfaces of various porous materials at nanoscale with special wettability towards superhydrophobicity-superoleophilicity, superhydrophilicity-superoleophobicity, and superhydrophilicity-underwater superoleophobicity is discussed in detail. Although the above nanoscale fabrication strategies are able to address most of the current challenges, intelligent superwetting materials developed to meet special oil-water separation demands and to further promote the separation efficiency are also reviewed for various special application demands. Finally, challenges and future perspectives in the development of more efficient oil-water separation materials and devices by nanoscale control are provided. It is expected that the biomimetic porous materials with nanoscale interface engineering will overcome the current challenges of oil-water emulsion separation, realizing their practical applications in the near future with continuous efforts in this field.

Drop Capturing Based on Patterned Substrate in Space

In this work, we introduced a method for capturing aqueous drop based on a patterned substrate in space. Through the manipulation test of a colloidal drop, it could be verified that this patterned substrate had excellent control ability for aqueous drop in microgravity condition. The confinement mechanism of this substrate was clarified, which showed that drops with different volume could be pinned and attracted at a given area on the substrate. The confinement capability was related to the gravity effect, and the patterned substrate could confine aqueous drops with larger volume under microgravity than in normal gravity. With advantages of simple operation and strong capability to control large drops, this technique exhibited the wide application prospect in the fields of fluid management, biosensing, and pharmacy in microgravity condition in the future.

Janus Gradient Meshes for Continuous Separation and Collection of Flowing Oils under Water

Gradient meshes with Janus wettabilities are fabricated to stably separate and collect spilled oils from a range of flowing oily wastewater. Here, we demonstrate an overflow with separation methodology, which combines selective oil overflow and membrane separation, to separate low content oils from dynamic flowing oil-water mixtures by a curved gradient mesh that covered on a solid edge. The microscaled air-oil-water-solid four-phase wetting state during the oil-water separation process is visualized and demonstrated. The fundamental understanding of this overflow with separation system and the superior gradient mesh materials would enable us to construct a wide variety of separation devices out of traditional designs and advance related applications, such as wastewater treatment and fuel purification.

Under-Oil Switchable Superhydrophobicity to Superhydrophilicity Transition on TiO2 Nanotube Arrays

Recently, smart interfacial materials that can reversibly transit between the superhydrophobicity and superhydrophilicity have aroused much attention. However, all present performances happen in air, and to realize such a smart transition in complex environments, such as oil, is still a challenge. Herein, TiO₂ nanotube arrays with switchable transition between the superhydrophobicity and superhydrophilicity in oil are reported. The switching can be observed by alternation of UV irradiation and heating process, and the smart controllability can be ascribed to the cooperative effect between the surface nanostructures and the chemical composition variation. By using the controllable wetting performances, some applications such as under-oil droplet-based microreaction and water-removal from oil were demonstrated on our surface. This paper reports a surface with smart water wettability in oil, which could start some fresh ideas for wetting control on interfacial materials.

Single-Step Fabrication of High-Throughput Surface-Enhanced Raman Scattering Substrates

The combination of surface-enhanced Raman scattering (SERS) with high-throughput screening (HTS) has significant importance for highly sensitive and massive workload assays. Although fabrication of HTS-SERS substrates can be achieved by several methods, the high cost as well as large-equipment dependence limit their applications. Here, we report a simple method to fabricate HTS-SERS substrates within one-step process. The HTS-SERS substrate is fabricated by simply UV-irradiating a fluoroalkylsilane (FAS)-modified liquid-repellent TiO₂ surface in AgNO₃ solution through a photomask. Owing to the photocatalytic nature of TiO₂, the UV irradiation simultaneously triggers the degradation of the attached FAS and the generation of liquid-adhesive Ag nanoparticles (NPs) on exposed area. A HTS-SERS substrate could be directly obtained after UV irradiation. The deposited Ag NPs evidently enhance Raman signals, and the significant difference between the wettability of exposed area and masked area enables fast formation of high-throughput liquid droplet arrays through a simple dragging solution process. The fabrication method is applicable to various substrate materials, to introduce additional functionalities. The photocatalytic activity of TiO₂ also allows us to photobleach the residual analyte and Ag NPs after detection to recycle substrate. This single-step method is a highly promising candidate for the fabrication of HTS-SERS substrates.

Electrically bioactive coating on Ti with bi-layered SnO2–TiO2 hetero-structure for improving osteointegration

SnO₂–TiO₂ surface with the bi-layered structure on Ti provides internal electric stimulation to promote osteointegration of implant.

Superlyophilic Interfaces and Their Applications

Superlyophilic interfaces denote interfaces displaying strong affinity to diverse liquids, including superhydrophilic, superoleophilic, and superamphiphilic interfaces. When coming in contact with these interfaces, water or oil droplets tend to spread completely with contact angles close to 0°, presenting versatile applications including self-cleaning, antifogging, controllable liquid transport, liquid separation, and so forth. Inspired by nature, scientists have developed various kinds of artificial superlyophilic (SLPL) interfaces in the past decades. In terms of dimensional characteristics, the artificial SLPL interfaces can be divided into four categories: i) 0D particles, whose dispersibility or catalytic performance can be notably enhanced by superlyophilicity; ii) 1D micro-/nanofibers or nanotubes/channels, which can efficiently transfer liquids with SLPL interfaces; iii) 2D flat SLPL interfaces, on which different functional molecules can be deposited uniformly, forming ultrathin and smooth films; and iv) 3D structures, which can be obtained by either constructing 0D, 1D, or 2D SLPL materials separately or directly fabricating random SLPL frameworks, and can always be used as functional coatings or bulk materials. Here, natural and artificial SLPL interfaces are briefly introduced, followed by a short discussion of the limit between lyophilicity and lyophobicity, and then a snapshot of methods to generate SLPL interfaces is given. Specific focus is placed on recent achievements of constructing SLPL interfaces from zero to three dimensions. Following that, broad applications of SLPL interfaces in commercial areas will be introduced. Finally, a short summary and outlook for future challenges in this field is presented.

Bioinspired Surfaces with Superwettability for Anti-Icing and Ice-Phobic Application: Concept, Mechanism, and Design

Ice accumulation poses a series of severe issues in daily life. Inspired by the nature, superwettability surfaces have attracted great interests from fundamental research to anti-icing and ice-phobic applications. Here, recently published literature about the mechanism of ice prevention is reviewed, with a focus on the anti-icing and ice-phobic mechanisms, encompassing the behavior of condensate microdrops on the surface, wetting, ice nucleation, and freezing. Then, a detailed account of the innovative fabrication and fundamental research of anti-icing materials with special wettability is summarized with a focus on recent progresses including low-surface energy coatings and liquid-infused layered coatings. Finally, special attention is paid to a discussion about advantages and disadvantages of the technologies, as well as factors that affect the anti-icing and ice-phobic efficiency. Outlooks and the challenges for future development of the anti-icing and ice-phobic technology are presented and discussed.

Superhydrophobic and superoleophobic poly(3,4-ethylenedioxypyrrole) polymers synthesized using the Staudinger-Vilarrasa reaction

Vegetal and animal reigns offer many examples of surfaces with surprising and interesting wetting properties. As example, springtails present superoleophobic properties allowing to live in soil and Lotus leaves show self-cleaning ability even under rainfalls. Indeed, it is known that self-cleaning properties can help to remove dust and particles during rainfalls and as a consequence to clean the surface. The bioinspiration of these surface properties is of a real interest for industrial applications in the nanotechnology field such as photovoltaic systems or anti corrosive material. Here, we use a strategy based on electropolymerization to obtain these properties. The Staudinger-Vilarrasa reaction is used to prepare innovative 3,4-ethylenedioxypyrrole (EDOP) monomers with fluorinated chains. Using C6F13 or C8F17 chains, the polymer surfaces formed after electrodeposition show superhydrophobic and superoleophobic features. Here we study the surface wettability depending on the surface energy (based on the perfluorinated chain length), the surface roughness and morphology.

Ti-Based Biomedical Material Modified with TiOx/TiNx Duplex Bioactivity Film via Micro-Arc Oxidation and Nitrogen Ion Implantation

Titanium (Ti) and Ti-based alloy are widely used in the biomedical field owing to their excellent mechanical compatibility and biocompatibility. However, the bioinert bioactivity and biotribological properties of titanium limit its clinical application in implants. In order to improve the biocompatibility of titanium, we modified its surface with TiOx/TiNx duplex composite films using a new method via micro-arc oxidation (MAO) and nitrogen ion implantation (NII) treatment. The structural characterization results revealed that the modified film was constructed by nanoarrays composed of TiOx/TiNx composite nanostitches with a size of 20~40 nm. Meanwhile, comparing this with pure Ti, the friction property, wear resistance, and bioactivity were significantly improved based on biotribological results and in vitro bioactivity tests.

A Low-Cost, Formaldehyde-Free and High Flame Retardancy Wood Adhesive from Inorganic Adhesives: Properties and Performance

Wood composites used in indoor living environments often pose formaldehyde emission and fire hazard problems. In this study, magnesium oxychloride cement-based (MOC) inorganic adhesives are presented as an effective and sustainable binder for plywood applications. The phase composition, microstructure, and thermal stability of the adhesives prepared with different ratios of MgO/MgCl₂ were investigated. In addition, the dry and wet shear strength and the combustion behavior of the plywood were also examined. The results indicated that the limiting oxygen index (LOI) values of the plywood bonded by the MOC adhesives were higher than those of the plywood bonded by urea-formaldehyde resin. The active MgO/MgCl₂ molar ratio of 7 was the optimal ratio for the dry and wet shear strength of the plywood with values of 1.02 and 0.88 MPa, respectively, which meet the interior use panel (Type II plywood) requirements. These improvements were ascribed to the increasing ratio of MgO/MgCl₂ that facilitated the formation of an excellent microstructure. Meanwhile, the continuous hydration phase strengthened the interaction between the MOC adhesive and the wood. With these improved properties, MOC adhesive is expected to be widely used for industrial applications in plywood fabrication.

Bioinspired Mechano-Sensitive Macroporous Ceramic Sponge for Logical Drug and Cell Delivery

On-demand, ultrahigh precision delivery of molecules and cells assisted by scaffold is a pivotal theme in the field of controlled release, but it remains extremely challenging for ceramic-based macroporous scaffolds that are prevalently used in regenerative medicine. Sea sponges (Phylum Porifera), whose bodies possess hierarchical pores or channels and organic/inorganic composite structures, can delicately control water intake/circulation and therefore achieve high precision mass transportation of food, oxygen, and wastes. Inspired by leuconoid sponge, in this study, the authors design and fabricate a biomimetic macroporous ceramic composite sponge (CCS) for high precision logic delivery of molecules and cells regulated by mechanical stimulus. The CCS reveals unique on-demand AND logic release behaviors in response to dual-gates of moisture and pressure (or strain) and, more importantly, 1 cm3 volume of CCS achieves unprecedentedly delivery precision of ≈100 ng per cycle for hydrophobic or hydrophilic molecules and ≈1400 cells per cycle for fibroblasts, respectively.

Immobilization of Pt Nanoparticles via Rapid and Reusable Electropolymerization of Dopamine on TiO2 Nanotube Arrays for Reversible SERS Substrates and Nonenzymatic Glucose Sensors

Inspired by mussel-adhesion phenomena in nature, polydopamine (PDA) coatings are a promising route to multifunctional platforms for decorating various materials. The typical self-polymerization process of dopamine is time-consuming and the coatings of PDA are not reusable. Herein, a reusable and time-saving strategy for the electrochemical polymerization of dopamine (EPD) is reported. The PDA layer is deposited on vertically aligned TiO₂ nanotube arrays (NTAs). Owing to the abundant catechol and amine groups in the PDA layer, uniform Pt nanoparticles (NPs) are deposited onto the TiO₂ NTAs and can effectively prevent the recombination of electron-hole pairs generated from photo-electrocatalysis and transfer the captured electrons to participate in the photo-electrocatalytic reaction process. Compared with pristine TiO₂ NTAs, the as-prepared Pt@TiO₂ NTA composites exhibit surface-enhanced Raman scattering sensitivity for detecting rhodamine 6G and display excellent UV-assisted self-cleaning ability, and also show promise as a nonenzymatic glucose biosensor. Furthermore, the mussel-inspired electropolymerization strategy and the fast EPD-reduced nanoparticle decorating process presented herein can be readily extended to various functional substrates, such as conductive glass, metallic oxides, and semiconductors. It is the adaptation of the established PDA system for a selective, robust, and generalizable sensing system that is the emphasis of this work.

Smart design of wettability-patterned gradients on substrate-independent coated surfaces to control unidirectional spreading of droplets

Highly adherent wettability patterns on the substrate-independent superhydrophobic surfaces of trimethoxyoctadecylsilane modified titanium dioxide (TiO₂)-based coatings were prepared by using commercial photolithography. Three custom unidirectional channels with gradient wettability patterns were obtained by spatially selective wettability conversion from superhydrophobic to superhydrophilic when the coatings were exposed to ultraviolet light (∼365 nm). The movement behavior of droplets on these unidirectional channels was studied and the displacement of droplet movement was effectively controlled. Integrating the idea of gradient wettability patterns into planar microfluidic devices (microreactors), a self-driven fluid transport was achieved to realize droplet metering, merging or reaction, and rapid transport. This self-driven fluid transport with gradient wettability patterns has great potential in fabricating a new category of pump-free microfluidic systems that can be used in various conditions.

Stable Hydrophobic Metal-Oxide Photocatalysts via Grafting Polydimethylsiloxane Brush

Polydimethylsiloxane (PDMS) can be grafted to metal-oxide photocatalysts such as titanium oxide by simple UV irradiation in solution or melt. The PDMS graft metal oxides are still photocatalytically active. They are hydrophobic, liquid repellent, self-cleaning, prevent biofouling and are long-term stable even in UV light.

Recent advances in the study and design of parahydrophobic surfaces: From natural examples to synthetic approaches

Parahydrophobic surfaces are an interesting class of materials that combines both high contact angles and very strong adhesion with wetting fluids, most commonly water. This unique set of properties makes parahydrophobic surfaces attractive for a variety of applications, including water harvesting and collection, guided fluid transport, and membrane development, amongst many others. Taking inspiration from natural surfaces that display this same behavior such as rose petals and gecko feet, synthetic approaches aim to incorporate the nano- and micro-scale topography as well as the low surface energy chemistry found on these interfaces. Here, we discuss the chemical and physical factors that contribute to parahydrophobic behavior and provide a comprehensive overview on the current technologies and procedures used towards constructing surfaces that mimic this behavior already observed in nature. This includes etching processes, colloidal assemblies, deposition methods, and in situ growth of surface features. Furthermore, issues such as ease of scale-up, efficiency of technical procedures, and other current challenges associated with these methods will be discussed to provide insight as to the future directions for this growing area of research.

RMS roughness-independent tuning of surface wettability by tailoring silver nanoparticles with a fluorocarbon plasma polymer

A layer of 14 nm-sized Ag nanoparticles undergoes complex transformation when overcoated by thin films of a fluorocarbon plasma polymer. Two regimes of surface evolution are identified, both with invariable RMS roughness. In the early regime, the plasma polymer penetrates between and beneath the nanoparticles, raising them above the substrate and maintaining the multivalued character of the surface roughness. The growth (β) and the dynamic (1/z) exponents are close to zero and the interface bears the features of self-affinity. The presence of inter-particle voids leads to heterogeneous wetting with an apparent water contact angle θ_a = 135°. The multivalued nanotopography results in two possible positions for the water droplet meniscus, yet strong water adhesion indicates that the meniscus is located at the lower part of the spherical nanofeatures. In the late regime, the inter-particle voids become filled and the interface acquires a single valued character. The plasma polymer proceeds to grow on the thus-roughened surface whereas the nanoparticles keep emerging away from the substrate. The RMS roughness remains invariable and lateral correlations propagate with 1/z = 0.27. The surface features multiaffinity which is given by different evolution of length scales associated with the nanoparticles and with the plasma polymer. The wettability turns to the homogeneous wetting state.

Flexible method for fabricating protein patterns on superhydrophobic platforms controlled by magnetic field

A flexible, magnetic-field controlled patterning method of water soluble proteins or other functional materials has been developed based on superhydrophobic platforms.

PDMS/camphor soot composite coating: towards a self-healing and a self-cleaning superhydrophobic surface

A novel self-cleaning polymer composite with self-healing ability to self-repair after chemical and mechanical damage using readily available materials like polydimethylsiloxane (PDMS) and camphor soot particles is developed.

Bioinspired Special Wettability Surfaces: From Fundamental Research to Water Harvesting Applications

Nowadays, the pollution of water has become worse in many parts of the world, which causes a severe shortage of clean water and attracts widespread attention worldwide. Bioinspired from nature, i.e. spider silk, cactus, Namib desert beetle, Nepenthes alata, special wettability surfaces have attracted great interest from fundamental research to water-harvesting applications. Here, recently published literature about creatures possessing water-harvesting ability are reviewed, with a focus on the corresponding water-harvesting mechanisms of creatures in dry or arid regions, consisting of the theory of wetting and transporting. Then a detailed account of the innovative fabrication technologies and bionic water-harvesting materials with special wetting are summarized, i.e. bio-inspired artificial spider silk, bio-inspired artificial cactus-like structures, and bio-inspired artificial Namib desert beetle-like surfaces. Special attentions are paid to the discussion of the advantages and disadvantages of the technologies, as well as factors that affect the amount of water-harvesting. Finally, conclusions, future outlooks and the current challenges for future development of the water-harvesting technology are presented and discussed.

Bionic anti-adhesive electrode coupled with maize leaf microstructures and TiO2 coating

Designing and fabricating a type of effectively anti-adhesive electrode via coupling the bionic microstructures and TiO₂ coating.

Understanding the Role of Dynamic Wettability for Condensate Microdrop Self-Propelling Based on Designed Superhydrophobic TiO2 Nanostructures

The ability to release the adhered drops on superhydrophobic surfaces is very important for self-cleaning, antifrosting/icing, microfluidic device, and heat transfer applications. In this paper, three types of in situ electrochemical anodizing TiO₂ nanostructure films are rationally designed and fabricated on titanium substrates with special superwettability, viz., TiO₂ nanotube arrays, irregular TiO₂ nanotube arrays, and hierarchical TiO₂ particle arrays (HTPA), and their corresponding behavior in condensate microdrop self-propelling (CMDSP) is investigated. Compared to the flat titanium counterpart, all three types of rough TiO₂ samples demonstrate a uniform distribution of smaller microscale droplets. Among the treated surfaces, the HTPA possesses the highest condensate density, and more than 80% of the droplets possess a diameter below 10 μm. Theoretical analysis indicates that the feature is mainly due to the morphology and structure induced extremely low droplet adhesion on super-antiwetting TiO₂ hierarchical surfaces, where the excess surface energy released from the migration leads to the self-propelling of merged microdrop. This work offers a way to rationally construct CMDSP surfaces with excellent self-cleaning, antifrosting/icing ability, and enhanced condensation heat transfer efficiency.

One-dimensional TiO2 Nanotube Photocatalysts for Solar Water Splitting

Hydrogen production from water splitting by photo/photoelectron-catalytic process is a promising route to solve both fossil fuel depletion and environmental pollution at the same time. Titanium dioxide (TiO2) nanotubes have attracted much interest due to their large specific surface area and highly ordered structure, which has led to promising potential applications in photocatalytic degradation, photoreduction of CO2, water splitting, supercapacitors, dye-sensitized solar cells, lithium-ion batteries and biomedical devices. Nanotubes can be fabricated via facile hydrothermal method, solvothermal method, template technique and electrochemical anodic oxidation. In this report, we provide a comprehensive review on recent progress of the synthesis and modification of TiO2 nanotubes to be used for photo/photoelectro-catalytic water splitting. The future development of TiO2 nanotubes is also discussed.

Recent advances on smart TiO2 nanotube platforms for sustainable drug delivery applications

To address the limitations of traditional drug delivery, TiO2 nanotubes (TNTs) are recognized as a promising material for localized drug delivery systems. With regard to the excellent biocompatibility and physicochemical properties, TNTs prepared by a facile electrochemical anodizing process have been used to fabricate new drug-releasing implants for localized drug delivery. This review discusses the development of TNTs applied in localized drug delivery systems, focusing on several approaches to control drug release, including the regulation of the dimensions of TNTs, modification of internal chemical characteristics, adjusting pore openings by biopolymer coatings, and employing polymeric micelles as drug nanocarriers. Furthermore, rational strategies on external conditions-triggered stimuli-responsive drug release for localized drug delivery systems are highlighted. Finally, the review concludes with the recent advances on TNTs for controlled drug delivery and corresponding prospects in the future.

3,4-Dialkoxypyrrole for the Formation of Bioinspired Rose Petal-like Substrates with High Water Adhesion

Self-organization is commonly present in nature and can lead to the formation of surface structures with different wettabilities. Indeed, in nature superhydrophobic (low water adhesion) and parahydrophobic (high water adhesion) properties exist, such as in lotus leaves and red roses, respectively. The aim of this work is to prepare parahydrophobic properties by electrodeposition. For this, pyrrole derivatives with two alkoxy groups of various lengths (from 1 to 12) were synthesized in 8 steps by adapting a method developed by Merz et al. We show that the alkyl chain length has a huge influence on the polymer solubility and as a consequence on the surface morphology and hydrophobicity. Moreover, the alkyl chain length should be at least greater than eight carbons in order to obtain parahydrophobic properties. The properties are also controlled by the electrolyte nature. These materials can be used for many potential applications in water harvesting and transportation and separation membranes.

Fast Growth of Highly Ordered TiO2 Nanotube Arrays on Si Substrate under High-Field Anodization

ABSTRACT

Highly ordered TiO₂ nanotube arrays (NTAs) on Si substrate possess broad applications due to its high surface-to-volume ratio and novel functionalities, however, there are still some challenges on facile synthesis. Here, we report a simple and cost-effective high-field (90-180 V) anodization method to grow highly ordered TiO₂ NTAs on Si substrate, and investigate the effect of anodization time, voltage, and fluoride content on the formation of TiO₂ NTAs. The current density-time curves, recorded during anodization processes, can be used to determine the optimum anodization time. It is found that the growth rate of TiO₂ NTAs is improved significantly under high field, which is nearly 8 times faster than that under low fields (40-60 V). The length and growth rate of the nanotubes are further increased with the increase of fluoride content in the electrolyte.

GRAPHICAL ABSTRACT

Highly ordered TiO₂ nanotube arrays (NTAs) on Si substrate have been fabricated by high-field anodization method. A high voltage (90-180 V) leads to a high growth rate of TiO₂ NTAs (35-47 nm s^-1), which is nearly 8 times faster than the growth rate under low fields (40-60 V). Furthermore, the current density-time curves recorded during the anodization provide a facial method to determine the optimal anodization parameters, leading to an easy obtaining of the desired nanotubes.

Biomimetic Multi-Functional Superamphiphobic FOTS-TiO2 Particles beyond Lotus Leaf

It is widely known that natural examples like lotus leaves can only repel room-temperature water but cannot repel hot water and oils. Even though superamphiphobic surfaces composed of re-entrant "mushroom-like" or "T-shaped" structures are promising, they are generally regarded as substrate-dependent and difficult to fabricate, and hence, their practical use on various materials has been limited. Here, we synthesize a flower-like superamphiphobic FOTS-TiO₂ powder by solvothermal process and self-assembly functionalization. These structured and functionalized submicron particles can repel the liquids with surface tension as low as 23.8 mN·m^-1 (n-decane), which is the lowest among powder samples. With respect to the biomimetic aspect, the surface morphology of FOTS-TiO₂ particle is similar to the hierarchical micro/nano-structures of the lotus leaf surface, but it is beyond the lotus leaf for superoleophobic capacity. The difference in the oleophobicity is suggested to be the interplay of quasi-spherical re-entrant structure and perfluorined modification. Because of superior superamphiphobicity of the powder, a facile yet versatile strategy is developed, adhesive-assisted sieve deposition fabrication (AASDF), for preparing superamphiphobic coatings on various substrates. The investigation results pertaining to the water/oil proofing, mechanical durability, self-cleaning, and antifouling performances prove that the FOTS-TiO₂ coating is robust and multifunctional, which will enable more opportunities for practical applications. Apart from these general applications, we find that the superamphiphobic FOTS-TiO₂ powders when coated on sponge as anti-icing surface have good ice delay and icephobic performances. Furthermore, they can be used to prepare magnetic Fe₃O₄&FOTS-TiO₂ composite particles through liquid marbles, implying significant scientific value.

TiO2 nanotube platforms for smart drug delivery: a review

Titania nanotube (TNT) arrays are recognized as promising materials for localized drug delivery implants because of their excellent properties and facile preparation process. This review highlights the concept of localized drug delivery systems based on TNTs, considering their outstanding biocompatibility in a series of ex vivo and in vivo studies. Considering the safety of TNT implants in the host body, studies of the biocompatibility present significant importance for the clinical application of TNT implants. Toward smart TNT platforms for sustainable drug delivery, several advanced approaches were presented in this review, including controlled release triggered by temperature, light, radiofrequency magnetism, and ultrasonic stimulation. Moreover, TNT implants used in medical therapy have been demonstrated by various examples including dentistry, orthopedic implants, cardiovascular stents, and so on. Finally, a future perspective of TNTs for clinical applications is provided.

Tunable superomniphobic surfaces for sorting droplets by surface tension

We utilized tunable superomniphobic surfaces with flower-like TiO2 nanostructures to fabricate a simple device with precisely tailored surface energy domains that, for the first time, can sort droplets by surface tension. We envision that our methodology for droplet sorting will enable inexpensive and energy-efficient analytical devices for personalized point-of-care diagnostic platforms, lab-on-a-chip systems, biochemical assays and biosensors.

Recent Progress in Fabrication and Applications of Superhydrophobic Coating on Cellulose-Based Substrates

Multifuntional fabrics with special wettability have attracted a lot of interest in both fundamental research and industry applications over the last two decades. In this review, recent progress of various kinds of approaches and strategies to construct super-antiwetting coating on cellulose-based substrates (fabrics and paper) has been discussed in detail. We focus on the significant applications related to artificial superhydrophobic fabrics with special wettability and controllable adhesion, e.g., oil-water separation, self-cleaning, asymmetric/anisotropic wetting for microfluidic manipulation, air/liquid directional gating, and micro-template for patterning. In addition to the anti-wetting properties and promising applications, particular attention is paid to coating durability and other incorporated functionalities, e.g., air permeability, UV-shielding, photocatalytic self-cleaning, self-healing and patterned antiwetting properties. Finally, the existing difficulties and future prospects of this traditional and developing field are briefly proposed and discussed.